Fakultät Agrarwissenschaften

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Die Fakultät entwickelt in Lehre und Forschung nachhaltige Produktionstechniken der Agrar- und Ernährungswirtschaft. Sie erarbeitet Beiträge für den ländlichen Raum und zum Verbraucher-, Tier- und Umweltschutz.

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Alien plant fitness is limited by functional trade‐offs rather than a long‐term increase in competitive effects of native communities
(2023) Brendel, Marco R.; Schurr, Frank M.; Sheppard, Christine S.
Alien plants experience novel abiotic conditions and interactions with native communities in the introduced area. Intra‐ and interspecific selection on functional traits in the new environment may lead to increased population growth with time since introduction (residence time). However, selection regimes might differ depending on the invaded habitat. Additionally, in high‐competition habitats, a build‐up of biotic resistance of native species due to accumulation of eco‐evolutionary experience to aliens over time may limit invasion success. We tested if the effect of functional traits and the population dynamics of aliens depends on interspecific competition with native plant communities. We conducted a multi‐species experiment with 40 annual Asteraceae that differ in residence time in Germany. We followed their population growth in monocultures and in interspecific competition with an experienced native community (varying co‐existence times between focals and community). To more robustly test our findings, we used a naïve community that never co‐existed with the focals. We found that high seed mass decreased population growth in monocultures but tended to increase population growth under high interspecific competition. We found no evidence for a build‐up of competition‐mediated biotic resistance by the experienced community over time. Instead, population growth of the focal species was similarly inhibited by the experienced and naïve community. By comparing the effect of experienced and naïve communities on population dynamics over 2 years across a large set of species with a high variation in functional traits and residence time, this study advances the understanding of the long‐term dynamics of plant invasions. In our study system, population growth of alien species was not limited by an increase of competitive effects by native communities (one aspect of biotic resistance) over time. Instead, invasion success of alien plants may be limited because initial spread in low‐competition habitats requires different traits than establishment in high‐competition habitats.
Antimicrobial activity of Thai traditional medicinal plants extract incorporated alginate-tapioca starch based edible films against food related bacteria including foodborne pathogens
(2009) Tepsorn, Racha; Böhm, Reinhard
In Thai traditional medicine, different plant extracts are known to have a bactericidal or at least a bacteriostatic effect on bacteria and/or fungi. In Thailand, medicinal plants have been used safely since ancient times as herbal medicines and also as food colouring and flavouring agents. The application of selected plant extracts to foods could prevent foodborne diseases and food spoilage. In this study the antimicrobial activities of Andrographis paniculata (Burm.f.) Nees, Curcuma zedoaria (Christm.) Roscoe, Garcinia mangostana Linn., Hibiscus sabdariffa Linn., Musa sapientum Linn., Nelumbo nucifera Gaertn., Piper betle Linn., Psidium guajava Linn., and Punica granatum Linn. used by Thai practitioners of traditional medicine were investigated against different strains of food related bacteria, including 3 strains of Escherichia coli 2 strains of Salmonella Typhimurium, Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus, 1 strain of Bacillus subtilis, Vibrio parahaemolyticus, Yersinia enterocolitica, and 2 strains of Pseudomonas sp. Minimum Inhibitory Concentration (MIC-value) and Minimum Bactericidal Concentration (MBC-value) of hot water extracts, ultra sonicated extracts, and ethanolic extracts were determined by using the method described by the DVG (Deutsche Veterinärmedizinische Gesellschaft). From the results, it can be investigated that all crude extracts exhibited antimicrobial activity at least against one of the test organisms at concentration of 15.0 g/100 ml or lower. The results also indicated that the antibacterial activity of hot water extracts was better than ultra sonicated extracts and the ethanolic extracts exhibited the best antibacterial activity. Among the ethanolic extracts, the highest inhibitory activity was caused by Hibiscus sabdariffa Linn. and Piper betle Linn. The antimicrobial activity of both extracts against the test organisms was determined as Minimum Inhibitory Concentrations (MIC-value) ranging from 0.1 to 3.0 g/100 ml and 0.1 to 2.5 g/100 ml, as well as Minimum Bactericidal Concentrations (MBC-value) ranging from 0.2 to 3.5 g/100 ml and 0.2 to 1.5 g/100 ml for the ethanolic extracts of Hibiscus sabdariffa Linn. and Piper betle Linn., respectively. Bactericidal activity of the extracts was determined using a modified suspension test method according DIN EN 1040 (Quantitative suspension test for the evaluation of basic bactericidal activity of chemical disinfectants and antiseptics) and DIN EN 1276 (Quantitative suspension test for the evaluation of bactericidal activity of chemical disinfectants and antiseptics used in food, industrial, domestic, and institutional areas). Concentrations of 15.0 g/100 ml of the pure ethanolic extract of Curcuma zedoaria (Christm.) Roscoe, Garcinia mangostana Linn., Hibiscus sabdarifa Linn., and Piper bettle Linn., demonstrated a lethal effect within 15 seconds contact time. The others required more than 1 hour contact time to inactivate the test organisms. Among the test organisms, spore forming Bacillus spp. exhibited the highest resistance. The bactericidal activity of Thai traditional medicinal ethanolic extracts was decreased when interfering substances were added. To determine the bactericidal activity on surfaces the ethanolic extract of Piper betle Linn. was coated on stainless steel discs, but the results indicated that stainless steel discs were not the suitable surfaces to use as an artificial antimicrobial surface. To simulate the application under use conditions the antimicrobial activity of Alginate-Tapioca starch-based edible films were studied by incorporation of those ethanolic extracts as a natural antimicrobial agent. The edible films exhibited antimicrobial activity against bacteria tested by using agar diffusion assay. The presence of 20.0 % v/v of those extracts in the edible films had the ability to inactivate the test organisms within 24 hours incubation time. These results revealed that ethanolic extracts of those medicinal plants had a good potential to be incorporated to make antimicrobial edible film or coating for various food applications. The cytotoxic effect of those ethanolic medicinal plants extract were also determined using 4 different cell lines. The results of the cytotoxicity screening showed that the activity of the extracts correlates more with their effect on microorganisms than with their possible effect on the mucous membranes of human. The antimicrobial edible films and coating were studied in model food. The results demonstrated that the edible film wrapping method had advantages and showed more excellent benefit in the application with food than the edible coating method. In addition, the storage temperature was an important factor. Antimicrobial edible films presented higher activity at room temperature than under cold conditions (4ºC). In summary, the extract of those Thai traditional medicinal plants by itself or incorporated into edible films had potential for inhibiting or inactivating foodborne pathogens or food related bacteria in microbiological media and model food system; therefore, they could be useful as a method for controlling growth of foodborne pathogens and food related bacteria.
Atmospheric and soil water deficit induced changes in chemical and hydraulic signals in wheat (Triticum aestivum L.)
(2022) Tatar, Özgür; Brück, Holger; Asch, Folkard
Plant responses to soil drying and the metabolic basis of drought‐induced limitations in stomatal opening are still being discussed. In this study, we investigate the roles of root‐born chemical and hydraulic signals on stomatal regulation in wheat genotypes as affected by soil drought and vapour pressure deficit. Twelve consecutive pot experiments were carried out in a glasshouse. Two bread wheat cultivars (Gönen and Basribey) were subjected to drought under high and low vapour pressure deficit (VPD) in a growth chamber. Total dry matter, specific leaf area, xylem ABA content, xylem osmotic potential, xylem pH, root water potential (RWP), stomatal conductance, leaf ABA content and photosynthetic activity were determined daily during 6 days after the onset of treatments (DAT). In the first phase of drought stress, soil drying induced an increase in the xylem ABA with a peak 3 DAT while RWP drastically decreased during the same period. Then the osmotic potential of leaves decreased and leaf ABA content increased 4 DAT. A similar peak was observed for stomatal conductance during the early stress phase, and it became stable and significantly higher than in well‐watered conditions especially in high vapour deficit conditions (H‐VPD). Furthermore, xylem pH and xylem osmotic potential appeared to be mostly associated with atmospheric moisture content than soil water availability. The results are discussed regarding possible drought adaptation of wheat under different atmospheric humidity.
Chamber‐based system for measuring whole‐plant transpiration dynamics
(2022) Pieters, Alejandro; Giese, Marcus; Schmierer, Marc; Johnson, Kristian; Asch, Folkard
Most of our insights on whole‐plant transpiration (E) are based on leaf‐chamber measurements using water vapor porometers, IRGAs, or flux measurements. Gravimetric methods are integrative, accurate, and a clear differentiation between evaporation and E can be made. Water vapor pressure deficit (VPD) is the driving force for E but assessing its impact has been evasive, due to confounding effects of other climate drivers. We developed a chamber‐based gravimetric method, in which whole plant response of E to VPD could be assessed, while keeping other environmental parameters at predetermined values. Stable VPD values (0.5–3.7 kPa) were attained within 5 min after changing flow settings and maintained for at least 45 min. Species differing in life form and photosynthetic metabolism were used. Typical runs covering the range of VPDs lasted up to 4 h, preventing acclimation responses or soilborne water deficit. Species‐specific responses of E to VPD could be identified, as well as differences in leaf conductance. The combined gravimetric‐chamber‐based system presented overcomes several limitations of previous gravimetric set ups in terms of replicability, time, and elucidation of the impact of specific environmental drivers on E, filling a methodological gap and widening our phenotyping capabilities.
Constant hydraulic supply and ABA dynamics facilitate the trade-offs in water and carbon
(2023) Abdalla, Mohanned; Schweiger, Andreas H.; Berauer, Bernd J.; McAdam, Scott A. M.; Ahmed, Mutez Ali
Carbon-water trade-offs in plants are adjusted through stomatal regulation. Stomatal opening enables carbon uptake and plant growth, whereas plants circumvent drought by closing stomata. The specific effects of leaf position and age on stomatal behavior remain largely unknown, especially under edaphic and atmospheric drought. Here, we compared stomatal conductance (gs) across the canopy of tomato during soil drying. We measured gas exchange, foliage ABA level and soil-plant hydraulics under increasing vapor pressure deficit (VPD). Our results indicate a strong effect of canopy position on stomatal behavior, especially under hydrated soil conditions and relatively low VPD. In wet soil (soil water potential > -50 kPa), upper canopy leaves had the highest gs (0.727 ± 0.154 mol m-2 s-1) and assimilation rate (A; 23.4 ± 3.9 µmol m-2 s-1) compared to the leaves at a medium height of the canopy (gs: 0.159 ± 0.060 mol m2 s-1; A: 15.9 ± 3.8 µmol m-2 s-1). Under increasing VPD (from 1.8 to 2.6 kPa), gs, A and transpiration were initially impacted by leaf position rather than leaf age. However, under high VPD (2.6 kPa), age effect outweighed position effect. The soil-leaf hydraulic conductance was similar in all leaves. Foliage ABA levels increased with rising VPD in mature leaves at medium height (217.56 ± 85 ng g-1 FW) compared to upper canopy leaves (85.36 ± 34 ng g-1 FW). Under soil drought (< -50 kPa), stomata closed in all leaves resulting in no differences in gs across the canopy. We conclude that constant hydraulic supply and ABA dynamics facilitate preferential stomatal behavior and carbon-water trade-offs across the canopy. These findings are fundamental in understanding variations within the canopy, which helps in engineering future crops, especially in the face of climate change.
CRISPR/SpCas9‐mediated double knockout of barley Microrchidia MORC1 and MORC6a reveals their strong involvement in plant immunity, transcriptional gene silencing and plant growth
(2021) Galli, Matteo; Martiny, Engie; Imani, Jafargholi; Kumar, Neelendra; Koch, Aline; Steinbrenner, Jens; Kogel, Karl‐Heinz
The Microrchidia (MORC) family proteins are important nuclear regulators in both animals and plants with critical roles in epigenetic gene silencing and genome stabilization. In the crop plant barley (Hordeum vulgare), seven MORC gene family members have been described. While barley HvMORC1 has been functionally characterized, very little information is available about other HvMORC paralogs. In this study, we elucidate the role of HvMORC6a and its potential interactors in regulating plant immunity via analysis of CRISPR/SpCas9‐mediated single and double knockout (dKO) mutants, hvmorc1 (previously generated and characterized by our group), hvmorc6a, and hvmorc1/6a. For generation of hvmorc1/6a, we utilized two different strategies: (i) successive Agrobacterium‐mediated transformation of homozygous single mutants, hvmorc1 and hvmorc6a, with the respective second construct, and (ii) simultaneous transformation with both hvmorc1 and hvmorc6a CRISPR/SpCas9 constructs. Total mutation efficiency in transformed homozygous single mutants ranged from 80 to 90%, while upon simultaneous transformation, SpCas9‐induced mutation in both HvMORC1 and HvMORC6a genes was observed in 58% of T0 plants. Subsequent infection assays showed that HvMORC6a covers a key role in resistance to biotrophic (Blumeria graminis) and necrotrophic (Fusarium graminearum) plant pathogenic fungi, where the dKO hvmorc1/6a showed the strongest resistant phenotype. Consistent with this, the dKO showed highest levels of basal PR gene expression and derepression of TEs. Finally, we demonstrate that HvMORC1 and HvMORC6a form distinct nucleocytoplasmic homo‐/heteromers with other HvMORCs and interact with components of the RNA‐directed DNA methylation (RdDM) pathway, further substantiating that MORC proteins are involved in the regulation of TEs in barley.
Density dependence of seed dispersal and fecundity profoundly alters the spread dynamics of plant populations
(2023) Zhu, Jinlei; Lukić, Nataša; Pagel, Jörn; Schurr, Frank M.
Plant population spread has fundamental ecological and evolutionary importance. Both determinants of plant population spread, fecundity and dispersal, can be density‐dependent, which should cause feedback between population densities and spread dynamics. Yet it is poorly understood how density‐dependence affects key characteristics of spread: spread rate at which the location of the furthest forward individual moves, edge depth (the geographical area over which individuals contribute to spread) and population continuity (occupancy of the spreading population). We present a general modelling framework for analysing the effects of density‐dependent fecundity and dispersal on population spread and parameterize this framework with experimental data from a common‐garden experiment using five wind‐dispersed plant species grown at different densities. Our model shows that density‐dependent fecundity and dispersal strongly affect all three population spread characteristics for both exponential and lognormal dispersal kernels. Spread rate and edge depth are strongly correlated but show weaker correlations with population continuity. Positive density‐dependence of fecundity increases all three spread characteristics. Increasingly positive density‐dependence of dispersal increases spread rate and edge depth but generally decreases population continuity. Density‐dependent fecundity and dispersal are largely additive in their effect on spread characteristics. For population continuity, the joint effects of density‐dependent fecundity and dispersal are somewhat contingent on the dispersal kernel. The common‐garden experiment and the experimentally parameterized mechanistic dispersal model revealed density‐dependent fecundity and dispersal across study species. All study species exhibited negatively density‐dependent fecundity, but they differed qualitatively in the density‐dependence of dispersal distance and probability of long‐distance dispersal. The negative density‐dependence of fecundity and dispersal found for three species reinforced each other in reducing spread rate and edge depth. The positively density‐dependent dispersal found for two species markedly increased spread rate and edge depth. Population continuity was hardly affected by population density in all study species except Crepis sancta in which it was strongly reduced by negatively density‐dependent fecundity. Synthesis. Density‐dependent fecundity and seed dispersal profoundly alter population spread. In particular, positively density‐dependent dispersal should promote the spread and genetic diversity of plant populations migrating under climate change but also complicate the control of invasive species.
Differences in mucilage properties and stomatal sensitivity of locally adapted Zea mays in relation with precipitation seasonality and vapour pressure deficit regime of their native environment
(2023) Berauer, Bernd J.; Akale, Asegidew; Schweiger, Andreas H.; Knott, Mathilde; Diehl, Dörte; Wolf, Marc‐Philip; Sawers, Ruairidh J. H.; Ahmed, Mutez A.
With ongoing climate change and the increase in extreme weather events, especially droughts, the challenge of maintaining food security is becoming ever greater. Locally adapted landraces of crops represent a valuable source of adaptation to stressful environments. In the light of future droughts—both by altered soil water supply and increasing atmospheric water demand (vapor pressure deficit [VPD])—plants need to improve their water efficiency. To do so, plants can enhance their access to soil water by improving rhizosphere hydraulic conductivity via the exudation of mucilage. Furthermore, plants can reduce transpirational water loss via stomatal regulation. Although the role of mucilage and stomata regulation on plant water management have been extensively studied, little is known about a possible coordination between root mucilage properties and stomatal sensitivity as well as abiotic drivers shaping the development of drought resistant trait suits within landraces. Mucilage properties and stomatal sensitivity of eight Mexican landraces of Zea mays in contrast with one inbred line were first quantified under controlled conditions and second related to water demand and supply at their respective site of origin. Mucilage physical properties—namely, viscosity, contact angle, and surface tension—differed between the investigated maize varieties. We found strong influences of precipitation seasonality, thus plant water availability, on mucilage production (R2 = .88, p < .01) and mucilage viscosity (R2 = .93, p < .01). Further, stomatal sensitivity to increased atmospheric water demand was related to mucilage viscosity and contact angle, both of which are crucial in determining mucilage's water repellent, thus maladaptive, behavior upon soil drying. The identification of landraces with pre‐adapted suitable trait sets with regard to drought resistance is of utmost importance, for example, trait combinations such as exhibited in one of the here investigated landraces. Our results suggest a strong environmental selective force of seasonality in plant water availability on mucilage properties as well as regulatory stomatal effects to avoid mucilage's maladaptive potential upon drying and likely delay critical levels of hydraulic dysfunction. By this, landraces from highly seasonal climates may exhibit beneficial mucilage and stomatal traits to prolong plant functioning under edaphic drought. These findings may help breeders to efficiently screen for local landraces with pre‐adaptations to drought to ultimately increase crop yield resistance under future climatic variability.
Editorial: Seed behavior in response to extreme environments
(2023) Zhu, Jinlei; Wang, Lei
Effects of biotic interactions on plant fecundity depend on spatial and functional structure of communities and time since disturbance
(2022) Walter, Hanna E.; Pagel, Jörn; Cooksley, Huw; Neu, Alexander; Schleuning, Matthias; Schurr, Frank M.
Biotic interactions in plant communities affect individual fitness and community dynamics. Interactions between plants vary in space, over time and with organisational complexity. Yet it is challenging to quantify temporal, spatial and functional determinants of different types of interactions between long‐lived perennial plant species and their effect on lifetime fecundity. We studied how plant–plant, pollinator‐ and seed predator‐mediated interactions affect year‐to‐year variation in three fecundity components (cone production, seed set and seed survival) during post‐fire recovery. Age‐stratified data on the three fecundity components were collected in 19 even‐aged communities comprising 20 serotinous Protea shrub species in the South African Fynbos. We analyse data on these fecundity components with neighbourhood models to infer the sign and strength of interactions throughout post‐disturbance recovery, the neighbour plant traits that shape them and the spatial scale at which interactions take place. For each fecundity component, these models describe how neighbourhood effects change over time and with spatial distance between plants. We then predicted neighbourhood effects on individual fecundity components and cumulative reproductive output at different post‐fire stand ages for each focal plant. Competitive effects on cone production and seed set increased with post‐fire stand age as biomass and floral resources for pollinators build up. In contrast, neighbourhood effects on seed survival were weak throughout post‐disturbance recovery. Plant–plant interactions were shaped by neighbour traits related to resource acquisition, whereas animal‐mediated interactions depended on neighbour traits related to resource availability for pollinators and seed predators. The spatial scale of the interactions increased from plant–plant over predator‐mediated to pollinator‐mediated interactions. The joint effect of these interactions on cumulative reproductive output caused the proportion of focal plants experiencing competition to increase with time since fire. Synthesis. We show that temporal changes in biotic interactions throughout post‐disturbance recovery of perennial plant communities depend on functional traits and can be integrated into neighbourhood effects on lifetime fecundity. Studying the temporal, spatial and functional determinants of neighbourhood effects on lifetime fecundity is important for predicting not only individual plant fitness but also population and community dynamics in changing environments.
Extensions of genomic prediction methods and approaches for plant breeding
(2013) Technow, Frank; Melchinger, Albrecht E.
Marker assisted selection (MAS) was a first attempt to exploit molecular marker information for selection purposes in plant breeding. The MAS approach rested on the identification of quantitative trait loci (QTL). Because of inherent shortcomings of this approach, MAS failed as a tool for improving polygenic traits, in most instances. By shifting focus from QTL identification to prediction of genetic values, a novel approach called 'genomic selection', originally suggested for breeding of dairy cattle, presents a solution to the shortcomings of MAS. In genomic selection, a training population of phenotyped and genotyped individuals is used for building the prediction model. This model uses the whole marker information simultaneously, without a preceding QTL identification step. Genetic values of selection candidates, which are only genotyped, are then predicted based on that model. Finally, the candidates are selected according their predicted genetic values. Because of its success, genomic selection completely revolutionized dairy cattle breeding. It is now on the verge of revolutionizing plant breeding, too. However, several features set apart plant breeding programs from dairy cattle breeding. Thus, the methodology has to be extended to cover typical scenarios in plant breeding. Providing such extensions to important aspects of plant breeding are the main objectives of this thesis. Single-cross hybrids are the predominant type of cultivar in maize and many other crops. Prediction of hybrid performance is of tremendous importance for identification of superior hybrids. Using genomic prediction approaches for this purpose is therefore of great interest to breeders. The conventional genomic prediction models estimate a single additive effect per marker. This was not appropriate for prediction of hybrid performance because of two reasons. (1) The parental inbred lines of single-cross hybrids are usually taken from genetically very distant germplasm groups. For example, in hybrid maize breeding in Central Europe, these are the Dent and Flint heterotic groups, separated for more than 500 years. Because of the strong divergence between the heterotic groups, it seemed necessary to estimate heterotic group specific marker effects. (2) Dominance effects are an important component of hybrid performance. They had to be included into the prediction models to capture the genetic variance between hybrids maximally. The use of different heterotic groups in hybrid breeding requires parallel breeding programs for inbred line development in each heterotic group. Increasing the training population size with lines from the opposite heterotic group was not attempted previously. Thus, a further objective of this thesis was to investigate whether an increase in the accuracy of genomic prediction can be achieved by using combined training sets. Important traits in plant breeding are characterized by binomially distributed phenotypes. Examples are germination rate, fertility rates, haploid induction rate and spontaneous chromosome doubling rate. No genomic prediction methods for such traits were available. Therefore, another objective was to provide methodological extensions for such traits. We found that incorporation of dominance effects for genomic prediction of maize hybrid performance led to considerable gains in prediction accuracy when the variance attributable to dominance effects was substantial compared to additive genetic variance. Estimation of marker effects specific to the Dent and Flint heterotic group was of less importance, at least not under the high marker densities available today. The main reason for this was the surprisingly high linkage phase consistency between Dent and Flint heterotic groups. Furthermore, combining individuals from different heterotic groups (Flint and Dent) into a single training population can result in considerable increases in prediction accuracy. Our extensions of the prediction methods to binomially distributed data yielded considerably higher prediction accuracies than approximate Gaussian methods. In conclusion, the developed extensions of prediction methods (to hybrid prediction and binomially distributed data) and approaches (training populations combining heterotic groups) can lead to considerable, cost free gains in prediction accuracy. They are therefore valuable tools for exploiting the full potential of genomic selection in plant breeding.
From alien to native Asteraceae : how effects of climate, functional traits, and biotic interactions on population growth change with residence time
(2023) Brendel, Marco; Sheppard, Christine
Biological invasions pose a major threat to native biodiversity and even drive native species to extinction. It is thus of utmost importance to gain a better understanding of limits to population growth and spread of invasive plants. Invasion success in the introduced area is determined by the combined effects of climatic mismatches between the area of origin and the introduced area as well as biotic resistance of resident native communities. Alien plants can respond to environmental selection via changes in functional traits and thereby adapt to novel abiotic conditions. Native community species are expected to adapt to the presence of the invader by gaining eco-evolutionary experience and build-up biotic resistance over time. The aim of this thesis is to investigate interactions of alien plants with the novel abiotic and biotic environment in their introduced range over eco-evolutionary timescales. To this end, I conducted common garden experiments based on an alien-native species continuum to cover a broad range of residence times in Germany (7 to 12,000 years before present). I followed the population growth of 47 annual Asteraceae (including neophytes, archaeophytes, and natives) over two years and measured their performance in intra- and interspecific competition to answer the following questions: 1) How are effects of climatic distances between the area of origin and the introduced area as well as functional traits on population dynamics of alien plants determined by residence time? 2) How is biotic resistance of native communities towards alien plants related to residence time? 3) How are competitive outcomes between single alien and native plants shaped by residence time and serve as a predictor of range sizes? For the first question, I followed population growth of the Asteraceae in monocultures. I calculated climatic distances between the area of origin and the introduced area and measured functional traits in terms of seed mass, maximum height, and specific leaf area. Firstly, I tested whether negative effects of climatic distances on population growth weaken with residence time. Secondly, I investigated trait-demography relationships and tested if functional traits converge towards values that increase population growth. I found a strong effect of seed mass and no effects climatic distances on population growth. A strong negative relationship between seed mass and population growth resulted in directional selection of seed mass towards low values with increasing residence time. For the second question, I measured population growth of the Asteraceae in a Central European grassland community. I tested if competitive effects of the community on the Asteraceae increase with residence time (i.e. co-existence time with the native community). I used a second community native to North American grasslands that never co-existed with the Asteraceae to disentangle competitive effects related to eco-evolutionary experience of the native community from inherent competitive abilities of the Asteraceae. I compared trait-demography relationships in both community types with monocultures and found very similar competitive effects of both communities on the Asteraceae and thus no evidence for a build-up of competition-induced biotic resistance over time. Instead, invasion success was determined by a strong seed-mass-mediated trade-off between population growth in low- vs. high-competition. For the third question, I tested if the response of biomass and seed production of native targets to competition with alien and native neighbours depends on residence time. I tested if competitive effects differ between invasion status groups and explain species’ range sizes in Germany. I generally did not find a higher tolerance of native Asteraceae to competition of neighbouring aliens and natives with increasing residence time. Both established neophytes and natives showed similar competitive abilities and species’ range sizes were not influenced by competitive effects. The detected trait-demography relationships and related directional selection as a mechanism of adaptation to novel abiotic conditions improve the understanding of constraints on population growth and spread of invaders. The lack of interspecific competitive superiority as a determinant of range sizes might indicate that other mechanisms are more important for invasion success. The functional trade-off between population growth in low vs. high competition reveals that invaders that are likely to escape this trade-off should be of highest management concern. By the combination of experimental macroecology with approaches of functional and community ecology used in my study, I strongly advanced the understanding of mechanisms of limits to population growth and spread of alien plants and provide a fundamental basis for future research in invasion ecology.
The functional diversity of the high-affinity nitrate transporter gene family in hexaploid wheat: Insights from distinct expression profiles
(2023) Sigalas, Petros P.; Buchner, Peter; Kröper, Alex; Hawkesford, Malcolm J.
High-affinity nitrate transporters (NRT) are key components for nitrogen (N) acquisition and distribution within plants. However, insights on these transporters in wheat are scarce. This study presents a comprehensive analysis of the NRT2 and NRT3 gene families, where the aim is to shed light on their functionality and to evaluate their responses to N availability. A total of 53 NRT2s and 11 NRT3s were identified in the bread wheat genome, and these were grouped into different clades and homoeologous subgroups. The transcriptional dynamics of the identified NRT2 and NRT3 genes, in response to N starvation and nitrate resupply, were examined by RT-qPCR in the roots and shoots of hydroponically grown wheat plants through a time course experiment. Additionally, the spatial expression patterns of these genes were explored within the plant. The NRT2s of clade 1, TaNRT2.1-2.6, showed a root-specific expression and significant upregulation in response to N starvation, thus emphasizing a role in N acquisition. However, most of the clade 2 NRT2s displayed reduced expression under N-starved conditions. Nitrate resupply after N starvation revealed rapid responsiveness in TaNRT2.1-2.6, while clade 2 genes exhibited gradual induction, primarily in the roots. TaNRT2.18 was highly expressed in above-ground tissues and exhibited distinct nitrate-related response patterns for roots and shoots. The TaNRT3 gene expression closely paralleled the profiles of TaNRT2.1-2.6 in response to nitrate induction. These findings enhance the understanding of NRT2 and NRT3 involvement in nitrogen uptake and utilization, and they could have practical implications for improving nitrogen use efficiency. The study also recommends a standardized nomenclature for wheat NRT2 genes, thereby addressing prior naming inconsistencies.
Functional traits shape plant–plant interactions and recruitment in a hotspot of woody plant diversity
(2023) Cooksley, Huw; Dreyling, Lukas; Esler, Karen J.; Griebenow, Stian; Neumann, Günter; Valentine, Alex; Schleuning, Matthias; Schurr, Frank M.
Understanding and predicting recruitment in species‐rich plant communities requires identifying functional determinants of both density‐independent performance and interactions. In a common‐garden field experiment with 25 species of the woody plant genus Protea, we varied the initial spatial and taxonomic arrangement of seedlings and followed their survival and growth during recruitment. Neighbourhood models quantified how six key functional traits affect density‐independent performance, interaction effects and responses. Trait‐based neighbourhood models accurately predicted individual survival and growth from the initial spatial and functional composition of species‐rich experimental communities. Functional variation among species caused substantial variation in density‐independent survival and growth that was not correlated with interaction effects and responses. Interactions were spatially restricted but had important, predominantly competitive, effects on recruitment. Traits increasing the acquisition of limiting resources (water for survival and soil P for growth) mediated trade‐offs between interaction effects and responses. Moreover, resprouting species had higher survival but reduced growth, likely reinforcing the survival–growth trade‐off in adult plants. Resource acquisition of juvenile plants shapes Protea community dynamics with acquisitive species with strong competitive effects suffering more from competition. Together with functional determinants of density‐independent performance, this makes recruitment remarkably predictable, which is critical for efficient restoration and near‐term ecological forecasts of species‐rich communities.
High-throughput field phenotyping reveals genetic variation in photosynthetic traits in durum wheat under drought
(2021) Zendonadi dos Santos, Nícolas; Piepho, Hans‐Peter; Condorelli, Giuseppe Emanuele; Licieri Groli, Eder; Newcomb, Maria; Ward, Richard; Tuberosa, Roberto; Maccaferri, Marco; Fiorani, Fabio; Rascher, Uwe; Muller, Onno
Chlorophyll fluorescence (ChlF) is a powerful non‐invasive technique for probing photosynthesis. Although proposed as a method for drought tolerance screening, ChlF has not yet been fully adopted in physiological breeding, mainly due to limitations in high‐throughput field phenotyping capabilities. The light‐induced fluorescence transient (LIFT) sensor has recently been shown to reliably provide active ChlF data for rapid and remote characterisation of plant photosynthetic performance. We used the LIFT sensor to quantify photosynthesis traits across time in a large panel of durum wheat genotypes subjected to a progressive drought in replicated field trials over two growing seasons. The photosynthetic performance was measured at the canopy level by means of the operating efficiency of Photosystem II (Fq′/Fm′) and the kinetics of electron transport measured by reoxidation rates (Fr1′ and Fr2′). Short‐ and long‐term changes in ChlF traits were found in response to soil water availability and due to interactions with weather fluctuations. In mild drought, Fq′/Fm′ and Fr2′ were little affected, while Fr1′ was consistently accelerated in water‐limited compared to well‐watered plants, increasingly so with rising vapour pressure deficit. This high‐throughput approach allowed assessment of the native genetic diversity in ChlF traits while considering the diurnal dynamics of photosynthesis.
Identification and analysis of a transcriptome of Douglas-fir (Pseudotsuga menziesii) and population structure inference using different next-generation sequencing techniques
(2015) Müller, Thomas; Schmid, Karl J.
Predictions assume severe changes in the climatic conditions in Central Europe in the coming decades. Longer periods of drought and less precipitation during summer are expected. Plants cannot change their habitat and have to adapt to the new conditions or their offspring has to colonize new ecological niches. Due to the long generation times in trees it is important to know if and how trees can cope with the expected climatic conditions. Forest managers already give thought to the composition of future forests, because they have to choose species and populations which have no or only few problems with the changed climate. Douglas-fir (Pseudotsuga menziesii) is a promising tree species for this purpose, because it is adapted to different habitats and climate zones in its natural distribution range in North America. The two main varieties, coastal and interior Douglas-fir, differ genotypically and phenotypically, e.g. in drought tolerance. Douglas-fir trees, mainly of the coastal variety, showed good growth performances in field trials in Germany. Hence, a research project called "DougAdapt" was designed to analyze and to link genotypic and phenotypic differences in several coastal and interior Douglas-fir provenances. In this project, trees from field trials and from greenhouse experiments were sampled. To analyze the genetic diversity of the provenances we first generated reference sequences. Even with modern and cost-efficient next-generation sequencing technologies it would be very expensive to decipher the ~ 19 gigabases of the Douglas-fir genome completely. An alternative to whole genome sequencing is transcriptome sequencing, in which only the coding regions of a genome are sequenced. The transcriptome sequencing, which was performed for the first time in Douglas-fir, resulted in a large number of putative unique transcripts (PUTs). Comparisons with published transcriptomes of other plant species showed that the PUTs represented the transcriptome of Douglas-fir comprehensively. As the sampled seedlings were part of a drought stress experiment and grew under controlled conditions, we were able to identify drought related candidate PUTs, which may be part of the trees response to drought. Furthermore, more than 27,000 previously unknown single nucleotide polymorphisms (SNPs) in Douglas-fir could be identified. SNPs can influence the phenotype of individuals, and they can be used for instance as markers or to analyze genetic diversity. The analysis of genetic diversity of Douglas-fir provenances and the search for genes which may be part of local adaptation were performed with a sequence capture experiment. In sequence capture only predefined regions of a genome are sequenced. We showed that sequence capture based on PUTs as target regions is applicable in species with large and mostly unknown genomes. The polymorphic drought related candidate PUTs showed higher genetic differentiation than the remaining genes. Nevertheless, none of them was among the candidate PUTs for positive selection, which in turn are probably part of the local adaptation of the trees. Despite a high level of gene flow between coastal and interior provenances, the SNP data showed genetic differentiation between both varieties but only very low differentiation between the coastal provenances. We also investigated if genotyping-by-sequencing (GBS) is a suitable method to detect polymorphisms in Douglas-fir and compared the results of two GBS experiments with the sequence capture. The genome is digested with one or several restriction enzymes in GBS. Afterwards, only fragments with a specific length are sequenced, which considerably reduces the part of the genome that is sequenced as well as the costs. The advantage compared to sequence capture is the possibility to sample more individuals at the same time with less effort and costs. We showed that a digestion with two restriction enzymes results in more SNPs with less missing data, compared to using only one restriction enzyme. Both GBS methods returned considerably less SNPs than the sequence capture. Nevertheless, it was possible to distinguish between southern interior, northern interior, and coastal provenances using SNP data of the GBS experiments. GBS, especially with two restriction enzymes, seems to be a promising approach to genotype a large number of Douglas-fir trees and to obtain SNPs at low costs, which can be used in several tasks like genome-wide association studies. A large amount of sequence data and SNPs were analyzed in this thesis. Together with phenotypic information, these data will be crucial for the analysis of useful traits in Douglas-fir, like drought tolerance. Furthermore, the results concerning the Douglas-fir genome and the genetic diversity of different provenances will be beneficial in breeding programs and association studies, which in turn can be helpful to choose the optimal provenances for a given location.
Identification of regulatory factors determining nutrient acquisition in Arabidopsis
(2011) Giehl, Ricardo Fabiano Hettwer; von Wirén, Nicolaus
The acquisition and translocation of mineral nutrients involves the orchestrated action of a series of physiological and biochemical mechanisms, which are, in turn, regulated by nutrient availability and demand. Furthermore, root morphological changes play an outstanding role for nutrient acquisition, especially when the availability of a certain nutrient is low. Although for most nutrients the molecular mechanisms involved in their acquisition from soils have been described, much less is known about the regulatory pathways underlying the uptake and translocation of nutrients in plants. Thus, the main aim of the present study was to characterize root morphological responses to nutrient supply and to identify novel regulatory components. The first part of the present thesis describes the morphological response of Arabidopsis roots to the essential element iron (Fe), which has a particularly low solubility in soils. Relative to a homogenous supply of Fe, localized Fe supply to horizontally-separated agar plates doubled lateral root length without a particular effect on lateral root number. The internal tissue Fe rather than external Fe triggered the local elongation of lateral roots. In addition, the Fe-stimulated emergence of lateral root primordia and root cell elongation was accompanied by a higher activity of the auxin reporter DR5:GUS in lateral root apices. A crucial role of the auxin transporter AUX1 in Fe-triggered lateral root elongation was indicated by Fe-regulated AUX1 promoter activities in lateral root apices and by the failure of aux-1 mutants to elongate lateral roots into Fe-enriched agar patches. Furthermore, a screening was designed to identify novel regulatory components involved in the Fe-dependent stimulation of lateral roots. One member of the GATA family of transcription factors was found to play a role in the local, root-endogenous regulation of lateral root development in response to local supplies of Fe. It was concluded that a Fe sensing mechanism in roots regulates lateral root development by modulating auxin transport. The second part of the thesis describes the use of multi-elemental analyses to identify novel regulators of nutrient accumulation in Arabidopsis. Firstly, it is shown that the disruption of transcription factors expression can lead to significant alterations in the accumulation of one or more nutrients in shoots. In addition, this approach allowed the identification of a so-far uncharacterized transcription factor ? NGAL1 ? that regulates primary root elongation in response to phosphorus (P) supply. The loss of NGAL1 resulted in hypersensitive inhibition of primary root growth under low P and a P-independent increase in lateral root elongation. The results presented here indicate that NGAL1 participates in a signaling pathway that modulates meristematic activity by controlling the expression of important root patterning regulators according to the local availability of P.
Impact of harvest time and pruning technique on total CBD concentration and yield of medicinal cannabis
(2022) Crispim Massuela, Danilo; Hartung, Jens; Munz, Sebastian; Erpenbach, Federico; Graeff-Hönninger, Simone
The definition of optimum harvest and pruning interventions are important factors varying inflorescence yield and cannabinoid composition. This study investigated the impact of (i) harvest time (HT) and (ii) pruning techniques (PT) on plant biomass accumulation, CBD and CBDA-concentrations and total CBD yield of a chemotype III medical cannabis genotype under indoor cultivation. The experiment consisted of four HTs between 5 and 11 weeks of flowering and three PTs-apical cut (T); removal of side shoots (L) and control (C), not pruned plants. Results showed that inflorescence dry weight increased continuously, while the total CBD concentration did not differ significantly over time. For the studied genotype, optimum harvest time defined by highest total CBD yield was found at 9 weeks of flowering. Total CBD-concentration of inflorescences in different fractions of the plant’s height was significantly higher in the top (9.9%) in comparison with mid (8.2%) and low (7.7%) fractions. The T plants produced significantly higher dry weight of inflorescences and leaves than L and C. Total CBD yield of inflorescences for PTs were significantly different among pruned groups, but do not differ from the control group. However, a trend for higher yields was observed (T > C > L).
Impacts of carbon dioxide enrichment on landrace and released Ethiopian barley (Hordeum vulgare L.) cultivars
(2021) Gardi, Mekides Woldegiorgis; Malik, Waqas Ahmed; Haussmann, Bettina I. G.
Barley (Hordeum vulgare L.) is an important food security crop due to its high-stress tolerance. This study explored the effects of CO2 enrichment (eCO2) on the growth, yield, and water-use efficiency of Ethiopian barley cultivars (15 landraces, 15 released). Cultivars were grown under two levels of CO2 concentration (400 and 550 ppm) in climate chambers, and each level was replicated three times. A significant positive effect of eCO2 enrichment was observed on plant height by 9.5 and 6.7%, vegetative biomass by 7.6 and 9.4%, and grain yield by 34.1 and 40.6% in landraces and released cultivars, respectively. The observed increment of grain yield mainly resulted from the significant positive effect of eCO2 on grain number per plant. The water-use efficiency of vegetative biomass and grain yield significantly increased by 7.9 and 33.3% in landraces, with 9.5 and 42.9% improvement in released cultivars, respectively. Pearson’s correlation analysis revealed positive relationships between grain yield and grain number (r = 0.95), harvest index (r = 0.86), and ear biomass (r = 0.85). The response of barley to eCO2 was cultivar dependent, i.e., the highest grain yield response to eCO2 was observed for Lan_15 (122.3%) and Rel_10 (140.2%). However, Lan_13, Land_14, and Rel_3 showed reduced grain yield by 16, 25, and 42%, respectively, in response to eCO2 enrichment. While the released cultivars benefited more from higher levels of CO2 in relative terms, some landraces displayed better actual values. Under future climate conditions, i.e., future CO2 concentrations, grain yield production could benefit from the promotion of landrace and released cultivars with higher grain numbers and higher levels of water-use efficiency of the grain. The superior cultivars that were identified in the present study represent valuable genetic resources for future barley breeding.
Improving measurements of the falling trajectory and terminal velocity of wind‐dispersed seeds
(2022) Zhu, Jinlei; Buchmann, Carsten M.; Schurr, Frank M.
Seed dispersal by wind is one of the most important dispersal mechanisms in plants. The key seed trait affecting seed dispersal by wind is the effective terminal velocity (hereafter “terminal velocity”, Vt), the maximum falling speed of a seed in still air. Accurate estimates of Vt are crucial for predicting intra‐ and interspecific variation in seed dispersal ability. However, existing methods produce biased estimates of Vt for slow‐ or fast‐falling seeds, fragile seeds, and seeds with complex falling trajectories. We present a new video‐based method that estimates the falling trajectory and Vt of wind‐dispersed seeds. The design involves a mirror that enables a camera to simultaneously record a falling seed from two perspectives. Automated image analysis then determines three‐dimensional seed trajectories at high temporal resolution. To these trajectories, we fit a physical model of free fall with air resistance to estimate Vt. We validated this method by comparing the estimated Vt of spheres of different diameters and materials to theoretical expectations and by comparing the estimated Vt of seeds to measurements in a vertical wind tunnel. Vt estimates closely match theoretical expectations for spheres and vertical wind tunnel measurements for seeds. However, our Vt estimates for fast‐falling seeds are markedly higher than those in an existing trait database. This discrepancy seems to arise because previous estimates inadequately accounted for seed acceleration. The presented method yields accurate, efficient, and affordable estimates of the three‐dimensional falling trajectory and terminal velocity for a wide range of seed types. The method should thus advance the understanding and prediction of wind‐driven seed dispersal.

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