Browsing by Subject "Phenology"

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Influence of ambient temperature on the phenology of the greater mouse‐eared bat (Myotis myotis)
(2023) Matthäus, Laura; Kugelschafter, Karl; Fietz, Joanna
In order to assess the consequences of climate change and evaluate its impacts on wildlife, it is essential to do so on a species-specific level. It is assumed that changes in the ambient temperature influence energy consumption as well as food availability and thus foraging behavior, reproduction, survival, and therefore population dynamics in bats. Based on this assumption, the present study aims to gain insights into the roosting and breeding behavior of the greater mouse-eared bat (Myotis myotis) in relation to changes of the ambient temperature. For this purpose, we investigated the effect of ambient temperature on the phenology of the greater mouse-eared bat by using activity data of the bats collected using light barriers at the maternity roosts. The light barrier used in this study is a system that detects the interruption of two light beams, for example, by a flying bat, and displays it as an electrical signal. The investigations have shown that 1. the higher the winter temperatures, the earlier the greater mouse-eared bats returned to the roosts to form the maternity colony; however, this was only true for ambient temperatures below 0.5°C, 2. birth season started earlier at higher spring temperatures, 3. the dissolution of maternity roosts occurred earlier with earlier birth season and at higher ambient temperatures during lactation. The results revealed that ambient temperature has an influence on the phenology of the greater mouse-eared bat. Depending on the respective life history stage, an increase in ambient temperature can have a positive or negative effect on the fitness of the animals. In recent years, mild winters have been recorded more frequently, which can have an influence on the behavior of bats. Warm winters within certain limits seem to lead to an earlier formation of the maternity colony, which can be positive or negative for the bats depending on persistent weather conditions and thus insect availability. In the course of climate change, we can also expect earlier spring events and an increase in spring temperature, as well as hot spells in summer. These warm springs and summers seem to lead to an earlier beginning of births, a faster development of the juveniles and an earlier dissolution of the maternity roost. An advance of reproductive activities can be assumed to increase the chance to survive the following winter in both mothers and their young, as they have more time to build up sufficient energy reserves for hibernation before winter starts. Due to the climatic changes, phenological changes of the bats be expected. This study highlights that in order to understand the impact of climate change on biodiversity, it is necessary to investigate in detail effects on a species-specific level and also to consider direct and indirect effects of ambient temperature on different life history stages.
Screening tools for late drought resistance in tropical potato
(2023) Hölle, Julia; Asch, Folkard
Potato (Solanum tuberosum L.) is a drought sensitive crop, and even short drought spells or infrequent irrigation during stolon formation, tuber initiation, or tuber bulking reduces tuber yields. A number of morphological traits have been described that potentially improve genotypic performance of potato under moisture deficit conditions. In breeding processes, a large set of genotypes are tested at the same time and because the genotypes differ in their phenology, various phenological stages occur simultaneously in the field. Consequently, during a drought spell different varieties will be subjected to soil moisture deficit at different phenological stages. We tested thirteen contrasting genotypes under field conditions in a desert in South Peru in four different irrigation treatments at two different soil types. The irrigation was withheld after 50, 65 and 80 days after planting until final harvest after 120 days. Sequential harvests, remote sensing and phenological evaluation was conducted in five to ten-days intervals. In literature, the belowground and aboveground development of potato has been described as closely and linearly related, meaning that in many studies belowground development is estimated according to aboveground development. The synchrony of the aboveground and belowground development is strongly influenced by both, water deficit and development stage at drought initiation. Under early drought, the aboveground development was accelerated and belowground development slowed. The opposite was found at later development stages. The earlier drought was initiated, the longer the tuber-filling phase, while the bulking phase was shortened. Water deficit also slowed down the aboveground development of flowering by a couple of days. In further drought experiments it is important to evaluated the belowground development separately, as we cannot conclude from the above to the belowground development stage. In conventional breeding experiments often only one final harvest is used to analyze the final tuber yield. This proceeding do not describe under which circumstances like stress intensity the tuber yield was achieved. Genotype evaluation in breeding experiments often relies only on visual evaluation of the aboveground biomass with no harvest of the plant. Besides the phenological stage at drought initiation the stress severity is another important aspect to determinate the drought stress response of potato genotypes. The stress severity depends on the water availability in term of soil water tension and the drought duration. In this study we developed a stress severity index (SSI) which combines all three important parameters, phenology, soil water tension and drought duration. With this SSI the selection processes should be improved and genotypes can be compared independently from environment, seasons and years. The SSI combines the yield response of potato to water deficit based on the soil tension the genotype was subjected to for the duration of the stress modified by the development stage of the genotype and drought duration. SSI allows for comparison of genotypic performance independent of year, location, season, soil type effects, and drought scenario. An SSI value of up to 1000 is able to differentiate between sensitive genotypes from more resistant genotypes. Beyond 1000, yields were generally reduced by more than 60% and a differentiation between genotypes was not possible anymore. SSI allows accumulating stress severity and thus, the higher the yield at a high SSI the stronger are the plants defense and adaptation mechanisms. Therefore, other indices that have looked into stay-green syndrome, rooting depth adaptations, leaf surface temperature, or canopy reflectance indices with only medium success, may benefit from including SSI in their indices to identify the underlying mechanisms of drought tolerance in potato. Remote sensing allows to evaluated many genotype simultaneously at field level. Proven indicators in drought tolerance screening are the normalized vegetation index (NDVI), the photochemical reflectance index (PRI) and thermography which describes the transpirational cooling of the leaves. Therefore, the last objective of this study was to validate the suitability of the SSI in remote-sensing stress diagnosis. The cluster analysis, including SSI, tuber yield reduction, NDVI, PRI and thermography identified three SSI groups with their corresponding physiological reactions under drought. The first group include SSI<1000 with fast decreasing NDVI, PRI and temperature deficit, in the second group matched SSI values from 1000 to 2000 with almost constant NDVI and temperature deficit and in the third group we found SSI beyond 2000 with corresponding small changes of NDVI, PRI and temperature deficit. The combination of these four parameters (tuber yield reduction, NDVI, PRI, thermography) explained 76 % of the variance which indicates this combination as valuable dataset analyzing drought tolerance in potato. Thus, combining these indicators with SSI and tuber yield reduction proved to be a first promising step for a new screening method for drought tolerance in a wider genotypic range. Whereas reflectance data can be recommended for assessing responses under mild to moderate stress severity, thermal imaging should rather be used to screen under mild or early drought stress.
Suitability of the stress severity index combined with remote‐sensing data as a tool to evaluate drought resistance traits in potato
(2023) Hoelle, Julia; Asch, Folkard; Khan, Awais; Bonierbale, Merideth
Potato is a drought susceptible crop and even short drought spells reduce tuber yields notably. In an earlier study we developed a stress severity index (SSI) based on the development stage of a genotype at the onset of drought and the soil water deficit based on soil water tension. Here, we test the suitability of the SSI combined with remotely sensed data as a screening tool to select drought‐tolerant potato genotypes. Normalized difference vegetation index (NDVI) and the photochemical reflectance index (PRI) were obtained from reflectance measurements and thermography. Temperature data from the thermography allow using the difference between leaf and air temperature (∆T) to estimate the transpirational cooling of the leaves. Via cluster analysis including SSI, tuber yield reduction under drought, NDVI, PRI and thermography, three groups were distinguished: 1. SSI < 1000 with fast decreasing NDVI, PRI and ∆T, 2. SSI 1000–2000 with almost constant NDVI and ∆T and 3. SSI > 2000 described by small changes of NDVI, PRI and temperature deficit. For SSI < 1000, ∆T, PRI and NDVI showed to be good indicators of genotypic performance under drought. Potential strategies for drought resistance in potato detectable through remote sensing are discussed.
Transplanting as an option to cope with abiotic stress in high‐altitude lowland rice production systems in East Africa
(2021) Abera, Bayuh Belay; Senthilkumar, Kalimuthu; Cotter, Marc; Asch, Folkard
The current practice of direct seeding in East‐African high‐altitude rice farming systems is constrained by water availability early in the season and low temperatures later in the season at the crop's critical reproductive stage. Thus, productivity is restricted as only short‐duration varieties can be grown due to the risk of crop failure. To fully exploit the yield potential of such rainfed systems, the best combination of crop establishment methods and climatic ‘best fit’ genotypes is required. In this study, nine rice genotypes were evaluated under direct seeding and transplanting in the 2016 and 2017 cropping seasons with the aim of identifying genotype by environment by management combinations best fitting the high‐altitude, rainfed rice production systems. On average across all genotypes, transplanting had a positive yield effect of 18% in 2016 and 23% in 2017. Regarding the phenological development, individual phenophases were not significantly affected by transplanting relative to direct seeding; however, vegetative development stages in transplanted rice tended to be about 15% longer than when direct seeded. Even though transplanting led to extended vegetative growth, the time in the nursery allowed the plants to escape the cold spell late in the season. The results from the current study provide options to adapt cropping calendars by combining genetic resources with targeted crop management, thus improving and stabilizing yields of rainfed lowland rice farming systems at high altitude.
Use of modeling to characterize phenology and associated traits among wheat cultivars
(2008) Herndl, Markus; Claupein, Wilhelm
Predicting phenology of wheat is important for many aspects of wheat production as for example facilitating accurate timing of pesticides, fertilizers and irrigation, avoiding stress at critical growth stages, and adapting cultivar characteristics to specific environmental constraints or global changes in climate. The aim of the dissertation was to characterize and test the impact of wheat phenology on agronomic traits through integrated use of crop models and information on the genetic makeup of cultivars. In an initial study, cultivar differences in vernalization requirement, photoperiod response and earliness per se were distinguished by field-based indices and compared with corresponding model parameters in CSM-Cropsim-CERES-Wheat model Version 4.0.2.0. To determine whether field-based indices can provide accurate characterization of vernalization requirement, photoperiod response and earliness per se, 26 winter wheat cultivars were evaluated under field conditions at Ihinger Hof, Germany using two natural photoperiod regimes (from different transplanting dates) and vernalization pre-treatments. Results indicated that combining planting dates with vernalization pre-treatments can permit reliable, quantitative characterization of vernalization requirement, photoperiod response and earliness per se of wheat cultivars. Furthermore, genotypic model parameters appeared to be reliable estimates of cultivar differences in response to vernalization and photoperiod. In a second study, the model parameters for vernalization requirement (P1V) and photoperiod response (P1D) were estimated using gene information. To estimate these model parameters through integrating effects of Vrn and Ppd loci, flowering data obtained for 29 cultivars tested in the International Winter Wheat Performance Nursery (IWWPN) were used. Summarizing, results indicated that gene-based estimation of model coefficients was effective for prediction of phenology over a wide range of environments and appears feasible for studying wheat response to environment. To assist plant breeding with crop models, a possibility could be to assess model parameters for designing improved plant types (ideotypes). CMS-Cropsim-CERES-Wheat was used in a third study to test model parameters concerning plant development and grain yield. In ideotyping sequences, the parameters were varied and the model was run in four different scenarios in the North China Plain. The parameter G1 (corresponding trait: kernel number per spike) showed the highest influence on yield over all scenarios followed by G2 (corresponding trait: kernel weight). Results obtained in this study could help breeders to select the relevant traits and integrate them in their breeding program for a specific population of environments. To investigate the coherences between pre-anthesis phenology and grain protein content in a fourth study the statistical analysis of causal relationships with genotypic model parameters was used. It was tested whether model-based characterizations of vernalization requirement, photoperiod response and earliness per se can help explain genotype x environment interactions for grain protein content. Twenty four winter wheat and five spring wheat cultivars (IWWPN) and twelve winter wheat cultivars (of a two year field study at Ihinger Hof, Germany) were characterized using CSM-Cropsim-CERES-Wheat. Covariance analyses indicated that vernalization requirement, photoperiod response, and earliness per se all influenced grain protein content, but their effects varied with site and year within region. Path analyses using data from two seasons in Germany confirmed that grain protein content increased with a shorter pre-anthesis phase and indicated in accordance with the covariance analyses the environmental dependence of this trait. The results proposed that efforts to improve grain protein content should target levels of vernalization requirement, photoperiod sensitivity and earliness per se to specific populations of environments and seek to reduce the apparent large influence of environment on grain protein content. The improved understanding of traits affecting phenology and the linkage with genotypic model parameters can be applied e.g. in China to solve arising and existing agricultural challenges. Model-based analyses can help adapting cropping systems to global warming. In the North China plain a more accurate timing of N-fertilizers and irrigation, as a result of modeling, can ensure a sustainable resource use while maintaining high yields. Summarizing, the findings of this dissertation showed that traits affecting phenology in wheat can be successfully characterized by field-based indices, genotypic model parameters and gene-based estimates of genotypic model parameters. Furthermore, the research showed how genotypic model parameters can be used for breeding purposes, and to test causal relationships both at regional and local geographic scales.