Institut für Landschafts- und Pflanzenökologie

Permanent URI for this collectionhttps://hohpublica.uni-hohenheim.de/handle/123456789/11

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Coffee berry borer control, but not coffee yield, is mediated by non-additive interaction between birds and ants across different cultivation systems
(2026) Cardona Tejada, Damaris A.; Parra, Juan L.; Grass, Ingo; Schurr, Frank M.
Coffee is one of the most traded tropical crops, cultivated in some of the most biodiverse regions on the planet. Coffee production can be seriously reduced by the coffee berry borer (CBB), a specialized beetle that feeds on the endosperm of coffee berries. Given the CBB's economic relevance, coffee-producing countries have developed extensive Integrated Pest Management programs. Nonetheless, most of these programs fail to incorporate CBB control by natural enemies such as birds and ants. While the effects of birds and ants on CBB suppression have been demonstrated to be positive when studied in isolation, their interactive effects have been little studied. To better understand the effects of the trophic interaction between birds and ants on CBB control, we conducted a full-factorial block experiment excluding birds and ants from coffee shrubs. We distributed 49 experimental blocks across three different coffee systems in a Colombian landscape: sun-exposed coffee, coffee-plantain intercropping, and shade coffee. We found birds to be key control agents of CBB: in the presence of ants, bird exclusion increased CBB infestation by 36 %. However, in the absence of ants, birds had little effect on CBB infestation, demonstrating that the effects of birds and ants were non-additive. This suggests that birds control CBB through a trophic cascade mediated by ants. We also found that the effects of exclusions were modified by the cultivation system, with the shade coffee system consistently reducing CBB infestation. Our experiment demonstrates that crop diversification is an effective measure for integrating local enemies into IPM strategies. Nonetheless, we acknowledge that trophic interactions are highly complex and exhibit a context-dependency that can result in the suppression of biological pest control. Therefore, we recommend conducting future analysis on evaluating the effects of predator´s community composition to encourage the development of IPM programs that leverage biodiversity in agroecosystems.
Drought impacts on plant–soil carbon allocation - integrating future mean climatic conditions
(2025) Leyrer, Vinzent; Blum, Juliette; Marhan, Sven; Kandeler, Ellen; Zimmermann, Telse; Berauer, Bernd J.; Schweiger, Andreas H.; Canarini, Alberto; Richter, Andreas; Poll, Christian
Droughts affect soil microbial abundance and functions—key parameters of plant–soil carbon (C) allocation dynamics. However, the impact of drought may be modified by the mean climatic conditions to which the soil microbiome has previously been exposed. In a future warmer and drier world, effects of drought may therefore differ from those observed in studies that simulate drought under current climatic conditions. To investigate this, we used the field experiment ‘Hohenheim Climate Change,’ an arable field where predicted drier and warmer mean climatic conditions had been simulated for 12 years. In April 2021, we exposed this agroecosystem to 8 weeks of drought with subsequent rewetting. Before drought, at peak drought, and after rewetting, we pulse‐labelled winter wheat in situ with 13CO2 to trace recently assimilated C from plants to soil microorganisms and back to the atmosphere. Severe drought decreased soil respiration (−35%) and abundance of gram‐positive bacteria (−15%) but had no effect on gram‐negative bacteria, fungi, and total microbial biomass C. This pattern was not affected by the mean precipitation regime to which the microbes had been pre‐exposed. Reduced mean precipitation had, however, a legacy effect by decreasing the proportion of recently assimilated C allocated to the microbial biomass C pool (−50%). Apart from that, continuous soil warming was an important driver of C fluxes throughout our experiment, increasing plant biomass, root sugar concentration, labile C, and respiration. Warming also shifted microorganisms toward utilizing soil organic matter as a C source instead of recently assimilated compounds. Our study found that moderate shifts in mean precipitation patterns can impose a legacy on how plant‐derived C is allocated in the microbial biomass of a temperate agroecosystem during drought. The overarching effect of soil warming, however, suggests that how temperate agroecosystems respond to drought will mainly be affected by future temperature increases.

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