Drought and Herbivory Drive Physiological and Phytohormonal Changes in Soybean (Glycine max Merril): Insights From a Meta-Analysis.

With climate change, abiotic and biotic stresses such as drought and herbivory are predicted to further diminish agricultural productivity. Soybean (Glycine max [L.] Merrill), a crop of global economic importance, is vulnerable to both. However, the interactive effects of drought and herbivory on soybeans haven't been explored, especially through the lens of physiological and phytohormonal changes. To address this, we conducted a meta-analysis from 114 published studies, further reduced to 31 after removing redundancy, with data on physiological (photosynthesis and stomatal conductance) and phytohormonal traits (jasmonic acid [JA] and salicylic acid [SA]) of soybeans under drought, herbivory, and their combination. With existing studies so far, we show that drought has negative impacts on soybean photosynthesis and stomatal conductance whereas herbivory has negative effects on photosynthesis but neutral effects on stomatal conductance. And the effects of drought and herbivory on phytohormones had opposite effects, with JA levels increasing. To our understanding, this is the first meta-analysis assimilating studies to understand the combined impacts of drought and herbivory on soybean physiological and phytohormonal changes. We also put forward potential questions and avenues for further research in expanding our understanding about the regulatory pathways and consequences of other abiotic and biotic stressors in agroecosystems.