Resiliency of arbuscular mycorrhizal soybean to water stress in a Southern Ontario agroecosystem

Background/Question/Methods

Assessing the consequences of changing precipitation regimes on agricultural crop growth and yield, and evaluating mitigation strategies, is of critical importance. Alternative agricultural management regimes, namely agroforestry (AF) systems, are likely to confer greater agricultural resilience to climatic change, however, to date studies have primarily focussed on crop physiological or yields response. Few have assessed how key biological processes, namely plant-fungal, interactions may change under shifting climate. For example, soybean (Glycine max) is a key agricultural crop in Canada, whose growth and yield that are highly dependent on arbuscular mycorrhizal fungal (AMF) associations. We designed an in situ rainfall exclusion experiment at a model AF system in Ontario to address the following research question: do fungal communities co-vary with soybean physiological performance under water stress in agroecosystems? Soybean and AMF communities were sampled under conventional monoculture (CM) and AF systems, where we employed rainfall reduction shelters to simulate water deficiencies. Rainfall treatments were removed at 8 weeks after planting to evaluate AMF and soybean resilience to water stress. AMF community structure was assessed using terminal restriction fragment length polymorphism while soybean physiological responses were assessed based on rates of leaf-level photosynthesis (A_max), stomatal conductance (g_s), and water use efficiency (WUE).

Results/Conclusions

Within rainfall exclusion treatments, A_max and WUE were both higher for plants grown in CM as compared to those in AF system, whereas, g_s showed the opposite trend. Following the removal of rainfall exclusions however, we did detect evidence of physiological recovery following water stress. Specifically, following the removal of rainfall reduction shelters, there were no significant differences in any leaf physiological parameters among plants in CM and AF. However, for soybean plants grown in CM, absolute rates of A_maxdeclined following water stress yet increased for soybean plants grown in AF, following water stress.

We found some evidence that these physiological paramaters co-vary with changes in AMF community structure. Generally, AMF community diversity was higher in the AF system as compared to the CM system; similarly, AMF community diversity was reduced under water deficit conditions. This further suggests that the ability of AF systems to mitigate the effects of changes in water availability is at least to some degree linked with AMF community dynamics and may confer greater resilience to water stress but a better understanding between mitigation measures and resilience in agroecosystems is still needed.