Abstract:

Aims: Climate change is poised to increase the frequency and severity of extreme climate events like drought. In China, drought in the upper reaches of the Minjiang River is increasing. Zanthoxylum bungeanum is an important tree species in the region because of its prominent role in local economic and social development. Therefore, it is urgent to investigate whether Z. bungeanum mixed with legume plants can mitigate the effects of drought in agroforestry systems.
Method: We conducted an agroforestry experiment under simulated drought conditions that involved three planting systems: monocultures of the focal species Z. bungeanum, mixed cultures of Z. bungeanum and Medicago sativa, and mixed cultures of Z. bungeanum and Glycine max. We collected soil samples after 30 days of simulated drought in August, and after 15, 30, and 45 days of restoration to assess whether Z. bungeanum agroforestry systems can alleviate the residual effect of drought on soil chemical properties and soil biology.
Results: Repeated measure ANOVA showed that in the monoculture of Z. bungeanum, soil nitrate nitrogen content was significantly higher than that of the control after 45 days of drought recovery. Furthermore, microbial biomass and the fungal-to-bacteria ratio was not significantly different from the control. While nematode density was not significantly different from the control, nematode functional groups did not recover to the control level. In the mixed cultures of Z. bungeanum and M. sativa, there were no significant differences in soil water content, NO₃^--N content, NH₄⁺-N content, dissolved organic carbon content and dissolved organic nitrogen content, microbial biomass, fungal-to-bacteria ratio, nematode density, or nematode functional groups, but the relative abundance of nematode genus Boleodorus was significantly higher than that of the control. In the mixed cultures of Z. bungeanum and G. max, there were no significant differences in soil water content, NO₃^--N content, NH₄⁺-N content, dissolved organic carbon content and dissolved organic nitrogen content, microbial biomass, or fungal-to-bacteria ratio between the two groups after 45 days of drought recovery, but there were significant differences in nematode density, functional groups, and community structure. Among these three planting patterns of Z. bungeanum, the residual effect of drought had minimal effects on soil nutrients and organisms under the intercropping pattern of Z. bungeanum and M. sativa.
Conclusion: Our study revealed that the differing functional traits of potential neighbors in agroforestry systems can have additive effects and lead to a marked divergence of soil food-web resistance and resilience. The presence of certain neighbor species can indirectly alleviate the impacts of drought on focal species via increasing the stability of the soil food web under future climate change.

Key words: drought, agroforestry system, legume, microorganism, nematode