干旱对不同花椒种植模式下土壤微生物和线虫群落的影响

随着全球气候变暖, 我国岷江上游干旱区面积呈现增加的趋势。花椒(Zanthoxylum bungeanum)是岷江上游重要的经济树种之一, 对当地经济和社会发展起着重要作用, 提高花椒生态系统应对干旱干扰已成为迫切的问题。本研究设置了花椒单作、花椒-苜蓿(Medicago sativa)间作和花椒-大豆(Glycine max)间作3种种植模式, 在2015年8月对每种种植模式模拟干旱30 d, 每种种植模式包括干旱和对照处理, 在模拟干旱结束后、恢复15 d、30 d和45 d后分别采集土壤样品, 分析土壤化学性质、土壤微生物和线虫群落, 以探究花椒林下豆科植物能否缓和干旱的遗留效应对土壤化学性质和土壤生物的影响。重复测量方差分析表明: 在花椒单作模式下, 干旱恢复45 d后土壤硝态氮含量显著高于对照, 微生物量和真菌/细菌比与对照无显著差异, 线虫密度与对照无显著差异, 但线虫功能团没有恢复到对照水平; 在花椒-苜蓿间作模式下, 干旱恢复45 d后土壤含水量、铵态氮、硝态氮、溶解性有机碳、溶解性有机氮、微生物量、真菌/细菌比、线虫密度和线虫功能团组成与对照无显著差异, 但植食性线虫属Boleodorus相对多度显著高于对照; 在花椒-大豆间作模式下, 干旱恢复45 d后土壤含水量、铵态氮、硝态氮、溶解性有机碳、溶解性有机氮、微生物量和真菌/细菌比与对照无显著差异, 但线虫密度和功能团组成与对照有显著差异。在3种花椒种植模式中, 花椒-苜蓿间作模式下干旱的遗留效应对土壤养分和生物的影响最小。因此, 在干旱背景下, 花椒林下间作豆科植物可以加快土壤养分、土壤微生物和线虫群落的恢复, 进而有利于目标作物生长。

Effects of Zanthoxylum bungeanum agroforestry systems on soil microbial and nematode communities under drought

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.