氮添加对荒漠草原植物群落组成与微生物生物量生态化学计量特征的影响

大气氮(N)沉降增加加速了土壤N循环, 引起微生物生物量碳(C):N:磷(P)生态化学计量关系失衡、植物种丧失和生态系统服务功能降低等问题。开展N添加下植物群落组成与微生物生物量生态化学计量特征关系的研究, 可为深入了解N沉降增加引起植物多样性降低的机理提供新思路。该文以宁夏荒漠草原为研究对象, 探讨了N添加下植物生物量和群落多样性的变化趋势, 分析了微生物生物量C:N:P生态化学计量特征独立及其与其他土壤因子共同对植物群落组成的影响。结果表明: N添加下猪毛菜(Salsola collina)生物量呈显著增加趋势, 牛枝子(Lespedeza potaninii)生物量呈逐渐降低趋势, 其他植物种生物量亦呈降低趋势但未达到显著水平; 沿N添加梯度, Shannon-Wiener多样性指数、Simpson优势度指数和Patrick丰富度指数均呈先略有增加后逐渐降低的趋势; N添加提高了微生物生物量N含量和N:P, 降低了微生物生物量C:N; 植物群落组成与微生物生物量N含量、微生物生物量C:N、微生物生物量N:P、土壤NO₃ ^--N浓度、土壤NH₄ ⁺-N浓度以及土壤全P含量有较强的相关关系; 微生物生物量C:N:P生态化学计量特征对植物种群生物量和群落多样性变化的独立解释力较弱, 但却与其他土壤因子共同解释了较大变差, 意味着N添加下微生物生物量C:N:P生态化学计量特征对植物群落组成的影响与其他土壤因子高度相关。

Effects of nitrogen addition on plant community composition and microbial biomass ecological stoichiometry in a desert steppe in China

Aims Increasing atmospheric nitrogen (N) deposition accelerates soil N cycling, potentially resulting in decoupling of microbial biomass carbon (C):N:phosphorus (P), loss of plant species, and reductions of provision of ecosystem service. Studies on how the changes of elemental balance in microbes affect plant community composition, could provide a new insight for making clear the mechanism of N-induced loss of plant species. Methods We conducted a manipulative N addition experiment in a desert steppe in Ningxia, northwestern China to quantify the changes in plant biomass and species composition over two years. We analyzed the individual effects of microbial biomass C:N:P ecological stoichiometry and the joint effects with other key soil factors on plant community composition. Important findings The responses of plants to N addition appeared species-specific. The biomass of Salsola collina increased substantially; the biomass of Lespedeza potaninii decreased gradually. Other species showed slightly decreasing in biomass although statistically insignificant (p > 0.05). Along the N addition gradient, Shannon-Wiener diversity index, Simpson dominance index, and Patrick richness index of the plant community increased initially but decreased over time later. With increase in N addition level, the N content and N:P ratio of the microbial community increased, but the C:N ratio decreased. Plant community composition showed stronger correlations with microbial biomass N content, microbial biomass C:N ratio, microbial biomass N:P, soil NO₃ ^--N concentration, soil NH₄ ⁺-N concentration, and the total P content of the soils. Microbial biomass C:N:P ecological stoichiometry explained <3% of the variation in aboveground plant biomass and community diversity index. Surprisingly, the joint influences from microbial biomass C:N:P ecological stoichiometry and other soil properties explained 51% of the variation in plant biomass and 26% of the change in plant community diversity. These results indicate that the effect of microbial biomass C:N:P ecological stoichiometry on plant community was highly related to the effects of other soil properties under N addition.