氮磷添加对荒漠草原植物群落多样性和土壤C:N:P生态化学计量特征的影响

为了深入了解P添加是否有助于缓解N沉降增加引起的植物群落多样性降低等问题,以宁夏盐池县长期围封的荒漠草原为研究对象,探讨了连续两年(2015—2016年) 5 g/m~2/a的N水平下,P添加对植物生物量、群落多样性和土壤C∶N∶P生态化学计量特征的影响,分析了植物群落多样性与土壤C∶N∶P比及其他关键因子的关系。结果表明:少量N添加下,增施P肥促进了植物生物量积累,但中高量P添加抑制了多数植物生长,使牛枝子(Lespedeza potaninii)、草木樨状黄芪(Astragalus melilotoides)和苦豆子(Sophora alopecuroides)等物种重要值降低;随着P添加量增加,Shannon-Wiener多样性指数和Patrick丰富度指数先增加后降低,Simpson优势度指数逐渐增加,Pielou均匀度指数变化幅度较小;随着P添加量增加,土壤C∶P和N∶P比逐渐降低;土壤N∶P比、C∶P比、全P含量、速效P浓度以及微生物量C∶P比与植物群落多样性关系密切,意味着N沉降增加下趋于解耦的土壤元素平衡关系可能会影响到植物群落组成。综合以上结果,适量P添加可以通过提高土壤P有效性、增加凋落物归还量和刺激微生物P释放等途径,调节土壤P供给和植物P需求间的压力,从而缓解N添加引起的植物群落多样性降低。

Effects of nitrogen and phosphorus addition on plant community diversity and soil C: N: P ecological stoichiometry in a desert steppe of China

In order to deeply understand whether P addition could alleviate the N deposition-induced decrease in plant community diversity, we explored the effects of P addition on plant biomass, community diversity, and soil C:N:P ecological stoichiometry under 2-year of 5 g/m²/a of N addition (2015-2016) in a long-term fenced desert steppe, located in Yanchi County, Ningxia, north-western China. We also analysed the relationships between plant community diversity indices and soil C:N:P ecological stoichiometry as well as other key soil factors. The results showed that combined with low N addition, low P addition promoted plant biomass accumulation, but moderate and high P addition inhibited the growth of most species, resulting in decreases in the importance values of Lespedeza potaninii, Astragalus melilotoides, and Sophora alopecuroides. With the increase of P addition, both Shannon-Wiener diversity index and Patrick richness index increased firstly and then decreased, while there were gradual increase in Simpson dominance index and little change in Pielou evenness index. Increasing P addition reduced soil C:P and N:P ratios; soil N:P ratio, C:P ratio, total P content, available P concentration, and microbial biomass C:P ratio were tightly related to plant diversity indices, indicating that the decoupling of elemental stoichiometry in soils will exert great impacts on plant community composition under increasing N deposition. Taken together, these results might suggest an appropriate amount of P addition could regulate the pressure between soil P supply and plant P demand through increasing soil availability, raising litter return amount, stimulating microbial P release, and other approaches, to further alleviate the N addition-induced decrease in plant community diversity.