氮磷添加和栽植密度对大叶相思林土壤微生物群落功能多样性的影响

Abstract

土壤微生物群落是土壤质量潜在的生态指标，在维持生态系统功能和服务中起着关键的作用。采用Biolog-ECO微平板法，探讨氮磷添加与不同栽植密度交互对大叶相思林（Acacia auriculiformis）土壤微生物功能多样性的影响，以便为建立合理的林分密度和氮磷施肥模式，提高土壤质量提供理论参考。以大叶相思林为研究对象，选择氯化铵（NH₄Cl）作为氮肥模拟大气氮沉降，用二水合磷酸二氢钠（NaH₂PO₄·2H₂O）进行磷添加。氮磷处理设置4个水平，即CK、施N、施P和施N+P。种植密度设置4个水平，即1667、2500、4444、10000株/hm²（分别以低密度、中密度、较高密度、高密度表示）。研究结果表明，施P显著提高了4个密度大叶相思林土壤微生物的AWCD值、碳源利用丰富度指数、McIntosh指数、Shannon指数和Simpson指数，而施N和N+P则相反。随着林分密度的减小，各处理的土壤微生物AWCD值趋于减少。通常低密度林分的土壤微生物的丰富度指数、Shannon-Wiener指数、McIntosh指数和Simpson指数较小。;Climate change affects the physiological activities of soil microbes, which causes changes of soil microbial community structure and functional diversity and cascades the effects on biogeochemical cycling and climate-ecosystem feedbacks. Among them, nitrogen (N) and phosphorus (P) are considered as the limiting factors that influences the plant biodiversity and primary productivity in forest ecosystems. The external N addition or atmospheric N deposition has been found to affect the aboveground biology processes and the underground biochemistry of soil, both directly and indirectly. Chronic elevated N input has been shown to lead to many adverse impacts, including soil acidification, nutrients imbalance, and the increased greenhouse gas emissions. Forest soils of southern China are P-limited, because they are highly weathered and leached, and little P is released even from the weathering of primary P-bearing minerals. As a result, P fertilization is widely used in the subtropical forests of southern China. As an important component in regulating belowground ecological processes, the soil microbes are primary mediators of organic matter decomposition and nutrient cycling, and thus play a key role in maintaining function and sustainability of terrestrial ecosystems. Additionally, changes in soil microbial function and community composition may trigger a series of responses, such as impacting litter and organic matter decomposition rates, humus formation nutrient transformation and cycling, and then alter the interaction between soil microbes and plant communities. In this study, Biolog-ECO microplate method was used to investigate the interactive effects of nitrogen and phosphorus additions and different stand densities on soil microbial functional diversity of Acacia auriculiformis stands, which can provide a basis for establishing reasonable stand density, fertilization method, and improve soil quality. NH₄Cl and NaH₂PO₄·2H₂O were selected to simulate atmospheric nitrogen and phosphorus additions with 4 treatments (CK, N, P and N+P) and stand density was set at 4 levels (1667, 2500, 4444, and 10000 seedlings/hm²). The results showed that P treatment promoted the average well color development (AWCD) values, richness index, McIntosh index, Shannon index, and Simpson index of soil microbes in the four density stands, while the N and N+P treatments were opposite. With the decrease of forest density, the AWCD values of soil microbes in all treatments decreased. Generally, soil microbial richness index, Shannon-Wiener index, McIntosh index and Simpson index were small in the low density stands.