长期氮添加对亚热带森林土壤微生物碳源代谢多样性的影响

土壤微生物功能多样性对维持生态系统功能和稳定性具有非常重要的意义。人类活动造成全球氮沉降量激增,会引起土壤微生物群落结构和功能的改变,但是目前有关亚热带森林生态系统土壤微生物碳源利用多样性对模拟N沉降的响应还不是很清楚。依托位于鼎湖山的长达15年的长期野外模拟氮沉降试验样地平台,借助Biolog-Eco微平板技术,分析探讨了不同N添加量对季风常绿阔叶林中土壤微生物群落碳代谢功能多样性的影响差异及机制。研究结果表明:(1)与对照相比,长期低N、中N和高N量添加使土壤微生物碳源代谢活性(AWCD)分别显著降低了15.3%、32.9%和38.0%;并且显著降低了微生物碳源利用Shannon多样性指数和丰富度指数;(2)微生物对糖类、羧酸、氨基酸、胺类和酚酸类的利用随着施N水平的提高而显著降低;其中胺类最为敏感,长期高N添加下其利用强度与对照相比显著降低了80.2%;(3)主成分分析表明,不同N添加水平显著影响了土壤微生物碳源利用(P=0.001);(4)分类变异分析表明,土壤和植物因素可解释不同N水平下碳源利用差异的90.7%;(5)典型对应分析发现,土壤pH(P=0.009)是解释不同N水平添加处理间土壤微生物碳源代谢多样性差异的主要环境因子;而植被丰富度和凋落物量没有显著影响。综上所述,长期不同N添加显著影响了亚热带森林土壤微生物碳源代谢多样性,并且结果表明土壤pH是影响碳源利用多样性的主要影响因素。研究结果对于揭示全球变化影响下热带森林生态系统地下生物多样性维持机制提供了重要理论依据。

Effects of long-term nitrogen addition on the metabolic diversity of microbial carbon sources in subtropical forest soils

Soil microbial functional diversity plays an important role in maintaining the function and stability of the ecosystem. The rapid increase in global nitrogen deposition caused by human activity will cause changes in the structure and function of the soil microbial community. However, we know very little about how elevated N inputs over the long-term will influence microbial carbon source utilization diversity in tropical forests. We investigated the soil microbial community diversity of carbon metabolism and their driving factors based on a 15-year long field experiment monitoring different N levels at the Dinghushan biosphere reserve station using Biolog-Eco microplate technology. The results showed that:(1) compared with the control, carbon metabolic activity (AWCD) significantly decreased by 15.3%, 32.9% and 38.0% under low, medium, and high N treatments, respectively. In addition, the Shannon diversity and richness indexes significantly decreased after N application; (2) The utilization of carbohydrate, carboxylic acids, amino acids, amines, and phenolic acids significantly declined with increasing applications of N. Of these, amines showed the strongest response, and the intensity of their utilization reduced significantly by 80.2% after long-term high N addition. (3) The principal component analysis showed that there were significant differences in the microbial utilization of carbon at different N levels (P=0.001); (4) The variation portioning analysis showed that soil and plant factors explained 90.7% of the variations in microbial carbon source metabolism. (5) The canonical correspondence analysis (CCA) showed that soil pH (P=0.009) was the most important environmental factor influencing variations in the utilization of microbial carbon sources in different N treatments. However, plant richness and litterfall had no significant effect on utilization. Thus, our study suggests that N addition over the long-term significantly alters the diversity of soil microbial carbon source utilization in subtropical forests with soil pH as the main influencing factor. The results of this study provides an important theoretical basis for understanding belowground diversity of subtropical forests under global climatic changes.