氮素添加对贝加尔针茅草原土壤团聚体微生物群落的影响

大气氮沉降增加作为全球气候变化的重要因素，其对土壤生态系统影响的研究受到了生态学家的广泛关注。土壤微生物是有机物分解和养分循环的主要参与者，在维持土壤的功能多样性和可持续发展方面发挥着重要的作用。氮沉降的激增会引起土壤微生物群落结构和功能的改变。土壤中营养物质在不同团聚体组分中分布的不均匀，为微生物提供了空间异质微生境。为揭示草原土壤不同粒径团聚体中微生物群落分布及其对氮素添加响应特征。自2010年起，在内蒙古贝加尔针茅草原典型地段设置N₀（0 kg hm^-2 a^-1）、N₁₅（15 kg hm^-2 a^-1）、N₃₀（30 kg hm^-2 a^-1）、N₅₀（50 kg hm^-2 a^-1）、N₁₀₀（100 kg hm^-2 a^-1）、N₁₅₀（150 kg hm^-2 a^-1）6个氮素添加处理模拟氮沉降野外控制试验。采用磷脂脂肪酸（phospholipid fatty acid，PLFA）法测定>2 mm、0.25-2 mm和<0.25 mm 3个粒径土壤团聚体中微生物PLFA含量，探讨氮素添加对土壤团聚体微生物群落结构的影响。结果表明：氮素添加提高了土壤碳、氮含量，降低了土壤pH。氮素添加显著提高了0.25-2 mm土壤团聚体微生物群落磷脂脂肪酸总量、真菌磷脂脂肪酸含量和真菌/细菌（Fungi/bacteria，F/B）、革兰氏阳性菌/革兰氏阴性菌（Gram-positive bacteria/gram-negative bacteria，G⁺/G^-）的比值（P<0.05），降低了土壤团聚体微生物Margalef丰富度指数（P<0.05）。相关性分析表明，土壤团聚体微生物总PLFAs、真菌PLFAs含量、G⁺/G^-、F/B与土壤有机碳、全氮含量呈显著正相关关系，与C/N值负相关。综合研究表明，连续8年氮素添加显著提高了土壤有机碳和全氮含量、降低了土壤pH；提高了0.25-2 mm土壤团聚体真菌群落，土壤有机碳、全氮的固持与真菌群落的增加有关。

Effects of nitrogen addition on microbial community in soil aggregates of Stipa Baicalensis Steppe in Inner Mongolia, China

The increased atmospheric nitrogen deposition is an important part of global climate change. The study of the effects of nitrogen deposition on soil ecosystem is also attracted public attention to ecologists. Soil microorganisms, the main player in organic decomposition and nutrient cycling, play an important role in maintaining the functional diversity and sustainable development of soil. The notable increase of nitrogen deposition changes the structure and function of the soil microbial community. The different aggregate, with uneven distribution of nutrients components, provides the spatially heterogeneous microhabitat for microorganisms. In order to reveal the response of microbial community distribution on nitrogen addition in different particle size aggregates of grassland soil. Since 2010, We have set up six nitrogen addition treatments(N₀(0 kg hm^-2 a^-1), N₁₅ (15 kg hm^-2 a^-1), N₃₀ (30 kg hm^-2 a^-1), N₅₀ (50 kg hm^-2 a^-1), N₁₀₀ (100 kg hm^-2 a^-1) and N₁₅₀ (150 kg hm^-2 a^-1)) to simulate the field experiment of nitrogen deposition in Stipa baicalensis grassland in Inner Mongolia. Phospholipid fatty acid (PLFA) method was used to determine the content of microbial PLFA in three particle sizes soil aggregates (>2 mm, 0.25-2 mm and <0.25 mm diameter), to explore the effect of nitrogen addition on the microbial community structure. The results showed that the nitrogen addition increased the soil carbon and nitrogen content and decreased the soil pH. Nitrogen addition significantly increased the total PLFA content and fungal PLFA content in the microbial community of 0.25-2 mm soil aggregates. The addition of nitrogen also increased the ratio of fungal/bacterial and gram-positive bacteria/gram-negative bacteria (P<0.05) of 0.25-2 mm soil aggregates, but decreased the microbial Margalef index of soil aggregates (P<0.05). The correlation analysis showed that total PLFAs, fungi PLFAs content, the ratio of gram-positive bacteria/gram-negative bacteria and fungi/bacteria were positively correlated with soil organic carbon and total nitrogen content, but negatively correlated with C/N ratio. This study revealed that the nitrogen addition for 8 consecutive years significantly increased the soil organic carbon and total nitrogen content, decreased soil pH, and increased the fungal community of 0.25-2 mm soil aggregates, and the variation of soil organic carbon and total nitrogen was associated with the increased fungal community.