Differentiated Response Mechanisms of Soil Microbial Communities to Nitrogen Deposition Driven by Tree Species Variations in Subtropical Planted Forests

Zheng Hou ^1,2 Wen Chen ² Xiaohua Zhang ³ Donghui Zhang ⁴ Jinmei Xing ⁴ Yong Ba ¹ Jie Yu ¹ Keqin Wang ⁴ Ya Zhang ^1* Yali Song ^4*

• ¹ Kunming General Survey of Natural Resources Center, China Geological Survey, Kunming, Yunnan Province, China
• ² School of Ecology and Environment, Southwest Forestry University, Kunming, Yunnan Province, China
• ³ School of Soil and Water Conservation, Beijing Forestry University, Haidian, Beijing, China
• ⁴ Southwest Forestry University, Kunming, Yunnan Province, China

The increasing rate of atmospheric nitrogen deposition has severely affected the structure and function of these ecosystems. Although nitrogen deposition is increasing globally, the responses of soil microbial communities in subtropical planted forests remain inadequately studied. A four-year experimental simulation was conducted to assess the impacts of varying nitrogen deposition levels (CK:) on two subtropical tree species, Pinus yunnanensis Franch. and Pinus armandii Franch. The study investigated the shortterm responses of soil nutrients, bacterial communities, and fungal community structures to nitrogen deposition. Our results showed that species differences led to variations in soil properties between the two forests, particularly a significant increase in soil pH in Pinus yunnanensis Franch. forests and a significant decrease in soil pH in Pinus armandii Franch. forests. Nitrogen addition did not significantly affect microbial diversity in either Pinus yunnanensis Franch. or Pinus armandii Franch. soils; however, forest type differences had a significant impact on bacterial diversity. The nitrogen addition significantly affected the relative abundance of specific microbial communities in both forest types, particularly altering the fungal community structure in the Pinus yunnanensis Franch forests, while no significant changes were observed in the bacterial community structure in either forest type. Furthermore, nitrogen addition increased the network complexity of bacterial communities in Pinus yunnanensis Franch. forests while decreasing network complexity in Pinus armandii Franch. forests. Structural equation modeling indicated that nitrogen addition regulates soil bacterial and fungal diversity in both forest types by modifying nitrogen availability. These findings provide insights into the potential long-term impacts of nitrogen deposition on subtropical planted forest ecosystems and offer a theoretical basis for sustainable forest management and regulatory practices.