Roles of soil functional microbes driving soil phosphorus fractions in response to nitrogen addition differ among aggregate levels

Jia'Xin Hu¹Haiying Cui^2*Mingcai Fan²Min Liu²Shanling Wang²Xiuping Li²Xia Peng²Fengxue Shi³WENZHENG SONG⁴Wei Sun^2*

• ¹Institute of Grassland Science, School of Life Science, Northeast Normal University, Key Laboratory of Vegetation Ecology, Ministry of Education, Jilin Songnen Grassland Ecosystem National Observation and Research Station, Changchun, 130024, China, School of Chemistry, Northeast Normal University, Changchun, China
• ²School of Chemistry, Northeast Normal University, Changchun, China
• ³Jilin Provincial Natural History Museum，Northeast Normal University，Changchun，China, School of Chemistry, Northeast Normal University, Changchun, China
• ⁴College of Tourism, Resources and Environment, Zaozhuang University, Zaozhuang 277160, China, School of Chemistry, Northeast Normal University, Changchun, China

Phosphorus (P) as one of the most important limited nutrient elements for plant productivity in terrestrial ecosystems. As the key driver of P cycling processes, the changes of soil microbial diversity and community structure can influence soil P cycling and availability. Nitrogen (N) deposition as global change factors profoundly alters soil P cycling, yet how soil P fractions response to N addition of multiple gradients and the potential driven mechanisms of plant, microbial and soil properties at the soil aggregate levels remains unclear. Here, we conducted a seven-year long-term field experiment to investigate the response patterns of soil labile and non-labile P fractions to N addition at the four gradients (0, 5, 10, and 20 g N m-2 y-1) in macro-and microaggragates in a meadow steppe in Northeast China. We found that N addition reduced the contents of soil non-labile P in macroaggregates, but increased all P fractions in microaggregates. Soil functional microbes play different roles in driving soil P fractions. Soil labile and non-labile P fractions were mainly controlled by the diversity and gene abundance of soil phoD-harboring bacteria, and plant and soil properties in macroaggregates, but by soil microbial stoichiometry in microaggregates. Moreover, N addition indirectly regulated P fractions by altering microbial functional traits, rather than directly by the changes of soil nutrient availability. Our results demonstrate that the mechanisms by which soil functional microbes and microbial stoichiometry regulate soil P fractions and transformation vary among soil aggregates. Our study provides the new insight of soil functional microbes playing the crucial roles in improving P supply by accelerating the process of soil P fractions under global change scenarios. To enhance sustainable grassland development in the changing world, we need to prioritize the leveraging of soil aggregate-mediated processes in grasslands .