Carbon storage and plant-soil linkages among soil aggregates as affected by nitrogen enrichment and mowing management in a meadow grassland

Abstract

Soil aggregates constitute spatially-separated microbial habitats and architectural units for biogeochemical reactions. However, little is known about how aggregates varying in size can affect soil carbon (C) storage and mediate the direction of plant-soil interactions. In a meadow steppe, we assessed soil aggregate C storage affected by nitrogen (N) addition and mowing and to what degree plant-soil interactions differed among soil aggregate-size classes. Nitrogen addition increased plant biomass, soil C concentration in macroaggregates and relative abundance of bacteria, but decreased fungal relative abundance and the activity of oxidative enzymes. However, mowing counteracted N effects on plant productivity and enzyme activity. In macroaggregates, close linkages with plant biomass and species richness were found for soil available nutrients and ratio of fungi to bacteria (F:B ratio). In contrast, strong physical protection and restricted fungal dominance and activity contributed to C stabilization in microaggregates, where plant community and soil properties were less linked with each other. Our study clearly demonstrated that stronger plant-soil linkages occurred in macro- vs. microaggregates. This linkage was associated with a rise in plant biomass and soil C accumulation but a drop in F:B ratio in macroaggregates under N addition.