To determine how plant species richness impacts microbial assimilation of new photosynthate, and how this may be modified by atmospheric N deposition, we analyzed the microbial assimilation of recent photosynthate in a 6-year-long field experiment in which plant species richness, atmospheric N deposition, and atmospheric CO2 concentration were manipulated in concert. The depleted δ13C of fumigation CO2 enabled us to investigate the effect of plant species richness and atmospheric N deposition on the metabolism of soil microbial communities in the elevated CO2 treatment. To accomplish this, we determined the δ13C of bacterial, actinobacterial, and fungal phospholipid fatty acids (PLFAs). In the elevated CO2 conditions of this study, the δ13C of bacterial PLFAs (i15:0, i16:0, 16:1ω7c, 16:1ω9c, 10Me16:0, and 10Me18:0) and the fungal PLFA 18:1ω9c was significantly lower in species-rich plant communities than in species-poor plant communities, indicating that microbial incorporation of new C increased with plant species richness. Despite an increase in plant production, total PLFA decreased under N deposition. Moreover, N deposition also decreased fungal relative abundance in species-rich plant communities. In our study, plant species richness directly increased microbial incorporation of new photosynthate, providing a mechanistic link between greater plant detritus production in species-rich plant communities and larger and more active soil microbial community.
Bibliographical noteFunding Information:
Acknowledgments The BioCON experiment was funded by the Department of Energy (Program for Ecological Research Grant DE-FG02-96ER62291), National Science Foundation (Long Term Ecological Research program: 0080382, Biocomplexity program: 0322057), and by a grant-in-aid from the University of Minnesota. We thank the interns who assisted us with soil sampling at the BioCON site. We also acknowledge Katie Berlin, Jana Gastellum, Michelle Martin, and Dan Rivas for their help with lab analyses at the soils lab in the University of Michigan. Kees-Jan van Groenigen provided valuable comments on the earlier versions of this manuscript.
- Atmospheric N deposition
- Grassland ecosystems
- Phospholipid fatty acid (PLFA)
- Plant species richness
- Soil microorganisms