Whether the terrestrial biosphere will continue to act as a net carbon (C) sink in the face of multiple global changes is questionable. A key uncertainty is whether increases in plant C fixation under elevated carbon dioxide (CO2) will translate into decades-long C storage and whether this depends on other concurrently changing factors. We investigated how manipulations of CO2, soil nitrogen (N) supply, and plant species richness influenced total ecosystem (plant + soil to 60 cm) C storage over 19 y in a free-air CO2 enrichment grassland experiment (BioCON) in Minnesota. On average, after 19 y of treatments, increasing species richness from 1 to 4, 9, or 16 enhanced total ecosystem C storage by 22 to 32%, whereas N addition of 4 g N m−2 · y−1 and elevated CO2 of +180 ppm had only modest effects (increasing C stores by less than 5%). While all treatments increased net primary productivity, only increasing species richness enhanced net primary productivity sufficiently to more than offset enhanced C losses and substantially increase ecosystem C pools. Effects of the three global change treatments were generally additive, and we did not observe any interactions between CO2 and N. Overall, our results call into question whether elevated CO2 will increase the soil C sink in grassland ecosystems, helping to slow climate change, and suggest that losses of biodiversity may influence C storage as much as or more than increasing CO2 or high rates of N deposition in perennial grassland systems.
|Original language||English (US)|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Apr 27 2021|
Bibliographical noteFunding Information:
ACKNOWLEDGMENTS. We greatly appreciate K. Worm and many undergraduate interns for assistance with experimental operation and data collection. This research was supported by NSF Long-Term Ecological Research Grants DEB-0620652, DEB-1234162, and DEB-1831944; Long-Term Research in Environmental Biology Grants DEB-1242531 and DEB-1753859; Biological Integration Institutes Grant NSF-DBI-2021898; Ecosystem Sciences Grant DEB-1120064; Biocomplexity Grant DEB-0322057; and US Department of Energy Programs for Ecosystem Research Grant DE-FG02-96ER62291; and by the University of Minnesota.
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- Elevated CO2