Cleland, Elsa E. and Lind, Eric M. and Decrappeo, Nicole M. and DeLorenze, Elizabeth and Wilkins, R.A. and Adler, Peter B. and Bakker, J. and Brown, Cini and Davies, K and Esch, E. and Firn, Jennifer and Gressard, S. and Gruner, Daniel S. and Hagenah, Nicole and Harpole, W. Stanley and Hautier, Yann and Hobbie, Sarah E. and Hofmockel, Kirsten S. and Kirkman, Kevin P. and Knops, Johannes M. H. and Kopp, C.W. and La Pierre, K.J. and MacDougall, Andrew S. and McCulley, Rebecca L. and Melbourne, Brett A. and Moore, J. and Prober, Suzanne M. and Riggs, C.W. and Risch, Anita C. and Schuetz, Martin and Stevens, Carly Joanne and Wragg, Peter D. and Wright, J and Borer, Elizabeth T. and Seabloom, Eric W. (2019) Belowground biomass response to nutrient enrichment depends on light limitation across globally distributed grasslands. Ecosystems, 22 (7). 1466–1477. ISSN 1432-9840
Cleland_etal_Ecosystems_2019_revised2.pdf - Accepted Version
Available under License Creative Commons Attribution-NonCommercial.
Download (1MB)
Abstract
Anthropogenic activities are increasing nutrient inputs to ecosystems worldwide, with consequences for global carbon and nutrient cycles. Recent meta-analyses show that aboveground primary production is often co-limited by multiple nutrients; however, little is known about how root production responds to changes in nutrient availability. At twenty-nine grassland sites on four continents, we quantified shallow root biomass responses to nitrogen (N), phosphorus (P) and potassium plus micronutrient enrichment and compared below- and aboveground responses. We hypothesized that optimal allocation theory would predict context dependence in root biomass responses to nutrient enrichment, given variation among sites in the resources limiting to plant growth (specifically light versus nutrients). Consistent with the predictions of optimal allocation theory, the proportion of total biomass belowground declined with N or P addition, due to increased biomass aboveground (for N and P) and decreased biomass belowground (N, particularly in sites with low canopy light penetration). Absolute root biomass increased with N addition where light was abundant at the soil surface, but declined in sites where the grassland canopy intercepted a large proportion of incoming light. These results demonstrate that belowground responses to changes in resource supply can differ strongly from aboveground responses, which could significantly modify predictions of future rates of nutrient cycling and carbon sequestration. Our results also highlight how optimal allocation theory developed for individual plants may help predict belowground biomass responses to nutrient enrichment at the ecosystem scale across wide climatic and environmental gradients.