Nitrogen (N) and phosphorus (P) are limiting nutrients for many plant communities worldwide. Foliar N and P along with leaf area are among the most important controls on photosynthesis and hence productivity. However, foliar N and P are typically assessed as species level traits, whereas productivity is often measured at the community scale. Here, we compared the community-level traits of leaf area index (LAI) to total foliar nitrogen (TFN) and total foliar phosphorus (TFP) across nearly three orders of magnitude LAI in grazed and ungrazed tallgrass prairie in north-eastern Kansas, USA. LAI was strongly correlated with both TFN and TFP across communities, and also within plant functional types (grass, forb, woody, and sedge) and grazing treatments (bison or cattle, and ungrazed). Across almost the entire range of LAI values and contrasting communities, TFN:TFP ratios indicated co-limitation by N and P in almost all communities; this may further indicate a community scale trend of an optimal N and P allocation per unit leaf area for growth. Previously, results from the arctic showed similar tight relationships between LAI:TFN, suggesting N is supplied to canopies to maximize photosynthesis per unit leaf area. This tight coupling between LAI, N, and P in tallgrass prairie suggests a process of optimal allocation of N and P, wherein LAI remains similarly constrained by N and P despite differences in species composition, grazing, and canopy density.
Bibliographical noteFunding Information:
We thank John Briggs and the Konza Prairie Biological Station for the access and maintenance of the landscape treatments that made this work possible. AEK was supported by a NSF-REU fellowship to KSU Biology [NSF DBI-0851835], and JBN and ZR were supported by the Konza Prairie LTER program [NSF DEB-1440484]. GKP was partially supported by the Institute for Grassland Studies at KSU. We appreciate thoughtful discussion and editorial comments from John Blair, Tim Crews, and Anthony Joern.
© 2016, Springer-Verlag Berlin Heidelberg.