Nutrient limitation in rainforests and cloud forests along a 3,000-m elevation gradient in the Peruvian Andes
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We report results from a large-scale nutrient fertilization experiment along a “megadiverse” (154 unique species were included in the study) 3,000-m elevation transect in the Peruvian Andes and adjacent lowland Amazonia. Our objectives were to test if nitrogen (N) and phosphorus (P) limitation shift along this elevation gradient, and to determine how an alleviation of nutrient limitation would manifest in ecosystem changes. Tree height decreased with increasing elevation, but leaf area index (LAI) and diameter at breast height (DBH) did not vary with elevation. Leaf N:P decreased with increasing elevation (from 24 at 200 m to 11 at 3,000 m), suggesting increased N limitation and decreased P limitation with increasing elevation. After 4 years of fertilization (N, P, N + P), plots at the lowland site (200 m) fertilized with N + P showed greater relative growth rates in DBH than did the control plots; no significant differences were evident at the 1,000 m site, and plots fertilized with N at the highest elevation sites (1,500, 3,000 m) showed greater relative growth rates in DBH than did the control plots, again suggesting increased N constraint with elevation. Across elevations in general N fertilization led to an increase in microbial respiration, while P and N + P addition led to an increase in root respiration and corresponding decrease in hyphal respiration. There was no significant canopy response (LAI, leaf nutrients) to fertilization, suggesting that photosynthetic capacity was not N or P limited in these ecosystems. In sum, our study significantly advances ecological understanding of nutrient cycling and ecosystem response in a region where our collective knowledge and data are sparse: we demonstrate N limitation in high elevation tropical montane forests, N and P co-limitation in lowland Amazonia, and a nutrient limitation response manifested not in canopy changes, but rather in stem and belowground changes.
KeywordsFertilization Forest Montane Nitrogen Phosphorus Tropical
This project was supported by a NERC-funded grant (NE/D014174/1) and by the Gordon and Betty Moore foundation, and is a product of the Andes Biodiversity and Ecosystem Research Group (ABERG). Y.M. was supported by the Jackson Foundation. P.M. was supported by the Royal Society of Edinburgh and NERC Grant NE/F002149/1. We thank INRENA and Manu National Park for permits to work in the area, the Amazon Basin Conservation Association (ACCA) and their Wayqecha field station, and the Explorers’ Inn at Tambopata for supporting our work in Peru. We are grateful to, F.F. Amézquita, L.E.O.C. Aragão, L.D. Baca, K.G. Cabrera, R. Ccacya, K. Clark, C.A.J. Girardin, J.A.Q. Loayza, A.A.V. Maucaylla, J.K. Mamani, T. Marthews, P.O.C. Porroa, V. Qquellón, A.J.C. Quispe, J.S. Quispe, M.N.R. Quisiyupanqui, W.F. Ríos, N. Salinas, J.F.M. Solórzano, M.M. Solórzano, M.I.A. Soto, S.-Y. Tan, S. Ynuma, and M. Zimmermann for assistance and field work help. Two anonymous reviewers and the journal editors provided invaluable suggestions that substantially improved the manuscript.
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