Effects of chronic nitrogen additions on above- and belowground carbon dynamics in two tropical forests

TitleEffects of chronic nitrogen additions on above- and belowground carbon dynamics in two tropical forests
Publication TypeJournal Article
Year of Publication2011
AuthorsCusack, DF, Silver, WL, Torn, MS, William H. McDowell
JournalBiogeochemistry
Volume104
Issue1-3
Pagination203-225
Accession NumberLUQ.1018
KeywordsAboveground biomass, Dissolved organic carbon, nutrient limitation, Roots, Soil density fractions, soil respiration
Abstract

Anthropogenic nitrogen (N) deposition is increasing rapidly in tropical regions, adding N to ecosystems that often have high background N availability. Tropical forests play an important role in the global carbon (C) cycle, yet the effects of N deposition on C cycling in these ecosystems are poorly understood. We used a field N-fertilization experiment in lower and upper elevation tropical rain forests in Puerto Rico to explore the responses of above- and belowground C pools to N addition. As expected, tree stem growth and litterfall productivity did not respond to N fertilization in either of these N-rich forests, indicating a lack of N limitation to net primary productivity (NPP). In contrast, soil C concentrations increased significantly with N fertilization in both forests, leading to larger C stocks in fertilized plots. However, different soil C pools responded to N fertilization differently. Labile (low density) soil C fractions and live fine roots declined with fertilization, while mineral-associated soil C increased in both forests. Decreased soil CO2 fluxes in fertilized plots were correlated with smaller labile soil C pools in the lower elevation forest (R2 = 0.65, p < 0.05), and with lower live fine root biomass in the upper elevation forest (R2 = 0.90, p < 0.05). Our results indicate that soil C storage is sensitive to N deposition in tropical forests, even where plant productivity is not N-limited. The mineral-associated soil C pool has the potential to respond relatively quickly to N additions, and can drive increases in bulk soil C stocks in tropical forests.

URLhttp://link.springer.com/article/10.1007%2Fs10533-010-9496-4
DOI10.1007/s10533-010-9496-4