Cusack et al, 2011

Paper/Book

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

Cusack, D. F., Silver, W. L., and McDowell, W. H. (2011)
Biogeochemistry  

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 Nrich
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.

Citation

Cusack, D. F., Silver, W. L., and McDowell, W. H. (2011): Effects of chronic nitrogen additions on above- and belowground carbon dynamics in two tropical forests. Biogeochemistry. DOI: 10.1007/s10533-010-9496-4