Cusack,D.F., Silver,W.L., Torn,M.S. and McDowell,W.H.(2011): Effects of nitrogen additions on above- and belowground carbon dynamics in two tropical forests. Biogeochemistry, 104, 203-225.

『二つの熱帯林における地表と地下の炭素ダイナミクスに与える窒素添加の影響』


Abstract
 Anthropogenic nitrogen (N) deposition id 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 addition, and can drive increase in bulk soil C stocks in tropical forests.

Keywords: Aboveground biomass; Dissolved organic carbon; Nutrient limitation; Roots; Soil density fractions; Soil respiration』

Introduction
Methods
 Study site
 Aboveground carbon
 Belowground carbon
 Soil carbon fractions
 Statistical analyses
Results
 Aboveground responses to N fertilization
 Response of soil C pools and fluxes
  Changes in soil C and N concentrations
  Bulk soil C content
  Soil density fractions
  Soil respiration and fine roots
  Dissolved organic carbon
Discussion
Conclusions
Acknowledgements
Open access
Appendix 1
Appendix 2
Appendix 3
References


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