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

• Published in: Biogeochemistry Vol. 104; no. 1/3; pp. 203 - 225
• Main Authors: Cusack, Daniela F., Silver, Whendee L., Torn, Margaret S., McDowell, William H.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer 01-07-2011; Springer Netherlands; Springer Nature B.V
• Subjects: Aboveground biomass; Animal and plant ecology; Animal, plant and microbial ecology; Anthropogenic factors; Biogeochemistry; Biogeosciences; Biological and medical sciences; Biomass; Carbon dioxide; Dissolved organic carbon; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Ecosystems; Environmental Chemistry; ENVIRONMENTAL SCIENCES; Exact sciences and technology; Fertilization; Forest soils; Fundamental and applied biological sciences. Psychology; Geochemistry; GEOSCIENCES; Life Sciences; Marine and continental quaternary; Mineral soils; Montane forests; Nitrogen; Nutrient limitation; Nutrients; Organic soils; Rainforests; Roots; Sedimentation & deposition; Soil and rock geochemistry; Soil density fractions; Soil depth; Soil organic matter; Soil respiration; Soils; Surficial geology; Synecology; Terrestrial ecosystems; Tropical environments; Tropical forests; Tropical soils; Puerto Rico; Antilles; Greater Antilles; West Indies; Caribbean region; Dissolved organic carbon; Soil density fractions; Nutrient limitation; Soil respiration; Roots; Aboveground biomass; experimental studies; biomass; density; fertilization; nitrogen; fine-grained materials; concentration; respiration; carbon cycle; storage; trees; forests; nutrients; ecosystems; growth; primary productivity; soils; dissolved organic carbon
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-010-9496-4

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 fractions and live fine roots declined with fertilization, while mineral-associated soil 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 storage is sensitive to N deposition in tropical forests, even where plant productivity is not N-limited. The mineral-associated soil pool has the potential to respond relatively quickly to N additions, and can drive increases in bulk soil stocks in tropical forests.