Nutrient Constraints on Carbon Cycling in Seasonally Dry Tropical Forest
Abstract
Seasonally dry tropical forests account for large amounts of the total tropical forest cover, harbor unique biodiversity, and also support vital ecosystem services. Because carbon (C) cycling processes such as net primary production and decomposition in dry forests are thought to be limited by water, the question of how nutrient and C cycles interact is largely unexplored. We used a variety of approaches to fill this knowledge gap including: a nine year record of aboveground net primary production in forest plots located across soil fertility gradients in Costa Rica, an ecosystem-scale nitrogen (N) and phosphorus (P) fertilization experiment, and simulations with the ED2 vegetation demography model.
There were large variations in soil nutrients across our forest plots: total N varied by a factor of two, while total soil P varied by two orders of magnitude. Our observational data suggest that litterfall, woody growth, and litter decomposition were lower on infertile soils. Moreover, soil fertility affected the sensitivity of woody growth to inter-annual variation in rainfall: forests located on fertile soils showed enhanced stem growth in high rainfall years and lower growth in drier years, while forests on low fertility showed little variation in stem growth among years. In our large-scale fertilization experiment, added P increased fine root production by 40% and doubled nodulation by N-fixing legumes. By contrast, N addition did not affect C cycling. Model simulations confirmed the large role of nutrients in constraining C in dry forests. In simulations that used soil nutrient values from our observational plots, final aboveground biomass of forest plots differed by up to 30%. Soil nutrients also affected the functional composition and demographics of modeled forests, which is consistent with data on species distributions across edaphic gradients. Our complementary studies revealed that nutrient availability constrains C cycling in tropical dry forests. Limited nutrients led to decreases in tree growth and decomposition, while added P increased root production. Similar to rainforests, P appears more important than N. Last, nutrient availability interacted with rainfall, underscoring that efforts to predict how dry forests will respond to changing climates must account for variation in edaphic properties.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B43A..04P
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0428 Carbon cycling;
- BIOGEOSCIENCESDE: 0470 Nutrients and nutrient cycling;
- BIOGEOSCIENCESDE: 0486 Soils/pedology;
- BIOGEOSCIENCES