期刊
BIOGEOCHEMISTRY
卷 114, 期 1-3, 页码 135-147出版社
SPRINGER
DOI: 10.1007/s10533-013-9835-3
关键词
Costa Rica; Fertilization; Free-living nitrogen fixation; Micro-nutrient; Molybdenum; Nutrient limitation; Phosphorus; Rain forest
资金
- National Science Foundation
- Andrew W. Mellon Foundation
- Direct For Biological Sciences
- Division Of Environmental Biology [0919080] Funding Source: National Science Foundation
- Directorate For Geosciences
- ICER [1128040] Funding Source: National Science Foundation
Biological nitrogen (N) fixation is the primary source of new N to unmanaged ecosystems, and recent analyses suggest that terrestrial N inputs via free-living N fixation may be more important than previously assumed. This may be particularly true in some tropical rain forests, where free-living fixation could outpace symbiotic N fixation to represent the dominant source of new N inputs. However, our understanding of the controls over free-living N fixation in tropical rain forests remains poor, which directly constrains our ability to predict how N cycling will respond to changing environmental conditions. Although both phosphorus (P) and molybdenum (Mo) availability have been shown to limit free-living N fixation rates in the tropics, few studies have simultaneously explored P versus Mo limitation or the potential importance of P x Mo interactions. Here, an archived set of foliar, litter, and soil samples from a Costa Rican tropical rain forest provided an opportunity to simultaneously assess the relative strength of P versus Mo relationships with free-living N fixation rates. We also conducted a short-term, full-factorial (P x Mo) litter incubation experiment to directly assess nutrient limitation, allowing us to explore P and Mo controls over free-living N fixation rates using both observational and experimental approaches. We previously showed that N fixation rates were positively correlated with P concentrations in all substrates and, using the archived samples, we now show that Mo concentrations correlated with N fixation only in canopy leaves (where total Mo concentrations were extremely low). Likewise, fertilization with P alone (and not Mo) stimulated leaf litter N fixation rates. Thus, our results suggest that P availability dominantly controls free-living N fixation at this site, and when taken with data from other studies, our results suggest that attempts to identify the nutrient that limits N fixation in the tropics may be misguided. Rather, nutrient controls over free-living N fixation appear to be more nuanced-and the true nature of nutrient limitation to N fixation likely varies over a variety of scales across the vast tropical rain forest biome.
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