Effects of Increased Nitrogen Availability on C and N Cycles in Tropical Forests: A Meta-Analysis.

Marylin Bejarano-Castillo,Julio Campo,Lilia L Roa-Fuentes

doi:10.1371/journal.pone.0144253

Abstract

Atmospheric N deposition is predicted to increase four times over its current status in tropical forests by 2030. Our ability to understand the effects of N enrichment on C and N cycles is being challenged by the large heterogeneity of the tropical forest biome. The specific response will depend on the forest’s nutrient status; however, few studies of N addition appear to incorporate the nutrient status in tropical forests, possibly due to difficulties in explaining how this status is maintained. We used a meta-analysis to explore the consequences of the N enrichment on C and N cycles in tropical montane and lowland forests. We tracked changes in aboveground and belowground plant C and N and in mineral soil in response to N addition. We found an increasing trend of plant biomass in montane forests, but not in lowland forests, as well as a greater increase in NO emission in montane forest compared with lowland forest. The N2O and NO emission increase in both forest; however, the N2O increase in lowland forest was significantly even at first time N addition. The NO emission increase showed be greater at first term compared with long term N addition. Moreover, the increase in total soil N, ammonium, microbial N, and dissolved N concentration under N enrichment indicates a rich N status of lowland forests. The available evidence of N addition experiments shows that the lowland forest is richer in N than montane forests. Finally, the greater increase in N leaching and N gas emission highlights the importance of study the N deposition effect on the global climate change.

Highlights

Atmospheric nitrogen (N) deposition has increased globally by a factor of 3.6 since the preindustrial era due to fertilizer applications, fossil fuel combustion, and legume cultivation [1]
Recent climate models with C cycle component, that incorporate N deposition as a part of the CN-coupled models predict a lower net C uptake (37–74%) than values projected by models using C cycle components alone, demonstrating the importance of the N cycle in future climate change [9, 10]
84 references documenting the effects of N addition on C and N cycles in tropical forests were included (Fig 1)

Summary

Introduction

Atmospheric nitrogen (N) deposition has increased globally by a factor of 3.6 since the preindustrial era due to fertilizer applications, fossil fuel combustion, and legume cultivation [1]. Evidence from a wide variety of terrestrial ecosystems suggests that increases in N affect carbon (C) and N cycles in a coupled way, since organisms require C, N, and P in specific proportions, from the molecular to the global scale [5, 6, 7, 8]. The incorporation of this ecological stoichiometric approach is relevant for understanding future changes in both global nutrient cycles and the climate [8, 9, 10]. Recent climate models with C cycle component, that incorporate N deposition as a part of the CN-coupled models predict a lower net C uptake (37–74%) than values projected by models using C cycle components alone, demonstrating the importance of the N cycle in future climate change [9, 10]

Methods

Results

Discussion

Conclusion