Nutrient limitation of woody debris decomposition in a tropical forest: contrasting effects of N and P addition

Abstract

Summary1. Tropical forests represent a major terrestrial store of carbon (C), a large proportion of which is contained in the soil and decaying organic matter. Woody debris plays a key role in forest C dynamics because it contains a sizeable proportion of total forest C. Understanding the factors controlling the decomposition of organic matter in general, and woody debris in particular, is hence critical to assessing changes in tropical C storage.2. We conducted a factorial fertilization experiment in a tropical forest in South China to investigate the influence of nitrogen (N) and phosphorus (P) availability onwoody debris decomposition using branch segments (5-cm diameter) of four species (Acacia auriculaeformis, Aphanamixis polystachya, Schefflera octophylla, Carallia brachiata) in plots fertilized with +N, +P, or +NP, and controls. Accepted ArticleThis article is protected by copyright. All rights reserved.3. Fertilization with +P and +NP increased decomposition rates by 5-53% and the magnitude was species-specific. Contrary to expectations, we observed no negative effect of +N addition on decay rates or mass loss of woody debris in any of the four study species. Decomposition rates of woody debris were higher in species with lower C:P ratios regardless of treatment.4. We observed significant accumulation of P in the woody debris of all species in plots fertilized with +P and +NP during the early stages of decomposition. N-release from woody debris of Acacia (N-fixing) was greater in the +P plots towards the end of the study, whereas fertilization with +N had no impact on the patterns of nutrient release during decomposition.5. Synthesis: Our results indicate that decomposition of woody debris is primarily constrained by P availability in this tropical forest. However, contrary to expectations, +N addition did not exacerbate P-limitation. It is conceivable that decay rates of woody debris in tropical forests can be predicted by C:P or lignin:P ratios but additional work with more tree species is needed to determine whether the patterns we observed are more generally applicable.

Foliar phosphorus fractions reveal how tropical plants maintain photosynthetic rates despite low soil phosphorus availability

“…The soil is classified as a latosol developed from granite (Wang et al, ). Annual wet N deposition in the region was c. 40 kg N/ha in 2011 and 2012 (Chen et al, ; Mo et al, ).…”

Global change effects on humid tropical forests: Evidence for biogeochemical and biodiversity shifts at an ecosystem scale

“…Nitrogen fertilization (150 kg N/ha/yr) in N‐rich mature tropical forests in southern China showed no effect on bulk soil C storage, although more labile fractions of SOM declined with N fertilization after 4.5 years [ Liu et al ., ], suggesting stimulation of microbial decomposition rates for some portion of SOM. In contrast, another study on highly weathered soils in southern China observed no effect of N fertilization (150 kg N/ha/yr) on decomposition of woody SOM after 3 years [ Chen et al ., ]. These two Chinese studies suggest that decomposition rates of labile versus woody fractions of SOM may respond differently to N additions, with net changes in soil C storage apparent only if the relative magnitudes of the effects are not in balance.…”

Nutrient limitation of soil microbial processes in tropical forests

“…, Kaspari and Yanoviak , Chen et al. ). Unlike nutrients, C is overabundant in essentially all soils of the different tropical forest ecosystems discussed here, with C:nutrient ratios largely exceeding those of soil microbial biomass (Cleveland and Liptzin ).…”