Abstract
Abstract. Tropical forests play a significant role in the global carbon cycle and global climate. However, tropical carbon cycling and the feedbacks from tropical ecosystems to the climate system remain critical uncertainties in the current generation of carbon–climate models. One of the major uncertainties comes from the lack of representation of phosphorus (P), currently believed to be the most limiting nutrient in tropical regions. Here we introduce P dynamics and C–N–P interactions into the CLM4-CN (Community Land Model version 4 with prognostic Carbon and Nitrogen) model and investigate the role of P cycling in controlling the productivity of tropical ecosystems. The newly developed CLM-CNP model includes all major biological and geochemical processes controlling P availability in soils and the interactions between C, N, and P cycles. Model simulations at sites along a Hawaiian soil chronosequence indicate that the introduction of P limitation greatly improved the model performance at the P-limited site. The model is also able to capture the shift in nutrient limitation along this chronosequence (from N limited to P limited), as shown in the comparison of model-simulated plant responses to fertilization with the observed data. Model simulations at Amazonian forest sites show that CLM-CNP is capable of capturing the overall trend in NPP (net primary production) along the P availability gradient. This comparison also suggests a significant interaction between nutrient limitation and land use history. Model experiments under elevated atmospheric CO2 ([CO2]) conditions suggest that tropical forest responses to increasing [CO2] will interact strongly with changes in the P cycle. We highlight the importance of two feedback pathways (biochemical mineralization and desorption of secondary mineral P) that can significantly affect P availability and determine the extent of P limitation in tropical forests under elevated [CO2]. Field experiments with elevated CO2 are therefore needed to help quantify these important feedbacks. CO2 doubling model experiments show that tropical forest response to elevated [CO2] can only be predicted if the interactions between C cycle and nutrient dynamics are well understood and represented in models. Predictive modeling of C–nutrient interactions will have important implications for the prediction of future carbon uptake and storage in tropical ecosystems and global climate change.
Highlights
It is generally agreed that tropical forests play a significant role in the global carbon (C) cycle and global climate
In spite of the likely significance of tropical ecosystems to the global carbon cycle, tropical carbon cycle processes and the feedbacks to the climate system remain critically uncertain in current generation carbon–climate models (Friedlingstein et al, 2006)
We evaluate the performance of CLM-CNP by applying the model at sites along a chronosequence in Hawaii and at five additional tropical forest sites
Summary
It is generally agreed that tropical forests play a significant role in the global carbon (C) cycle and global climate. Yang et al.: The role of phosphorus dynamics in tropical forests increased temperature, CO2 fertilization, disturbances, and nutrient availability (Piao et al, 2013; Zaehle and Dalmonech, 2011; Arneth et al, 2010) Another important problem for the current generation of nutrient-enabled models, such as CLM-CN (Thornton et al, 2009, 2007) and O-CN (Zaehle et al, 2010), is the lack of consideration of the P cycle and P limitation. Despite the importance of the P cycle in regulating terrestrial carbon uptake, especially in tropical regions, very few carbon–climate models have considered P dynamics and C– N–P interactions with the exception of CASA (Carnegie– Ames–Stanford Approach)-CNP and JSBACH-CNP (Wang et al, 2007, 2009; Goll et al, 2012). P Pooolsoanlds fl auxneds o fflPucxomepso n oenft s Pin cCoLmM-pCNo(nsoeluntito n iPni s CaLssMum-e‐dCtNo b e(Sinoeqluuiltibioriunm Pwi t ihst h aeslasbuilemP peodol ) t. o be in equilibrium with labile P pool)
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