The role of phosphorus dynamics in tropical forests – a modeling study using CLM-CNP

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 current generation carbon-climate models. One of the major uncertainties comes from the lack of representation of phosphorus (P), the most limiting nutrient in tropical regions. Here we introduce P dynamics and C–N–P interactions into the CLM4-CN 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 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]) condition 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. Predictive modeling of C–P interactions will have important implications for the prediction of future carbon uptake and storage in tropical ecosystems and global climate change.

Potential and limitations of inferring ecosystem photosynthetic capacity from leaf functional traits

“…Furthermore, efforts have mostly focused on leaf nitrogen as a functional trait (in relation to ecosystem productivity, e.g., Kattge, Knorr, Raddatz, & Wirth, 2009), whereas other plant traits could also be suitable candidates. Foliar phosphorus, for example, improves the model prediction of carbon fluxes as reported by Mercado et al (2011), Goll et al (2012), and Yang, Thornton, Ricciuto, and Post (2014).…”

Global forest carbon uptake due to nitrogen and phosphorus deposition from 1850 to 2100

“…However, our current knowledge of nutrient cycling is more limited for P than for N, leading to high uncertainties in global ecosystem-level models (Goll et al, 2012;Wang et al, 2010;Yang, Thornton, Ricciuto, & Post, 2014). It is known that most of P is neither directly taken up by plant nor lost by leaching, but a large fraction of P is fixed by soils before being slowly transferred into a labile pool that can be used by plant (Aerts & Chapin, 2000;Sattari et al, 2012).…”

Increased influence of nitrogen limitation on CO2 emissions from future land use and land use change

“…First is the colimitation of phosphorus with nitrogen, especially in the moist tropics [Vitousek et al, 2010]. Only recently have models started to include phosphorus dynamics [Goll et al, 2012;Wang et al, 2010;Yang et al, 2013;Zhang et al, 2013], and only Zhang et al [2013] represent LULUC. Second are the impacts of LULUC on climate realized through biogeophysical pathways [Mahmood et al, 2013].…”