A representation of the phosphorus cycle for ORCHIDEE (revision 4520)

Abstract

Abstract. Land surface models rarely incorporate the terrestrial phosphorus cycle and its interactions with the carbon cycle, despite the extensive scientific debate about the importance of nitrogen and phosphorus supply for future land carbon uptake. We describe a representation of the terrestrial phosphorus cycle for the ORCHIDEE land surface model, and evaluate it with data from nutrient manipulation experiments along a soil formation chronosequence in Hawaii.ORCHIDEE accounts for the influence of the nutritional state of vegetation on tissue nutrient concentrations, photosynthesis, plant growth, biomass allocation, biochemical (phosphatase-mediated) mineralization, and biological nitrogen fixation. Changes in the nutrient content (quality) of litter affect the carbon use efficiency of decomposition and in return the nutrient availability to vegetation. The model explicitly accounts for root zone depletion of phosphorus as a function of root phosphorus uptake and phosphorus transport from the soil to the root surface.The model captures the observed differences in the foliage stoichiometry of vegetation between an early (300-year) and a late (4.1 Myr) stage of soil development. The contrasting sensitivities of net primary productivity to the addition of either nitrogen, phosphorus, or both among sites are in general reproduced by the model. As observed, the model simulates a preferential stimulation of leaf level productivity when nitrogen stress is alleviated, while leaf level productivity and leaf area index are stimulated equally when phosphorus stress is alleviated. The nutrient use efficiencies in the model are lower than observed primarily due to biases in the nutrient content and turnover of woody biomass.We conclude that ORCHIDEE is able to reproduce the shift from nitrogen to phosphorus limited net primary productivity along the soil development chronosequence, as well as the contrasting responses of net primary productivity to nutrient addition.

Contrasting nitrogen fluxes in African tropical forests of the Congo Basin

“…However, recent work has suggested an increasing role of nutrients limiting the productivity of ecosystems; both data and modeling efforts have shown that carbon dioxide (CO 2 ) uptake by terrestrial ecosystems strongly depends on nutrient availability (Bonan 2008, Peñuelas et al 2013, Fernandez-Martinez et al 2014. This has instigated the implementation of the effects of nutrient stocks and cycling in land-surface models (Wang et al 2010, Zaehle and Friend 2010, Goll et al 2012, 2017 and stressed the need for a profound and mechanistic understanding of nutrient cycling effects on the C cycle. Nitrogen (N) is of particular interest, being one of the important macronutrients to sustain plant life.…”

Nitrogen Deposition Maintains a Positive Effect on Terrestrial Carbon Sequestration in the 21st Century Despite Growing Phosphorus Limitation at Regional Scales

“…Global ecosystem models are progressively incorporating dynamic N and P cycles to test their control on the global C balance (Buendía et al, 2014;Goll et al, 2012Goll et al, , 2017Yang et al, 2014). The land surface model CABLE considers C, N, and P dynamics and has previously been employed to estimate the control of N and P limitation on the historical and future global C balance (Y.-P. Wang et al, 2010).…”

Low Phosphorus Availability Decreases Susceptibility of Tropical Primary Productivity to Droughts

“…At all three sites, nutrient availability is suboptimal when computed prognostically, this is indicated by leaf carbon:nitrogen:phosphorus ratios of 744:30:1, 1264:38:1, and 983:36:1 for BR‐Ma2, BR‐Sa1, and BR‐Sa3, respectively, which are elevated compared to the optimal ratio in ORCHIDEE of 267:17:1 (Goll et al, ). Furthermore, the nitrogen addition experiment (supporting information Text S3) and the elevated leaf nitrogen:phosphorus ratios indicate that nitrogen availability is not limiting plant productivity at all sites.…”

“…It has a detailed representation of root phosphorus uptake and accounts for root zone depletion of phosphorus as a function of root phosphorus uptake and phosphate ions diffusion controlled transport from the soil pores to the root surface. The major interactions between water and phosphorus cycling (Figure ) in ORCHIDEE are (1) the positive dependence of phosphate mobility on soil moisture (Equation 23 in Goll et al, ), which affects the uptake of phosphate by roots (Equation 4 in Goll et al, ) and its availability for plant growth, (2) the positive dependence of microbial mineralization on soil moisture (Section 2.1.3 in Goll et al, ), (3) the direct dependence of plant growth on plant internal phosphorus availability (Equation 13 in Goll et al, ), and (4) the indirect dependence of the photosynthetic capacity (maximum carboxylation rate) on leaf phosphorus. The latter is a consequence of constraints on the elasticity of the leaf nitrogen:phosphorus ratio (Equation 11 in Goll et al, ).…”

“…We exchanged the original formulation of phosphorus sorption, which assumes a fixed fraction of labile phosphorus being dissolved in soil solution (Goll et al, ) with a more realistic Freundlich Isotherm, which is parameterized based on a compilation of isotopic dilution data ( n = 379; Achat et al, ; Kvakić et al, ). Three different soil classes are distinguished in respect to sorption dynamics, namely, Oxisols, Molisols, and “others.” Details are given in supporting information Text S1.…”