A global model of carbon, nitrogen and phosphorus cycles for the terrestrial biosphere

Abstract

Abstract. Carbon storage by many terrestrial ecosystems can be limited by nutrients, predominantly nitrogen (N) and phosphorous (P), in additional to other environmental constraints, water, light and temperature. However the spatial distribution and the extent of both N and P limitation at global scale have not been quantified. Here we have developed a global model of carbon (C), nitrogen (N) and phosphorus (P) cycles for the terrestrial biosphere. Model estimates of steady state C and N pool sizes and major fluxes between plant, litter and soil pools, under present climate conditions, agree well with various independent estimates. The total amount of C in the terrestrial biosphere is 2526 Gt C, and the C fractions in plant, litter and soil organic matter are 21, 6 and 73%. The total amount of N is 124 Gt N, with about 94% stored in the soil, 5% in the plant live biomass, and 1% in litter. We found that the estimates of total soil P and its partitioning into different pools in soil are quite sensitive to biochemical P mineralization that has not been included in any other global models previously. The total amount of P is 26 Gt P in the terrestrial biosphere, 17% of which is stored in the soil organic matter if biochemical P mineralization is modelled, or 40 Gt P, with 60% in soil organic matter, otherwise. This model was used to derive the global distribution of N or P limitation on the productivity of terrestrial ecosystems. Our model predicts that the net primary productivity of most tropical evergreen broadleaf forests and tropical savannahs is reduced by about 20% on average by P limitation, and most of the remaining biomes are N limited; N limitation is strongest in high latitude deciduous needle leaf forests, and reduces its net primary productivity by up to 40% under present conditions.

Modeling permafrost thaw and ecosystem carbon cycle under annual and seasonal warming at an Arctic tundra site in Alaska

“…Heterotrophic respiration depends on sizes of different carbon pools in the soil and their turnover rates. The turnover rate of each soil carbon pool is a function of soil temperature and moisture [Wang et al, 2010]; therefore, heterotrophic respiration is also dependent on soil temperature and moisture in the rooting zone.…”

“…Warming can also increase water loss from soil or snow sublimation and accelerating snowmelt in spring time, hence soil water and temperature dynamics. Kowalczyk et al [2006] and Wang et al [2010Wang et al [ , 2011 have provided description of all key components of CABLE, including the model of soil temperature and moisture. Here we include a brief description of key carbon processes and the snow model and how processes in those two components vary with temperature.…”

Earth System Model Needs for Including the Interactive Representation of Nitrogen Deposition and Drought Effects on Forested Ecosystems

“…The most common allocation approach assigns C to each plant component (usually leaf, stem, and root) via fixed ratios that vary with plant functional type (PFT), but not spatially or temporally [38,85,88,95,107,[113][114][115]. For models that include N (and less often P), N uptake plays a strong role in governing C assimilation and drives competition between plants and decomposers.…”

“…Losses are from plant uptake, immobilization, leaching, and nitrification/denitrification processes. Models can represent N limitation in different ways, including using N to scale photosynthesis [105,106], downscaling potential gross primary productivity (GPP) to reflect N availability [38,84,85,107], defining a C cost of N uptake [108], optimizing N allocation for leaf processes [109], or adapting a flexible C:N ratio for N allocation [106]. Nitrogen uptake is scaled depending on demand, based on stoichiometry (see Section 5.2) and availability, where photosynthesis and decomposition may be downscaled.…”

Representing the root water uptake process in the Common Land Model for better simulating the energy and water vapour fluxes in a Central Asian desert ecosystem

“…The increase in EC data obtained from various terrestrial land surfaces facilitates research into poorly represented or missing ecosystem processes in models, leading to improvements of the model's performance (Baldocchi et al, 2001;Baker et al, 2008;Stockli et al, 2008;Williams et al, 2009;Choi et al, 2010;Schwalm et al, 2010;Li et al, 2011b). Commonly used LSMs include SiB (Sellers et al, 1986), Common Land Model (CLM) (Dai et al, 2003), ORCHIDEE (Krinner et al, 2005), CABLE (Kowalczyk et al, 2006) and their updated versions (Sellers et al, 1996;Wang et al, 2010;Bonan et al, 2011). These LSMs have been evaluated at different ecosystems including cropland, closed shrublands, deciduous broadleaf forest, evergreen broadleaf forest, evergreen needleleaf forest, grassland, mixed forest, open shrublands, savanna, wetlands, and woody savannah (Williams et al, 2009;Wang et al, 2012).…”