Diagnosing phosphorus limitations in natural terrestrial ecosystems in carbon cycle models

Abstract

Most of the Earth System Models (ESMs) project increases in net primary productivity (NPP) and terrestrial carbon (C) storage during the 21st century. Despite empirical evidence that limited availability of phosphorus (P) may limit the response of NPP to increasing atmospheric CO2, none of the ESMs used in the previous Intergovernmental Panel on Climate Change assessment accounted for P limitation. We diagnosed from ESM simulations the amount of P need to support increases in carbon uptake by natural ecosystems using two approaches: the demand derived from (1) changes in C stocks and (2) changes in NPP. The C stock‐based additional P demand was estimated to range between −31 and 193 Tg P and between −89 and 262 Tg P for Representative Concentration Pathway (RCP) 2.6 and RCP8.5, respectively, with negative values indicating a P surplus. The NPP‐based demand, which takes ecosystem P recycling into account, results in a significantly higher P demand of 648–1606 Tg P for RCP2.6 and 924–2110 Tg P for RCP8.5. We found that the P demand is sensitive to the turnover of P in decomposing plant material, explaining the large differences between the NPP‐based demand and C stock‐based demand. The discrepancy between diagnosed P demand and actual P availability (potential P deficit) depends mainly on the assumptions about availability of the different soil P forms. Overall, future P limitation strongly depends on both soil P availability and P recycling on ecosystem scale.

Anthropogenic global shifts in biospheric N and P concentrations and ratios and their impacts on biodiversity, ecosystem productivity, food security, and human health

“…The availability of key nutrients, such as K and P, are predicted to decrease the sensitivity of ecosystems to increasing CO 2 emissions and warming (Fernández‐Martínez et al, ; Penuelas, Ciais, et al, ; Wang, Zhang, et al, ). For example, climate‐system models have predicted that limited P availability and corresponding imbalances in N:P ratios will decrease the capacity of terrestrial ecosystems to remove CO 2 (Goll et al, ; Penuelas et al, , 2017; Sun et al, ; Wang, Zhang, et al, ). Similarly, other studies report that recent climatic warming has increasingly decreased the capacity of the biosphere to store C (Fernández‐Martínez et al, ), and only forests with nutrient‐rich soil had higher net primary production (NPP) in response to increases in gross primary productivity (Fernández‐Martínez et al, ).…”

“…N and P concentrations and ratios at regional scales generally tend to differ between agricultural areas with no or low levels of livestock and areas with higher densities of livestock. The ratios of N:P inputs tend to be higher in areas with low livestock densities that are treated with inorganic fertilizer (Dupas et al, 2015;Romero et al, 2019;Sardans et al, 2012b;Sun et al, 2017).…”

Estimates of mean residence times of phosphorus in commonly considered inorganic soil phosphorus pools

“…In our analysis, the clay variable includes not only clay minerals but also secondary minerals such Fe and Al oxyhydroxides, as it follows the particle size classification. Fe and Al oxyhydroxides are known to be key in inorganic P exchange behavior (Achat et al, 2016;Syers et al, 2008). For the samples where data on oxalate-and dithionite-extractable Al and Fe were available (n = 41-43), simple regression showed only weak correlations with MRTs and only significance for MRT of NaOH-P with oxalateextractable Al, dithionite-extractable Fe, and the sum of dithionite-extractable Al and Fe as explanatory variables (adjusted R 2 ≤ 0.16, p<0.05; data not shown).…”

Towards a more physiological representation of vegetation phosphorus processes in land surface models

“…In recent years, land surface models (LSMs) have developed from carbon (C)-only models to C-N-coupled models, and there is now a drive to include P cycle processes (Reed et al, 2015). The inclusion of C-N-P biogeochemistry is thought to be essential for understanding the C budget of ecosystems with P-poor soils (Ellsworth et al, 2017), and has been demonstrated to reduce estimates of future global C sequestration (Goll et al, 2012;Sun et al, 2017). P cycle processes can be split broadly into those that control external supply, namely the amount of P that is present in the soil and available to plants, and those that control the plant internal demand, namely the P concentration inside plant tissues required to sustain plant growth and function (Jin et al, 2015).…”

“…Modelling studies and reviews thus far have focused principally on the question of the magnitude of external supply and on improving representations of soil processes and plant acquisition strategies (Reed et al, 2015). The internal P demand, which ultimately drives plant productivity, has been mainly derived from heuristic relationships that assume growth is constrained by empirical C : N : P ratios (Achat et al, 2016;Sun et al, 2017). This empirical approach does not provide any indication of how plants use the acquired P for metabolism and growth nor how the tissue P concentration affects the physiology.…”