Abstract
Abstract. In old and heavily weathered soils, the availability of P might be so small that the primary production of plants is limited. However, plants have evolved several mechanisms to actively take up P from the soil or mine it to overcome this limitation. These mechanisms involve the active uptake of P mediated by mycorrhiza, biotic de-occlusion through root clusters, and the biotic enhancement of weathering through root exudation. The objective of this paper is to investigate how and where these processes contribute to alleviate P limitation on primary productivity. To do so, we propose a process-based model accounting for the major processes of the carbon, water, and P cycles including chemical weathering at the global scale. Implementing P limitation on biomass synthesis allows the assessment of the efficiencies of biomass production across different ecosystems. We use simulation experiments to assess the relative importance of the different uptake mechanisms to alleviate P limitation on biomass production. We find that active P uptake is an essential mechanism for sustaining P availability on long timescales, whereas biotic de-occlusion might serve as a buffer on timescales shorter than 10 000 yr. Although active P uptake is essential for reducing P losses by leaching, humid lowland soils reach P limitation after around 100 000 yr of soil evolution. Given the generalized modelling framework, our model results compare reasonably with observed or independently estimated patterns and ranges of P concentrations in soils and vegetation. Furthermore, our simulations suggest that P limitation might be an important driver of biomass production efficiency (the fraction of the gross primary productivity used for biomass growth), and that vegetation on old soils has a smaller biomass production rate when P becomes limiting. With this study, we provide a theoretical basis for investigating the responses of terrestrial ecosystems to P availability linking geological and ecological timescales under different environmental settings.
Highlights
Phosphorus (P) is an essential nutrient for life and its availability constrains the production of biomass by primary producers, especially on old and strongly weathered soils
Our simulations suggest that P limitation might be an important driver of biomass production efficiency, and that vegetation on old soils has a smaller biomass production rate when P becomes limiting
We described P dynamics during pedogenesis and its interaction with terrestrial vegetation in a simple but process-based way
Summary
Phosphorus (P) is an essential nutrient for life and its availability constrains the production of biomass by primary producers, especially on old and strongly weathered soils. To overcome P limitation, plants have evolved strategies to make P available from these occluded pools and take it up more efficiently These strategies in turn induce feedback processes between plants and soils, which lead to the enhancement of P availability (for a review on those strategies see Lambers et al, 2008). While at the global scale these feedback mechanisms between plants and P availability in the soil determine to some extent the production and storage of biomass in ecosystems, they are relevant for atmospheric C concentrations, and for the climate system (DeLucia et al, 1997; Zhang et al, 2011; Goll et al, 2012). P dynamics in soils and vegetation might be crucial for understanding the terrestrial vegetation feedback on the global C cycle (Sardans and Peñuelas, 2012; Cernusak et al, 2013)
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