CoupModel (v6.0): an ecosystem model for coupled phosphorus, nitrogen and carbon dynamics – evaluated against empirical data from a climatic and fertility gradient in Sweden

Abstract

Abstract. This study presents the integration of the phosphorus (P) cycle into CoupModel (Coup-CNP). The extended Coup-CNP enables simulations of coupled carbon (C), nitrogen (N) and P dynamics for terrestrial ecosystems which explicitly consider mycorrhizal interactions. The model was evaluated against observed forest growth and measured leaf C/P, C/N and N/P ratios in four managed forest regions in Sweden. The four regions form a climatic and fertility gradient from 64° N in the North to 56° N in South Sweden with the mean annual temperature varying between 0.7–7.1 °C and the soil C/N and C/P ratios between 19.8–31.5 and 425–633, respectively. The growth of the southern forests was found to be P-limited, with harvested biomass representing the largest P loss over the studied rotation period. The simulated P budgets revealed that southern forests are losing P while northern forests are close to a steady state in P availability. Mycorrhizal fungi account for half of the total plant P uptake across all four regions, which highlights the importance of fungal-tree interactions in Swedish forests. Sensitivity analysis results demonstrated that the highest forest growth occurs at a soil N/P ratio of 15 to 20. A soil N/P ratio above 15–20 resulted in decreased soil C sequestration and total P leaching, but significantly increased N leaching. The development and evaluation of the new Coup-CNP model demonstrate that P fluxes need to be further considered in studies of how climate change will influence C turnover and ecosystem responses. We conclude that the potential P-limitation of terrestrial ecosystems highlights the need of a proper consideration of the P cycle in biogeochemical models. The inclusion of the P cycle is necessary in order to make models reliable tools for assessing long-term impacts of climate change and N deposition on C sequestration and N leaching.

Water level variation at a beaver pond significantly impacts net CO2 uptake of a continental bog

“…The main structure is a one-dimensional, vertical model, with one or two layers of vegetation (e.g., a shrub and moss layer as in this application) on a multi-layered soil profile. In this application, we used the most recent model version (v.6) from He et al (2021), but without nitrogen and phosphorus cycles. The model is driven by measured climatic data -precipitation, air temperature, relative humidity, wind speed, and global radiation.…”

“…To link the varying boundary conditions and the associated CO 2 dynamics, the processbased CoupModel was used. We chose CoupModel (Jansson, 2012;He et al, 2021) because it includes detailed soil physics, hydrology, photosynthesis, and ecosystem respiration (ER) that can simulate the association of the peatland C dynamics with vertical and lateral hydrology flow (He et al, 2016). Furthermore, past studies have shown that the model can successfully simulate the C dynamics, the energy and water balance of managed European treeless peatlands (Metzger et al, 2015), but as yet it has not been applied to continental bogs.…”

Plant phosphorus‐use and ‐acquisition strategies in Amazonia

“…Currently, there are emerging approaches to representing mycorrhizal P i uptake explicitly. For instance, in the Coup-CNP model, plants allocate C to fungi as long as the P i return is advantageous (He et al, 2021). The fungi can explore both the available P i pool and P o pool, but ultimately P i uptake is limited by the fungal biomass (He et al, 2021).…”

“…For instance, in the Coup-CNP model, plants allocate C to fungi as long as the P i return is advantageous (He et al, 2021). The fungi can explore both the available P i pool and P o pool, but ultimately P i uptake is limited by the fungal biomass (He et al, 2021). Moreover, vegetation models are designed for modeling large-scale vegetation dynamics; consequently, the challenge lies in finding generalities of microscale dynamics occurring at the root surface that allow upscaling along resource gradients and projecting impacts of global change at the ecosystem scale.…”

Cutting peatland CO2 emissions with water management practices

“…5). Therefore, we think that our straightforward approach to estimate water management strategy ef-fectivity forms an alternative approach of intermediate complexity compared to either groundwater-table-CO 2 emission relationships (Couwenberg et al, 2011;Fritz et al, 2017;Tiemeyer et al, 2020;Arets et al, 2020;Evans et al, 2021) or models that resolve the entire carbon cycle (van Huissteden et al, 2006;He et al, 2021). The additional complexity of unsaturated zone modelling of water flow and introducing soil temperature and WFPS-activity curves requires a considerably higher modelling effort compared to approaches that rely on relationships between yearly average groundwater table and CO 2 emissions, but it allows us to investigate the effect differences between groundwater levels raised by ditchwater level manipulations or by applying SSI.…”