A new model of the coupled carbon, nitrogen, and phosphorus cycles in the terrestrial biosphere (QUINCY v1.0; revision 1996)

Abstract

Abstract. The dynamics of terrestrial ecosystems are shaped by the coupled cycles of carbon, nitrogen, and phosphorus, and these cycles are strongly dependent on the availability of water and energy. These interactions shape future terrestrial biosphere responses to global change. Here, we present a new terrestrial ecosystem model, QUINCY (QUantifying Interactions between terrestrial Nutrient CYcles and the climate system), which has been designed from scratch to allow for a seamless integration of the fully coupled carbon, nitrogen, and phosphorus cycles with each other and also with processes affecting the energy and water balances in terrestrial ecosystems. This new model includes (i) a representation of plant growth which separates source (e.g. photosynthesis) and sink (growth rate of individual tissues, constrained by temperature and the availability of water and nutrients) processes; (ii) the acclimation of many ecophysiological processes to meteorological conditions and/or nutrient availability; (iii) an explicit representation of vertical soil processes to separate litter and soil organic matter dynamics; (iv) a range of new diagnostics (leaf chlorophyll content; 13C, 14C, and 15N isotope tracers) to allow for a more in-depth model evaluation. In this paper, we present the model structure and provide an assessment of its performance against a range of observations from global-scale ecosystem monitoring networks. We demonstrate that QUINCY v1.0 is capable of simulating ecosystem dynamics across a wide climate gradient, as well as across different plant functional types. We further provide an assessment of the sensitivity of key model predictions to the model's parameterisation. This work lays the ground for future studies to test individual process hypotheses using the QUINCY v1.0 framework in the light of ecosystem manipulation observations, as well as global applications to investigate the large-scale consequences of nutrient-cycle interactions for projections of terrestrial biosphere dynamics.

Jena Soil Model (JSM v1.0; revision 1934): a microbial soil organic carbon model integrated with nitrogen and phosphorus processes

“…The simulated plant N and P uptakes at the quasi-equilibrium state were very close to the N and P inputs from the litterfall ( Table 1), indicating that realistic root biomass and uptake capacity enable the simulation of nutrient uptake for plants. This finding supports the recent change in plant uptake simulations in TBMs from plant demand driven (Yang et al, 2014b) to trait (root biomass, uptake capacity and inorganic nutrient pool) driven (Zaehle and Friend, 2010;Goll et al, 2017;Thum et al, 2019), which strengthens the interactions between soil nutrient availability and plant growth.…”

“…The C and N stocks in SOM as well as respiration and net N mineralisation are highly sensitive to the parameter changes of depolymerisation and organo-mineral association, whereas the organic or inorganic P stocks and P mineralisation are highly sensitive to the microbial processes. These trends support, and also explain, the finding of Post (2011) andTipping et al (2016) that the P cycle is decoupled from the C and N cycles in the soil. A more in-depth explanation of this difference, based on our results, is that the gross mineralisation associated with microbial DOM uptake can supply microbes and plants with sufficient N but not P; thus, a large amount of P needs to be mobilised, particularly from SOM as well as from mineral pools, to sustain microbial growth.…”

“…Following calibration, JSM could reproduce the main soil stocks of C, N and P; microbial biomass; and soil bulk density as well as their vertical patterns along the soil profile in a beech forest stand in Germany. The observed SOM C : N ratio (19.5) and the C : P ratio (348) in the first model layer -the O-A horizon -fit well within the ranges of the reported soil stoichiometry of temperate broadleaf forests , and there was a much stronger decreasing trend in the C : P ratio than in the C : N ratio with an increase in soil depth, indicating that organic P in SOM is "decoupled" from the C and N cycles (Yang and Post, 2011;Tipping et al, 2016).…”

“…The inorganic P cycle follows the QUINCY model and accounts for microbial interactions. JSM explicitly traces 13 C, 14 C and 15 N following Ahrens et al (2015) and Thum et al (2019).…”

“…It is, therefore, of great relevance to identify and understand these constraints on global carbon (C) cycling and storage for predicting potential future carbon-climate feedback (Ciais et al, 2013). There have been continuous efforts to integrate the N ( Thornton et al, 2007;Zaehle and Friend, 2010;Smith et al, 2014) and P cycles (Wang et al, 2010;Yang et al, 2014b;Goll et al, 2017;Thum et al, 2019;Zhu et al, 2019) in terrestrial biosphere models (TBMs) for improving the representation of C-nutrient interactions. However, despite major advances in simulating terrestrial biogeochemistry, these nutrient-enabled TBMs largely fail to reproduce the responses of ecosystems to elevated atmospheric CO 2 concentration, as observed in the free-air CO 2 enrichment experiments Medlyn et al, 2015Medlyn et al, , 2016Fleischer et al, 2019).…”