Implications of carbon saturation model structures for simulated nitrogen mineralization dynamics

[摘要] Carbon (C) saturation theory suggests that soils have a limited capacity tostabilize organic C and that this capacity may be regulated by intrinsic soilproperties such as clay concentration and mineralogy. While C saturationtheory has advanced our ability to predict soil C stabilization, fewbiogeochemical ecosystem models have incorporated C saturation mechanisms. Inbiogeochemical models, C and nitrogen (N) cycling are tightly coupled, with Cdecomposition and respiration driving N mineralization. Thus, changing modelstructures from non-saturation to C saturation dynamics can change simulatedN dynamics. In this study, we used C saturation models from the literatureand of our own design to compare how different methods of modeling Csaturation affected simulated N mineralization dynamics. Specifically, wetested (i) how modeling C saturation by regulating either the transferefficiency (ε, g C retained g⁻¹ C respired) or transferrate (k) of C to stabilized pools affected N mineralization dynamics, (ii)how inclusion of an explicit microbial pool through which C and N must passaffected N mineralization dynamics, and (iii) whether using ε toimplement C saturation in a model results in soil texture controls on Nmineralization that are similar to those currently included in widely usednon-saturating C and N models. Models were parameterized so that theyrendered the same C balance. We found that when C saturation is modeled usingε, the critical C : N ratio for N mineralization fromdecomposing plant residues (r_cr) increases as C saturation of asoil increases. When C saturation is modeled using k, however,r_cr is not affected by the C saturation of a soil. Inclusion ofan explicit microbial pool in the model structure was necessary to captureshort-term N immobilization–mineralization turnover dynamics duringdecomposition of low N residues. Finally, modeling C saturation by regulatingε led to similar soil texture controls on N mineralization as awidely used non-saturating model, suggesting that C saturation may be afundamental mechanism that can explain N mineralization patterns across soiltexture gradients. These findings indicate that a coupled C and N model thatincludes saturation can (1) represent short-term N mineralization byincluding a microbial pool and (2) express the effects of texture on Nturnover as an emergent property.

[学科分类] 地球化学与岩石