Multiple soil nutrient competition between plants, microbes, and mineralsurfaces: model development, parameterization, and example applications inseveral tropical forests

[摘要] Soil is a complex system where biotic (e.g., plant roots, micro-organisms) andabiotic (e.g., mineral surfaces) consumers compete for resources necessary forlife (e.g., nitrogen, phosphorus). This competition is ecologically significant,since it regulates the dynamics of soil nutrients and controls abovegroundplant productivity. Here we develop, calibrate and test a nutrientcompetition model that accounts for multiple soil nutrients interacting withmultiple biotic and abiotic consumers. As applied here for tropical forests,the Nutrient COMpetition model (N-COM) includes three primary soil nutrients(NH₄⁺, NO₃⁻ and PO_x; representing the sum ofPO₄³⁻, HPO₄²⁻ and H₂PO₄⁻) and fivepotential competitors (plant roots, decomposing microbes, nitrifiers,denitrifiers and mineral surfaces). The competition is formulated with aquasi-steady-state chemical equilibrium approximation to account forsubstrate (multiple substrates share one consumer) and consumer (multipleconsumers compete for one substrate) effects. N-COM successfully reproducedobserved soil heterotrophic respiration, N₂O emissions, freephosphorus, sorbed phosphorus and NH₄⁺ pools at a tropical forestsite (Tapajos). The overall model uncertainty was moderately wellconstrained. Our sensitivity analysis revealed that soil nutrientcompetition was primarily regulated by consumer–substrate affinity ratherthan environmental factors such as soil temperature or soil moisture. Ourresults also imply that under strong nutrient limitation, relativecompetitiveness depends strongly on the competitor functional traits(affinity and nutrient carrier enzyme abundance). We then applied the N-COMmodel to analyze field nitrogen and phosphorus perturbation experiments intwo tropical forest sites (in Hawaii and Puerto Rico) not used in modeldevelopment or calibration. Under soil inorganic nitrogen and phosphoruselevated conditions, the model accurately replicated the experimentallyobserved competition among nutrient consumers. Although we used as manyobservations as we could obtain, more nutrient addition experiments intropical systems would greatly benefit model testing and calibration. Insummary, the N-COM model provides an ecologically consistent representationof nutrient competition appropriate for land BGC models integrated in EarthSystem Models.

[学科分类] 地球化学与岩石