Modeling the effects of organic nitrogen uptake by plants on the carbon cycling of boreal forest and tundra ecosystems

[摘要] Boreal forest and tundra are the major ecosystems in the northern highlatitudes in which a large amount of carbon is stored. These ecosystems arenitrogen-limited due to slow mineralization rate of the soil organicnitrogen. Recently, abundant field studies have found that organic nitrogenis another important nitrogen supply for boreal forest and tundra ecosystems.In this study, we incorporated a mechanism that allowed boreal plants touptake small molecular amino acids into a process-based biogeochemical model,the Terrestrial Ecosystem Model (TEM), to evaluate the impact of organicnitrogen uptake on ecosystem carbon cycling. The new version of the model wasevaluated for both boreal forest and tundra sites. We found that the modeledorganic nitrogen uptake accounted for 36–87% of total nitrogen uptakeby plants in tundra ecosystems and 26–50% for boreal forests,suggesting that tundra ecosystem might have more relied on the organic formof nitrogen than boreal forests. The simulated monthly gross ecosystemproduction (GPP) and net ecosystem production (NEP) tended to be larger withthe new version of the model since the plant uptake of organic nitrogenalleviated the soil nitrogen limitation especially during the growing season.The sensitivity study indicated that the most important factors controllingthe plant uptake of organic nitrogen was the soil amino acid diffusioncoefficient (D_e) in our model, suggesting that the organicnitrogen uptake by plants is likely to be regulated by the edaphiccharacteristics of diffusion. The model uncertainty due to uncertainparameters associated with organic nitrogen uptake of the tundra ecosystem waslarger than the boreal forest ecosystems. This study suggests that consideringthe organic nitrogen uptake by plants is important to carbon modeling ofboreal forest and tundra ecosystems.

[学科分类] 地球化学与岩石