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

Abstract

Abstract. Boreal forest and tundra are the major ecosystems in the northern high latitudes in which a large amount of carbon is stored. These ecosystems are nitrogen-limited due to slow mineralization rate of the soil organic nitrogen. Recently, abundant field studies have found that organic nitrogen is another important nitrogen supply for boreal forest and tundra ecosystems. In this study, we incorporated a mechanism that allowed boreal plants to uptake small molecular amino acids into a process-based biogeochemical model, the Terrestrial Ecosystem Model (TEM), to evaluate the impact of organic nitrogen uptake on ecosystem carbon cycling. The new version of the model was evaluated for both boreal forest and tundra sites. We found that the modeled organic nitrogen uptake accounted for 36-87 % of total nitrogen uptake by plants in tundra ecosystems and 26-50 % for boreal forests, suggesting that tundra ecosystem might have more relied on the organic form of nitrogen than boreal forests. The simulated monthly gross ecosystem production (GPP) and net ecosystem production (NEP) tended to be larger with the new version of the model since the plant uptake of organic nitrogen alleviated the soil nitrogen limitation especially during the growing season. The sensitivity study indicated that the most important factors controlling the plant uptake of organic nitrogen was the soil amino acid diffusion coefficient (D e ) in our model, suggesting that the organic nitrogen uptake by plants is likely to be regulated by the edaphic characteristics of diffusion. The model uncertainty due to uncertain parameters associated with organic nitrogen uptake of the tundra ecosystem was larger than the boreal forest ecosystems. This study suggests that considering the organic nitrogen uptake by plants is important to carbon modeling of boreal forest and tundra ecosystems.

Multiple soil nutrient competition between plants, microbes, and mineral surfaces: model development, parameterization, and example applications in several tropical forests

“…To date, many terrestrial ecosystem biogeochemistry models assume that microbes outcompete plants and immobilize nutrients first (Wang et al, 2007;Zhu and Zhuang, 2013), although CLM currently assumes constant and relative demand competitiveness of plants and microbes. Few models, to our knowledge, consider the role of abiotic interactions in the competitive interactions.…”

Climate, soil organic layer, and nitrogen jointly drive forest development after fire in the North American boreal zone

“…Rather, we are only able to examine the competitive dynamics between aspen and black spruce species-types with changes in environmental forcing. Additionally, some observations indicate that a number of boreal species are able to uptake organic nitrogen, alleviating some of the nitrogen stress due to a lack of available mineralized nitrogen [N€ asholm et al, 1998;Zhu and Zhuang, 2013]. However, in the interest of parsimony, we did not include this process in our model.…”

Multiple soil nutrient competition between plants, microbes, and mineral surfaces: model development, parameterization, and example applications in several tropical forests

“…Q 75 and Q 25 are 75 and 25 % percentage quantile of each parameter. UR is a useful metric (Zhu and Zhuang, 2014), because it quantitatively reveals the reduction in the range of a particular parameter after calibration with MCMC. It does not, however, indicate that the parameter itself is more consistent with observed values of the parameter.…”