Modeling the effects of organic nitrogen uptake by plants on the carbon cycling of boreal forest and tundra ecosystems 1Purdue Climate Change Research Center, Purdue University, West Lafayette, Indiana, USA
06 Dec 2013
2Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA
3Department of Agronomy, Purdue University, West Lafayette, Indiana, USA
Received: 10 Jul 2013 – Published in Biogeosciences Discuss.: 13 Aug 2013 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 (De) 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.
Revised: 05 Nov 2013 – Accepted: 06 Nov 2013 – Published: 06 Dec 2013
Citation: Zhu, Q. and Zhuang, Q.: Modeling the effects of organic nitrogen uptake by plants on the carbon cycling of boreal forest and tundra ecosystems, Biogeosciences, 10, 7943-7955, doi:10.5194/bg-10-7943-2013, 2013.