TY - JOUR

T1 - Nitrogen transport in a tundra landscape

T2 - the effects of early and late growing season lateral N inputs on arctic soil and plant N pools and N2O fluxes

AU - Rasmussen, Laura H.

AU - Zhang, Wenxin

AU - Ambus, Per

AU - Michelsen, Anders

AU - Jansson, Per Erik

AU - Kitzler, Barbara

AU - Elberling, Bo

N1 - CENPERM[2021] Funding Information: We gratefully acknowledge the financial support from the Danish National Research Foundation (CENPERM DNRF100). Funding Information: We gratefully acknowledge the financial support from the Danish National Research Foundation (CENPERM DNRF100). We thank Arctic Station for collaboration and logistics in performing fieldwork, E. Kolstad for NO measurements in 2018, W. Xu, B. Danielsen and A. Lambæk for help in the field in 2019, S. Ludvigsen, M. Wahlgren and G. Sylvester and E. V. Nielsen for help with lab analyses. M. Nilsson was invaluable for sample preparation. K. Rousk kindly helped with knowledge and advice. We thank the three anonymous reviewers and the handling editor for constructive and useful comments, which improved the manuscript markedly. 2 Publisher Copyright: © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG.

PY - 2021

Y1 - 2021

N2 - Understanding N budgets of tundra ecosystems is crucial for projecting future changes in plant community composition, greenhouse gas balances and soil N stocks. Winter warming can lead to higher tundra winter nitrogen (N) mineralization rates, while summer warming may increase both growing season N mineralization and plant N demand. The undulating tundra landscape is inter-connected through water and solute movement on top of and within near-surface soil, but the importance of lateral N fluxes for tundra N budgets is not well known. We studied the size of lateral N fluxes and the fate of lateral N input in the snowmelt period with a shallow thaw layer, and in the late growing season with a deeper thaw layer. We used 15N to trace inorganic lateral N movement in a Low-arctic mesic tundra heath slope in West Greenland and to quantify the fate of N in the receiving area. We found that half of the early-season lateral N input was retained by the receiving ecosystem, whereas half was transported downslope. Plants appear as poor utilizers of early-season N, indicating that higher winter N mineralization may influence plant growth and carbon (C) sequestration less than expected. Still, evergreen plants were better at utilizing early-season N, highlighting how changes in N availability may impact plant community composition. In contrast, later growing season lateral N input was deeper and offered an advantage to deeper-rooted deciduous plants. The measurements suggest that N input driven by future warming at the study site will have no significant impact on the overall N2O emissions. Our work underlines how tundra ecosystem N allocation, C budgets and plant community composition vary in their response to lateral N inputs, which may help us understand future responses in a warmer Arctic.

AB - Understanding N budgets of tundra ecosystems is crucial for projecting future changes in plant community composition, greenhouse gas balances and soil N stocks. Winter warming can lead to higher tundra winter nitrogen (N) mineralization rates, while summer warming may increase both growing season N mineralization and plant N demand. The undulating tundra landscape is inter-connected through water and solute movement on top of and within near-surface soil, but the importance of lateral N fluxes for tundra N budgets is not well known. We studied the size of lateral N fluxes and the fate of lateral N input in the snowmelt period with a shallow thaw layer, and in the late growing season with a deeper thaw layer. We used 15N to trace inorganic lateral N movement in a Low-arctic mesic tundra heath slope in West Greenland and to quantify the fate of N in the receiving area. We found that half of the early-season lateral N input was retained by the receiving ecosystem, whereas half was transported downslope. Plants appear as poor utilizers of early-season N, indicating that higher winter N mineralization may influence plant growth and carbon (C) sequestration less than expected. Still, evergreen plants were better at utilizing early-season N, highlighting how changes in N availability may impact plant community composition. In contrast, later growing season lateral N input was deeper and offered an advantage to deeper-rooted deciduous plants. The measurements suggest that N input driven by future warming at the study site will have no significant impact on the overall N2O emissions. Our work underlines how tundra ecosystem N allocation, C budgets and plant community composition vary in their response to lateral N inputs, which may help us understand future responses in a warmer Arctic.

KW - Arctic tundra

KW - Climate change

KW - Nitrate

KW - Solute transport

KW - Winter N mineralization

U2 - 10.1007/s10533-021-00855-y

DO - 10.1007/s10533-021-00855-y

M3 - Journal article

AN - SCOPUS:85117256432

VL - 157

SP - 69

EP - 84

JO - Biogeochemistry

JF - Biogeochemistry

SN - 0168-2563

ER -