Are Trees Dormant During the Dormant Season? Determining the Importance of Plant Nutrient Uptake in Changing Cold Seasons in Cold-Region Catchments
Authors
Christine Goodale1* (clge33@cornell.edu), Stephanie Freund1, Peter Groffman1, Peter Hess3, Qing Zhu4
Institutions
1Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY; 2Department of Earth and Environmental Sciences, City University of New York–Brooklyn, NY; 3Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY; 4Climate Department, Lawrence Berkeley National Laboratory, Berkeley, CA
Abstract
Most Earth system models tie plant nutrient uptake to photosynthetic demand and predict that uptake ceases over winter. However, plants may be more active belowground during winter than previously recognized. Yet, the extent of plant nitrogen (N) uptake during the dormant season is not known, nor how it varies with plant traits or in response to warming winters. Researchers are conducting a set of experiments and modeling activities to characterize cold-season plant N uptake, its controls, and its response to shrinking snowpacks in seasonally cold temperate forests. The team’s overarching hypothesis is that temperate trees take up biogeochemically important amounts of N over winter and that this uptake changes along with winter climate conditions. Researchers are testing this hypothesis with 15N tracer studies of cold-season N uptake, snowpack manipulation experiments, and the equilibrium chemical approximation (ECA) version of the E3SM land model. First (Objective I), researchers are both simulating (ELM-ECA) and measuring (15N tracers) winter plant N uptake by juvenile and adult trees spanning a range of plant functional traits. Next, at the ecosystem scale (Objective II), researchers are both simulating (ELM-ECA) and measuring (15N tracers) competition for N among mature trees, microbes, and gaseous and hydrologic N losses in response to experimentally reduced winter snowpacks at Arnot Forest, NY, and Hubbard Brook, NH, two watersheds with contrasting stream nitrate seasonality. Last (Objective III), the team will use ELM-ECA to assess how cold-season plant N uptake and changing winter snowpacks will alter terrestrial carbon and nitrogen dynamics under future scenarios of additional warming and rising atmospheric CO2. Together, the proposed activities will test and strengthen E3SM-ELM representation of plant N uptake, which is one of the largest annual N fluxes in terrestrial ecosystems and a central constraint on terrestrial-carbon sequestration.