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Are Trees Dormant During the Dormant Season? Determining the Importance of Plant Nutrient Uptake in Changing Cold Seasons in Cold-Region Catchments

Active Dates 9/1/2023-8/31/2026
Program Area Environmental Systems Science
Project Description
Are Trees Dormant During the Dormant Season? Determining the Importance of Plant Nutrient Uptake in Changing Cold Seasons in Cold-Region Catchments

C.L. Goodale, Cornell University (Principal Investigator)

P. Hess, Cornell University (Co-Investigator)

P. M. Groffman, City University of New York (Co-Investigator)

Q. Zhu, Lawrence Berkeley National Laboratory (Co-Investigator)

Plant uptake of nitrogen, a vital nutrient, is typically assumed to cease over winter in cold-region forests, in concert with seasonal patterns of plant growth. Most models built to simulate Earth’s future climate and atmospheric CO2 concentrations (Earth System Models) link plant nutrient uptake to growth, and predict large nitrogen losses from soils during the dormant season and subsequent scarcity during the growing season that limits the ability of plants to sequester carbon. However, plants are more active belowground during the dormant season than previously recognized, and some can take up nitrogen over winter. Yet, it is not known whether dormant-season plant nitrogen uptake is widespread or how the process varies with plant traits or in response to warming winters. Winter temperatures have increased steeply across the northeastern US, with less snowfall, more thaws, and decreased depth and duration of snow cover. Snow insulates the soil, and prior snowpack-reduction experiments caused soil frost that damaged fine roots and their capacity to take up nitrogen.

We propose a set of activities designed to characterize cold-season nitrogen uptake by temperate forests. Our overarching hypothesis is that temperate trees take up ecologically important amounts of nitrogen over winter and that this uptake varies with tree type and with warming winter conditions. We will test this hypothesis with a set of studies that add an isotopically distinct form of nitrogen (the stable isotope 15N) to track plant N uptake, as well as experimental snowpack manipulation experiments and use of a state-of-the-art Earth System Model (the ELM-ECA version of the E3SM model). Instead of linking nutrient uptake to plant growth, this model simulates plant nitrogen uptake based on root properties and interactions with the soil environment. First, we will both simulate (ELM-ECA) and measure (15N tracers) winter plant N uptake by trees spanning a range of plant traits, and we present preliminary data indicating surprisingly large amounts of cold-season N uptake by six species of juvenile trees. Next, at the ecosystem scale, we will both simulate (ELM-ECA) and measure (15N tracers) competition for nitrogen among mature trees, microbes, and gaseous and hydrologic N losses in response to experimentally reduced winter snowpacks at two temperate watersheds with contrasting stream nitrate seasonality: Arnot Forest, New York, and Hubbard Brook Experimental Forest, New Hampshire. Last, we will use the model to assess how future conditions (warming, rising atmospheric CO2) will alter winter snowpacks, cold-season plant N uptake, and terrestrial carbon and nitrogen dynamics. Together, the proposed activities will advance fundamental understanding and model representation of plant nitrogen uptake, as well as its seasonality, controls, and effects on terrestrial carbon and nitrogen balances.
Award Recipient(s)
  • Cornell University (PI: Goodale, Christine)