Nutrient Content of Developing Northern Hardwoods
Nutrient Uptake and Content
M.S. Lucash, R.D. Yanai and J.D. Joslin
Plant nutrient uptake is difficult to estimate at the ecosystem scale. Several indirect methods are used to quantify stand-level nutrient uptake such as nutrient budgets and simulation models. In nutrient budgets, nutrient uptake is generally estimated by using fluxes such as litter fall, biomass accumulation, and root turnover. Simulation models, on the other hand, predict uptake utilizing measurements such as root length, soil solution concentrations, and uptake capacity.
Many studies of uptake capacity in trees have been conducted using seedlings, despite the fact that seedling uptake may differ dramatically from that of mature trees. Other studies in forest ecosystems have used excised roots to estimate uptake, even though carbohydrate and water supply is halted at the time of excision. In this study we plan to measure uptake capacity of intact roots at several sites across the US in order to improve model estimates of ecosystem uptake. Results from the simulation models will also be compared with nutrient budgets.
Nutrient Uptake Modeling
We use a steady-state model of nutrient uptake (Nye and Tinker 1977, Yanai 1994), because it allows parameters such as root length, root diameter, root length density (root length per unit soil volume), average soil solution concentration, buffer capacity, and the effective diffusion coefficient to vary over time. In natural ecosystems, root length increases and decreases seasonally, and nutrient concentrations in solution reflect processes such as mineralization, immobilization, and weathering in addition to nutrient uptake. We supply the model with values of root length, rooting density, soil solution and solid phase concentrations, transpiration rates, and soil moisture content at whatever time resolution data and depth resolution are available for each of our 6 sites (link to map of sites).
A multi-dimensional sensitivity analysis shows that the most important parameters in simulating nutrient uptake are the root length, soil solution concentration, and uptake kinetics (Williams and Yanai 1996). Uncertainty analysis will be conducted for each site by running the model repeatedly using the observed distribution of parameter values (Gardner et al. 1983). We will also test the value of time-varying input by simulating uptake using annual average values and comparing them to simulations at finer resolution.
To download the model:
http://www.esf.edu/for/yanai/models/nut
Modeling Soil Solution Chemistry: YASE
YASE is a model that simulates the chemical composition of soil solutions as determined by chemical equilibria, organic matter transformations, and mineral weathering. Different properties can be assigned to different soil layers in the model. Uptake of solutes from the soil by plants, addition of organic matter, movement of soil solution between soil layers, and influx of solution from above or below the soil can be provided as inputs to YASE, either by the TREGRO model or by the user. YASE can be run alone at any time step; when called by TREGRO it is called on a daily time step.
Chemical equilibria in YASE are based on the Chemical Equilibria in Soils and Solutions model, CHESS (Santore 1991). CHESS uses a matrix representation of solution chemistry (Morel, 1983). Equilibrium problems of any composition and complexity (or simplicity) can be simulated using this model, because the chemical components and the rules for combining them into species are supplied by the user.
Decomposition in YASE follows the algorithm of GEM (Rastetter et al., 1991): transformations among extractives, cellulose, lignin, and humus are affected by temperature, soil moisture, N availability, and a ligno-cellulose index. Weathering in YASE is defined by the user using mineral compositions, weathering rates, and reaction orders with respect to pH and the amount of mineral present. Cation exchange is treated as an equilibrium between adsorbed and dissolved species interrelated by selectivity coefficients.
YASE was developed to be compatible with TREGRO. To be used in combination with TREGRO, YASE must be parameterized to include the nutrients of possible importance to the plant. A HyperCard interface aids in the parameterization and running of the model, whether alone or in combination with TREGRO.
Nutrient Uptake using SUM Columns
M.S. Lucash, R.D. Yanai, J.D. Joslin and J.M. Scholberg
Most estimates of nutrient uptake are obtained using excised roots or roots recently excavated from soil. Using this sand-culture method, we are able to obtain estimates of nitrate and ammonium uptake of seedlings. We installed these SUM (soil uptake monitoring) columns in the field and plan to test this method using mature sugar maple and eastern hemlock in spring, 2004.
Root Growth and Developement
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Last updated
02/08/08
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