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MORPHOLOGICAL PLASTICITY AND MINERAL NUTRIENT CAPTURE IN TWO HERBACEOUS SPECIES OF CONTRASTED ECOLOGY.

Developmental plasticity and nitrogen capture were compared in Agrostis stolonifera and Scirpus sylvaticus grown in compartmentalized root growth arenas which allowed simulation of the spatial and temporal patchiness distinguishing the conditions of mineral nutrient supply associated with fertile and infertile soils. Despite the small root system, higher rates of nitrogen capture and dry matter production were achieved by A. stolonifera at both high and low external concentrations of mineral nutrients. This species also showed a marked ability rapidly to adjust partitioning of growth between parts of the root system, thus allowing local proliferations of fine roots into sectors of high mineral nutrient concentration. Under the conditions of the experiment, this form of plasticity was only weakly developed in S. sylvaticus, which instead maintained a large but relatively unresponsive root mass under each experimental treatment. It is concluded that the high plasticity observed in A. stolonifera allows the dynamic exploitation of fertile soil by competing roots. It is predicted that the more stable pattern of root development in S. sylvaticus will confer a selective advantage in environments where mineral nutrients are strongly limiting upon productivity and become available in temporally unpredictable pulses.