Influence of Soil Heterogeneity on the Coexistence of Grassland Species

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Abstract
In 15 lowland grasslands [composed of various combinations of Agrostis capillaris, Holcus lanatus, Plantago lanceolata, Festuca rubra, Dactylis glomerata, Molinia caerulea, Agrostis canina, Carex disticha, Anthoxanthum odoratum, Deschampsia caespitosa, Briza media and Poa pratensis, P. trivialis, Lolium perenne], as the quotient of root density in the lower (5-10 cm) layer of soil to that in the upper (0-5 cm) layer increases there is a decrease in number of species per unit area and in an index of dominance. This quotient, a measure of the heterogeneity of root development, was not related to the difference in pH or concentration of extractable phosphate or K in the 2 soil layers. In a pot experiment an infertile acid sand and a fertile calcareous loam, either mixed or in distinct upper and lower soil layers, were used to grow a standard mixture of 5 grassland plants. Dominance of 1 or 2 spp. was less marked where there was a distinct lower layer of soil and this was true irrespective of the total aboveground biomass of all plants. The amount of Ca in the shoots indicates that the species differed in rooting depth, although the spatial distribution of the root system was not analyzed. Soil heterogeneity can influence the coexistence of species. The distribution of roots in the field may be of great importance in this respect.

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