Importance of soil solution chemistry to field performance of Galium odoratum and Stellaria nemorum.
Six Swedish beech forest sites, representing the range of pH for soils which support Galium odoratum and Stellaria nemorum, were sampled during 1 year using percolation lysimeters installed immediately under the root horizon of the studied species. Chemical analyses were made of DOC, Al, Ca, Cl, Fe, K, Mg, Mn, Na, NH4, NO3, PO4, SO4 and Zn. Within each site the sample plots were selected for a well-developed cover of mainly Galium odoratum, mainly Stellaria nemorum or a mixture of both species to allow inter- and intra-species comparisons within the limits of their occurrence. The percolation water had lowest concn of most constituents in the summer, probably due to high uptake by the vegetation. This was most evident for productive sites, where the substantial decrease might have approached limiting levels. The concn in the percolation water varied greatly between sampling events, this variation being especially pronounced for NH4, NO3 and phosphate, but 10-fold differences in concn were also found for Al, Cl, Fe, K and Mn. The soil chemistry regimen for a few months during the summer explained above-ground growth of the plants better than means over a longer period. The concn of Mn and H in the percolation water was negatively related to biomass of Galium odoratum, and Na to Stellaria nemorum. Concn of Al and Mn were lower in Galium odoratum than in Stellaria nemorum plots, which might indicate a lower tolerance of Galium odoratum to these constituents. The small but easily available element pool of the percolation water seems to illustrate a plant-soil relationship either by reflecting or being the most relevant water fraction in the soil.