Arsenate tolerance in Agrostis castellana and Agrostis delicatula

Experiments were made to elucidate why many field-layer plants in beech forests do not grow in mor (raw humus), a layer of organic matter in various stages of decay containing little or no mineral soil particles. Three possibilities were considered directly or indirectly: (i) tree root competition and litter shading, (ii) phytotoxic and nutrient complexing organic compounds in the soil solution, and (iii) high H-ion concentration in the solution. Rhizomes of eight species (Allium ursinum, Carex sylvatica, Convallaria majalis, Deschampsia flexuosa, Galium odoratum, Poa nemoralis, Stellaria holostea, Stellaria nemorum) were collected in late winter and used in a soil experiment to test reestablishment and growth in untreated mor (soil solution pH 3.6) and after pH was raised to 4.3 by addition of SrCO₃. A flowing solution experiment was used with five of the species mentioned. The solution was composed according to the soil solution of the untreated mor but lacking organic compounds. pH was adjusted to and maintained at 3.6 and 4.3. The experiments showed that even when root competition, litter shading and organic compounds were excluded as limiting factors, only Deschampsia flexuosa, and partly Convallaria majalis, could produce new roots in the untreated mor or in the pH 3.6 solution treatment. Some shoot biomass developed in all species except in Galium odoratum, though significantly less than at pH 4.3.It was concluded that high H-ion concentration of the soil solution precludes establishment and growth of many forest plants in beech forests developed on mor podzols.