NITROGEN SOURCE AND THE TOLERANCE OF DESCHAMPSIA FLEXUOSA, HOLCUS LANATUS AND BROMUS ERECTUS TO ALUMINIUM DURING SEEDLING GROWTH.

(1) The growth of three grasses whose natural distribution ranged from acidic to calcareous soils was measured in response to the concentration of two major pH-linked soil chemical factors, nitrogen and aluminium, supplied in flowing culture. (2) All three species showed one or more of the basic responses proposed in four hypotheses based on their ecological distribution. (3) Deschampsia Jlexuosa grew equally fast with either NO3-N or NH4 N as the nitrogen source. It was tolerant of any combination of N source and aluminium except for the highest concentration of Al (5.4 mg 1-1) supplied with NO3 N. (4) Holcus lanatus grew significantly faster in NO3 N than it did in NH4N and showed classical symptoms of aluminium toxicity in the presence of NO3-N. The strongly adverse effect of NH4- N was significantly ameliorated by the addition of aluminium. (5) Bromus erectus also grew significantly faster in NO3-N than it did in NH4-N and was susceptible to aluminium toxicity in the presence of NO3-N. The very small extent of growth in NH4-N masked any possible effects of aluminium and growth was not increased in the presence of aluminium. (6) A revision of ideas on the roles of inorganic toxins in acidic soils is proposed. [ABSTRACT FROM AUTHOR]