ECO-PHYSIOLOGICAL ASPECTS OF INTER-SPECIFIC AND SEASONAL VARIATION IN NITRATE UTILIZATION IN THE GENUS AGROSTIS.

Nitrate utilization, as judged by dry matter production and nitrate reductase activity, was examined in species of the genus Agrostis and compared with species of Lolium and Poa. A. setacea had the lowest ability to utilize nitrate which correlated with its restricted ecological distribution in areas of low nitrate availability. In contrast, A. tenuis which may also be found in low nitrate sites, exhibited a higher nitrate reductase activity but lower dry matter production than the species A. stolonzfera and L. multiflorum, both of which are characteristic of sites with higher nitrate availability. A high potential to utilize nitrate may be important in low nitrate areas subjected to marked fluctuations in supply. Correlations between nitrate utilization and growth were, in general, non-significant and often negative. The results suggest that the efficiency of incorporation of reduced nitrogen into plant structure may bring about differences between species in the production of dry matter. Significant variations between species and response to nitrate were found in relation to the time of year. Maximum enzyme activities were found during the winter months with little change, after a drop in activity in the early spring, during the growth period. The peaks in activity found may not represent nitrate utilization but rather the induction of high levels of enzyme with little subsequent reduction of nitrate. Variation in soil pH did not modify the seasonal pattern and had little overall effect on either nitrate utilization or dry matter production although significant differences were found between species in both of these factors. [ABSTRACT FROM AUTHOR]