The use of a closed system flow-through enclosure apparatus for studying the effects of partial pressure of dinitrogen in the atmosphere on growth of Trifolium repens L. and Lolium perenne L
1993
McNeill, A.M. | Wood, M. | Gates, R.P.
A closed system flow-through enclosure apparatus was constructed and used to enclose mixtures of Lolium perenne L. (perennial ryegrass cv. Trani) and nodulated Trifolium repens L. (white clover cv. Blanca) growing in soil in pots. There were no significant differences between the shoot growth, in terms of dry matter accumulation and nitrogen content, of mixtures in the system compared to that of mixtures grown in a standard growth cabinet. This demonstrated that stable ambient conditions could be achieved by the closed system and its control circuits and that there were no apparent side-effects of the recirculatory gases. Reducing the partial pressure of dinitrogen in the atmosphere affected white clover, but not perennial ryegrass. A fairly rapid effect was observed 4 h after reduction in dinitrogen partial pressure as some of the clover leaves folded downwards along the petiole. These same effects were observed at two different partial pressures of dinitrogen (22% and 39%) and with two different replacement gases (argon and helium). In the longer term (11 to 16 d) dry matter accumulation and nitrogen content of the clover shoots were significantly reduced. These effects of reduced partial pressure of dinitrogen were observed in both nodulated (NOD+) and nitrate-dependent (NOD-) clover. Possible reasons for these effects were discussed with particular reference to impurities in the gases used, stomatal responses and plant water relations. It was concluded that the closed system flow-through apparatus provides a useful tool for studying whole plant-soil systems and, in particular, the cycling of nitrogen. However, the use of a replacement gas to reduce the cost of labelled dinitrogen was obviously not a viable proposition.
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