Effect of temperature and nitrogen supply on the growth of perennial ryegrass lolium perenne cultivar s 23 and white clover trifolium repens cultivar s 100 2. a comparison of monocultures and mixed swards

Davidson, I.A.; Robson, M.J.

Annals of Botany 57(5): 709-720


ISSN/ISBN: 0305-7364
Accession: 005274700

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White clover (Trifolium repens L.) and Perennial ryegrass (Lolium perenne L.) plants were grown, in Perlite, in simulated swards as either monocultures or mixtures of equal plant numbers. They were supplied with a nutrient solution either high (220 .mu.g g-1) or low (40 .mu.g g-1) in 15N-labelled nitrate and grown to ceiling yield at either high (20.degree. C day/15.degree.C night) or low (10.degree. C day/8.degree.C night) temperature. Temperature had little effecton the maximum rates of gross canopy photosynthesis which were similar in High-N grass and High-N and Low-N clover monocultures. However these maxima were reached more slowly in clover than grass, and more slowly at low rather than high temperature. Nitrogen supply increased photosynthesis in grass but not in clover. Clover had higher N contents than grass in all four treatments, although in any given treatment its N content was lower, and contribution of N2-fixation relative to nitrate uptake higher, in mixture than in monoculture. Conversely, grass had higher N contents in mixture than monoculture, because more nitrate was available per plant and not because of transfer of biologically fixed N from clover. Under Low-N, clover outyielded grass in mixture, particularly at high temperature. The grass plants in the Low-N mixtures had higher N contents and higher SLA, LAR and shoot:root ratios than those in monoculture. It is proposed that competition for light is the cause of the low relative yield and negative aggressivity of grass in these swards. Under High-N, grass outyielded clover in monoculture and mixture, at both temperatures but particularly at low temperature when grass had a high aggressivity. Nitrogen and yield component analyses shed no light on clover's apparently low competitive ability and evidence is drawn from the previous paper to demonstrate that grass grew faster than clover only as spaced individuals during non-competitive growth. The relative merits of measures of competitive ability based on final harvest data and physiological data taken over a growth period are discussed.