Effects of Soil Temperature on the Growth and Hormone Content ofDactylis glomerataL. (Cocksfoot) in Controlled Environments

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Abstract
A comparison was made of effects of ‘low’ and ‘high’ soil temperature (LST and HST, about 9 and 21·5 °C respectively) on shoot growth of Norwegian and Portuguese populations of Dactylis glomerata. In experiments lasting 8 short days (SD, 8 h photoperiods) LST decreased leaf extension more markedly in the Portuguese population. No differential effect of LST on leaf growth was recorded in experiments lasting 20 or 21 SD or in experiments of 8 d duration in long days (LD, 16 h photoperiods). Since the meristem and region of cell extension is close to the soil surface LST could directly influence both root and shoot growth. The application of gibberellic acid enhanced leaf extension, particularly in plants grown at HST. 6-Benzylaminopurine tended to decrease leaf length. Extractable gibberellin levels were relatively low after 8 SD in shoots of both races grown at LST. Cytokinin levels increased at LST, more so in shoots of Portuguese plants which sustained the greater reduction in leaf extension. The data suggest that LST may reduce the production of endogenous gibberellins important for leaf growth in Dactylis glomerata. Cytokinins are probably necessary for growth processes but their level may reflect, rather than direct, the rate of leaf growth.

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