Effects of Temperature and Irradiance on Seedling Growth of Smooth Bromegrass1

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Abstract
Smooth bromegrass (Bromus inermis Leyss.) seedlings grown in four environments were used to study effects of temperature and irradiance on seedling growth. Differences between environments, between stages of growth, and their interaction were significant for tiller number, leaf number, leaf area, specific leaf weight, shoot‐to‐root ratio, dry weight of leaf, shoot and root, and seedling dry weight. Both main effects and their interaction were highly significant for relative growth rate (RGR) and leaf area ratio (LAR), while for net assimilation rate (NAR) differences between environments were non‐significant. Seedlings grown in high light and high temperature environments produced higher dry matter than those grown in low light or low temperature. The effect of irradiance was greater than that of temperature for most characters studied. Both RGR and NAR declined gradually with advancing plant age in all environments; LAR declined only in high light environments. Simple correlation coefficients revealed that increasing RGR and LAR could be accompanied by increasing tiller number, leaf number, leaf area, seedling dry weight and shoot‐to‐root ratio. Highly significant correlations were obtained between RGR and LAR (0.69 to 0.93 at 0.001 level), whereas there was no correlation between RGR and NAR. It is apparent that variation among environments in dry matter production of bromegrass seedlings was attributed to differences in LAR rather than NAR. Specific leaf weight was negatively correlated with RGR at the 0.001 level (−0.90) and LAR (−0.97), but positively correlated with NAR at the 0.05 level (0.47).