Effects of temperature & light intensity on CO2 uptake, respiration, & growth of white clover

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Abstract
CO2 uptake by white clover (Trifolium repens) leaves was measured at all combinations of 10,20, and 30C temperatures and 800, 1,200 and 4,200 ft.-c. light intensity. Maximum rates occurred at 30[degree]C for all light intensities. At 10[degree]C, CO2 uptake did not change significantly as light increased from the lowest to the highest intensity. At 20[degree] and 30[degree]C, significant increases in CO2, uptake occurred as light intensity was increased. Temperature effects on respiration rates of leaf discs and stolon internode sections were measured in a Warburg apparatus. Rates in leaf discs increased as temperature increased from 20 to 35[degree]C but declined at higher temperatures; almost no O2 exchange occurred after the second hour at 50[degree]C. Stolon tissue was more tolerant of high temperature, and cumulative O2 uptake for a five hour period was in this order 50C [greater than or equal to] 45C>40C>35C. Two factorial growth chamber experiments measured growth and development under different day temperature (DT), night temperature (NT), and light intensity regimes. One experiment employed 600 ft.-c. light intensity and tested 10, 17, 23, and 30[degree]C in all combinations as DT and NT. Plant responses to DT were generally greater than to NT. Dry weight, leaf production, and leaf size were maximum at 17 and 23[degree]C DTs. A regression of dry weight on average leaf area present during the six-week experiment accounted for 90% of the differences in plant weights. The second growth chamber experiment tested all combinations of three levels of light intensity (600, 900, and 2,000 ft.-c.) and NT (10, 17, and 30C) on plants at a DT of 30[degree]C. The higher light intensities increased leaf production, leaf size, and plant weights, but decreased the average life span of leaves. In this experiment each unit of leaf area yielded nearly the same amount of dry matter regardless of light intensity; shorter life spans of leaves apparently offset higher photosynthetic rates at 900 and 2,000 ft.-c. light intensity. It was concluded that both temperature and light intensity influence growth rates of white clover plants by affecting the rate of leaf area production.

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