Leaf temperature effects on net photosynthesis, dark respiration, and photorespiration of seedlings of black locust families with contrasting growth rates

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Rates of net photosynthesis, dark respiration, and photorespiration of six half-sib families of black locust (Robiniapseudoacacia L.) were measured at leaf temperatures ranging from 10 to 40 °C. Rates of dark respiration increased with increasing leaf temperature in all families and reached as high as 67% of gross photosynthesis at 40 °C in one family. Dark respiration of foliage accounted for 12.5 to 59% of the reduction in net photosynthesis at temperatures higher than those optimum for net photosynthesis. Rates of photorespiration peaked at 10 to 20 °C, exhibiting the same pattern as net photosynthesis, and did not contribute to the decline in net photosynthesis at high temperatures. The families with high rates of net photosynthesis also had high rates of photorespiration. Rates of dark respiration were significantly different among the families, and the slow-growing families had the highest rates of dark respiration. A significant interaction between half-sib families and leaf temperatures was noted for dark respiration. The data indicated the possibility of improving the growth of black locust by selection and breeding for large leaf area, high rates of net photosynthesis and low rates of dark respiration.