Leaf respiration in light and darkness - A comparison of slow- and fast-growing Poa species

We investigated whether leaf dark respiration (nonphotorespiratory mitochondrial CO2 release) is inhibited by right in several Poa species, and whether differences in light inhibition between the species ave related to differences in the rate of leaf net photosynthesis. Four lowland (Poa annua L., Poa compressa L., Poa pratensis L., and Poa trivialis L.), one subalpine (Poa alpina L.), and two alpine (Poa costiniana Vick. and Poa fawcettiae Vick.) Poa species differing in whole plant relative growth rates were grown under identical controlled conditions. Nonphotorespiratory mitochondrial CO2 release in the light (R(d)) was estimated according to the Laisk method. Photosynthesis was measured at ambient CO2 partial pressure (35 Pa) and 500 mu mol photons m(-2) s(-1). The rate of photosynthesis per unit leaf mass was positively correlated with the relative growth rate, with the slow-growing alpine Poa species exhibiting the lowest photosynthetic rates. Rates of both R(d) and respiration in darkness were also substantially lower in the alpine species. Nonphotorespiratory CO2 release in darkness was higher than R(d) in all species. However, despite some variation between the species in the level of light inhibition of respiration, no relationship was observed between the level of inhibition and the rate of photosynthesis. Similarly, the level of inhibition was not correlated with the relative growth rate. Our results support the suggestion that rates of leaf respiration in the light are closely associated with rates in darkness.