LEAF RESPIRATION IN LIGHT AND DARKNESS - A COMPARISON OF SLOW-GROWINGAND FAST-GROWING POA SPECIES

We investigated whether leaf dark respiration (nonphotorespiratory mit ochondrial CO2 release) is inhibited by right in several Poa species, and whether differences in light inhibition between the species ave re lated to differences in the rate of leaf net photosynthesis. Four lowl and (Poa annua L., Poa compressa L., Poa pratensis L., and Poa trivial is L.), one subalpine (Poa alpina L.), and two alpine (Poa costiniana Vick. and Poa fawcettiae Vick.) Poa species differing in whole plant r elative 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 cor related with the relative growth rate, with the slow-growing alpine Po a species exhibiting the lowest photosynthetic rates. Rates of both R( d) and respiration in darkness were also substantially lower in the al pine species. Nonphotorespiratory CO2 release in darkness was higher t han R(d) in all species. However, despite some variation between the s pecies in the level of light inhibition of respiration, no relationshi p was observed between the level of inhibition and the rate of photosy nthesis. Similarly, the level of inhibition was not correlated with th e relative growth rate. Our results support the suggestion that rates of leaf respiration in the light are closely associated with rates in darkness.