Reduction of PSII photosynthetic performance by low temperature is the reason for the growing inhibition of Kobresia pygmaea Clarke

Kobresia pygmaea Clarke is mainly distributed in the alpine region from 3800 to 4500 m elevation on the Qinghai-Tibet Plateau. It is excellent in low-temperature tolerance and trampling resistance and plays an important role in maintaining the stability of regional ecological environments. Mainly based on the chlorophyll fluorescence imaging technique, using grass sods blocks with a size of 20 × 20 cm 2 collected from K. pygmaea forb meadow, simulated a low-temperature treatment in cultural room with 8 °C/4 °C (day/night) at diurnal photoperiod, we analyzed the effects of low temperature on PSII photochemical efficiency and non-photochemical quenching, as well as the interaction between low temperature and light intensity. The results showed that low temperature could significantly decrease the maximum quantum efficiency of PSII photochemistry ( F v / F m ) and inhibit the leaf growth of K. pygmaea . The light response curve of PSII relative linear electron transport rate was reduced by low temperature, while it recovered to almost normal level after two days of removing adversity. Further experiments under steady-state actinic light confirmed that light intensity was the main factor affecting the PSII photochemical efficiency, and its reduction caused by the low temperature showed a certain degree of reversibility. The non-photochemical quenching (NPQ) was significantly affected by light intensity, and its fast and slow components (NPQ f and NPQ s ) in NPQ accounted for 36% and 64% of NPQ, respectively. The decrease in NPQ f and corresponding increase in NPQ s slowly recovered after relieving from low-temperature condition. The relative inhibition of photosynthesis ( P inh ) was significantly enhanced by low temperature and reduced after removal of adversity. Strong light intensity could intensify the adverse effect of low temperature on PSII operating efficiency F q ′/ F m ′ and efficiency factor F q ′/ F v ′, as well as NPQ. In conclusion, low temperature was one of the main reasons limiting the photosynthetic performance of K. pygmaea on the Qinghai-Tibet Plateau and could aggravate photosynthetic photoinhibition. The adversity of low temperature frequently occurring in the plant growing season on the Qinghai-Tibet Plateau was constituted of the main factor of the low productivity level in alpine meadow.