Effects of regulated deficit irrigation on photosynthetic characteristics in Perennial Ryegrass and the determination for irrigation threshold

This study was conducted in the greenhouse with perennial ryegrass (Lolium perenne) varieties Premier and Panterra, which are largerly planted in semiarid areas. The experiment with controlled soil water contents was conducted to study the effects of five treatments repeated drying and rewatering on photosynthetic characteristics. The results indicated that variation tendency of two varieties of perennial ryegrass on photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs)and photochemistry activity of PSⅡ (Fv/Fm) decreased with RSWC decreasing. The activities of photosynthetic parameters in different relative soil water content had different variation trends and also had different recovery level after rehydration. When the relative soil water content was the lower irrigation limit which is 50% RSWC caused stress effect to grasses, it will not cause greater harm. While the treatment which lower irrigation limit was 40% RSWC, two varieties of Perennial ryegrass injury were more and more serious. Both of the two grasses at the end of the drought stage showed severe stress (lower irrigation limit of 20% RSWC) injury, and can not recovered rapidly in the physiological function after rehydration. The comparative result between the two grasses: Premier has the better drought resistance than Panterra. These are suggested that Regulated irrigation on Perennial ryegrass has obvious for RSWC, and showed different result between the two grasses: Premier is 40% RSWC; Panterra is 50% RSWC.