Response of Physiological and Ecological Characteristics of Pinus sylvestris var. mongolica to Irrigation Intensity in Mu Us Sandy Land

The potential risk of premature aging of plantation in Mu Us Sandy land caused by drought stress, 3 irrigation gradients were set with 6-year-old Pinus sylvestris var. mongolica, and the irrigation amount was 2 times, 3 times and 4 times of the average precipitation of recent 5 years(487.56 mm), respectively. The relationship between photosynthetic index, physiological index and irrigation intensity was analyzed, and the response of physiological characteristics of photosynthesis and water to soil water status was found out. The findings indicated that with the increase of irrigation intensity, the growth capacity, tissue moisture content, photosynthetic physiological indexes increased first and then decreased at 43.20 %, 1.40 % and 37.60 %, respectively, and the content of malondialdehyde and superoxide free radical increased significantly by 27.28 % and 136.59 % with the extension of growth period, and it decreased significantly by 7.5 % and 18.15 % with the increase of irrigation amount. Growth capacity was positively correlated with tissue water content and photosynthetic rate, and negatively correlated with superoxide anion and malondialdehyde content. Furthermore, the photosynthetic rate was positively correlated with tissue water content, while the content of superoxide anion and malondialdehyde was negatively correlated with tissue water content. According to regression analysis, the optimal irrigation intensity of 6 a P. sylvestris var. mongolica plantation in Mu Us Sandy Land was 2.5–3.5 times of the local precipitation. These results indicated that irrigation intensity, tissue moisture content, photosynthetic physiology, water physiology and growth ability were integrated as a continuous driving process. Irrigation intensity played a key role in regulating drought resistance function and improving physiological adaptability of P. sylvestris var. mongolica plantation, and also a efficient way to improving forest water condition and delaying or avoiding premature aging of P. sylvestris var. mongolica plantation.