Water deficiency plays an important role in plant growth and metabolism. Response and adaptation to drought stress has become one of the hotspots of plant physiological research. Prunus sibirica、Hippophae rhamnoides and Pinus tabulaeformis are common afforestational tree species in arid and semi-arid region of North China.However, changes of the physiological and biochemical responses to different soil drought stress and their drought resistance are not clear at present.The objective of this study is to explore the quantitative relationship of the changes of the physiological and biochemical indexes and the soil moisture and to evaluate the drought-resistant ability of the three tree species. It will help us to further understand their physiological and ecological characteristics of the water and drought-resistant physiology. The results will also provide guidance for the cultivation of the three tree species in arid area.
The physiological and biochemical responses of three-year-old of P. sibirica, H. rhamnoides and P. tabulaeformis to soil drought stress were investigated by natural drought method. The results showed that leaf relative water content (LRWC) and the chlorophyll (Chl) content decreased while the cell membrane permeability increased gradually in the three tree species following the relative water content (RWC) of soil reduced. The changes of the tested responses in P. sibirica and H. rhamnoides were bigger than those in P. tabulaeformis.LRWC, Chl content and the cell membrane relative permeability changed significantly when the soil RWC were lower than 54.7%, 46.7%, and 48.4% for P. tabulaeformis, P. sibirica and H. rhamnoides, respectively.Superoxide dismutase (SOD) and peroxidase (POD) which are the most important protective enzymes to eliminate reactive oxygen species (ROS) maintain higher activity to prevent ROS poisoned. The activity of SOD and POD in the three tree species increased first and then decreased following the soil water reduced.The response time and the defensive role of SOD and POD to drought stress were different. SOD played an more important role in the early drought stress and POD played a bigger role in the late drought stress when drought stress was intensified.The soil RWC required to maintain higher enzyme activity were 32.9%-76.4%, 46.7%-77.9% and 35.8%-78.2% for P. tabulaeformis, P. sibirica, and H. rhamnoides, respectively. Osmotic regulation is also an important physiological mechanism of plants adapted to drought stress. Plants can reduce the osmotic potential and maintain cell turgidity through the accumulation of the solute, such as the soluble sugar (Ss) and the proline (Pro) which can help plant to resist and adapt to drought stress. The Pro content and the Ss content increased following the soil water reduced, with the higher level in P. tabulaeformis. The Pro increased faster than Ss. So we conclude that the three tree species enhance their tolerance and adaptability to drought stress by osmotic adjustment and protective enzyme system.The comprehensive evaluation was made about the drought-resistant capability of the three tree species by using the subject function method. The order was P. tabulaeformis>H. rhamnoides>P. sibirica.