Research Of Artificial Forest Carbon And Water Tradeoff And Influencing Factors In Loess Plateau

The Loess Plateau is located in the middle reaches of the Yellow River. It is a typical ecosystem fragile area. In order to deal with the problem of ecological degradation in the region, a series of ecological restoration work is carried out in this area, especially the typical returning farmland to forest. However, due to the arid and semi-arid climate in the Loess Plateau, the expansion of plantation area increase in local carbon storage and add to the burden of water resources, the contradiction between artificial forest carbon sequestration and water resources scarce have become increasingly prominent. Therefore, the research that carbon and water tradeoff and its influence factors of artificial forest in arid and semiarid region for the comprehensive evaluation of returning farmland to forest ecological and environmental benefits and strengthen the scientific management of artificial forest ecosystem has important significance.From prospective of tree age and aspect, this paper choose the yangjuangou small watershed of loess plateau as the study area, the common Robinia pseudoacacia of artificial afforestation as the object, the internal control factors and external environmental factors which affect the water and carbon tradeoff of plants are explored. The results showed that the mainly internal factor of influence water and carbon tradeoff include leaf physiological and ecological indexes and leaf traits. The process of water and carbon tradeoff refers to photosynthetic carbon fixation and water consumption of transpiration. Photosynthesis and transpiration are limited by stomatal conductance(gs) and intercellular CO2 concentration(Ci). Leaf nutrient elements is close to the water and carbon tradeoff, on the other hand, based on the area of scale of the relationship between the nutrient element content and photosynthetic physiological indexes is more significant than quality scale. The gs and Ci were higher in the leaves with weaker water holding capacity, which promote the transpiration of plant leaves, and resulte in the decrease of WUE. Under natural conditions, the most important two environmental factors that affect water and carbon tradeoff are the light intensity and the atmospheric humidity at small watershed scale. For another, environmental factors by adjusting internal control factor influence plant water and carbon tradeoff. In a certain range, the improvement of illumination intensity and atmospheric moisture will cause gs and Ci rising and leaf blade vapor pressure deficit(VpdL) decrease, and this phenomenon will lead to the improvement of photosynthetic rate and transpiration rate, and the changes of WUE eventually.With the age increased, the leaf properties and physiological and ecological indicators will change. On the one hand, this change reflect the impact of environment on plant, on the other hand, it is also a reflection of adaptability of plant to the external environment.With different age, the leaf nutrient absorption and preservation are difference. 12 years old Robinia pseudoacacia in the vigorous growth period with big stomatal conductance and strong CO2 supply capacity, which promote the photosynthetic carbon fixation and transpiration and decrease water use efficiency. 28 years old Robinia pseudoacacia in the stable growth period with small stomatal conductance and weak CO2 supply capacity, which decrease the photosynthetic carbon fixation and transpiration and promote WUE. In addition, at different stages of growth and development, Robinia pseudoacacia will adopte different water use strategies to adapt to the environment, and to maintain water and carbon tradeoff and maximize the carbon sequestration benefits.Slope is an important factor which causes the difference of the environmental conditions of the forest land. Arid and semi-arid regions, in sunny slope, the higher average temperature and lower atmospheric relative humidity will lead to the consumption of water, and this phenomenon is not conducive to the growth of Robinia pseudoacacia. Therefore, compared with the sunny slope, semi-sunny slope is more suitable for the growth of Robinia pseudoacacia.