Abstract
Global climate change is likely to change precipitation patterns with consequences for tree water use and growth in semi-arid areas. However, little is known about the effects of variability in precipitation on growth- and water-related physiological processes of native trees in dry areas of northwestern China. In this study, sap flow and stem radial variability in four Qinghai spruce trees (Picea crassifolia) were monitored in the Qilian Mountains, China. Tree water deficit (ΔW) and basal area increment (BAI) were calculated using stem radial variation; water-use efficiency (WUE) was then estimated as the ratio of BAI and sap flow (Jt). The results showed that sap flow density (Js) increased logarithmically with increasing ΔW when ΔW < 50 μm, and then gradually stabilized. Multiple factor generalized additive models (GAM) showed that Js was closely related to all measured environmental variables except for daily mean temperature and relative air humidity. ΔW was related to the minimum daily temperature and soil water content. WUE exhibited higher values in early July. Low WUE was observed under conditions of prolonged dry weather, but it quickly increased during rainy days. WUE decreased after precipitation events due to high transpiration. We concluded that, in these semi-arid areas, precipitation is the most important controlling factor in tree growth and transpiration.
Highlights
Climate change extensively affects natural mountain forests in semi-arid areas [1].Changing precipitation patterns associated with climate change influences plant-available water and leads to changes in phenology, growth and water relations [2]
The Qilian Mountains are sensitive to climate change
Precipitation events resulted in fluctuation of soil water content, which subsided with a continuous heavy rainfall (Figure 2h,j)
Summary
Climate change extensively affects natural mountain forests in semi-arid areas [1].Changing precipitation patterns associated with climate change influences plant-available water and leads to changes in phenology, growth and water relations [2]. Climate change extensively affects natural mountain forests in semi-arid areas [1]. Climate change leads to increase in the frequencies of heat waves and drought events [3,4], which may affect growth and mortality rates of trees [5]. The Qilian Mountains, in the northeastern Tibetan Plateau, are the most important water source for the arid area of northwestern China, feeding the Shiyanghe, Shullehe, and the Heihe Rivers. Forests in these mountains play an important role in preventing desertification, and in water conservation, which maintains the stability of oasis ecosystems in the middle and lower.
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