Abstract
Soil water shortage is a major factor influencing the ecology and hydrology of vegetation in China’s semihumid Loess Plateau. However, few studies have experimentally assessed how expected changes in precipitation will affect sap flow in semihumid forest ecosystems. In this study, we measured the sap flow of black locust (Robinia pseudoacacia Linn.) under ambient and drought (induced by throughfall exclusion) conditions in 2015 and 2016, and investigated the relationship between stand transpiration and environmental factors in the semihumid China’s Loess Plateau. Throughfall exclusion significantly decreased sap flux density and stand transpiration by 39% and 28%, respectively, in 2016, which may have been due to the cumulative droughts effect from both 2015 and 2016. Throughfall exclusion caused a significant reduction in soil moisture, leaf area index (LAI), and stem diameter. Stand transpiration was positively correlated with LAI (P < 0.01), but precipitation and soil moisture did not correlate with stand transpiration at a daily timescale, suggesting that LAI can be used as a proxy for stand transpiration. Our results highlight that precipitation must be considered when planting black locust in semihumid regions. These findings provide basic information about the management of water resources and vegetation restoration in the semihumid China’s Loess Plateau and possibly other water-limited regions around the world.
Highlights
As an area with high atmospheric evaporative demand and low rainfall[1], the semihumid Loess Plateau is facing increasing water shortages[2]
In 2015, there was no difference in leaf area index (LAI) between treatments, LAI decreased by 21% after throughfall exclusion compared to the ambient treatment in 2016
This study investigated the discrepancy in transpiration for black locust stands in drought and ambient conditions on the Loess Plateau of China
Summary
As an area with high atmospheric evaporative demand and low rainfall[1], the semihumid Loess Plateau is facing increasing water shortages[2]. A series of large afforestation campaigns, including the ‘Grain for Green’ program (GFGP), were initiated by the Chinese government at the end of the 1990s4 These campaigns resulted in increasing carbon sequestration[5], a reduction in water loss, and improved control of soil erosion[6]. The effects of drought stress on the physiology of black locust, such as changes to the developed root systems, photosynthesis, and stomatal control of transpiration, have been documented on the Loess Plateau[1,10,11,12]. There is limited information about the transpiration and sap flow characteristics of individual large trees in relation to soil moisture stress within a forest stand. With wide implementation of GFGP, it was hypothesized that the sap flow and growth of black locust would be inhibited with the intensification of soil moisture stress despite of its characteristic of drought tolerance. The objectives of this study were: (1) to estimate the whole-tree transpiration, stem growth, and LAI of black locust under different soil moisture conditions (“drought” soil moisture conditions, implemented with throughfall exclusion, and “ambient” soil moisture conditions), and (2) to compare the relationships among biological, edaphic, and environmental characteristics
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