The Relationship between Sap Flow Density and  Environmental Factors in the Yangtze River Delta  Region of China

Abstract

Abstract:Canopy transpiration is an important component of evapotranspiration, integrating physical and biological processes within the water and energy cycles of forests. Quercus acutissima and Cunninghamia lanceolata are two important, fast-growing and commercial tree species that have been extensively used for vegetation restoration, water conservation and building artificial forests in the Yangtze River Delta region of China. The primary objective of this study was to characterize sap flow densities of the two species by comparing daytime and nocturnal sap flow patterns and their relationships with environmental factors. Sap flow densities (S d ) were measured between September 2012 and August 2013 using the commercially-available thermal dissipation probes. Hourly meteorological data were measured in an open field, located 200 m away from the study site, including photosynthetically-active radiation (P ar ), air temperature (T a ), relative air humidity (R h ), vapor pressure deficit (V pd ) and precipitation (P). Soil water content (S wc ) data were logged hourly in different layers at Q. acutissima and C. lanceolata forests. Results indicated that the mean S d in summer was higher than that in spring and autumn. Both the S d of Q. acutissima and C. lanceolata showed distinct diurnal patterns. Nocturnal sap flow densities (S dn ) were noticeable, and both species followed similar declining patterns during our study period. The daytime sap flow density (S dd ) was more sensitive to environmental factors than S dn . Sap flow density was significant linearly correlated with P ar , V pd and T a , and P ar and V pd explained the greatest amount of variation in daytime sap flow of Q. acutissima and C. lanceolata, respectively. Our study will enrich knowledge of plantation forest physical and biological processes and provide valuable information for plantation forest management in the Yangtze River Delta region of China.

Tree Water Dynamics in a Semi-Arid, Pinus brutia Forest

“…However, in contrast to our study, they found that higher levels of nocturnal sap flow occurred during the dry period than the wet period. Liu et al [72] reported similar seasonality of nocturnal sap flow as found in our study. According to these authors, the reason for this seasonality is because the nighttime period during spring and autumn is longer than in summer, meaning there is more time for nocturnal sap flow to accumulate.…”

Growing Season Stem Water Status Assessment of Qinghai Spruce through the Sap Flow and Stem Radial Variations in the Qilian Mountains of China

“…High soil water content is beneficial for root water uptake, increasing sap flow. A number of research papers reported that sap flow was positively correlated with air temperature [6,56,57], and this was consistent with our results. Generally, high air temperature increased transpiration and promoted sap flow.…”

Stand-Level Transpiration Increases after Eastern Redcedar (Juniperus virginiana L.) Encroachment into the Midstory of Oak Forests

“…Water use by a tree is regulated by environmental factors [15,18,51]. Most studies indicate that sap flow in a tree is strongly affected by VPD [35,52,53]. The rate of transpiration of redcedar increased with increasing VPD and the availability of soil water [15,18].…”