Changes in spatial variations of sap flow in Korean pine trees due to environmental factors and their effects on estimates of stand transpiration

Transpiration is an important component of the water balance in forest ecosystems. 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 diurnal, nocturnal and seasonal sap ﬂow patterns and their relationships with environmental factors. Sap ﬂow densities (Sd) 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. Standard meteorological data were logged hourly at this site, including photosynthetically active radiation (Par), air temperature (Ta), relative air humidity (Rh), vapor pressure deficit (Vpd) and precipitation (P). Soil water content (Swc) data were logged hourly in different layers at Q.acutissima and C.lanceolata forests. Results indicated that the mean Sd in summer was higher than that in spring and autumn, and was lowest in winter. The Sd of Q. acutissima showed distinct diurnal patterns during the growth period (between May and October), and C. lanceolata followed similar sap ﬂow patterns in all months except February. Nocturnal sap flow densities (Sdn) were noticeable and both species followed similar patterns during the growth period, in which Q. acutissima followed a power function from April to November and C. lanceolata followed similar patterns in all months except February. Pearson correlation analysis suggested that the sap flow density responded to environmental factors differently among each of the growing stages. The diurnal sap flow density (Sdd) was more sensitive to environmental factors than Sdn. The Sd during the growth period was more sensitive to environmental factors than in the dormant period. Par, Vpd and Ta were significantly correlated with Sdd in the whole year. In the nighttime, the sap flow density was also effected by the Vpd, Ta and Rh. The results of this study can be used to estimate the transpiration of Q. acutissima and C. lanceolata.

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Robust Estimation of Absorbing Root Surface Distributions From Xylem Water Isotope Compositions With an Inverse Plant Hydraulic Model

Frontiers in Forests and Global Change ◽

10.3389/ffgc.2021.689335 ◽

2021 ◽

Vol 4 ◽

Author(s):

Hannes P. T. De Deurwaerder ◽

Marco D. Visser ◽

Félicien Meunier ◽

Matteo Detto ◽

Pedro Hervé-Fernández ◽

...

Keyword(s):

Environmental Factors ◽

Soil Water ◽

Robust Estimation ◽

Inverse Modeling ◽

Sap Flow ◽

Soil Water Potential ◽

Modeling Method ◽

Flow Monitoring ◽

Root Surfaces ◽

Water Isotope

The vertical distribution of absorbing roots is one of the most influential plant traits determining plant strategy to access below ground resources. Yet little is known of natural variability in root distribution since collecting field data is challenging and labor-intensive. Studying stable water isotope compositions in plants could offer a cost-effective and practical solution to estimate the absorbing root surfaces distribution. However, such an approach requires developing realistic inverse modeling techniques that enable robust estimation of rooting distributions and associated uncertainty from xylem water isotopic composition observations. This study introduces an inverse modeling method that supports the assessment of the root allocation parameter (β) that defines the exponential vertical decay of a plants’ absorbing root surfaces distribution with soil depth. The method requires measurements obtained from xylem and soil water isotope composition, soil water potentials, and sap flow velocities when plants’ xylem water is sampled at a certain height above the rooting point. In a simulation study, we show that the approach can provide unbiased estimates of β and its associated uncertainty due to measuring errors and unmeasured environmental factors that can impact the xylem water isotopic data. We also recommend improving the accuracy and power of β estimation, highlighting the need for considering accurate soil water potential and sap flow monitoring. Finally, we apply the inverse modeling method to xylem water isotope data of lianas and trees collected in French Guiana. Our work shows that the inverse modeling procedure provides a robust analytical and statistical framework to estimate β. The method accounts for potential bias due to extraction errors and unmeasured environmental factors, which improves the viability of using stable water isotope compositions to estimate the distribution of absorbing root surfaces complementary to the assessment of relative root water uptake profiles.

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The interaction between nonstructural carbohydrate reserves and xylem hydraulics in Korean pine trees across an altitudinal gradient

Tree Physiology ◽

10.1093/treephys/tpy119 ◽

2018 ◽

Vol 38 (12) ◽

pp. 1792-1804 ◽

Cited By ~ 12

Author(s):

Ai-Ying Wang ◽

Shi-Jie Han ◽

Jun-Hui Zhang ◽

Miao Wang ◽

Xiao-Han Yin ◽

...

Keyword(s):

Altitudinal Gradient ◽

Korean Pine ◽

Carbohydrate Reserves ◽

Nonstructural Carbohydrate ◽

Pine Trees

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Environmental Control on Transpiration: A Case Study of a Desert Ecosystem in Northwest China

Water ◽

10.3390/w12041211 ◽

2020 ◽

Vol 12 (4) ◽

pp. 1211 ◽

Cited By ~ 1

Author(s):

Shiqin Xu ◽

Zhongbo Yu

Keyword(s):

Sap Flow ◽

Environmental Control ◽

Arid Ecosystems ◽

Desert Ecosystem ◽

Time Lags ◽

Evaporative Demand ◽

Threshold Control ◽

Stand Transpiration ◽

Semi Arid

Arid and semi-arid ecosystems represent a crucial but poorly understood component of the global water cycle. Taking a desert ecosystem as a case study, we measured sap flow in three dominant shrub species and concurrent environmental variables over two mean growing seasons. Commercially available gauges (Flow32 meters) based on the constant power stem heat balance (SHB) method were used. Stem-level sap flow rates were scaled up to stand level to estimate stand transpiration using the species-specific frequency distribution of stem diameter. We found that variations in stand transpiration were closely related to changes in solar radiation (Rs), air temperature (T), and vapor pressure deficit (VPD) at the hourly scale. Three factors together explained 84% and 77% variations in hourly stand transpiration in 2014 and 2015, respectively, with Rs being the primary driving force. We observed a threshold control of VPD (~2 kPa) on stand transpiration in two-year study periods, suggesting a strong stomatal regulation of transpiration under high evaporative demand conditions. Clockwise hysteresis loops between diurnal transpiration and T and VPD were observed and exhibited seasonal variations. Both the time lags and refill and release of stem water storage from nocturnal sap flow were possible causes for the hysteresis. These findings improve the understanding of environmental control on water flux of the arid and semi-arid ecosystems and have important implications for diurnal hydrology modelling.

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