Scaling Up Sap Flow Measurements from the Stem Scale to the Individual Scale for Multibranched Caragana Korshinskii on the Chinese Loess Plateau

Guohui Wang,Baoru Mo,Xianlong Yang,Yuying Shen,Zhixue Chen

doi:10.3390/f10090785

Abstract

The traditional heat balance method for measuring plant sap flow (SF) becomes troublesome and uneconomic for multibranched shrub species if all their stems are used for the measurement. The objectives of this study were to explore specific relationships between stem-scale SF and plant morphological traits and then to scale up SF measurements from the stem scale to the individual scale for Caragana korshinskii Kom., a dominant shrub species on the Chinese Loess Plateau. Sap flow was measured for twenty-one stems from three representative individuals from July to September 2018 during the rainy season. The results indicated that the stem-scale SF in C. korshinskii presented a positive linear correlation with the stem base diameter (SBD), stem length (SL), primary branch numbers in the stem (PBN), and estimated stem biomass (W). The SBD-based statistical models performed well in estimating the stem-scale SF, with an R2 value of 0.9726 and root mean squared error (RMSE) of 2.5389 g h−1. Over the canopy projection area, the individual-scale transpiration flows for the three selected C. korshinskii were 1.91, 1.10, and 1.59 mm·d−1. In addition, stem-scale SF was positively and linearly correlated with air temperature, photosynthetically active radiation, vapor pressure deficit, reference crop evapotranspiration, and variable transpiration. This study sheds light on morphological and meteorological influences on stem-scale SF and has made contributes to the accurate and rapid estimation of the plant sap flow from easily available morphological traits for multibranched shrub species in semiarid regions. Limitations, however, may exist for the established model when it is used to estimate SF of C. korshinskii during the water-limited dry season. Our study deserves further exploration of a more general model to have a better estimation of SF for C. korshinskii in both dry and rainy seasons.

Highlights

Soil water is a key factor that limits vegetation growth in arid and semiarid areas
This area consists of perennial artificial bush and has a semiarid climate; the mean annual precipitation is 386 mm, and most of the rain falls during July and September
In the morning was similar to that of variable of transpiration (VT), and the decrease of Sap flow (SF) in the afternoon slightly lagged behind the decrease of VT

Summary

Introduction

Soil water is a key factor that limits vegetation growth in arid and semiarid areas. An understanding of plant water use patterns of vegetation could contribute to the effective management of limited water resources [1]. Sap flow (SF) is the water flux across a given section of stem diameter at a given period and is an important component of the water balance in forest ecosystems [2,3,4]. Sap flow can reflect water transportation and water utilization characteristics in plants. The heat balance technique was used to determine sap flow rate (g·h−1 ) and sap flux density (m3 ·m−2 ·h−1 ) [5]. The majority of Forests 2019, 10, 785; doi:10.3390/f10090785 www.mdpi.com/journal/forests

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Conclusion