Assessing the Impact of Soil Moisture on Canopy Transpiration Using a Modified Jarvis-Stewart Model

Abstract

In dryland regions, soil moisture is an important limiting factor for canopy transpiration (T). Thus, clarifying the impact of soil moisture on T is critical for comprehensive forest—water management and sustainable development. In this study, T, meteorological factors (reference evapotranspiration, ETref), soil moisture (relative soil water content, RSWC), and leaf area index (LAI) in a Larix principis-rupprechtii plantation of Liupan Mountains in the dryland region of Northwest China were simultaneously monitored during the growing seasons in 2017–2019. A modified Jarvis—Stewart model was established by introducing the impact of RSWC in different soil layers (0–20, 20–40, and 40–60 cm, respectively) to quantify the independent contribution of RSWC of different soil layers to T. Results showed that with rising ETref, T firstly increased and then decreased, and with rising RSWC and LAI, T firstly increased and then gradually stabilised, respectively. The modified Jarvis—Stewart model was able to give comparable estimates of T to those derived from sap flow measurements. The contribution of RSWC to T in different soil layers has obvious specificity, and the contribution rate of 20–40 cm (13.4%) and 0–20 cm soil layers (6.6%) where roots are mainly distributed is significantly higher than that of 40–60 cm soil layer (1.9%). As the soil moisture status changes from moist (RSWC0–60cm ≥ 0.4) to drought (RSWC0–60cm < 0.4), the role of the soil moisture in the 0–20 cm soil layer increased compared with other layers. The impacts of soil moisture that were coupled into the Jarvis—Stewart model can genuinely reflect the environmental influence and can be used to quantify the contributions of soil moisture to T. Thus, it has the potential to become a new tool to guide the protection and management of forest water resources.

The Seasonal Variability and Environmental Factors Influencing the Transpiration of Western Juniper (Juniperus occidentalis) Saplings

“…This study evaluated the interannual variability of transpiration of western juniper saplings and its correlation with several environmental variables of interest (i.e., SM, ST, Pr, SR, AT, RH, and VPD). Plant transpiration rates are affected by water availability and weather variables [10,[36][37][38]. Study results showed that juniper sapling transpiration in both the Mays-East and Mays-West sites followed a similar pattern, conforming to the effects of seasonal precipitation on soil moisture availability in cool-climate rangeland ecosystems of semiarid central Oregon, USA.…”

“…Many environmental variables, including soil moisture, soil temperature, air temperature, solar radiation, relative humidity, vapor pressure deficit, and precipitation, help explain the process of plant transpiration [8]. Different studies have indicated that soil moisture plays an important role in transpiration [9][10][11]. Other studies [8,12] have reported that tree transpiration was closely related to changes in solar radiation and vapor pressure Hydrology 2023, 10, 232 2 of 14 deficit.…”

Canopy Transpiration and Stomatal Conductance Dynamics of Ulmus pumila L. and Caragana korshinskii Kom. Plantations on the Bashang Plateau, China

“…Transpiration and related water-use strategies are fundamental to understanding the physiological processes of plantations and play a vital role in their survival and growth, especially in semiarid and arid regions, where water availability is greatly affected by the increased frequency and intensity of droughts [8,9]. However, previous studies have shown that the effects of excessive water loss caused by transpiration and its environmental driving factors differ significantly, resulting in different growth performances among different functional types [10][11][12]. Therefore, it is imperative to understand the transpiration processes and dynamics of planted tree and shrub species and how these processes change from their normal functions.…”

Variations in Sap Flux Density of Three Urban Tree Species and Their Main Environmental Influencing Factors in Different Timescales in the Beijing Metropolitan Area

“…Jarvis [36] proposed a serial empirical formula to express the relationship between leaf stomatal conductance and environmental factors; this formula has been widely used and modified [37,38]. Transpiration and sap flow have also been linked directly with environmental factors by analogy with the stomatal conductance formulation [39][40][41][42]. In this study, we used sap flux density to investigate the environmental controls using Equation (3).…”