Abstract

Quantifying the water balance within areas with sparse vegetation requires frequent measurement of transpiration in water-limited, arid, desert ecosystems. Field experiments were conducted in Shapotou, northwestern China, to examine the feasibility of up-scaling the transpiration of C3 and C4 xerophytic shrubs (Reaumuria soongorica and Salsola passerina, respectively) from the leaf to the canopy level throughout the growing season in 2015. The large weighing lysimeter method and LI-6400XT portable photosynthesis system were used to make relatively long-term measurements of transpiration. The results indicated that meteorological factors coupled with stomatal conductance affected the transpiration rate of the two shrubs at the leaf level, and that the vapor pressure deficit other than net radiation and the air temperature affected the transpiration rate of S. passerina at the canopy level. Precipitation and vegetation characteristics determined the transpiration amount of the C3 and C4 xerophytic shrubs. The leaf gas exchange measurements were arithmetically scaled up to the canopy level based on the leaf area. The validity of the extrapolation was evaluated by comparing the upscale values of transpiration with the calculated values obtained from lysimeter measurement. The up-scaling approach accurately (±0.005 mm h−1, RMSE = 35%) obtained canopy transpiration from the leaf measurements. Our study suggests that the up-scaling method based on leaf area can be adopted to determine the canopy transpiration of C3 and C4 xerophytic shrubs in arid desert environments.

Highlights

  • Transpiration (T) is the process whereby water is transported from the soil to the plant, via the roots, and to the atmosphere through the plant

  • The results indicated that the transpiration responses of the C3 shrub R. soongorica and the C4 shrub S. passerina to soil matric potential were opposite, since the C3 shrub R. soongorica had less plant-available soil water compared to the C4 shrub S. passerina (Figure 2).Transpiration was not affected by soil moisture under well-watered conditions [47]

  • The transpiration rates dependent on net radiation and air temperature and the transpiration rates of the C4 shrub S. passerina were dependent on the vapor pressure deficit

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Summary

Introduction

Transpiration (T) is the process whereby water is transported from the soil to the plant, via the roots, and to the atmosphere through the plant. It serves as an important component of evapotranspiration (ET) and is a dominant force in the global water cycle, as it accounts for 61%. (±15% s.d.) of ET at the ecosystem scale and accounts for more than two-thirds of total surface water. The ability to independently measure soil evaporation (E) and canopy T is important for the detection of sparse vegetation water balance [5]. Areas covered by sparse vegetation, such as the Shapotou area of Tengger

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