Nocturnal sap flow of Hedysarum scoparium and its response to meteorological factors in semiarid Northwest China

Abstract

Nocturnal sap flow of shrub may indicate transpiration and water recharge storage at night. Hedysarum scoparium is an important sand fixation shrub in semiarid regions. This paper deals with the water use of Hedysarum scoparium at night in the semiarid Northwest China. Our primary goal was to reveal and understand the nature of nocturnal sap flow and its functional significance. Granier’s stem heat balance method was used to determine the nocturnal sap flow of Hedysarum scoparium (stem of 25, 16, 13 and 9mm). Nocturnal sap flow was substantial and showed seasonal variation similar to the patterns of daytime sap flow. Mean nocturnal sap flow was higher in more precipitation months of year 2011 for more daytime transpiration and high soil water availability which can be the cause of more nocturnal sap flow. And vapour deficit pressure, mean air temperature and wind velocity were significantly correlated with nocturnal sap flow, they could explain a small fraction of the variance in nocturnal sap flow of studied trees. And the meteorological factors have greater impact on nocturnal sap flow rate of Hedysarum scoparium with smaller stem diameter than other diameter classes of Hedysarum scoparium.