Soil-moisture-dependent nocturnal water use strategy and its responses to meteorological factors in a seasonal-arid poplar plantation

Quantification of nocturnal water use and its composition in a Eucalyptus urophylla ×E. grandis plantation on the Leizhou Peninsula, South China

“…Although the increase in WS accelerated canopy and upper canopy air exchange, the improvement in canopy air RH was extremely limited. Previous studies suggest that SWC is also an important factor affecting nocturnal water use (Di et al, 2022;Phillips et al, 2010;Zeppel et al, 2010;Zhao et al, 2017), as it not only affects nocturnal stomatal opening and closing through changes in hydraulic conductivity (Cavender-Bares et al, 2007;Zeppel et al, 2012), which in turn affects Tn, but is also a direct source of nocturnal stem Re (Chen et al, 2020;Wu et al, 2020). Contrary to these studies, no statistically significant correlation between nocturnal J C and SWC was found in our study.…”

“…The nocturnal sap flow was partitioned into Re and Tn using the following method. First, several representative days were selected in each year, when daytime transpiration was weak due to cloudiness or rain, resulting in no stem water deficit or little stem water deficit but can filling to saturate it quickly, while considerable VPD exists at night, implying that sufficient transpiration driving force exists at night (Chowdhury et al, 2022;Di et al, 2019Di et al, , 2022. Figure 2 shows the continuous variation of sap flow and DBH on one of the selected typical special days.…”

“…This method is relatively accurate, but the technique of installing probes in branches or below the main crown is difficult (which is not feasible for many trees) and costly. Fisher et al (2007) first proposed three concepts for distinguishing between Tn and Re (Timeseparation, back-extrapolation and forecasted refilling, respectively), which have been applied in many studies (Di et al, 2019(Di et al, , 2022. However, Fisher et al (2007) also found that the results of the three methods varied considerably, with the forecasted refilling method estimated a greater proportion of Re than the time-separation method, while the back-extrapolation method estimated a smaller proportion of Re than the time-separation method.…”

“…Contrary to these studies, no statistically significant correlation between nocturnal J C and SWC was found in our study. This may be because the soil water supply at the present study site did not reach the stress threshold required to limit the nocturnal sap flow.SWC restrictions on nocturnal water use may be more pronounced in arid and semi-arid ecosystems (Di et al, 2022).…”

“…Previous studies have investigated the drivers of Tn in trees. However, they have come to different conclusions (Chen et al,2020;Chowdhury et al, 2022;Di et al, 2019Di et al, , 2022Rosado et al, 2012;Sellin &Lubenets, 2010). For example, Siddiq & Cao (2018) found that VPD was the driver of Tn in 18 broadleaf species in a tropical seasonal climate and was independent of wind speed (WS).…”