Sapflow characteristics of mangrove Avicinia marina and its affecting factors in Zhangjiang estuary
ABSTRACT:
Xylem sapflow of Avicinia marina (Forsk.) Vierh (A. marina)
and environment factors were investigated over a year period (June 2011 to May
2012) by continuous sapflow density (SFD) measurements in Zhangjiang estuary in
Yunxiao County of Fujian province, China. Diurnal SFD patterns for A. marina
belonged to single curves following the variation of photosynthetically active
radiation (PAR) and vapor pressure deficit (VPD,) but time lag between sapflow
and PAR as well as VPD in both a wet month (summer) and a dry month (winter)
are discussed .PAR exhibited diurnal peak values earlier than sap flow by 30
min (winter) to 60 (summer). However, VPD lagged behind sapflow by 30 in winter
and earlier than sap flow by 30 min in summer. The sapflow rate of A. marina
was much higher than those of terrestrial tree species.
However, the daily
water use was still conservative. Daytime half-hourly mean stand sapflow was
positively linearly correlated with photosynthetically active radiation (PAR)
and vapor pressure deficit (VPD) in during the study period (all P<0.001), whereas daily daytime mean stand transpiration was less tightly coupled to PAR and VPD, especially in the winter. A pronounced hysteresis was observed between stand sapflow and PAR or VPD, but the extent of the hysteresis varied seasonally and between species. However, the mechanisms and ecological implications of mangrove water use deserve further investigation.><0)
whereas daily daytime mean stand transpiration was less tightly coupled to PAR
and VPD, especially in the winter. A pronounced hysteresis was observed between
stand sapflow and PAR or VPD, but the extent of the hysteresis varied
seasonally and between species. However, the mechanisms and ecological
implications of mangrove water use deserve further investigation.
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