Nocturnal sap flow characteristics of two typical forest tree species and responses to environmental factors in the loess region of West Shanxi,China
Aims Understanding the nighttime water use of typical forest tree species in the west Loess Plateau is crucial for accurately evaluating the watershed-scale water and carbon cycles.However,the nighttime sap flow dynamics and its response to environmental factors are currently unclear for typical forest species in the west Loess Plateau.Methods We monitored the sap flow with thermal dissipation probes(TDP)and concurrent environmental factors of Robinia pseudoacacia plantation and Quercus mongolica natural forest in the Caijiachuan watershed from June to September 2021.The time series model(ARMAX model)was used to distinguish between nighttime transpiration(Tn)and stem water replenishment(Re)in nocturnal sap flow(QNighttime).We used the machine learning model XGboost and Shapley additive interpretation framework to analyze and explain the relationship between QNighttime and nighttime environmental factors.Important findings The proportion of nighttime transpiration(Tn/QNighttime)was 73.97％and 30.12％for the R.pseudoacacia and the Q.mongolica,respectively,during the growing season.The proportion of stem water filling(Re/QNighttime)was 26.03％and 69.88％for the two species,respectively.The XGboost model showed that nighttime vapor pressure deficit(VPD)and nighttime soil water content(SWC)were the main factors driving QNighttime in R.pseudoacacia and Q.mongolica,respectively.VPD,nighttime air temperature(Ta),nighttime relative humidity(RH),and daily sap flow(QDaily)can promote the QNighttime when they reach 0.30 kPa,19.84 ℃,85.3％,and 339.11 kg·h-1.For Q.mongolica,VPD inhibited QNighttime when it reached 1.5 kPa,while Ta and nighttime wind speed(WS)promoted QNighttime when it reached 23.11 ℃ and 0.58 m·s-1,respectively.The effects of SWC on QNighttime in R.pseudoacacia and Q.mongolica were similar.The SWC within 0-12.9％range would promote the occurrence of QNighttime.Therefore,our study highlights the importance of considering the magnitude of all environmental factors in establishing the nocturnal sap flow model.This study revealed the characteristics of QNighttime composition and their responses to environmental factors of two typical tree species in the west Loess Plateau.Our findings are of great significance for accurately understanding the stability of typical forest tree species in the loess region under climate change.
nocturnal sap flowenvironmental factornocturnal transpirationthe loess areamachine learning model
万方数据
维普
