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以黄土丘陵区油松-沙棘混交林为研究对象,运用热扩散式探针(TDP)于2015年6—10月对油松和沙棘的树干液流密度(F_d)进行连续观测,同步测定了光合有效辐射(PAR)、水汽压亏缺(VPD)和土壤水分(SWC)等环境因子,分析两树种对降雨利用的差异.采用Threshold-delay模型、多元回归分析和偏相关分析方法,研究两树种F_d对降雨的响应过程,并确定环境因子对F_d的影响.结果表明:随着降雨量递增,两树种F_d的最大变化量都先上升后降低;其中0~1 mm降雨范围内,油松F_d(-16.3%)和沙棘F_d(-6.3%)都明显降低;1~5 mm降雨范围内,油松F_d(-0.4%)降低而沙棘F_d(9.0%)明显升高.油松和沙棘F_d对降雨响应的最小降雨阈值(R~L)分别为6.4和1.9 mm,滞后时间(τ)为1.96和1.67 d.降雨前油松F_d峰值集中在12:00—12:30(70%),沙棘F_d峰值分别集中在10:30—12:00(48%)和16:00—16:30(30%);降雨后油松F_d峰值集中在11:00—13:00(40%),沙棘F_d峰值分别集中在12:00—13:00(52%)和16:30—17:00(24%).降雨前影响油松和沙棘F_d的环境因子大小顺序为PAR>VPD;降雨后影响油松F_d的环境因子大小顺序为PAR>VPD>0~20 cm SWC(SWC_(0~20)),影响沙棘F_d的环境因子大小顺序为SWC_(0~20)>PAR>VPD.油松-沙棘混交林对水分利用的稳定性较高.
Taking the Pinus tabulaeformis and Seabuckthorn mixed forest in the loess hilly region as the research object, the trunk flow density (F_d) of Pinus tabulaeformis and Seabuckthorn was continuously observed from June to October in 2015 by using thermal diffusive probe (TDP) (PAR), water vapor pressure deficit (VPD) and soil moisture (SWC) were measured to analyze the differences in rainfall use.Threshold-delay model, multiple regression analysis and partial correlation analysis were used to study the effects of two And the effect of environmental factors on F_d was determined.The results showed that with the increase of rainfall, the maximum change of F_d of both species firstly increased and then decreased. Among 0-1 mm rainfall, Pinus tabulaeformis F_d (-16.3%) and seabuckthorn F_d (-6.3%) decreased significantly. F_d (-0.4%) and Pinus tabulaeformis F_d (9.0%) decreased significantly in the rainfall range of 1 ~ 5 mm. The minimum rainfall threshold (R ~ L) for F_d response to rainfall was 6.4 and 1.9 mm, respectively, and the lag time (τ) was 1.96 and 1.67 d, respectively. The peak value of F_d was mainly between 12: 00-12: 30 (70% , And the peak value of Fd in seabuckthorn was mainly between 10: 30-12: 00 (48%) and 16: 00-16: 30 (30% , Seabuckthorn F_d peak Respectively, between 12: 00-13: 00 (52%) and 16: 30-17: 00 (24%). The order of environmental factors influencing the F_d of Pinus tabulaeformis and seabuckthorn before rainfall was PAR> VPD. The order of environmental factors of F_d was SW> 0-20 cm SWC (SWC 0-20), and the order of environmental factors affecting F_d was SWC 0-20> PAR> VPD. The stability of forest to water use is high.