Canopy Interception Of Cryptomeria Japonica And Its Physical Process In Lushan

Canopy interception is an important part of forest hydrology processes,and it is significant in forest ecosystem hydrologic cycle.Cryptomeria japonica is the main temperate coniferous forest in the Lushan Nature Protection Area,and it is of great significance to the diversity of vegetation landscape.We continuously monitored the dynamic changes of rainfall,throughfall,and stem flow in Cryptomeria japonica artificial forest in Lushan Natural Protection Area from April to September in 2017,and simultaneously collected precipitation samples at different scales（inter-storm and intra-storm）for indoor isotope measurement,to find out the characteristic of the canopy interception of Cryptomeria japonica and the rule of its distribution physical process.The results of the study are as follows:（1）The canopy interception of Cryptomeria japonica ranged from 0.14 to 3.67 mm.Interception,throughfall and stem flow increased with the increase of the gross rainfall.Interception rate and throughfall rate decreased with the increase of the gross rainfall,and a minus interception occurred in some rain event.The spatial variability of throughfall rate was obviously related to the canopy coverage when gross rainfall was below 25 mm.The temporal stability of throughfall rate was found in each sample plot,and the variation tendency of throughfall amount accumulation was the same as gross rainfall accumulation.There was a time lag at the beginning and the end of throughfall and stem flow,and the time lag was related to rainfall intensity at the beginning of rain event rather than rainfall amount.（2）Canopy interception and throughfall had a significant correlation with rainfall amount,rainfall intensity,rainfall duration and solar radiation（p<0.01）,rainfall amount had the highest contribution degree.Vapor pressure deficit and wind speed affected the canopy interception（p<0.05）and interval of rain event affected the throughfall（p<0.05）.There was an extreme significant correlation between leaf area index and throughfall rate（p<0.01）when the gross rainfall was below 25 mm.Besides,there was a significant one existing between the minimum radiation distance from the adjacent trunk to the sample plot and throughfall rate（p<0.01）,and a significant negative one between leaf area index and throughfall rate（p<0.05）.（3）The reason why isotope fractionated of throughfall and stem flow in Cryptomeria japonica in Lushan was not evaporation,but mainly due to the effects of exchange between liquid and vapor and selective transmittance of temporally varying rainfall along varying canopy flowpaths.Exchange and selection also caused extreme fractionation of lighter water isotope in 0～10 mm and>50 mm rain events.Isotopic composition of each sample plot of throughfall and stem flow remained relatively stable during the study.In the pre-and medium-term periods of rainfall,there were severe evaporation and imbalanced fractionation phenomena in the stable isotopes of gross rainfall,throughfall,and stem flow.In the late period of rainfall,the isotopic imbalanced fractionation rate of gross rainfall,throughfall,and stem flow decreased.TheΔδ¹⁸O andΔd of throughfall and stem flow had little correlation with rainfall amount during the intra-storm.