A Study On The Cavitation Of The Major Tree Species In Northeast China Based On Ultrasonic Acoustic Emissions Features

Xylem embolism under drought stress is one of the key processes leading to tree mortality.The ultrasonic acoustic emissions(UAEs)technique were proved to be a powerful tool to assess the vulnerability of xylem embolism simultaneously in woody stems.However,there are still controversy viewpoints on UAEs indexes and signals extraction in relationship with the occurring phenomena during the dehydration of tree stems from in-situ detected UAEs.To obtain a better quantification of embolism,the characteristics of the cumulated UAEs indexes(i.e.,count,energy,and amplitude),and the relative UAEs rate distribution were analyzed at four amplitude peak ranges(35-40,40-50,50-60,and ?60 d B)and all the UAEs signals monitored with the Micro-II Digital UAE System for Betula platyphylla,Acer mono,Quercus mongolica,Ulmus japonica,Larix gmelinii,and Pinus koraiensis in northeast China.The end points of the three indexes for five groups of signals were determined mathematically,and filtered out the data.The P50 values,indicator of xylem embolism vulnerability,were calculated based on five groups of unfiltered and filtered data.The results showed that:The cumulative signal curves of three indexes for five groups for each of six tree species were all “S” shaped.The cumulative curves for the indexes at ?60 d B were shifted right in varying degrees in B.platyphylla,Q.mongolica,L.gmelinii and P.koraiensis,of which P.koraiensis exhibited the longest lag time(60 h).The three indices at 40-50 d B and 50-60 d B were shifted left 0-25 h in all the tree species except for Q.mongolica.In addition,diffuseporous B.platyphylla and A.mono,as well as ring-porous Q.mongolica and U.davidiana corresponded only to below 30% of the cumulative UAE signals at a water potential of about-3 MPa.But at about-3.5 MPa,non-porous L.gmelinii and P.koraiensis corresponded to 50%-90% of the cumulative UAE signals.These indicated that the calculation of P50 based on total signal for the diffuse-porous and ring-porous trees would lead to severely underestimated results.The maximum relative rates of energy at 40-50 d B and 50-60 d B for six tree species were higher than those at 35-40 d B and ?60 d B.Besides,the arrival time of the end point of relative UAEs rate for the tree species with three wood properties was the longest for nonporous L.gmelinii and P.koraiensis,which was around 90-220 h(except for L.gmelinii in energy with 35-40 d B).As for the diffuse-porous and ring-porous species,the arrival time was between 30-40 h.The P50 values calculated based on the filtered three indices for five groups of six tree species were higher than the corresponding unfiltered values.These indicated that signal filtration significantly increased the P50 of four hardwoods,while not significantly changing the P50 calculation results of conifers.For Q.mongolica,U.japonica,B.platyphylla,A.mono,and L.gmelinii,no significant differences were found in P50 between count,energy,and amplitude based on unfiltered or filtered signals at five groups.For P.koraiensis,P50 calculated from the total signals of three unfiltered indices showed no significant difference.However,values based on filtered total signals of energy were significantly higher than those of the filted amplitude.This indicates that the application effect of the evaluation of three indices on the embolism vulnerability varies in P.koraiensis.For P.koraiensis,energy is more suitable for vulnerability analysis.The three indexes for five groups of cumulative signals of six tree species exhibited fairly consistent seasonal variation characteristics.Except for Q.mongolica which had the most cumulative signals in May,all the remaining species had the most cumulative signals in the summer(June to August).And less cumulative signals were noted in the autumn(October).The five groups averages P50 calculated based on the filtered three indices for specie: B.platyphylla and ring-porous species: Q.mongolica and U.davidiana exhibited fairly obvious seasonal fluctuation,the maximum changing range of P50 in six month reached up to 50%.For non-porous species: L.gmelinii and P.koraiensis,the five groups averages P50 calculated based on the filtered three indices exhibited fairly smooth variation over the entire growing season,the maximum changing range of P50 in six month were below 30%.The six month averages P50 calculated based on the filtered three indices for five groups was the highest for ring-porous species: Q.mongolica and U.davidiana,ranged from-0.85--1.20 MPa,and from-0.84--1.06 MPa,respectively,followed by diffuse-porous species: B.platyphylla and A.mono,ranged from-1.74--2.15 MPa,and from-1.56--2.14 MPa,respectively.The non-porous species: L.gmelinii and P.koraiensis had the lowest P50,ranged from-2.24--2.73 MPa,and from-2.57--3.42 MPa,respectively.Based on the result above,xylem embolism vulnerability of six tree species ranked as U.davidiana > Q.mongolica > A.mono > B.platyphylla > L.gmelinii > P.koraiensis.