Research On Indicators Diagnosing Tree’s Water Deficit Based On Trunk Diameter Fluctuation Of Populus Tomentosa

As the important fast-growing and high yield plantation wood species, triploid Populustrmentosawas widely cultivated. The technology system of real-time andconvenient monitoring of trees’ water status had not been established, which greatly influencedthe scientific and rational formulation of water-saving irrigation schemes.Consequently, we used triploid clones Populustomentosa to study the day process of the trunk diameter variations, the regulation of the trunk diameter growth fluctuation, the response of the trunk diameter to meteorological indicators, the sensitivity of the indicators deprived from trunk diameter fluctuation to the water deficit of trees, with monitoring the indicators deprived from trunk diameter fluctuation and meteorological indicatorsby LVDT and automatic weather station,tolay the foundation of ensuring that the indicators deprived from trunk diameter fluctuation could indicate the tree water deficit condition and also to provide technical support for precision irrigation depending on indicator system of the diagnosis of timber forest water deficit.Conclusions were as follows.(1)The daily variation of trunk diameterhad obvious periodic trends inday and night alternate change, which shows that there is shrinking in the day because of water loss which is caused by transpiration and swelling in the night resulted from water absorption of root, which has great correlation with trees’ water status, and can be used for the diagnosis of trees’water status.(2)The trunk diameter fluctuation is different under different weather styles. The maximum daily trunk shrinkage (MDS) in sunny day is distinctly larger than that in cloudy day, which stated that the solar radiation was the main factor influencing the trunk diameter fluctuation. The appearance time of MNTD fall behind the peak value of solar radiation’s appearance time, and was similar with maximum value of vapor pressure deficit. The influence of meteorological indicatorsto trunk diameter variationswas complicated.The daily trunk diameter variations are mainly affected by factors of air relative humanity(RH), air temperature (Ta), vapor pressure deficit (VPD), solar radiation (Rs) and wind speed (WS). The main factors were RH, Ta, and VPD in sunny day. And Rs and WS were the main factors in cloudy day. In rainy weather, the daily trunk diameter change was mainly affected by RH, Ta, VPD, Rs. The expansion stage or recovery phase was primarily influenced by solar radiation (Rs).(3)The meteorological factor effected MDS was ET0, VPI), Tmean, Tmax, Tmin, RH and Qs, the main factor effected DG was Qs. And the meteorological factors which effected MXTD and MNTD were Tomcan, Tax and Tin,MDS which can indicate atmospheric drought conditions well could indicate tree water status. Temperature was an important meteorological indicator of influencing the growth of trunk diameter.(4)The signal intensity of MXTD and MNTD was always keeping the steady state during the experiment, but there had not been obvious correction between MXTD, MNTD and soil water content, which may be caused by varioustree species. All in all,MXTD, MNTDwas not suitable for indicating the water status of trees. Although DG was sensitive to the change of soil water, its fluctuation range was large. So DG was not suitable as diagnosis indicators of water deficit of trees. The response of MDS to soil water variation was slow, so that MDS was also not suitable as diagnosis indicators of water deficit of trees. TGR between T0and T1had continuous difference, and it was sensitive to the soilmoisture not only in the surface soil but also in the deep soil layer which were the main root distribution area.So TGR was suitable as diagnosis indicators of water deficit of trees.