| Quercus variabilis is an important tree species and ecological and soil conservation tree in our country,and similar to most oaks,it has high mortality in the seedling stage of cork,especially the seedling stage of the initial seedling[1].At present,in the severe case of the population destruction of Chinese cork oak,it is an important way to accelerate the reconstruction and ecological restoration of cork oak population by reducing the seedling mortality rate[2].This is from the exploration of quercus variabilis seedlings death reason of seedling stage,seedling stage,the cause of dead plants,there are two,the first is the internal cause:its biomass to the harsh habitat adaptation and adjustment ability is poor;Another is the external cause,namely the habitat conditions,including light,temperature,water,soil and other environmental factors,which lack of single factor will be "wooden barrel effect" short board,decision factor become dead plants[3].The Yellow River xiaolangdi is located in the rocky mountain area of taihang mountain in north China,and the vegetation coverage is not high,and the light is not the limiting factor for the quercus oak trees with more local distribution.The growth season is high with high temperature and sufficient heat.In winter,rare seedlings are killed due to hypothermia,and the temperature is not a limiting factor.The soil layer is thin and the soil is mostly fertile soil.The limiting effect of water factor on seedling survival is obvious.Due to large annual precipitation variation in the region,more precipitation in the year,the young plants had a higher survival rate for growth and biomass accumulation,and more,and less rainfall years,seedling growth slow or even have higher SiMiaoLv phenomenon.The occurrence of dead seedling caused by water shortage is the problem of the occurrence of drought and continuous stress.It is very important to study this process to determine the boundary between the occurrence of dead seedling and the stress of water.This paper studies several soil texture types of the Yellow River xiaolangdi,the taihang mountains clearly the influence of drought stress on the seedlings of quercus variabilis photosynthesis,cork oak seedling drought stress of soil moisture index is determined.Research results:1)different texture relationship between soil water potential and soil water content measurement method,compared with pressure membrane tension meter method,each have advantages and disadvantages:tension meter method is convenient,more measurement data can be obtained,but the measurable water potential range is small;The pressure film method can measure the high water potential,but the quantity of the measured water potential value is limited,and it needs a long determination time.This study found that the tension meter method simulating the water along with the change of soil moisture curve,to low soil moisture content(high suction segment)extrapolation results and measured by the method of pressure membrane water potential value contrast,both related significantly.That is,the tension meter can compensate for the lack of water potential in the high suction segment by the curve of the water potential changing with the soil moisture content.2)6 different texture of soil,SandA,QuanShuLing B,plain loam C,lookout point D,weather stationsE,evapotranspiration F,according to the proportion of silt from less to more sorting for A<B<C<D<E<F analysis on the relationship between the soil moisture content and water potential,under the same soil moisture and water from small to large order for A,B<C,D<E,F under the same soil moisture,the bigger the silt content of the soil,the higher the water potential of the corresponding,the utilization rate of water from the lower,with the loss of the soil moisture content,soil clay content is larger than sandy powder soil to make plants under drought stress.3)expected to establish the test water potential value of the cork oak seedling index of soil drought stress,the theoretical analysis,different types of soil texture soil water potential drought stress index should be unified.Based on the same chlorophyll fluorescence parameters of quercus variabilis seedlings under different soil water potential index of visible under drought stress,soil texture type A,B,C,D is close,soil texture type E and F close to the water potential value difference is obvious.This may be due to the measurement process,the lower when the soil moisture content of the water with soil moisture changes rapidly,the soil samples to determine the drought stress and the waters prevailed,and acquire quite test has not been unified water drought stress index.4)test 6 chlorophyll fluorescence parameters Fv/Fm,Y(Ⅱ),qL,qN,Y(NO)and Y(NPQ)began to drop point theta by θk and A 50%drop in corresponding soil drought stress index,analysis of variance results under 0.05 reliability will be 6 different texture of soil is divided into two categories:soil texture type A,B,C,D and E,F.Soil texture type A,B,C,D drought stress indicators(soil moisture):at the beginning of the decline point θk(Fv/Fm)was 9.6%,θk(Y(Ⅱ))was 12.9%,θk(qN)was 7.18%,θk(qL)was 11.53%,θk(Y(NO))was 8.1%,θk(Y(NPQ))was 8.7%.Dropping 50%of theta 50,θ50(Fv/Fm)is 5.7%,θ50(Y(Ⅱ))is 7.9%,θ50(qL)is 5.83%.The soil texture type E and F drought stress indicators(soil moisture):start to drop point θk(Fv/Fm)is 14.9%,θk(Y(Ⅱ))is 18.7%,and θk(qN)is 12.43%,θk(qL)is 17.45%,θk(Y(NO))is 12.25%,θk(Y(NPQ)is 12.1%;Dropping 50%of theta 50 θ50(Fv/Fm)is 9.8%,θ50(Y(Ⅱ))is 12.8%,θ50(qL)is 11.2%.5)comprehensive start falling point 6 chlorophyll fluorescence parameters of soil volumetric water content 0k value,it can be seen that the common characteristics of 6 types of soil texture is:(1)with the soil moisture is reduced,θk(Y(Ⅱ))are before θk(Fv/Fm)began to decline.That is,the photosynthetic intensity Y(Ⅱ)was first affected by drought stress,and soil moisture decreased further,and Fv/Fm decreased light system to cause damage.(2)The value of θk(qL)is closer to the value of θk(Y(Ⅱ))and higher than that of(Fv/Fm).This is because the qL is photochemical quenching,and the expression is the strength of photosynthesis,which is similar to the meaning of Y(Ⅱ).(3)θk(qN)、θk(Y(NO))、θk(Y(NPQ))are below the θk(Y(Ⅱ))and below the θk(Fv/Fm).When the drought stress occurred,the photosystem PSⅡ of the oak leaves was affected,then the PSⅡ was damaged,and the PSⅡ damaged by the PSⅡ would reduce the thermal dissipation mechanism of the light protection.6)(1)comprehensive analysis of six different textures of soil,the trend of water potential changes with soil moisture content;(2)Based on the same chlorophyll fluorescence parameters,the water potential index of the seedling drought stress of Quercus variabilis seedlings;(3)Under the drought stress of the seedling of quercus,the comparison of the size of k was started based on the same chlorophyll fluorescence parameters.(4)the chlorophyll fluorescence parameters θk(qN)、θk(Y(NO))、θk(Y(NPQ)).the change rule of 6 different texture of soil can be divided into two categories:different soil texture type A,B,C,D and different soil texture type E and F.There is no significant difference between the C soil in the plain area and the sandy soil in the mountain.However,there are significant differences between the clay E,F and sandy soil in the mountain,and the effect of different soil texture on water efficiency is further explained.These two kinds of soil texture show the different soil characteristics of the sand-soil and the soil. |
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