Study On Drought Resistance And Anatomical Characteristics Of Three Introducing Varieties Of Pecan

In order to expanding the planting area and selecting suitable varieties of pecan in Anhui,the paper tested the drought resistant index about the stem and leaf of mainly introduced pecan varieties in China.The author studied the relationship between the micro structure with hydraulic properties.The stem and leaf tissues of different thin shell pecans were embedded in paraffin and sliced,and the microscopic features of the stem and leaf were photographed using an optical microscope and a camera.Comparison of mesophyll structural characteristics,including mesophyll tissue indexes such as upper epidermis thickness,palisade tissue thickness,sponge tissue thickness,lower epidermis thickness.Compare the indicators such as the ratio of palisade tissue to spongy tissue,the ratio of palisade tissue to leaf thickness and the ratio of spongy tissue to leaf thickness;and pass the indexes such as the stoma diameter,stoma density,and vein density.Compare the structural characteristics of the xylem,including the diameter of the pipe,the density of the pipe,the span of the inner diameter of the pipe.,and calculate the reinforcement coefficient of the pipe wall to explore the causes of the difference in the water loss rate of different pecan varieties in the natural state,and to understand the mechanism of pecan drought resistance.The promotion of pecans provides a scientific basis.The main results were as follows:(1)This study was carried out during the drought in Anhui province to determine the percentage loss of conductivity(or embolism degree)of three varieties on pecans in 2019.The results showed that the embolism degree of‘Pawnee’(P)and‘Western’(W)were 23.3%and 22.2%,which were significantly lower than that of‘Mahan’(M)(P<0.05)which were32.9%.It shows that P and W are more drought-resistant in areas with less rainfall.(2)The sequence of the leaf thickness,palisade tissue thickness,the ratio of palisade tissue to spongy tissue and the ratio of spongy tissue to leaf thickness were all showed that:P>W>M,which showed that P and W were significantly stronger than M in ability of water regulation and transpiration resistance.Their adaptability in adversity was also stronger than M.(3)Upper epidermis thickness,lower epidermis thickness these data are W>P>M,sponge tissue thickness and the ratio of spongy tissue to leaf thickness those data are all M>W>P,P and W the leaf thickness is thicker,the leaf protection tissue is more developed,so their ability to regulation ability and the adaption of drought habitat is more stronger.(4)The order of stoma diameter is M>W>P,the order of stoma density is P>W>M,the order of leaf veins density is P>W>M.As a result,P and W have a more developed leaf vein system and‘smaller and densier’s stoma characteristics,which also means they are more resistant to drought than M and are better able to maintain plant function in adversity.In terms of leaf traits,P had the best drought resistance,followed by W and M,which was consistent with the actual embolization degree of pecan under drought stress.(5)The vessel diameter in xylem of M is significantly larger than that of P and W, which means that M has a greater probability of embolization under drought stress,which is not conducive to the survival of plants in dry conditions.The catheter density of M is significantly lower than that of P and W,so its effective water conduction area is the smallest,which leads to its sapwood water conductivity is the lowest phenomenon.(6)M has the smallest(t/b)~2 and the largest conduit wall span(b),which indicates that it has a high probability of resisting embolism,which is consistent with its performance in the actual dry environment.From the perspective of xylem anatomy,P had the best drought resistance,followed by W and M,which was consistent with leaf characters.(7)P and W(which are native to arid habitats)were actively adapted to the arid environment by shortening the length of the new shoots and increasing the diameter of the new shoots after being subjected to the same intensity of drought stress.The dry matter content of the leaves is significantly higher than that of M,which not only shows strong drought resistance,but also shows better recovery ability under stress.(8)The stem and leaf anatomy and hydraulic characteristics of the comprehensive varieties are known,and the drought resistance of the tested varieties is ranked as P>W>M.The drought tolerance of W is better than that of M native to rich water habitats,which provides a scientific basis for the selection of thin-shell hickory varieties.