Camellia Oleifera's Response Mechanism To Drought Stress

Camellia oleifera is an important subtropical oil trees and ecology trees in China.It is one of the economic tree developed greatly in the red soil hilly region of Southern.However,the seasonal drought in the red soil region of China is serious,and the water deficit caused by it has a great impact on the survival and growth and development of Camellia oleifera in the region.Ganwu Camellia oleifera is the main cultivars of new plantation in Jiangxi province,but there are few researches on drought in their seedling stage,which limits the scienti fic planting of Camellia oleifera to some extent.In this paper,the physiological and biochemical responses of different degrees of drought stress such as morphology,growth,water consumption and photosynthetic were studied,and the drought resistance mechanism of different Camellia oleifera cultivars was discussed.The drought resistance of four Camellia oleifera clones was evaluated scientifically and comprehensively.This study can provide theoretical basis for the breeding of drought-resistant Camellia oleifera varieties and water management of Camellia oleifera seedlings.The main findings are as follows:Under drought stress,the plant height growth,ground diameter growth and dry matter accumulation of the four Camellia oleifera clones all significantly decreased,except for the Xing-46 plants with high,dry matter accumulation and Wu-12 ground diameter growth under mild stress,which were more than the normal water supply.With the increase of the degree of drought stress,the total root length,root dry weight,ground dry weight and high diameter ratio of the four Camellia oleifera clones decreased,while the lateral root number and root crow n ratio and the number of dead leaves increased.Under severe drought stress,the dry matter accumulation of Gan-190,Wu-12,Wu-2,and Xing-46 all significantly decreased,and the total root length of Wu-12 and Wu-2 also significantly decreased,while the lateral root number of Wu-12 significantly increased.Correlation analysis showed that the accumulation of gan-190 and Wu-12 and the plant height growth of Gan-190 and Wu-2 and the ratio of height to diameter of Wu-2 and Wu-12had significant positive correlation with soil water content.The anatomical structure of the leaves of different clones of Camellia oleifera.showed that the drought stress caused damage to the stomata of four Camellia oleifera sinensis strains,and the leaf thickness decreased sign ificantly under moderate and severe stress,especially the stomata sag under severe stress.The epidermal cells are dry.With the increase of drought stress,the thickness of the leaves,the thickness of the epidermis,the palisade tissue and the thickness of the sponge tissue of the four Camellia oleifera clones decreased.Under severe stress conditions,the stomatal density,stomatal opening,stomatal opening rate,leaf thickness,epidermis thickness,palisade tissue thickness and sponge tissue thickness were all greater than those of other clones.Correlation analysis showed that the stomatal opening of the four Camellia oleifera clones was significantly positively correlated with soil water content.Under different water gradients,the daily variation cur ves,water consumption and water consumption rate of four Camellia oleifera clones were all single peak type,and the peaks of Gan-190,Wu-12 and Xing-46 were advanced 1 h earlier under moderate stress.Under drought stress,the daily water consumption and average daily water consumption rate of the four Camellia oleifera clones decreased significantly.Relative water content of leaves decreased significantly under moderate and severe drought stress.Under mild and moderate drought stress,the daily water consumption and relative water content of leaves of Xing-46decreased the most;under severe drought stress,the daily wat er consumption of Gan-190 decreased the most,and that of leaves Wu-12 decreased the most,while that of leaves Wu-2 decreased the least under drought stress.With the aggravation of drought stress,the?¹³C values of the leaves of the four Camellia oleifera clones increased,and under the four water gradients,the?¹³C values of the leaves with Wu-2 water gradients were higher than those of the other clones.Under different water gradients,the diurnal variation curves of Pn and Gs of four Camellia oleifera clones were double peak,except for Gan-190,the daily variation curve of Gs was single peak type under mild stress.And the absence of Wu-2 under severe stress,the daily variation curve of Gs changed from double peak to single peak type.Under drought stress,the Pn maximum of the four Camellia oleifera clones decreased significantly,and the Pn minimums of Gan-190,Wu-12 and Wu-2 also significantly decreased.Under different water gradients,the midday depression of photosynthesis of Gan-190 and Wu-12 were mainly restricted by non-stomatal factors,while Xing-46 was mainly restricted by stomatal factors.Under sufficient water supply,the midday depression of photosynthesis of Wu-2were mainly restricted by non-stomatal factors,while under drought stress,they were restricted by both stomatal and non-stomatal factors.Correlation analysis showed that Ci of Xing-46 and Gs of Wu-12 showed significant positive correlation with soil water content,and Ls of Gan-190 and Wu-2 showed significant negative correlation with soil water content.Under drought stress,the soluble sugar,soluble protein,proline,SOD activity and malondialdehyde content of the four Camellia oleifera leaves increased significantly,and the relative water content of Gan-190 and Wu-12 leaves decreased significantly,while Wu-2 and Xing-46 The relative water content of leaves under moderate and severe drought stress was significantly reduced.Under drought stress,the relative water content of the Wu-2 leaves decreased the least,the content of proline in the leaves increased the most,the content of soluble sugar and soluble protein in the leaves increased greatly,and the content of malonaldehyde in the leaves increased the least.Correlation analysis showed that the content of proline in l eaves with Wu-12,Wu-2 and Xing-46 had significant negative correlation with soil water content,and the SOD activity in leaves with Gan-190,Wu-2 and Xing-46 had significant negative correlation with soil water content.Under drought stress,the contents of ABA and Me JA in the leaves of four Camellia oleifera clones increased significantly.The ABA content in the leaves of Xing-46 increased the most under mild and moderate drought stress,and the largest was Wu-12 under severe drought stress.Me JA content increased the most under drought stress.With the increase of drought stress,the ZR content of leaves of Gan-190,Wu-12 and Xing-46 decreased,while the content of ZR in Wu-2 leaves increased significantly under mild and moderate drought stress.In additio n,the content of IAA in Wu-2 leaves increased compared with the normal water supply under drought stress.Correlation analysis showed that the ZR content of Gan-190,Wu-12 and Xing-46 leaves were significantly positively correlated with soil water content.Using principal component analysis,the morphological,growth,physiological and biochemical twenty-eight indexes related to drought resistance of Camellia oleifera were summarized into three main components,and the accumulative contribution rate was 100%,which has strong information representative.The first principal component can be summarized as photosynthetic parameters and leaf anatomical parameters.the second principal component is growth indicators,the third principal component is stomatal opening and proline,and the corresponding drought resistance identification indexes are Pn,Gs,Tr,and leaves thickness,upper epidermis thickness,stomatal opening,stomatal density,dry matter accumulation,plant height growth and leaf proline content.Usin g subordinative function value analysis,the drought resistance of four Camellia oleifera clones was comprehensively evaluated,and the order of droug ht resistance was Wu-2>Gan-190>Xing-46>Wu-12.The drought resistance mechanisms of four Camellia oleifera clones were different.Gan-190 could be summarized as SOD mechanism,stomatal response mechanism,photosynthetic reaction mechanism and growth rate mechanism.That is,with the increasing of drought stress,transpiration water consumption reduced mainly by reducing stomatal openi ng,Gs and Tr,and excessive water consumption reduced by reducing Pn,plant height growth and dry matter accumulation,and by increasing the content of antioxidant substances,to reduce osmotic potential,alleviate superoxide anion damage to cells,and en hance drought tolerance.Xing-46 could be summarized as ABA mechanism,stomatal reaction mechanism,photosynthetic reaction mechanism and growth rate mechanism,that is,increasing the content of endogenous hormone ABA to improve water retention of leaves,alleviate the damage of cell membrane caused by drought stress,and reduce water consumption by reducing the growth of ground diameter.Wu-12 mild drought stress,it could be concluded as SOD mechanism,soluble protein mechanism under moderate drought stress,ABA mechanism under severe drought stress,stomatal reaction mechanism and photosynthesis mechanism.Under Wu-2 mild drought stress,it could be concluded as Me JA mechanism,which can enhance the drought resistance of plants by increasing the content of endogenous hormone Me JA;under moderate drought stress,it c ould be concluded as SOD mechanism and growth rate mechanism,which can reduce water consumption by reducing the growth of ground diameter;under severe drought stress,it c ould be concluded as SOD mechanism and photosynthetic reaction mechanism,which can mainly reduce transpiration water consumption by reducing Gs and Tr.