Effects Of PP₃₃₃ On Physiological And Ecological Characteristics Of Phyllostachys Edulis Seedlings Under Drought Stress

In this study,We investigated the effects of paclobutrazol(PP₃₃₃)on the photosynthetic characteristics,osmotic adjustment substances,protective enzymes,nonstructural（NSC）content and related synthase,root activity,NPK,C/N ratio,chloroplast ultrastructure,stomatal scanning,high increment and biomass on one-year-old Phyllostachys edulis seedlings.Experiments were degined with three water treatments（W1:well-watered with 75%field capacity;W2:water stress with 50%FC;W3water stress with 35%FC）and two levels of PP₃₃₃33 treatments（P1:0 mg/L;P2:40 mg/L）.The effects of paclobutrazol and water treatment on the growth characteristics,physiological and biochemical indexes of Phyllostachys edulis seedlings were further studied.,and to explore the mechanism of Phyllostachys edulis seedlings on paclobutrazol and water treatment.The results provide a theoretical basis and technical support for the efficient cultivation of bamboo seedling.The main results of this study are as follows:（1）With the increase of drought intensity and the prolongation of drought time,the leaf color of Phyllostachys edulis seedlings gradually faded,and the total contents of chlorophyll a,chlorophyll b,carotenoid,chlorophyll a/b and chlorophyll decreased significantly,Pn,Tr and WUE decreased significantly,Ls increased significantly,ΦPSII,ETR,NPQ and qP were significantly decreased,chloroplast degradation caused by drought at the same time,but also inhibit the initial reaction phase of photosynthesis,resulting in photosynthetic electron transport chain blocked,photosynthetic capacity decreased;paclobutrazol treatment significantly improved leaf photosynthetic pigment Content and the degree of openness of the PSⅡreaction center,enhanced the utilization of light energy and enhanced the ETR value,indicating that the photosynthetic electron transport efficiency was improved,the photosynthetic rate was enhanced and Pn was significantly improved.（2）The photosynthesis of non-stomatal factors in the leaves of Phyllostachys edulis seedlings at late stage of drought period began to loose the cysts in the chloroplast.As the degree of membrane lipid peroxidation increased,the accumulation of Russian particles increased significantly and the transport of photosynthetic products was blocked,resulting in the accumulation of starch granules;paclobutrazol treatment can protect the integrity of the chloroplast to ensure the photosynthesis of the normal stomatal factors,and then synthesize more photosynthetic products,stored in the chloroplast in the form of starch granules,but with the deepening of the drought,starch particles reduced,it may be that the starch was broken down into soluble sugar and so on,to participate in the osmotic regulation of plants to resist the damage caused by drought.（3）With the increase of drought intensity and the prolongation of drought time,the accumulation of free proline and soluble protein,maintained the cell swelling,the relative water content of the leaves decreased,the water absorption and transformation efficiency decreased,and the water retention capacity decreased,accumulation of reactive oxygen species by MDA increasing significantly,The activity of CAT and POD began to decrease at 14 days after drought,and the activity of SOD,POD and CAT decreased significantly at 21 days after drought,and the defense ability of antioxidant system decreased;The relative water content of leaves was significantly improved by the PP₃₃₃33 treatment,and reached maximum after treatment with P2W3 for 7 days,14 days and 21 days,indicating that paclobutrazol was beneficial to improve the ability of bamboo to regulate its own water balance,and the content of MDA was significantly decreased,Paclobutrazol treatment significantly improved the activity of protective enzymes,in the 21 days of drought,failed to change the trend of its decline.（4）With the increase of drought stress,the content of soluble sugar,sucrose and fructose increased significantly in leaves and roots of Phyllostachys edulis seedlings.Under heavy drought,the increase was the highest,and the content of starch was significantly decreased under drought stress,but the total sugar content,fructose and sucrose content were significantly increased,all reached the maximum under P2W3 treatment;Starch hydrolysis was soluble sugar,which could not only reduce the cellular potential but also provide carbon skeleton and energy for the synthesis of various compounds.At the same time,FBP,SPS enzyme accumulation,indicating that drought stress to enhance the sugar glycolysis pathways,and thus promote the accumulation of carbohydrates,not only can reduce the water potential,but also for other types of adaptive response to provide material and energy supply.（5）With the increase of drought stress,root activity,seedling height increment and biomass decreased significantly,and the root/shoot ratio increased significantly.Exogenous PP₃₃₃33 significantly increased the root activity of Phyllostachys edulis seedlings,and the seedling height decreased significantly,the crown ratio increased significantly with increasing drought intensity.