Water Competition And Drought Response In Symbiosis Between Platycarya Longipes And Lindera Communis

In this paper,the coexisted species of Platycarya longipes and Lindera communis in karst ecologically fragile area are taken as the research object.Under drought stress,it is of great theoretical and practical significance to study the differences in physiological and ecological responses,relative competition intensity,L.communis characteristics and antioxidant enzyme gene expression levels of coexisted species in karst areas.To reveal the water competition strategies and drought response of the two symbiotic plants,and to understand the dynamics of community structure,is of great significance for promoted vegetation restoration and reconstruction in karst areas.The main research results are as follows:1.Dure the experiment,the net increment of ground diameter,plant height and crown width of P.longipes and L.communis per plant would decrease with the increase of soil water deficit.The net increment of plant height and crown width per plant decreased with the increase of stress degree,but the net increment of ground diameter increased under mild stress and then decreased.Under mild stress,only the plant height and crown width of P.longipes and L.communis were significantly inhibited.However,under severe stress,the inhibition effect on ground diameter,crown width and plant height was obvious.With the intensification of drought stress,the net increment of plant height and crown width of the two mixed plants decreased continuously,while the net increment of ground diameter increased.The plants could improve their competitiveness by increased ground diameter and decreased crown width.The net increment of ground diameter and crown width of P.longipes was higher than that of L.communis,but the net increment of plant height was smaller than that of L.communis.Drought stress had inhibitory effects on plant height and crown width of P.longipes and L.communis in mixed planted.The lower the soil water content,the stronger the inhibition effect.2.The two plants had different degree of competition in ground diameter under drought stress.The RCI^D of P.longipes and L.communis decreased first and then increased with the intensification of stress degree.The net increment of ground diameter in the stress group was greater than that in the control group,L.communis RCI^D>P.longipes RCI^D.Before15 days of P.longipes stress,there was no competitive intensity except for moderate stress.L.communis plant height was subjected to certain intensity of competition in different periods.L.communis RCI^H>P.longipes RCI^H.The effects of competition and drought stress on the growth of different plants are different,and there is a synergistic effect between biotic and abiotic environments on the community shaped.The relative competition intensity of P.longipes in the population is small,indicated that its competitive ability is strong and the competitive pressure is small,while the competition of L.communis for water resources is relatively weak.The results showed that the competitive ability of P.longipes was greater than that of L.communis under drought stress.3.With the extension of drought treatment time,SOD,POD,APX and Ss of single P.longipes seedled all showed a trend of first increased and then decreased,while CAT and MDA indexes showed a trend of gradually increased.MDA increased gradually in L.communis per plant,while MDA increased first and then decreased in other L.communis plants.SOD and APX of mixed planted P.longipes increased gradually with stress time,and APX and MDA of mixed planted L.communis increased gradually.The synthesis of SOD,POD and CAT in L.communis was inhibited with the intensification of stress and the extension of stress time.The activities of SOD and CAT in mixed planted P.longipes were higher than those in L.communis,and the SOD in mixed planted P.longipes reached the maximum value at 20 days of stress.The SOD enzyme of L.communis under mixed cultivation reached the maximum value at 15 days of stress.The results indicated that P.longipes had stronger drought tolerance than L.communis under long-term drought stress.The MDA content of L.communis under mixed cultivation had little change in the early stress process,while the MDA content of P.longipes under mixed cultivation gradually increased,indicated that the protection system of mixed planted L.communis had a strong ability to remove membrane lipid peroxides.The content of Ss and Pro per plant of L.communis increased rapidly in the early stage of stress,and decreased after reached the maximum value on 10d,and the content of SS and Pro per plant in all stress groups was higher than that in CK.Compared with single plant P.longipes,the osmotic regulatory substances of P.longipes were still higher than those of L.communis at the later stage of stress,indicated that both P.longipes and L.communis had strong drought tolerance,and P.longipes had stronger drought tolerance than L.communis.4.The Pn,Gs and Tr of P.longipes and L.communis were inversely proportional to the drought stress intensity under the two planted modes.It showed mild drought>moderate drought>severe drought,indicatedthat of photosynthetic and L.communis were sensitive to drought stress.The Ci of mixed planted increased with the increase of drought stress at the later stage of stress,which might be due to the loss of normal operation of photosynthetic apparatus due to damage.Under different soil water content environment,the photosynthetic characteristics of P.longipes were better under single plant planted(the highest photosynthetic rate),and the net photosynthetic rate and transpiration rate of P.longipes in the late stress period were lower than those of L.communis under mixed planted.These results indicated that L.communis could more effectively utilize light energy and accumulate more organic matter to promote plant growth in the early stage of drought stress.It may be that the net increase of P.longipes plant height was lower than that of L.communis in the late stage of drought stress,which affected the photosynthetic capacity of P.longipes in interspecific competition.With the extension of stress time,WUE of single P.longipes group T1 and T3 increased to vary degrees,while that of single P.longipes group T2 decreased first and then increased.WUE of L.communis per plant firstly decreased and then increased with the decrease of soil water content,and decreased with the extension of stress time.There was no significant difference in WUE of CK between the two plants.However,with the deepened of drought stress,WUE of P.longipes in the early stage of stress decreased more than that of L.communis,and that of L.communis in the late stage of stress decreased more than that of P.longipes.WUE of mixed P.longipes T1 and T3 groups increased with the prolongation of treatment time.The WUE of L.communis increased first and then decreased.The regulation effect of mixed planted L.communis on drought stress was higher than that of single planted L.communis,and the resistance of seedlings to drought increased,which indicated that L.communis had certain drought resistance.However,the WUE of P.longipes was higher than that of L.communis under the same water condition.Under long-term drought stress,L.communis seedlings had a conservative water use strategy.Under drought stress,leaf Gs decreased to reduce water loss,resulted in reduced intercellular CO₂and limited carbon assimilation,which was also an important reason for the sharp decline in soil diameter growth of L.communis in the later period of stress under the symbiosis of P.longipes and L.communis.The results indicated that P.longipes had stronger drought resistance in the late stress period.5.Under drought stress,the expression levels of Cu/Zn-SOD,Fe-SOD,Mn-SOD,POD1 and Cat1 in P.longipes were different.Under mild stress,the expression levels of Cu/Zn-SOD in P.longipes decreased first and then increased with the extension of stress time.Cu/Zn-SOD gene decreased first and then increased under mixed culture.The relative expression levels of Fe-SOD,Mn-SOD,POD1 and CAT were all up-regulated under mild and moderate drought stress,and down-regulated in the later period of stress.These results indicate that the accumulation of a small amount of reactive oxygen species induced by a short period of mild drought may act as signal transduction molecules in cells to participate in the cellular antioxidant response,and induce the upregulation of Cu/Zn-SOD,Fe-SOD,Mn-SOD,POD1 and CAT to maintain the metabolic balance of reactive oxygen species,which plays an important role in drought resistance system.The relative expression level of Cu/Zn-SOD gene in mixed P.longipes was higher than that in L.communis,the relative expression level of CAT gene was lower than that in L.communis at late stress period,and the relative expression level of POD1 gene was lower than that in L.communis.The variation trend and amplitude of POD1 and CAT genes were not completely consistent with that of enzyme activity.This indicated that the enzyme activity and its expression did not have complete synchronization.Under drought stress,the expression of five antioxidant enzymes in L.communis was better than that in P.longipes,which was the same as the results of enzyme activity measurement in early stress.