| In this study,the test materials were used by 3-year-old Cupressus chengiana S.Y.Huseedlings,which grow in the dry hot valley area of West Sichuan.By designing a drought-rewatering pot experiment at the nursery in Xue Cheng forest farm,different drought time and rewatering time on the biomass index,moisture index,photosynthetic indexand chlorophyll fluorescence index of C.chengiana seedlings were measured(WS),which were determined by WP4 C water dew point meter,gas analyzer Li-6400 and so on.At the same time,these indexes have compared with the control group(CK).By using modified rectangular hyperbolic model to fit light response curves of C.chengiana,and SPSS software for single factor analysis of variance and correlation analysis and other data processing methods,the response of 3-year-old seedlings of C.chengianato drought and the adaptation process of rewatering after drought were studied.It tried to discuss the ability of C.chengiana to adapt to arid environment and the compensatory growth mechanism after rewatering,so as to provide the basic theoretical basis for afforestation and breeding of C.chengiana,and the ecological restoration and management of the arid valley.Theresultswereasfollows:(1)Under drought stress,soil relative water content(SRWC)of C.chengianaseedlings decreased gradually.In SRWC dropped to 4.643%(WS-30),4.043%(WS-36)and 3.862%(WS-42),restoring the SRWC to the control level.It was found that the seedlings still had the activity,which indicated that the seedlings of C.chengiana were very resistant to drought resistance.When the SRWC fell to 1.872%,the seedlings died.(2)Under drought stress,the plant height,basal diameter,specific leaf area(SLA)and rhizome ratio of C.chengiana seedlings decreasedwith the significant differences between treatments(P<0.05),and the decline gradually increased.Drought 30 d,respectively,these indexes dropped to-3.545 cm,-0.095 cm,73.770 cm2·g-1 and 0.889.After rewatering,the biomass indexes of each drought treatment group were restored to different extents.The growth of seedlings of WS-30 group was more than the control level,showing super-compensation effect.And the remaining two groups of SLA and rhizome ratio were more than the control level,showing a certain compensatory growth.(3)Under drought stress,the leaf relative water content(LRWC)and leaf water potential of C.chengiana seedlings decreased gradually.Drought 30 d these indexes significantly(P<0.05)decreased,and the values were 39.784% and-17.40 MPa.After rewatering,the leaf water potential of each drought treatment group gradually recovered,but did not reach the control level.While the LRWC of the WS-30 group reached 86.617%,it exceeded the control level and showed a super-compensatory growth effect.(4)Under drought stress,the light compensation point(LCP)and intercellular CO2 concentration(Ci)of C.chengiana seedlings showed the trend of increasing first and then decreasing,and the water use efficiency(WUE)decreased first and then increased.The apparent quantum yield(AQY),net photosynthetic rate(Pn),dark respiration rate(Rd),stomatal conductance(Gs)and transpiration rate(Tr)decreased.Drought 30 d these indexes significantly(P<0.05)decreased,and Pn,Gs andTrwere 0.412 ?mol·m-2·s-1,0.009 ?mol·mol-1,0.169 mmol·m-2·s-1.Drought 42 d the stomatahadclosed,and seedling photosynthetic capacity was basically lost.After rewatering,the photosynthetic indexes of each drought treatment group recovered to varying degrees,but showed hysteresis effect.Pn,Gs and Tr were not up to the control level.It may be due to drought stress after rewatering,the mesophyll cell activity and function of seedlings were destroyed.The stomata were not completely open,and the ability of photosynthesis was affected.Other indexes of the WS-30 group returned to the control level,showing compensatory growth.The photosynthetic indexes of WS-36 group recovered to the control level,showing some compensatory growth,and the indexes of WS-42 group did not return to the control level.(5)Under the drought stress,the minimum initial fluorescence(F0)and non-photochemical quenching coefficient(qN)of C.chengiana seedlings were increased.The minimum light fluorescence(F0'),the maximum light fluorescence(Fm')and the steady-state fluorescence(Fs)increased first and then decreased.Maximum fluorescence(Fm)and photochemical quenching coefficient(qP)decreased gradually,and there was significant difference between each drought treatment(P <0.05).The highest photochemical efficiency(Fv/Fm),light energy capture efficiency(Fv'/Fm'),actual photochemical efficiency(?PSII)and electron transfer efficiency(ETR)gradually decreases.Drought 30 d these indexes significantly(P<0.05)decreased,and the values were0.051,0.048,0.064,39.986.To drought 42 d,these dropped to the lowest.After rewatering,the chlorophyll fluorescence parameters of each drought treatment group were restored to some extent,but showed hysteresis effect.Which in addition to F0,qN and qP,the other indexes did not reach the control level.This may be due to drought stress on the leaf PSII reaction center producing a certain degree of damage,and only a part of the PSII reaction center was open.As well as the light energy dissipated in the leaves was gradually reduced,so that the light energy for photosynthesis gradually increased,and plant photosynthesis gradually recovered,but did not return to the control level.Among them,the WS-30 group set fastest recovery.In addition,under the drought stress,the growth and photosynthesis of C.chengiana seedlings were increased to a certain extent,and then obviously inhibited.The results showed that the seedlings had strong drought resistance,which could adapt to the drought environment by adjusting the internal physiological activities.In the short term drought,the seedlings can quickly recover to normal growth level,and even show compensatory effect.Under long-term drought stress,the damage of mesophyll cells was serious,and the photosynthetic organs were damaged.So their structure and function were slow to repair,and could not be restored to the normal level.Although the seedlings had a certain ability to compensation for growth,can not be restored to normal levels. |
PDF Full Text Request