Effect Of Soil Drought Stress On The Water Metabolism And Photosynthesis Characteristics Of Prunus Mongolica Seedlings

In this paper, the Prunus mongolica Maxim. seedlings were studied, analyzed dynamically of the effect of soil drought stress on water metabolism and photosynthesis characteristics of Prunus mongolica seedlings by using naturally-dehydrated-soil method, sought the adaptive mechanism of Prunus mongolica seedlings to drought stress, wanted to provide experimental basis for the recovery of desert ecosystem and the exploration of drought tolerance mechanism of desert plants. The main results were summarized as follows:1. The relationship between LWP and SRWC was consistent with cubic model, LWP = -2.804+1.549S-2.502S2+2.679S3. Not only soil drought stress increased water absorbing ability of Prunus mongolica seedlings, but also decreased the water transportation ability. When the 5th day of soil drought stress, SRWC decreased to 36.57%, LWP decreased to -2.05MPa, hydraulic conductivity of twigs decreased by 65.00% compared with that under the adequate moisture conditions. Hydraulic conductivity recovered 70.38% by one night rehydration. In the aspect of water parameters, when the 8th day of soil drought stress, SRWC decreased to 17.45%, LWP decreased to -2.60MPa, AWC and Vb/Vf increased by 80.53% and 48.79% compared with that under the adequate moisture conditions,ψπ0,ψπ100,RWCtlp,ROWCtlp andεmax decreased by 27.04%,10.56%,31.15%,34.15% and 48.14% compared with that under the adequate moisture conditions. Showed that, with the increased intensity of soil drought stress, AWC and Vb/Vf increased significantly,ψπ0,ψπ100,RWCtlp,ROWCtlp andεmax decreased significantly. Indicate that, Prunus mongolica seedlings had strong enduring dehydrate, turgor maintaining and cell elastic regulating ability. In the aspect of stomata behavior, before SRWC was 24.92%,LWP was -1.97MPa(the 5th day of drought stress), diurnal variation of stomata open of Prunus mongolica seedlings showed obvious single peak curve. After that(the 5th day of drought stress),maximum stomata open rate and stomatal aperture were decreased significantly, and the peak of diurnal variation of stomata open was not obvious. Therefore, -1.97MPa was the critical leaf water potential value to caused Prunus mongolica seedlings stomatal feedback reaction. In the preceding stage of soil drought stress, there was no significant change with Tr and when SRWC≤35.47%, it had significant decrease.2. Soil drought stress leaded to maximum photosynthesis rate(Pmax),apparent quantum yield(AQY) and light saturation point(LSP) of Prunus mongolica seedlings decreased.However, when the 8th day of soil drought stress, SRWC decreased to 24.37%,LWP decreased to -2.60MPa, it still kept 47.96% of Pn and 48.94% of AQY,this showed Prunus mongolica seedlings had strong drought resistance ability. WUE was increased obviously under moderate drought stress (SRWC≥43.08%). Rd kept a stable level under soil drought stress, when SRWC≤35.47%, it had significant decrease. It showed that, there had little influence to Prunus mongolica seedlings under mild drought stress and moderate drought stress, which taken high photosynthesis and low transpiration water saving strategy under severe drought stress(SRWC≤35.47%).In the aspect of oxygen evolving activity of chloroplast, hill reaction activity of Prunus mongolica seedlings decreased with the decrease of SRWC. When the 8th day of soil drought stress, SRWC decreased to 14. 01%,LWP decreased to -2.59MPa, Prunus mongolica seedlings still kept 42.81% of hill reaction activity. Hill reaction activity recovered 55.57% by one night rehydration. It showed that, Prunus mongolica seedlings had strong drought-resistance ability in the aspect of photosynthesis.3. With the aggravation of soil drought stress, Fv/Fm of Prunus mongolica seedlings was declining, and the light translation extent was declining. The decline of FV/Fm affected photosynthetic electron transport natural progress and plant photosynthesis. However the decline was not obvious under mild drought stress and moderate drought stress (SRWC≥58.24%). With the aggravation of soil drought stress, Yield of Prunus mongolica seedlings was declining. The decline was not obvious under mild drought stress and moderate drought stress (SRWC≥58.24%), but it was obvious under severe drought stress (SRWC≤30.59%). With the aggravation of soil drought stress, qP and qN of Prunus mongolica seedlings had decreased and increased trend, furthermore they had significant changes under severe drought stress(SRWC was 12.31%,LWP was -5.59MPa). With the aggravation of soil drought stress, qN of Prunus mongolica seedlings increased, the photoinhibition was strengthen and heat dissipation ability was also strength. Mild drought stress and moderate drought stress(SRWC≥58.24%)not had significant effect to the functions and activities of PSⅡof Prunus mongolica seedlings. The open rate of PSⅡreaction center declined obviously under extreme conditions (SRWC was 12.31%,LWP was -3.59MPa), and it leaded to the decline of electron transport quantum yield of PSⅡ. It showed Prunus mongolica seedlings had strong drought tolerance ability in the aspect of chlorophyll fluorescence parameters.4. In the aspect of enzyme activity of carbon assimilation, PEPCday activity of Prunus mongolica seedlings under adequate moisture conditions was 0.7589μmol·NAD+·mg-1·protein·h-1, PEPCnight activity was 0.6591μmol·NAD+·mg-1·protein·h-1, the diurnal activity of PEPC were lower. With the aggravation of soil drought stress, the activity of PEPCnight showed rising trend, and PEPCday showed decreased first and then increased trend. When the 8th day of soil drought stress, SRWC decreased to 7.50%,LWP decreased to -2.86MPa, PEPCnight activity increased to 4.74 times of that under adequate moisture conditions, and PEPCday activity increased to 1.91 times of that under adequate moisture conditions. And the difference of diurnal PEPC activity was increasingly enlarged. After the drought stress removed for one day, the diurnal activity of PEPC basically recovered to pre-treated level. Indicate that with the induction of soil drought stress, the carbon assimilation pathway of Prunus mongolica seedlings probably had transformation.5. With the aggravation of soil drought stress, GO activity of Prunus mongolica seedlings overall tended to decrease. When the 7th day of soil drought stress, SRWC decreased to 11.53%,LWP decreased to -2.46MPa,Prunus mongolica seedlings still kept 51.50% of GO activity. GO activity recovered 78.54% by one night rehydration. Showed that, Prunus mongolica seedlings kept high GO activity to protected photosynthetic apparatus.In summary, not only Prunus mongolica seedlings had strong drought resistance ability but also recovery capability after drought stress.