| In the present study, the effects of water stress on both photosynthetic and physiological responses in strawberry plants were studied and the possible response mechanisms discussed. Rate of net photosynthesis, gas exchange, chlorophyll fluorescence and activities of antioxidant enzymes were detected as the main indexes to be compared and analyzed when strawberry plants were subjected to gradual soil drying, different soil drought, successive and repeated. Osmotic stress was used to testify the effects of soil drought on photosynthesis, gas exchange and activities of PS reaction center.In addition, by means of detecting dynamic changes in ABA and SA contents both in leaves and roots when half of root exposed to drought, drought signals in strawberry were analyzed and hypothesized. Finally, the effects of salicylic acid on antioxidant enzymes as well as relation with drought tolerance in strawberry plants were explored in the aim of providing alternative methods for strawberry growers. The main results of this study were as folio wings:1. Drought decreased Pn and light saturation point, changed diurnal curves of Pn, limited gas exchange with increasing the possibility of light inhibition. Well- watered CK plants had high Pn with an apparent midday depression of Pn (MDP) and light saturation point was 600 mol .m-2. s-1. Plants under moderate drought had a similar Pn pattern with CK but short in size. Pn in plants under severe drought condition fell to zero.2. Based on analysis of changes in water status, chl content, chl fluorescence of reaction center in PSII, activities of antioxidant enzymes and MDA content brought about by drought, MDP in CK was caused by stomatal closure because of VPD between air and inter-cell being raised by decrease of W.P. at noon. Both stomatal and non-stomatal limitation contributed to decrease in Pn of plant under moderate drought. It was non-stomatal limitation that caused the decrease of Pn under severe drought, including significant reduction in both contents of chlorophyll, protein and in Fv/Fm, PS and qP in PS reaction center with concomitant elevating in NPQ, as well as damage to photosynthetic apparatus and increase of peroxidation. Gs and Tr were more sensitive to drought stress than Pn in strawberry leaves, while w was not fully controlled by LWC. The Pn was more related with w than with LWC. Recovery of Gs and Tr were faster than that of Pn, which was decided by status of Gs.Repeated successive drought significantly affected photosynthetic apparatus in strawberry leaves. There were no difference between 2 times of successive drought in chl contents and in decrease of W w in plants subjected to moderate drought. In 1st time drought, decease in Pn was due to non-stomatal limitation because of inhibition of activity of PSII reaction center. 2nd time treatment reduced PSII but not Fv/Fm and Fo, indicating PSII was still in good condition, which indicated decrease in Pn was due to stomatal limitation. Both times of repeated successive severe drought caused severe inhibition of PSII reaction center, and more severe during 2nd time including more damage of PSII reaction center, lower of contents in chl and Vw. The results showed strawberry plants under repeated moderated drought would improve their tolerance to drought, while repeated severe drought might cause permanent injuries.3. The investigation on change in activities of antioxidant enzymes related to protection of PSII reaction center were conducted. The activities of SOD, A-POD, DHAR increased during soil gradual drying until moderate drought appeared* when MDA content kept increase until rehydrtion. That is probably the mechanisms that PSII reaction center was not obviously inhibited under moderate drought conditions but significantly injured under severe drought conditions. G-POD responded more slowly to change of soil water condition as proline did. It seemed that coordination between A-POD and DHAR in strawberry might make a more important role in AOS scavenging during drought and...
|
PDF Full Text Request