Adaptability Of Physiological Ecology Of Cupressus Funebris Endl. Seedling Under Water Stress In Limestone Area In Chongqing

Karst landscape,one of the three vulnerable ecotones,is very general in the word, especially in the southwest of China.It is often short of water for plants due to low water retention capacity and high exposure of rocks.Therefore,it becomes to be a very important issue to find some drought-resistant plants for vegetation restoration and reconstruction in limestone area.In order to adapt to the drought condition in rocky desert terrain,plants have developed a series of mechanisms,such as organic protective movement,morphology remodeling and metabolic regulation.The plants maybe will have different adaption ways because of different stress strengths or different extents of water stress.In order to understand the suitable trees in limestone area how to resist water stress wholly and completely,we selected Cupressus funebris Endl.as our material,studied the growth characteristics,photosynthetic characteristics,antioxidant system and osmotic adjustment as well as the repair ability after re-watering by water controlled experiment.The experiment was set four water levels,that is,CK,light water stress(LS),middle water stress(MS) and severe water stress(SS) and,three stress stages, that is,early stage,middle stage and end stage.The main results are as following:1.Water stress had no effects on the length,surface area,average diameter and volume of roots of Cupressusfunebris Endl.seedlings at the early stage.But with the aggravation of stress,they all decreased.The heights and diameters of Cupressus funebris Endl.seedlings dropped with the decline of water content in soil.The above-ground biomasses did not suffer from water stress at the early and middle stage, however,they had significant differences with CK.The under-ground biomasses decreased with the aggravation of stress.For the total biomasses,they also decreased at all three stages,but they had no difference between LS and CK at early and middle stages.The root and shoots ratio of Cupressusfunebris Endl.seedlings had the trend of decrease at the early and middle stages,but no differences at the end stage.When re-watering,the root surface area and root volume that had decreased when suffered MS at the end stage recovered to the level of CK,and they could not come back to the level of CK when suffered SS at the middle and end stages.The height of Cupressus funebris Endl.seedlings did not recover,while the diameter recovered at certain degree. Re-watering promoted the accumulation of above-ground biomass,under-ground biomass and total biomass.This effect was more obvious with lowering of water content in soil.2.The net photosynthetic rate(Pn),transpiration rate(E) and stomatal conductance (Gs)of Cupressus funebris Endl.seedlings were all decreased under water stress. However,Intercellular CO₂ concentration(Ci) did not decrease with Gs.It increased remarkably at the early and middle stages when Gs decreased to a certain value,and kept steady at the end stage.Stomatal limitation value(Ls) went up with the CK,LS and MS at the early and middle stages,while went down under SS.But at the end stage,it went down from CK to SS.Mesophyll conductance(Pn/Ci) fell remarkably under SS at the early stage.But it fell under MS at the middle stage,and under LS at the end stage. Before SS at the early and middle stage,we calculated water use efficiency by intrinsic WUE,which increased or kept unchangeable with the lessening of water content in soil. While instantaneous water use efficiency was used to SS at early and middle stages and all the treatments at end stage,it behaved decreased.After re-watering,Pn,E,Gs and WUE recovered with different degrees.Compensation effect was visible before serious stress when the photosynthesis indexes recovered greatly,while they recovered little under serious stress due to the hurt of physiological function of Cupressusfunebris Endl. seedlings.3.Photosynthetic pigment content and the extent increased with the aggravation of water stress,which correlated with the stress time and leaf concentration.After re-watering,the pigment decreased owing to leaf expansion growth and higher water content.Car/Chl went up at water stress while went down after re-water.Chl.a/Chl.b had no change under any stress.4.Fv/Fm of well-water Cupressusfunebris Endl.seedlings(CK) was 0.81-0.82, nevertheless,it decreased notably under water stress and the extent increased with the aggravation of water stress.Similarly,Fv/F₀ had the same trend,qP decreased,while NPQ increased with the CK,LS,MS and SS.The extent greatened with the aggravation of water stress.φPSâ…¡and ETR had the same trend with Fv/Fm and Fv/F₀.After re-watering,all the chlorophyll fluorescence indexes came back to the level of CK when stress was not very severe,whereas they could not recovered to the level of CK when stress was severe. 5.Relative water content(RWC) in leaves of Cupressusfunebris Endl.seedlings had the trend of decline and the extent greatened with the aggravation of water stress. After re-watering,RWC could come back to the same as CK when the stress was not very serious but it did not when the stress was too serious.During the period of stress, free water transformed to bound water so that the ratio of free water and bound water decreased.On the contrary,the bound water transformed to free water and so the ratio of free water and bound water increased.Soluble protein of the four treatments increased first and decreased afterwards as treatment was prolonged.MDA of the four treatments consistently increased as treatment was prolonged.But there was no significant difference between the neighboring treatments of the early and end stage, MS and LS of the middle stage.However,MDA of SS at any stage was higher than that of CK,and could not recovere to that of CK when re-watering.As for protective enzyme,SOD,POD,CAT,ASP,they went up continuously with the water content lowering in the soil.Re-watering caused SOD go down,but still higher than that of CK; POD,CAT,ASP come back to that of CK under LS,but not under serious stress.6.Soluble sugar and proline(Pro) increased consistently with the treatment prolonged and the stress aggravated.After re-watering they could decreased to that of CK.It means that they were good osmotic regulation matter.K⁺ declined obviously under water stress.But for Na⁺,it increased in the shoots of Cupressusfunebris Endl.at early stage,and also increased under LS and MS at middle stage,nevertheless,it decreased under SS at middle stage and all treatments of end stage.Ca²⁺,Mg²⁺ did not accumulate not only in the shoots but also in the roots of Cupressusfunebris Endl..The main osmotic regulation matter,soluble sugar and Pro were higher in the roots than that of in the shoots,while Na⁺ was opposite.Experiment showed that,Cupressus funebris Endl.could tolerate a certain extent water stress and adapt the changeable environment of "temporary water deficit" by the ways of adjusting photosynthetic physiology,protective enzyme active,osmotic regulation and its good compensatory growth ability.