Physiological Response To Soil Drought Stress In Three Ornamental Grasses

The drought resistance of 10 ornamentral grass species collecting from both at home and abroad was evaluated preliminarily in the experiment, on the basis of the results,three ornamentral grass species were selected as strong drought–resistance,medium drought–resistance and weak drought–resistance experiment materials to study the physiological characteristics under different drought stress in order to esplore their adaptation mechanism to drought stress.The main results and conclusions were followed:1. The drought resistance of 10 ornamentral grass species was evaluated preliminarily with subordinate function analysis according to growth indexes and physiological indexes.The drought resistance,s order of ornamentral grass from better to worse is Cortaderia selloana'White', Cortaderia selloana'Rosea', Deyeuxia arundinacea, Pennisetum alopecuroides'Caudatum', Cymbopogon goeringii, Pennlseturn alopecuroides, Themeda japonica, Pennisetum alopecuroides'Little Bunny', Eragrostis ferruginea,Eragrostis curvula. Strong drought-resistance (Cortaderia selloana'White'), medium drought-resistance (Pennlseturn alopecuroides) and weak drought-resistance (Eragrostis curvula) were chosen for the further study.2. The antioxidation enzyme activity such as SOD,POD,CAT,APX and the contents of antioxidation substance such as ASA and Car increased in the leaves of strong drought-resistance(Cortaderia selloana) under drought stress.The lower basic activity of POD indicated that the POD was,t the main enzyme eliminating H2O2 in Cortaderia selloana leaves. Compared with strong drought-resistance species, the activity of SOD,CAT,APX and the contents of ASA and Car decreased significantly in the leaves of Eragrostis curvula,which showed the metabolize of active oxygen was out of balance severely. The descending order of membrane damaging degree in 3 grass species could be listed as followed: Eragrostis curvul is highest, Pennisetum alopecuroides is medium, Cortaderia selloana is lowest under different drought stress.3. The results showed that the osmotic adjustment ability of these three ornamental grasses have something to do with stress duration. The osmotic adjustment ability of the drought sensitive variety Eragrostis curvula decreased with the elongation of stress time. In contrast, which of strong drought -resistant variety Cortaderia selloana changed slightly at early stress stage and constantly increased with the elongation of stress time. The osmotic adjustment ability of moderate drought-resistant variety Pennisetum alopecuroides was higher than that of Cortaderia selloana during water stress, but decreased with the intensity of water stress and the elongation of stress time. Furtherly,,its osmotic adjustment ability decreased mostly after rewatered. The main osmoregulation substance within the three grass species were different from each other; the soluble suger contributed most to osmotic adjustment ability, the soluble protein was the second,while the role of the free amino acid was smaller as for Cortaderia selloana. But the soluble suger and free amino acid contributed more to osmotic adjustment ability as for Pennisetum alopecuroides and Eragrostis curvul. The proline was not osmoregulation substance but drought stress sensitivity index.Under water stress, the inorganic ion such as K+, Na+, Ca2+, Mg2+ participated in ornamental grass osmotic adjustment, but K+, Ca2+ played the main roles.4. The net photosynthetic rate, stomatal conductance and transpiration decreased dramatically in the leaves of ornamental grass with the enhancement of drought stress intensity.But the decreasing extent of Pn in strong drought -resistant variety Cortaderia selloana leaves was the smallest and its recovery level was highest compared with the other two ornamental grass.The water utility efficiencies of Pennisetum alopecuroides and Eragrostis curvul decreased under drought stress.,while that of Cortaderia selloana increased at first then fell .The non-stomatal restriction had been the main factor of the Pn,s decrease in the leaves of Pennisetum alopecuroides and Eragrostis curvul since moderate drought stress.Until severe drought stress was non-stomatal restriction the main factor of the Pn,s decrease in the leaves of Cortaderia selloana.The contents of chlorophylla, chlorophyll b, chlorophyll a+b, carotenoids in the leaves of Pennisetum alopecuroides and Eragrostis curvul were all decreased under drought stress,but the contents of chlorophyll b in the leaves of Eragrostis curvul decreased slightly with no remarkable difference among treatments. Compared with the other two species, the contents of those in the leaves of Cortaderia selloana all increased when treated with drought stress. The ratios of Car and Chl increased in the leaves of Pennisetum alopecuroides while that in the leaves of Cortaderia selloana and Eragrostis curvul decreased with the reduction of soil moisture content.The three ornamental grass,s Fv/Fm,Fv/Fo,qP andφPSⅡall decreased under drought stress .The decrease extent of above chlorophyll fluorescence parameter was lower in strong drought-resistance variety and its capability of recover to the normal level was higher than those of the other two grass species. However, the weak drought-resistance variety was just the opposite.The non-photochemical Quenching (NPQ) in three ornamental grasses increased under drought stress,while the NPQ in strong drought-resistance variety Cortaderia selloana was the minimum. Correlation analysis showed that Fv/Fm, qP andΦPSII were more important chlorophyll fluorescence parameteres used as to evaluate photosynthesis of ornamental grass under drought stress.5. The content of ABA in the leaves of ornamental grasses increased under drought stress. Furthermore, the increasing degree of strong drought-resistance variety Cortaderia selloana was lowest and that of weak drought-resistance variety Eragrostis curvul was highest. IAA in the leaves of ornamental grasses decreased,but the decreasing degrees of Eragrostis curvula and Pennlseturn alopecuroides with no obvious difference was significantly higher than that of Cortaderia selloana. The content of GA of Cortaderia selloana increased under moderate drought stress and decreased under severe drought stress and that of Pennlseturn alopecuroides showed the opposite trend. GA of Eragrostis curvula decreased during water stress and the decreasing degrees increased with the enhancement of drought stress intensity.ZR content in the leaves of ornamental grasses all decreased under drought stress.The general trend of coordination among four endogenesis hormones was closing the stoma and restraining the growth.The lower ABA/ (IAA+GA+ZR) of Cortaderia selloana.indicated that drought stress had lesser effect on the growth, whereas drought stress had a major effect on growth of Pennlseturn alopecuroides under moderate stress and on growth of Eragrostis curvula under severe stress.6. The contents of Spm, Spd and the total polyamines all increased, but the content of Put decreased under drought stress. Spd played main role in enhancing drought-resistance of ornamental grasses. The ratio (Spd+Spm) /Put of three grass species all increased, furthermore, the ratio of strong drought-resistance variety was higher than that of weak drought-resistance variety.