| The drought resistance of six Lavender species, which are Lavandula vera, L. stoechas cv. Pedunculata, L. angustifolia cv. Munstead, L. stoechas, L. angustifolia and L. angustifolia cv. Provence Blue, were evaluated comprehensively. The change rule of physiology characteristics (including enzyme activity, osmolytes and membrane permeability etc.) and photosynthetic characteristics (including chlorophyll, net photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency and intercellular CO2concentration) were investigated under light, moderate and heavy drought stresses for0,10,20,30and40days using the negative pressure water supplying and controlling device to control soil volumetric moisture content in order to understand the drought resistance characteristics and mechanism. The main results are as follows:1) Growth responses to drought stressWith the increase of drought stress intensities, the growth of6species was seriously affected, and they stopped growing under the heavy drought stress. At the same time, the biomasses of shoots and roots were significantly reduced while more biomass was allocated to the roots, and the root to shoot ratio was increased as well.2) Physiology and biochemical responses to droughtThe relative water content (RWC) of6species showed a declined trend, and the RWC under light drought stress declined slower, and the range was from25.66%to64.22%, with the increase of drought stress intensities, the RWC was significantly reduced, L. angustifolia was only39.02%, which was the lowest among6species. The relative electronic conductivity (REC) of leaf followed an increasing trend. In which, the REC of L. stoechas cv. Pedunculata with poor drought resistance was increased by300%compared to the control. And that of L. stoechas with strong drought resistance showed a lowest increasing range which indicated that the plasma membrane was not severely damaged.The malondialdehyde contents (MDA) of6species were increased with the increase of drought stress intensities, and L. stoechas, L. angustifolia, L. angustifolia cv. Munstead and L. vera were slight decreased during10to20days, which suggested their ability to adapt the drought stress. The MDA content of L. stoechas was below30umolg"1when it was treated for40d, which was the highest among6species and performed strong drought resistance. So, it could be concluded that MDA can be used as a drought stress sensitivity index and the soluble sugar content might play a role for osmotic adjustment.The solube sugar content (SSC) showed an increasing trend under drought stress. The SSC of L. stoechas with strong drought resistance was significantly increased, and the increasing extent was about423.82%under the heavy stress, so it relieved the plasma membrane damage caused by MDA accumulation; In contrast, the SSC of L. stoechas cv. pedunculata with poor drought stress was not obviously increased, and which were the lowest among6species.The antioxidation enzyme activity (SOD and CAT) of6species showed the up and down trend under the drought stress from0to40days. The SOD and CAT activity of L. stoechas with strong drought resistance was significantly higher than other5species with the peak value stressed for20days. With the increase of drought stress intensities, the SOD and CAT were declined obviously. And they were were significantly higher under the light stress than those under the moderate and severe drought stress (169.73u·g-1and72.54u·g-1·min-1respectively, P<0.05). While the change of SOD and CAT of L. angustifolia cv. Munstead with poorest drought resistance was not obvious, which suggested that SOD and CAT might not be its main enzyme eliminating H2O2.3) Photosynthesis responses to the drought stressWith the increase of drought stress intensities, the Chl a, Chl b and Chl (a+b) contents of L. angustifolia cv. Munstead and L. angustifolia showed thegradual decline trends, while the other4species were the increasing trends; On contrast, the variation pattern of Chl (a/b), Chl a, Chl b and Chl (a+b) were opposite. The total chlorophyll content of L. angustifolia cv. Munstead with poor drought resitance was only0.56mg·g-1under the heavy drought stress, which was significantly lower than other5species.The net photosynthetic rate, transpiration rate and stomatal conductance decreased dramatically in the leaves of6species with the increase of drought stress. But the decreasing extents of Pn and Tr in species with strong drought resistance were the lowest compared with other species. The water use efficiencies of L. stoechas showed a continuious downward trend with the increased drought stress, which indicated that the non-stomatal limitation of photosynthesis strated under moderate drought stress; while the other5species showed a down and then up trends, which indicated that the stomatal limitation was the main constraint under moderate drought stress. And the intercellular CO2consistence were increased gradually under drought stress.4) Comprehensive evaluation of drought resistanceThe RWC, REC, MDA, SSC, SOD, CAT6physiological indexes were evaluatied comprehensively using the subordinate function method,a preliminate evaluation of their drought resistance to40d of6lavenders.The order of drought resistance of6species were L. stoechas> L. angustifolia> L. vera> L. angustifolia cv. Provence Blue> L. stoechas cv. Pedunculata> L. angustifolia cv. Munstead. |
