| The change patterns of photosynthesis prosperities and physiological resistance of Dafozhi Ginkgo under drought stress were studied using 5-year-old potted seedlings as the experimental materials. This research provide some suggestions on the water management of Ginkgo cultivation in semi-arid and arid district. The main results are as follows:1,The chlorophyll contents and net photosynthetic rate of maturity and senescence leaves in Ginkgo decreased under drought tress. The correlation analysis indicate a significant positive correlation between the chlorophyll content and Pn in mature and senescent's leaves (r is 0.947 in mature leaves, while 0.960 in senescent's leaves). This result show that decrease in chlorophyll content of leafs is one of the contributing factors to the net photosynthetic rate drop off. In the early treatment, the low stomatal conductance induced by stomatal closure is the main reason of the falloff of the net photosynthetic rate. With the increasement of the arid treatment, nonstomatal limitation becomes predominant.In different times of Ginkgo leaves, the maximal photochemical efficiency(Fv/Fm) is reduced followed by the decreasement of photochemical efficiency of PSII. The number of reaction center(RC/CSo) and of active reaction center (RC/ABS) in different leaves of Ginkgo are decreased rapidly, while the energy absorption per active reaction center (ABS/RC) and the energy passed to the QA (TRo/RC) are increased. At the same time, Sm, N and Mo in different times of Ginkgo leaves are increased, while To and cpEo are decrased. These results mean that dought tress decreased the energy efficiency of PS II, implied that reaction center absorbs more light energy and more extra energy are released in the form of heat dissipation, indicate more electrons transmittance and accumulation of QA, decrased electron transport capacity in PS II acceptor side.The electron transport chain is more stable with subtle energy vibration in mature leafs.On the contrary,it is inhibited with little driven energy in senescent's leafs which resulted in more deep inhibition of photosynthesis.2,The leaf relative water content in mature leaves of Ginkgo can maintain at the high level, while in senescent's leaves decreased quickly. The early stages of drought, the activities of antioxidant enzymes in mature and senescent's leaves inceased to remove oxygen radicals. As the drought aggravated, the accumulation of oxygen radicals decreased the activities of enzyme, resulting in unbalanced of the production and scavenging of oxygen radicals, membrane permeability increased. In order to maintain the balance of intracellular osmotic potential, osmotic adjustment of plant cells (proline and soluble sugar) increased to control several times, keeping osmotic balance of cells, maintaining the normal physiological cell metabolism.The drought stress resistance are different in different times in Ginkgo leaves. Under drought conditions, SOD may not be important inactive oxygen radicals scavenging enzymes in mature leaves of Ginkgo, while SOD played an important role in scavenging reactive oxygen radicals in the aging of leaves. |
