A Study Of Application Of Alnus Cremastogyne To Vegetation Restoration On Beach Of Donting Lake

The Dongting Lake Region is flat in topography, and every year in the flood period the "FourRivers" and "Three Outlets" of Yangtze River bring large quantity of silt into the lake to bedeposited, amounting to be 0.1 billion tons every year, which forms broad area of fertile beaches.Peak water level in high water period may be 10m higher than the lowest level in low water period.The deposited silt in a year is approximately 98.4 million cubic meters in average, depositing up thelake bottom by 3.7cm each year and thus making the water depth gradually shallow. Area of beachenlarges at an average speed of 4,000 square ha per year, which is a favorable basis for the formationand enlargement of wet land resources. However, most usable islets and beaches are submerged todifferent extent during flood period; as a result, there are relatively strict requirements for forestationtrees of vegetation restoration in such areas. Firstly, the trees shall be able to endure flood forrelatively long time, and secondly, the trees shall be able to grow at relatively high speed undersubmergence stress. On such a background, Alnus Cremastogyne is to be introduced into theDongting Lake Region to be forested together with varieties such as poplar and osier, aiming for anecological system which integrates ecological, economical and social benefits. The study measuredthe photosynthetic physiology indexes of four Alnus Cremastogyne families under submergenceconditions by LI-6400, which is manufactured by LI-COR, and demonstrated the applicationprospect of Alnus Cremastogyne to the forestation on beaches of Dongting Lake by considering theactual field forestation conditions. The study results indicated that:(1) Main physiological factors that affect net photosynthetic rate of Alnus Cremastogyneconsist of photosynthesis active radiation (PARi), relative humidity of air (RH-R), intercellularconcentration (Ci) and concentration of CO₂ in air, however, the factors affecting net photosyntheticrate varies with different submergence period. Photosynthesis active radiation (PARi) is observed tobe the critical factor, which decides the tendency of net photosynthetic rate, and concentration ofCO₂ in air to be the second.(2) During the submergence stress period, light saturation points of the four families of AlnusCremastogyne are obviously lower than those grow under normal conditions. The developing law oflight saturation point of four families are basically identical to that of maximum net. photosyntheticrate, meanwhile, it is also discovered that light saturation point is positively correlated to maximumnet photosynthetic rate, indicating that the increase of light saturation point enhances utilization oflight energy by the plants. K-2 achieved peak value after being submerged for more than one month,i.e. October 4, and the net photosynthetic rate reached maximum value as well. However, no obviousdifference was found on the light compensation point from that of Alnus Cremastogyne under normal conditions. Apparent quantum efficiency was ranged in 0.019-0.035, which was much lessthan the normal value of Alnus Cremastogyne, 0.032-0.046 mol.mol^-1, and less than apparentquantum efficiency of ordinary plants (0.03-0.05 mol.mol^-1).(3) During the submergence stress period, the CO₂ saturation points of four families were in therange of 1270-540 umol. mol^-1. Differences among families were obvious and were rather marked indifferent submergence period. No great difference was observed between the CO₂ compensationpoints and those of Alnus Cremastogyne under normal growing conditions.(4) Except K-2, the four families were not observed with obvious changes of Fv/Fm valuesduring the 35 days of submergence. The Alnus Cremastogyne fit well during the submergenceperiod with no obvious photo inhibition. The change of photochemical efficiency qP is relativelyobvious for the same family during difference periods. For H-1 and H-11, the qP values decreasewith the time of submergence, which is most obvious at the time of 15 days submergence, indicatingthat the plants are photo inhibited at the time. The photochemical quenching qP values of K-2 andK-10+ are relatively small during initial submergence (about a week of submergence) and end ofsubmergence (around 35 days of submergence). Especially for K-10+ at initial submergence, the qPvalue decreases rapidly. The values for family of H-1 and H-11, however, retains at relatively highlevel. By regression analysis between PhiPS2 and light intensity, it was discovered that duringdifferent submergence period and among different families, the relationship between PhiPS2 andlight intensity were obviously exponent functions, i.e. Y_PhiPS2=Ae^-bx, while R² were all above 0.95and some even reached 0.99.(5) Based on the physiological and ecological property of Alnus Cremastogyne and thehydrologic performance of lake regions, suitable introducing regions of Alnus Cremastogyne in lakeregions are divided as follows:â‘ For forestation by cremastogyne on exterior beach of DongtingLake where there are water flows, rapid growing and high-yield forest base can be planned wherethe annual average submergence days are less than 40;â‘¡For beaches where annual averagesubmergence days are in the range of 40-80d, Alnus Cremastogyne can be introduced to be forestedtogether with poplars, and industrial material forest, snail control forest and wave preventing andembankment protecting forest can be constructed. Poplars are submergence endurable as well, theroot system of which is relatively deep. Root system of Alnus Cremastogyne is relatively shallow.Combination of the two varieties can fully utilize the nutrition elements in various layers of the soil.Moreover, roots of Alnus Cremastogyne employ nodule bacteria, which are nitrogen-fixing andenhance the biological throughput. The lower root systems interlock mutually, stabilizing and fixingthe soil, further reducing the soil erosion by water flows, buffering the energy of waves and reducingthe impact on embankments;â‘¢for beaches where annual average submergence days are more than 80d, if no engineering measures such as trench excavation and ridge raising are adopted, then thesurvival rate of forestation and timber throughput will be rather low, and therefore AlnusCremastogyne is not fit to be used for forestation.