On Biology, Ecology Of Leersia Japonica And Its And Integrated Management

Leersia japonica (Makino) Honda), a paddy weed species, has caused serious damages to rice production in the suburb of Shanghai. In order to forecast its invasive potential, ecological risk and to control its damages, we conducted the researches on its population distribution pattern, sensitivity to glyphosate, bioaccumulation capacity to chromium (Cr3+), its ecological adaptability to temperature and soil water content, also on the the mechanical method by cutting them. The main results were concluded as follows:(1) The ecological importance values of L. japonica and its associated species were surveyed at abandoned paddy field and the ditch-pond wetland in the suburb of Jinhua city, Zhejiang province, a total of 28 weed species were recorded from these sites. The niche breadth and the overlaps of these weeds were calculated. Based on their overlaps, the two-dimensional ordination plot and minimal spanning tree of 28 weeds was drawn using the method of minimal spanning tree and Principal axes ordination. The results showed that:①The niche width of L. japonica in the studied area is 0.6434, Polypogon fugax (0.7957), Beckmannia syzigachne (0.7326), Ranunculus sieboldii (0.6728), Paspalum paspaloides (0.5734) and Alternathera phioxeroides (0.5340) had the similar niche as L. japonica.②The first six weeds having bigger niche overlaps with L. japonica were Polypogon fugax (0.5310), Beckmannia syzigachne (0.5131), Paspalum paspaloides (0.5011), Alternathera phioxeroides (0.3199), Ranunculus sieboldii (0.284) and Veronica undulata (0.2774).③On the two-dimentional ordination plot and minimal spanning tree revealing the ecological relationships of L.japonica with its associated species, we could easily find that L. japonica and Polypogon fugax, Beckmannia syzigachne, Paspalum paspaloide, Alternathera phioxeroides were located closely, indicating their similar ecological distribution and strong inter-specific competition.(2) we tested the photosynthetic and chlorophyll-fluorescence parameters of the Jiading population of L. japonica under natural condition and in a growth chamber treated with glyphosate, and compared with those of Jinhua population of L. japonica. Our experiments showed:①The actual maximal net photosynthetic rate of L. japonica is 11.8-8.10μmol C02·m-2·s-1, with light compensation point of 3.21-2.70μmol.m-2.s-1and light saturation point of 1234-1008μmol.m-2.s-1, revealing that L. japonica is a shady weed but also with well-adapted capacity to sunny environments;②the photosynthetic capacity of Jiading population of L. japonica is higher than that of Jinhua population; and③the sensitivity of Jiading population to glyphosate is lower than that of Jinhua population.(3) By laboratory simulation, the effects of dry time and cutting intensities on rhizome survival rata, AMD content and chlorophyll content of L.japonica were determined. The results showed that:①L. japonica had strong drought tolerance and suited arid circumatances well.②After treatment of rhizome water loss, AMD content of leaf increased rapidly with the increase of water lose rate, but had no obvious influence on rhizome survival rate and plant height, and some of the treatment could promote the growth of plant height of L. japonica.③Cutting treatment increased the number of new tillers of L.japonica substantially. So cutting treatment was not a good way to control L.japonica.(4) The impact of temperature stress at different levels of 35/30℃,25/20℃and 10/5℃on AMD content, proline content,chlorophyll content and photosynthesis of L. japonica were studied. The results showed that:①The chlorophyll content of L. japonica decreased under temperature stress, and reduced more obviously under low temperature stress.②Comparison with the control treatment, proline content of L. japonica under temperature stress increased obviously, especially under high temperature treatment, revealing its stronger ability to resist high temperature stress.③The AMD content of L. japonica under three levels of temperature stress ranked from high to low as low temperature stress to normal temperature treatment to high temperature treatment, showing its weaker resist to low temperature stress.(5) The effects of different soil water conditions on on the growth of L. japonica were tested. The results showed, with the decrease of soil water content, the leaf dry weight per unit area, chlorophyll content, biomass, net photosynthetic rate, stomatal conductance, transpiration rate and intercellular CO2 concentration declined, while the water use efficiency, the ratio of belowground/aboveground biomass, soluble carbohydrate content and proline content in leaf increased. Anayses showed that L. japonica could adapt to the soil water stress to some extent.③Soluble carbohydrate content, proline content and AMD content in leaf increased significantly after water stress and also increased significantly in various drought treatments, but not its root, showing higher osmotic adjustment ability of leaf than that of root.(6) In hydroponic experimental condition, we examined the bioaccumulation capacity of L. japonica to chromium, and its photosynthesis, physiological and root morphology. We found that:①Cr concentration in rhizome and leave of L. japonica increased from 0 to 40 mg.L-1 chromium (Cr3+), reaching 2292.00 mg.kg-1 with a bioaccumulation of 57.30 in rhizome when treated with Cr3+at 40 mg.L-1.②there was little influence of chromium from 10 to 40 mg.L"1 on photosynthesis, contents of chlorophyll a and b, intercellular CO2 concentration and stomatal limitation of L. japonica;③the proline content in leaves varied from low to high, then to low when treated with Cr3+from 10 to 40 mg. L-1, with a peak at 20 mg.L-1.④the tip number and root surface of L. japonica increased with the chromium concentration. The above results indicate that L. japonica could significantly accumulate chromium and has stronger tolerance to chromium, and it could be applied in the phytoremediation of Cr-contaminated soil and water.