Ecophysiological Mechanism Of Interaction Between Hemarthria Compressa And Its Mixture Species

Limpograss (Hemarthria compressa) is a very important grass in the grassland husbandry system of Southern China, but it has some disadvantages such as slowly growth , stopping growth in cool-season, and the lower quality with ripe in autumn quickly. So to improve the yield , quality , productivity of soil , stable supply fresh forage of limpograss land, it is a good choice to apply the legume-grass mixture system , warm-season and cool-season complementary system. Limpograss inhibit growth and development of mixture species for its allelopathy . So to explore the ecophysiological mechanism of high yield and quality forages in the mixture community of limpograss, the interaction, characteristics of photosynthesis ecophysiology, canopy structure have been researched in the system mixed by limpograss and companion species. The results show that:1. The extraction solution of root, shoot, leaf of limpograss delay or inhibit the germination of other grass seeds for its allelopathy. Different concentration allelopathic substance extraction solution promote or inhibit the root and shoot elongation, some even make the roots deformity. After experiment, annual ryegrass (Lolium multiflorum ) and red clover (Trifolium pratense) are the better companion species of limpograss.2. The anatomy of leaf blades showed limpograss is C₄ plant with "Kranz anatomy "structure, while red clover is C3 plant, which decide their different pathway for initial products of photosynthetic fixation of carbon. The light compensation point of limpograss and red clover are 5.89 and 30.48μmol.m^-2.s^-1 respectively, but no light saturation point of limpograss even under 2200umol.m^-2.s^-1 light intensity. The light saturation point of red clover is 1517.71μmol.m^-2.s^-1. The optimum temperature of photosynthesis of limpograss and red clover are 28³6.5℃and around 27 °C, respectively. The daily change of net photosynthesis rate of limpograss is single peak curve in sunny day in January or July, the highest point in January is around 12:00 noon while that in July is about 11:00 a.m. The daily change of net photosynthesis rate of red clover is single peak curve in January and double peak curve in July, the highest point is 10:00 a.m. and 14:00 p.m., the lowest point is about 12:00 noon. Seasonal change of net photosynthesis rate is obvious, limpograss, higher in July and August, lower in winter, late autumn and early spring. The annual average photosynthesis rate of limpograss is higher than that of red clover , the same as the yield per unit in whole year.3. Limpograss and red clover are different from height, pasture of plant and leaf blade, tillers, and leaf area of canopy structure. According to the difference of the morphological and ecophysioloigical characteristics, construction a system mixed by perennial warm-season grass and cool-season legume can make good use of the incidence solar radiation from all orientation, and the higher light utilization ratio is . Limpograss, a light-like grass, with upper stem and leaf blade , smaller mean leaf inclination angle (MFIA) , higher light saturation point and utilization ratio, has little influence on the light utilization of the companion specie, red clover , for it can use the upper layer radiation of canopy. Red clover, with lower light saturation point and quantity of chloroplasts in the mesophyll cells, use the lower layer radiation under limpograss . So the system mixed by limpograss and red clover can take advantage of the space, time, productivity of land, and improve the utilization radio of radiation.4. The canopy structure and the light distribution are different in the communities monocultured and mixed by limpograss and red clover. Radiation penetration (TR) and diffuse penetration (TD) are different in the canopy for different height and components of plant, posture and distribution of leaves, which cause the different net photosynthesis rate in single plant and community. The canopy structure, a complicated system, change the parameters with the growth and development of plant. The optimum leaf area index (LAI) decide by light intensity and posture of plant, the plant canopy extinction coefficient (K) of high yield forage is much bigger in the up-middle canopy, that means the canopy can get more light interception. The meanleaf inclination angle (MFIA) affected the interception and distribution of solar radiation in canopy, illustrated how much the leaves get the light interception and have great influence on K . Radiation penetration (TR) and diffuse penetration (TD) decreased exponentially. Daily changes of photosynthesis of communities are relative to the predominant specie. The photosynthesis rate at different layer canopy has different contribution, the monocultured red clover group, middle layer> upper layer> lower layer, The mixture groups and monocultured limpograss group, upper layer > middle layer > lower layer. The photosynthesis rate in the upper and middle layer increased with more limpograss in the community. Mixture system cause the change of morphology characters such as tillers, height, diameter of shoot, which affect the biomass per plant and the total yield of community. The monocultuerd limpograss canopy , wasting some radiation, can intercept more radiation after mixing with limpograss. Among the mixture groups, the group mixed by 75% limpograss and 25% red clover is the best, which means the mixture community can produce high yield and quality forages if keeping a reasonable components and canopy structure.5. The yield of forage is poor in the early stage in the system mixed by limpograss and red clover. The nutritions of grass change a little with growth. The relative competition of limpograss is predominant in the mixture system, which cause the system damage about one year for short of red clover, so it is necessary to supply red clover seeds in the mixed system to keep the system. After experiment, the group mixed by 75% limpograss and 25% red clover is the best, yield amount to 12777.78 kg/hm2-DM, from the point of yield and quality.6. The system mixed by limpograss and red clover can make a reasonable canopy structure and change the ecotope of field. Under situation of mixture, the grass density is much bigger than that of monoculture. The weeds, growing under the grass canopy, can not get enough light and die. Mixture systems also change the weeds ecosystem ,which make them not propagate and keep the high quality grass population, reasonable canopy structure , high yield of forages.7. The water content of surface soil (0²0cm) fluctuated constantly in the system mixed by red clover and limpograss, mainly affected by rainfall. Limpograssgrassland system mixed with different percentage red clover can increase the nutrients of soil, such as organic matter 8.18% 16.09%, total N 6.25% 11.71 %, N 13.36%-17.43% , and the P or K level in the soil as well.8. In the limpograss- annual ryegrass complementary system , the two grasses belong to C4, C3 plant, with different optimum growth time, space niche and photosynthesis rate , and contribute different yield forage. Overseeding annual ryegrass into limpograss pastures in autumn can increase the yield of forage. The yield of forage get to 13254.6 kg/hm2 DM after harvesting 6 times (from Oct. 10 to July 14 next year), overseeding on Oct. 10 and overseeding rate 22kg/hm2. The total yield of forage by different overseeding rate (15kg/hm2, 22kg/hm2, 30kg/ hm2), increase 1749.0 kg/ hm2 DM, 1874.4 kg/ hm2 DM, 1515.5 kg/ hm2 DM respectively, which are higher than the yield of that without overseeding treatment significantly. The yield is the highest (13080.7 kg/ hm2 DM) which overseeding rate by 22kg/ hm2, and cure protein improve 750.9 kg/ hm2 DM, more than that of no overseeding treatment. Overseeding change the dominant species in limpograss grassland. Ryegrass is dominant position (56% of total production) during winter and spring, and can control weeds efficiently.9. Ryegrass does not affect the stability and persistence of limpograss grassland when it vanished from the complementary system. The community structure would be recover and the yield increase with the optimum growth time coming of limpograss. The emergerance, elongation and senescence of ryegrass leaf blades are controlled by genetic and environmental factors. So cutting at right time can control senescence of lower leaves and increased the yield of forage. The best overseeding time should be September to October for the limpograss-annual ryegrass complementary system in the humid subtropic area, from the point of forage yield and sustainable utility of limpograss grassland.