The Study On Herbages Yield Effect And Ecophysiological Mechanism In Eucalyptus Grandis+Herbage Inter-cropping System

For the synthetic improvement of the degraded slope farmland environment in the high precipitation area of western China, adjustment of the agricultural structure, and exertion of the important effect of forest and grass ecosystem in converting agricultural lands to forestland, these herbages were inter-cultivated in Eucalyptus grandis forest with different canopy densities. The purpose of the study was also providing the essential basic theory for the sustainable management of the pattern of tree and herbage intercropping system. Eucalyptus grandis was widely introduced tree species in Sichuan, and was the preferred tree species in sloping land conversation project area and re-vegetation area. Dactylis glomerata L., Lolium perenne L. and Hemarthria compressa (L.F.) R..Br. which had very strong adaptability in the area were chosen. Those kinds of herbage were fit the climate of the high precipitation area of western China and were extended in production at the present time. By investigating the data of the microecological surrounding of forestland, the yield and physiological foundation of three herbage species, we found the growth regularity, yield effect, ecophysiological regularity of the three herbage species and the features of microecological surrounding factor distribution in space and time in the various models of herbage inter-cropping system. The interacting mechanism between microclimate and herbage was also analyzed. The conclusion was given as follows:1. In the forest- herbage inter-cropping system, the micro-ecological environment of the forest land was changed. The canopy density had the greatest effect. Following the incensement of the canopy density changing, the micro-ecological environment factors, including relative light intensity, air temperature, land temperature, air relative humidity and soil water content, their day-changing character and distribution regularity in space were all changed a bit than CK(without shading). Based on the data of the relative light intensity, air temperature, air relative humidity and soil water content, the regression function of the four micro-ecological environment factors with canopy density was simulated. In the inter-cropping system, the change scope of daily average soil temperature diminished with the incensement soil depth and temperature ascend lagged. There were minus correlations between different depth soil temperature and canopy density. The greater of canopy density, the lower of the average soil temperature.The correlations between daily average light intensity (P) and canopy density (X):P_{(daily average light intensity)}=-571.09X+745.86 (R²=0.9938)The correlations between daily average air temperature (P) and canopy density (X):P_{(daily average air temperature)}=-1 .5036X+28.2 1 3 (R²=0.8449) The correlations between daily average air relative humidity (P) and canopy density (X):P_{(daily average air relative humidity)}=2.6918X+56.024 (R²=0.8478)The correlations between average soil water content (P) and canopy density (X):P_{(average soil water content)}=0-218X+0.1514 (R²=0.8684)2. During the growth, the stem diameter, the leaf length of the herbages ascended gradually with time processed, the leaf width changed less. The average layer height and the average height declined gradually with the incensement canopy densities. The average stem diameter of D. glomerata and H. compressa declined gradually. The average stem diameter of L. perenne increased at first, and then decreased. The average leaf length of L. perenne and H. compressa declined gradually, but declined very slowly. The average leaf length of D. glomerata increased at first, and then decreased when the canopy density reached about 0.73. The average leaf width of the three herbage species declined gradually, but declined very slowly. The root biomass of D. glomerata and L. perenne declined gradually, that of H. compressa increased at first, and then decreased when the canopy density reached about 0.54. The yield of D. glomerata and L. perenne increased at first, and then decreased, that of H. compressa declined gradually.3. As canopy densities increased, chlorophyll contents (Chl) of three herbage species increased, and chlorophyll a/b (Chla/Chlb) decreased. Chlorophyll contents (Chl) of three herbage species were higher than CK, and chlorophyll a/b (Chla/Chlb) were less than CK. Daily photosynthesis of three herbage species demonstrated a curve with one peak. Light compensation point (LCP) and light saturation point (LSP) of the three herbages declined gradually with the enhanced canopy densities, but apparent quantum yield (AQY) increased gradually. As canopy density increased, PS II efficiency Fv/Fm) of D. glomerata and L. perenne increased at first, and then decreased when the canopy density reached about 0.6. The Fv/Fm values of D. glomerata and L. perenne were higher than that of H. compressa, but under the shading the increment of the value was lower than that of H.compressa. Daily transpiration rate of three herbage species demonstrated a curve with one peak. Daily average transpiration rate of three herbage species declined gradually. Daily average net photosynthesis rate of three herbage species increased at first, and then decreased. Leaf water potential of three herbage species declined gradually.Soluble sugar(SS) and soluble protein(SP) of the three herbages declined gradually with the incensement canopy densities, and were smaller than CK. Malondialdehyde(MDA) increased gradually with the incensement canopy densities, but increase scope minished when the canopy density reached about 0.73. The change rules of activity of superoxide dismutase (SOD) were same with MDA, which increased gradually with the incensement canopy densities. Proline content (Pro) of the three herbages declined gradually with the incensement canopy densities, and were smaller than CK apparently.4. The correlation between all physiological indexes of the three herbages and canopy density was very remarkable. The average subordinative function method was used to carry out a comprehensive evaluation and a comparison research on the three herbages. The shade-tolerance adaptability of the three herbages was in an ordination of D. glomerata > L. perenne > H. compressa. In the forest- herbage inter-cropping system, H. compressa demand for light intensity very strongly, basing on biomass, it can plant when the canopy density was below 0.56. D. glomerata and L perenne demand for light intensity were less strongly than H. compressa, those could grow well under certaint shading. When the canopy density was below 0.67 for D. glomerata and below 0.70 for P. ryegrass, that can get good biomass.