Study On Growth And Photosynthesis Characteristic Of Two Stylosanthes Guianensis Varieties Under Different Defoliation

The effects of defoliation on the growth, chlorophyll content and photosynthetic characteristics of two Stylosanthes guianenesis varieties was studied in potted plant. There were 9 treatments involving three defoliation intervals, 20d, 40d and 60d and three residual heights, 5cm, 15cm and 25cm respectively. The indexes of growth include plant height, regrowth speed, tiller number, biomass, fresh/dry ratio and stem/leaf ratio and winter-survival rate. The indexes of chlorophyll content include chlorophyll a, chlorophyll b, gross chlorophyll and chlorophyll a/chlorophyll b.The photosynthetic characteristics including net photosynthetic rate (Pn), stomatal conductance(Gs), intercellular CO₂ concenTrations (Ci), Transpiration rate (Tr) and water use efficiency (WUE).The results showed that the effects of defoliation on the growth, chlorophyll content and photosynthetic characteristics of two Stylosanthes guianenesis varieties markedly whether mixture or single grassland, the main representation was that:1) The net cumulate plant height of 9 treatments were extremely significant differences respectively after cutting whether mixture or single grassland. When defoliation interval was 40d, the net cumulate plant height of two Stylosanthes guianenesis varieties was highest; when residual height was 25cm, the height of Stylosanthes guianenesis cv. Reyan No. 13 was highest, the Stylosanthes guianenesis cv. Reyan No. 7 and two Stylosanthes guianenesis varieties mixture grassland were shortest.2) Whether mixture or single grassland, the regrowth speed of two Stylosanthes guianenesis varieties was fastest in July, August and September entirely. Frequent defoliation (20d) stimulated regrowth, highest residual height (25cm) reduced regrowth speed.3) The tiller number of two Stylosanthes guianenesis varieties increased with treatment carried out whether mixture or single grassland in whole experimental stage. When defoliation interval was 20d and residual height was 5cm, the tiller number of two Stylosanthes guianenesis varieties was least, they can not stimulated tiller to increase tiller number.4) Whether mixture or single grassland, the treatment of frequent defoliation and lowest residual height affected forage biomass, the biomass was lowest when defoliation interval was 20d and residual height was 5 cm, it was disadvantage of forage production of good quality and grassland construction.5) The stem/leaf ratio increased approximately with treatment carried out whether mixture or Stylosanthes guianenesis cv. Reyan No. 7 single grassland in whole experimental stage; For Stylosanthes guianenesis cv. Reyan No. 13, it increased in mixture grassland and reduced in single grassland. The stem/leaf ratio was highest entirely when defoliation interval was 60d and residual height was 5 cm whether mixture or single grassland.The change of fresh/dry ratio of two Stylosanthes guianenesis varieties presented"S"style with treatment carried out whether mixture or single grassland in whole experimental stage. The fresh/dry ratio was highest entirely when defoliation interval was 20d and residual height was 5 cm.6) The winter-survival rate of two Stylosanthes guianenesis varieties was lowest when treatment of highest frequent defoliation (20d) and lowest residual height (5 cm), it is inadvisable for forage production.7) The chlorophyll a, chlorophyll b and gross chlorophyll of two Stylosanthes guianenesis varieties increased whether mixture or single grassland, and chlorophyll a/chlorophyll b reduced, but chlorophyll a increased more than chlorophyll b in the same treatment.8) The Pn, Gs, Ci and Tr reduced with treatment carried out whether mixture or single grassland, but WUE increased.9) This paper has used the Related-Degree Theory of Grey- System and analytic hierarchy process (AHP) of fuzzy theory to evaluate comprehensive effect of defoliation on two Stylosanthes guianenesis varieties. The score of comprehensive assessment were that: 15cm20d >5cm20d>15cm40d>25cm40d in Stylosanthes guianenesis cv. Reyan No. 7 single grassland; 25cm20d>15cm40d>15cm20d> 25cm40d in Stylosanthes guianenesis cv. Reyan No. 13 single grassland; 15cm40d> 25cm40d>15cm20d >25cm20d in mixture grassland. The score of comprehensive assessment of 5cm60d and 5cm40d treatment were lowest.On the mowing cycle, the score of comprehensive assessment was that: 20d >40d >60d whether mixture or Stylosanthes guianenesis cv. Reyan No. 13 single grassland; bur for Stylosanthes guianenesis cv. Reyan No. 7 single grassland, it was that: 20d >60d> 40d. On the residual heights, the score of comprehensive assessment was that: 15cm >25cm >5cm, whether mixture or Stylosanthes guianenesis cv. Reyan No. 7 single grassland; but for Stylosanthes guianenesis cv. Reyan No. 13 single grassland, it was that: 25cm >15cm >5cm.