| This paper takes the leguminous plant white clover(Trifolium repens) as the main research object for the study. Under the different fertilizations (P / K) and defoliations (D10/D40) , the possible effects on morphological and physiological characteristics of Trifolium repens, and the physio-ecological responses to these experimental treatments were studied in this paper. The experiment was conducted from June to September, 2007 in the Jilin University, China (N 43°54'27.5″,E 125°15′34.7″). Vegetative plant materials of T. repens were transplanted (3 plants/plot) in each plot (0.6m×0.6m each) on June 6, and were watered daily during the nurturing period after transplantation. 2007, June 7 to July 13 is the time of nurturing period. There are two kinds of frequency of defoliation, that is, every 10 days and 40 days , recorded as D10 and D40. Phosphate (CaHPO4) and Potassium (K2SO4) were applied in this experiment. these experimental, plots were deal with the fertilization were respectively marked as P, K, D10P, D10K, D40P and D40K.In addition to a control group (CK) ,the experiment was composed of 9 treatments (every treatment with 5 replicates). Fertilization treatment is one-time treatments (CaHPO4: 7.5g/m2, K2SO4: 15g/m2),began in July 10. The plants were defoliated originally in July 14, 2007. At defoliation, all plants were manually cut and left 1/4 leaves and 2cm stubbles. The measurements commenced on July 14 and continued to September 15, and modules densities and morphological character were measured on each weekend. On September 13, all of the plants were removal from the field for subsequent measurements of biomass and caloric value of modules. The main results were summarized as the following:1. Fertilization and defoliation affects significantly on stolon density of T. repens. In detail, total growth rate of the D40P group's total stolon density is higher than that of control group. As for the positive effect on stem thickness of T. repens. D40, Fertilization group and potassium-fertilization is more significant than D10, defoliation group and phosphorous-fertilization, respectively. Proper defoliation and phosphorous-fertilization interactively promote the growth of stolon density of T. repens, while the effect of D40K treatment is insignificant. The diameter of the stolon under heavy defoliation, is smaller than that under light defoliation; potassium and phosphorous fertilization has insignificant effect on the diameter; Fertilization or defoliation factor respectively could cause a narrow diameter range and low diameter measurement; The interaction of fertilization and proper defoliation cause a wider range of diameter and larger measurement of diameter. 2. The effect of fertilization and defoliation on the leaves density of Trifolium repens was significant. Under heavy defoliation treatment, the leaves density is much more lower than that under little defoliation and no defoliation; phosphorous affects the foliage thickness greater than potassium; Potassium fertilization only has a similar effect on foliage thickness with 40-day defoliation; D40P treatment can cause the maximum measurement of leaf density. The experiment result indicated that the interaction of phosphorous and defoliation has a significant effect on the growth of the foliage thickness of T. repens (P<0.01), while the interaction of potassium and defoliation has insignificant effect (P>0.05). The interaction of D40 and phosphorous has a positive effect on the growth of the leaves density of the T. repens. Compared with the control group, which is not interfered by defoliation, defoliation group heavily affected the foliage characteristics of the experimental group. Highly-frequent defoliation will decrease the foliage area. In the experiment the potassium and phosphorous fertilization has insignificant effect on the foliage area.3. Fertilization and proper defoliation would promote the reproduction of the root, but excessive defoliation has a negative effect on the growth of the root of T. repens. According to the experimental data, the root density of D40P is almost two times as large as that of CK, while the root density of D40K increased by only 13% compared with that of CK, which indicated that the interaction of phosphorous and defoliation has a significant effect on the growth of T. repens, while the interaction of potassium and defoliation is insignificant. 4. The experiment result indicated that, the branch angle of K, D40, D40K and D40P groups mainly ranged from 40-80°,with a few in the larger angle range. Potassium fertilization only or proper defoliation or the interaction of fertilization and defoliation would apparently increase the branch angle. As for the interaction of fertilization and defoliation, the interaction of phosphorous with potassium is better than with potassium.5. Fertilization could effectively promote the elongation of leaf-stem, increase the plant's vertical height and increase the capacity of the T. repens to exploit the resources in the vertical space. The phosphorous fertilization group has the longest leaf-stem, with a seasonal average of 6.5cm, then the potassium fertilization group, with a seasonal average of 6.3cm, 0.3cm and 0.1cm higher than their respective control group. CK group has a seasonal leaf-stem average of 6.2cm. Defoliation has an effect on the leaf-stem length, decreases the height of the T. repens, which indicated the morphological plasticity of T. repens.6. The spatial distribution of stolons of T. repens widens with time, which indicated that the T. repens moves by the stolons and occupies the bare field, which increase the rate of resource utilization. Different treatment causes different spatial distribution. D40P group has the largest distribution area, while the D10, D10K and D10P groups the smallest. The differences between D40, D40K and CK are insignificant, the phosphorous and potassium treatment causes longer creeping-stem and fewer branches. D40P treatment causes the wider range of creeping stem distribution and more branches, which cause the larger distribution of the T. repens population, the better utilization of environmental resources, surviving probability of creeping stem per unit area and the adaptability of the population.7. The study indicated that, either single-factor disturbance or bi-factor disturbance would affect the biomass of T. repens. Single fertilization or defoliation has little positive effect on the accumulation of biomass, while the interaction of fertilization and defoliation has a significant effect on the accumulation of stem and foliage biomass. Excessive defoliation greatly affects the biomass accumulation. Either fertilization or defoliation or their interaction has insignificant effect on root net weight, and the excessive defoliation would lower the biomass of root accumulation, which is unfavorable for the plant to absorb the nutrient in the soil and affect the biomass above the ground.8. Different fertilization and defoliation treatment has a significant effect on the energy distribution among different components. Under D40P and D40K treatment the accumulation of stem and foliage is significantly higher than that under other treatment and the control group, the energy accumulation of root is similar to control group and significantly higher than that under other treatment, which is super-compensation growth. Energy accumulation in root, stem and foliage under D10P, D10K and D10 defoliation treatment is significantly lower than that of control group, which is compensation growth.By the study of the interactive effect of fertilization and defoliation on the T. repens, through the observation and analysis of the law of the seasonal and yearly change of the population biomass, the module density and the spatial distribution, the most proper defoliation period, frequency and proper fertilization could be worked out, providing a theoretical basis for the proper exploitation of grassland, which is meaningful for the regeneration and sustainable use of grass. |
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