| The possible effects of over-clipping on morphological and physiological characteristics of Trifolium repens, and the physio-ecological responses to over-clipping were studied in this paper. The experiment was conducted from June to September, 2005 in the Jinlin University, China (N 44°16' , E 125°47'). Vegetative plant materials of T. repens were transplanted (3 plants/plot) in each plot (0.6m×0.6m each) on June 6, 2005, and were watered daily during the initial 10 days after transplantation. The plants were defoliated originally in July 2, 2005. At defoliation, all plants were manually cut and left 1/4 leaves and 2cm stubbles. The experiment was composed of 5 treatments (every treatment with 5 replicates). Defoliation periodicity was 0, 10, 20, 30 and 40 days, respectively (i.e. Control, D10, D20, D30 and D40). The measurements commenced on July 2 and continued to September 10, and modules densities and shape 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. There was a significant positive correlation between the stolon density of T. repens and the other module densities (p<0.01). With the increase of defoliation frequency, module densities decreased gradually. Densities of stolons (elongated, new and total), leaves, roots and branches tended to be highest in D40, generally followed by Cont, D30, D20 and D10, which can be explained in two ways: firstly, moderate defoliation frequency destroyed partial apical dominance of the grass, which resulted in the increase of densities of stolons and branches. Secondly, moderate defoliation frequency improved light environment in the sward, growth of new leaves and photosynthesis rate of T. repens, which was in favor of plant growth and module density increase.2. With the change of defoliation frequency, number of branches, branch intensity, the differences of branching angle and stolon diameter among different groups were significant (p<0.01), which led to various branching patterns. Under the frequency of D40, higher branch density and stolon diameter with larger branching angle could enable the plant to stay and exploit more favorable microenvironment efficiently. On the contrary, over-clipping resulted in smaller branching angle and lower stolon diameter, which could enable the plant to reduce the chance of staying in unfavorable environment and'escape'quickly.3. T. repens showed remarked foraging character, which could be quantitatively described with formula of foraging intensity. Compared with the moderate defoliation, higher defoliation frequency led to lower architecture density and foraging intensity of T. repens. Compared with Control, the grass showed lower spacer length and higher branch density under D40, which was in favor of promoting the foraging intensity.4. With the increase of growth days, the stolons extended gradually. The phenomenon showed that the plant exploited microenvironment by expanding stolons, which led to the increased availability of soil resource. Spatial distribution patterns of stolons in 4 groups were different. Under the treatment of D40, the grass achieved maximal spatial utilization at the final measurement (96 days after transplantation), followed by Control, D30, D20 and D10, respectively. Moderate defoliation could improve over-compensatory growth of stolons and promote densities of stolons and branches, which resulted in extending of spatial occupation of the plant population.5. Module and total plant yields were affected remarkably by defoliation frequency (p<0.01). Compared with Control, total production of D40 treatment exhibited overcompensation, while D30 exhibited full compensation, and total production reducing significantly in D10 and D20 indicated either partial compensation or damage.6. Following long-term defoliation, caloric values of stolons and leaves were remarkable higher than unclipping control. However, the caloric value of roots was lower than that in Control group. The results showed that defoliation was in favor of both the development of stolons and leaves and transporting the higher caloric nurture to the aboveground modules. Caloric content in the modules (including roots, stolons and leaves) were highest in D40 than those in other groups, which indicated over-compensatory growth. Moreover, with the increase of defoliation frequency, more and more energy was gradually removed to leaves than roots and stolons.Our results have significant implications to grassland management and utilization. Firstly, better developing status after defoliation is in favor of plant biomass increase, which would be beneficial for sustainable grassland utilization. Secondly, the studies on compensatory growth of white clover responding to defoliation can help us establish reasonable defoliation regime to achieve optimal grassland management and obtain maximal grassland productivity. |
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