| The plant organs foraged partially or entirely by herbivores are common in grassland ecosystems.The response of plants to herbivores was not only affected by the characteristics of ontogenic stage,but also affected by foraging time,foraging intensity and recovery time after foraging.During the long evolutionary process,plants adapt to foraging disturbance by changing phenotypic and physiological characteristics after the plants foraging.Tillers number increased due to the breaking of apical dominance,photosynthetic rate of leaves increased,the storage resources reallocated after foraging,which cloud explain the compensatory growth of plants.There are three forms of compensatory growth,which are under-compensation,complete compensation,and over-compensation.Compensatory growth can be evaluated by a variety of quantitative indicators,and previous studies on compensatory growth mainly focused on biomass or the number of sexually propagated offspring.However,for perennial clonal grasses,the compensation growth on the number of vegetative reproduction is more important for the continuous regeneration of plant populations in grassland ecosystems.Hordeum brevisubulatum is a quality forage grass with short rhizomes,which was prefered to foraged by all kinds of livestocks.This grass species is widely distributed in Songnen grasslands of northeastern China,and often forms a single dominant species community.The H.brevisubulatum meadow is an excellent grazing land.Therefore,the population of H.brevisubulatum in natural grassland and three-year-old experimental population of H.brevisubulatum in artificially planted grassland were chosed as the research objects.Our study was conducted with different removing apex intensities(0%,25%,50%,75% and 100%)and different clipping intensities(control,light,medium and heavy)in different growth stages(jointing stage,booting stage,heading stage and flowering stage)to simulate foraging of herbivores,the samples were sampled at the same interval periods after clipping.The response of the number and composition of vegetative reproductive modules,biomass,productivity of tillers,the ability of vegetative reproduction,the photosynthetic physiology and the change of compensatory index to simulate foraging were analyzed.Which not only help us to explore the inherent mechanism of compensatory growth of clonal plants in theory,but also conduce to sustainable production and rational utilization management of grassland ecosystem.We obtained the important results as follows.(1)There were different response on the number of vegetative reproductive modules to different treatments of H.brevisubulatum population.Among them,young clones(tuft diameter less than 10 cm)in natural population were sensitive to remove apex.The number of buds cloud significantly increase after damage under 25%,50% and 100% removing apex intensities in jointing and booting stages,under 25% and 100% removing apex intensities in heading stage,under 75% removing apex intensity in flowering stage.The number of juvenile tillers significantly increased under 100% removing apex intensity in jointing stage.The number of tillers significantly increased under 75% and 100% removing apex intensities in jointing stage,under 25% and 100% removing apex intensities in booting and heading stages,under 100% removing apex intensity in flowering stage.From jointing stage to flowering stage,the change on the number of tillers after damage generally showed that the earlier the stage of removing apex occurred,the increase on the number of tillers after damage was more obvious.Different clipping intensities in booting and flowering stages significanlty increased the number of buds in experimental population at the first and second weeks after clipping.More than three weeks after clipping,light and medium clipping still significantly increased the number of buds.In most cases,clipping treatments cloud increase the number of juvenile tillers,and the increase was more significant when clipping occurred in jointing stage.Clipping treatments cloud decrease the number of tillers,and the decreasing trend gradually weakened with the prolongation of the recovery growth time after clipping.The number of buds,juvenile tillers and tillers for experimental population of H.brevisubulatum population when clipping in jointing stage were higher than flowering stage.(2)There were same response on the composition of vegetative reproductive modules to different treatments of H.brevisubulatum population.No matter for most tuft degrades of natural population after different intensities of removing apex,or for experimental population after different intensities of clipping,the damage treatment cloud increase the ratio of buds and decrease the ratio of tillers,and there was no significant effect on ratio of juvenile tillers.The increasing treand of buds ratio and the decreasing trend of tillers ratio gradually weakened with the prolongation of the recovery growth time after clipping.(3)There were different response on the matter productivity to different treatments of H.brevisubulatum population.In most cases,the biomass of vegetative tillers and total biomass of young clones in natural population cloud significantly increase after removing apex.The biomass of vegetative tillers and total biomass were higher when removing apex in earlier stage than later stage,and with the increase of age classes(tuft diameter degrades),the negative effect of removing apex on biomass will increase.In most cases for experimental population,light and medium clipping in jointing stage cloud significantly increase the biomass of vegetative tillers,and heavy clipping significantly decreased the total biomass.There was no significant effect of clipping in flowering stage on biomass of vegetative tillers,but different clipping intensities in flowering stage significantly decreased the total biomass.The negative effect of clipping on the biomass of vegetative tillers and total biomass gradually weakened with the prolongation of recovery growth time after clipping.The negative effect of clipping on the biomass when the damage treatment occurred in earlier stage were lower than later stage.(4)There were different response on the ability of vegetative reproduction to different treatments for H.brevisubulatum population.Among them,the vegetative reproductive of buds and total cloud significantly increase after removing apex for young and old clones(tuft dameter greater than 25cm)in natural population.In most cases for clones in experimental population,clipping cloud increase the vegetative reproductive of buds and total,and the promote effect of clipping would gradually decrease with the prolongation of recovery growth time after clipping.The promote effect of treatments on the vegetative reproductive of buds and total when the damage treatment occurred in earlier stage were higher than later stage.(5)There were some difference on the compensatory growth to different treatments for H.brevisubulatum population.Among them,the biomass of vegetative tillers,total biomass,buds number,juvenile tillers number and tillers number of young clones for natural population after removing apex mainly showed over-compensation and complete compensation.For the clones of other age classes,the total biomass showed under-compensation,the biomass of vegetative tillers,buds number,juvenile tillers number and tillers number mainly showed complete compensation and undercompensation.The biomass of vegetative tillers of clones for experimental population showed over-compensation and complete compensation when clipping in joingting stage,the total biomass showed complete compensation and under-compensation.While the biomass of vegetative tillers showed complete compensation and the total biomass showed under-compensation when clipping in flowering stage.The number of buds showed over-compensation at the first four weeks after clipping,and showed complete compensation when over 4 weeks after clipping.The number of juvenile tillers showed over-compensation and complete compensation and the number of tillers showed under-compensation when clipping in jointing satge at the first four weeks after clipping,while the number of juvenile tillers showed complete compensation and under-compensation and the number of tillers showed complete compensation when over 4 weeks after clipping.The number of juvenile tillers showed over-compensation and complete compensation when clipping in flowering stage at the first three weeks after clipping,while showed complete compensation and under-compensation when over 3 weeks after clipping.The number of tillers showed under-compensation when clipping in flowering stage.(6)For the response of physiology to clipping for H.brevisubulatum population,the photosynthetic rate of leaves increased significantly over a long periods after clipping(8d).The chlorophyll content,malondialdehyde content,the superoxide dismutase and peroxidase dismutase content of leaves increased in different degrees after clipping,while the proline content and the souble soluble sugar content decreased after clipping.The soluble sugar content decreased firstly in roots and secondly in leaves.The response process of the above physiological indicators mainly occurred and reached a significant level in the periods from 1 to 4 days after clipping.The results of our study indicated that removing apex and clipping under different intensities in different growth stages had different effects on the vegetative reproductive,biomass,productivity of tillers and compensatory index of H.brevisubulatum population.The conclusions were as follows:(1)The matter productivity and vegetative reproductive of young clones for H.brevisubulatum population mainly showed over-compensation,which indicated that the young clones for H.brevisubulatum population had stronger tolerance to grazing.(2)After the jointing stage,when the damage time was earlier,the adverse effect of damage treatments was less,and the clones would showe over-compensation more easily.Therefore,it is proposed that the recovery ability of H.brevisubulatum grassland after foraging was stronger when the grazing treatment occurred in earlier period of growth.(3)After a certain period of recovery growth,the biomass and the vegetative reproductive may reach over-compensation or complete compensation growth after moderate foraging.Therefore,it is suggested that the grassland of H.brevisubulatum can obtain higher productivity and economic value after moderate grazing and utilization.(4)There were many ways of mechanism of compensatory growth for H.brevisubulatum population to removing apex and clipping.For the physiologically,the net photosynthetic rate of leaves cloud significantly increase and the soluble sugars in roots will redistribute.For the recruitment and regeneration of population,the secondary growth of underground meristem began to produce compensatory vegetative buds after the broken of top dominance when froaging.The buds of vegetative reproductive then grow and develop into juvenile tillers and tillers.The decrease of leaf density and increase of spatial resources after foraging promoted the process of vegetative reproductive and buds flow,then mad it showe compensatory growth state after moderate foraging. |
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