【作者】 高莹；

【导师】 王德利；

【作者基本信息】 东北师范大学 ， 生态学， 2008， 博士

【摘要】 植物放牧耐受性是植物防御系统的重要组成部分,经历草食动物采食后的植物具有补偿性再生生长和提高繁殖水平的能力。本论文以羊草（Leymus chinensis）为对象,采用刈割模拟放牧干扰的手段,系统研究了植物耐牧性对模拟放牧强度、资源水平、竞争强度、克隆整合作用等因素的响应;深入探讨了在模拟放牧条件下,羊草启动补偿性再生效应的调节机制和生理基础。本文着重从植物对资源及非资源因素适应性的角度,阐释了在多个外部影响因子交互作用之下,羊草种群生长、发育、防御等不同功能之间的权衡,为进一步探讨动植物之间的协同进化与草地资源的合理利用提供一定的理论基础。本实验采用野外控制实验和盆栽控制实验相结合的方法,对羊草耐牧性的研究结果与主要结论如下:羊草具有极强的耐牧性,能够在不同条件下调整自身的适应性策略,面对外界放牧或刈割干扰等不利环境。天然草地上,生长季中后期的模拟放牧处理对羊草分蘖具有明显刺激作用。羊草增加了在冬性植株输出及休眠芽形成上的能量投入,其中,留茬8cm的中度模拟放牧处理对于翌年羊草的返青及种群的延续最为有利。人工草地上,羊草对于生长季前期的初次刈割处理、及生长季中后期的二次刈割处理做出了不同的响应。初次刈割后,羊草采取增加植株地上部分营养生长、控制新生分株数量的策略,种群得以迅速恢复。由于二次刈割处理后是羊草大量的芽和冬性植株形成阶段,因此,羊草此时采取先扩大种群密度、再增加新生植株或叶片生长的适应性策略。羊草种群密度对其营养生物量、繁殖生物量及芽的数量均有明显的制约效应,种群密度和刈割强度的交互作用（P≤0.05）共同影响着羊草的种群调节。轻度刈割处理后,羊草种群密度对地下生物量累积的限制作用增强（b=-0.9621）。在轻度放牧条件下,少量植物组织的损失并未威胁植物的存活,因此,羊草更多资源分配于植株地上部分恢复生长的需要;地上植株完全刈割（除去植株地上部分的100%）后,密度制约效应结果是对地上生物量累积的限制更为明显（b=-0.9929）,更多资源分配于植株地下部分。此时,完全刈割直接影响到个体的存活及种群的延续,因此,高密度条件下加大对植物地上生物量累积的制约,目的是保证植株的存活及营养繁殖的顺利进行。植物生长发育需要光照、水分、营养等必需资源的供给,因此,环境中资源可利用性对植物生长、繁殖及防御有显著的影响效应。单一资源与模拟放牧处理之间交互作用的结果,在低水分条件下羊草耐牧值下降程度（0.57）大于高水分条件下羊草耐牧值的降低（0.32）。可见水分与刈割之间的“协同型交互作用”加剧了资源限制与刈牧干扰因素对植物种群所造成的负面效应;而营养与刈割之间的“拮抗型交互作用”则缓解了这种负效应,减小植物的适合度的降低程度。因此,我们在限制资源模型（Limiting Resource Model,LRM）基础上,假设植物表现对放牧强度做出线性反应,并提出了简化的限制资源模型,进一步发展了LRM模型。基于两个营养强度、两个光照条件及两个水分条件的模拟放牧实验结果表明,环境中资源因子之间多存在强烈的交互作用,共同影响着羊草的生长、繁殖和耐牧性。其中,光照资源是植物生长发育的首要影响因子。低光照条件下植物表现出地上部分徒长,缺少繁殖投入等特征,而且,受到刈牧干扰后恢复生长的能力差,生物量补偿指数（CI）与耐牧值（TS）都显著低于高光照条件下的植物。在光照充裕的生境中,决定羊草耐牧性大小的环境中的营养条件,其次才是水分条件。克隆整合作用是克隆植物的典型特征,有助于克隆植物在异质性较强的生境中生存和发展。羊草是典型的根茎型禾本科牧草,分株间具有地下相连的根茎,可以进行营养物质的转运和传递。在我们的研究中,羊草同一克隆片段的不同分株生长在土壤中营养水平不同的生境之中。实验结果显示,在无模拟放牧影响条件下羊草的根茎整合作用有利于羊草克隆片段整体生物量的累积,其收益（0.564±0.016）大于其成本投入（0.4838±0.0448）;但在重度模拟放牧干扰处理组内,羊草克隆整合作用的成本收益（0.185±0.018）明显降低,低于其成本投入（0.583±0.019）。放牧强度过大导致克隆整合的能量投入远远大于该特征的正向产出。从表观来看,植物能够在草食动物采食之后能够进行补偿性再生生长,弥补动物采食所造成的损失。事实上,植物的补偿性效应是与碳水化合物和氮素在植物体各部分之间的转移,以及外界的环境干扰对植物体内源激素的产生及传递直接相关的。在模拟放牧处理后几个小时内,羊草贮存在根茎、分蘖节等储藏器官中的碳水化合物和氮素即开始迅速（刈割后5h内）向地上部分转移。可见,植物体地下部分贮存的碳水化合物和氮在短时间内向地上的迅速转移为羊草在模拟放牧后的恢复生长提供了物质和能量基础。而且,模拟放牧处理后植株生长促进型激素IAA和GA₃含量的增加,生长抑制型激素ABA含量的降低,羊草叶片及芽中IAA/ABA比值迅速上升,分别从无模拟放牧干扰时的1.32与0.86,升为1.66和3.80。其中,芽中IAA/ABA相对比例升高超过4倍。植物体内碳水化合物、氮素的迅速合成或吸收,并在植物不同部位间转移,以及植物内源激素含量变化及其相对消长平衡,均是植物在草食动物放牧干扰下再次进入生理活跃状态的生理基础和调节机制。通过本论文对羊草耐牧性的系统研究,我们确定羊草属于放牧耐受物种,在放牧利用后具有较强的补偿再生能力。羊草的耐牧性及适应性策略具有较强的可塑性和可调节性。羊草的耐牧性受到放牧强度、放牧时间、放牧频度等动物采食行为的影响,同时,随着环境中资源水平的变化、种内竞争强度的变化、及地下根茎克隆整合状态的变化,植物采取不同的耐牧性策略,力求使得自身适合度最大化。而且,羊草贮存的碳水化合物与氮素储备为羊草耐牧性提供物质和能量基础。植物体各部分内源激素的合成与传递,以及内源激素之间的相对消长关系为羊草耐牧性的生理调节机制。更多还原

【Abstract】 Herbivory tolerance of plants is an importnat component of plant defensive system against herbivores.Plants have considerable ability to respond to herbivory with compensatory regrowth and increased reproduction.We selected Leymus chinensis as our study material,and simulated herbivory disturbance by removing above-ground biomass of plants.This study mainly focused on the responses of L.chinensis to simulated herbivory intensities,resource availability in environments,competition intensity,and clonal integration.We also studied the ecological and physiological mechanisms of controlling compensatory regrowth in L.chinensis.We analyzed the regrowth, reproduction,and grazing tolearance of L.chinensis under the interactions of many outside factors,and determined the trade-off among growth,reproduction and defence, which will provide theoretical basis for co-evolution between plants and herbivores,and reasonable utilization of grassland.Herbivory tolerance of L.chinensis was investigated by combining the results of controlled conditions in the natural grassland and in the pot experiments.The main results and conclusions which could be obtained from our experiments were as follows.L.chinensis,with great tolerance to herbivory,has the ability to adjust its adaptive strategies to cope with unfavorable environments such as grazing or clipping disturbance. In the middle of August,simulated grazing treatment in natural grassland improved the capacity of building new tillers of L.chinensis with the increased energy input for winter seedlings and dormant buds.The clipping treatment with 8 cm stubble height was most beneficial to the population development of L.chinensis in the next year.There were two different responses of L.chinensis to the first and second simulated grazing treatments. The first simulated grazing treatment was conducted in the beginning of June.After this, L.chinensis adopted the adaptive strategy that increased above-ground vegetative growth with the limitation of building new tamers.The second clipping treatment was conducted in the middle of August when a number of buds and winter seedlings were forming.Thus, the adaptive strategy of L.chinensis was to increase the growth of new seedlings or leaves following increasing population density.There were significantly limiting effects of population density on vegetative biomass, reproductive biomass,and bud number in L.chinensis.The interaction between density and clipping influenced the adjustment of L.chinensis population.The limiting effects of population density on under-ground biomass（b = -0.9621） increased with the light clipping treatment.Therefore,more energy was input for the regrowth of above-ground biomass.Removal of 25%shoots was not the lethal damage to L.chinensis seedlings.The limiting effects of population density on above-ground biomass（b = -0.9929） increased with the complete clipping treatment（removal of 100%shoot）,which could lead to the death of seedlings.Therefore,the limiting effects on above-ground biomass under high density conditions were to ensure the survival of seedlings and vegetative propagation.The availability of light,water and nutrient in environments significantly affects plant growth and reproduction.They are the necessary resources for plant survival and growth.The results on the interactions between the availability of one resource and simulated grazing intensities showed that the "cooperative" interactions between water and simulated grazing aggravated the negative effects on tolerance scores,and the "antagonistic" interactions between nutrient and simulated grazing alleviated the negative effects of shoot removal on fitness reduction.Therefore,we assumed the linear responses of plant performance to herbivory intensity,and proposed a modified and simplified graphic model of the Limiting Resource Model（LRM）.The pot experiment with two nutrient levels,two light levels,and two water treatments was conducted to study the interactions among several factors influencing regrowth,reproduction,and grazing tolearance of L.chinensis.The results showed that plants in low light environments increased the growth of leaves,and decreased reproduction input.What is more,plants under low light conditions always failed to recover from disturbance and damage,even lead to the death of seedlings.Thus,light energy is the most important key factors for plant growth and tolerance.For plants growing in sufficient light environments,nutrient level in the soil was more important in determining tolerance capacity of plants than water conditions.Clonal integration,as the typical characteristic of clonal plants,is helpful for the individual survival and population development of plants growing in the heterogeneous environments.L.chinensis is a typical clonal plant,depending mainly on vegetative propagation for regeneration.Its highly branched rhizomes can be used for reserving and transporting carbohydrate and minerals among different ramets.The ramets of L. chinensis in the same clones were grown in different nutrient environments in our study. The results showed that clonal integration could improve biomass accumulation without simulated grazing,while the benefit of clonal integration in L.chinensis significantly decreased after heavy simulated grazing treatment.Plants have the ability to regrow and recover following grazing disturbance, compensating for the loss of herbivory.This is directly relative with the transportation of carbohydrate and nitrogen among different organs of plants,and the inductive synthesis of endogenesis hormones.In the following hours after simulated grazing,the reservation of carbohydrate and nitrogen in the rhizomes and tillering nodes was immediately transported to the above-ground organs.Thus,the quick transportation of soluble sugar and nitrogen provides the energy basis for the regrowth and recovery from grazing. Furthermore,simulated grazing could improve the concentration of IAA and GA₃,and reduce the concentration of ABA.The increase of IAA/ABA ratio in leaves and buds of L. chinensis can be considered as the physiological mechanism for herbivory tolerance of plants.In conclusion,L.chinensis is determined as a tolerant species,based on our study on grazing tolerance.L.chinensis has strong compensatory regrowth ability,adapative plasticity and adjustment after herbivory.Herbivory tolerance of L.chinensis is influenced by grazing intensity,grazing frequency,and time of grazing.At the same time,the performance of L.chinensis can respond to the level of resource in the environments, intra-specific competition intensity,and clonal integration.Moreover,the reservation of carbohydrate and nitrogen in under-ground organs can provide energy basis for herbivory tolerance.The synthesis and transportation of endogenesis hormones,the relative concentration of different hormones can be regarded as the physiological mechanism of grazing tolerance in L.chinensis.更多还原