Impacts Of Sheep Saliva On Growth Of Leymus Chincnsis (Trin.) Tzvclev.

Plant-animal relationship is a critical issue in ecology, and with long co-evolutionaryhistory there is complex adaptation and mutualism between grazer and grass in grasslandecosystems. Impacts of foraging on plant include influence of mechanical damage andsaliva effects. Cues in animal saliva can induce plant chemical defense, and regulatephysiological process of plant regrowth. The stimulatory effect of animal saliva is one ofthe mechanisms for plant compensatory response to herbivory. Therefore, the study onsalivary effects on plant growth and the mechanism can improve our knowledge on theco-evolutionary and mutualistic association between plants and animals. However, thereis little work on the impact of saliva on plant growth, and the mechanism keeps unclear.We performed a set of experiments to explore the effects of sheep saliva on growthof Leymus chinensis (Trin.) Tzvelev., which is a dominate species in the SongnenGrassland. This study was conducted to examine,(1) impacts of animal saliva on plantgrowth,(2) influence of herbivory intensity on saliva impacts,(3) change of saliva effectswith time,(4) response of plant growth to chemical components of animal saliva, and (5)effects of animal saliva on remobilization of carbohydrate reserve.Experiments were conducted in controlled environments with completelyrandomized design and carbohydrate was measured with high performance liquidchromatography (HPLC). The main results and conclusions are present as following:Sheep saliva stimulated growth of L. chinensis, especially for tillers and buds.Results in2006and2007showed that sheep saliva promoted growth of L. chinensis,increasing biomass, buds and tillers, but had no influence on height. Recruitment ofperennial growth depends mainly on vegetative growth, including elongation and tillering.Elongation is regulated by intercalary meristem and dynamic of tillers results fromoutgrowth of buds. The two growth patterns work at different time within one growingseason. At early period of development, plant growth comes from shoot elongation, inwhich there is accumulative increase in plant height and leaf area, and consequent highcapacity of photosynthesis and accumulation of assimilate. In the middle of development,elongation declines and even stops, and belowground buds begin to outgrowth. Whentreatments were performed in this study, L. chinensis began to tiller, and at this time basalmeristem started to regulate plant growth. In results of this study, tillers and budsresponded sensitively to saliva application, which can enhance plant tolerance toherbivory and keep the coexistence between plant and animal.Impact of animal saliva on plant growth was herbivory intensity dependent, andat light and complete herbivory intensities it was strongest. Results in three yearsshowed that sheep saliva had higher impacts on growth of L. chinensis at light (25%) andcomplete clipping (100%) levels. We suggested that this was associated with meristem distribution pattern within perennial herbaceous plants. Development of perennial grasseswas regulated by apical meristem, intercalary meristem and basal meristem. Intercalarymeristem controls plant elongation, and basal meristem and rhizomatous buds determinedynamic of tillering. Activity of both the meristem is regulated by apical meristem. Theresults showed that at light and complete clipping levels, sheep saliva had strongestpromotive effects on plant growth because the two positions were most close to apical andbasal meristem respectively. Tillers of L. chinensis came from outgrowth of buds at thebase of shoot and along the rhizome. The complete clipping level was most close to theground, and so it was easiest for growth regulators in animal saliva to reach belowgroundbud bank and stimulate tillering. Light clipping level was close to apical meristem andanimal saliva could regulate tillering through the regulation on apical meristem. Therefore,effect of sheep saliva on growth of L. chinensis was clipping level dependent, and at lightand complete clipping levels it was strongest.Effect of animal saliva on plant growth was time dependent. In this study, therewas response in carbohydrate content to sheep saliva within half a day after treatments.Plant height responded to saliva10days after treatments and30days after treatments,there was significant response in tillers, buds and biomass. Regrowth capacity of plantfollowing herbivory depends on the remobilization of restored carbohydrate and activityof meristem. Transfer of carbon reserve can respond to herbivory in a short time, andplant elongation and tillering differs in the sensitivity to herbivory. In this study,carbohydrate in every plant part changed within half a day after treatments, ten days laterthere was response to plant height, and thirty days after treatments impacts of sheep salivaon tillers and buds emerged. So, impact of animal saliva on plant growth was timedependent and there was difference in plant growth parameters to respond to saliva.The main salivary components had no positive effects on plant growth. There isa huge amount of growth factors and regulators within animal saliva, and saliva plays animportant role in plant-animal interaction. In this study, we compared different responseof L. chinensis growth to sheep saliva, epidermal growth factor (EGF), thiamine and themixture of the two chemicals. Results showed that EGF, thiamine or their mixture did notpromote growth of L. chinensis, and sheep saliva had high promotive effects than EGF,thiamine and their mixture. EGF or thiamine had no stimulation on growth of L. chinensis,and this may result from the favourable growth condition, in which plant growth is notlimited by growth factors.Animal saliva promoted remobilization of carbohydrate reserve. Rapidremobilization of carbohydrate reserve is one of the mechanisms of plant tolerance toherbivory and its capacity of compensatory growth. Results of this study showed that inevery plant part fructan content decreased by30-50%three days after treatments, and thekept in the later period of the experiment. Sucrose in leaf and stem increased by2to3times one days after treatments and then decreased to the level before treatments, while inrhizome and fine root sucrose content increased gradually three times. In every plant part,concentration of glucose and fructose increased gradually by2to10times. Compared with clipping, sheep saliva promoted hydrolization of fructans and accumulation ofglucose and fructose in every plant part, while it suppressed the accumulation of sucroseand then improved its concentration. The results demonstrated that during the short periodafter herbivory, fructans decreased, monosaccharides increased and were transported intonew tissues. In the process of herbivory, the saliva deposited on plant surface promotedmobilization of carbohydrate to support energy for compensatory growth.Results of this study showed that sheep saliva promoted growth and saliva effectswere herbivory intensity dependent. We proposed that this was associated withdistribution pattern of meristem within plant, and at the point of apical and basal meristemthe effects of animal saliva were most effective. The promotive effect of saliva on plantgrowth at intensive herbivory levels was associated with plant adaptation to long termgrazing, and the stimulatory impact of saliva on plant compensation at light herbivoryintensity can increase plant compensatory response to herbivory that gave support to theoptimal grazing hypothesis. The time dependence of animal saliva on plant growthaddressed the significance of delaying grazing and rotational grazing. Animal salivapromoted remobilization of carbohydrate during regrowth, with provided physiologicalmechanism of plant compensatory response and tolerance to herbivory. The stimulatoryeffects of animal saliva on plant growth and remobilization of carbohydrate expanded themutualism and coevolution theory, and gave guide to scientific grassland management.