Approach To Allocation Of Ecological Cost And Adaptive Strategy Of Rosa Xanthina In Responding To Simulated Grazing

Phenotypic plasticity and defense strategy of plants play a very important role in theirco-evolution with herbivores. Hierarchical organization of plants offers various levels ofphenotypic plasticity in their adaptation to environmental changes including mowing.In Tianjingyuan nursery, Jiutai city, Jilin province, the phenotypic plasticity, quantity andbiomass allocation pattern of organs, including rhizome, stem, leaf, thorn responding tomowing in the experiment of Rosa xanthina consisting of different mowing intensitiesincluding no mowing, light mowing, moderate mowing, heavy mowing. The research wasconducted over two growth seasons from 2004 to 2005. The results indicate that:Mowing reduced the average leaflet length. The length in un-mowed plots was 1.59cm,the length in light mowing, moderate mowing, heavy mowing were1.44, 1.29 and 1.28cmafter once mowed, the length in light mowing, moderate mowing, heavy mowing were 1.17,1.17 and 1.10cm after twice mowed of the year 2004, and there was the same change trend ofthe year 2005. Leaflet length in mowed plot is longer than that in un-mowed plot, leafletlength shorten with mowing intensified, the difference is significant, so as the leaflet areachange in different plots with mowing intensified.The leaflet obliquity increased with mowing intensified. The obliquities in mowed plotswere small;the change is insignificant during the whole growth season. The shape is steady.The leaflet obliquity increased when mowing intensified, the leaflet growth vertically.Quantity of the thorn on leaflet back increased and thorn length shorten when mowingintensified, and thorn length in un-mowed plots were 7.756mm, the length in light mowing,moderate mowing, heavy mowing were 7.459, 7.395 and 7.370mm after once mowed, thelength in light mowing, moderate mowing, heavy mowing were 7.322, 6.837 and 6.675mmafter twice mowed in 2004, and there was the same change trend in 2005.The thorn density increased with mowing intensified, and thorn density in un-mowedplot was 1.47 no.cm-1, the density in light mowing, moderate mowing, heavy mowing were1.50, 1.61 and 2.15 no.cm-1 after once mowed, the density in light mowing, moderate mowing,heavy mowing were 1.85, 2.37 and 2.95no.cm-1 after twice mowed in 2004, and there was thesame change trend in 2005. The difference is remarkably significant. The mechanical defenseis increased with mowing intensities. The angle of each two thorn increased with mowingintensified, the angles in mowed plots are larger than that of in un-mowed plots.Mowing also changed the patterns of biomass accumulation and biomass allocation in R.xanthina. It reduced the biomass per organ, and the above-ground biomass in mowed plotswere 53.80, 57.02, 62.08 and 83.76%, and these of rhizome biomass were 40.28, 37.02, 35.80and 15.56%, while these of thorn biomass were 1.26, 2.68, 2.48 and 0.56%, respectively.The ratio of above-ground biomass and underground biomass decreased with increase ofmowing intensities, which indicated that rhizome biomass decreased more quickly than theabove-ground and relatively less biomass was allocated to stem in un-mowed plot, while morein mowing plots. Furthermore, much more biomass was allocated to leaves when mowingintensities increased.The ratio of defense and vegetative biomass is smaller in un-mowed plots than that of inlight mowing and moderate mowing plots, showing the invest to defense is large so as todecrease the effect when the plant incurred disturbance.As a result, the phenotypic plasticity and biomass allocation of R. xanthina wereinvestigated at the levels of organization, which supported the idea that the phenotypicplasticity is selected to increase the performance of R. xanthina in habitats with differentmowing intensities.The quantity of leaflets and the obliquity of leaflets increased with mowing intensified.The leaflets distribute vertically. The main survival strategy is to decrease thorn length andincrease thorn density, meanwhile, when leaf length decreased, leaf area decreased, and thebranching increased.The allocation percentage with different pattern can be described as follows:The individual is taller, the leaflet area is larger, investing more to stem, less of the wholeecology cost to defense. The results are opposite in mowed plots. More ecology cost invest tothorn, the thorn density increased, and the structure could be available to defense, that is toshow, mechanical defense increasing.