Effects Of Sediment Types,Temperature And CO₂ Concentration On Vallisneria Spiralis,Radix Auricularia And Their Plant-herbivore Interaction

The impacts of climate change on ecosystems are mainly reflected in the increase in temperature and CO₂ concentration,as well as its indirect effects on other environmental factors（matrix nutrition,etc.）.The herbivory relationship is also affected by a variety of environmental factors,which may be synergistic or antagonistic.However,the current research on the herbivory relationship between snails and aquatic plants mainly focused on the effects of snail grazing on aquatic plants,but lacks attention to herbivores.Therefore,this paper selected three factors,namely sediment types,temperature and CO₂concentration,in the context of global climate change,and explored the effects of these factors on Vallisneria spiralis,Radix auricularia and their plant-herbivore interaction.The main results are as follows:（1）Herbivory and sediment types have a significant impact on the growth and total nitrogen content of V.spiralis.In the presence of snail herbivory,the relative growth rate of V.spiralis in mixture and sand sediment both were significantly reduced.The shoot biomass of V.spiralis in mixture,sand and mud sediment were decreased by 67.74%,58.58%and 17.84%,respectively,and the root:shoot biomass ratio increased by177.51%,217.23%and 1.44%,respectively.Under different sediment types,herbivory had no significant effect on the total carbon content of V.spiralis.However,the snail herbivory significantly reduced the total nitrogen content of V.spiralis,and C:N ratio increased significantly in mud and mixture sediment.The total phenols content of V.spiralis was significantly reduced in sand sediment.Sediment types had no effect on the morphological characteristics（except for shell width）,growth and element content of R.auricularia.In conclusion,the sediment types influenced on the snail herbivory and the defense of strategy of V.spiralis in some extent,but had no effect on the growth,total carbon content and total nitrogen content of R.auricularia.（2）Herbivory decreased the total biomass of V.spiralis by 28.6%and 25.3%under low and high CO₂ conditions,respectively.Compared with A（ambient air without snails）group,ES（elevated CO₂ with snails）group reduced the total plant biomass by 43.3%.Elevated CO₂ and herbivory both affected the growth of V.spiralis and change its resource allocation patterns.Total nitrogen content of V.spiralis leaves decreased under herbivory condition,and total phenols increased under the interactions condition between elevated CO₂ and herbivory.However,total carbon content of R.auricularia increased under elevated CO₂ condition.（3）Herbivory had a negative effect on the growth and biomass accumulation of V.spiralis in all treatments.High temperature（27℃）treatment has a significant inhibitory effect on the growth of V.spiralis.V.spiralis may adopt different strategies to resist herbivory under different environmental conditions.The total carbon content and total nitrogen content of V.spiralis leaves decreased in all treatments,while the total phenols content increased.The shell length and shell width of the snails are reduced under high CO₂ and high temperature conditions,and the acidification of water caused by high CO₂may have an inhibitory effect on the growth of the snail shell.