Growth And Physiological Responses Of Typical Plants At Two Altitudes To Soil Temperature Changes

Global climate change is mainly reflected in changes of climate factors such as temperature and precipitation.One important characteristic is the continuous rise in surface temperature and ocean temperature.Temperature has significant effects on survival,growth,morphological characteristics,physiological characteristics and distribution of plants.Obviously,a rise in surface temperature is bound to lead to changes in soil temperature,and studies have shown that soil temperature is a key factor affecting survival and growth of plants.However,due to the difficulty of strictly separating air temperature from soil temperature,most of the studies showed effects of air and soil temperature as a whole,and it was difficult to achieve synchronous changes in air and soil temperature during the experiment.Therefore,there are few studies to strictly control air or soil temperature,and to study its effects on survival,growth and physiology of plants respectively.The survival and establishment of seedlings plays an important role in the restoration and regeneration of forest,and determines the distribution of plants to some extent.Temperature,moisture and human factors all could affect survival and settlement of seedlings.Therefore,it is of great significance to study the effects of environmental and human factors on the survival and growth and the specific forms on research of the restoration of forests and the dynamic changes of plants under global climate change.This study was carried out in Walk-In artificial climate chambers.The indoor temperature was kept constant.Five different soil temperature were strictly controlled by tanks of a novel device,and the air temperature was strictly separated from the soil temperature.The purpose of this study was to explore the effects of soil temperature on survival,growth and physiology of plants.And,the study has added the environmental factor of soil moisture and the disturbance factor of shoot removal of plants(e.g.animal gnawing and human felling).Picea balfouriana seedlings that are sensitive to climate changes and Indocalamus decorus seedlings that are also sensitive to climate changes and have strong plasticity and could quickly response to climate changes were selected as research materials.Effects of soil temperature,soil moisture,shoot removal of older ramets and interactions on survival,growth and physiology of plants were studied by nested design.The storage and utilization of nitrogen,phosphorus and carbohydrates under different soil temperature and moisture,as well as effects of soil temperature and shoot removal of older ramets on the survival rate and growth of young ramets were discussed.The main conclusions are as follows:(1)Effects of soil temperature and soil moisture on P.balfouriana seedlings.The decrease of soil temperature significantly reduced root biomass and root to shoot ratio,which indicated that roots were more sensitive to soil temperature changes.Soil moisture had a significant effect on root biomass and root to shoot ratio,water stress significantly reduced root biomass and root to shoot ratio at the higher soil temperatures(17 and 22 ?),but had no significant effect at the lower temperature.Soil temperature has a significant effect on the nitrogen and phosphorus concentration(mg/g)of organs.The nitrogen and phosphorus concentration tended to decrease with soil temperature decreasing,especially for annual needles.Soil moisture had a significant effect on nitrogen and phosphorus concentration and content,water stress significantly reduced nitrogen and phosphorus content in annual needles and roots at 17 and 22?,while water stress had no significant effect at the lower temperature.Soil temperature and moisture had significant effects on non-structural carbohydrates(NSC)concentration in organs.The NSC and soluble sugar concentrations in annual needles,soluble sugar in stems,NSC,soluble sugar and starch concentrations in roots increased significantly with soil temperature decreasing.So,low soil temperature did not lead to carbon limitation.While drought stress significantly reduced starch and NSC concentration in annual needles,especially under low temperature.That is to say,drought may lead to“carbon starvation”under low soil temperature.(2)Effects of soil temperature and shoot removal of older ramets on young ramets of I.decorus.Soil temperature and shoot removal had significant effects on the survival rate of young ramets.When shoots were retained,low soil temperature significantly increased the survival rate of young ramets.Shoot removal significantly increased the survival rate of young ramets,especially in 17 and 22 ?,with a significant increase of 56%.Soil temperature had no significant effect on aboveground biomass,stem biomass,leaf biomass and leaf number,but biomass reached its peak at 7 and 12 ? when shoots of older ramets were removed.Shoot removal had significant effects on biomass and leaf number.Biomass increased significantly at7 and 12 ?,and number of leaves increased significantly at 17 and 22 ?.Soil temperature,shoot removal and their interaction had significant effects on photosynthetic rate of young ramets.Low temperature significantly reduced photosynthetic rate.Photosynthetic rate was very sensitive to low temperature and reached the highest at 22 ? and it decreased sharply with temperature decreasing.Although low temperature significantly reduced photosynthetic rate,it had no significant effect on NSC,soluble sugar and starch concentration,that is,low temperature did not lead to carbon limitation.To sum up,low soil temperature and water stress led to the deficiency of nitrogen and phosphorus in seedlings,but water stress had no significant effect on nitrogen and phosphorus at low soil temperatures.NSC concentration in P.balfouriana seedlings and young ramets of I.decorus did not decrease with soil temperature decreasing,increased significantly or remained unchanged instead.Therefore,low soil temperature did not lead to carbon limitation.Low soil temperature significantly increased the survival rate of young ramets and decreased photosynthetic rate,but had no significant effect on biomass.Interactions between soil temperature and shoot removal had significant effects on the survival and growth of young ramets.Shoot removal could significantly increase the survival rate and growth of young ramets at some levels of soil temperature,so there was no clonal integration between ramets at this time,instead,the competition between older ramets and young ramets for resources in rhizomes affected the establishment and growth of young ramets.Additionally,NSC concentration in the annual needles of P.balfouriana seedlings increased with soil temperature decreasing,indicating that plants can maintain normal photosynthesis or can maintain a certain photosynthetic yield at low temperature.Similarly,although low soil temperature significantly reduced the photosynthetic rate of young ramets of I.decorus,but it did not lead to carbon limitation,indicating that leaves can still maintain a high photosynthetic yield under low soil temperature conditions.These results suggest that the impact of soil temperature should be considered in models that simulate the impacts of global climate change.In addition,it is suggested that future studies should focus on the combination of photosynthesis and nutrient elements and carbohydrate and should extend the observation period in order to improve the understanding of physiological and biochemical processes in plants under changes of soil temperature.