| Temperature is one of the most important factors that affect plant growth.With a growing concern for warmer climate,a he ightened interest in the effect of temperature changes on plant growth thus has been aroused.However,previous studies mainly focused on the effect of temperature on plant shoot part,offering little understanding for the effect of temperature on root system,especially root architecture.Root architecture,referring to as the spatial configuration of the root system in the growth medium,can significantly affect many physiological functions such as nutrient and water acquisition.Furthermore,root architecture exhibits great plasticity to the changes in growth environmental conditions,including biotic and abiotic.Plant roots not only play an important role in plant growth and development,but also affect community structure through root interactions.In addition to changes in individual traits,global warming also causes huge changes in vegetation dynamics.Researches concerning the influence of temperature changes on root interactions are helpful to predict vegetation dynamics under warmer climate.In this study,three different life forms of tropical-subtropical plants were chosen as target plants and the seeds sourced from Heishiding,Guangdong Province.A 3-D transparent growth system combined with Win RHIZO root analysis system was used to non-destructively observe root growth and root interaction in situ under five temperature gradients,including high and low temperature.Here,we took the herb and the shrub as focal species,when examining how root interactions respond to temperature changes.Meanwhile,the quantification of aboveground and belowground plant functional traits enabled us to explore how temperature directly affected plant growth,and indirectly affected plant growth through root interactions comprehensively,which profoundly affected vegetation dynamics.The main results were shown as follows:1)The effects of temperature increasing on plant roots differed among life forms.Corchorus capsularis had larger root system at low temperature(22?),which was mainly reflected in root width and depth.Mimosa sepiaria had larger root at high temperature(34?),which was not only reflected in root width and depth,but also in total root length.While,temperature changes exhibited little impact on root system of Ormosia glaberrima,because cotyledons were the main source of nutrients which supported O.glaberrima seedling growth.For all the three plant materials,the aboveground biomass was more sensitive to temperature changes than belowground biomass,and root architecture parameters were more sensitive to temperature than root biomass,which came to a conclusion that the root development was essential to plant growth and root architecture(mainly root depth,root width and branch intensity),especially root plasticity played a major role in plant adapting to temperature changes.The extent of photosynthesis improved under high temperature was obviously greater than that of nutrition absorption for C.capsularis.Therefore,nutrition absorption might be one of the reasons that limit plant growth under warmer climate.2)The results of fitted root width and depth growth curves of C.capsularis and M.sepiaria combined with the real emergence of lateral roots showed temperature not only affected the final growth of plant root system,but also root growth dynamics.High temperature shortened the time to accomplish a certain stage of growt h.Global warming might change competition pattern underground,through affecting root growth dynamics and even root phenology.3)The relationships of aboveground and belowground traits varied with species and were affected by temperature.For examples,the specific root length(SRL)and the specific leaf area(SLA)of C.capsularis SMAs(standard major axis)fitted within each temperature treatment significantly differ in slope(p < 0.001)and the average root diameter and SLA of M.sepiaria SMAs fitted within each temperature treatment significantly differ in slope(p = 0.029).The mechanism which resulted in those differences might be related to plant internal resource al ocation.4)The root width peak absolute growth rate(AGR)of C.capsularis decreased when grown with conspecies,while increased when grown with other species.Furthermore,the extent of reduction in peak root depth AGR of C.capsularis when interacting with conspecies was less than when interacting with other species.C.capsularis exhibited kin selection in root interaction,with which interspecific competition was reduced through inhibition of root width growth.And from an evolutionary perspective,weakening the intraspecific competition would improve the fitness of the whole population.5)Temperature not only affected the strength of root interaction,but also changed the direction of the root interaction.Interacting with O.glaberrima generally promoted the growth of M.sepiaria,while remarkable increase was only observed at 22?.Interacting with M.sepiaria and O.glaberrima increased the growth of C.capsularis at 26?,while decreased at 30?.M.sepiaria had larger root system(root length,root depth and width)at high temperature,which led to greater negative effect to C.capsularis.Plants with root system more adapted to high temperature would have a competitive advantage under global warming.6)C.capsularis invested less resource to leaf and more resource to stem,while resource allocation to root system reached its minimum value at 30??Both high and low temperature(18? and 34?)reduced resource allocation to M.sepiaria leaf,only high temperature significantly increased resource invested to stem,while resource allocation to root system remarkably increased at low temperature.Warmer climate would decrease resource investment into leaf and increase into stem,while there was still some uncertainty about root.Plant resource allocation mainly determined by plant size,growth and development and temperature mainly affected the basic al ocation.In conclusion,root trait plasticity plays an important role in plant adapting to global warming.Different life forms differ in response to temperature change.Plants with larger root system(mainly total root length)at high temperature will be more competitive under warmer climate.The influence of temperature changes on root interaction cannot be ignored,when predicting the impact of global warming on vegetation dynamics.In addition to the productivity of the vegetation,the resource al ocation structure of vegetation will be changed by global warming. |
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