Effects Of Warming On The Growth And Physiology Of Acer Mono Seedlings

Natural regeneration in forests is the basis for forest formation/development and the guarantee of their function.Seedling growth is an important part of woody plant development and determines the success of forest regeneration,and is extremely sensitive to the environment,with temperature being a key environmental factors affecting seedling growth and physiology.Global warming is affecting the growth and future population dynamics of woody plant seedlings.The results of studies are controversial on the physiological effects of warming on the growth of woody plant seedlings are closely related to the symmetry of diurnal warming and the characteristics of the tree species.Northeast China(temperate zone)is one of the sensitive areas for climate warming,but the extent to which diurnal warming symmetry affects the growth physiology of temperate woody plant seedlings is still unknown..Therefore,we selected Acer mono as the research object in this study,a key maple species that is the most widely distributed in the temperate zone and plays an important role in maintaining sustainable development of temperate forests.Five temperature treatments were simulated as diurnal symmetrical and asymmetrical warming by means of indoor thermostatic light incubators,i.e.,control(CK;no warming in daytime or nighttime),daytime warming(DW;3 °C warming in daytime and no nighttime warming),nighttime warming(NW;3 °C warming in nighttime and no daytime warming),symmetric warming(SW;3 °C warming in both daytime and nighttime)and asymmetric warming(AW;2 °C warming in daytime and 4 °C warming in nighttime).Spring phenology,growth(basal diameter,plant height,root length,leaf area,and biomass accumulation and allocation),and physiological(photosynthetic indices,antioxidant indices,non-structural carbohydrates,and endogenous hormones)indices of 2-yr-old A.mono seedlings grown under various warming conditions were compared to provide scientific guidance for predicting the direction of A.mono population development in the context of future climate change and achieving sustainable forest development in Northeast China.The specific findings of the study were as follows:(1)Compared with CK,warming treatments advanced the spring phenological periods(including bud break period,bud opening period,and leaf development period)of A.mono seedlings.Spring phenology of A.mono seedlings was advanced the most(around 14 to 17 days)in the DW and AW treatments.The advance of spring phenology extends the time for seedling shoots and leaves to participate in photosynthesis,increases the accumulation of photosynthetic products,and finally promotes the growth and productivity of A.mono seedlings.(2)The effects of different temperature treatments on the growth and physiology of A.mono seedlings differed significantly.DW,NW and SW had a positive effect on the growth indices of A.mono seedlings compared to CK.DW significantly increased the base diameter,plant height,root length and leaf area of seedlings,but did not significantly affect the antioxidant indices of seedling leaves,indicating that seedlings were not stressed in this environment.NW significantly increased base diameter and root length of the seedlings,and there was an insignificant increasing trend for superoxide dismutase activity in the leaf antioxidant indices,suggesting that NW still had a positive effect on the growth of A.mono seedlings in the short-term(6 months)warming treatment.SW produced an environmental stress,but seedlings adapted to stress by significantly increasing leaf antioxidant enzyme activity,root tip indole acetic acid content,and root length.AW had no significant effect on the growth of A.mono seedlings,but the seedlings exhibited considerably higher antioxidant indices,indicating that AW was a stressful environment for seedlings and was detrimental to their growth and development.For A.mono seedlings,leaf area and chlorophyll fluorescence metrics(PSII real photochemical efficiency and electron transfer rate)were the most influential determinants on seedling growth under various temperature treatments.According to the principal component analysis,the overall scores were ranked according to seedling growth as: DW>SW>NW>CK>AW,indicating that when the temperature difference between day and night increased,the diurnal photosynthetic rate increased,which was more conducive to the accumulation of photochemical products.The larger the temperature difference between day and night,the better the growth of A.mono seedlings.