| Global warming has become an indisputable fact.Due to the influence of the south subtropical monsoon climate,the plants of the evergreen broad-leaved forest in southern China are particularly sensitive to global warming.Therefore,exploring the changes in leaf functional traits of dominant tree species in the subtropical monsoon forest under artificial temperature increase can provide a thorough understanding of the law of forest plant response to warming in this region and its regulation mechanism.In this study,four dominant tree species(Ormosia pinnata,Syzygium rehderianum,Castanopsis hystrix,and Schima superba)in the south subtropical monsoon evergreen broad-leaved forest were used as the research objects and the experiment was based on the simulated warming research platform of the Dinghushan Biosphere Reserve(DBR),which increased temperature by infrared radiators.Combined with long-term fixed-point environmental factors such as atmospheric temperature,soil temperature,soil water content,and plant growth(ground diameter,tree height)measurement,analysis of plant growth indicators,leaf construction costs,gas exchange parameters,leaf water potential,stomatal conductance degree,stomatal characteristics,leaf nutrient concentrations,non-structural carbohydrate concentrations,leaf anatomy and other indicators to explore the adaptation strategies and response mechanisms of four dominant tree species in the South subtropical monsoon evergreen broadleaf forest under warming.This study aims to reveal the physiological and ecological adaptation mechanism of plants to rising temperatures.The results of the study can provide a scientific basis for further analysis of the impact of global changes on the south subtropical monsoon forest ecosystem.The main conclusions of this study are as follows:(1)Infrared radiators treatment significantly increased the annual average temperature and maximum temperature by 2.01 ? and 8.74 ?,respectively(p <0.05),while increased the average soil temperature by 0.83 ?,the increase in atmospheric temperature is greater than the soil temperature.The temperature-increasing treatment reduced the soil volumetric water content by 1.38 %,but with the passage of time,the soil volumetric water content of the temperature-increasing plot and the control group showed no difference.(2)Warming has a significant effect on plant growth,and the growth of the four tree species(D2H)has an inter-species difference.The warming promoted the growth of Castanopsis hystrix and Ormosia pinnata(except June 2017)but inhibited the growth of Schima superba(after December 2016)and Syzygium rehderianum.(3)Under the warming,the leaf construction cost per unit area(CCa)of Syzygium rehderianum decreased by 18.89 %(p <0.05)in December 2017(dry season);The CCa per unit area of the leaf in the month(wet season)and December 2018(dry season)increased by 19.07 % and 18.23 %(p <0.001),respectively.The CCa of Castanopsis hystrix per unit area has been reduced by 25.60 %,while the CCa of Castanopsis hystrix per unit area has increased by 5.88 % in December 2018(dry season)(p <0.05);The CCa of Schima superba per unit area of leaf in the month(wet season)and December 2017(dry season)was reduced by 4.00 % and20.85 %(p<0.05),respectively.This indicates that Ormosia pinnata have a good adaptability to warming,while Syzygium rehderianum,Castanopsis hystrix and Schima superba are all suppressed to a certain extent.(4)Warming leads to a significant decrease in the predawn water potential of Syzygium rehderianum,Castanopsis hystrix and Schima superba,the midday water potential of Syzygium rehderianum significantly decreases;the stomatal conductance of Schima superba significantly decreases,while the stomatal conductance of Ormosia pinnata and Castanopsis hystrix Significantly increased.At the same time,the stomatal density of Ormosia pinnata and Schima superba significantly decreased,while the stomatal size of Castanopsis hystrix and Schima superba significantly increased.Therefore,under warming conditions,all four tree species are subject to a certain degree of water stress,and they change the stomatal structure(stomata size and density)to reduce the loss of water.The photosynthetic rate(Aa)of Schima superba and Syzygium rehderianum was significantly reduced,while the Aa of Ormosia pinnata was significantly increased,Castanopsis hystrix unchanged.This indicates that Ormosia pinnata have a good adaptability to warming,and under the background of global changes in the future,Ormosia pinnata may be in an advantageous position relative to Syzygium rehderianum and Schima superba.(5)We found that N was the key factor of soluble sugars and non-structural carbohydrates in plant leaves during dry season,while P was the key factor determining soluble sugars and non-structural carbohydrates in plant leaves during wet season.The concentrations of N and P in Ormosia pinnata were significantly higher than those in other 3 plants.(6)Under warming treatment,the photosynthetic N use efficiency(PNUE)of Syzygium rehderianum in July 2018(wet season)and July 2019(wet season)decreased significantly(p<0.05);The PNUE of Ormosia pinnata in July(wet season)increased significantly(p<0.05);the PNUE of Schima superba in July2019(wet season)decreased significantly(p<0.05).The photosynthetic P use efficiency(PPUE)of Syzygium rehderianum in July 2018(wet season)decreased significantly(p<0.05);the PPUE of Ormosia pinnata in July 2019(wet season)increased significantly(p<0.05);The PPUE of Schima superba in July 2019(wet season)decreased significantly(p<0.05).This shows Ormosia pinnata that has a better adaptability to warming,and has better PNUE and PPUE under warming,while Syzygium rehderianum and Schima superba of the PNUE and PPUE is reduced.Under the background of global changes in the future,Ormosia pinnata may be in an advantageous position relative to Syzygium rehderianum and Schima superba.In summary,the growth of Schima superba and Syzygium rehderianum seedlings is inhibited under the condition of temperature increase,and the Ormosia pinnata grow well under the warming,and have suitable leaf construction cost,better stomatal strategy and stronger N and P absorption ability,good photosynthetic N and P use efficiency,under the background of global warming in the future,Ormosia pinnata may be in an advantageous position relative to Syzygium rehderianum and Schima superba. |
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