Effects Of Simulated Warming On The Carbon Budget Of Phragmites Australis Rhizosphere Soil In Chongming Dongtan And Related Mechanisms

Coastal reed(Phragmites australis)wetland is the ecosystem with an important carbon sink function.It has sustainable ability and high rate in carbon sequestration.The interaction between the reed roots and the rhizosphere microorganisms plays an important role in the soil organic carbon accumulation.So far,the knowledge about the changes in root and rhizosphere microbial-mediated carbon processes and their effects on the rhizosphere soil carbon budget under warming conditions has been still limited,which has largely restricted the understanding of the response and feedback mechanism of the coastal wetland soil carbon cycle to the global climate change.This study took the reed wetland at the Chongming Dongtan of the Yangtze Estuary as the research object,the reed-soil continuum was transplanted into an open-top growth chamber(OTC)to conduct the in-situ simulated warming experiment.In 2020,the average annual temperature rise of air and soil within OTC was 1.90?and 0.68?respectively.The samples were collected at the end of each month from May to October.The root growth dynamics,reed root exudate secretion rate,rhizosphere microbial structure and respiration of reed in the 0-20cm soil layer were observed and systematically analyzed by minirhizotron method,in-situ root exudate collection method,Micro Resp ^TMmethod,fluorescence quantitative PCR method and high-throughput sequencing technology,in order to elucidate the effect of warming on the input and decomposition of the organic carbon in the rhizosphere of the coastal reed wetland,and to reveal the response mechanism of the rhizosphere soil carbon budget in the coastal reed wetland to the warming climate.The main findings were as follows:(1)Warming significantly increased the total organic carbon content in the0-10cm soil layer of the reed wetland by 13.73%.Warming had no significant effect on the total carbon,total nitrogen,available nitrogen,available phosphorus and carbon nitrogen ratio in 0-10cm soil layer.Warming had no significant effect on the soil nutrients in 10-20cm soil layer.(2)Warming significantly increased the total root length,total surface area and fine root biomass of reed in 0-10cm soil layer by 202.84%,151.36%and 196.70%respectively.Warming significantly reduced the specific surface area of fine roots by11.87%,but had no significant effect on the net growth rate and specific root length of the fine roots.Warming had no significant effect on the root morphology and the growth in the 10-20 cm soil layer.Warming also accelerated the turnover rate of the fine roots by 41.16%and 9.80%in the 0-10cm and 10-20cm soil layers,respectively,but did not reach a significant level.Thus,warming increased the fine root biomass,and accelerated the turnover rate,resulting in more carbon input into the fine root turnover.In the soil layer of 0-10 cm and 10-20 cm,the fine root turnover carbon input increased by 309.55%and 42.02%respectively.(3)Warming significantly increased the rate of C secretion per unit fine root biomass of reed,which were 69.72?g/g·h and 77.70?g/g·h in the control group(CK)and the warming group(ET),respectively,with an increase of 11.45%.On the other hand,the biomass of reed fine roots of reed in ET was significantly higher than that in CK,so warming significantly increased the organic carbon input of reed root exudates,which were 237.41%and 51.13%in the 0-10cm and 10-20cm soil layers,respectively.Warming had no significant effect on the relative contents of various components in the exudates of reed roots,but decreased the number of types of chemical components in the exudates.The chemical components of CK and ET were 23 and 17,respectively.(4)Warming had no significant effect on the number,richness,?-diversity and respiration rate of the soil microbes in the reed wetland,but it changed the community structure and dominant population of the bacteria and fungi.Differential species from phylum to genus level,LEf Se analysis showed that there were 8 and 27 bacterial species with significant differences in the relative abundance of the CK and ET in the0-10 cm and 10-20 cm soil layers,respectively.There were 3 and 4 fungi species with significant differences in the relative abundance between the CK and ET in the 0-10cm and 10-20 cm soil layers,respectively.However,different microorganisms tended to have different preferences for soil organic carbon components,thus affecting the accumulation of the soil organic carbon.In conclusion,in-situ warming in the reed wetland increased the fine root biomass per unit soil by increasing the total root length of reed,and it also accelerated the turnover rate of the reed fine roots to a certain extent.Meanwhile,warming also increased the carbon input rate of root exudates.Therefore,warming increased the input of organic carbon to the soil of the reed wetland.However,warming had no significant effect on the microbial respiration,resulting in no significant change in the soil organic carbon output mediated by the microbial community.Finally,the effect of warming on the rhizosphere soil carbon budget in the coastal reed wetlands was reflected in the net carbon input and organic carbon accumulation,which was mainly due to the accumulation of the inert carbon.Under the warming treatment,the inert carbon in 0-10cm soil layer increased by 68.82%.The proportion of the inert carbon in the reed coastal wetland is as high as 70%.Therefore,under the background of the global warming,the response of the inert carbon to the warming tended to determine the potential changes in the soil carbon pool of the coastal reed wetland.The result of this study also provided a theoretical basis for the sustainable protection and restoration of the coastal wetland carbon sink resources.