Effects Of Salt On The Temperature Sensitivity Of Soil Organic Carbon To Anaerobic Mineralization In Wetland Of The Yellow River Estuary

Global climate change has gradually become the focus in geoscience,ecology and environment,and the changes in ecosystem carbon storage play an important role in it.Estuarine wetland is located at the confluence of river and marine ecosystem.Its unique geographical environment characteristics and the rich carbon reserves make it an important carbon pool of terrestrial ecosystem.Under the influence of climate warming and seawater intrusion,soil salinity and thermal conditions of estuarine wetlands will change significantly.Anaerobic mineralization is an important part of estuarine wetland carbon process.Exploring the response to salinity and heat conditions is the key to understand the feedback mechanism of estuarine wetland carbon-climate change.However,the mechanism of salinity in response to the temperature of soil organic carbon anaerobic mineralization in estuarine wetlands is not clear.In this study,the Yellow river estuary wetland was selected,combining the field fixed-point sampling and incubation experiment,to study the different community type’s soil organic carbon anaerobic mineralization characteristic.It has been clear about the effect of salt for the temperature sensitivity of soil carbon anaerobic mineralization,reveals biochemical mechanism affected by the salt in the estuary wetland.The results are as follows:（1）Under anaerobic conditions,the order of soil CO₂ accumulation production amount of different community types in Yellow River estuary varied in the range of136.5～404.2μg C·g^-1（10℃）,407.3～887.9μg C·g^-1（20℃）,859.6～1541.7μg C·g^-1（30℃）during 48 days of cultivation,which was in order of Spartina alterniflora>Phragmites australis>Suaeda salsa>Tamarix chinensis.The accumulation production amount of CH₄ varied from 0.198 to 51.2μg C·g^-1（10℃）,from 10.4 to 649.6μg C·g^-1（20℃）,and from 502.6 to 1454.3μg C·g^-1（30℃）in Phragmites australis>Spartina alterniflora>Suaeda salsa>Tamarix chinensis.In terms of soil depth,the rate of anaerobic mineralization in the topsoil（0～10 cm）was higher than that of the subsoil（10～20 cm）.The increasing of temperature promoted the anaerobic mineralization of soil organic carbon in estuarine wetland.When the temperature increased from 10℃to 20℃,the increase rates of soil CO₂ and CH₄ in the four community types ranged from 1.13 to2.16 times and 7.88 to 290.3 times.When the temperature increased from 20℃to 30℃,the corresponding values were 0.648 to 1.22 times and 1.07 to 69.9 times.The increase rate at lower temperature is higher than that at higher temperature.Temperature sensitivity(Q_10-CO2 and _Q10-CH4)ranged from 1.89 to 3.17 and 19.8 to 252,respectively,which showed that Tamarix chinensis>Suaeda salsa>Phragmites australis>Spartina alterniflora,and the subsoil organic carbon anaerobic mineralization(Q_10-CO2,1.60～3.17;Q_10-CH4,2.53～252.9)was more sensitive to temperature increase than the topsoil(Q_10-CO2,1.43～2.89;Q_10-CH4,1.46～102.6).Correlation analysis showed that TOC and TN contents were positively correlated with anaerobic mineralization of organic carbon,while EC and p H values were negatively correlated with Q_10-CO2 and Q10_-CH4 values.（2）Under salinity treatment,the accumulation production amount of soil anaerobic mineralization decreased with the increase of salinity.Under 5‰,10‰,20‰and 30‰salinity treatment,the accumulation production amount of CO₂ production decreased by 11.2%,14.3%,30.6%,41.4%（10℃）,9.59%,20.1%,36.6%,40.0%（20℃）and5.31%,16.7%,25.3%,0.5%（30℃）,while the CH₄ production decreased by 23.1%,31.3%,45.9%,63.8%,and 24.3%,44.0%,75.5%,92.1%and 5.08%,19.6%,33.4%,42.9%.The interaction between salinity and temperature has a significant effect on the anaerobic mineralization.At lower temperature,the anaerobic mineralization of organic carbon in lower-salt treatment（0‰～5‰）increased greatly with the temperature rising（CO₂,1.45～1.79 times;CH₄,96.0～163.0 times）,while,in the higher-salt treatment（10‰～30‰）increased more significantly at higher temperature（CO₂,0.828～1.48 times;CH₄,2.75～30.4 times）.The input of salt enhanced the sensitivity of soil organic carbon anaerobic mineralization response temperature rising.The values of Q_10-CO2 and Q_10-CH4 were both lower under low salinity treatment（1.52～3.09 and 2.64～51.6）,and higher under high salinity treatment（1.78～3.15and1.69～133.7）.The Q₁₀ value of the subsoil(Q_10-CO2,1.52～3.16;Q_10-CH4,21.8～133.7)was significantly higher than that of the topsoil(Q_10-CO2,1.71～2.49;Q_10-CH4,1.69～51.6).（3）The composition of microbial community and enzyme activities were changed by the increase of temperature and salinity in estuarine wetland soil.The abundance and diversity of microorganisms increased with the increase of temperature under the medium and low salinity conditions,but decreased with the increase of temperature under the high salinity conditions.The abundance and diversity of microbial species was limited by the increased salinity.At the class level,the abundance of Bacteroidota,Actinobacteriota and Desulfobulbia was significantly negative correlation with the incubation temperature,while the abundance of Dehalococcoidia,Phycisphaerae,Spirochaetia,Kryptonia,Syntrophia,Amiinicenantia,Syntrophorhabdia,unclassified Bacteria were significantly positive correlation with the incubation temperature.The above correlation between microbiota-temperature was highly consistent with the correlation between microbiota-the rates of CO₂ and CH₄ production.The abundance of Anaerolineae and Gammaproteobacteria decreased significantly under high salt treatment,while Clostridia,Bacilli,Bacteroidota and Desulfuromonadia have shown a significant increase in abundance with increasing salinity.There was a positive correlation between the microbial community structure and the production of CO₂ and CH₄under low salinity condition,while there was a negative correlation between the microbial community and the production of CO₂ and CH₄ under high salinity condition.The activities ofα-glucosidase,β-glucosidase,cellulodisylhydrolase,xylosidase and DOC were positive correlation with salinity and negative correlation with temperature,while negative correlation with soil organic carbon anaerobic mineralization.（4）Under the addition of SO₄^2-,NO₃^-and Fe（Ⅲ）,CO₂ production decreased by22.4～28.7%,21.3～38.9%,24.2～34.4%and 4.81～7.82%,4.34～9.35%,9.07～13.2%and 7.25～9.28%,0.028～15.0%,5.14～11.1%,at 10℃,20℃and 30℃.The CH₄production fell by 36.8～76.2%,50.6～92.3%,13.7～84.2%and 16.3～23.9%,12.5～17.3%,13.7～38.6%and 3.79～12.5%,17.1～19.4%,19.7～28.8%.Comperaed with CO₂,the inhibition effect on CH₄ was more significant.Under the addition of different electron acceptors,the response of soil organic carbon anaerobic mineralization in estuarine wetland to different temperature ranges is different.For CO₂,when the incubation temperature increased from 10℃to 20℃,the increase amplitude was in the order of NO₃^->Fe（Ⅲ）>SO₄^2-,and the increase amplitude was the largest under the addition of high concentration SO₄^2-and Fe（Ⅲ）.When the incubation temperature increased from 20℃to 30℃,the increase amplitude of CO₂ was Fe（Ⅲ）>SO₄^2->NO₃^-,and the increase amplitude was the largest under the addition of low concentration electron acceptor.For CH₄,when the incubation temperature increased from 10℃to20℃,the increase amplitude was in the order of NO₃^->SO₄^2->Fe（Ⅲ）.When the incubation temperature increased from 20℃to 30℃,the increase amplitude was SO₄^2->Fe（Ⅲ）>NO₃^-.The addition of SO₄^2-,NO₃^-and Fe（Ⅲ）at lower temperature has more significant inhibitory effect on CH₄.The Q_10-CO2 value varied in the range of 1.38～3.94and the Q_10-CH4 value varied in 1.93～132 under different electron receptor addition treatments.The Q_10-CO2 and Q_10-CH4 was in the order of NO₃^->SO₄^2->Fe（Ⅲ）>CK among different electron acceptor treatments.In conclusion,the temperature sensitivity of soil organic carbon anaerobic mineralization varies with community types in the Yellow River estuary wetland.The increasing of temperature promotes the anaerobic mineralization,whiles the increasing of salinity inhibites the anaerobic mineralization and improves the temperature sensitivity of the anaerobic mineralization.The increasing of temperature and salinity significantly changed the soil microbial community structure and enzyme activities in estuarine wetlands,which were closely related to anaerobic mineralization and its temperature sensitivity.The addition of electron acceptor inhibited the anaerobic mineralization of organic carbon in estuarine wetland,and improved the temperature sensitivity of the anaerobic mineralization.The results showed that the temperature range,salinity,microbial community structure,enzyme activity and the type and number of electron acceptors all had important effects on the response temperature of soil organic carbon anaerobic mineralization in estuarine wetland.