The below-ground biomass contributes more to wetland soil carbon pools than the above-ground biomass-a survey based on global wetlands

The biomass of wetland plants is highly responsive to environmental factors and plays a crucial role in the dynamics of the soil organic carbon(SOC)pool.In this study,we collected and analyzed global data on wetland plant biomass from 1980 to 2021.By examining 1134 observations from 182 published papers on wetland ecosystems,we created a comprehensive database of wetland plant above-ground biomass(AGB)and below-ground biomass(BGB).Using this database,we analyzed the biomass characteristics of different climate zones,wetland types and plant species globally.Based on this,we analyzed the differences between the biomass of different plant species and the linkage between AGB and BGB and organic carbon.Our study has revealed that wetland plant AGB is greater in equatorial regions but BGB is highest in polar areas,and lowest in arid and equatorial zones.For plant species,the BGB of the Poales is higher than the AGB but Caryophyllales,Cyperales and Lamiales have higher AGB.Moreover,our findings indicate that BGB plays a more significant role in contributing to the organic carbon pool compared to AGB.Notably,when BGB is less than 1 t C ha^(-1),even slight changes in biomass can have a significant impact on the organic carbon pool.And we observed that the SOC increases by 5.7 t C ha^(-1)when the BGB content is low,indicating that the SOC is more sensitive to changes in biomass under such circumstances.Our study provides a basis for the global response of AGB and BGB of wetland plants to organic carbon.

Sensitivity of Labile Soil Organic Carbon Pools to Long-Term Fertilizer, Straw and Manure Management in Rice-Wheat System

Labile soil organic carbon （SOC） pools, estimated through chemical fractionation techniques, are considered sensitive indicators of management-induced changes in quality and composition of soil organic matter. Although the impacts of organic manure and crop residue applications on C sequestration in rice-wheat system are fairly well documented, their influence on labile SOC pools is relatively less known. Impacts of organic manure, rice straw, and inorganic fertilizer nitrogen （N） applications on soil total organic carbon （TOC） and SOC pools including water-extractable organic C （WEOC）, hot water-soluble organic C （HWOC）, potassium permanganate- oxidizable organic C （KMnO4-C）, microbial biomass C （MBC）, mineralizable organic C （Cmin）, and the oxidizable fractions of decreasing oxidizability （easily-oxidizable, oxidizable, and weakly-oxidizable） were investigated in an ll-year field experiment under rice-wheat system. The field experiment included treatments of different combinations of farmyard manure, rice straw, and fertilizer N application rates, with C inputs estimated to be in the range from 23 to 127 Mg ha-1. After 11 years of experiment, WEOC, HWOC, and KMnO4-C were 0.32%-0.50%, 2.2%-3.3%, and 15.0%-20.6% of TOC, respectively. The easily-oxidizable, oxidizable, and weakly-oxidizable fractions were 43%-57%0, 22%-27%, and 10%-19% of TOC, respectively. The applications of farmyard manure and rice straw improved WEOC, HWOC, KMnO4-C, easily-oxidizable fraction, Cmin, and MBC, though the rates of change varied considerably from -14% to 145% and -1170 to 83% of TOC, respectively. At the C input levels between 29 and 78 Mg C ha-1 during the ll-year period, the greatest increase was observed in WEOC and the minimum in KMnO4-C. Water-extractable organic C exhibited a relatively greater sensitivity to management than TOC, suggesting that it may be used as a sensitive indicator of management-induced changes in soil organic matter under rice-wheat system. All the other labile SOC pools exhibited almost the same sensitivity to management as TOC. Most of the SOC pools investigated were positively correlated to each other though their amounts differed considerably. Long-term applications of farmyard manure and rice straw resulted in build-up of not only the labile but also the recalcitrant pool of SOC, emphasizing the need for continued application of organic amendments for permanence of the accrued C under the experimental conditions.

Uncertainty and Sensitivity Analyses for Modeling Long-Term Soil Organic Carbon Dynamics of Paddy Soils Under Different Climate-Soil-Management Combinations

Reporting modeling results with uncertainty information can benefit decision making by decreasing the extent that variability exerts a disproportionate influence on the options selected. For making decisions with more confidence, the uncertainty interval should be as narrow as possible. Here, the soil organic carbon （SOC） dynamics of the major paddy soil subgroup from 4 different paddy field regions of China （located in 4 counties under different climate-soil-management combinations） were modeled using the DeNitrification- DeComposition （DNDC） model for the period from 1980 to 2008. Uncertainty intervals associated with the SOC dynamics for these 4 subgroups were estimated by a long-term global sensitivity and uncertainty analysis （i. e., the Sobolt method）, and their sensitivities to 7 influential factors were quantified using the total effect sensitivity index. The results, modeled with high confidence, indicated that in the past 29 years, the studied paddy soils in Xinxing, Yixing, and Zhongjiang counties were carbon （C） sinks, while the paddy soil in Helong County was a C source. The 3 C sinks sequestered 12.2 （5.4, 19.6）, 17.1 （8.9, 25.0）, and 16.9 （-1.2, 33.6） t C ha-1 （values in the parentheses are the 5th and 95th percentiles, respectively）. Conversely, the C source had a loss of -5.4 （-14.2, 0.06） t C ha-1 in the past 29 years. The 7 factors, which changed with the climate-soil-management context, exhibited variable influences on modeled SOC. Measures with potential to conserve or sequestrate more C into paddy soils, such as incorporating more crop residues into soils and reducing chemical fertilizer application rates, were recommended for specific soils based on the sensitivity analysis results.