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Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We examined the regularity of distribution and chemical structure characteristics of organic carbon in soda alkaline fluvo-aquic soil aggregates after straw returning. We set up six different straw returning treatments in 2020, including 0 (CK), 2100 (ST 1 ), 4200 (ST 2 ), 6300 (ST 3 ), 8400 (ST 4 ) and 10500 kg·hm -2 (full straw returning, ST 5 ). We measured organic carbon (OC) content and infrared spectroscopy characteristics of aggregates and internal different components through physical fractionation method and infrared spectroscopy technology. The results showed that: 1) the OC content of soil and all aggregates increased with the increasing amount of returned straw; 2) different straw returning treatments significantly increased the content of light organic carbon (LOC) in 53-250 μm aggregates. Compared with CK, ST 3 and ST 4 treatments significantly increased the content of mineral-bound organic carbon (MOC) in 250-2000 μm aggregates and the content of fine particulate organic carbon (fPOC) in 53-250 μm aggregates. The OC content of different components in aggregates followed the order of LOC>MOC>POC. The fPOC content in 250-2000 μm aggregates was higher than that of coarse particulate organic carbon (cPOC); 3) the results of principal component analysis showed that OC chemical structure of different components in aggregates was seldom affected by the straw returning, but was mainly affected by particle size; 4) the OCs in >250 μm aggregates were mainly derived from aromatic carbon and polysaccharides. The OCs in 53-250 μm aggregates were mainly derived from carbohydrates, such as monosaccharides and polysaccharides, while the OC in <53 μm aggregates was mainly derived from aliphatic carbon, alkyl carbon, aromatic carbon and phenolic alcohols. Within different aggregates, LOC was mainly derived from aliphatic carbon, aromatic carbon and phenolic alcohols. Particulate organic carbon (POC) was mainly derived from carbohydrates. MOC was mainly derived from alkyl carbon. In summary, straw returning increased organic carbon content in soil aggregates in short term, but did not alter organic carbon chemical structure. The organic carbon chemical structures of the same particle size fractions in different aggregates were similar. The organic carbon content increased with the decreases of particle size, and the chemical structure tended to be stable. Therefore, straw returning promoted the fixation of organic carbon by saline soil aggregates in short term, but did not change their chemistry structural characteristics, indicating that the location and protection degree of soil organic carbon in aggregates were the main factors affecting the chemical structure of organic carbon.

To examine the effects of management measures on carbon and nitrogen contents, as well as their distribution and structural characteristics of different soil fractions in Moso bamboo plantations, we compared three types of the bamboo forests (undisturbed, extensively managed, and intensively managed) and the control secondary broadleaved evergreen forest using the methods of physical fractionation, chemical and biological analysis and Fourier-transform infrared spectroscopy (FTIR). The results showed that soil total organic carbon (TOC) and total nitrogen (TN) content, as well as free particulate organic carbon and nitrogen, soluble organic carbon and nitrogen (DOC, DON), and mineral-associated organic carbon and nitrogen in the undisturbed and extensively managed Moso bamboo plantations were significantly increased compared with that in the control. The distribution ratio of free particulate organic carbon and nitrogen in the undisturbed Moso bamboo plantation significantly increased, with mineral-associated organic carbon being the largest reservoir of soil organic carbon (67.6%). Intensive management resulted in the decrease of soil organic carbon, total nitrogen storage, and the contents of each component, but significantly increased DOC/TOC, the ratio of microbial biomass nitrogen to TN as well as the ratio of microbial biomass carbon to TOC (microbial quotient). Management measures significantly affected the chemical structure of SOC. Compared with the control, the relative intensities of phenolic and alcoholic-OH, aliphatic methyl and methylene, aromatic C=C, and carbonyl C=O absorption were higher in the SOC of undisturbed and extensively managed Moso bamboo plantations, and soil hydrophobicity was significantly increased. Results from correlation analysis showed that soil hydrophobicity and the content of aliphatic and aromatic groups were negatively correlated with microbial quotient and positively correlated with TOC and TN content. In conclusion, the increased inputs of organic matter residues (such as litter and roots) could contribute to the relative accumulation of chemical resistance compounds with reduced human disturbance, which significantly enhanced chemical stability of soil organic carbon. Soil clay minerals played a key role in protecting soil organic carbon through the formation of mineral-organic compounds, which facilitate the stability of soil carbon storage and the long-term preservation of soil carbon.