Effects Of Soil Enzymes And Microorganisms On Organic Carbon And Inorganic Carbon Of Saline-alkali Farmland Soil In Western Jilin Province

The soil carbon pool is the largest carbon pool of terrestrial ecosystems. Any change in the soil carbon pool has profound implications for global climate change. Both the soil organic carbon(SOC) pool and the soil inorganic carbon(SIC) pool are important components of the soil carbon pool. However, only a few studies have explored the effects of SIC on carbon pool in arid and semiarid regions. Soil microorganism is an important driving force for carbon cycle. And soil enzyme indicates the ability of nutrient transformation. With the semi-arid and semi-humid climate and the saline-alkali soil, the effects of soil microorganism and soil enzyme on SIC and SOC are new problems of soil carbon cycle.Western Jilin Province is the largest area of soda saline-alkali soil in China. It is an important area of global climate change and carbon cycle. The saline–alkali farmland soil in western Jilin Province are taken as the research object. This study adopted the methods of field sample collection, environmental monitoring, molecular biology, statistical analysis and model simulation. The variations in SOC and SIC content were observed firstly. The changes of microbial numbers and enzyme activities were indicated in the soil then. The community structure of soil microorganisms was investigated afterwards. The effects of soil enzymes and microorganisms on the SOC and SIC variations were explored finally. The key results are as follows.1 The SOC content of saline–alkali paddy soil initially decreased at the seedling and tillering stages, then increased at the heading stage, and finally decreased at the mature stage. However, the SOC content of saline–alkali dryland soil initially increased at the seedling and jointing stages, and then decreased at the heading and mature stages. The variations in SIC content of saline–alkali farmland soil were opposite. The SOC content decreased gradually with the increase in soil depth. However, The SIC content increased gradually with the increase in soil depth. The SOC content of loam was the maximum. Whereas the SIC content of silty loam was the maximum.2 The activities of catalase, invertase, amylase of saline–alkali paddy soil reached the maximum at the heading stage. However, those of saline–alkali dryland soil reached the maximum at the jointing stages. The activity of β-glucosidase of farmland soil reached the maximum at the mature stages. The activities of catalase, invertase, β-glucosidase and amylase in the surface soil were larger than those in the subsoil, and the difference was significant.3 The total microbial number of saline-alkaline farmland soil was relatively small. The bacterial number was dominant. The numbers of bacteria, actinomycete and fungi of paddy soil initially decreased at the seedling and tillering stages, then increased at the heading stage, and finally decreased at the mature stage. However, those of dryland soil initially increased at the seedling and jointing stages, and then decreased at the heading and mature stages. The numbers of bacteria, actinomycete and fungi in the surface soil were larger than those in the subsoil, and the difference was significant. The numbers of bacteria, actinomycete and fungi of dryland soil were larger than those of paddy soil.4 The abundance of bacteria and actinomycete was small at the seedling and tillering(jointing) stages, then reached the maximum at the heading stage, and finally tended to be stable at maturity stage. There were obvious variations of various microbial communities during the growth period. The community diversity of saline-alkali farmland soil reached the maximum at the mature stage, and the minimum at tillering(jointing) stage. The species abundance of farmland soil was high at the mature, heading and seeding. The species distribution of farmland soil was uniformity at the heading and seedling stages. The similarity of microbial community was high at the mature and heading stages, and that at tillering(jointing) was different from other stages. The dominant sequence of saline-alkali farmland soil was Proteobacteria, and the sub-dominant sequences of the surface and subsoil were different. The species abundance of paddy soil of sandy loam was the highest, and that of dryland soil of silty loam was high. The similarity of microbial community of paddy soil of silty loam and sandy loam is high, and that of dryland soil of sandy loam and loam is high. The community diversity of subsoil of saline-alkali farmland was higher than that of surface soil, and the species distribution of subsoil was more uniform. The functional microbes played key roles in the carbon turnover in saline-alkali soil. There were Xanthomonadales, Clostridiales, Cytophagaceae, Hyphomicrobiaceae, Flavobacterium, Pseudomonas, Vibrio, Lysobacter, Sphingomonas, Gemmatimonas, arthrobacter and photosynthetic bacteria in the saline-alkali soil.5 SOC was negatively correlated with SIC of saline–alkali farmland. SOC was positively correlated with invertase, amylase, catalase, β-glucosidase and the numbers of bacteria, actinomycete and fungi of paddy and dryland soil. SIC of paddy soil was negatively correlated with invertase, amylase, catalase, β-glucosidase and the numbers of bacteria, actinomycete and fungi, whereas SIC of dryland soil was negatively correlated with invertase, amylase, catalase, β-glucosidase and the fungal number. The regression analyses demonstrated that the amylase, bacteria and invertase exerted the greatest effects on SOC in paddy soil, while the invertase, fungi and β-glucosidase exerted the greatest effects on SOC in dryland soil. However, the catalase exerted the greatest effects on SIC in paddy and dryland soil. The principal component analysis showed that bacteria, fungi, actinomycete, amylase, invertase, catalase and β-glucosidase were main influence factors of soil carbon variations of saline–alkali farmland soil.Previous studies mainly focused on SOC, whereas SIC is included in the study of carbon cycle in saline-alkali soil area in the paper. The feature is to reveal the effects of soil enzymes and microorganisms on SOC and SIC under saline-alkali stress. It is a new attempt to explore the effect of fuctional microorganisms on soil carbon changes by using molecular biology technology.