| Soil aggregates are the basic units of soil structure, and the niche of microbes. Microorganisms play an important role in soil aggregate formation. The properties of dry aggregate in soil surface layer play an important role in soil quality, crop production and sustainable development of ecological system in dry and semi-dry area which ecological systems is very unstable. The amount and quality of soil aggregate have directly affect on keeping water and nutrient and the ability of resistant wind erosion., in this study, seven soils with different managements were collected from Inner Mongolia in semi-arid area; the soils were woodland, non-irrigated soil, irrigated soil and grassland soil. The soil aggregates of >5 mm, 5-2 mm, 2-1 mm, 1-0.5 mm, 0.5-0.25 mm and <0.25 mm were respectively obtained by dry-sieving method and the soil microbial biomass, activity and community structure and function were determined. Our studies have important significance to improving soil fertility, increasing water usage and decreasing wind erosion. The following results were obtained in this study.The content of MBC were range from 153 mg kg-1 and 336 mg kg-1, and the irrigated soil had the highest amount of microbial biomass carbon (MBC). The large aggregates (>2 mm) contained more higher amounts of both the soil organic C and microbial biomass C than the small aggregates it was related to the reason of the formation of macroaggregate. The content of K2SO4-extractable C were 11 and 59 mg kg , respectively, the small aggregates (<1 mm) contained much higher K2SO4-extractable C than the large aggregates. The irrigated soil had the highest proportion of large soil aggregates and the correlation between MBC and organic C was very significantly.The content of total N (TN), microbial biomass N (MBN), K2SO4 extractable N (K2SO4-N) of the soil and aggregates were all highest in irrigated arable and were lowest in grassland. The results showed that the different inputs of organic materials and nitrogen fertilizer of the sampled soils significantly affect not only the contents of total N, microbial biomass N and K2SO4-extractable N, but also their distributions in soil aggregates. Generally, the small aggregates contained significantly lower total N and microbial biomass N than the larger aggregates in the soils with low inputs of organic materials and N fertilizer. In contrast, the small aggregates contained much higher total N and microbial biomass N than the larger aggregates in the soils with high input. It is implied that, under natural condition, N was firstly cycled in the large aggregates. Thus, the N of the large aggregates may play much more important role in natural low nutrition condition than that of the small aggregates.The amount of microbial biomass P (MBP) and organic P (OP) were highest and lowest in the irrigated arable soil and the grassland soil, respectively. Moderately labile organic P (MLOP) and moderately resistant organic P (MROP) were the first mainly component, which took up 70-88% of OP and highly resistant organic P (HROP) and labile organic P (LOP) were the second mainly component. The large aggregates (>2 mm) had the higher content of MSOP and HROP, the small aggregates were rich in LOP and MLOP. Relative activity of OP in grassland soils and irrigated arable soil were higher than other soils.The amount of total PLFAs were from 19.82 - 47.28 ng g-1, the irrigated arable soil had thehighest amount of total phospholipid fatty acid (PLFA) and the woodland soil had the lowest value, hi total PLFAs, the content of monosaturate PLFA was highest, the second and the third amount were branch and straight PLFA. The content of soil bacterial had significant difference among soils, the value of bacterial in irrigate soil were three times than in grassland soil, the amount of fungi were higher in woodland and grassland than arable soil. The principle component analysis (PCA) showed 14:0 3OH was the fatty acid that had most significant contribution to the whole soil microbial community structure. The PCA...
|
PDF Full Text Request