Eucalyptus are a widely used short‐rotation species for timber production in South China. There are growing concerns regarding the influences of successive planting of Eucalyptus urophylla on microorganisms and soil. The aim of this work was to determine the effects of the successive planting of E. urophylla on soil characteristics. Five different stands, including 5‐, 10‐, 15‐, and 18‐year‐old E. urophylla plantations (abbreviated as 5yr, 10yr, 15yr, and 18yr, respectively) and one native evergreen broadleaf forest as a 0‐year‐old E. urophylla plantation (abbreviated as CK) were used. All of measured chemical indicators, microbial biomass, and enzyme activities were significantly lower in E. urophylla plantations compared with CK stand. The microbial biomass and enzyme activities significantly decreased in 5yr stand, significantly increased in 10yr stand, and subsequently declined in 15yr and 18yr stands. The relative abundance of Ascomycota in 15yr (77.10%) and 18yr (72.71%) plantations was significantly higher than in other stands. Basidiomycota relative abundance in the E. urophylla plantations was significantly lower than in the CK stand. In addition, the bacterial diversity was significantly decreased in 15yr and 18yr stands, whereas the fungal diversity was the lowest in 5yr stand and significantly increased in 10yr, 15yr, and 18yr stands. Furthermore, structural equation modelling showed that successive planting of E. urophylla decreased the soil bacterial community diversity, microbial biomass, and enzyme activity but increased the fungal community diversity. Thus, successive planting of E. urophylla negatively influenced the soil bacterial diversity, microbial biomass, and enzyme activity and positively influenced soil fungal diversity.

No abstract

Physicochemical properties and antioxidant activities of Desmodesmus armatus polysaccharides (DAP) were studied. They were extracted by microwave‐assisted constant temperature extraction and purification by DEAE‐cellulose 52. Four eluents of water (DAP1), 0.25 mol/L NaCl (DAP2), 0.5 mol/L NaCl (DAP3), and 1.0 mol/L NaCl (DAP4) were collected. Four polysaccharides fractions were analyzed, and they were all composed of mannose, rhamnose, glucuronic acid, galacturonic acid, arabinose, and fucose. Gel Permeation Chromatography (GPC) analysis showed that the four polysaccharides fractions have a uniform molecular weight distribution. Scanning electron microscope showed that DAP1 had a dense structure and a smooth but uneven surface, while DAP2, DAP3, and DAP4 were amorphous solids in sheets. Oxidation in vitro experiments showed that DAP2 and DAP3 had scavenging effects on ABTS, DPPH, and hydroxyl radicals. Practical applications In the determination of the antioxidant activity, it was found that the antioxidative activity of the polysaccharide of Desmodesmus armatus measured was significantly stronger than the crude polysaccharide of other microalgae. After the polysaccharide was purified, two polysaccharide fractions (DAP2 and DAP3) of Desmodesmus armatus were found to have strong scavenging ability to ABTS, DPPH, and hydroxyl radicals. They can be regarded as a new type of antioxidant, and the differences in the physicochemical properties between the parts can provide a preliminary explanation for the differences in antioxidant activity. But the connection between them needs further analysis. The Desmodesmus armatus used in the experiment is easy to cultivate and easy to obtain, which greatly increases its applicability. This research opens up new possibilities for the development of antioxidants and provides favorable evidence for the use of Desmodesmus armatus in food and feed.

No abstract

No abstract