Soil microbial activity and community structure as affected by exposure to chloride and chloride-sulfate salts

Mixed or chloride salty ions dominate in saline soils, and exert wide-ranging adversely affect on soil biological processes and soil functions. The objectives of this study were to（1） explore the impacts of mixed（0, 3, 6, 10, 20 and 40 g Cl–/SO42–salt/kg dry soil） and chloride（0, 1.5, 3, 5, 8 and 15 g Cl– salt/kg dry soil） salts on soil enzyme activities, soil physiological functional（Biolog） profiles and microbial community structure by using soil enzymatic, Biolog-Eco microplates as well as denaturing gradient gel electrophoresis（DEEG） methods, and（2） determine the threshold concentration of soil electronic conductivity（EC1：5） on maintaining the functional and structural diversity of soil microbial community. The addition of either Cl– or mixed Cl–/SO42–salt obviously increased soil EC, but adversely affected soil biological activities including soil invertase activity, soil microbial biomass carbon（MBC） and substrate-induced respiration（SIR）. Cl– salt showed a greater deleterious influence than mixed Cl–/SO42–salt on soil enzymes and MBC, e.g., the higher soil MBC consistently appeared with Cl–/SO42–instead of Cl– treated soil. Meanwhile, we found that SIR was more reliable than soil basal respiration（SBR） on explaining the changes of soil biological activity responsive to salt disturbance. In addition, microbial community structures of the soil bacteria, fungi, and Bacillus were obviously affected by both salt types and soil EC levels, and its diversity increased with increasing of mixed Cl–/SO42–salt rates, and then sharply declined down after it reached critical point. Moreover, the diversity of fungal community was more sensitive to the mixed salt addition than other groups. The response of soil physiological profiles（Biolog） followed a dose-response pattern with Cl–（R2=0.83） or mixed Cl–/SO42–（R2=0.89） salt. The critical threshold concentrations of salts for soil physiological function were 0.45 d S/m for Cl– and 1.26 d S/m for Cl–/SO42–, and those for soil microbial community structural diversity were 0.70 d S/m for Cl– and 1.75 d S/m for Cl–/SO42–.

Soil Microbial Activity and Functional Diversity in Primeval Beech Forests

Virgin forests are unique ecosystems, which can be used as etalon for basic biocoenotic investigation. Soil microorganisms are very sensitive reagents on influence of biotical factors, and at the same time are the active producers of phytotoxic and phytostimulating exometabolites. Studies of soil microbiota were conducted in virgin beech forests of Shyrokoluzhansky massif of the Carpathian Biosphere Reserve. It was found the ratio and the number of different ecological-trophic groups of soil microorganisms changes with altitude. So the number of ammonificators with increasing of altitude above sea level was reduced. The soil at altitude of 1,100 meters above sea level was characterized by minimum content of organotrophes -1.22 × 10^6 （CFU-colony forming units/lg.a.d.s.）. At the altitude of 500 meters content of ammonificators increased at six times and was 7.07 ×10^6 CFU/lg.a.d.s., which indicates to accumulation of the soil organic matter. Similar changes occurred with the number of bacteria which are using mineral forms of nitrogen for their nutrition. Their maximum quantity （4.32 × 10^6 CFU/lg.a.d.s.） was in the soil of biotope disposed at altitude of 500 meters above sea level. Fluctuations in the number of soil micromycetes of virgin forest ecosystems have not been as significant as the bacterial microbiota （within 17 ×10^3-28 × 10^3 CFU/lg.a.d.s.）. Among a wide spectrum of bacterial microbiota were isolated strains with high phytostimulating action.

Soil Fertility in Agroforestry System of Chinese Fir and Villous Amomum in Subtropical China

A trial of interplanting and non-interplanting villous amomum (Amomum villosum Lour.) under the canopy of Chinese fir (Cunninghamia lanceolata Hook.) at age 22 was established in Sanming, Fujian of China, and a survey on soil fertility was carried out 10 years after its establishment. Compared with the control (non-interplanting), the properties of soil humus in agroforestry system were ameliorated, with a higher level of humification and resynthesis of organic detritus. The soil microbial population and enzymatic activities were both higher under the influence of villous amomum. Both the nutrient supplying and nutrient conserving capacities of the soil were improved. This agroforestry system exhibited an advantage of improved soil fertility as well as an accelerated growth of Chinese fir, it was, therefore, a sustainable management system suited for Chinese fir in South China.