The study was conducted in Zhifanggou Watershed, Shaanxi Province, China, to evaluate the effect of different vegetation types on hot-water extractable C, N and P fractions, with the aim to determine whether hot-water extractable fractions could be used as indicators of soil quality change in Loess Plateau. The six vegetation types established in 1975 were (i) Robinia pseudoacacia L., (ii) Caragana korshinkii Kom., (iii) Pinus tabulaeformis Carr., (iv) P. tabulaeformis-Amorpha fruticosa L., (v) R. pseudoacacia-A. fruticosa, and (vi) grassland. A cropped hillslope plot and a Platycladus orientalis L. native forest plot were used as references. The results indicated that the conversion of native forest to cropland resulted in a significant decline in the hot-water extractable C, N and P fractions. Hot-water extractable C, N, and P increased when cultivated land was revegetated, but after 30 years the amount of hot-water extractable C, N, and P in revegetated fields was still much lower compared to native forest. Hot-water extractable fractions increased more under mixed-forest than under pure-forest stands. Furthermore, there was a significant correlation between the hot-water extractable fractions and soil chemical and microbiological properties. The results showed that hot-water extractable fractions could be used as indicators of soil quality change on the Loess Plateau.

The Loess Plateau in China is one of the most eroded areas in the world. Accordingly, vegetation restoration has been implemented in this area over the past two decades to remedy the soil degradation problem. Understanding the microbial community structure is essential for the sustainability of ecosystems and for the reclamation of degraded arable land. This study aimed to determine the effect of different vegetation types on microbial processes and community structure in rhizosphere soils in the Loess Plateau. The six vegetation types were as follows: two natural grassland (Artemisia capillaries and Heteropappus altaicus), two artificial grassland (Astragalus adsurgens and Panicum virgatum), and two artificial shrubland (Caragana korshinskii and Hippophae rhamnoides) species. The microbial community structure and functional diversity were examined by analyzing the phospholipid fatty acids (PLFAs) and community-level physiological profiles. The results showed that rhizosphere soil sampled from the H. altaicus and A. capillaries plots had the highest values of microbial biomass C, average well color development of carbon resources, Gram-negative (G-) bacterial PLFA, bacterial PLFA, total PLFA, Shannon richness, and Shannon evenness, as well as the lowest metabolic quotient. Soil sampled from the H. rhamnoides plots had the highest metabolic quotient and Gram-positive (G+) bacterial PLFA, and soil sampled from the A. adsurgens and A. capillaries plots had the highest fungal PLFA and fungal:bacterial PLFA ratio. Correlation analysis indicated a significant positive relationship among the microbial biomass C, G- bacterial PLFA, bacterial PLFA, and total PLFA. In conclusion, plant species under arid climatic conditions significantly affected the microbial community structure in rhizosphere soil. Among the studied plants, natural grassland species generated the most favorable microbial conditions.

This study aimed to determine the characteristics of soil microbial community composition and its relationship with soil chemical properties during natural recovery in the Loess Plateau. The soil microbial community composition was analyzed by comparing the soil microbial phospholipid fatty acids (PLFAs) of eight croplands abandoned for 1, 3, 5, 10, 13, 15, 20, and 30 yr in the Dunshan watershed, northern Loess Plateau, China. The results showed that soil organic carbon, total nitrogen, soil microbial biomass carbon, and soil microbial biomass nitrogen significantly increased with the abandonment duration, whereas the metabolic quotient significantly decreased. The Shannon richness and Shannon evenness of PLFAs significantly increased after 10 yr of abandonment. Gram-negative, Gram-positive, bacterial, fungal, and total PLFAs linearly increased with increased abandonment duration. Redundancy analysis showed that the abandonment duration was the most important environmental factor in determining the PLFA microbial community composition. The soil microbial PLFAs changed from anteiso- to iso-, unsaturated to saturated, and short- to long-chain during natural recovery. Therefore, in the Loess Plateau, cropland abandonment for natural recovery resulted in the increase of the soil microbial PLFA biomass and microbial PLFA species and changed the microbial from chemolithotrophic to a more heterotrophic community.