[Soil nematode community characteristics of alfalfa field with different growing ages in the semi-arid Loess Plateau of Central Gansu, Northwest China]. / 陇中黄土高原半干旱区不同种植年限紫花苜蓿土壤线虫群落分布特征.

To clarify the impacts of long-term alfalfa plantation on the soil nematode community, soil samples were collected from different alfalfa growing ages (2 a, 9 a, 18 a) in the semi-arid area of Loess Plateau in Central Gansu by Illumina Miseq sequencing technology. The main controlling factors affecting its community change were also explored. The results showed that soil nematode belongs to 2 classes, 7 orders, 16 families and 21 genera. Among them, Chromadorea was the dominant group (44.6%-81.4%), the relative abundance of which decreased with alfalfa growing ages. Paratylenchus, Helicotylenchus, Xiphinema, Pristionchus, Ditylenchus, Panagrolaimus, Longidorus, Aprutides, Isolaimium and Aglenchus were the special nematode species of alfalfa, among which Paratylenchus (54.1%), Helicotylenchus (23.9%) and Xiphinema (21.9%) were the dominant nematodes in 2 a, 9 a and 18 a alfalfa soil respectively. Plant-parasitic nematode was the dominant group in alfalfa soil (31.8%-67.1%), and its relative abundance decreased at first and then increased with alfalfa growing ages. Results of redundancy analysis showed that soil available phosphorus and total nitrogen were the dominant environmental factors affecting community structure of soil nematodes in the region.

[Soil bacterial community characteristics and ecological function prediction of alfalfa and crop rotation systems in the Loess Plateau, Northwest China]. / 黄土高原苜蓿-粮食作物轮作下土壤细菌群落特征和生态功能预测.

In order to understand the effects of lucerne cropping rotation on the bacterial community of loess soil, a long-term field experiment was conducted in rain-fed agricultural area of Loess Plateau. The cropping systems included continuous lucerne (Medicago sativa, LC), lucerne removed and rotated with spring wheat (Triticum aestivum, LFW), lucerne removed and rotated with corn (Zea mays, LFC), lucerne removed and rotated with potato (Solanum tuberosum, LP), and lucerne removed and rotated with continuous millet (Panicum miliaceum, LM). Based on 16S rRNA high-throughput sequencing technology, we investigated soil bacterial community structure and diversity in different cropping systems, and predicted ecological function using PICRUSt method. The results showed that the dominant phyla of loess soil bacteria were Actinomycetes (20.3%-32.0%), Proteobacteria (19.2%-23.0%), Acidobacteria (12.4%-14.2%) and Chloroflexus (11.0%-12.7%). The dominant genus was Bacillus (1.9%) in lucerne-corn system and Pseudarthrobacter (2.5%) in other treatments. Rotation with annual crops decreased the relative abundance of Actinobacteria and increased that of Chloroflexi and Firmicutes. Redundancy analysis showed that the main soil factors driving soil bacterial community structure were nitrate, ammonium, and total nitrogen. PICRUSt function prediction results showed that metabolism (78.6%-79.1%) was the main function of soil bacterial communities in loess soil. Rotation with continued annual crops significantly decreased the abundance of soil bacterial carbohydrate metabolism functional genes, and significantly increased the abundance of functional genes for soil bacterial cofactors and vitamin metabolism, neurodegenerative diseases, and immune system. In conclusion, lucerne removed and rotated with continuous annual crops changed soil bacterial community structure and ecological functions. This study provided theoretical reference to explore succession characteristics of soil bacteria and to select succeeding crops for alfalfa in loess soil.

[Soil dryness characteristics of alfalfa cropland and optimal growth years of alfalfa on the Loess Plateau of central Gansu, China].

This paper investigated soil moisture in alfalfa (Medicago sativa) cropland with different growth years (1, 3, 8, 12 and 14 years) and discussed the optimum growth years of alfalfa on the Loess Plateau of central Gansu. The results showed that the soil moisture along 0-300 cm soil profile of alfalfa croplands with different growth years was obviously lower than that of the local soil stable moisture. The soil water contents in croplands with alfalfa that had grown for 12 and 14 years were only 9.2% and 7.1% of local soil stable moisture, respectively, which were even lower than the lower limit of alfalfa growth. The average soil dryness indexes along 0-300 cm soil profile in 1, 3, 8, 12 and 14 years alfalfa croplands were 125.4%, 30.5%, 18.4%, -34.2% and -83.3% respectively. The results indicated that soil dryness occurred to varying degrees with different growth years except croplands with alfalfa grown for 1 year. With the increase of growth years of alfalfa, the soil dryness intensity increased and the soil dryness rate decreased. According to the soil moisture and alfalfa productivity results in this study, it could be concluded that the optimum growth years of alfalfa are 8-10 years in semiarid areas of the Loess Plateau.