| Shouguang is well known as the vegetable production county in China, located at the mid of Shandong Province. Due to the economic reason, the trend moves increasingly towards the cultivation rate and output via continuous mono-cropping, excessive fertilizer application and frequent irrigation during the two growing seasons yearly. Therefore, this kind of vegetable production system have recently posed various environment risks including reduced yield, poor vegetable quality, soil salinization/ acidification, groundwater nitrate contamination or high nitrate vegetable exceeding the standard. Nematodes are one of the most abundant and widely distributed invertebrate animal taxa in edaphic habitats. Because they intervene to a great extent in trophic chains in ecosystems, nematodes has been found to play an important role in the decomposition of soil organic matter, nutrient cycling and maintenance of ecosystem stability. Due to their central role in soil process, they can be used as sensitive ecosystem indicators.Several studies on nematode community for greenhouse vegetable production have been conducted recently. The aim of this study was to investigate the trend of vertical distribution and seasonal fluctuation of the abundance and trophic groups of nematode community under the excessive fertilizer input. Additionally, three rates of fertilizer were applied to evaluate the effects of fertilization on the nematode density, nematode community structure and diversity, soil microorganism and the activity of soil enzymes. To improve the growth of vegetable the natural fatty acids including oleic acid and palmitic acid were added to the soils which appreciable poor vegetable growth were occured. The impacts of the two fatty acids were determined on cucumber and tomato seedlings in the continuously mono-cropped soil. Our study might provide insights into soil nematode community, especially on the most prevalent phytopathogenic nematodes, Meloidogyne spp. and be useful for forming a sustainable vegetable production system.1) Seasonal and spatial dynamics of soil nematode communities in greenhouses with continuous tomato production. Twelve nematode families encompassed 24 genera were observed in the investigated greenhouses. Cephalobus, Aphelenchus, Meloidogyne and Tylenchus, Pungentus were the dominant genera in CT6, while Eucephalobu, Aphelenchus, Meloidogyne and Pratylenchus, Doryldimus were the dominant genera in CT10. Plant-parasites were the most abundant trophic group, accounting for 67.6% of the total nematodes density in CT6 and 71.8% in CT10. The different patterns of vertical distribution of different nematode trophic groups were investigated. Free-living nematodes exhibited a typical surface accumulative type. Plant-parasites, however, the majority were observed in the 20-30cm in CT6, whereas most individuals were distributed in the 10-20cm layer in CT10. As to the dynamics, the maximum values of total nematodes were found at late harvest stage, and the minimum values were observed at full fruit stage in CT6. Unlike CT6, the total numbers were reached the maximum at seedling stage and the minimum at post harvest stage in CT10. In the study period, the mean abundance of total nematodes in CT10 was higher than that in CT6. And There were similar patterns for the population dynamics and vertical distribution of Meloidogyne spp. in both greenhouses. The abundance of total plant parasitic nematodes and Meloidogyne were both negatively correlated with the proportion of free-living nematodes. Among several ecological indices, PPI and PPI/MI were found to be most useful for distinguishing differences between the two greenhouses.2) Effects of fertilization treatment on the soil nematode communities. Three treatments were applied including control (NN), recommended treatment (SN) and conventional treatment (CN). With increasing nitrogen levels, soil organic matter and total nitrogen were gradually increased whereas soil pH was obviously decreased. SN increased soil actinomycetes number, the value of B/F, the activity of soil urease and catalase. In contrast, CN decreased the B/F value and the activity of soil catalase compared with NN. The abundance of plant-parasites and bacterivores increased in the SN and CN treatments, especially higher abundance of Tylenchus and Helicotylenchus were observed when compared to NN. The ecological indices, MI、ΣMI and PPI/MI showed the significant differences among the treatments. Spearman correlation analysis exhibited that the total nematode abundance, plant-parasites, bacterivores, the dominant genera Meloidogyne, Tylenchus and Helicotylenchus significantly correlated with soil factors. The results of this study suggested that recommended treatment has positive effect on vegetable yield and soil quality in greenhouse vegetable production system.3) Effects of natural fatty acids on the growth of cucumber and tomato seedlings in the continuously mono-croped soil in greenhouse. The combination of oleic and palmitic acids significantly promoted the growth of the both cucumber and tomato seedlings in this study. In the high level treatment group of pot experiments, growth indexes such as shoot diameter, shoot dry weight and root dry weight, lateral number, and activity of root system increased significantly in comparison with the control plants. The seedbed experiments performed under the field conditions further confirmed positive effect of fatty acids on the plant growth. Moreover, when cultured in Petri dishes, the mycelial growth and spore germinations of four common phytopathogenic fungi were significantly inhibited by the addition of palmitic acid, but not by adding oleic acid. The present study suggested that the oleic and palimitic acids could be potential and reliable natural substances for promoting seedling growth of some vegetable crops in greenhouse. |
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