Effect Of Rice Species And Arsenic Pollution On Soil Dissolved Organic Carbon, Nitrogen And Microbial Community Structure

Soil arsenic (As) pollution is a major threat to the safety of agricultural products and human health. Compared to other crops, rice is inclined to accumulate more arsenic, because of high bioavailability due to long-term flooding. The consumption of high As rice grain is a major exposure route, which resulted in increasing concern regarding the cultivation of rice on As contaminated soils. Soil microorganisms largely determine the biogeochemical cycling, soil organic matter turnover and soil fertility as well as quality. It is an important driving factor of the ground plant diversity and productivity of terrestrial ecosystems. Soil microbial community is an important measure of sustainable land use and is sensitive to changes in the soil chemical properties. In this paper, two paddy soils were selected to study the influence of rice species and As pollution on the amount of soil DOC and DON, and microbial community structure analyzed by PLFA. MRT and ABT analysis were used to calculate relative contribution of soil type, As pollution and rice species to microbial biomass and community structure. This is of great importance for maintaining a healthy and sustainable soil ecology system.The conclusions are as follows:1. Soil type, As pollution and rice species had a significant effect on DOC and DON. Over all, the content of DOC and DON were higher in the yellow mud field than the red mud field, with18.3%higher of DOC, and31.4%higher of DON. The amount of DOC and DON decreased with As pollution. Compared to DOC, DON dropped more sharply. On the whole, the content of DOC was highest when planted hybrid rice (41.09±0.80mg·kg-1), and it was similar when planted japonica rice (37.74±1.32mg·kg-1) and indica rice (38.10±1.18mg·kg-1). While the content of DON was highest when planted japonica rice (2.94±0.34mg·kg-1), and hybrid rice (2.58±0.37mg·kg-1) took the second place, and the indica rice was in the least.Under As pollution, DOC decreased by14.4%,11.1%in the yellow mud field and red mud field, respectively. While DON decreased by65.0%and46.1%, respectively.Effect of rice species changed when in different soil type and As level. Different rice species has varied tolerance of As pollution, which gave rise to different impact on DOC and DON. With As pollution, hybrid rice showed no significance in DOC, but japonica and indica rice had an evident influence on DOC, which descended by21.4%,15.8%, respectively. While DON descended by66.3%,65.4%,11.3%when planted japonica, hybrid, and indica rice, respectively.2. Soil type, As pollution and rice species had a significant effect on microbial community, which explained29.8%,17.6%and52.6%of the variation for microbial biomass, and37.7%,12.1%and21.9%of the variation for microbial community structure.Microbial biomass was higher in the yellow mud field (57.25±0.13nmol·g-1) than red mud field (42.50±0.09nmol·g-1). In the uncontaminated soil, yellow mud field was13.3%higher than red mud field. While in the contamination soli, yellow mud field was34.6%higher than red mud field. Microbial community variation was showed between the two paddy soils, with higher ratio of F/B, GP/GN and SF/AMF in the yellow mud field than red mud field.Compared with the uncontaminated soil, microbial biomass increased by24.8%in As contaminated yellow mud field, and6.6%in As contaminated red mud field. There was a significant effect on microbial community with different As level, and the effect varied in different soil type and rice species.Rice species made distinct impact on microbial biomass in yellow mud field and red mud field separately. In former paddy soil, microbial biomass was higher after planted hybrid and japonica rice than indica rice. However, the result was opposite in latter paddy soil.Rice species also had significant influence on microbial community structure. In yellow mud field, under As pollution, the ratio of F/B went up when planted hybrid rice, however it came down when planted indica rice. In red mud field, it went up when planted indica rice, while it came down when planted hybrid and japonica rice. The ratio of GP/GN descended. The ratio of SF/AMF also decreased in yellow mud field, but no obvious change in red mud field.