[Effects of wheat-straw returning into paddy soil on dissolved organic carbon contents and rice grain yield].

A tank experiment using conventional rice cultivar Nanjing 44 as experimental material was conducted at the Experimental Farm of Yangzhou University to investigate the dynamics of wheat straw decomposition rate and the amount of carbon release in clay and sandy soils, as well as its effects on the content of dissolved organic carbon (DOC) and rice yield. The two rates of wheat straw returning were 0 and 6000 kg · hm(-2), and three N application levels were 0, 225, 300 kg · hm(-2). The results showed that, the rate of wheat straw decomposition and the amount of carbon release in clay and sandy soils were highest during the initial 30 days after wheat straw returning, and then slowed down after, which could be promoted by a higher level of nitrogen application. The rate of wheat straw decomposition and the amount of carbon release in clay soil were higher than that in sandy soil. The DOC content in soil increased gradually with wheat straw returning into paddy soil and at the twenty-fifth day, and then decreased gradually to a stable value. The DOC content at the soil depth of 15 cm was significantly increased by wheat straw returning, but not at the soil depth of 30 cm and 45 cm. It was concluded that wheat straw returning increased the DOC content in the soil depth of 0-15 cm mainly. N application decreased the DOC content and there was no difference between the two N application levels. Straw returning decreased the number of tillers in the early growth period, resulted in significantly reduced panicles per unit area, but increased spikelets per panicle, filled-grain percentages, 1000-grain mass, and then enhanced grain yield.

Matrix metalloproteinases in human sclerotic dentine of attrited molars.

OBJECTIVE: The relationship between the major proteinases in dentine matrix metalloproteinases (MMPs) and the formation of collagen-less sclerotic dentine is still unknown. This study is to compare the concentrations of dentinal MMP-1, -2, -3, -8, and -9 between human sound and sclerotic dentine. DESIGN: Eleven sound third molars from young patients and twenty-two attrited molars with sclerotic dentine from old patients were collected and three groups of dentine samples were obtained: sound dentine of young tooth (SDY), non-sclerotic dentine of attrited tooth (NDA) and sclerotic dentine of attrited tooth (SDA). The dentine powder from each group was subjected to demineralization and protein extraction in turn. Then the contents of MMP-1, -2, -3, -8 and -9 were quantitatively evaluated by Fluorescent Microsphere Immunoassay. The occlusal and fractured axial surfaces of sound and sclerotic dentine were observed using FEI-SEM. RESULTS: There was no significant difference in the concentration of MMP-1 amongst all tested groups (p>0.05). The contents of MMP -2 and MMP-3 in SDY were significantly higher than those in NDA and SDA (p<0.05). The contents of MMP -8 and MMP -9 in SDA were significantly higher than those in SDY and NDA (p<0.05). The surface hypermineralised layer and sclerotic casts were all detected in sclerotic dentine under SEM. CONCLUSIONS: The morphological characteristics of sclerotic dentine from the attrited molars were comparable to that from noncarious cervical lesions. Although depended on the type of MMP, the contents of dentinal MMPs changed during the formation of sclerotic dentine and long-term ageing.