Relationships for vitamin D with childhood height growth velocity and low bone mineral density risk.

Objective: To investigate how serum 25-hydroxyvitamin D (25[OH]D) affects height growth velocity and the risk of low bone mineral density (BMD) in children. Design: A population-based prospective cohort study. Patients and methods: A total of 10 450 participants with complete follow-up records from a cohort were included in the current study. Serum 25(OH)D concentrations were measured at baseline and 2-year follow-up, and the average of 2-time measurements was used for analysis. Low BMD was defined as calcaneus speed of sound Z-score ≤ -1. The associations of vitamin D with height growth velocity and the risks of incident low BMD were evaluated using adjusted ß and risk ratio (RR). Results: After multivariable adjustment, an inverse L-shaped association between serum 25(OH)D concentrations and height growth velocity was observed, leveling off up to 40-60 nmol/L. Overall, each 10 nmol/L higher serum 25(OH)D concentration was associated with a 0.15 cm/year higher height growth velocity (P < 0.001) and a 7% decreased risk of low BMD [RR (95%CI): 0.93 (0.87~0.98)]. Compared to those with vitamin D deficiency, participants who had sufficient vitamin D had a 22% lower risk for low BMD [RR(95%CI): 0.78 (0.62~0.98)]. However, no significant associations between vitamin D and the risk of low BMD were found in overweight and obese children. Conclusion: These findings highlight the importance of maintenance of sufficient 25(OH)D concentrations and healthy body weight during childhood in height growth and bone health promotion.

[Effects of Soil Moisture and Temperature Variations on Organic Carbon Mineralization of Purple Soil in the Hydro-fluctuation Belt of the Three Gorges Reservoir].

Soil sampling in the field and an incubation experiment in the laboratory was conducted to investigate the effects of soil moisture and temperature on soil organic carbon (SOC) mineralization of purple soil in the hydro-fluctuation belt of the Three Gorges Reservoir. Three incubation temperatures (10, 20 and 30℃) and four moisture levels (40% water holding capacity (WHC), 70% WHC, 100% WHC and submerged condition) were used in the experiment. In the entire incubation period (66 d), the SOC cumulative mineralization reached the maximum at 100% WHC, but there was no significant difference between 100% WHC and submerged condition (P>0.05). At 10℃ and 20℃, the SOC cumulative mineralization at 100% WHC and under submerged condition was not significantly different from that at 70% WHC treatment, but significantly higher than that at 40% WHC treatment. While the cumulative mineralization of organic carbon at 100% WHC and under submerged condition was significantly higher than that at 70% WHC and 40% WHC when the temperature was 30℃ (P<0.05). The results indicated that compared with 70% WHC treatment, the higher moisture content (100% WHC and submerged condition) had no negative effects but rather promotion effects on the mineralization of SOC at high temperature (30℃). Under the same soil moisture conditions, the SOC cumulative mineralization of purple soil in the hydro-fluctuation belt increased as temperature increased. Moreover, the analysis of variance showed that SOC cumulative mineralization was significantly affected by temperature and soil moisture, and there was a significant interaction with temperature and soil moisture (P<0.05). Fitting of two-pool first-order model was performed to indicate that temperature and soil moisture influenced the contents of labile SOC fraction and the mineralization rates of recalcitrant SOC fraction, which led to the differences of SOC cumulative mineralization under the different treatments. With the increasing temperature, the temperature sensitivity was significantly decreased in the 40% WHC treatment, but there was no obvious difference when the soil moisture content was not less than 70% WHC.

[Effects of variable temperature on organic carbon mineralization in typical limestone soils].

Soil sampling in the field and incubation experiment in the laboratory were conducted to investigate the responses of soil organic carbon (SOC) mineralization to variable temperature regimes in the topsoil of limestone soils from forest land and dry land. Two incubated limestone soils were sampled from the 0-10 cm layers of typical forest land and dry land respectively, which were distributed in Tianlong Mountain area of Puding county, Guizhou province. The soils were incubated for 56 d under two different temperature regimes including variable temperature (range: 15-25 degrees C, interval: 12 h) and constant temperature (20 degrees C), and the cumulative temperature was the same in the two temperature treatments. In the entire incubation period (56 d), the SOC cumulative mineralization (63.32 mg x kg(-1)) in the limestone soil from dry land (SH) under the variable temperature was lower than that (63.96 mg x kg(-1)) at constant 20 degrees C, and there was no significant difference in the SOC cumulative mineralization between the variable and constant temperature treatments (P < 0.05). While the cumulative mineralization (169.46 mg x kg(-1)) of organic carbon in the limestone soil from forest land (SL) under the variable temperature was significantly lower than that (209.52 mg x kg(-1)) at constant 20 degrees C. The results indicated that the responses of SOC mineralization to the variable temperature were obviously different between SL and SH soils. The SOC content and composition were significantly different between SL and SH soils affected by vegetation and land use type, which suggested that SOC content and composition were important factors causing the different responses of SOC mineralization to variable temperature between SL and SH soils. In addition, the dissolved organic carbon (DOC) content of two limestone soils were highly (P < 0.01) positively correlated with daily mineralization of soil organic carbon in both temperature treatments, which implied that controlling DOC production was an important way for the temperature influence of SOC mineralization. During the incubation period, SOC mineralization was independent of microbial biomass carbon (MBC) content in both temperature treatments. Combined with mineralization kinetic data, the results showed that, compared to constant temperature 20 degrees C, variable temperature mainly influenced SOC mineralization by changing microbial community activity rather than by changing microbial quantity.