Environmental and management controls of soil carbon storage in grasslands of southwestern China.

In order to predict the effects of climate change on the global carbon cycle, it is crucial to understand the environmental factors that affect soil carbon storage in grasslands. In the present study, we attempted to explain the relationships between the distribution of soil carbon storage with climate, soil types, soil properties and topographical factors across different types of grasslands with different grazing regimes. We measured soil organic carbon in 92 locations at different soil depth increments, from 0 to 100 cm in southwestern China. Among soil types, brown earth soils (Luvisols) had the highest carbon storage with 19.5 ±â€¯2.5 kg m-2, while chernozem soils had the lowest with 6.8 ±â€¯1.2 kg m-2. Mean annual temperature and precipitation, exerted a significant, but, contrasting effects on soil carbon storage. Soil carbon storage increased as mean annual temperature decreased and as mean annual precipitation increased. Across different grassland types, the mean carbon storage for the top 100 cm varied from 7.6 ±â€¯1.3 kg m-2 for temperate desert to 17.3 ±â€¯2.9 kg m-2 for alpine meadow. Grazing/cutting regimes significantly affected soil carbon storage with lowest value (7.9 ±â€¯1.5 kg m-2) recorded for cutting grass, while seasonal (11.4 ±â€¯1.3 kg m-2) and year-long (12.2 ±â€¯1.9 kg m-2) grazing increased carbon storage. The highest carbon storage was found in the completely ungrazed areas (16.7 ±â€¯2.9 kg m-2). Climatic factors, along with soil types and topographical factors, controlled soil carbon density along a soil depth in grasslands. Environmental factors alone explained about 60% of the total variation in soil carbon storage. The actual depth-wise distribution of soil carbon contents was significantly influenced by the grazing intensity and topographical factors. Overall, policy-makers should focus on reducing the grazing intensity and land conversion for the sustainable management of grasslands and C sequestration.

On the ratio of intercellular to ambient CO2 (c i/c a) derived from ecosystem flux.

The ratio of intercellular to ambient CO2 concentrations (c i/c a) plays a key role in ecophysiology, micrometeorology, and global climatic change. However, systematic investigation on c i/c a variation and its determinants are rare. Here, the c i/c a was derived from measuring ecosystem fluxes in an even-aged monoculture of rubber trees (Hevea brasiliensis). We tested whether c i/c a is constant across environmental gradients and if not, which dominant factors control c i/c a variations. Evidence indicates that c i/c a is not a constant. The c i/c a exhibits a clear "V"-shaped diurnal pattern and varies across the environmental gradient. Water vapor pressure deficit (D) is the dominant factor controls over the c i/c a variations. c i/c a consistently decreases with increasing D. c i/c a decreases with square root of D as predicted by the optimal stomatal model. The D-driving single-variable model could simulate c i/c a as well as that of sophisticated model. Many variables function on longer timescales than a daily cycle, such as soil water content, could improve c i/c a model prediction ability. Ecosystem flux can be effectively used to calculate c i/c a and use it to better understand various natural cycles.

Tropical forest soils serve as substantial and persistent methane sinks.

Although tropical forest soils contributed substantially global soil methane uptake, observations on soil methane fluxes in tropical forests are still sparse, especially in Southeast Asia, leading to large uncertainty in the estimation of global soil methane uptake. Here, we conducted two-year (from Sep, 2016 to Sep, 2018) measurements of soil methane fluxes in a lowland tropical forest site in Hainan island, China. At this tropical forest site, soils were substantial methane sink, and average annual soil methane uptake was estimated at 2.00 kg CH4-C ha-1 yr-1. The seasonality of soil methane uptake showed strong methane uptake in the dry season (-1.00 nmol m-2 s-1) and almost neutral or weak soil methane uptake in the wet season (-0.24 nmol m-2 s-1). The peak soil methane uptake rate was observed as -1.43 nmol m-2 s-1 in February, 2018, the driest and coolest month during the past 24 months. Soil moisture was the dominant controller of methane fluxes, and could explain 94% seasonal variation of soil methane fluxes. Soil temperature could not enhance the explanation of seasonal variation of soil methane fluxes on the top of soil moisture. A positive relationship between soil methane uptake and soil respiration was also detected, which might indicate co-variation in activities of methanotroph and roots and/or microbes for soil heterotrophic respiration. Our study highlights that tropical forests in this region acted as a methane sink.

[Clinical observation of axial offset after treatment by Ilizarov bone transport technology].

OBJECTIVE: To observe the incidence, causes and deviation angle of axial offset in patients with fracture ununited treated by Ilizarov bone transport technology. METHODS: From January 2007 to December 2012, 10 patients with fracture ununited were treated by Ilizarov bone transport including 8 males and 2 females with an average age of (30.3 ± 10.6) years old ranging from 18 to 49 years old. The segment of bone defect involved upper tibial in 2 cases, medial tibia in 2 cases, lower tibial in 5 cases, upper femoral in 1 case. For Paley type of bone defect, 6 cases were type B1, 4 cases were B3. The incidence and deviation angle of axial offset after Ilizarov bone transport technology were observed and evaluated on bone result by Paley assessment. RESULTS: All patients were followed up from 19 to 32 months with an average of (22.0 ± 5.6) months. Three cases were natural healed at fracture ends, the other 7 cases were healed after bone graft. The time of external fixator was 16 to 28 months. At the last follow-up, there were 3 cases occurred coronal angulation of angle 5° to 11° with an average of (8.7 ± 3.2). Sagittal angulation was in 4 cases, angle 6° to 9° with an average of (8.5 ± 2.1)°. There were 4 cases occurred axial offset. In the last follow-up, according to Paley evaluation criteria, osseous results were excellent in 7 cases, good in 3 cases; functional results were excellent in 6 cases, good in 4 cases. CONCLUSION: Axial deviation after the Ilizarov bone transport treatment is relatively common, which will result in delayed healing of bone and poor limb alignment. In order to improve the bone healing, corresponding measurements should be taken to avoid or reduce the incidence of axial deviation during and after the operation.

[Repair of the soft tissue defects of the anterior foot and the ankle with the reversed sural neurocutaneous flap].

OBJECTIVE: To investigate the operative method and effect of the reversed sural neurocutaneous flap in repairing soft tissue defects of the anterior foot and the ankle. METHODS: From March 1999 to November 2004, 19 cases (17 male, 2 female) of soft tissue defects of the anterior foot and the ankle were repaired with the reversed sural neurocutaneous flaps. The flap sizes range from 18 cm x 9 cm to 30 cm x 18 cm. RESULTS: All flaps survived well, while 1 flap had distal partial necrosis and healed after dressing change. The follow-up from 6 months to 2 years showed that all flaps were satisfactory. CONCLUSION: Sural neurocutaneous flap is easy to get and to survive. It is an effective method to repair the soft tissue defects of the anterior foot and the ankle.