Alpine Grassland Soil Organic Carbon Stock and Its Uncertainty in the Three Rivers Source Region of the Tibetan Plateau

<div><p>Alpine grassland of the Tibetan Plateau is an important component of global soil organic carbon (SOC) stocks, but insufficient field observations and large spatial heterogeneity leads to great uncertainty in their estimation. In the Three Rivers Source Region (TRSR), alpine grasslands account for more than 75% of the total area. However, the regional carbon (C) stock estimate and their uncertainty have seldom been tested. Here we quantified the regional SOC stock and its uncertainty using 298 soil profiles surveyed from 35 sites across the TRSR during 2006–2008. We showed that the upper soil (0–30 cm depth) in alpine grasslands of the TRSR stores 2.03 Pg C, with a 95% confidence interval ranging from 1.25 to 2.81 Pg C. Alpine meadow soils comprised 73% (i.e. 1.48 Pg C) of the regional SOC estimate, but had the greatest uncertainty at 51%. The statistical power to detect a deviation of 10% uncertainty in grassland C stock was less than 0.50. The required sample size to detect this deviation at a power of 90% was about 6–7 times more than the number of sample sites surveyed. Comparison of our observed SOC density with the corresponding values from the dataset of Yang et al. indicates that these two datasets are comparable. The combined dataset did not reduce the uncertainty in the estimate of the regional grassland soil C stock. This result could be mainly explained by the underrepresentation of sampling sites in large areas with poor accessibility. Further research to improve the regional SOC stock estimate should optimize sampling strategy by considering the number of samples and their spatial distribution.</p></div

Different strategies for landing from different heights among people with chronic ankle instability

Background Lateral ankle sprain (LAS) usually occurs during landing from heights among people with chronic ankle instability (CAI). Although the kinematics when landing on the flat surface has been reported, no studies have explored the effect of different heights on the landing strategies using a trapdoor device among people with CAI. Research question Do people with CAI adopt different landing strategies when drop-landing on the trapdoor device from three heights? Methods Thirty-one participants with CAI (24 males and 7 females, age=21.1±1.8 years, height=176.9±7.4 cm, body mass=71.9±9.2 kg, injured side=18 R&13 L) were recruited. They dropped from three different heights (low height (16 cm), medium height (23 cm), high height (30 cm)) with their affected foot landing on a movable surface of a trapdoor device, which was tilted 24° inward and 15° forward to simulate LAS. Kinematic data was collected using a twelve-camera motion capture system. One-way analysis of variance with repeated measures was used to compare the differences between the three heights. Results Significant height effects were detected in the peak ankle inversion angle (p=0.009, η2p=0.280) and angular velocity (pd: 0.14–0.44) and high heights (p: 0.001–0.023, d: 0.28–0.66), except for the ankle plantarflexion angle, which was lower at a low height than at medium (pd=0.44) and high (p=0.021, d=0.38) heights. Significance People with CAI adopt a protective strategy during drop-landing at medium and high heights compared to a low height. This strategy involves increased ankle dorsiflexion angle as well as knee and hip flexion angles. </p

The study area, distribution of sampling sites and soil organic carbon density by grassland type in the Three River Source Region.

<p>The study area, distribution of sampling sites and soil organic carbon density by grassland type in the Three River Source Region.</p

Mean SOC stocks with uncertainty estimates (95% confidence intervals) for alpine grasslands in the Three Rivers Source Region from our data, the dataset of Yang et al.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097140#pone.0097140-Yang1" target="_blank">[2]</a>, and the pooled dataset.</p

Probability (power) of detecting a 10% uncertainty in soil organic carbon density with a 0.05 level of significance for grassland types at three soil depths.

<p>The numbers above each bar represent the number of sampling sites needed to be taken at three depths for each alpine grassland to detect the tolerated uncertainty with 90% probability.</p

Predicted SOC densities by kriging of our data against observed values of Yang et al.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097140#pone.0097140-Yang1" target="_blank">[2]</a>.</p

Comparisons of soil organic carbon concentration (A) and density (B) between present and previous studies.

<p>The present SOC values (open squares) were extracted from our kriged prediction map. The dark grey circles (A) indicated the measured SOC concentration values from previous study, while the previous corresponding SOC densities (B) were re-calculated using different bulk density values derived from pedotransfer functions of Yang et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097140#pone.0097140-Yang2" target="_blank">[22]</a> (dark circles) and Zhong et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097140#pone.0097140-Zhong1" target="_blank">[23]</a> (gray circles), since bulk density was not measured in the previous study <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097140#pone.0097140-Liu1" target="_blank">[21]</a>.</p

Soil sampling locations from our survey and the extracted dataset of Yang et al.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097140#pone.0097140-Yang1" target="_blank">[2]</a>.</p

Sliding window analyses showing the nucleotide diversity based on alignment of complete mtDNAs of four species in <i>Moschus</i> (<i>M</i>. <i>chrysogaster</i>, <i>M</i>. <i>moschiferus</i>, <i>M</i>. <i>berezovskii</i> and <i>M</i>. <i>anhuiensis</i>).

<p>The black line shows the value of nucleotide diversity (<i>π</i>) in a sliding window analysis of window size 300 bp with step size 10, the value is inserted at its mid-point. Gene boundaries are indicated with an indication of the total number of variable positions per gene; ATP8 with ATP6, ND4L with ND4, and ND5with ND6 are overlapping.</p

Geographic distribution of <i>Moschus</i> species and consensus mitochondrial gene tree.

<p>Tree is equivalent to that of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0134183#pone.0134183.g003" target="_blank">Fig 3</a>. All the information about geographic distribution of <i>Moschus</i> species were came from IUCN (<a href="http://www.iucnredlist.org/" target="_blank">http://www.iucnredlist.org/</a>), except a new distribution area of <i>M</i>. <i>berezovskii</i>, which was marked by a star [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0134183#pone.0134183.ref039" target="_blank">39</a>].</p