Light grazing facilitates carbon accumulation in subsoil in Chinese grasslands: A meta-analysis.

Grazing by livestock greatly affects the soil carbon (C) cycle in grassland ecosystems. However, the effects of grazing at different intensities and durations on the dynamics of soil C in its subsoil layers are not clearly understood. Here, we compiled data from 78 sites (in total 122 published studies) to examine the effects of varying grazing intensities and durations on soil C content at different depths for grasslands in China. Our meta-analysis revealed that grazing led to an overall decrease in soil C content and productivity of above-ground vegetation (e.g., above-ground biomass and litter) but an increase in below-ground biomass. Specifically, the effects of grazing on soil C content became less negative or even positive with increasing soil depths. An increase of soil C content was consequently found under light grazing (LG), although soil C content still decreased under moderate and heavy grazing. The increase in soil C content under LG could be largely attributed to the increase of soil C content in subsoil layers (>20 cm), despite that soil C content in surface soil layer (0-20 cm) decreased. Moreover, the magnitude of increase in soil C content under LG in subsoil layers increased with grazing duration. A possible reason of the increase in soil C content in the subsoil layers was due to the increases in below-ground biomass. Our study highlights that LG may modify the allocation of C input and promote its accumulation in subsoil layers, thus offsetting the negative impact of grazing on surface soil C content, a finding that has significant implications for C sequestration in grasslands.

Revealing the spatio-temporal variability of evapotranspiration and its components based on an improved Shuttleworth-Wallace model in the Yellow River Basin.

Identifying the spatio-temporal variations of evapotranspiration (ET) from its components (soil evaporation and plant transpiration) can greatly improve our understanding of water-cycle and biogeochemical processes. However, partitioning evapotranspiration into evaporation (E) and transpiration (T) at regional scale with high accuracy still remains a challenge. This study has aimed to reveal the spatio-temporal variations of evapotranspiration and its components by using an improved Shuttleworth-Wallace (SWH) model to partition ET in the Yellow River Basin during 1981-2010. The environmental factors affecting the spatial and temporal variations of evapotranspiration and its components were also assessed. Results showed that the mean annual ET, T and E in the Yellow River Basin were 372.18 mm, 179.64 mm, and 192.54 mm, respectively, over the last 30 years. The spatial pattern of mean annual ET and T displayed a decreasing trend from southeast to northwest in the Yellow River Basin, and the temporal variation showed a significant increasing trend with rates of 1.72 mm yr-1 and 1.54 mm yr-1, respectively. It meant that T accounted for the variations of ET, while E showed no significant changes in recent decades. Moreover, the normalized differential vegetation index (NDVI) and temperature were identified as the main factors controlling the variations of ET and T in the Yellow River Basin. Among them, the area with NDVI as the dominant factor for ET and T could reach 63.82% and 78.47% of the whole basin respectively. However, the variations of E were affected by complex factors, and evaporation in the western alpine region was mainly controlled by temperature. Our findings are expected to not only have implications for developing sustainable policies of water management and ecological restoration in this region, but also provide valuable insight in methodology of ET partitioning in regional or global scale.

Dew water isotopic ratios and their relationships to ecosystem water pools and fluxes in a cropland and a grassland in China.

Dew formation has the potential to modulate the spatial and temporal variations of isotopic contents of atmospheric water vapor, oxygen and carbon dioxide. The goal of this paper is to improve our understanding of the isotopic interactions between dew water and ecosystem water pools and fluxes through two field experiments in a wheat/maize cropland and in a short steppe grassland in China. Measurements were made during 94 dew events of the D and (18)O compositions of dew, atmospheric vapor, leaf, xylem and soil water, and the whole ecosystem water flux. Our results demonstrate that the equilibrium fractionation played a dominant role over the kinetic fractionation in controlling the dew water isotopic compositions. A significant correlation between the isotopic compositions of leaf water and dew water suggests a large role of top-down exchange with atmospheric vapor controlling the leaf water turnover at night. According to the isotopic labeling, dew water consisted of a downward flux of water vapor from above the canopy (98%) and upward fluxes originated from soil evaporation and transpiration of the leaves in the lower canopy (2%).

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Global changes have a profound impact on ecosystems. If the disturbance caused by global change exceeds a certain degree, ecosystem resilience will be reduced, extreme events will be frequent, and ecosystem services will be degraded or even lost. Quantifying the risks of global change and developing appropriate adaptation strategies is an important way to deal with the risks of global change. Global change may reduce ecosystem resilience, leading to increased vulnerability and the risk of ecosystem degradation. The risk of ecosystem degradation is currently quantified mainly by the safe operating space assessment method based on planetary boundary theory. Understanding the concepts of ecosystem resilience, vulnerability, planetary boundaries, and safe operating spaces and their relationships is an important prerequisite for addressing the risks of global change. By summarizing the relevant theories of ecosystem vulnerability, we combined the concepts related to ecosystem resilience and vulnerability, global change risk and human adaptation, proposed a conceptual framework of ecosystem global change risk and human adaptation based on the vulnerability theory. Based on the logic of this proposed framework, we successively introduced the characteristics and mechanism of global change interference on ecosystem vulnerability, elaborated the assessment theories and methods of ecosystem vulnerability, and how to adopt human adaptation measures to alleviate the risk of global changes, aiming to provide ideas for coping with the risk of global change.

Construction of ecological network using morphological spatial pattern analysis and minimal cumulative resistance models in Guangzhou City, China.

Construction of ecological network is important for improving urban ecological environment under the scenarios of rapid urbanization. We extracted the core area with good connectivity as the ecological sources with the methods of morphological spatial pattern analysis (MSPA) and landscape index with Guangzhou City as the study area. The ecological network was then constructed by minimal cumulative resistance (MCR) model and was quantitatively analyzed by gravity model and connectivity indices. After that, an optimized ecological network was finally constructed. The results showed that ten core patches could be used as ecological sources. In addition, eighteen important corridors as well as twenty-seven general corridors were identified, which were mainly distributed in the northeast part of the city. Five more ecological sources and thirteen more planning corridors were suggested under the optimized ecological network. Our results indicated that forests were the main composition of ecological corridors. The appropriate width for the important corridor and planning corridor was 60-100 m and 30-60 m, respectively. Our results provide scientific guidance for designing urban ecological network.

Exogenous N addition enhances the responses of gross primary productivity to individual precipitation events in a temperate grassland.

Predicted future shifts in the magnitude and frequency (larger but fewer) of precipitation events and enhanced nitrogen (N) deposition may interact to affect grassland productivity, but the effects of N enrichment on the productivity response to individual precipitation events remain unclear. In this study, we quantified the effects of N addition on the response patterns of gross primary productivity (GPP) to individual precipitation events of different sizes (Psize) in a temperate grassland in China. The results showed that N enrichment significantly increased the time-integrated amount of GPP in response to an individual precipitation event (GPPtotal), and the N-induced stimulation of GPP increased with increasing Psize. N enrichment rarely affected the duration of the GPP response, but it significantly stimulated the maximum absolute GPP response. Higher foliar N content might play an important role in the N-induced stimulation of GPP. GPPtotal in both the N-addition and control treatments increased linearly with Psize with similar Psize intercepts (approximately 5 mm, indicating a similar lower Psize threshold to stimulate the GPP response) but had a steeper slope under N addition. Our work indicates that the projected larger precipitation events will stimulate grassland productivity, and this stimulation might be amplified by increasing N deposition.

[Influence of nitrogen and phosphorus addition on the aboveground biomass in Inner Mongo- lia temperate steppe, China].

The plants in arid environment are constrained not only by water availability, but also by soil nutrient conditions. In order to clarify to what extent nutrient addition would facilitate the growth of plants in semi-arid region, we conducted a nitrogen (N) and phosphorus (P) addition experiment in Inner Mongolia temperate grassland in 2012 and 2013. In our experiment, N was added at 10 and 40 g N · m(-2) · a(-1) alone or in combination with P addition (10 g P · m(-2) · a(-1)). N addition significantly improved plant aboveground biomass (AGB) during the two study years. AGB in the treatments of 10 and 40 g · m2 · a(-1) was enhanced by 50.8% and 65.9% in 2012, and 71.6% and 93.3% in 2013, respectively. However, no significant difference in AGB enhancement was found between two N addition treatments. Compared with N addition treatments at the rates of 10 and 40 g · m(-2) · a(-1), N plus P addition improved AGB by 98.4% and 186.8% in 2012, and 111.7% and 141.4% in 2013, respectively. N addition generally increased all the three main functional types (i.e., Gramineae, Asteraceae and others) , and the three functional types contributed nearly equally to the increase of the community AGB. In comparison, Asteraceae contributed largest to the increments of AGB under the N plus P addition treatments. Our results also indicated that N and P addition remarkably increased the ground coverage, resulting in improved surface soil moisture condition, which might be one important reason that N and P addition could facilitate plant growth in arid environment.

[Characteristics of carbon storage of Inner Mongolia forests: a review].

Forests in Inner Mongolia account for an important part of the forests in China in terms of their large area and high living standing volume. This study reported carbon storage, carbon density, carbon sequestration rate and carbon sequestration potential of forest ecosystems in Inner Mongolia using the biomass carbon data from the related literature. Through analyzing the data of forest inventory and the generalized allometric equations between volume and biomass, previous studies had reported that biomass carbon storage of the forests in Inner Mongolia was about 920 Tg C, which was 12 percent of the national forest carbon storage, the annual average growth rate was about 1.4%, and the average of carbon density was about 43 t · hm(-2). Carbon storage and carbon density showed an increasing trend over time. Coniferous and broad-leaved mixed forest, Pinus sylvestris var. mongolica forest and Betula platyphylla forest had higher carbon sequestration capacities. Carbon storage was reduced due to human activities such as thinning and clear cutting. There were few studies on carbon storage of the forests in Inner Mongolia with focus on the soil, showing that the soil car- bon density increased with the stand age. Study on the carbon sequestration potential of forest ecosystems was still less. Further study was required to examine dynamics of carbon storage in forest ecosystems in Inner Mongolia, i. e., to assess carbon storage in the forest soils together with biomass carbon storage, to compute biomass carbon content of species organs as 45% in the allometric equations, to build more species-specific and site-specific allometric equations including root biomass for different dominant species, and to take into account the effects of climate change on carbon sequestration rate and carbon sequestration potential.

[A multicenter study of respiratory multiple index in predicting weaning from mechanical ventilation in patients with acute exacerbation of chronic obstructive pulmonary disease].

OBJECTIVE: To study the result of respiratory multiple index(compliance, respiratory rate, oxygenation, pressure, CROP) in predicting weaning from mechanical ventilation in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). METHODS: A prospective study was conducted. Two hundred and fifteen patients weaning from mechanical ventilation with AECOPD in intensive care unit (ICU) of five tertiary hospitals from September 2010 to October 2012 were enrolled. All of the AECOPD patients were troubled with respiratory failure and received non-invasive mechanical ventilation for more than 24 hours. They were conscious and cooperative at the time of extubation, and passed the spontaneous breathing trial (SBT) for 30 minutes. Before weaning, the maximal inspiratory pressure (PImax), the peak airway pressure (Ppeak), the total positive end expiratory pressure (PEEPtot), tidal volume (VT) and respiratory frequency (f) were recorded; the arterial partial pressure of oxygen (PaO2) and arterial partial pressure of carbon dioxide (PaCO2) were detected; the effective compliance of the respiratory system (Crs) and alveolar oxygen pressure(PAO2) were calculated. The above indexes were substituted into the formula: CROP= Crs × 1/f × PaO2/PAO2× PImax to get the value of CROP. Successful weaning from mechanical ventilation was defined if there was no indication for intubation within 72 hours. The receiver operating characteristic curve (ROC curve) was drawn to analyze the predict value of CROP on result of weaning from mechanical ventilation in patients with AECOPD. RESULTS: In 215 patients, 182 patients successfully weaned from mechanical ventilation, and 33 failed. There were no significant differences in gender, age and the acute physiology and chronic health evaluation II (APACHEII) score between the successfully weaned patients and the failed. Before weaning from mechanical ventilation, PaCO2 in failed group was significantly higher than that in successful group (60.69 ± 10.47 mm Hg vs. 51.24 ± 8.81 mm Hg, P<0.05), the CROP was significantly lowered (10.286 ± 1.392 ml × breath⁻¹ ×min⁻¹ vs. 58.746 ± 7.283 ml×breath⁻¹×min⁻¹, P<0.01), and the duration of mechanical ventilation was prolonged (10.28 ± 3.94 days vs. 6.21 ± 2.87 days, P<0.05). The best critical value of CROP which could predict the result of weaning from mechanical ventilation was 13.521 ml×breath⁻¹×min⁻¹. CROP≥ 13.521 ml×breath⁻¹×min⁻¹ had a specificity of 91.9% and sensitivity of 87.9% in predicting extubation succeed. The positive predicted value was 0.97, and the negative predicted value was 0.58; Odds ratio (OR)<1, which confirmed that CROP was a strong and independent predictor of extubation. CONCLUSIONS: For the AECOPD patients received mechanical ventilation, most extubation parameter was limited. Complex parameter of CROP has higher specificity and sensitivity, and has important value in predicting extubation outcome. When CROP ≥ 13.521 ml×breath⁻¹×min⁻¹, the successful rate is high, otherwise the rate is low.