Search

Considering the crucial role of soil diazotrophs and root arbuscular mycorrhizal fungi (AMF) in soil nutrient cycling during ecosystem restoration, diazotroph and AMF communities may be determined by slope position. However, the effect of slope position on diazotroph and AMF abundance, diversity, and community composition of karst ecosystems remains unknown. In this study, soil diazotrophs and root AMF characteristics on varying slope positions were assessed in a karst shrub ecosystem. The results displayed that the abundance of soil diazotrophs and root AMF diversity were significantly affected by slope position. Diazotroph abundance accompanied by soil nutrient and plant richness was higher on the lower slopes than the upper slopes, whereas root AMF diversity displayed the opposite trend. The soil diazotroph and root AMF community composition differed among the upper, middle, and lower slopes. The dominant taxa of soil diazotrophs and root AMF at the order level were Rhizobiales and Glomerales, respectively. Moreover, the diazotroph order of Nostocales and the AMF order of Paraglomerales were richer on the upper slopes than on the lower slopes. The slope position directly affected the plant diversity and soil nutrient distribution, indirectly affecting the diazotroph and AMF communities. Increased available nitrogen on the lower slope caused great diazotroph abundance by stimulating plant growth with sufficient carbohydrates. However, low soil nutrients and plant diversity but high plant root biomass induced more root AMF diversity on the upper slope than on the lower slope. Therefore, this study expands the knowledge of soil diazotroph and root AMF ecological functions along different slope positions during vegetation recovery for the successive stages of grass and shrub in the karst region. [ABSTRACT FROM AUTHOR]

Purpose: Changes in climate and land use may disrupt the soil carbon (C), nitrogen (N), and phosphorus (P) cycles, which affect the availability of essential nutrients differently, including soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP). Nevertheless, lithologic impact on soil C:N:P stoichiometry over a broad climatic gradient remains largely unknown. We aimed to determine the variation in nutrient limitations between karst and non-karst forests and croplands across a climate gradient. Materials and methods: This study investigated soil C:N:P stoichiometry in mature forest (MF) and nearby cropland rotation (CR) (as a control) soils on limestone (karst) and clastic rock (non-karst) throughout a climatic gradient in southwest China through analysis of soil samples. Result and discussion: The SOC and TN contents in the karst MF were 1.3 and 1.6 times greater, respectively, than that in the non-karst MF. Consequently, the karst MF had a lower C:N ratio than did the non-karst MF. The SOC and TN contents were considerably higher in the MF than they were in the CR under both lithologies, leading to higher C:P and N:P ratios in the MF compared to those in the CR. The increasing temperature resulted in a shift from TN and TP to SOC limitation, due to the increased decomposition of SOC by microbes with an increase in temperature. Soil pH and Ca content are controlled by the lithology, and they were closely related to C:N:P stoichiometry in this study, whereas a combination of lithology and temperature controlled soil microbial activity and plant growth. Importantly, the magnitude of lithology-induced changes in the stoichiometry was greater as temperature increased, which was more pronounced in the non-karst than it was in the karst. Conclusions: These findings highlight the responses of soil C, N, and P to climate warming in relation to stoichiometry, and soil-microorganism-plant response strategies may be the key to the mitigating the effect of temperature increase on nutrient cycles in karst ecosystems. [ABSTRACT FROM AUTHOR]

This research presents two unique techniques for engineering system reliability analysis of multi-dimensional non-linear dynamic structures. First, the structural reliability technique works best for multi-dimensional structural responses that have been either numerically simulated or measured over a long enough length to produce an ergodic time series. Second, a novel extreme value prediction method that can be used in various engineering applications is proposed. In contrast to those currently used in engineering reliability methodologies, the novel method is easy to use, and even a limited amount of data can still be used to obtain robust system failure estimates. As demonstrated in this work, proposed methods also provide accurate confidence bands for system failure levels in the case of real-life measured structural response. Additionally, traditional reliability approaches that deal with time series do not have the benefit of being able to handle a system's high dimensionality and cross-correlation across several dimensions readily. Container ship that experiences significant deck panel pressures and high roll angles when travelling in bad weather was selected as the example for this study. The main concern for ship transportation is the potential loss of cargo owing to violent movements. Simulating such a situation is difficult since waves and ship motions are non-stationary and complicatedly non-linear. Extreme movements greatly enhance the role of nonlinearities, activating effects of second and higher order. Furthermore, laboratory testing may also be called into doubt due to the scale and the choice of the sea state. Therefore, data collected from actual ships during difficult weather journeys offer a unique perspective on the statistics of ship movements. This work aims to benchmark state-of-the-art methods, making it possible to extract necessary information about the extreme response from available on-board measured time histories. Both suggested methods can be used in combination, making them attractive and ready to use for engineers. Methods proposed in this paper open up possibilities to predict simply yet efficiently system failure probability for non-linear multi-dimensional dynamic structure. [ABSTRACT FROM AUTHOR]

Grain for Green project could result in high evapotranspiration (ET), exacerbate water shortage, and intensify conflicts in water demand between ecosystems and humans in many water‐limited areas. However, it is still unclear how vegetation restoration would influence ET in humid karst regions where abundant precipitation but quick leakage. Particularly, it is challenging that existing ET measurement methods are not applicable simultaneously for various ecosystems in such highly heterogeneous and fragmented landscapes. To solve this issue, this study, for the first time, develops a new ET measurement system, by integrating multi‐techniques, to quantify ET for multiple vegetation restoration types and identify their controlling factors in a humid karst region for three consecutive years. The results show that (a) for different succession stages during natural restoration, the ET of secondary forest (680 ± 7 mm yr−1) > shrub (564 ± 16 mm yr−1) > grass (546 ± 12 mm yr−1) > cropland (513 ± 8 mm yr−1) (P < 0.05); (b) ET of all ecosystems are far less than that of precipitation (1,059 ± 63 mm yr−1) but closer to potential ET (849 ± 11 mm yr−1), and soil moisture has been maintained at >0.20 cm3cm−3 in the growing season; (c) solar radiation and vapor pressure deficit are the two predominant factors on the ET (P < 0.01), while there is no significant relationship between ET and soil moisture (P > 0.05). The results suggest that vegetation restoration returned from cropland in humid karst regions increased ET but may not induce water scarcity for vegetation sustainability, at least under normal climatic conditions. Key Points: Vegetation restoration will increase the rate of water consumption, but may not threaten ecosystem's sustainability in humid karst regionEnergy rather than water is the limiting factor for humid karst ecosystem water consumptionA new evapotranspiration measurement system is developed to quantify evapotranspiration for multiple vegetation restoration types [ABSTRACT FROM AUTHOR]