Contribution of Recycled Moisture to Precipitation in Northeastern Tibetan Plateau: A Case Study Based on Bayesian Estimation

(1) Background: The degree to which local precipitation is supplied by recycled moisture is a reflection of land surface–atmosphere interactions and a potentially significant climate feedback mechanism. This study tries to figure out the water cycle and precipitation mechanism at a mountainous region and then provides a reference for similar mountainous regions outside China. (2) Methods: The dual-isotopes and Bayes-based program MixSIAR is used to assess contributions of advected, transpirated and evaporated vapor to local precipitation. (3) Results: The average percent contribution of recycled moisture (i.e., the sum of surface evaporated vapor and transpirated vapor) to local precipitation at the Qilian Mountains during 2017 plant growing season is about 37% (the upper quartile and the lower quartile was 30% and 43%, respectively). (4) Conclusions: Although the contribution of advection vapor dominated during the plant growing season, the contribution of recycled moisture is also important in such an alpine region. Furthermore, the commonly used simple linear mixing models often yield contributions greater than 100% or less than 0% and are likely to underestimate the contribution of recycled moisture to local precipitation. Although the alternative Bayesian model is not perfect, either, it is still a big improvement.

Drought in forest understory ecosystems – a novel rainfall reduction experiment

Precipitation patterns across Central Europe are expected to change over the 21st century due to climate change. This may reduce water availability during the plant-growing season and hence affect the performance and vitality of forest ecosystems. We established a novel rainfall reduction experiment on nine sites in Germany to investigate drought effects on soil–forest–understory ecosystems. A realistic, but extreme annual drought with a return period of 40 years, which corresponds to the 2.5% percentile of the annual precipitation, was imposed. At all sites, we were able to reach the target values of rainfall reduction, while other important ecosystem variables like air temperature, humidity, and soil temperature remained unaffected due to the novel design of a flexible roof. The first year of drought showed considerable changes in the soil moisture dynamics relative to the control sites, which affected leaf stomatal conductance of understory species as well as evapotranspiration rates of the forest understory.

Drought in forest understory ecosystems – a novel rainfall reduction experiment

Climate change is predicted to severely affect precipitation patterns across central Europe. This may reduce water availability during the plant-growing season and hence affect the performance and vitality of forest ecosystems. We established a novel rainfall reduction experiment on nine sites in Germany to investigate drought effects on soil-forest-understory-ecosystems. A realistic, but extreme annual drought with a return period of 40 years, which corresponds to the 2.5% percentile of the annual precipitation, was imposed. At all sites, we were able to reach the target values of rainfall reduction, while other important ecosystem variables like air temperature, humidity and soil temperature remained unaffected due to the novel design of a flexible roof. The first year of drought showed considerable changes in the soil moisture dynamics relative to the control sites, which affected leaf stomatal conductance of understory species as well as evapotranspiration rates of the forest understory.

Bioavailability of heavy metals in the soil from different locations of medicinal herbs

SUMMARY Medicinal herbs and their mixtures, which are widely used for prevention and treatment of some disease, can also present health risks due to the presence of toxic metals such as Pb and Cd. The application of different agrotechnical practices during plant growing season, as well as the process of circulation of substances in nature, may be the cause of plant contamination. The aim of this study was to determine the content of lead, cadmium and copper from soil which are bioavailable for absorption by plant, as well as the total content of these metals in some medicinal herbs that were cultivated in two different locations. The presence of these metals in the samples was detected using highly sensitive microanalytical technique potentiometric stripping analysis (PSA). The mean value of lead total content in the analyzed samples of medicinal herbs Chamimillae flos, Urticae folium, Menthae folium, Altheae radix and Basilici herba, which were grown at the sites near the industrial zone, was about 1.55 μg/g, 1.82 μg/g, 1.90 μg/g, 1.99 μg/g and 2.74 μg/g, respectively. Contrary to this, the total content of this toxic metal in the analyzed plant samples grown on rural areas was detected only on some sites. Based on the results of this study, it can be concluded that medicinal herbs contained a certain amount of lead and that its content varied depending on the location at which the plant species were grown as well as on plant affinity to certain metal. Cadmium and copper were not detected in the tested plant material.

Wet and Dry Atmospheric Depositions of Inorganic Nitrogen during Plant Growing Season in the Coastal Zone of Yellow River Delta

The ecological problems caused by dry and wet deposition of atmospheric nitrogen have been widespread concern in the world. In this study, wet and dry atmospheric depositions were monitored in plant growing season in the coastal zone of the Yellow River Delta (YRD) using automatic sampling equipment. The results showed thatSO42-and Na+were the predominant anion and cation, respectively, in both wet and dry atmospheric depositions. The total atmospheric nitrogen deposition was ~2264.24 mg m−2, in which dry atmospheric nitrogen deposition was about 32.02%. The highest values of dry and wet atmospheric nitrogen deposition appeared in May and August, respectively. In the studied area,NO3-–N was the main nitrogen form in dry deposition, while the predominant nitrogen in wet atmospheric deposition wasNH4+–N with ~56.51% of total wet atmospheric nitrogen deposition. The average monthly attribution rate of atmospheric deposition ofNO3-–N andNH4+–N was ~31.38% and ~20.50% for the contents ofNO3-–N andNH4+–N in 0–10 cm soil layer, respectively, suggested that the atmospheric nitrogen was one of main sources for soil nitrogen in coastal zone of the YRD.

Effects of Soil Moisture on Vegetation Invasion into Active Dune Areas

Soil moisture and soil seed bank are primary dependent factors during the vegetation natural regenerations in semi-arid sand areas. But the binary correlation analysis between seedling density and soil seed bank density as well soil moisture in transition zones between the windword slope of active dune and interdune lowland indicated that the correlation between seedling density and soil seed bank density was not significant (P>0.05) in the plant growing season; but the one between seedling density and soil moisture was significant and positive (P<0.05). The conclusions revealed that soil moisture was a primary dependent factor during seedling emergence and establishment in the transition zone

Grazing depresses soil carbon storage through changing plant biomass and composition in a Tibetan alpine meadow

Grazing-induced variations in vegetation may either accelerate or reduce soil carbon storage through changes in litter quantity and quality. Here, a three-year field study (2005&ndash;2007) was conducted in Tibetan alpine meadow to address the responses of surface soil (0&ndash;15 cm) organic carbon (SOC) storage in the plant growing season (from May to September) to varying grazing intensity (represented by the residual aboveground biomass, with G₀, G₁, G₂, and G₃ standing for 100%, 66%, 55%, and 30% biomass residual, respectively), and to explore whether grazing-induced vegetation changes depress or facilitate SOC storage. Our results showed that: (i) Higher grazing intensity resulted in lower biomass of grasses and sedges, lower root biomass, and in a change in plant community composition from palatable grasses and sedges to less palatable forbs. (ii) Increased grazing reduced the SOC content and storage with only G₃ showing an SOC loss during the plant growing season. (iii) Soil organic carbon storage exhibited a highly positive correlation with the residual aboveground biomass and root biomass. Our results imply that a grazing-induced reduction in plant biomass productivity and changes in species composition would depress soil carbon storage, and that an increase in grazing pressure can lead to a gradual change of alpine meadow soils from being 'carbon sinks' to become 'carbon sources'.