Geochemical characteristics of soil selenium and evaluation of Serich land resources in the central area of Guiyang City,China

Based on the results of multipurpose regional geochemical surveys of the Guizhou Province, geochemical characteristics of soil Se and Se-rich land resources in the central area of Guiyang City were studied and evaluated.Major conclusions are as follows:(1) the Se content in surface soil of the central area of Guiyang City was 0.17–2.89 mg kg^(-1), and the average was 0.78 mg kg^(-1), which were respectively 2.6 and 3.9 times of the national background value of soil and the world background value of soil.The Se content in deep soil was 0.11–1.48 mg kg^(-1), and the average was 0.44 mg kg^(-1), which were respectively 1.5 and2.2 times of the national background value of soil and the world background value of soil. The soil Se content decreased with the increase in the soil depth on the vertical profile, and the surface soil had a higher Se content.(2)Distribution of Se content was mainly affected by parent material, physicochemical properties of soil and other components, soil type, and land use type. Parent material played a key role, as the soil Se content was mainly originated from parent rock and increased with the background value of Se in parent rock, physicochemical properties of soil and other components had certain influences upon the Se content. Se was shown to have a significant linear positive correlation with S and organic carbon but no significant correlation with p H value. Se content varied with different types of soil as follows: skeleton soil > yellow soil > paddy soil > limestone soil > purple soil. Land use type also hadcertain influences upon the soil Se content as follows: dry land > construction land > garden plot > grassland =garden plot > forest land.(3) Taking 0.4 mg kg^(-1)B x(Se) <3.0 mg kg^(-1) as the standard for Se-rich soil, Se-rich soil of the study area covered an area of 2224 km^2 and 92.5% of the total area; the remaining is general soil. The study area had no Se-excess soil. Therefore, the central area of Guiyang City has a high proportion of Se-rich land, a large area of Serich land resources, and a moderate selenium enrichment strength, which have been rarely seen anywhere and provide advantageous resources for the development of Se-rich featured agriculture.

Evidence for Expensive Tissue Hypothesis in the Asian Common Toad(Duttaphrynus melanostictus)

Dear Editor,Phenotypic plasticity of an organism by modifying morphological and physiological traits responding to diverse environments is widely recognized across animal taxa(Muñoz-Muñoz et al.,2021;Donihue et al.,2021;Giacomini et al.,2022;Zamora-Camacho et al.,2022;Jiang et al.,2022;Chen et al.,2023).The brain,as a critical phenotypic trait,displays a significant variation in size among different species(Striedter,2006).

Automatic,long-term frequency-stabilized lasers with sub-hertz linewidth and 10-16 frequency instability

We report two ultra-stable laser systems automatically frequency-stabilized to two high-finesse optical cavities.By employing analog-digital hybrid proportional integral derivative(PID)controllers,we keep the merits of wide servo bandwidth and servo accuracy by using analog circuits for the PID controller,and,at the same time,we realize automatic laser frequency locking by introducing digital logic into the PID controller.The lasers can be automatically frequency-stabilized to their reference cavities,and it can be relocked in 0.3 s when interruption happens,i.e.,blocking and unblocking the laser light.These automatic frequency-stabilized lasers are measured to have a frequency instability of 6×10^(-16)at 1 s averaging time and a most probable linewidth of 0.3 Hz.The laser systems were tested for continuous operation over 11 days.Such ultrastable laser systems in long-term robust operation will be beneficial to the applications of optical atomic clocks and precision measurement based on frequency-stabilized lasers.