Mechanism of Cu(Ⅱ) adsorption inhibition on biochar by its aging process

Biochar exposed in the environment may experience a series of surface changes, which is called biochar aging. In order to study the effects of biochar aging on Cu（Ⅱ） adsorption, we analyzed the surface properties before and after biochar aging with scanning electron microscopy（SEM） coupled to an energy-dispersive X-ray spectrometer（EDX） and diffuse reflectance infrared Fourier transform spectroscopy（DRIFTS）, and then explored the influence of the aging process on Cu（Ⅱ） adsorption by batch experiments. After the aging process, the oxygen concentration, phenolic hydroxyl groups, aromatic ethers and other oxygen-containing functional groups on the biochar surface increased, while carboxyl groups slightly decreased. Thus, over a range of pH, the cation exchange capacity（CEC） and adsorption capacity of Cu（Ⅱ） on the aged biochar were smaller than those of new biochar,indicating that when biochar is incubated at constant temperature and water holding capacity in the dark, the aging process may inhibit Cu（Ⅱ） adsorption. Meanwhile, the dissociation characteristics of oxygen-containing functional groups changed through the aging process, which may be the mechanism by which the biochar aging process inhibits the Cu（Ⅱ） adsorption. Carboxyl groups became more easily dissociated at low pH（3.3–5.0）,and the variation of maximum adsorption capability（qm） of Cu（Ⅱ） on the old biochar was enlarged. Phenolic hydroxyl groups increased after the aging, making them and carboxyl groups more difficult to dissociate at high pH（5.0–6.8）, and the variation of qmof Cu（Ⅱ） on the aged biochar was reduced.

Changes in soil fungal community on SOC and POM accumulation under different straw return modes in dryland farming

We conducted a 2.5-year field experiment to test the effects of straw incorporated evenly into the soil(EIS)on soil fungal community,SOC chemical composition,and particulate organic matter fractions via comparing with no straw returning(CK),straw mulching(SM),straw plowed into the soil(SP),and identified the linkages between soil fungal community as well as organic C accumulation and POM formation.Our results showed that EIS treatment significantly increased the concentrations of SOC and the proportion of carbohydrate C,di-O-alkyl C,and O-alkyl C in SOC structure,increased the mass proportion and OC contents of MA(c)POM and mM-POM in the upper 40 cm of soil.Meanwhile,EIS treatment increased the relative abundance of Ascomycota,Zygomycota,Chytridiomycota,and Dothideomycetes in 0-20 cm depths,and also had the highest relative abundance of Glomeromycetes and Dothideomycetes in the 20-40 cm soil.Also,our study suggests that straw return enhanced the relative abundances of fungi involved in the carbon cycle and sequestration,including Zygomycota,Chytridiomycota,and Glomeromycota,and Ascomycota.The shifts in fungal community structure can accelerate organic C accumulation and the formation of soil particulate organic matter,especially in EIS treatment.