Soil erosion can be effectively controlled through vegetation restoration. Specifically, roots combine with soil to form a root-soil complex, which can effectively enhance soil shear strength and play a crucial role in soil reinforcement. However, the relationship between root mechanical traits and chemical compositions and shear performance and reinforcing capacity of soil is still inadequate. In this study, we determined the root chemical properties, performed root tensile tests and root-soil composite triaxial tests using two plants-one with a fibrous root system (ryegrass, Lolium perenne L.) and the other with a tap root system (alfalfa, Medicago sativa L.)-and calculated the factor of safety (FOS). The results revealed that the relationship between root diameter and tensile strength differed among different root characters. Holocellulose content and cellulose content were the main factors controlling the root tensile strength of ryegrass and alfalfa, respectively. The shear properties of the root-soil complex (cohesion (c) and internal friction angle (phi)) are correlated with soil water content (SWC) and root mass density (RMD). Root traits had a more substantial effect on c than phi, with significant differences in c between ryegrass and alfalfa at 7 % and 11 % SWC. The root-soil complex had an optimum RMD, and the maximum increase rates of c were 80.57 % and 34.4 %, respectively. Along slopes, sliding first occurs at the foot of the slope, thus demanding emphasis on protection and reinforcement. On steep gradients with low SWC, ryegrass strongly contributes to soil reinforcement, whereas alfalfa is more effective on gentle gradients with high SWC. The results provide scientific references for species selection for vegetation restoration in the Loess Plateau and a deeper understanding of the mechanical mechanism of soil reinforcement by roots.

Aerosol microphysical properties, scattering and absorption characteristics, and in particular, the vertical distributions of these parameters over the eastern Loess Plateau, were analyzed based on aircraft measurements made in 2020 during a summertime aircraft campaign in Shanxi, China. Data from six flights were analyzed. Statistical characteristics and vertical distributions of aerosol concentration, particle size, optical properties, including aerosol scattering coefficient (Sigma sp), backscattering ratio (beta sc), Angstro spacing diaeresis m exponent (alpha), single-scattering albedo (SSA), partially-integrated aerosol optical depth (PAOD), and black carbon concentration (BCc), were obtained and discussed. Mean values of aerosol particle number concentration (Na), particle volume concentration (Va), mass concentration (Ma), surface concentration (Sa), and particle effective diameter (EDa) were 854.92 cm-3, 13.37 mu m3 cm- 3, 20.06 mu g/m3, 170.08 mu m3 cm- 3, and 0.47 mu m, respectively. Mean values of BCc, Sigma sp (450, 525, 635 nm), beta sp (525 nm), alpha(635/450), and SSA were 1791.66 ng m- 3, 82.37 Mm- 1 at 450 nm, 102.57 Mm- 1 at 525 nm, 126.60 Mm-1 at 635 nm, 0.23, 1.47, and 0.92, respectively. Compared with values obtained in 2013, Na decreased by 60% and Ma decreased by 45%, but the scattering coefficients increased in different degrees. In the vertical direction, aerosol concentrations were higher at lower altitudes, decreasing with height. Vertical profiles of Sigma sp, beta sp, alpha(635/450), and BCc measured during the six flights were examined. Two peaks in Na were identified near the top of the boundary layer and between 2000 and 2200 m. Fine particles with EDa smaller than 0.8 mu m are dominant in the boundary layer and coarse aerosols existed aloft. Aerosol scattering properties and BCc in the lowest layer of the atmosphere contributed the most to the total aerosol radiative forcing. SSA values were greater than 0.9 below 2500 m, with lower values at higher levels of the atmosphere. On lightly foggy days, SSA values were greater than 0.9, and aerosols played a cooling role in the atmosphere. On hazy days, lowerlevel SSA values were generally greater than 0.85, with aerosols likely having a warming effect on the atmosphere. 48-hour backward trajectories of air masses during the observation days showed that the majority of aerosol particles in the lower atmosphere originated from local or regional pollution emissions, contributing the most to the total aerosol loading and leading to high values of aerosol concentration and radiative forcing.