Reforestation in southern China: revisiting soil N mineralization and nitrification after 8 years restoration

Nitrogen availability and tree species selection play important roles in reforestation. However, long-term field studies on the effects and mechanisms of tree species composition on N transformation are very limited. Eight years after tree seedlings were planted in a field experiment, we revisited the site and tested how tree species composition affects the dynamics of N mineralization and nitrification. Both tree species composition and season significantly influenced the soil dissolved organic carbon (DOC) and nitrogen (DON). N-fixing Acacia crassicarpa monoculture had the highest DON, and 10-mixed species plantation had the highest DOC. The lowest DOC and DON concentrations were both observed in Eucalyptus urophylla monoculture. The tree species composition also significantly affected net N mineralization rates. The highest rate of net N mineralization was found in A. crassicarpa monoculture, which was over twice than that in Castanopsis hystrix monoculture. The annual net N mineralization rates of 10-mixed and 30-mixed plantations were similar as that of N-fixing monoculture. Since mixed plantations have good performance in increasing soil DOC, DON, N mineralization and plant biodiversity, we recommend that mixed species plantations should be used as a sustainable approach for the restoration of degraded land in southern China

A Joint Theoretical and Experimental Study of Phase Equilibria and Evolution in Pt-Doped Calcium Titanate under Redox Conditions

Pseudoternary phase diagrams of the PtOx-CaO-TiOx system were constructed using first-principles theoretical methods to interpret experimental observations of phase formation and evolution in Pt-doped CaTiO3 made by aberration-corrected scanning transmission electron microscopy. In this system, promoted as a self-regenerative automotive exhaust-gas catalyst, Pt precipitates as metallic particles from the doped perovskite under reducing conditions and tends to redissolve under oxidizing conditions. Due to the likely influence of kinetic limitations on experimental observations, we focus on a restricted (metastable) phase diagram in which single and other unobserved oxides of Pt are intentionally excluded. Various titanate phases appear, however, and their presence helps inform the calculation of the phase diagrams, which in turn confirm that the self-regenerative effect is a consequence of thermodynamic phase stability under the specific redox environments examined