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Soil pore structure over a wide range of pore sizes regulates soil functions and relies heavily on pedogenic processes. To date, limited knowledge is available on the spatial variations of soil pore structure and underlying mechanisms over a broad geographic scale. Herein, seven typical zonal soils with increased status of soil development in heavy-textures were collected at different genetic horizons under forests along the mid-temperate to tropic climate gradient in eastern China. Pore size distribution (PSD, 0.006 ∼ 800 μm) of aggregates (sized ∼ 1 cm3) and other pore structure characteristics (void ratio, pore area and average diameter) were determined by mercury intrusion porosimetry. Differential PSD displayed tri- or bi-modal patterns and different pore size classes followed diverse geographic trends. Textural pores most influenced by soil type exhibited larger void ratio and pore area in highly than in moderately developed soils; structural porosity most influenced by soil horizon overall decreased with increased soil depth, indicating the decreased levels of hierarchical aggregation whatever soil type. Relative to soil texture and total organic matter (0.70≤|r|≤0.92), total and textural pores were more related to inorganic cementing agents (0.71≤|r|≤0.95, p < 0.001), where kaolinite and free iron/aluminum oxides (mainly crystalline form) exerted the positive effects on void ratio and pore area through clayey pores, in contrast to vermiculite and exchangeable cations; void ratio and pore size of structural pores could be separately promoted by sand-silt size organic matter and vermiculite (r = 0.79 and 0.73, p < 0.001). Additionally, clay-sized organic matter, sand, and free manganese oxides played a secondary effect (R2 = 0.04 ∼ 0.30, p < 0.05) and their specific roles differed with pore size class. The overall results suggest that the dramatic geographic variations of soil pore structure are controlled by both inorganic cementing agents and specific organic components to a large extent at the regional scale. [ABSTRACT FROM AUTHOR]

• Mixed forests show a higher soil erosion control benefit than monocultures. • Tree-shrub mixtures reduce runoff and sediment more than tree-tree mixtures. • Mixed forests have the strongest positive impact on soil erosion control in dry areas. • Mixed forests are found to affect soil erosion most efficiently after 20 years of tree growth. • Mixed forests have the highest impact on soil erosion control on slopes of 16–20°. Soil erosion poses a major threat to the sustainability and stability of global terrestrial ecosystems. Mixed forests have more advantages in restoring degraded land and enhancing soil fertility than monocultures, but their influence on soil erosion remains uncertain. Therefore, we presented a meta -analysis consisting of 261 paired observations of mixed forests and the corresponding monocultures from 65 studies to evaluate the effect of tree diversity on soil erosion in China. The results showed that compared with monocultures, mixed forests significantly reduced the annual runoff and sediment yield by 17.4% and 23.6%, respectively. Tree-shrub mixtures showed more efficiency in reducing runoff (24.2%) and sediment yield (32.1%) than tree-tree mixtures. However, the positive effect of mixed forests on soil erosion control was significant > 20 years after stand establishment. Mixed forests showed the highest capacity to control soil erosion at slope angles of 16°-25° (runoff: 27.7%; sediment yield: 37.7%). In terms of soil textures, mixed forests performed better with respect to soil erosion control on sandy soils (runoff: 21.4%; sediment yield: 30.1%), whereas significant differences were not observed between different stand types on clayey soils. In addition, in the dry areas (humidity index (HI) < 30), mixed forests conferred the greatest benefits in reducing runoff and sediment yield (25.8% and 33.0%, respectively). Our results indicate that increasing tree species richness is a suitable approach to controlling soil erosion in China. This research provides a scientific basis for the management and sustainable development of forest ecosystems in the future. [ABSTRACT FROM AUTHOR]