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With the combination of airborne Lidar and panchromatic images in 1981 and 2021, we investigated the canopy height structure of tropical forests in Menglun sub-reserve in the Xishuangbanna National Nature Reserve of Yunnan Province, and analyzed its relationship with environmental factors by using multiple regression tree (MRT) method. The results showed that forests in the Menglun sub-reserve could be clustered into seven types based on canopy height structures, with tropical rainforest, monsoon evergreen broad-leaved forest, secondary forest, and flood plain forest as the main types. The potential solar radiation, altitude, terrain profile curvature, slope and the brightness value of imageries in 1981 and 2021 were main factors that drove the classification. The tropical seasonal rainforest dominated by Pometia pinnata occupied the largest area in valley and low-land. The monsoon evergreen broad-leaved forest dominated by Castanopsis echinocarpa mainly distributed in the ridge and disturbed areas. The secondary forests had homogeneous canopy surface, which was significantly different from the primary forests. The activities of swidden agriculture about three decades ago had legacy impacts on the physiognomy of secondary forests. [ABSTRACT FROM AUTHOR]

A growing body of evidence indicates that tree mycorrhizal association and species richness pronouncedly affect soil nitrogen (N) cycling. However, most studies have been conducted in temperate forests, and the roles of soil microbial communities have been largely overlooked. Here, based on 11 long-term dynamic monitoring sites in tropical forests, we investigated the effects of the dominance of trees associated with arbuscular mycorrhizal (AM) (by basal area) and tree species richness on soil N cycling, and explored the role of soil bacteria, archaea and fungi. Our results showed contrasting effects of AM tree dominance and tree species richness, with AM tree dominance-induced increases in soil ammonium N, nitrate N and the rate of net N nitrification, and tree species richness-caused decreases in ammonium N, nitrate N, the rate of net N mineralization and ammonification. Moreover, we found that the "plant-soil-microbe" interactions mainly triggered the changes in net N mineralization, ammonification and nitrification. It was mainly bacterial composition that directly affected soil N mineralization and ammonification, while fungal diversity only changed soil N ammonification. For soil N nitrification, the abundance of ammonia-oxidizing archaea (AOA) was the main drivers. These findings reveal the discrepancy in effects of the AM tree dominance and tree species richness on soil N cycling, highlighting microbe-mediated mechanisms in regulating soil N mineralization, ammonification and nitrification. • AM tree dominance and tree species richness oppositely affected soil N cycling. • AM tree dominance and tree species richness modulated soil microbiome. • Microbes were crucial in mediating tree effects on soil N cycling. [ABSTRACT FROM AUTHOR]