Despite extensive research on tree species diversity in tropical rainforests, the differences in diversity between lowland and montane rainforests, as well as the underlying mechanisms, remain unclear. This study utilizes tree inventory data from two dynamic monitoring sample plots, each with an area of 1 hm 2 , established in the lowland rainforest and montane rainforest regions of Diaoluo Mountain, Hainan Island. We analyzed the composition, diversity, spatial distribution patterns, and interspecific relationships within the tree communities. In total, 154 tree species with DBH > 3 cm were recorded in lowland rainforests, and 119 were recorded in montane rainforests, with lowland rainforests harboring 51 rare species compared to 40 rare species in montane rainforests. The distribution pattern of small trees (with DBH ≤ 7.5 cm) exhibited clustering at a small scale but random distribution at a larger scale. This phenomenon was more prevalent in tropical lowland rainforests, indicating that the negative density dependence effect is more pronounced in lowland rainforests compared to montane rainforests. Moreover, a higher proportion of negative associations and lower niche overlaps were observed in the lowland rainforest compared to the montane rainforest, suggesting that niche differentiation among tree species is more pronounced in the lowland rainforest. In conclusion, the more intense negative density dependence effect and niche differentiation are the primary factors contributing to the higher tree species diversity observed in lowland rainforests.

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Xylaria is a large and complex genus of macrofungi, playing a critical role in ecosystems as decomposers and possessing antimicrobial, anticancer, and antioxidant properties. This paper described two new Xylaria species discovered on fallen leaves in Hainan Tropical Rainforest National Park, based on morphological characteristics and genetic sequences. Detailed color illustrations and comparisons with similar species were provided. The main characteristics of X.acifer included long, needle-shaped stromata, ellipsoid to fusoid ascospores, and prominent non-cellular appendages. The stromata of X.tuberculosa had an aggregated, knobby fertile part, with smaller ascospores also featuring non-cellular appendages. Additionally, a key to 46 Xylaria species associated with fallen leaves and petioles worldwide was established.

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Four new Daphniphyllum alkaloids, daphnipaxianines A-D ( 1- 4), along with six known ones, have been isolated from the leaves and fruits of Daphniphyllum paxianum. Daphnipaxianines A and B ( 1, 2), a pair of epimers differing at C-10, are the first caliciphylline A type Daphniphyllum alkaloids with a Delta (9(15))-unsaturated cyclic ketone unit, and daphnipaxianine D ( 4) is the first yuzurine-type Daphniphyllum alkaloid containing a hexacyclic ring system. The structures of these alkaloids were characterized by spectroscopic methods, especially 2D NMR techniques. A single-crystal X-ray diffraction analysis was used to confirm the structure of 1.

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[structure: see text] The first diamino Daphniphyllum alkaloid, daphnipaxinin (1), with an unprecedented hexacyclic fused skeleton, along with a known alkaloid, daphnicyclidin A (2), was isolated from the stem of Daphniphyllum paxianum Rosenth. The structure and absolute stereochemistry of 1 were established by spectral methods, especially two-dimensional NMR techniques and CD analysis.

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Two novel alkaloids, paxdaphnidine A (1) with a unique pentacyclic skeleton and paxdaphnidine B (2) with an uncommon tetracyclic skeleton, were isolated from the stems and leaves of Daphniphyllum paxianum. Their structures were established by spectral methods, especially two-dimensional NMR techniques ((1)H-(1)H COSY, HSQC, HMBC, and NOESY).

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