Spatial dispersion patterns of trees at different life stages are an important aspect to investigate in understanding the mechanisms that facilitate species coexistence. In this paper, Ripley's univariate L(r) and bivariate L 12 (r) functions were used to analyze spatial distribution patterns and spatial associations across different life stages of 131 tree species in a 20-ha plot of a tropical rainforest in Xishuangbanna, southwest China. Our results show that: (1) Saplings of 109 (83.2%) species have a significant clumped distribution, which confirms the ubiquity of clumped spatial distributions among tropical tree species.(2) Adults of 126 (96.2%) species have a random distribution suggesting that density-dependent mortality can make the spatial pattern of tropical trees more regular with time.(3) At small scales (0-10 m), 95 (72.5%) species have a neutral or negative sapling-adult association, implying that there is recruitment limitation within the vicinity of their conspecific adults. The reduction in spatial clumping in going from younger to older life stages and the neutral or negative sapling-adult association imply densitydependent mortality in the vicinity of adult trees. In accordance with the Janzen-Connell hypothesis, such density-dependent mortality can free up space for other species to colonize, contributing to the maintenance of species diversity.

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The chemical bonding mechanism, electronic structure, and the energy level alignment at the terephthalic acid (TPA)/TiO2 (110)-(1×1) interface were investigated in situ by means of X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoemission spectroscopy (SRPES). It has been found that the adsorption of TPA on TiO2(110)-(1×1) at room temperature leads to the formation of dicarboxylate species at lower coverage (∼0.2 ML) followed by the formation of monocarboxylate species below 1 ML, indicating a geometry variation from flat-lying to upright adsorption. Further deposition of TPA onto the first monolayer results in a multilayer growth without deprotonation. The energy level alignment at the TPA/TiO2 (110) interface demonstrates a straddling lineup of the organic frontier molecular levels with respect to the oxide bands at the interface. A large energy difference with a value of ∼1.1 eV is present between the lowest unoccupied molecular orbital (LUMO) of TPA and the conduction band (CB) of TiO2, suggesting an energetically favorable electron transfer from TPA into TiO2. Fundamental understanding of the chemical interactions and electronic properties at the TPA/TiO2 interface could facilitate unravelling the microscopic mechanism for interfacial charge transfer dynamics, which is desirable for exploring a new generation of hybrid energy devices.

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