ABSTRACT
BACKGROUND: Abies faxoniana is the dominant plant species of the forest ecosystem on the eastern edge of Qinghai-Tibet Plateau, where the treeline is strongly defined by climate. The tree-ring chronologies and age structure of Abies faxoniana were developed in the treeline ecotones on the northwestern and southeastern aspects of the Min Mountains in the Wanglang Nature Reserve to examine the treeline dynamics of recent decades in response to climate change. RESULTS: On the northwestern aspect, correlation analysis showed that the radial growth was significantly and positively correlated with precipitation in current January and monthly mean temperature in current April, but significantly and negatively correlated with monthly mean temperature in previous August. On the southeastern aspect, the radial growth was significantly negatively correlated with monthly mean temperature in previous July and August. CONCLUSIONS: The different responses of radial growth to climatic variability on both the aspects might be mainly due to the micro-environmental conditions. The recruitment benefited from the warm temperature in current April, July and September on the northwestern aspect. The responses of radial growth and recruitment to climatic variability were similar on the northwestern slope. Recruitment was greatly restricted by competition with dense bamboos on the southeastern aspect.
ABSTRACT
Based on the litterbag method, we explored the decomposition dynamics of the litter from the evergreen broad-leaved forests, the mixed evergreen and deciduous broad-leaved forests, and the deciduous broad-leaved forests along an altitude gradient in Mt. Shennongjia, Hubei, China. According to the decomposition rate, the decomposition of the litter could be divided into early stage (0-360 days) and later stage (361-720 days). With the increase of altitude, the mass loss rates of the litter from the three types of forests at the early stage were 2.62-4.08 times that of the later stage, the litter decomposition rates at the early stage were 2.71, 1.72 and 2.69 times of that at the later stage, respectively, and 95% decomposition of the litter needed 3.84, 4.54 and 4.16 years respectively. The decomposition rate at the later stage was significantly correlated with C/N, and the contents of N, hemicelluloses, cellulose and lignin.
Subject(s)
Altitude , Forests , Soil/chemistry , China , Plant Leaves , TreesABSTRACT
Ternary lead magnesium niobate-lead zirconate titanate system 0.4Pb(Mg(1/3)Nb(2/3))O(3)-0.25PbZrO(3)-0.35PbTiO(3) (40PMN-25PZ-35PT) thin film with a thickness of 1.5 µm was grown on Pt(111)/Ti/SiO(2)/Si substrate via chemical solution deposition. X-ray diffraction and transmission electron microscopy results suggested the film obtained was highly (111)-oriented. The remanent polarization and coercive electric field of the film were found to be 25.5 µC/cm(2) and 51 kV/cm, respectively. In addition, at 1 kHz, the dielectric constant was measured to be 1960 and the dielectric loss 0.036. The film was observed to undergo a diffuse ferroelectric-to-paraelectric phase transition at around 209°C. The leakage current appeared to depend on the voltage polarity. If the Au electrode was biased positively, the leakage current was dominated by the Schottky emission mechanism. When the Pt electrode was biased positively, the conduction current curve showed an ohmic behavior at a low electric field and space-charge-limited current characteristics at a high electric field.
