Seed germination ecology of endangered plant Horsfieldia hainanensis Merr. In China.

BACKGROUND: Horsfieldia hainanensis Merr., an indicator species of China's humid tropical rainforests, is endangered due to difficulties with population regeneration. In this study, the biological characteristics and germination adaptability of the seeds were studied for the first time, in order to provide a basis for analyzing the causes of endangerment and strategies for the artificial cultivation of H. hainanensis. The effects of biological characteristics (population, arils, seed coat, seed weight, seed moisture content) and environmental factors (temperature, light, drought, substrate, burial depth) on seed germination and seedling growth of H. hainanensis were studied. RESULTS AND DISCUSSION: The fruits were found to be capsules containing seeds wrapped in a pericarp and fleshy aril, which provide protection and assist in seed dispersal, but also pose risks to the seeds, as the peel and fleshy aril can become moldy under high temperature and humidity conditions. There were significant differences in fruit morphology and germination characteristics among different populations, and the seed quality of populations in Niandian village, Daxin County, Chongzuo City, Guangxi Zhuang Autonomous Region was better. The arils significantly inhibited seed germination, the germination of large seeds was better, and seedling growth from medium seeds was superior. H. hainanensis seeds were sensitive to dehydration, and intolerant to drought and low temperature, which is typical of recalcitrant seeds. The seeds are suitable for germination on a moist substrate surface with good water retention and breathability at 30-35℃.

Changes in Soil Properties, Microbial Quantity and Enzyme Activities in Four Castanopsis hystrix Forest Types in Subtropical China.

It is well established that forest type can have a profound impact on soil physicochemical properties but the associated changes in soil microbial communities and the mechanisms by which soil quality is improved by various plantations are not fully understood. In this study, soil physicochemical properties and microbial and enzyme activities were investigated in four forest types-Castanopsis hystrix pure forests (CHPF), C. hystrix-Pinus elliottii mixed forests (CHPEF), C. hystrix-Michelia macclurei mixed forests (CHMMF), and C. hystrix-Mytilaria laosensis mixed forests (CHMLF) in the subtropical region of China. The purpose of this study was to assess the effects of afforestation types on characteristics of soil-its physical, chemical, and biological properties. The results showed that the contents of soil total organic carbon (TOC), soil total nitrogen (TN), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) were significantly improved in both CHMMF and CHMLF mixed forest stands when compared to the CHPF pure stand. Soil enzyme activities were enhanced in the mixed forests. In particular, high phosphatase activity was observed in CHMLF stands, leading to the transformation of soil phosphorus to available phosphorus in this forest type. Our study demonstrated that the broad-leaved mixed forests, but not coniferous mixed forests, could significantly improve soil quality in the study region. Our research provides a scientific insight into the promotion of vegetation restoration and plantation forest management in plantation regions of subtropical areas.

Photosystem II of Ligustrum lucidum in response to different levels of manganese exposure.

The toxic effect of excessive manganese (Mn) on photosystem II (PSII) of woody species remains largely unexplored. In this study, five Mn concentrations (0, 12, 24, 36, and 48 mM) were used, and the toxicity of Mn on PSII behavior in leaves of Ligustrum lucidum was investigated using in vivo chlorophyll fluorescence transients. Results showed that excessive Mn levels induced positive L- and K- bands. Variable fluorescence at 2 ms (VJ) and 30 ms (VI), absorption flux (ABS/RC), trapped energy flux (TRo/RC), and dissipated energy flux (DIo/RC) increased in Mn-treated leaves, whereas the performance index (PIABS), electron transport flux (ETo/RC), maximum quantum yield (φPo), quantum yield of electron transport (φEo), and probability that an electron moves further than QA- (ψo) decreased. Also, excessive Mn significantly decreased the net photosynthesis rate and increased intercellular CO2 concentration. The results indicated that Mn blocked the electron transfer from the donor side to the acceptor side in PSII, which might be associated with the accumulation of QA-, hence limiting the net photosynthetic rate.

Effects of cadmium on photosynthesis of Schima superba young plant detected by chlorophyll fluorescence.

Contamination by heavy metals has become a serious environmental pollution issue today due to its potential threat to plant, wildlife, and human health. Photosynthesis, a process in which light energy is used to produce sugar and other organic compounds, is sensitive to heavy metals. In the present study, the response of photosynthetic process and carbon assimilation of Schima superba was investigated under cadmium (Cd) stress. Three Cd concentrations (0, 300, and 600 mg kg-1) were used designated as control (CK), low Cd (L1), and high Cd treatment (L2) of plants. Results showed that photosystem II (PSII) acceptor and donor side electron transport were more easily blocked in treatment compared to control, and L2 have more significant changes than L1. A substantial decrease of 820 nm reflection curve absorption was observed both in L1 and L2 treatments. Special energy fluxes showed significant difference between the control group and the treated group, which indicated that low concentration Cd stress can cause decrease in quantum yield of PSII in plants studied. Non-stomatal factors resulted in a decrease in net photosynthetic rate and a decrease in photosystem activity. Our results suggested that Cd can damage structure and function of the photosynthesis of S. superba young plants.