Natural regeneration is an essential component of forest dynamics and the recovery of ecosystem functions. Therefore, understanding regeneration status, and how abiotic and biotic factors affect it, is important for ecological studies. This study discovered different regeneration statuses of tropical forests in response to differences in rainfall in Myanmar, and the environmental and overstory factors that had the most influence on understory regeneration. Study sites were set up in regions with 625 to 2035 mm of annual rainfall, and ecological characteristics were measured. According to the results, natural regeneration increased with rainfall, showing a good regeneration status at all sites. Forests within a range of 1411-2035 mm of annual rainfall had a significantly higher density and species diversity at specific natural regeneration stages than those with 625-1029 mm. Not only abiotic but also overstory structure affected the natural regeneration of forests. However, not all factors influenced natural regeneration status. Overstory size distribution parameters did not show a significant influence on natural regeneration. Average annual rainfall (abiotic), as well as ecosystem complexity, density, species richness, and diversity (overstory), were found to be the most influential factors for the density and diversity of natural regeneration. The results of this study will support silviculture and the management of tropical forests.
An understanding of how species diversity, structural pattern, and species distribution vary across different environmental regions is crucially important for tropical ecology. In this study, we explored how these ecological parameters vary across various rainfall regions in the tropics with annual rainfall levels ranging from 843 to 2035 mm. Diversity, similarity, structure, and forest classification, and their correspondence with rainfall regions were tested. We found that species diversity, site class, and structural complexity increased with rainfall, with differences of 1000 mm having significant effects on diversity. The structure and heterogeneity of forests were higher in the high rainfall regions than the low rainfall regions. The forest structure was significantly correlated with rainfall, and the structure differed substantially where annual rainfall differed among sites by approximately 200 or 400 mm. Forests could be classified into two types according to whether they had high annual rainfall (1411-2035 mm) or low annual rainfall (843-1029 mm). In addition, the dominance of species changed noticeably from high-to low-rainfall regions, with Tectona hamiltoniana and Terminalia oliveri only being abundant in the low rainfall region. Species diversity and richness were significantly correlated with rainfall and average temperature. These findings will provide invaluable information for forest management and ecological phytogeography.
Abstract:Plants can undergo external fluctuations in the natural light and dark cycle. The photosynthetic apparatus needs to operate in an appropriate manner to fluctuating environmental factors, especially in light. Yellow-poplar seedlings were exposed to nighttime artificial high-pressure sodium (HPS) lighting to evaluate night light-adaptation strategies for photosynthetic apparatus fitness relative to pigment contents, photosystem II photochemistry, photosynthetic parameters, histochemical analysis of reactive oxygen species, and plant biomass. As a result, seedlings exhibited dynamic changes including the enhancement of accessory pigments, the reduction of photosystem II photochemistry, increased stomatal limitation, downregulation of photosynthesis, and the decreased aboveground and belowground biomass under artificial night lighting. Histochemical analysis with 3,3 -diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) staining indicates the accumulation of in situ superoxide radicals (O 2 − ) and hydrogen peroxide (H 2 O 2 ) in leaves exposed to the lowest level of artificial night lighting compared to control. Moreover, these leaves exposed to artificial night lighting had a lower nighttime respiration rate. These results indicated that HPS lighting during the night may act as a major factor as repressors of the fitness of photosynthesis and growth patterns, via a modification of the photosynthetic light harvesting apparatus.
We investigated the net photosynthetic rates and antioxidative enzyme activity in Platanus occidentalis trees growing on two separate streets in Seoul, and representing different degrees of air pollution. In general, concentrations of SO2, NO2, and PM10 decreased from May to September. The photosynthetic rate was reduced significantly on the street with higher levels of pollution. Moreover, activities of two antioxidative enzymes, ascorbate peroxidase and glutathione reductase, were greater in May along the more polluted street. These data suggest that P. occidentalis growing in highly polluted environments may increase their antioxidant enzyme activity to compensate for and to minimize the damage from this stress.Keywords: antioxidative enzymes, stress compensation Stress due to environmental pollutants can cause major evolutionary changes in plant species (Kangasjarvi et al., 1994;Elkarmi and Eideh, 2006), affecting the selection process and occasionally causing the loss of sensitive genotypes, while enhancing the survival of resistant genotypes. In urban environments, trees play an important role in improving air quality by taking up gases and particles (Beckett et al., 2000). These street trees intercept a greater percentage of aerosols than do the shorter vegetation, resulting in a higher deposition rate of gaseous pollutants and particulates. However, their uptake rates depend upon many factors, e.g., leaf-surface conditions, depth of the boundary layer, and stomatal openness.Abiotic stresses such as air pollution can limit plant productivity and survival (Meloni et al., 2003;Vollenweider et al., 2003;Perrings et al., 2005). Over the past few decades, this pollution has become a serious problem in Seoul, Korea. In particular, O:~ concentrations continue to rise as a direct consequence of human activity. Emissions from automobiles have not been successfully restricted and, by the end of 2004, ambient SO2 and O~ concentrations had risen by 4 to 5%. The Ministry of Environment, Korea, has reported that 126 ozone warnings were issued nationwide during 2005, compared with only 48 in 2003 and 52 in 2000. These more-frequent ozone warnings may possibly be attributed to hot and dry weather, rather than increased air pollution, such that in years with higher rainfall, the environment would experience a cooling effect and lower density of ozone (Chung, 2005).Ozone exposure has been correlated with decreased plant growth and photosynthesis, and these processes are reduced further by additional air pollutants (Lawson et al., 2002;Grantz et al., 2003; Vollenweider and G~Jnthardt-Goerg, 2005). In response to abiotic stress, the mitochondria and chloroplasts increase production of reactive oxygen species (ROS), including superoxide, H202, and hydroxyl radicals (Lascano et al., 2001 ;Fornazier et al., 2002;Meloni et al., 2003). To limit the damage caused by these ROS, trees activate complex defense systems that incorporate ~'Corresponding author; fax +82-2-2210-2838 e-mail wsy@uos.ac.kr low-molecular-mass antioxidants as w...
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