Abstract:Danxia Mountain in Guangdong Province was investigated on the special ecological effects of ravines in Danxia Landform. The results showed that its geomorphologic ecological effects could be manifested in the following two aspects. Firstly, multitudinous ridgy stone peaks and hollow ravines were shaped in the forming process of Danxia Landform. Ecological factors were different between the ravines and other open regions. Relatively close microclimate and high moisture condition in ravines could provide suitable living environment for tropical species which preferred hot and humid environment. Geomorphologic environment in ravines, like smooth degree of surrounding cliffs, would affect intensity of light reflected into ravines. All the aspects had influence on the temperature and humidity in ravines. Secondly, the special ecological effects of ravines in Danxia Landform provided a possibility to gestate a group of taxa with greater tropical characteristics. There, tropical plant flora was markedly increased in comparison with other vegetations at similar latitude. Tropical plant distributions were obvious in most ravines of Danxia Landform. Its proportion was 10% more than that of other regions at the similar latitude. The ravines in Danxia Landform were rich in liana, ferns and other plants with high water-logging resistance. Collectively, the phenomena that some typical species in south subtropical regions appeared in mid-subtropical regions revealed latitudinal shift of plant distribution. This kind of climax communities, which were coordinated and balanced with their geomorphologic environments due to the special ecological effects of ravines in Danxia Landform, could be called geo-climax communities.

Abstract:As main photosynthetic organs, leaves are very sensitive to exterior environments. Water deficiency obviously affects the biological and physiological characteristics of leaves. Xylem pathways increase when trees grow tall, which results in the increase in water gravity as well as pathway resistance. Accordingly, the physiological characteristics of leaves change along with tree height. In this research, the photosynthetic characteristics and carbon isotope ratio (δ¹³C) in the leaves of 4 tree species, Platanus hispanica, Robinia pseudoacacia, Fraxinus chinensis and Ginkgo biloba, were measured. The results showed that the leaf photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Cond) and internal CO₂ concentration (Ci) reduced along with tree height, while the leaf δ¹³C increased along with tree height. The One Way ANOVA and LSD tests showed that the leaf photosynthetic characteristics and δ¹³C varied significantly at different tree heights (P < 0.05). The decrease in leaf photosynthetic capability and the increase in δ¹³C along with tree height indicate that the leaves at the tree tops suffer from water stress. These results support the hydraulic limitation hypothesis.

Abstract:Model predictions can be improved by parameter estimation from measurements. It was assumed that measurement errors of net ecosystem exchange (NEE) of CO₂ follow a normal distribution. However, recent studies have shown that errors in eddy covariance measurements closely follow a double exponential distribution. In this paper, we compared effects of different distributions of measurement errors of NEE data on parameter estimation. NEE measurements in the Changbaishan forest were assimilated into a process-based terrestrial ecosystem model. We used the Markov chain Monte Carlo method to derive probability density functions of estimated parameters. Our results showed that modeled annual total gross primary production (GPP) and ecosystem respiration (Re) using the normal error distribution were higher than those using the double exponential distribution by 61–86 gC m^-2 a^-1 and 107–116 gC m^-2 a^-1, respectively. As a result, modeled annual sum of NEE using the normal error distribution was lower by 29–47 gC m^-2 a^-1 than that using the double exponential error distribution. Especially, modeled daily NEE based on the normal distribution underestimated the strong carbon sink in the Changbaishan forest in the growing season. We concluded that types of measurement error distributions and corresponding cost functions can substantially influence the estimation of parameters and carbon fluxes.

Abstract:Spatial patterns of ramet population of Iris japonica Thunb. and their effect on species diversity in the herb layer of 3 microsites (open area of forest edge (OAFE), bamboo forest (BF) and evergreen broad-leaved forest (EBF)) on Jinyun Mountain were studied using spatial pattern, niche and diversity analyses in a combination of population and community methods. The results were as follows: (1) judged by V/m and Morisita index (I_δ), ramet population of I. japonica in 3 microsites all clumped from scale 0.5 m 0.5 m to 2 m 2 m; (2) the pattern scale and pattern intensity both gradually decreased on all scales, and the density of ramet population of I. japonica decreased with the increase in canopy density and the decrease in relative photon flux density (RPFD) and R/FR from OAFE to EBF. In OAFE and BF, widespread I. japonica had significantly negative influence on the dominance of original dominant species and on species diversity in the herb layer (p < 0.05), while those influences in EBF were extremely weak. The mechanisms that pattern characteristics of ramet population of I. japonica influence herb diversity in 3 microsites were different. In OAFE, strong regeneration niche (above-ground spatial and below-ground root) and trophic niche (nutrient) competition had significantly negative influence on the species diversity of rare herbs and dwarf herbs. In BF, strong regeneration niche (below-ground root) and trophic niche (above-ground for light and below-ground for nutrient) competition had negative effect on the occurrence of rare species and on the survival of other herb species. In EBF, weak niche competition had little effect on the survival of herb species. Intensity of regeneration niche and trophic niche competition between I. japonica and other herb species is the determinant to the mechanism that ramet population of I. japonica influences herb diversity.

Abstract:Biomass estimation of old-growth forests in the upper Minjiang River (UMR) is important in quantifying carbon (C) sequestration and C sink size because majority of the natural forests in UMR are mature or over-mature. Based on the forest resource data from 27 fixed sampling plots that have been surveyed consecutively, the dynamics of the aboveground biomass density (AGBD) were characterized by the allometric relationships, and the space-time variations of the C sink size in the sub-alpine old-growth forests of UMR were explored. Our results showed that 1) the net increase in AGBD was (27.311 ± 15.580) Mg·hm^-2 and the mean annual growth rate and mean annual death rate were (1.930 ± 1.091) and (2.271 ± 1.424) Mg·hm^-2a^-1 during 1988–2002, respectively. 2) The aboveground biomass (AGB) largely depended on the growth and death rates of the trees with different diameters at the breast height (DBH) classes and the recruitment rate from one DBH class to another as well. The largest increment component of AGB came from the DBH class of 20 to 40 cm, whereas the minimum increment component of AGB was above 80 cm in DBH. The net negative increment of AGB occurred at DBH classes of 40–60 and 60–80 cm. 3) There were space-time variations of AGB in the alpine old-growth forests, indicated by AGB changing over time in the same sampling plot and varying among the locations or plots during the same sampling period. These variations were not only reflected in numerical value but also in positive or negative biomass increment.

Abstract:Bursaphelenchus xylophilus (Pine wood nematode, PWN) is a serious pest in pines that changes the original biological and geographical distribution as well as the structure and function of the natural ecosystems. The nematode and associated pine wilt disease have great impact on the stand growth of Masson pine forests in China. The growth rule of individual forest factors after the PWN invasion was analyzed using “the technique of censusing every individual” and “quadrat method”. The results showed that the invasion of PWN in 1996 had significant impact on the diameter growth of the pines, but PWN only seldom affected the height growth of the pines. Based on this, the paper also established the grey forecast and grey-Markov combination models of the growth of Masson pines attacked by PWN. This series of models had a high simulation accuracy and could be applied to predict stand description factors in Masson pine forest, no matter whether it was attacked by PWN or not.

Abstract:By simulating the anaerobic conditions with agar nutrient solutions, effect of arsenic (As) on the growth and As uptake by hybrid, conventional and glutinous rice cultivars were studied. It showed insignificant effect of As on the root dry weights of three rice cultivars when treated by As of different concentrations. The shoot dry weights of hybrid and glutinous decreased with As concentrations increasing, while low concentrations of As (0.5 mg L^-1) could enhance the growth of conventional rice. Generally, As concentrations in roots and shoots increased as As concentrations of treatment solutions increasing. The root system had strong ability to uptake and accumulate As. The root As concentrations ranged from 156 to 504 mg kg^-1, representing 63.40%–81.90% of the total As concentrations in rice, which were much higher than shoot As concentrations. The fact that the glutinous rice had higher biomass, higher tolerance, and lower As concentrations in its roots and shoots than the other two rice cultivars proved that the glutinous rice was more applicable to As-polluted soils.

Abstract:Five diploidy wheat species were chosen as research materials to determine the differences in stomatal and photosynthetic characteristics. The results of the study showed that species with S genomes (Ae. Sect. Sitopsis) had the largest values in stomatal length, girth and area, and the lowest values in stomatal width, density and index. On the contrary, the species with D genomes (Ae. Tauschii) had the highest values in stomatal width, density and index, and the lowest values in stomatal length, girth and area. The net photosynthetic rate (Pn) and stomatal conductance (Gs) were higher in species with D genomes (Ae. Tauschii) and lower in species with S genomes (Ae. Sect. Sitopsis), respectively. The net photosynthetic rate showed significant correlation with stomatal conductivity, and the changes in intercellular CO₂ content showed the opposite trend to the changes in stomatal limitation, indicating that the stomatal conductivity is the main factor limiting the photosynthetic rate. T. urartu with higher net photosynthetic ability showed higher values in stomatal conductivity and stomatal limitation, and lower values in intercellular CO₂ content. However, T. boeoticum showed the opposite trend. T. urartu had higher values of chlorophyll content in flag leaf area, while T. boeoticum had lower values, indicating that there might be higher chlorophyll content.

Abstract:Classification of spatial scales and measurement of edge effects in ecology were reviewed. The spatial scales can be classified into large scale (biome ecotone), meso-scale (ecological ecotone) and small scale (community ecotone) through the formation and maintenance of edge effects in ecology based on the synthetic analysis of published literatures. The biome ecotone is influenced by climate, regional dominant vegetation and terrain environment. The ecological ecotone is usually distributed in the transitional region with remarkable habitat heterogeneity. It connects adjacent ecosystems and affects the flow of energy and nutrient. Nowadays, study on edge effects in ecology mainly focuses on boundary sensitivity which associates with urban-rural ecotone, forest-grassland ecotone, agro-pastoral ecotone, forest-farmland ecotone, water-land ecotone and forest-swamp ecotone. As to the community ecotone which links with different patches to the interior of the community, previous studies focused on community edge, gap edge and treelines. The borderlines of different biome ecotones and the gradients of species distribution in the biome ecotones have been investigated through the method of quantitative ecology. The dynamic change, location and width of the ecological ecotone have been studied using the Geographic Information System (GIS), Remote Sensing (RS) and Global Positioning System (GPS) technologies and the landscape ecology theory. As important indicators, distance from edge, population, structure and diversity determined for establishing models can be applied to measure the intensity of edge effects and decide the positive or negative impact on communities. Although study on the edge effects in ecology was mostly reported at the meso-scale and small scale, study at large scale should be paid more attention as it is the potential value in ecology and global change fields.

Abstract:The characteristics and scientific values of ecological succession in Danxia Landform of China were discussed. It was known that research on vegetation succession was quite difficult for its long-term and intricate process. Space-time substitution is an important method to study the succession, while it needs intact spatial succession series. In Danxia Landform, there are such primary and secondary succession series. On the hilltops, there are typical low shrubberies and arboreal forests of primary succession. The surrounding slopes are subjected to seasonal rainfall erosion, weathering action, gravitational collapse and so on. The primary succession constantly starts from bare rocks, and then moss and herbal communities of early primary succession are formed. With further weathering of rocks and effects of moss and lichen, soil layers are getting thicker and thicker, which pushes primary succession ahead. New collapses are ceaselessly induced by the special geological geomorphological process, and then a new primary succession starts from bare rocks. Thus, different stages of primary succession are formed in Danxia Landform. In addition, the secondary succession series exist in Danxia Landform, including the pioneer forests, transitional forests and steady forests. Danxia Landform provides ideal sites for vegetation succession study. The relative studies would be helpful for the vegetation management and protection in this area. As ecological restoration reference, it is also meaningful for the vegetation restoration.

Abstract:The hilltop ecological effect of Danxia Landform generated by the distinct physiognomy and topography was investigated. The characteristic differences in ecological factors, community structure and species ecotype between hilltop and foot gulch and those of adjacent non-Danxia Landform were determined. The results showed that the mean daily temperature on the hilltop was higher than that at the foot gulch. But the average relative humidity and community diversity on the hilltop were lower than those at the foot gulch. In contrast to those on the hilltop, plants at the foot gulch showed stronger tropical character. All of the characteristics above were different from those in other landforms. In addition, ecotypic differentiations in leaf area, specific leaf area, bark, height under branch and crown width were found in the studied species between the hilltop and the foot gulch. Moreover, the hilltop of Danxia Landform was thought to be of significance in the scientific research of ecotype, island biogeography and adaptive evolution. Further studies are needed in order to better understand the universality of ecological effect on the hilltop of Danxia Landform.