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Karsts are recognized as fragile environments where, forest degradation is faster and the composition and growth rate of vegetation is considered as a product of the interactions between karst ecological factors. A representative sample of vegetation plots from a systematic sampling was analyzed in Longhushan, southwest China. The sampling combined measurements of species number with extensive information on geological, environmental, and soil factors to establish species response to the single or combined influence of these factors. Both General and Generalized Linear Models predicted richness as a function of the combination of variables from the three groups. Richness increased with elevation, slope, moisture, and in dolomite dominated areas, but decreased with organic matter. Patterns of richness were dependent on complex relationships between soil, geological, and environmental factors, within this complexity it appeared that rock type played an important role. Evidence of significant variations was provided after combining variables from the three groups, suggesting their interactions influence on plants. Our findings have implications for the understanding of these interactions and suggest that plant species can be affected by it, and also carbonate rock type may be an important parameter to consider while examining relationships between plant and environmental factors in karst areas.
The main purpose of this study conducted from August 2010 was to find biomass and productivity of epilithic algae and their relations to environmental factors and try to explore the restrictive factors affecting the growth of algae in the Gufu River, the one of the branches of Xiangxi River located in the Three Gorges Reservoir of the Yangtze River, Hubei Province, Central China. An improved method of in situ primary productivity measurement was utilized to estimate the primary production of the epilithic algae. It was shown that in rivers, lakes, and reservoirs, algae are the main primary producers and have a central role in the ecosystem. Chlorophyll a concentration and ash-free dry mass (AFDM) were estimated for epilithic algae of the Gufu River basin in Three Gorges Reservoir area. Environmental factors in the Gufu River ecosystem highlighted differences in periphyton chlorophyll a ranging from 1.49 mg m (origin) to 69.58 mg m (terminal point). The minimum and maximum gross primary productivity of epilithic algae were 96.12 and 1439.89 mg C m day, respectively. The mean net primary productivity was 290.24 mg C m day. The mean autotrophic index (AFDM:chlorophyll a) was 407.40. The net primary productivity, community respiration ratio (P/R ratio) ranged from 0.98 to 9.25 with a mean of 2.76, showed that autotrophic productivity was dominant in the river. Relationship between physicochemical characteristics and biomass was discussed through cluster and stepwise regression analysis which indicated that altitude, total nitrogen (TN), NO-N, and NH-N were significant environmental factors affecting the biomass of epilithic algae. However, a negative logarithmic relationship between altitude and the chlorophyll a of epilithic algae was high. The results also highlighted the importance of epilithic algae in maintaining the Gufu River basin ecosystems health.
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