Phosphorus (P) loss from soil to water bodies is an important process associated with eutrophication of lakes and reservoirs. Phosphorus concentration in China's waterbodies changes geographically, increasing substantially with latitude. It is assumed that the geographical pattern results from change in soil retention and loss features of P. To test this assumption, we designed a soil column leaching experiment to measure the P retention capacity of three common types of soils in China: red, black and loess. Results showed that red soil possessed a much higher P retention capacity than black and loess soils. Red soil retained P primarily through binding by aluminium and iron, with half of the total retained P contributed by iron binding. Phosphorus loss in all three soils was influenced by pH of the used acid solution and the leaching rate. Specifically, acidification tends to promote soil P loss, whereas leaching rate decreases P loss.
The favorable natural conditions and variety of habitats in the Beibu Gulf provide a basis for harboring a high diversity of marine organisms. Sustainable coastal ecosystem management can be benefited from a comprehensive assessment of species diversity. In this study, we analyzed the seasonal changes in nektonic phylogenetic and community structures in the waters of Weizhou Island in the northern Beibu Gulf. The results showed that both the nektonic phylogenetic diversity and community structure in the northern Beibu Gulf exhibited strong seasonal differences between spring and autumn. The catch density was 291.9 kg per km2 in spring and 1081.1 kg per km2 in autumn. Phylogenetic diversity of nektonic communities obviously increased from spring to autumn, while phylogenetic patterns changed from clustering to overdispersion. The seasonal patterns of nektonic communities were mainly related to the different fishing intensities in spring and autumn. Summer fishing intensity in the Beibu Gulf was effectively controlled by a mid-summer fishing moratorium, during which nektonic diversity and fish stocks rapidly recovered from the larval pool. Our study revealed that fishing intensity had a greater impact on nektonic communities at smaller spatial scales, and even exceeded the effects of environmental factors.
Body size is a functional trait that influences the overall biology and ecology of an organism. Studying the shape of size–frequency distributions and size variability within different scales, approximates the influence of large-scale ecological and evolutionary processes on a species. In this study we examine the patterns of distribution and variability of body size among freshwater Cladocera across different taxonomic levels, geographic distribution and habitat association. Using extensive literature data, we show the global distribution of body size in freshwater Cladocera. Hierarchical models were used to assess the effect of different categorical variables on size variability. Our results show that almost all size–frequency distributions were skewed right in all categories. The hierarchical model showed that taxonomic affiliation contributes the most to size variability in our dataset, suggesting that size might be a conserved trait. Large genera (≥1mm) have larger estimated variability compared to smaller genera. In general, our observations on size–frequency distributions and size variability show a brief insight in the varying advantages of adaptive body size in this group of organisms in both biology (physiology) and ecology (competition and co-existence). Thus, body size is a trait important to the survival and continuing evolution of Cladocera.
There is increasing evidence that rare species play an important role in trophic interactions, but how rare species with low biomass disproportionately function in these processes remains unclear. Phytoplankton is placed at the base of lentic and marine food webs and is characterised by a few dominant species and many rare species. While the dominant species contribute most to the primary production, they are often low-quality food for primary consumers. The rare species may instead provide the essential biochemical nutrients for consumers, especially in eutrophic waters. We hypothesised that the biomasses of rare phytoplankton species signi cantly determine the concentrations of particulate PUFAs (polyunsaturated fatty acids), directly linking them to the functioning of aquatic ecosystems. We applied redundancy analysis and Lasso regression models to identify the species whose population dynamics explain the variations of particulate fatty acids concentrations in tropical reservoirs and lakes. The model predicted that the dominant phytoplankton species determined the concentration of saturated particulate fatty acids and that rare phytoplankton species were the main determinant for PUFAs. In particular, the biomass of the rare species Scenedesmus obliquus was a key variable explaining the variations of ALA (α-linolenic acid), LIN (α-linoleic acid), GLA (γ-linolenic acid) and EPA (eicosapentaenoic acid) concentrations in the studied waterbodies. We conclude that the population dynamics of rare phytoplankton species can de ne the food quality associated with PUFAs for consumers and thus play a critical role in the trophic transfer in the food webs of tropical waterbodies.
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