Study On Ecological Stoichiometry Of Aquatic Plants In The Inland Waters In Eastern China

In recent years, severe eutrophication and other pollutions which caused by rapid growth of population, economy, industrialization and urbanization in eastern China, have changed the cycle of biogeochemistry in aquatic ecosystems. Ecological stoichiometry is a subject to study the balance and mobility of elements on different levels of organization of life, which provides ecologists with a unique perspective to study the elements of organisms and relationships between the growth and elements from the molecular level to the global scale. Ecological stoichiometry has been one of the focuses of ecological research at present. Studies of ecological stoichiometry in aquatic plants started earlier, somehow most studies focused on the comparisons between individual and communitie level on a small scale. However, few research have been conducted to study the patterns of aquatic plants stoichiometry on the large scale and the driving forces behind them. There are many kinds of water bodies and diverse climates in eastern China from18-53°N, resulting in the high species richness of aquatic plants in this region. So we can well study the geographic distribution of ecological stoichiometry of aquatic plants in this region on a large scale. Because severe eutrophication and other pollutions in this area, studies on ecological stoichiometry of aquatic plants not only have the important theoretical significance, but also have important practical significance, and which can provide a scientific basis for the protections and managements of unpolluted water, and controls and ecological restorations of polluted water.Based on species investigation, specimen collection and community survey, I got familiar with genealogical classification, floristic geography and community ecology. And, then I selected the study on ecological stoichiometry of aquatic plants in the inland waters in eastern China as the research subject of my PhD period. We collected samples from213plots across sample transect (18.35?52.94°N,108.68?134.47°E) in eastern China which included122species in55genera and35families, and then determined Carbon. Nitrogen, and Phosphorus concentrations of aquatic plants. We studied:1) the stoichiometry characteristic of aquatic plants,2) the relationships between elements.3) the difference between aquatic and terrestrial plants,4) the difference between aquatic plants in this area and other areas,5) the difference between different life forms and phylogenetic groups.6) the distribution pattern of the aquatic plants stoichiometry characteristic, including latitude pattern and altitude pattern,7) the main driving force of this pattern used the climate data, sediment nutrients, and water physical and chemical factors (pH, conductivity, dissolved oxygen, turbidity, salinity). Main results are as follows:(1) In eastern China, leaf C, N. P concentrations and C:N. C:P, N:P ratios were respectively369.70mg g-1.25.89mg g-1,3.28mg g-1.17.10,148.62and9.50, the coefficient of variation (CV) were respectively13.18%,40.75%,48.78%,51.35%,62.79%and62.84%. The C:N:P molar ratio was291:17:1in arithmetic mean, and320:18:1in median. The N:P ratio in the present study was9.50, which is much lower than14, indicating that N was the limited nutrient in aquatic macrophytes.(2) Strong correlations between element concentrations and element ratios were observed. Leaf C exhibited strong negative correlations with leaf P and positive correlations with leaf N; leaf N exhibited strong positive correlations with leaf P. The equation of N. P of aquatic plants was:lg10N=0.8424*lg10P+0.9589. The slope of the regression line of log10-transformed N against log10-transformed P concentrations used standardized major axis regression (SMA) was0.8424. which is larger than2/3in terrestrial plants, suggesting that leaf N concentration increases faster relative to leaf P concentration in aquatic than terrestrial plants. And. the slopes of emergent plant, floating plants, floating-leaved plants, submerged plants, monocotyledons and dicotyledons were respectively0.9601.0.7004.0.7674.0.6861.0.8473and0.8098.(3) The concentrations of elements vary in different functional groups. Leaf C concentrations were higher in emergent plants (392.29mg g-1) than submerged plants (336.64mg g-1). The highest mean N concentrations (31.63mg g-1) and P concentrations (3.70mg g-1) were observed in floating plants, while leaf N:P ratios were conserved and no significant difference among the four life forms. No significant differences in element concentrations and ratios were detected between the seed plants and ferns in this study. Leaf N concentrations in dicotyledons (27.22mg g-1) was higher than that in monocotyledons (25.35mg g-1). no significant differences were observed for leaf P concentrations and N:P ratios.(4) A considerable discrepancy in ecological stoichiometry characteristics had emerged among different families of aquatic plants, but there is no difference in leaf N, P concentrations and N:P ratios in five close phylogenetic families (Alismataceae, Najadaceae, Potamogetonaceae, Hydrocharitaceae, Ceratophyllaceae), also the same as in six genera (Blyxa, Hydrilla, Hydrocharis, Ottelia, Vallisneria) of Hydrocharitaceae. And also, there are no differences among different areal-types of genera of aquatic plants in leaf C:N:P ratios.(5) As latitude increased, leaf N concentrations and leaf N:P ratios decreased, while leaf P concentrations decreased; as altitude increased, leaf N concentrations and leaf N:P ratios decreased, while leaf P concentrations exhibited no significant linear relationship with altitude.(6) Leaf N concentrations increased as temperature increased which supported temperature-biogeochemical hypothesis. In contrast, leaf P concentration increased as temperature decreased which was consistent with temperature-plant physiological hypothesis and the soil P pattern of China. And leaf N:P ratios decreased as temperature decreased which could be a robust evidence to support the growth rate hypothesis. Leaf N concentrations and N:P ratios exhibited a positive correlation with MAP, while leaf P concentrations exhibited no correlation with MAP. There was no significant correlation with soil nutrients including soil total nitrogen and phosphorus. Some stoichiometry traits exhibited quadratic correlation with water physicochemical characteristics, including pH, conductivity, turbidity, dissolved oxygen and salinity.(7) Results of general linear model analysis indicated that genus explained more than20%of the variation of elements and element ratios. Life form explained the most variation of leaf C. and the second more variation of other leaf element traits except leaf N:P. Because life form consisted of phylogenetic factors, phylogeny which including life form and genus, explaining46.23%for C,29.54%for N,26.35%for P.37.51%for C:N,33.50%for C:P,22.81%for N:P of the variations. Temperature was the most important environmental factor, explaining1.34%for C.4.89%for N,1.54%for P,3.43%for C:N,2.09%for C:P,9.10%for N:P of the variations. Generally, temperature can influence the distribution and species composition of aquatic plants, and then, influenced the stoichiometry characteristic of aquatic plants indirectly. However, temperature can affect the stoichiometry characteristic of widely-distributed species directly. Therefore, temperature was the most important environmental factor that influenced stoichiometry pattern of aquatic plants in our study.In conclusion, author carried out the study first time of ecological stoichiometry pattern and the driving force of aquatic plants on a large scale. Findings indicated that the stoichiometry characteristics of aquatic plants were affected in some way by the different life forms and phylogenetic groups. Temperature can influence the geographical pattern of stoichiometry characteristics of aquatic plants directly, or indirectly through species distribution and species composition. There was some difference in stoichiometry characteristics between aquatic and terrestrial plants, indicating that adaptive strategies were in the presence of aquatic plants in water bodies.