Influence of the concentration ratio of nitrogen to phosphorus on the growth and interspecies competition of two red tide algae

The growth and interspecies competition of two red tide algal species Thalassiosira pseudonana Hasle et Heimdal and Gymnodinium sp. were studied under different concentration ratios of nitrogen to phosphorus, and the algal hatch culture experiments were conducted. The physiological and biochemical indexes were measured periodically, including the maximum comparing growth rate, relative growth rate, average double time and chlorophyll a concentration. The results showed that when the concentration ratio of nitrogen to phosphorus was 16： 1, the maximum comparing growth rate, relative growth rate and chlorophyll a concentration of Thalassiosira pseudonana all reached the highest,and average double time was the shortest. This implied that the optimal concentration ratio of nitrogen to phosphorus of Thalassiosira pseudonana is 16： 1. When the concentration ratio of nitrogen to phosphorus was 6：1, the maximum comparing growth rate, relative growth rate and the chlorophyll a concentration of Gymnodinium sp. reached the highest, and average double time was the shortest, so the optimal concentration ratio of nitrogen to phosphorus of Gymnodinium sp. is 6： 1. From the growth curves as indicated both in the cell density and the chlorophyll a concentration, it is suggested that the influence of concentration ratio of nitrogen to phosphorus on the chlorophyll a concentration and the cell density are almost the same. Different concentration ratios of nitrogen to phosphorus had weak influence on community succession and the competition between the two algae. Gymnodinium sp. may use the phosphorus in vivo for growth, so it is important to pay attention to the concealment of phosphorus, in order to avoid the outbreak of red tide. On the basis of the importance of nitrogen and phosphorus and the ratio of their concentration, the possible outbreak mechanism of red tide of the two algae was also discussed.

Critical phosphorus concentrations in winter wheat genotypes with various phosphorus efficiencies

Under greenhouse conditions, a pot experiment was conducted to seek critical phosphorus concentrations of wheat genotypes with high and low phosphorus use efficiency. Results indicated that low efficient genotype was much more sensitive to phosphorus deficiency, with low or without phosphorus application, seed yield and dry matter of biomass were much lower. The yield of all the genotypes gradually got higher as application rate increased, but high efficient genotype——Lofflin produced relatively higher yields of seeds and biomass with low or without phosphorus input. Highly tolerate to low availability of soil phosphorus and efficient activation and absorption for soil unavailable phosphorus had been displayed. As application rates increased, yields of both genotypes were increased but high efficient genotype maintained stable while low efficient one showed continuously increase with remuneration decrease progressively. Critical phosphorus concentrations in high efficient genotypes of winter wheat were lower than that in low efficient ones and changed with various development stages, for example, at seedling state, the concentrations of high efficient genotype were 4.50—4.60 g/kg while low efficient one was 5.0 g/kg. They were 2.25—2.30 g/kg and 2.52 g/kg at flower stage, 1.96—2.05 g/kg and 2.15 g/kg at maturity respectively. But the values in seeds were reversal, higher in high efficient genotype(4.05—4.10 g/kg) than that in low efficient(3.90 g/kg). Therefore, phosphorus high efficient genotypes belong to the phosphorus resource saving type.

TOTAL PHOSPHORUS RELEASE FROM BOTTOM SEDIMENTS IN FLOWING WATER

In this paper, the bottom of the Dianshan Lake was selected as a test sample. The dynamic release of contaminated sediments into the overlying water column was experimentally investigated in an open water channel under different hydrodynamic conditions. The experimental results indicate that the Total Phosphorus （TP） release process can be divided into three stages： rapid release, slow release and equilibration release. In the initial release stage the measured TP concentration changes along the depth. The TP concentration near the sediment-water interface is higher than that near the water surface, but the TP concentration becomes uniform along the depth after 3 h. The dynamic release of re-suspension sediment pollutants is about 6 times higher than the static release of sediment-water interface. There are three main types of release mechanism： diffusion release, re-suspended pore water mixing release and re-suspended particles desorbing release.

Resorption efficiency of leaf nutrients in woody plants on Mt. Dongling of Beijing, North China

Aims To explore resorption efficiency of nitrogen(NrE)and phosphorus(PrE)of woody plants in relation to soil nutrient availability,climate and evolutionary history,in North China.Methods We measured concentrations of nitrogen([N])and phosphorus([P])in both full expanded mature green and senescent leaves of the same individuals for 88 woody species from 10 sites of mt.Dongling,beijing,China.We built a phylogenetic tree for all these species and compared NrE and PrE among life forms(trees,shrubs and woody lianas)and between functional groups(N-fixers and non-N-fixers).We then explored patterns of NrE and PrE along gradients of mean annual temperature(MAT),soil inorganic N and available P,and phylogeny using a general linear model.Important Findingsmass-based NrE(NrEm)and PrE(PrEm)averaged 57.4 and 61.4%,respectively,with no significant difference among life forms or functional groups.Neither NrEm nor PrEm exhibited significant phylogenetic signals,indicating that NrEm and PrEm were not phylogenetically conserved.NrEm was not related to[N]in green leaves;PrEm was positively correlated with[P]in green leaves;however,this relationship disappeared for different groups.NrEm decreased with[N]in senescent leaves,PrEm decreased with[P]in senescent leaves,for all species combined and for trees and shrubs.NrEm decreased with soil inorganic N for all species and for shrubs;PrEm did not exhibit a significant trend with soil available P for all species or for different plant groups.Neither NrEm nor PrEm was significantly related to MAT for overall species and for species of different groups.