Varietal Differences in Plant Growth, Phosphorus Uptake and Yield Formation in Two Maize Inbred Lines Grown Under Field Conditions

Selection for phosphorus （P）-efficient genotypes and investigation of physiological mechanisms for P-use efficiency in maize has mainly been conducted at the seedling stage under controlled greenhouse conditions. Few studies have analyzed characteristics of plant growth and yield formation in response to low-P stress over the whore growth period under field conditions. In the present study, two maize inbred lines with contrasting yield performances under low-P stress in the field were used to compare plant growth, P uptake and translocation, and yield formation. Phosphorus accumulation in the P-efficient line 154 was similar to that of line 153 under high-P. Under low-P, however, P uptake in line 154 was three times greater than that in line 153. Correspondingly, P-efficient line 154 had a significantly higher yield than P-inefficient line 153 under low-P conditions （Olsen-P=1.60 mg kg-1）, but not under high-P conditions （Olsen-P=14.98 mg kg-1）. The yield difference was mainly due to differences in the number of ears per m2, that is, P-efficient line 154 formed many more ears under low-P conditions than P-inefficient line 153. Ear abortion rate was 53% in the P-inefficient line 153, while in line 154, it was only 30%. Low-P stress reduced leaf appearance, and delayed anthesis and the silking stage, but increased the anthesis-silking interval （ASI） to a similar extent in both lines. The maximum leaf area per plant at silking stage was higher in P-efficient line 154 than in P-inefficient line 153 under both P conditions. It is concluded that low-P stress causes intense intraspecific competition for limited P resources in the field condition which gives rise to plant-to- plant non-uniformity, resulting in a higher proportion of barren plants. As soon as an ear was formed in the plant, P in the plant is efficiently reutilized for kernel development.

Influence of Lanthanum on Phosphorus Uptake and Its Chemical Fractions in Rice Crop (Oryza Sativa)

The effects of lanthanum on rice growth, phosphorus uptake and phosphorus chemical fractions in rice were studied with split root solution culture. Results show that low concentration of La (0.05～1.5 mg·L -1 ) significantly increases rice yield while high La concentration (9～30 mg·L -1 ) markedly decreases rice yield. When La concentration is 0.05～0.75 mg·L -1 , La increases stem and root dry weight, but the difference is not statistically significant. La significantly increases EDTA P and inorganic P content in the stem and root. More than 80% of the increase of phosphors content in roots attributing to increase of EDTA P and inorganic P. Low La concentration (0.05～0.75 mg·L -1 ) increases nucleic P content in root, but high La concentration (30 mg·L -1 ) decreases nucleic P and ester P content in root. The residue P content increases in the root and stem. Also the relationship between the chemical fractions of phosphorus and its uptake by rice was discussed.

Effects of benthic algae on release of soluble reactive phosphorus from sediments: a radioisotope tracing study

To evaluate the effect of benthic algae on soluble reactive phosphorus（SRP） release from sediments in shallow lakes, experiments on SRP release with and without benthic algae in sediment cores and an experiment on SRP uptake by benthic algae were conducted using the radioisotope（32P） tracing method. The dissolved oxygen（DO） concentration in sediment cores was also investigated. The results show that benthic algae effectively reduce the release of SRP from sediments to overlying water. The uptake of SRP by benthic algae, which is the direct way in which benthic algae affect the SRP release from sediments, is low in filtered water and increases with the SRP concentration. However, in the experiment, the increased uptake rate lasted for a short time（in one hour）, and after that it returned to a low rate. Benthic algae make the DO concentration and the oxic layer thickness increased, which can indirectly reduce the SRP release from sediments. These findings indicate that benthic algae can reduce the SRP release from sediments in both direct and indirect ways. It seems that the indirect way also plays an important role in reducing the SRP release from sediments.

Long-term grazing exclusion influences arbuscular mycorrhizal fungi and their association with vegetation in typical steppe of Inner Mongolia,China

It is not certain that long-term grazing exclusion influences arbuscular mycorrhizal （AM） fungi and their association with steppe vegetation. In this study, soil and plant samples were collected from two sites of grazing exclusion since 1983 （E83） and 1996 （E96）, and one site of free-grazing （FG） in the typical steppe of Xilinguole League, Inner Mongolia, China, and assayed for soil basic physicochemical properties, AM fungal parameters, aboveground biomass and shoot phosphorus （P） uptake as well. The results showed that long-term grazing exclusion of E83 and E96 led to less drastic seasonal changes and significant increases in spore density, hyphal length density and root colonization intensity of AM fungi and even soil alkaline phosphatase activity, by up to 300, 168, 110 and 102％, respectively, compared with those of FG site. In addition, the total aboveground biomass and shoot P uptake of E83 and E96 were 75-992％ and 58-645％, respectively, higher than those of FG. Generally, the root colonization intensity, spore density, and hyphal length density of AM fungi were all positively correlated with the aboveground biomass and even shoot P uptake of plant. These results may imply that grazing exclusion play a critical role in increasing the growth of AM fungi, and subsequently, may increase plant P uptake and aboveground biomass production. Moreover, the spore density could sensitively reflect the impacts of long-term grazing exclusion on AM fungi since survival strategy of spores in soil.

Biomass Fraction of Phosphate-Accumulating Organisms Grown in Anoxic and Aerobic Stages under Optimum Nitrate Concentration

The effects of nitrate concentration on the capability of phosphorus uptake in the main anoxic stage were investigated.Meanwhile, the biomass fractions — heterotrophs, phosphateaccumulating organisms( PAOs),and nitrifying organisms in a pilot-scale enhanced biological phosphorus removal( EBPR) system— were both experimentally and theoretically evaluated( from the mass balance calculations of organic matter, nitrogen and phosphorus),under optimum nitrate concentration in the main anoxic stage,in which the influent chemical oxygen demand( COD)concentration was stabilized at( 290 ± 10) mg·L- 1and the influent total phosphorus( TP) concentration was stabilized at( 7. 0 ± 0. 5)mg · L- 1. In long term operations,the process exhibited high performance in removing organic matter, nitrogen, and phosphorus. Approximately 46. 41% of organic matter,57. 21% of nitrogen,and 48. 14% of phosphorus were removed from the influent in the form of carbon dioxide,nitrogen gas,and polyphosphate,respectively. XH( heterotrophs),XPAO( PAOs),and XAUT( autotrophs) were regarded as the major organisms responsible for biomass production. The yield fractions of XHgrowth in the first anoxic,the second anoxic,and the aerobic stages were 10. 24%,19. 11%,and 19. 71%,respectively; the yield fractions of XPAO growth in the second anoxic and the aerobic stages were 24. 34% and19. 86%,respectively; the yield fraction of XAUTgrowth in the aerobic stage was 6. 74%. These results showed that XHand XPAOformed the major community. Moreover,a higher amount of XPAOgrowth on stored poly-hydroxyalkanoates( PHAs) under the anoxic condition was seen in this EBPR system for municipal wastewater treatment.

Characteristics of Nutrients Removal under Viscous Sludge Bulking Treating Synthetic Wastewater

Viscous sludge bulking is a rare phenomenon in activated sludge process.The performances of nutrients removal were investigated with normal sludge and viscous bulking sludge.The results showed that when COD loading and C/N ratio were around 0.13 mg COD/(mg MLSS·d)and 7.67,the effect of viscous sludge bulking on the maximum specific oxidation rates of NH_(4)^(+)⁃N was very little,while the maximum specific oxidation rates of NO_(2)^(-)⁃N decreased from 24.69 mg/(g·h)to 1.20 mg/(g·h).Compared with normal sludge,viscous bulking sludge had bigger particle size and more extracellular polymeric substances(EPS).The mass transfer resistance in sludge flocs might be the main cause of the difference in NO-2⁃N oxidation rates.Therefore,this study demonstrates that viscous sludge bulking is beneficial to enhance simultaneous nitrification and denitrification(SND),and excessive EPS will exhibit storage function during phosphorus removal process.

The relationship between light intensity and nutrient uptake kinetics in six freshwater diatoms

In order to find effective measures to control diatom blooms, a better understanding of the physiological characteristics of nutrient uptake in diatoms is needed. A study of P and Si-uptake kinetics for diatom species from two light regimes was conducted at low（LL）,moderate（ML） and high light intensities（HL）（2, 25 and 80 μmol photons/（m2·sec））,respectively. The results showed that P uptake of diatoms was heavily influenced by historic light regimes. P affinity changed with growth and photosynthetic activity. The lowest half saturation constant for P uptake（Km（P）） was under HL for high-light adapted diatoms while the lowest half-saturation constant for low-light adapted diatoms was observed under LL. The Si half-saturation constant（Km（Si）） increased with increasing light intensities for pennate diatoms but decreased for centric diatoms. Diatom volumes were correlated with the maximum Si uptake rates（Vm（Si）） at HL and K m（Si）at ML and HL for six diatom species. Our results imply that when we assess the development of diatom blooms we should consider light intensity and cell volume in addition to ambient Si or P concentration. The relationship between light intensity and P-uptake suggests that we can find suitable methods to control diatom blooms on the basis of reducing phytoplankton activity of P-uptake and photosynthesis simultaneously.

Comparison of biochemical characteristics between PAO and DPAO sludges

A successful enhanced biological phosphorus removal （EBPR） was observed in both anaerobic- aerobic sequencing batch reactor （An-Ox SBR） to induce growth of phosphorus accumulating organism （PAO） and anaerobic-anoxic （An-Ax） SBR to induce growth of denitrifying PAO （DPAO）. Although the EBPR performance of An-Ox SBR was higher by 11.3% than that of An-Ax SBR, specific phosphorus release rates in the An-Ax SBR （22.8 ± 3.5 mg P/（g VSS.hr）） and the An-Ox SBR （22.4 ± 4.8 mg P/（g VSS.hr）） were similar. Specific phosphorus uptake rates under anoxic and aerobic conditions were 26.3 ± 4.8 mg P/（g VSS.hr） （An-Ax SBR） and 25.6 ± 2.8 mg P/（g VSS.hr） （An-Ox SBR）, respectively, which were also similar. In addition, an analysis of relationship of poly-β-hydroxyalkanoates （PHA） synthesized under anaerobic conditions with phosphorous release （Preleased/PHAsynthesized） and of PHA utilized under anoxic and aerobic conditions with phosphorous uptake （Puptaked/PHAutilized） verified that biological activities of EBPR per unit biomass between DPAO and PAO were similar. An analysis of the specific denitrification rate of DPAO showed that NO3-N can be denitrified at a rate that does not substantially differ from that of an ordinary denitrifier without additional consumption of organic carbon when the PHA stored inside the cell under anaerobic conditions is sufficiently secured.