Nodulation and growth ofLablab purpureus (Dolichos lablab) in relation to rhizobium strain,liming and phosphorus

Summary Greenhouse experiments were done with two purposes: (1) to identify strains of rhizobia effective and acid-tolerant in symbiosis withLablab purpureus, and (2) to determine whether soil acidity or the symbiotic condition increased the phosphate requirement for growth.Five rhizobial strains were tested in one neutral soil, two acid soils, and the two acid soils limed to pH 6.6. In the neutral and limed soils, three of the strains were effective (CB1024, CB756, TAL169), but only two strains (CB756, TAL169) remained effective in acid soil.Strain CB756 and plus-N treatments were further compared in a factorial trial involving combinations of five levels of P with lime, no lime and CaCl₂ treatments, applied to an acid soil. Some of the treatments were also applied to plants inoculated with CB1024. Between the N-fertilized and CB756 treatments there was no clear difference in growth response to applied P, and the critical internal concentration of P for 95% of maximal growth was the same (0.22% shoot dry weight). Increasing P beyond levels needed for maximal growth increased nodulation and N concentration in plants inoculated with CB756. It lowered N concentration in N-fertilized plants. There was evidence suggesting that the P requirement of symbiotic plants increased if the soil was acid, or if CB756 were replaced by CB1024 as microsymbiont; but the critical statistical interactions were not significant.     

有毒赤潮甲藻塔玛亚历山大藻(香港株Ⅱ)的生长特性研究

在室内条件下研究温度、N和P、维生素、抗生素对有毒赤潮甲藻塔玛亚历山大藻(香港株Ⅱ生长的影响。结果表明,塔玛亚历山大藻的适宜生长温度和N、P浓度分别为21-25℃,882-1765μmol／L和18-72μmol／L。复合维生素B的加入有利于塔玛亚历山大藻的生长,而50Uml^-1以上的抗生素则对其有明显的抑制作用。     

氮磷限制对锥状斯氏藻孢囊形成的作用

在实验室研究了锥状斯氏藻(Scrippsiellatrochoidea)在N、P单因子营养限制(N:500μg.L-1,P:74～0.74μg.L-1和P:74μg.L-1,N:500～5μg.L-1)条件下的生长和孢囊形成。结果显示N、P限制不利于锥状斯氏藻的快速生长,其中低P对细胞生长的限制作用更显著。其孢囊形成率在15～99%之间,中度N限制能促进孢囊的形成,形成率几乎可达100%。孢囊一般在对数生长期结束、细胞数量达到最大值时开始形成。但由于接种后营养盐浓度的急剧降低,营养极度限制组孢囊可在接种后第1d就开始形成。结果显示稳定生长期孢囊的大量形成大大降低了锥状斯氏藻营养细胞数量,能在一定程度上促进其赤潮的消亡。     

Soluble Reactive Phosphorus Transport and Retention in Tropical, Rainforest Streams Draining a Volcanic and Geothermally Active Landscape in Costa Rica. : Long-Term Concentration Patterns, Pore Water Environment and Response to ENSO Events

Soluble reactive phosphorus (SRP) transport/retention was determined at four sites in three rainforest streams draining La Selva Biological Station, Costa Rica. La Selva is located at the base of the last remaining intact rainforest transect from 30 m above sea level to 3000 m along the entire Caribbean slope of Central America. Steam SRP levels can be naturally high there due to regional, geothermal groundwater discharged at ambient temperature. Monitoring since 1988 has revealed distinctive long-term differences in background SRP and total P (TP) for three streams in close proximity, and identified the impact of ENSO (El Nino Southern Oscillation) events on SRP-enriched reaches. Mean interannual SRP concentrations (± standard deviation) were 89 ± 53μg/l in the Salto (1988–1996), 21 ± 39μg/l in the Pantano (1988–1998), and 26 ± 35μg/l in the Sabalo (1988–1996). After January, 1997 the separate upland-lowland contributions to discharge and SRP load were determined monthly in the Salto. SRP in Upper Salto was low (19 ± 8μg/l, 1997–2002) until enriched at␣the upland-lowland transition by regional groundwater. Mean SRP concentration in Lower␣Salto (108 ± 104μg/l) was typically highest February–April, the driest months, and lowest July–September, the wettest. SRP concentration was positively correlated to the inverse of discharge in Lower Salto when ENSO data were omitted (1992 and 1998–1999), but not in the Upper Salto, Pantano, or Sabalo. TP was positively correlated to the inverse of discharge in all three streams when ENSO data were omitted. High SRP springs and seeps along the Lower Salto contributed 36% of discharge but 85% of SRP export 1997–2001. Annual SRP flux from the total Salto watershed (1997–2001) averaged 2.9 kg/ha year, but only 0.6 kg/ha year from the Upper Salto. A dye tracer injection showed that pore water environments were distinctly different between Upper and Lower Salto. Upper Salto had high surface water–pore water exchange, high dissolved oxygen, low SRP, and low conductivity similar to surface water, and Lower Salto had low surface water–pore water exchange, low dissolved oxygen, high SRP, and high conductivity reflecting geothermal groundwater influence. SRP export from the Salto was controlled by regional groundwater transfer, which in similar volcanic settings could be a significant P source. However, ENSO events modified the SRP concentration in the Salto suggesting that long-term monitoring is required to understand underlying SRP dynamics and P flux to downstream communities.     

The effects of phosphate supply on growth of plants from the Brasilian Cerrado: experiments with seedlings of the annual weed,Bidens gardneri Baker (Compositeae) and the tree,Qualea grandiflora (Mart.) (Vochysiaceae)

Summary Plants of the cerrado tree species Qualea grandiflora and the annual herb Bidens gardneri were grown from seed in controlled environment rooms at 30/20° C and 12 hour photoperiod. Seedlings were grown in pots or small tubes containing sand and provided with various amounts of mineral solutions based on the formulation of Hoagland and Arnon but with the phosphate content modified in some cases. In a long-term experiment lasting 213 days, plants supplied with full strength Hoagland's solution all died but plants of Qualea given 1/10 strength solution survived, although they grew very slowly. Low relative growth rates (0.008–0.036 d^–1) were also a feature of other experiments with Qualea and calculated rates of net assimilation rate gave values of 3–7 mg CO₂ dm^–2 h^–1. Expansion of the photosynthetic surface proceeded slowly and the cotyledons were the main site of photosynthesis for more than 40 days. The low rates of growth occurred despite significant uptake of phosphorus by young plants and in shortterm experiments growth was independent of the amount of phosphate supplied and accumulated. In contrast, the values of R found for plants of Bidens reached 0.24 d^–1. Growth of young plants was dependent on the external supply of phosphorus, being reduced when this was low and also when it was very high. Growth of the photosynthetic surface was also much more rapid than for Qualea and also varied with supply of phosphorus. The results are discussed in the context of the occurrence of these species in the Cerrado.     

Development and physiology of follicular atresia during ovarian growth in the house fly, Musca domestica

Atretic follicles regularly occur in the ovary of the house fly, Musca domestica. The frequency of ovarian follicular atresia and the proportion of atretic follicles per ovary are related to the stage of oögenesis and to the age of the females. Only vitellogenic follicles may become atretic. The atresia may occur at any stage of vitellogenesis, though most follicles become atretic in mid-vitellogenesis. Atretic follicles are completely resorbed within 24–36 hr. The follicle cells may play a synthesizing role during growth and disintegrating one during follicle resorption. The induction of glycogen synthesis by the cessation of RNA and protein synthesis and by vitellogenesis in normal follicles is discussed. The same processes occur prematurely in the atretic follicle which can be thus distinguished by a high content of glycogen.     

Phosphate sorption isotherms for evaluating phosphorus requirement of wetland rice soils

Summary Phosphate sorption isotherms were developed for five Philippine wetland rice soils using the conventional technique and a modified one. In the conventional method, P requirements of soils varied between 280 and 810 g P/g soil. In the modified method, they varied from 160 to 540 g P/g soil at 0.2 ppm P in solution. Soils with high P-sorption capacities had vermiculite and halloysite as the dominant clay minerals. Soil reduction by flooding decreased P-sorption by 28–70 percent at 0.2 ppm P in solution. The decrease in P-sorption due to soil reduction was greatest in a crystalline soil with vermiculite and halloysite as the dominant clay minerals and least in a soil with dominant X-ray amorphous silicates in the clay fraction.Desorption of freshly adsorbed P under reduction was greater in HCO ₃ ^– solution than in CaCl₂ and it increased with level of applied P. Desorption patterns of freshly adsorbed P were similar to adsorption patterns but values of P in solution were lower at desorption. Soils varied with respect to desorption of freshly sorbed P. Desorption studies indicate that soils vary in intensity factor with respect to P and thus influence P availability to plants. Use of P-sorption and P-desorption data obtained under reduced soil condition was proposed for detecting P needs of submerged rice soils.Results of a pot study with IR36 at different levels of solution P (reduced) in one soil indicated a high degree of correlation between adjusted P levels and the measured growth parameters. About 0.12 ppm P in the soil solution or 0.46 ppm P desorbed in HCO ₃ ^– solution (equivalent to 100 mg P/kg soil) was adequate for near-maximum plant height, tiller production, total dry matter yield, plant P content, and total P uptake.     

Phosphorus nutrition of jarrah (Eucalyptus marginata) seedlings

Summary Effects of calcium phosphate supply on plant dry matter and phosphorus concentrations of parts of jarrah (Eucalyptus marginata) seedlings grown in a lateritic topsoil from the jarrah forest were examined in two glasshouse trials. Phosphorus deficiency depressed root and shoot dry weights and severely deficient leaves were smal and purple with prominent red major veins. Phosphorus deficiency severely reduced stem phosphorus levels (0.5% to 0.02%, experiment 1). Phosphorus concentrations were higher in bark than wood and the amount of phosphorus in the bark was sensitive to stem age and phosphate supply. Phosphorus adequate plants had bark phosphorus concentrations in the range 0.2–0.9% compared to <0.1% in deficient plants (experiment 2). Jarrah leaves accumulated dry matter up to 80 days after expansion and some leaves exported phosphorus during this period. Bark analysis may therefore be preferable to leaf analysis for detecting phosphorus deficiency in this species.     

Leaf nutrient concentration as an indicator of Populus and Tamarix response to flooding

Plants growing in infertile environments are able to produce more biomass per unit of nutrient taken up than plants of fertile habitats, and also to minimize nutrients loss by resorbing them from senescing leaves. The leaf nutrient concentration variability of two co-existing riparian tree genera (Populus and Tamarix) along a flood inundation gradient was examined to infer nutrient limitation and to compare nutrient use strategies in the two genera. To that end, seasonal and spatial variability in leaf nitrogen (N) and phosphorus (P) concentration (i.e., % dry mass of N and P) were analyzed in 720 samples of leaves (2 tree genera × 3 seasons × 12 sites × 10 tree replicates). Both Populus and Tamarix showed strong seasonal variability in leaf N and P concentrations, with values decreasing throughout the growing season. However, while N:P atomic ratio remained seasonally constant in Populus (N:P = 33), Tamarix shifted from N:P = 29 in spring to N:P = 36 and 37 in summer and fall. %N, %P and N:P atomic ratios were also spatially variable, but leaf litter N and P concentration (i.e., nutrient resorption proficiency) and leaf litter N:P generally followed the local flood inundation gradient as shown by linear mixed effects models. In particular, nutrient resorption was usually less proficient (higher terminal nutrient concentrations) at higher flood durations (in gravel bars and natural levees), whereas N:P increased in the drier sites (floodplain terrace). At floodplain level, a P-limitation that is higher than N-limitation seems to characterize the plant nutrient circulation in the riparian ecosystem studied. Tamarix was slightly more proficient in P resorption than Populus. The study shows that leaf nutrient concentration (e.g., N and P) derived from nutrient availability is partly controlled by the flood inundation regime and can be used as an indicator of nutrient limitation in forested floodplains. Subtle differences between tree genera provide an additional, novel explanation for the recent expansion of Tamarix in many arid and semi-arid rivers with altered hydrogeomorphic regimes.     

Enhanced denitrification in a bioaugmented horizontal subsurface flow filter

The effect of adding low concentrations of a sediment/microbial community suspension to speed up the development of the denitrification capacity in the restored HSSF of a hybrid CW was studied during a one-year period after the filling of the horizontal filter with new light weight aggregates (LWA). Two HSSF filters with the same LWA substrate but different wastewater flow regimes were used as donor systems for the bioaugmentation. NO₃-N concentrations in the outflows of all variants of studied MCs were significantly influenced by the time factor (p < 0.001, repeated measures ANOVA). Post hoc comparison indicated that MCs bioaugmented with the sediment suspension from a similar HSSF had significantly lower NO₃-N concentrations than the control MCs (p < 0.05, Fisher LSD test), whereas MCs bioaugmented with the sediment suspension from a less similar HSSF did not show significant differences compared to the control MCs. This finding emphasizes the importance of the similarity of flow regime and water parameters in choosing a donor system for bioaugmentation. High variability of the effect of bioaugmentation shows that its importance for full scale operation may be overshadowed by the effect of other factors determining denitrification intensity.