The Uptake of Phosphate by Plants from Flowing Nutrient Solution: IV. EFFECT OF PHOSPHATE CONCENTRATION ON THE GROWTH OF TRIFOLIUM REPENS L. SUPPLIED WITH NITRATE, OR DEPENDENT UPON SYMBIOTICALLY FIXED NITROGEN

Breeze, V. G. and Hopper, M. J. 1987. The uptake of phosphateby plants from flowing nutrient solution. IV. Effect of phosphateconcentration on the growth of Trifolium repens L. suppliedwith nitrate, or dependent upon symbiotically fixed nitrogen.—J.exp. Bot. 38: 618–630. Nodulated white clover plants were subjected to a range of phosphateconcentrations in flowing solution culture (0.32 to 8.0 mmolm^–3 P) at 41 d from sowing, either supplied with nitrateor dependent on symbiotically-fixed nitrogen. No effect of phosphateconcentration in solution on dry matter production, relativegrowth rate, root/shoot ratio, or water soluble carbohydrateconcentration of the plant tissue was observed after 24 d fromthe start of the experiment, although the plants supplied withnitrate yielded more than the others. Phosphate uptake throughoutthe experimental period was related to the solution concentration,but the source of nitrogen did not affect the phosphorus concentrationsof the shoots. However, the roots of the plants dependent onsymbiotically-fixed nitrogen had higher concentrations of phosphorusthan those supplied with nitrate, but this did not appear tobe due to an increased phosphorus requirement for nitrogen fixation,because the amount fixed was unaffected by the phosphate concentrationin solution. The cation-anion balance showed that plants dependenton nitrogen fixation had no larger requirement for calcium thanplants supplied with nitrate, but a requirement for hydroxylions equivalent to over 130 kg lime per tonne of dry shoot.It is suggested that the enhanced phosphate uptake by plantsdependent on nitrogen fixation is due to this need for a cation-chargebalancing anion. Key words: Phosphate uptake, nitrogen fixation, Trifolium repens L., repens L., cation-anion balance, flowing solution culture     

Inter-plant variation in temperate crops of maize

Maize grown at northern latitudes suffers from variation in the yield from individual plants, as well as uneven uniformity in the stage of maturity. The contributions of genotype, environment and some seed characteristics to phenotypic variation of weight and stage of development were studied in maize from experiments that included treatments of sowing date, density and planting arrangement, and which used hybrids with differing uniformity of genotype. It was not possible to divide the variation simply into genotypic or environmental components, and the performance of varieties was inconsistent. Single cross material was only slightly more uniform than a double cross variety Using large sized seed led to 1–2 days earlier silking but to little effect on final yields. The size of plants was not influenced by the size of neighbouring plants along the row and spacing in a square arrangement only had a small effect on improving uniformity of plants. More variation occurred at a high density planting. Inter-plant variation appeared to occur either in dry weight or in the stages of development, but also there was an association between the two, e.g. the largest plants tended to be the most advanced. There was a tendency for the first emerged plants to silk first and to produce the highest grain yield (although this was not consistent in the double cross INRA 200). The first plants to silk in a crop were up to 7 days earlier than the average at harvest and yielded double the grain weight. As reliability of harvest limits the acceptance of grain maize in north-west Europe, it is suggested that one method that could improve the uniformity in stage of maturing, without seriously reducing final grain yield, is to use a somewhat lower planting density (6 plants/m² for grain) than has hitherto been recommended.     

The Uptake of Phosphate by Plants from Flowing Nutrient Solution: II. GROWTH OF LOLIUMPERENNEL. AT CONSTANT PHOSPHATE CONCENTRATIONS

The effect of phosphate concentration in flowing solution cultureat a range between 0.04 and 32 mmol m^–3 P on the growthof perennial ryegrass was studied in two experiments, each lastingabout 45 d after sowing. Phosphorus contents of seedlings wereaffected by the concentration in solution within about 5 d fromgermination, and dry weight differences were first observedat about 6 d after this. The rate of uptake of phosphate byseedlings was affected by the concentration in solution beforethe root fresh weight or root/emdash shoot ratio had changed.Young plants (less than 4 weeks old) were more sensitive tophosphate concentration in solution than older ones. In conditionsof high rate of growth, older plants required a solution concentrationbetween 0.1 and 0.4 mmol m^–3 P to achieve maximum potentialgrowth rate, whereas for plants of similar age but less dryweight, 0.04 mmol m^–3 P was adequate. Towards the endof the experimental period, plants growing at a nominal solutionconcentration of 0.04 mmol m^–3 P were able to obtain phosphatefrom a solution of about 0.01 mmol m^–3P. Phosphate toxicity was not observed, nor were there visual symptoms(other than reduced growth) of phosphate deficiency in plantswhose growth was limited by phosphate concentration in solution. Key words: Lolium perenne, Phosphate uptake     

The Uptake of Phosphate by Plants from Flowing Nutrient Solution: III. EFFECT OF CHANGED PHOSPHATE CONCENTRATIONS ON THE GROWTH AND DISTRIBUTION OF PHOSPHATE WITHIN PLANTS OF LOLIUM PERENNE L.

Perennial ryegrass (Lolium perenne L.) was grown from seed for29 d in flowing solution culture containing 0.1, 0.4 or 6.4mmol m^–3 P before the concentrations were changed (0.1and 0.4 raised to 6.4; 6.4 lowered to 0.4; controls unchanged)for an experimental period of two weeks to test the hypothesisthat after the seedling stage, the maximum rate of plant growthcould be sustained by a lower concentration of phosphate atthe root/solution interface than was necessary for the maximumrate of seedling growth. During the 29 d seedling period growthwas greatest on 6.4 mmol m^–3 P achieving 179 mg per plantdry weight compared with 122 and 26 mg on 0.4 and 0.1 mmol m^–3P respectively. During the experimental period growth on thetreatment 6.4 lowered to 0.4 mmol m^–3 P continued at thesame rate as the 6.4 control achieving 981 and 983 mg per plantdry weight respectively. Similarly growth of the treatment 0.4raised to 6.4 mol m^–3 P was unaffected by the change inconcentration and was comparable with the 0.4 control. Bothresults support the hypothesis for seedlings exceeding about100 mg per plant dry weight. In contrast the small plants ofthe treatment 0.1 raised to 6.4 mmol m^–3 P behaved similarlyto seedlings and responded rapidly to the increased concentrationof phosphate in solution, achieving high rates of phosphateuptake and increasing the growth of shoot more than the growthof root so that the ratio of root: shoot declined from 065 to0.34, a value similar to that for the seedlings grown on 6.4mmol m^–3 P. Key words: Lolium perenne L, Phosphate concentration, Seedling growth     

The Uptake of Phosphate by Plants from Flowing Nutrient Solution: I. CONTROL OF PHOSPHATE CONCENTRATION IN SOLUTION

An existing system of flowing solution culture in which pH andthe concentration of several nutrient ions in solution are automaticallymonitored and controlled has been extended to include the monitoringand control of orthophosphate in the range 0.0013 to 0.3 mgP l^–1 (4.2 ? 10^–8–10^–5 M). Continuous-flowcolorimetry is used for the analysis of phosphate and a computeris employed to hold concentrations constant by the operationof nutrient pumps. A brief account is given of the performanceof the system with perennial ryegrass (Lolium perenne L.) asthe experimental plant.     

Uptake of the herbicide [14C] 2,4-D iso-octyl in the vapour phase by tomato and lettuce plants and some effects on growth and phytotoxicity

Tomato and lettuce plants were exposed to vapour of the herbicide [¹⁴C-phenyl] 2,4-D iso-octyl at concentrations in the range 0–450 pg litre^-1 for periods of 6, 24 and 72 h in separate experiments using a flowing-air system. The rate of uptake, as indicated by plant content of radiolabel, was both linear with respect to the vapour concentration and independent of the duration of exposure. The uptake rate of tomato was greater than that of lettuce at any given vapour concentration. Uptake by the apical leaves of lettuce was higher than by the older leaves expressed on an area basis; tomato showed no effect of leaf position. Visible symptoms of phytotoxicity were shown by both species 40 days after exposure to the highest doses. Advantages of using the low-volatile ester (iso-octyl) of 2,4-D to reduce vapour drift damage are discussed in terms of plant uptake.     

Some Effects of Temperature and Substrate Content upon Respiration and the Carbon Balance of Field Beans (Vicia faba L.)

The effects of substrate content and temperature upon the productionof carbon dioxide in the dark were investigated in Vicia fabaand Sorghum vulgare, using the time courses for carbon dioxiderelease. No endogenous rhythms were found. With V. faba at highsubstrate contents, a steady rate of respiration was measuredat low temperatures, suggesting that the rate of respirationis limited by a third factor such as enzyme activity. This steadyrate eventually decreased rapidly. There was a first order rateof decrease with time at higher temperatures. Low substratecontents gave a complex decay. The rate of decrease of the rateof respiration was affected by the initial state of the plantsover the same range of rates. Reasons for this are discussed.The temperature sensitivity of respiration was investigated.The respiration of plants with high substrate contents had alower temperature sensitivity than those with low substratecontents. This was further investigated by measuring the stoichiometryof carbon dioxide production in the dark from total solublecarbohydrate (as hexose equivalent). It is likely that incompletehexose respiration, which occurs at high substrate contents,is less temperature sensitive than complete hexose respirationor the respiration of some other substrate. Vicia faba, Sorghum oulgare, carbon dioxide, respiration, temperature, substrate content     

The use of an antimicrobial removal device in the sterility testing of a non-aqueous antibiotic preparation

An antimicrobial removal device was used successfully in a sterility test on a viscous, non-aqueous formulation containing streptomycin and benzylpenicillin. Conventional techniques such as dilution, enzymic inactivation and membrane filtration having failed, it is suggested that use of the devices be considered as an alternative to established procedures for sterility testing of antimicrobial preparations.