A. E. S. Macklon

Uptake and transport of phosphorus by Agrostis capillaris seedlings from rapidly hydrolysed organic sources extracted from32 P-labelled bacterial cultures

Cultures of the soil bacterium Serratia liquifaciens grimesii were grown with32 P labelled phosphate, to produce a uniformly32 P labelled source of microbial P. Extracts of the bacteria were prepared by sonication, dialysis and filtration to provide a clear sterile solution which was characterised in terms of dissolved organic and condensed P (DOP and DCP) and molecular weight range. The extract was used as a source of P to Agrostis capillaris L. seedlings in nutrient solution from which orthophosphate was omitted. In a time course experiment, root surface phosphatase activity increased as soon as extract was added to the root medium, DOP was rapidly hydrolysed and orthophosphate concentration increased rapidly. These processes were complete within about 8 h, after which phosphatase activity fell to its original level, and the plants absorbed molybdate reactive P from the nutrient solution so that it reached its original concentration over 48 h. DCP concentrations did not change significantly throughout the experiment. This work clearly demonstrated that DOP but not DCP, as a component of a bacterial extract produced by a relatively straightforward method, was quickly hydrolysed and the P made available for plant uptake.

Inorganic and organic P in soil solutions from three upland soils

The effects of defoliation and NPK fertilizer addition on the amounts of inorganic orthophosphate (Pi), organically combined phosphorus (Po), total phosphorus (Pt) and the residual fraction Pr=Pt−(Po+ Pi) in soil solution from three P-deficient Cambisols with grass/clover swards were determined. The defoliation treatments, carried out in the first year, were regular cutting every 2–4 weeks to 2 cm, and cutting at the end of the growing season. The fertilizer treatments, applied in the second year, were 25 g m-2 of 25:5:5 and 20:10:10 NPK fertilizer. In both years, soil solution was also taken from bare soil plots. Defoliation influenced the concentration of Pi, Po, Pr and Pt in soil solutions, which mostly increased in the order no cut>cut 2 cm>bare soil treatment. Fertilizer additions increased dry matter production, and the amount of P in the crop, but had relatively little influence on soil solution concentrations of Pi, Po, Pr and Pt compared with the previous year. There were no significant differences in either dry matter production, P uptake or the Pi, Po, Pr and Pt concentrations of soil solution between the plots receiving 25:5:5 or 20:10:10 fertilizer treatments.Phosphorus in soil solutions from the most acid of the three cropped soils was significantly correlated with Fe during August and October. The linear correlation coefficients (r) between Fe and Pi, Po or Pt were between 0.73 and 0.94.

Soil P resources, plant growth and rooting characteristics in nutrient poor upland grasslands

A field study was undertaken to establish the demand for P by mixed herbage, manipulated by cutting regimes, and the extent to which orthophosphate alone in soil solution could meet this demand from three cambisols derived from different parent materials. Differences in soil types were sufficient to produce significantly different rooting patterns at each site. Yields for 7-and 10-cm treatments generally exceeded those for swards cut to 2-and 4-cm. The highest yields were from plots cut once at the end of the season, or when herbage was cut in June and October only. Yields fell in the second season by an average of 30%. Two cuts in the season resulted in almost twice the P uptake compared with other treatments, leading to the view that a “silage” cut stimulated root growth. Rooting was deepest in Tarves Association soil (Dystric cambisol), densest in Insch Association soil (Eutric cambisol) and intermediate in Foudland Association soil (Dystric cambisol) but herbage yield at each site was similar. Whole season mean P and N content in roots ranged from 1.0 to 3.4 and from 8.1 to 27.9 mg g−1 dry weight, respectively. The lowest values were in once cut herbage and were half those in herbage cut in June and October only. Data for the total P resources of the soils, extractable P, and shoot and root P at each site are presented together with data for P in soil solution (principally organic) from an associated soil solution study. There was a disparity between daily uptake and orthophosphate in soil solution. These findings suggested that it was probable that soluble organic forms of P are important for P nutrition in these nutrient poor soils, and could account for the excess of observed P uptake (from soils low in P) over that predicted by mechanistic mathematical models.

Uptake of ammonium and nitrate ions from acid mist applied to Sitka spruce [Picea sitchensis (Bong.) Carr.] grafts over the course of one growing season

AbstractCloned Sitka spruce grafts were subjected to NH4NO3 mist (1 mm day-1 equivalent) acidified with H2SO4, for 4 days a week, from April until November. Three N treatments at pH 5.0 used 0.01 mol m-315NH415NH3, 1.6 mol m-315NH4 NO3 or 1.6 mol m-3 NH415NO3. At pH 2.5, the treatments were15NH415NO3,15NH4NO3 and NH415NO3 all at 1.6 mol m-3. At the end of the growing season,15N was found in every part of the trees, even when NH4NO3 was supplied at 0.01 mol m-3. It was shown that both

Active and Passive Transport of the Major Nutrient Ions across the Root of Ricinus communis

NH_{4^ + }

Phosphate uptake and transport in Agrostis capillaris L Effects of non-toxic levels of aluminium and the significance of P and Al speciation

and

Modifying Effects of a Non-Toxic Level of Aluminium on Phosphate Fluxes and Compartmentation in Root Cortex Cells of Intact Ryegrass Seedlings

NO_{3^ - }