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Notes: Abstract: The kinetic properties of type A and type B monoamine oxidase (MAO) were examined in guinea pig striatum, rat striatum, and autopsied human caudate nucleus using 3,4-dihydroxyphenylethylamine (dopamine, DA) as the substrate. MAO isozyme ratio in guinea pig striatum (28% type A/72% type B) was similar to that in human caudate nucleus (25% type A/75% type B) but different from that in rat striatum (76% type A/24% type B). Additional similarities between guinea pig striatum and human caudate nucleus were demonstrated for the affinity constants (Km) of each MAO isozyme toward DA. Endogenous concentrations of DA, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid were also measured in guinea pig and rat striatum following selective type A (clorgyline-treated) and type B (deprenyl-treated) MAO inhibition. In guinea pig, DA metabolism was equally but only partially affected by clorgyline or deprenyl alone. Combined treatment with clorgyline and deprenyl was required for maximal alterations in DA metabolism. By contrast, DA metabolism in rat striatum was extensively altered by clorgyline but unaffected by deprenyl alone. Finally, the deamination of DA in synaptosomes from guinea pig striatum was examined following selective MAO isozyme inhibition. Neither clorgyline nor deprenyl alone reduced synaptosomal DA deamination. However, clorgyline and deprenyl together reduced DA deamination by 94%. These results suggest that the isozyme localization and/or isozyme affinity for DA, rather than the absolute isozyme content, determines the relative importance of type A and type B MAO in synaptic DA deamination. Moreover, based on the enzyme kinetic properties of each MAO isozyme, guinea pig striatum may serve as a suitable model of human DA deamination.

Notes: Abstract. The soil of a restored opencast site in Northumberland is described and compared with the surrounding undisturbed soil. The most serious change in the soil was increased bulk density at the surface of the subsoil (0.3 m depth). Only a small overall reduction in pore space occurred, at the expense of continuous macropores. More of the pore space in the restored soil occurred as fine fissures as opposed to biotic channels, and the restored soil was weaker because of subsoiling and a loss of stability in microstructures. These changes are discussed in relation to root exploration, water movement and land management.

Notes: Measurements of rates of growth and senescence of leaf lamina per tiller and of changes in tiller population densities were made in three experiments designed to investigate the influence of sward slate on leaf turnover and net production under continuous stocking.In each experiment initially uniform swards were fenced to provide four plots on which animal numbers were adjusted twice weekly to give a series of swards maintained as nearly as possible in a steady state with respect to sward surface height (range 1.1–6.4 cm) and herbage mass (range 440–2690 kg OM ha−1). Two experiments were carried out in July–September on vegetative swards and one in May–June on a reproductive sward. Measurements were begun 3–7 weeks after treatments were started and were repeated weekly during 3–4 week measurement periods.In all three experiments the rate of lamina growth per tiller increased linearly with an increase in sward surface height and herbage mass. In the two experiments conducted in July–August this relationship was partially offset by a linear increase in the rate of senescence per tiller but net production per tiller also increased linearly in relation to sward height and mass. In the experiment conducted in May–June the rates of growth and senescence per tiller increased in parallel so that net production per tiller showed no relationship with sward condition.Tiller population densities in the July–August experiments were highest in swards maintained between 2 and 3 cm surface height and declined in swards maintained above and below this height. In the experiment in May–June tiller numbers were similar in all treatments prior to the summer solstice but diverged in a manner similar to the other experiments later in the year.The rate of lamina growth per unit area increased in a manner consistent with an asymptotic relationship and the rate of senescence increased linearly with increasing sward height and mass in all three experiments. Net production per unit area was reduced on swards below about 2.5 cm in height but was insensitive to variation in sward surface height between 2.5 and 6.0 cm (approximately 1000–2500 kg OM ha−1 herbage mass).The effectiveness of adjustments in tiller numbers and production per tiller and of changes in the balance between growth and senescence as mechanisms of sward homeostatis, together with their implications in the scope for manipulating herbage production by grazing management are discussed briefly.

Notes: The possibility of increasing the herbage utilized over a grazing season was investigated in a study comparing continuously stocked steady-state swards maintained at optimum height (3.5 cm) with intermittently grazed swards. The intermittent systems were designed (a) to allow periodic increase in leaf area and hence growth rate, (b)to ensure that the accumulated herbage was eaten before it senesced, and (c) lo retain high tiller density by alternating periods of herbage accumulation with periods of continuous stocking.Two treatments (no animals or animal numbers reduced to half those on the 3.5 cm steady-state treatment) were used during the 17-18-d periods of herbage accumulation. Grazing down was completed in 3–4 d, after which two treatments (14 d or 28 d) were used for the intervening periods of continuous stocking when sward height was maintained at 3.5 cm.Herbage production was estimated using the tissue turnover technique, with tiller population densities and rates of growth, senescence and net production per tiller measured at frequent intervals.Intermittent grazing treatments where animals were removed during herbage accumulation resulted in changes in tiller size and number, and in growth rates, but not senescence rates, per tiller such that short-term deviations in the net rate of herbage production occurred compared with the continuously stocked control. The periods of advantage during phases of herbage accumulation were counterbalanced by those of disadvantage during the subsequent steady-state phases. Where animal numbers were reduced during herbage accumulation, sward conditions differed little from those of the continuously stocked control, implying that intake per individual animal was increased.It was concluded that intermittent grazing systems offered no advantage over simpler continuous stocking systems, provided that a flexible approach to conservation was incorporated to allow control of sward conditions on the grazed area.

Notes: Measurements of sward surface height and of the ratio of light at 660 and 730 nm reflected from a pasture canopy were correlated with measurements of leaf area index (LAI) and herbage mass of two ryegrass dominant swards. Both pastures were continuously stocked by sheep to maintain a range of sward heights from 2 to 6 cm corresponding approximately to LAI 2 to 5.Sward height appeared to be linearly related to both LAI and herbage mass, whereas 660/730 reflectance displayed a non-linear relationship with both parameters. The accuracy of prediction by the two methods over the range LAI 1 to 3 or herbage mass 700 to 1800 kg DM ha-1 was very similar. However, reflectance measurements could not be used above about LAI 3–4 and to this extent were less useful. Nevertheless, reflectance measurements have a potential advantage in their ability to sample large areas of pasture very quickly.

Notes: The relationship between the rate of canopy gross photosynthesis and LAI was investigated for ryegrass swards released from grazing after a period of continuous stocking to maintain the pasture at LAI 2–3. The regrowing swards were allowed to increase to about LAI 5 over a period of about 2 weeks while the rate of photosynthesis was measured and compared with that for continuously stocked swards maintained at LAI values between 2 and 6. Gross photosynthesis was found to increase more rapidly than LAI on the regrowing swards than on the steady-state control pastures. However, this response appeared to be influenced by seasonal factors. The potential increase in net COi uptake was estimated to range from 0 to 22%. The response was attributed to an increasing proportion of young photosynthetically-efficient leaves near the top of the canopy, modified by seasonal changes in the rate of tillering. The agronomic implications of the results are iscussed.

Notes: An experiment was carried out in which simulated swards of ryegrass (cv. S23) were grown in boxes. In the first instance the swards were cut at weekly intervals to maintain five levels of leaf area index (LAI) from LAI 1 to 4–5 in simulation of continuous grazing. Measurements were made of growth, senescence and net growth rate and of net canopy photosynthesis at constant irradiance. The results showed that the swards adapted to the defoliation regimes mainly by changes in tiller population density and pseudostem length. When the swards had equilibrated to the cutting regime growth rate increased with LAI but, since tiller density and the partitioning of growth between herbage harvested and that lost by sensecence also changed with LAI, net growth rate was constant over the LAI range 2–4·5. Maximum weight of herbage harvested was obtained between LAI 2 and 3.After 10 weeks of weekly cutting all the swards were cut back to LAI 1 and allowed to regrow. Growth rate showed almost no response to the previous culling treatments. The relationship of net canopy photosynthesis to LAI was linear for the frequently defoliated swards and curvilinear for regrowing swards. The reasons for this difference were examined.

Notes: The relationship between net canopy photosynthesis (Pnc) measured at 400 J m−2 s-1 and leaf area index (LAI) was determined on ryegrass-dominant swards over a range of her bage masses in five grazing experiments. In three experiments the swards were continuously stocked either by sheep or by cattle to maintain a number of herbage heights and hence LAI values. In two experiments the swards were intermittently grazed with 21 -d regrowth intervals. On the continuously stocked swards measurements were made over nine periods each of 7 to 21 d in length. On the intermittently grazed swards measurements were made over six periods while the herbage was being grazed down from a high to a low LAI and over three periods during the regrowth phase.On all the swards where measurements were made while grazing was in progress, the relation of Pnc to LAI was linear. The photosynthetic rate was greater on the continuously grazed than on the intermittently grazed swards up to LAI 35 and in two experiments to LAI 5. The relationship of Pnc to LAI of swards in the regrowth phase was predominantly curvilinear and such that over much of the LAI range they had a greater photosynthetic potential than the same swards being grazed down from high to low mass. Daily rates of CO2 uptake and growth in the field were calculated for one continuously stocked experiment. Both were linearly related to LAI in the range LAI 2–4·5. The agronomic implications of the results are discussed.

Notes: An investigation of the carbon economy of single S184 white clover plants nodulated with an effective strain of Rhizobium trifolii growing on N-free nutrient solution and supplied with 150 parts/106 N as NH4NO3 has shown that 10% more of the C fixed per day is available for growth in the plants supplied with combined N. The difference between the two groups of plants is a result of higher respiratory activity in the roots of plants growing exclusively on N2. In terms of shoot growth, however, the difference in growth rate is likely to be less than 10%, because the rate of root growth is greater in the plants supplied with a moderate level of combined N. There is no evidence that NO-3 and CO2 compete for photosynthetically produced reductant in the leaves of plants grown on N2+NH4NO3, since no reduction in net photosynthesis was observed in plants assimilating combined N.An experiment carried out on detached leaflets of white clover grown on N2 and on N2+ NH4NO3 has shown that NO-3 -reducing activity is present in the leaflets of plants grown on N2+ NH4NO3 but not in plants grown on N2 and that the activity is light-dependent. Measurements of 14CO2 respired in the light and dark by leaflets previously allowed to photosynthesize 14CO2 showed that the ratio of 14CO2 output in the light to 14CO2 output in the dark was no higher in plants grown on N2+ NH4NO3 than in plants grown on N2. This observation is consistent with the finding that N source does not affect net photosynthesis in whole plants.