THE BACTERIOLOGY OF THE ROOT REGION OF THE OAT PLANT GROWN UNDER CONTROLLED POT CULTURE CONDITIONS

SUMMARY: The bacteriology of the root region of oat plants grown under controlled conditions has been studied by means of improved techniques for separate estimation of the microfloras of the rhizosphere soil and of the root surface. The plate count of bacteria in the root region increased during the growing period of the plants; superphosphate produced a greater increase, which was probably due to increased plant growth, as no such effect was observed in uncropped soil.
The numbers of acid producing and dicalcium phosphate dissolving bacteria were increased in the root region, but the latter were not preferentially stimulated. Dressings of superphosphate and dicalcium phosphate also did not preferentially stimulate either group. No evidence was obtained, by the plate method used, of the presence of organisms capable of dissolving variscite, strengite, or gafsa rock phosphate, although the plants showed appreciable response to gafsa rock phosphate.     

THE COMPETITION BETWEEN BARLEY AND CERTAIN WEEDS UNDER CONTROLLED CONDITIONS

One of the commonest agricultural practices in Britain is the undersowing of barley and other corn crops with clover as a preparation for a clover ley after the corn crop has been reaped. The effect of the clover growing among the corn, where manuring (especially with nitrogen) is made as favourable as possible for the corn crop, is not clear. If nitrogen is deficient, it is well known that clover can furnish nitrogen for the corn, but where the supply is ample, the clover may act as a competitive crop.
When barley and clover were planted together, with abundance of water and nutrients for both, it was found that the presence of even a small number of barley plants reduced the growth of the clover by over 50%, but that an increase in the density of the barley did not increase the effect. The presence of the clover reduced the barley crop by an amount which tended to get less as the density of the barley was increased. In a sparse crop of barley, increase in clover density reduced the growth of barley very little, while that of the clover was again found to be little more than half what was obtained when this plant was grown alone.
There is no evidence of any specific effect of the roots of the one plant on the other. In the circumstances of these experiments it would seem that, far from the clover supplying nitrogen to the barley, it tends to steal some of that which would otherwise be available to the latter, when they are grown together.     

A GROWTH COMPARISON OF SPARTINA ALTERNIFLORA LOISEL. ECOPHENES UNDER AEROBIC AND ANAEROBIC CONDITIONS

Spartina alterniflora Loisel. culms were collected from tall (creekbank), short (highmarsh) and dieback sites in a North Carolina salt marsh and grown in aerobic and anaerobic simulated marsh systems in the greenhouse. There were no significant differences between density, aerial live biomass, height, leaf width or root biomass and sprig source. All variables were significantly different between aeration treatments. Aerated systems had an average of 6.3 times more biomass than the unaerated treatments. There was a significant interaction between sprig source and aeration treatments based on a multivariate analysis of variance representing overall plant performance. These results demonstrated that pioneer sprigs from the dieback sites had an advantage over the other sprigs when exposed to unaerated systems. Tall plants performed better than plants from short or dieback zones in the aerobic systems.     

THE COMPETITION BETWEEN BARLEY AND CERTAIN WEEDS UNDER CONTROLLED CONDITIONS

Chickweed (Stellaria media) is one of the commonest annual weeds on almost all soils, and forms 20–30 % of the weed herbage on the lower greensand soils of Woburn, Beds. It occurs in all crops in this area except on very acid soils.
When barley and chickweed are planted together, with abundance of water and nutrients for both, it is found that increasing the density of planting of the barley reduces the loss due to chickweed competition, but even with very close-planted barley, the loss caused by the weed amounts to nearly two-thirds of the total fresh weight and to four-fifths of the grain yields. This is much greater than with the two annual weeds previously studied (spurrey and mayweed). In a sparse crop of barley, increase in chickweed growth may reduce the barley to less than 10 % of its growth without the weed, while the chickweed itself is relatively little affected by the presence of the barley.
There is no evidence of any specific effect of the roots of the one plant on the other; they intertwine without any sign of attraction or repulsion between them.
Comparisons are made with other annual weeds previously studied, and it is suggested that the method adopted furnishes a means of assessing the relative effectiveness of these weeds in competing with barley.     

SOYBEAN GROWTH RESPONSES TO ENHANCED LEVELS OF ULTRAVIOLET-B RADIATION UNDER GREENHOUSE CONDITIONS

Soybean (Glycine max [L.] Merr. cv. Essex) was grown in an unshaded greenhouse under three levels of biologically effective ultraviolet-B (UV-B_BE) radiation (effective daily dose: 0, 11.5 and 13.6 kJ m^–2) for 91 days. Plants were harvested at regular intervals beginning 10 days after germination until reproductive maturity. Mathematical growth analysis revealed that the effects of UV-B radiation varied with plant growth stage. The transition period between vegetative and reproductive growth was the most sensitive to UV-B radiation. Intermediate levels of UV-B had deleterious effects on plant height, leaf area, and total plant dry weight at late vegetative and reproductive stages of development. Specific leaf weight increased during vegetative growth but was unaffected by UV-B during reproductive growth stages. Relative growth, net assimilation, and stem elongation rates were decreased by UV-B radiation during vegetative and early reproductive growth stages. Variation in plant responses may be due in part to changes in microclimate within the plant canopy or to differences in repair or protection mechanisms at differing developmental stages.     

THE GROWTH OF A MIDWESTERN STRAIN OF SORGHUM HALEPENSE UNDER CONTROLLED CONDITIONS

Ingle , M., and B. J. Rogers . (Purdue U., Lafayette, Indiana.) The growth of a midwestern strain of Sorghum halepense under controlled conditions. Amer. Jour. Bot. 48(5): 392–396. Illus. 1961.—This grass, adapted to midwestern growing conditions, increased growth up to 32°C. under long-day conditions (16 hr.). In a 12-hr. photoperiod, growth increased up to 27°C; at 32°C. growth was reduced. Flowering usually occurred under photoperiods of 12 hr. or less, but this requirement was not absolute. Rhizome bud sprouting was found to be proportional to temperature. Regardless of the environmental conditions and variations tested, all buds on the rhizomes developed into aerial shoots and never into rhizomes.     

NATURE OF THE PLANT COMMUNITY. VI. TEXAS GRASSLAND COMMUNITIES UNDER TRANSPLANTED CONDITIONS

Mc Millan , Calvin . (U. Texas, Austin.) Nature of the plant community. VI. Texas grassland communities under transplanted conditions. Amer. Jour. Bot. 48(9): 778–785. Illus. 1961.—Clones of 7 grass taxa, Bouteloua gracilis (H. B. K.) Lag., B. eriopoda (Torr.) Torr., B. curtipendula (Michx.) Torr., Panicum virgatum L., the Andropogon scoparius Michx. complex, the Andropogon gerardi Vitman-hallii Hack. complex, and Sorghastrum nutans (L.) Nash, were transplanted from throughout their distribution in Texas and studied in an experimental garden at Austin. Restricted to western Texas and Panhandle areas, Bouteloua gracilis and B. eriopoda contained similar early-flowering clones throughout their distribution. Less restricted to western sites, B. curtipendula contained later-flowering types from eastern and central areas. In the 4 remaining, widespread taxa, early-flowering potential characterized clones from western sites. These 4 widespread taxa contain the latest-flowering clones from the coast of southern Texas. Clones of Stipa leucotricha Trin. and Rupr. from a broad area in Texas lacked a flowering gradient. Grassland communities of western Texas and the Panhandle, attuned to short growing seasons and low rainfall, were composed of opportunists, the Bouteloua species, and early-flowering variants within the widespread species. Communities of central Texas in habitats of highly unpredictable moisture pattern and a relatively long growing season contained later-flowering variants. Coastal communities attuned to a long growing season contained the latest-flowering variants.