Effect of soil moisture and phosphate level on root hair growth of corn roots

Summary Root hairs have been shown to enhance P uptake by plants growing in low P soil. Little is known of the factors controlling root hair growth. The objective of this study was to investigate the influence of soil moisture and P level on root hair growth of corn (Zea mays L.). The effect of volumetric soil moistures of 22% (M₀), 27% (M₁), and 32% (M₂) and soil (Raub silt loam, Aquic Argiudoll) P levels of, 0.81 (P₀), 12.1 (P₁), 21.6 (P₂), 48.7 (P₃), and 203.3 (P₄) mol P L^–1 initially in the soil solution, on shoot and root growth, P uptake, and root hair growth of corn was studied in a series of pot experiments in a controlled climate chamber. Root hair growth was affected more by soil moisture than soil P. The percentage of total root length with root hairs and the density and length of root hairs on the root sections having root hairs all increased as soil moisture was reduced from M₂ to M₀. No relationship was found between root hair length and soil P. Density of root hairs, however, was found to decrease with an increase in soil P. No correlation was found between root hair growth parameters and plant P content, further suggesting P plays a secondary role to moisture in regulating root hair growth in soils. The increase in root hair growth appears to be a response by the plant to stress as yield and P uptake by corn grown at M₀ were only 0.47 to 0.82, and 0.34 to 0.74, respectively, of that measured at M₁ across the five soil P levels. The increase in root hair growth at M₀, which represents an increase of 2.76 to 4.03 in root surface area, could offset, in part, the reduced rate of root growth, which was the primary reason for reduced P uptake under limited soil moisture conditions.Journal Paper No. 10,066 Purdue Univ. Agric. Exp. Stn., W. Lafayette, IN 47907. Contribution from the Dep. of Agron. This paper was supported in part by a grant from the Tennessee Valley Authority.     

The present situation and problems of mariculture in Japan

Summary Recently, rearing techniques for various kinds of fish have advanced markedly, and the number of fish species in commercial production increases every year. The establishment of methods for stable, reproducible mass culture of live foods that are highly nutritious is still necessary to improve the survival and growth rates of larval fish. Since, however, the mass propagation of live foods requires costly equipment and depends upon weather conditions, the development of artificial larval diets to replace live foods will be essential. In mariculture local trash fish are commonly used as a feed for juvenile fish because of their low cost and high acceptability to the cultured fish. However, this frequently results in deterioration of water environments, leading to the appearance of fish diseases and pollution. The development of artificial diets such as moist pellets will also improve these conditions.Mass-cultured fish seed are mainly used for the culture of commercial-sized fish, even though they are generally poorer in taste than wild fish. They are also used for release into coastal waters to promote inshore fishery, but it is difficult to evaluate the effect of stocking on the total catch. Another type of mariculture depends upon raising wild juveniles, though there are clearly too few caught to supply enough fish seed to satisfy the ever-growing demands of fish breeders. Thus, the cultivation of broodstock to produce high-quality eggs is important.     

Modelling growth responses of soil nitrifiers to additions of ammonium sulphate and ammonium chloride

Summary Following the addition of 0–75 mole N g^–1 as ammonium chloride or ammonium sulphate to a sandy loam soil the nitrate formed was measured daily for a period of 15–17 days. The nitrate produced as a function of time was described using the Monod equation for microbial growth. An optimisation technique is described for obtaining, from the nitrification time course data, the maximum specific growth rate, the affinity constantant and an index limited by the concentration of ammonium in soil solution. Additions of more than 7.3 moles N g^–1 soil as ammonium chloride were found to inhibit nitrification. The inhibition was interpreted as being caused by osmotic pressure or by chloride ion. A similar effect was not found with ammonium sulphate, because the salt concentration in the soil solution was restricted by the precipitation of calcium sulphate. The model developed was capable of accounting for nitrate production in the soil under non-steady state conditions of substrate concentrations and nitrifier biomass.     

Quantity and quality of seston in an impounded and a free-flowing river in Virginia,U.S.A.

Seston in the impounded North Anna River (NAR) was analyzed and compared to that in the free-flowing South Anna River (SAR) in Virginia, U.S.A. A wet filtration technique was used to separate seston into five size classes. The overall quantity of organic seston was much lower in the NAR than in the SAR. The seston in the NAR was composed of more living organisms, in particular zooplankters in the medium large (234–864 µm) and small (105–234 µm) size classes and diatoms and other algae in the fine (43–105 µm) and very fine (25–43 µm) size classes. The percentage of zooplankton declined sharply before reaching the downstream study site (32 km). The seston in the NAR tended to consist of slightly larger particles, but 80–85% of the seston in both rivers was in the ultrafine (0.45–25 µm) size class, which was almost entirely composed of detritus. One indication of seston food quality, the organic/inorganic ratio, was considerably higher for the medium large and small size classes in the NAR immediately below the dam and for the fine and very fine size classes farther downstream. Another indication of food quality, the usable caloric content, showed that the seston in the NAR contained considerably less total assimilable energy as far as 32 km downstream from the dam, but that the medium large and small size classes were rich in assimilable energy immediately below the dam because of zooplankton released from the reservoir. Thus, the overall quantity and quality of seston was lower in the NAR, but the quality of the seston, for at least a short distance below the dam, was higher in a well-defined size range that can be effectively utilized by certain filter feeders.     

The effect of phytoplankton and suspended sediment on the growth of Corbicula fluminea (Bivalvia)

Juvenile Corbicula fluminea Müller (1774) were cultured at 15.3 °C in the laboratory on eight combinations of suspended sediment and phytoplankton. Sediment concentrations were 2.6, 25, 50, and 150 mg l^–1. Chlorophyll a levels were 15.6 and 62.5 µg l^–1. Clam tissue growth was found to be independent of silt concentration but increased at the higher chlorophyll level (p < 0.05). The growth experiment was repeated at 24 °C with chlorophyll a concentrations of 18.9 and 112.6 µg l^–1. Growth was again greater at the higher phytoplankton level (p < 0.05). These results demonstrate that Asiatic clam populations are food-limited most of the growing season in the Northern and Western portions of California's eutrophic Sacramento-San Joaquin Delta where chlorophyll a levels average less than the lower of these values. Comparisons of clam growth in the laboratory and estuary support the food limitation hypothesis as at the higher food concentration laboratory tissue growth was 2.3 and 3.8 times greater during the high and low temperature evaluations than in the estuary.     

The influence of oxygen concentrations on denitrification in soil

Summary The influence of different O₂ concentrations on denitrification was studied in an agricultural soil. In both nitrate and nitrite amended soil, denitrification was not observed until the O₂ concentration decreased to 0.20 and 0.21 mol/ml, respectively. Denitrification was not observed in soil samples with O₂ concentrations above 0.28 mol/ml in the gas phase. These findings suggest that a completely anoxic environment is not required for denitrification to occur in soil.     

The impact of grazing on plant communities,plant populations and soil conditions on salt marshes

Grazing an abandoned salt marsh causes retrogressive succession, since mid salt-marsh communities change into lower salt-marsh communities. Grazing and mowing are compared in detail. Both management practices enhance species diversity in an abandoned salt marsh. This can be attributed to the removal of litter. The finding that lower salt-marsh species appear more with grazing than with mowing or abandoning is not related to a higher soil salinity as compared to mowing or abandoning, but probably to locally baring of the soil by grazing animals. Only species of pioneer or unstable environments seem to have a persistent seed bank, for other species seed dispersal seems to be a limiting factor for their establishment.Nomenclature follows Heukels & van Ooststroom (1977) for species; Westhoff & den Held (1969) for syntaxa.Mrs R. Rusthoven analyzed the soil samples, Mr E. Leeuwinga drawed the figures, and Mrs J. O'Brien corrected the English text.     

Food and feeding habits of Labeo niloticus (Pisces,Cyprinidae) in Jebel Aulia Reservoir,Sudan

Basic knowledge on the feeding ecology of one of the common and commercially important fish species in Jebel Aulia Reservoir is provided.The structure of the feeding apparatus indicates that Labeo niloticus is a bottom feeder, depending on soft and decayed vegetation, organic debris and whatever small organisms found within. However, juveniles and fry are prone to explore all layers and depths of the river selectively for plankton. There is little evidence of seasonal selection of food. Changes in diet quality are governed by the availability of type of food. Variability of feeding activity is connected with climate and breeding season.     

Ultrastructural studies on the reproductive organs of Porphyra haitanensis T. J. Chang et B. F. Zheng

A study of food and food selection of Penaeus monodon (Fabricius) on the Sudanese Red Sea coast was carried out. Juveniles feed mainly on algal material. Adults feed on crustacea, annelids, algae, mud and unidentified matter. Adults were opportunistic in their feeding behaviour, but their preference was towards animal protein.Antennae, mouth parts and fore-chelipeds were found to carry long, slender setae which are probably of sensory function. Some setae on the carpus of the endopodite were serrated and seem to be used in grooming. Numerous tufts of setae in the chela of the fore periopods may hold a gustatory function. The inner edges of the chela are lined with a row of peg-like setae, which are probably another site of reception.     

The vegetation of a New Zealand dune slack

The vegetation of a dune slack at Mason Bay, Stewart Island, New Zealand was found to comprise a mosaic of communities. Although the broad vegetational patterns could be correlated with the depth of the water table, the patterns were far from simple. Species diversity over the whole slack was lower than values reported from European dune slacks; even the most diverse communities did not reach European mean values.For nomenclature see Wilson in press. Vascular plants of Stewart Island. D.S.I.R., Wellington, New Zealand; Sainsbury (1955). A handbook of the New Zealand mosses. N.Z. R. Soc. 5: 1–490 & Hamlin (1972). Hepaticae of New Zealand, Dominion Museum, Wellington.