Alternating Perturbation Response of the Water Regulatory System in Arena Leaves

The transpiration response of excised primary Avena leaves was studied when pulse perturbations were given to the water regulatory system. Repeated light pulses given to the leaf caused regularly alternating transpiration responses, i.e. the magnitude alternated regularly between a high and a low value. This effect, denoted alternating pulse response, could be recorded under quite different light pulse conditions but was not found when the pulse interval was too long or too short (longer than about 60 min. shorter than about 15 min). Sodium chloride given to the transpiration stream induced and increased the effect. Alternating pulse response could also be recorded when mannitol pulses were given to the root system of intact plants.     

Algal nitrogen fixation on temperate arable fields

Summary N₂-fixation by algae on the Broadbalk continuous wheat experiment was measured over a two year period using the acetylene reduction technique. The plots studied receive spring fertilizer treatments including farmyard manure and combinations of nitrochalk and Na, P, K and Mg which have remained much the same since the experiment started in 1843.Nitrogen applied at 196 kg ha^–1 in spring suppressed algal N₂-fixation until late in the season but at lower levels (48 kg N ha^–1) the denser plant canopy increased both surface moisture and fixation. Herbicide treatment decreased fixation on plots of moderate nutritional status early in the season but had little effect on unfertilised plots where weed cover was sparse. On plots where weed and crop cover was very dense herbicide treatment increased fixation in August.Algal N₂-ase activity, assayed by C₂H₂ reduction, continued throughout the night at a rate which averaged 33% of the midday value. Laboratory experiments indicate that dark fixation is very temperature sensitive and this value may represent a maximum. Algal crust in the field dried to 4.5–6.8% H₂O content became active 3 1/2 h after rewetting and reached a steady state after 7 h which represented only 6–22% of that at the previous maximum suggesting that many cells had been killed.In a year with average rainfall algae on plots receiving 48 kg N ha^–1 were estimated to fix 25–28 kg N ha^–1 and plots without fertiliser 13–19 kg N ha^–1. Algal fixation appeared to make a substantial contribution to the continuing fertility of unfertilised plots.     

Correction of severe manganese deficiency in wheat with chemical fertilizers

Summary Manganese, N and P fertilizers were applied to wheat in field experiments on a soil so deficient in Mn that it caused the wheat to die before heading. Yields of wheat were increased linearly by soil banded Mn to 44.8 kg/ha, giving a yield of 3.03 tonnes/ha. Yields were increased to a lesser extent by foliar-applied Mn and least by soil-broadcasted Mn. Soil N and P appeared to be adequate, yet ammonium sulphate at 56 kg N/ha where applied alone caused a yield of 1.69 tonnes/ha and ammonium sulphate nitrate gave a yield of 0.98 tonnes/ha, the increases being primarily due to the release of Mn to the plants. Calcium nitrate and triple superphosphate were much less effective in releasing Mn.     

Ammonia volatilization after injection of anhydrous ammonia into arable soils of different moisture levels

Laboratory experiments have shown appreciable losses of ammonia after injection of anhydrous ammonia into dry and wet soils. In this study losses of ammonia injected into a moist (tension 10 kPa), dry (tension 160 kPa) and a wet (tension 1.6 kPa) sandy loam were measured under field conditions using wind tunnels. Losses were insignificant from a moist soil. However losses from a dry and a wet soil were 20% and 50% of injected ammonia, respectively. From the dry soil, losses of gaseous ammonia took place within the first hours after injection, which indicates a rapid transport through cracks and voids. From the wet soil, 20% of the injected ammonia was lost more gradually between 6 h and 6 d. This indicates that upward movement of water due to evaporation may be the cause of these ammonia losses which proceeded for longer periods.     

Carbon isotope discrimination at vegetative stage as an indicator of yield and water use efficiency of spring wheat (Triticum turgidum L. var. durum)

A field experiment was conducted to investigate if carbon isotope (¹³C) discrimination () measured at the vegetative stage of spring wheat (Triticum turgidum L. var. durum) is related with the yield and water use efficiency (WUE) at ripening. A line source sprinkler irrigation system exposed the wheat genotypes to different watering regimes, from rainfed to full irrigation and thereby increased the range in yield and WUE attainable in the four genotypes studied. The results indicated that values measured at the late stem elongation stage 60 days after planting (DAP), showed strong positive correlation with total dry matter yield (r=0.732^***), and a highly significant negative correlation with WUE (r=–0.755^***) measured at ripening 105 DAP. The data suggest that the imprints of measured at vegetative growth stage persists throughout the entire growth period, until maturity. Subject to confirmation from additional studies in other crops and locations, early measurements of may prove a useful tool for rapid and early screening of cultivars, for high yield and high WUE.     

Plant-induced changes in the redox potentials of rice rhizospheres

Redox potentials in microsites of the rhizosphere of flooded rice were continuously measured for several days. Close to the root tips redox potential markedly increased. The highest increase was measured in the rhizosphere of the tips of short lateral roots. Aerobic redox conditions were reached there, except in a very strongly reduced soil. Both the extension of the oxidation zone around the root tips and the maximum redox potential reached were influenced by the reducing capacity of the soil. The radius of the redox rhizosphere varied from less than 1 mm in a strongly reduced soil up to 4 mm in a weakly reduced one. The root-induced oxidation processes in the rhizosphere depended on the atmospheric oxygen supply to the roots.     

First record of Crustacea Malacostraca from fresh waters in the Canary Islands

Crustacea Malacostraca were hitherto unknown from fresh waters of the Canary Islands. A new species of Amphipoda, Rhipidogammarus rheophilus, has recently been discovered in springs and spring brooks in Tenerife.

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Resumen Crustacea Malacostraca era hasta ahora desconocida de las aguas dulces de las Islas Canarias. Una nueva especie de anfípodo, Rhipidogammarus rheophilus, ha sido recientemente descubierto de fuentes y manantiales de Tenerife.

     

A form-function analysis of photon capture for seaweeds

A large material of planktonic and semiplanktonic micro-crustaceans from various type of waters in south and central Sweden was computerized. The more frequent species were listed according to pH-preference and relation to humic content measured as mg Pt/l. Species indicating oligotrophy have their optima just below the neutral point, eurytopic ones around this level, while the eutrophic species Daphnia cucullata and D. magna were closely correlated with higher pH-levels. No really extreme pH-preference was observed. There is no link between trophic indication and the ranking list for humic content. Most planktic species occur at lower humic contents and semiplankters at higher.     

Seasonal and areal features of the lagoonal environment in Lake Nakanoumi,a shallow coastal lagoon in Japan

Lake Nakanoumi is a shallow coastal lagoon connected with the Japan Sea by a narrow channel. Over the past decade, land reclamation resulted in a 33% reduction of the lagoon's surface area. The remaining water basin of Lake Nakanoumi is scheduled to be artificially freshened to supply irrigation water for the newly reclaimed lands. This paper deals with the seasonal and areal features of the lagoonal environment prior to the beginning of the artificial desalinization.