Shona G. McInroy

Phenotypic characteristics and composition of rhizobia associated with woody legumes growing in diverse Kenyan conditions

Over 480 rhizobia were isolated from root nodules of woody legume and herbaceous trap host species grown in soils collected from 12 different Kenyan sites. The isolates were differentiated by growth and morphological characteristics, intrinsic antibiotic resistance (IAR) and salt (NaCl) tolerance levels (STL) when grown on yeast mannitol mineral salts agar and broth media.The bulk of the isolates (91%) were watery, milky-translucent and curdled milk types with moderate to copious extracellular polysaccharide (EPS). The rest were creamy or white opaque with little to moderate EPS production. Overall, they showed a wide range of growth rates: very fast-growing (mean generation time 1.6–2.5 h), fast-growing (2.8–4.8 h), intermediate between fast- and slow-growing (5.6–5.7 h) and slow- and very slow-growing (6.4–8.8 h). The isolates were tentatively grouped into Rhizobium spp., to include very fast, fast and intermediate (acid-producing) types; and Bradyrhizobium spp., to include very slow, slow and intermediate (alkali-producing) types.Bradyrhizobium spp. were more sensitive to antibiotics (40 μg mL-1) than Rhizobium spp., contrary to the general opinion which indicates that they are normally resistant. Cluster analysis based on sensitivity responses of IAR and STL could not distinguish Rhizobium spp. from Bradyrhizobium spp., neither was there any association by site nor host of isolation except for those isolates trapped with Phaseolus vulgaris at Kibwezi.Our data demonstrated a high diversity of tropical rhizobia associated with trees.

Constitutive nitrate reductase activity in the leguminosae

Abstract The occurrence of constitutive nitrate reductase activity (NRA) was examined in 101 species from 25 tribes in the Leguminosae. Constitutive NRA was undetectable in all species from the sub-families Caesalpiniodeae and Mimosoideae. Within the Papilionoideae it occurred in root and shoot of Lotus uliginosus (Loteae) and leaves of all members of the tribe Phaseoleae but was absent in all other plants tested. For L. uliginosus , root and shoot activity was similar in light and darkness, but for Glycine max and Phaseolus vulgaris (both Phaseoleae) leaf activity was greater in light.

Single and multi-strain rhizobial inoculation of African acacias in nursery conditions

Abstract Inoculation experiments were conducted in Kenya on seven African Acacia species/subspecies (Faidherbia albida, Acacia karroo, A. arenaria, A. nilotica ssp. kraussiana, A. tortilis ssp. spirocarpa, A. tortilis ssp. heteracantha, A. senegal) in sterilised and untreated soil. The untreated soil contained 103 rhizobia g−1. In six of seven species in untreated soil the multi-strain inoculated plants contained significantly more total nitrogen than control plants. The exception was A. arenaria in which significant increase in total nitrogen was achieved only with the single strain inoculum in sterile soil. In A. tortilis ssp. spirocarpa the single strain was better than the multi-strain inoculum. Significant increases over controls in dry weight ranged from 19 to 75% and in total nitrogen from 11 to 89%. Nitrogen derived from fixation (Ndff) was determined for three species/subspecies using the natural abundance 15N method. Values for fixation for the best treatments in these species were A. nilotica 53%, A. tortilis ssp. heteracantha 45% and A. tortilis ssp. spirocarpa 44%. These are conservative values because of the relatively small δ15N values (−2.85‰ for A. nilotica and −2.52‰ for both species of A. tortilis) determined as the 100% fixation values. We conclude that: inoculation can result in substantial gains in nitrogen fixation in African acacias; multi-strain inoculation is preferable to single strain inoculation in some circumstances; A. nilotica and A. tortilis have at least moderate nitrogen fixation potential and the wide genetic variation found suggests that substantial improvement may be obtained by selection for this character.

Culture of Chara hispida

Culture conditions that support high growth rates of Chara hispida L and Nitella flexilis (L.) Ag. are described. The optimum conditions for both rhizoid and shoot growth are obtained using a substrate of 425–710 μm sand particles and a solution of inorganic salts in distilled water. The highest rates of linear extension and dry weight increase of shoots are obtained with sand substrates less than 710 μm in size.

Growth, nodulation and nitrate reductase activity in the aquatic legume Neptunia plena (L.) benth. At different external nitrate concentrations

The effects of different external nitrate concentrations (0 (control), 1, 50, 100, 500, 1000 and 20 000 mmol m−3) on growth, nodulation and nitrate-reductase activity (NRA) of inoculated Neptunia plena (L.) Benth. were examined. Plants given 500 and 1000 mmol m−3 nitrate had greater (P < 0.05) shoot length, leaf, stem and root dry mass, and carbon and nitrogen contents than the controls and plants given 20 000 mmol m−3 nitrate. Nodule number was not significantly affected by nitrate concentration up to 50 mmol m−3, but 100 mmol m−3 nitrate reduced nodulation by 68% and concentrations above 100 mmol m−3 completely inhibited nodule development. Plants given 100–20000 mmol m−3 nitrate had a greater nitrate content per g leaf, stem and root dry mass (DM) than controls. Nitrate per g root DM did not increase with external nitrate concentration above 500 mmol m−3, but levels in leaf and stem were greater at 20 000 mmol m−3 nitrate than at all other concentrations. NRA per g leaf, stem and root fresh mass (FM) was greater for plants given 500–20000 mmol m−3 than for controls, but there was no significant increase with nitrate concentration above 500 mmol m−3. Substantial proportions of total plant nitrate and NRA were found in both root and shoot over the entire range of external nitrate concentrations given. Findings for N. plena are compared with data obtained previously for terrestrial legumes.

Altritol synthesis by Notheia anomala

The linear hexitol altritol has only been identified in six genera, all of them in the order Fucales of the brown algae. Five of these genera are closely related according to molecular phylogenetic and other data, while the sixth (Notheia) is an obligate epiphyte on two other altritol-containing genera with which it is symphanic. The possibility that Notheia obtains altritol from the algae on which it is epiphytic rather than by synthesizing altritol independently was investigated by supplying 13C-inorganic carbon in the light followed by mass spectrometric and nuclear magnetic resonance analysis. Notheia separated from the phorophyte Hormosira during exposure to 13C showed 13C enrichment in both altritol and mannitol, while the Hormosira only showed significant labelling of mannitol. These data show that altritol can be synthesized by Notheia, with implications for the number of gains and losses of the capacity to synthesize altritol in the evolution of the Fucales.

Carbon isotope ratios of photolithotrophs from allt meall nan damh, a burn at ardeonaig, Perthshire, and their ecophysiological significance

Summary δ13C measurements were made of dissolved inorganic C, and of submerged benthic cyanobacteria, algae and bryophytes, from Allt Meall nan Damh, a burn at Ardeonaig, Perthshire. The δ13C of the CO2, HCO3/- and CO3/2- components of the inorganic C were computed, and the Δ values of the organic C in the photolithotrophs were then calculated relative to dissolved CO2. The decreasing order of A values in the Ardeonaig Burn is Lemanea and bryophytes ≥ green macroalgae and Audouinella > diatom mats, which is the same as in the Dighty Burn. However, the Δ values of Lemanea and the bryophytes, which depend on diffusive CO2 entry, are lower at Ardeonaig than in the Dighty Burn, suggesting greater diffusive limitation to photosynthesis in the Ardeonaig Burn. It is not easy to relate this difference in Δ values in Lemanea to the higher C:N atomic ratio in the Ardeonaig Burn (21.2 ± 0.64) than in the Dighty Burn (9.5–11.0). The Δ values relative to HCO3/- for the HCO3/--using diatom mat in the Ardeonaig Burn is also lower than that in the Dighty Burn; this is consistent with a greater diffusion limitation of photosynthesis in the thicker mats in the Ardeonaig Burn. The δ13C of a Lyngbya mat overlying a Lemanea population stranded by low summer water levels indicates that some of the C fixed by the HCO3/--using Lyngbya comes from respiration of low-δ13C inorganic C by the Lemanea which is shaded by the Lyngbya. The δ13C values of Mesotaenium in its mucilage sheath on a thinly vegetated bank is suggestive of predominant use of the higher CO2 concentrations with lower δ13C from groundwater rather than of atmospheric CO2 yielding lower dissolved CO2 concentrations with a higher δ13C value.

Early growth and final yield of autumn sownVicia faba L cultivars given different forms of fertiliser N over winter

SummaryBetween 3 Nov. 1983 and 9 Apr. 1984, six applications of fertiliser N (ammonium, nitrate or urea) were given to four autumn sown (26 Oct. 1983)Vicia faba L cultivars, Banner Winter (BW) and Maris Beagle (MBg), cold tolerant cultivars normally sown in the autumn, and Herz Freya (HF) and Maris Bead (MBd), cold sensitive cultivars more commonly sown in the spring. The effects of additional N were determined by comparison with plants given zero-N (controls).Application of N, regardless of form, had no effect on % emergence at the first sampling (15 Dec. 1983); >90% for BW, MBg and HF, but only 40–60% for MBd. At this time the dry weight, carbon content and nitrogen content of all cultivars was approximately 20% less than that of the seed on planting. No more plants emerged after 15 Dec. 1983. Between 15 Dec. 1983 and 20 Feb. 1984, all cultivars, regardless of N treatment, showed little change in dry weight, carbon content and nitrogen content but the proportion of total plant dry weight, carbon content and nitrogen content in the cotyledons decreased while the proportions in root, stem and leaf tissue increased. On 20 Feb. 1984 there were no N effects. All cultivars but especially BW and MBg, showed progressive increases in dry weight, carbon content and nitrogen content during the period 20 Feb. 1984 to 8 May 1984. Pooled results for all four cultivars indicated that on 8 May 1984, plants given ammonium and urea had a greater dry weight, carbon content and nitrogen content than controls.At harvest (1–3 Sep. 1984), BW and MBg outyielded (g dw seed m−2) HF and MBd. Pooled results for all cultivars indicated that application of N regardless of form gave increased yield and an increased N concentration (mg N g−1 dw) in the seed.

Oxygen-Insensitive Growth of Algae with and Without CO 2 -Concentrating Mechanisms

The present atmosphere contains some 0.208 moles of O2 per mole of total gas. This normoxic situation corresponds to some 21 kPa O2 with the standard sea-level atmospheric pressure of 101.3 kPa, which is equivalent to an equilibrium concentration in solution of between 0.1 mol O2 m−3 for very saline water at close to the upper temperature limit for eukaryotic O2-evolvers (e.g. the Dead Sea) and 0.4 mol O2 m−3 for freshwater close to the freezing point (1,2). Physical phenomena such as decreasing atmospheric pressure with altitude and pressure from breaking waves and from formation of ice from snow followed by melting can respectively produce dissolved O2 which are respectively higher and lower than the equilibrium value. However, it is biological activity which produces the most extreme O2 concentration in the biosphere. Hypoxia and thence anoxia develop when the rate of organic O2 supply for growth and maintenance of organisms exceeds the O2 supply needed for aerobic performance of these functions. Hyperoxia of up to several times the air-equilibrium value can occur in (i) water bodies containing O2-evolvers with abundant inorganic C and restricted O2 exchange with the atmosphere (ii) cells and tissues of organisms with CO2 concentrating mechanisms, including CAM and PEPck- and NADme-C4 plants and (iii) a combination of (i) and (ii) (3). Thus, the photosynthetic apparatus of many of the 325,000 or so currently described species of O2-evolving organism (4) spend at least part of their life cycle under anoxic, hypoxic or hyperoxic conditions.