Mineralization of soil nitrogen in three forest communities from the New England region of New South Wales

Nitrogen (N) mineralization rates and the temperature response patterns of mineral N production in surface (0–7.6 cm) soils were compared in laboratory incubation studies based on disturbed, composite samples. Seasonal variation in the field levels of mineral N, and mineralization potential of intact (7.6 × 5.6 cm diameter) soil cores, were also investigated. Ammonification proceeded rapidly in each soil. Nitrification did not occur in grassy forest (GF) soil but was active in both layered forest (LF) and mossy forest (MF) soils, especially the former. Total mineral N production was greatest in MF and least in LF. Ammonification in disturbed samples was maximal at 50°C in all three soils with a secondary peak at 10°C in LF soil. Nitrification in LF and MF soils was most rapid at 25°C. Several species of ammonifying bacteria with different temperature optima were isolated, indicating that the process of ammonification is a composite of the activities of a variety of decomposer microbes. Mean field levels of mineral N and NH₄–N throughout the year were greatest in MF and least in LF. Seasonal fluctuations in NH₄–N were evident, concentrations being universally low in mid-winter (about 1.5 μgg^-1), increasing to a maximum in late summer (about 5 μg g^-1 in LF: 16–18 μg g^-1 in GF and MF). Field levels of NO₃–N were more constant and never more than 5 μg g^-1 in any community. Both total mineralization and ammonification in intact cores were greatest in MF and least in LF while nitrification was greatest in LF and almost negligible in GF, thus confirming the results obtained with disturbed samples. The potential for mineralization was large in mid-winter when the amount of mineral N was very low, and small in late summer when field levels were higher: this is interpreted as indicating that seasonal climatic factors regulate the availability of substrates for decomposers. Spatial variability in field levels of mineral N and mineral N production in the laboratory was evidenced by significant ‘sampling site’ effects in each community: however, at the sampling intensity used, the presence of bark mounds around Eucalyptus saligna trees could not be shown to affect these attributes. The inability of GF soil to nitrify when incubated in the laboratory could not be ascribed to a high C/N ratio, low pH, lack of substrate ammonium, or a low population of autotrophic nitrifying bacteria. No attempt was made to investigate the presence of allelopathic nitrification inhibitors. No evidence was obtained to support the view that nitrification is atypical of climax communities in situ. The most productive forest (LF) had the greatest capacity to nitrify and the least productive community (GF) the smallest capacity to do so.     

Detection of aphid remains in predatory insects and spiders by ELISA

An ELISA was developed which would detect and quantify ingested aphids in predators found in and around cereal crops. The detection limit of the assay was less than one hundredth of an homogenised adult aphid. Tests with 13 species of aphid showed that those which had been used as the principal immunogens reacted most strongly in the assay. Nearly a hundred species of invertebrates, both predators and alternative prey, have been tested in the assay and no evidence of significant cross-reaction was found with any of these species or with a number of samples of plant material on which aphids may be found. Aphid material could still be detected in predators which had been stored for up to 7 days in 4% formalin or 70% ethanol.     

Are Roots a Source of Abscisic Acid for the Shoots of Flooded Pea Plants?

Flooding the soil for 2–5 d decreased stomatal conductancesof pea plants (Pisum sativum L., cv. Sprite) with six or sevenleaves. This coincided with slower transpiration, increasedleaf water potentials and increased concentrations of abscisicacid (ABA) in the leaves. No increase in ABA was found in theterminal 20 mm of roots of flooded plants over the same timeperiod. Small stomatal conductances associated with increases in foliarABA were also found in plants grown in nutrient solution whenaeration was halted, causing the equilibrium partial pressuresof dissolved oxygen to fall below 05 It Pa. No increase in ABAconcentration in young secondary roots of the non-aerated plantswas detected after 24, 48 or 72 h, even when the shoot, thepresumed site of deposition for any ABA from the roots, wasremoved 5–6 h before analysis. Similarly, ABA concentrations in roots were not increased whenthe nutrient solution was de-oxygenated by continuous purgingwith nitrogen gas. The abscisic acid concentration in leaf epidermis,the tissue most likely to be the recipient of any ABA movingin the transpiration stream from oxygen-deficient roots, waslower than in the remaining parts of the leaf when examinedin the mutant Argenteum which possesses easily removable epidermallayers. It is concluded that the leaves of plants subjectedto flooding of the soil or oxygen shortage in the root environmentare not enriched substantially with ABA from the roots. A moreprobable source of this growth regulator is the leaf itself. Key words: Pisum sativum, flooding, roots, hormones, aeration stress, abscisic acid, Argenteum mutant     

Shoot Regeneration from Fragmented Flower Buds of Carnation (Dianthus caryophyllus)

Adventitious shoots were regenerated from fragmented flowerbuds, individual petals and receptacles in a number of differentcarnation cultivars. The major site of shoot formation was thesubepidermal cells at the proximal end of the petals. The yieldof shoots from a single flower bud was high, ranging between70 and 275, for the 11 cultivars tested. The regeneration mediumcontained Murashige and Skoog basal medium supplemented with4–8 µm -naphthaleneacetic acid and 4–8 µmbenzyladenine. The preferred regeneration protocol appears highlysuited to the development of gene transfer systems. Adventitious shoots, Dianthus caryophyllus L., tissue culture, explant, auxin, cytokinin, cut flowers, floriculture, organogenesis     

The Fine Structure of Trypanosoma congolense in Its Bloodstream Phase

SYNOPSIS. The fine structure of 2 isolates of Trypanosoma congolense maintained in laboratory rodents has been studied from thin sections of osmium- and aldehyde-fixed flagellates. The pellicular complex, nucleus, and flagellar apparatus are all similar to those of other African trypanosomes. Aberrant intracellular differentiation of the flagellum is occasionally found. As in bloodstream forms of other salivarian trypanosomes the single mitochondrion forms an irregular canal running from one end of the body to the other, with a shallow bowl-shaped expansion forming a capsule for the fibrous kinetoplast (mitochondrial DNA). A connexion between the mitochondrial envelope of the kinetoplast and the basal body of the flagellum is not evident, and sometimes the flagellum base is not even apposed to the kinetoplast but lies behind it. Tubular cristae are present in the mitochondrial canal and, by light microscopy, this structure gives a positive reaction for NAD diaphorase suggesting at least some activity in electron transport, even tho at this stage in its life cycle respiration is doubtfully sensitive to cyanide and cytochrome pigments are in all probability absent. The region of the cytoplasm between the nucleus and the flagellar pocket has all the trappings associated with secretory cells in higher animals, or with the secretion of surface structures in phytoflagellates. just behind the nucleus a limb of granular reticulum subtends a Colgi stack of flattened saccules with attendant vesicles. Close to the distal pole of the Golgi complex is a network of smooth-membraned cisternae, termed here the agranular or secretory reticulum, which undergoes localized swelling with the accumulation of a secretory product to form large spherical sacs or vacuoles. These network-linked vacuoles probably correspond to the post nuclear vacuole complex visible by light microscopy. From its apparent secretory function this complex is regarded here as being possibly an extension or derivative of the Golgi complex, the smooth-membraned tubules lying alongside the 2 structures possibly representing a link between them. By analogy with phytoflagellates and the secretory cells of higher animals, it is suggested that the secretion is transported for discharge into the flagellar pocket by way of multivesicular bodies and smooth-walled tubules or vesicles. Spiny pits in the wall of the flagellar pocket, and similar-sized vesicles in the nearby cytoplasm, could be stages in either exocytosis of secretion or endocytosis (pinocytosis). It is tentatively suggested that the secretion may be the material from which the surface coat is formed. Neither a cytostome nor a contractile vacuole has been observed in T. congolense.     

Studies in Garcinia, dioecious tropical forest trees: the phenology, pollination biology and fertilization of G. hombroniana Pierre

RICHARDS, A. J., 1990. Studies in Garcinia , dioecious tropical forest trees: the phenology, pollination biology and fertilization of G. hombroniana Pierre . Garcinia hombroniana is a facultative agamosperm which is pollinated by Trigona bees. Nectar is restricted to the large discoid stigma (or pistillode in male flowers), which also captures and hydrates pollen. The 'wet' stigma and binucleate pollen suggest that Garcinia arose from hermaphrodite plants with a gametophytic self-incompatibility system.
On stigmas, nectar is secreted early on three or four successive days. On male pistillodes, nectar is secreted when anthers dehisce, on the second morning after anthesis. Pollen is most viable when freshly collected, but some viability remains four days after collection. Pollen germinates within 24 h of hydration. Similar results to pollinations are obtained by germinating pollen in 1 % sucrose.
Garcinia hombroniana flowers principally from January to June. Cultivated females are considered as 'big bang' strategists. Male flowers are considered as 'steady state' strategists.     

The control of incompatibility in distylous Pulmonaria affinis Jordan (Boraginaceae)

In P. affinis, pin pollen is shorter on average than thrum pollen. Pins have more coronal hooks on stigmatic papillae than thrums, but gaps between papillae are relatively smaller for thrums. Pin stigmas receive more pollen than thrum stigmas. Thrum stigmas receive more (dissortive) pin pollen, but pin stigmas are assortively pollinated. Pollen only germinates when trapped below papilla coronas. On thrum stigmas, most trapped pollen is pin. Pollen germination is better on thrum stigmas than pin stigmas, and thrum stigmas show a close relationship between numbers of legitimate pollen grains, numbers of germinating grains, and numbers of pollen tubes in the style. There is no inhibition of illegitimate pollen germination. Illegitimate pollen tubes are inhibited in the style. Incompatibility operates by a combination of dissortive pollination, dissortive pollen trapping, and stylar pollen tube inhibition. All heteromorphic features differing between pins and thrums are implicated in the inhibition of within-morph fertilization in thrums.     

Physical variability,diversity gradients and the ecology of temperate and tropical reefs

Traditionally, compared with the tropics, temperate systems are believed to: (i) have environments which are less favourable (i.e. harsher, more variable and less predictable); and (ii) support communities which are less diverse. Explanations for differences between temperate and tropical communities, including differences in diversity, generally rely on the former notion. The evidence for these ideas is, at best, equivocal. Organisms are subjected to physical stresses and disturbances on both temperate and tropical reefs. Communities on temperate reefs are not invariably less diverse than those in the tropics, at least at small spatial scales. Finally, there is as yet little evidence of genuine differences between the ecology of temperate and tropical communities. There is, however, much small-scale, spatial patchiness in the structure of reef communities and their physical environment. This patchiness in structure may result from patchiness in biological factors (e.g. recruitment) or in the physical environment. This small-scale variation in environmental factors may prove to be a more important determinant of community structure than the large-scale, latitudinal trends some ecologists have been obsessed with.