Dry Mass Loss Research Articles

Nitrogen enrichment during decomposition of mangrove leaf litter in an east African coastal lagoon (Kenya): Relative importance of biological nitrogen fixation

In situ decomposition of senescent leaves of twoabundant mangrove species (Rhizophora mucronataLamarck and Ceriops tagal (Perr) C.B. Rob),enrichment of nitrogen and activity of dinitrogenfixing bacteria during decomposition were investigatedduring both rainy and dry seasons in a tropicalcoastal lagoon (Gazi, Kenya). Rates of leafdecomposition were higher for R. mucronata thanfor C. tagal and were highest, for both species,during rainy season. Rates of decomposition, expressedas percentage dry mass loss, over a decompositionperiod of 50 days was: C. tagal (rainy season),69%; C. tagal (dry season), 27%; R.mucronata (rainy season), 98%; and R.mucronata (dry season), 48%. High rainfall anddiurnal tidal inundation appear to enhance the leafdecomposition process. Maximum rates of nitrogenfixation were 380 nmol N2 h-1 g-1 dw forC. tagal (rainy season), 78 nmolN2 h-1 g-1 dw for C. tagal (dryseason), 390 nmol N2 h-1 g-1 dw for R. mucronata (rainy season) and 189 nmolN2 h-1 g-1 dw for R. mucronata (dry season). Although N2 fixation rates werehighest during rainy season, total nitrogenimmobilised in the leaves was highest during the dryseason. Biological nitrogen fixation can account forbetween 13 to 21% of the maximum nitrogen immobilisedin the decaying mangrove leaves. Nitrogen fixation, asa source of allochthonous nitrogen, sustains anitrogen input to the mangrove ecosystem, which addssignificantly to the nitrogen input through leaflitterfall.

Nuclear (DNA, RNA, histone and non-histone protein) and nucleolar changes during growth and senescence of may apple leaves

Quantitative interference microscopy was used to determine changes in nuclear and nucleolar indices (dry mass and cross-sectional area) in upper and lower epidermal cells and adjacent leaf-margin hair cells of the May apple ( Podophyllum peltatum L.) leaves over a 42-day period (after leaves emerged above the ground litter). These indices decreased in a highly correlated manner. A ploidy variation may exist between epidermal cells and leaf-margin hair cells. Using the leaf-margin hair cells model, six nuclear macromolecule indices (total nucleic acid, DNA, RNA, total nuclear protein, histone and non-histone protein), nuclear volume, nucleolar volume and perinucleolar volume (measured using quantitative epifluorescence-phase contrast microscopy) all declined with age (42-day study) in a highly correlated manner. The degeneration of the nucleus and nucleolus in the three leaf locations studied followed the patterns observed for programmed cellular senescence and death (necrosis) in epidermal cells of onion leaf bases (stored tissue; leaf bases did not contain chlorophyll) and human epithelial cells (buccal; cervical). We conclude that the epidermal cells and leaf-margin hair cells from green leaves of the May Apple are ideal for the study of programmed cell senescence and death in plants, especially for the partitioning of this process into the study of: the point-of-no-return (solubilization of the karyoskeleton and loss of non-histone proteins and RNA associated with the karyoskeleton from the nucleus); nuclear pycnosis (loss of nuclear dry mass and volume and loss of nuclear internal support structure); chromatin condensation, margination along the inner nuclear envelope; and DNA-histone degeneration; degeneration of the nucleolus and loss of the perinucleolar zone of exclusion. The characterization of chlorenchyma cells during the 42-day period should now be undertaken (leaf senescence as indicated by the beginning of yellowing about 35 days after emergence) to determine whether these cells with functional chloroplasts undergo nuclear changes like those lacking functional chloroplasts.

Mammary sensitivity to protein restriction and re-alimentation.

The present study tested the influence of protein undernutrition and re-alimentation on mammary gland size and secretory cell activity in lactating rats. During gestation, female Sprague-Dawley rats were offered a high-protein diet (215 g crude protein (N x 6.25; CP)/kg DM; H); litters were standardized to twelve pups at parturition. During lactation, two diets were offered ad libitum, diet H and a low-protein diet (90 g CP/kg DM; L). Lactational dietary treatments were the supply ad libitum of either diet H (HHH) or diet L (LLL) for the first 12 d of lactation, or diet L transferring to diet H on either day 6 (LHH) or 9 (LLH) of lactation. On days 1, 6, 9 and 12 of lactation, rats from each group (n > or = 6) were used to estimate mammary dry mass, fat, protein, DNA and RNA; the activities of lactose synthetase (EC 2.4.1.22) enzyme and Na+,K(+)-ATPase (EC 3.6.1.37) were also measured. Rats offered a diet considered protein sufficient (H) from day 1 of lactation showed a decrease in mammary dry mass and fat but an increase in DNA, RNA and protein on day 6, after which there was no further change, except for mammary protein which continued to increase. However, rats offered diet L showed a steady loss in mammary mass and fat throughout the 12 d lactation period and no change in mammary DNA, RNA or protein. Rats previously protein restricted for either the first 6 or 9 d of lactation had their mammary dry mass and mammary fat loss halted and showed a rapid increase in mammary DNA, RNA and protein on re-alimentation. Lactose production in group HHH, as measured by lactose synthetase activity, was similar on days 1 and 6 of lactation, after which a significant increase was seen. Protein-restricted rats showed no change in lactose synthetase activity during the 12 d experimental period. Changing from diet L to diet H led to a significant increase in lactose synthetase activity to levels comparable with those offered diet H from day 1. These results show that rats offered a protein-restricted diet during lactation suffer mammary underdevelopment, but this may be rapidly reversed by re-alimentation with a high-protein diet.

Species diversity of freshwater hyphomycetes in some streams of Pakistan. III. Autumnal colonization of freshwater hyphomycetes on bait leaves

Significantly more species of freshwater hyphomycetes colonized bait leaves of alder (16 species) and willow (14 species) during early submersion period (1 wk) than those of oak (8 species). Production of conidia was also higher on alder and willow leaves than on oak leaves. Higher amounts of dry mass were lost from the alder (28.6%) and willow leaves (29.4%) than from the oak leaves (18.7%). Rapid loss of dry mass was accompanied by rapid development of a fungal community. Fungal species took a longer time (6 wk) to reach their peak of occurrence on oak than on willow and alder leaves (3–4 wk).Flagellospora curvula dominated the assemblages of freshwater hyphomycetes on alder and willow leaves, andLunulospora curvula dominated the assemblage on oak leaves. The freshwater hyphomycete community showed higher values of species diversity (H value) on oak leaves than on alder and willow leaves.

Pigment Accumulation, Dark Respiration and Photosynthesis during the Greening of Sunflower Cotyledons

Summary Sunflower seedlings ( Helianthus annuus L.) were grown in darkness or irradiated with continuous white light (WL) of medium intensity (100 micromole quanta per square meter per second). During the first 6 days after sowing, seedling development was accompanied by a significant loss in dry mass. In cotyledons of etiolated seedlings the carotenoid lutein is the dominant pigment that causes the yellow colour of the organs. In WL, a large increase in the rate of carotenoid accumulation occurred. Synthesis of chlorophylls a and b was induced rapidly upon exposure to WL. In etiolated cotyledons the rate of oxygen uptake (dark respiration) increased until day 3 after sowing, and thereafter declined. In WL, a stimulation of dark respiration was measured. The rate of photosynthetic oxygen evolution of lightgrown cotyledons was positively correlated with the chlorophyll content of the organ (r = 0.96). It follows that chlorophyll biosynthesis is one of the limiting factors that determines the rate of photosynthesis during de-etiolation of the seedling. However, oxygen evolution was significantly lower than the rate of dark respiration. Our results indicate that the green, de-etiolated cotyledons of the sunflower seedling are still heterotrophic organs.

Polyamine Mediated Modifications of Bean Leaf Response to Nitrogen Dioxide

Summary This study of exogenous polyamine effects on NO 2 sensitivity of bean was designed to elucidate relationships between spermine and spermidine, NO 2 exposure and nitrogen nutrition, and their effects on leaves at different physiological stages. Green bean ( Phaseolus vulgaris L. cv. Kinghorn Wax) seedlings were raised on nutrient solution without nitrogen either in the dark for 7 d or in a 14-h photoperiod for 14 d. The plants were then treated with nutrient solution containign 0 or 5 mM nitrate as nitrogen source and 100 μM spermine or spermidine with our without nitrate, and exposed to 0.3 μLL -1 NO 2 for 3 d in a 14 h photoperiod. Protective effects against NO 2 -induced loss of leaf dry mass were demonstrated in greening leaves on plants treated with a combination of nitrate and spermidine, in secondary leaves on plants given either polyamine with or without nitrate, and in senescing primary leaves on plants treated with nitrate and spermine or nitrate and spermidine. These protective effects could not be consistently related to differential levels of total chlorophyll or total organic nitrogen induced by the treatments. It is suggested that polyamines applied to plants supplied with nitrate are able to ameliorate the injurious effects of NO 2 on growth by restricting NO 2 conversion to injurious products, and/ or protecting tissues from injurious products.

Processing and Macroinvertebrate Colonization of Black Cherry (Prunus serotina) Leaves in Two Streams Differing in Summer Biota, Thermal Regime and Riparian Vegetation

-The processing of black cherry (Prunus serotina) leaf packs was studied during the summer of 1992 in two streams, Linesville Creek (LC) and Powdermill Run (PMR). The streams differed considerably in: (1) summer macroinvertebrate (shredder) fauna; (2) thermal regime, and (3) streamside riparian flora. Except for one species (Brilliaflavifrons), LC lacked shredders, whereas PMR supported numerous shredder populations during the summer months. Fastand medium-processed leaf material dominated the LC riparian zone whereas slow-processed leaf material was nearly absent. In contrast, the PMR riparian assemblage was well-represented in each processing category. Leaf packs were processed, as loss of dry mass, in near-equal rates using either days or degree-days as an independent variable. Gathering-collectors (e.g., Polypedilum spp.) and shredders (Tallaperla maria) dominated macroinvertebrate abundance and biomass colonizing the LC and PMR packs, respectively. Our results suggest that: (1) gathering-collectors (e.g., Polypedilum spp.) may compensate for the reduced abundance of shredding detritivores in processing of summer leaf detritus and (2) the absence of slow-processed riparian foliage in small woodland streams (e.g., LC) may prevent the establishment of a spring-summer shredder fauna.

A Leaf-Toughness Method for Directly Measuring the Processing of Naturally Entrained Leaf Detritus in Streams

The leaf pack method has been used extensively as the standard protocol for tracking the in-stream processing of leaf detritus. However, a major deficiency of the method has been that it does not directly measure the processed condition of natural, multispecies accumulations of leaves. The method reported here allows mass loss of leaf detritus to be related to leaf toughness. Studies of dry-mass loss and leaf toughness of black cherry (Prunus serotina) leaves were conducted in summer 1992 in Linesville Creek and Powdermill Run (Pennsylvania, USA), and during fall/winter 1992-1993 in Powdermill Run. Leaf toughness was measured with a digital force-gauge penetrometer. Penetrometer measurements determined the peak force (nearest 0.001 Newton) necessary to drive a steel rod through the leaf tissue. In all studies, dry mass loss was best explained by a linear regression model and leaf toughness loss by a negative exponential regression model. The natural logarithm of mean toughness per leaf pack predicted perc...

Effects of Photoperiod History and Temperature on Male Collared Lemmings, Dicrostonyx groenlandicus

Adult collared lemmings, Dicrostonyx groenlandicus (87 days of age), transferred from long (20L:4D) to short (8L:16D) photoperiod showed an increase in body mass, while those transferred from 8L:16D to 20L:4D showed a decrease in body mass. Exposure to short photoperiod resulted in an increase in length of body relative to exposure to long photoperiod. Temperature affected body mass only under 20L:4D with animals housed at 5°C being significantly heavier than lemmings housed at 18°C. Temperature did not affect length of body. Changes in body mass in response to photoperiod exposure primarily were due to the deposition or loss of fat-free dry mass and water. The mass of the reproductive organs (testes and seminal vesicles) was significantly increased in lemmings maintained at 5°C relative to animals house at 18°C. Mass of reproductive organs at 87 days of age was not affected by the photoperiod experienced during the subadult stage. However, at 167 days of age, lemmings originally housed under 8L:16D conditions (from weaning to 87 days of age) had significantly heavier mass of reproductive organs than did lemmings maintained on 20L: 4D from weaning to 87 days of age, regardless of secondary photoperiod exposure (87–167 days of age). Photoperiod conditions seen early in life may have long-term effects on mass of reproductive tissues in this species.

The feeding behaviour of the red mangrove crabSesarma meinertiDe Man, 1887 (Crustacea: Decapoda: Grapsidae) and its effect on the degradation of mangrove leaf litter

Feeding of Sesarma meinerti de Man was studied in the laboratory and at the Beachwood Mangrove Reserve. In the field, mangrove leaf litter formed 74,6% of the diet. Crabs showed a preference for leaves in the order: yellow Bruguiera gymnorrhiza (L.) Lam. > yellow Avicennia marina (Forssk.) Vierh. > green B. gymnorrhiza > green A. marina. In the laboratory, a positive correlation was observed between relative consumption and degree of decomposition. Crabs fed with both tannin and tannin-free leaves showed a preference for the latter. Removal of B. gymnorrhiza leaves by S. meinerti was high throughout the year, whereas dry mass loss attributable to consumption varied according to season. It is suggested that S. meinerti plays an important role in the degradation of mangrove leaf litter.

Abiotic and microbial decomposition of pre- and post-bloom leaves of water hyacinth (Eichhornia crassipes (mart.) Solms)

Rates of abiotic and microbial decomposition in pre- and post-bloom leaves of water hyacinth are determined under laboratory conditions. Decomposition in all types of hyacinth leaves is dominated by physical leaching in an initial phase of 4 days duration, and later by microbial processes. The largest part of physical leaching takes place within the first 4 h. Thereafter, the weight loss due to physical leaching declines exponentially. The weight loss by microbial decomposition is minimal in the initial phase but increases exponentially in the later phase. Pre-bloom leaves decompose significantly faster than post-bloom leaves, and post-bloom green leaves decompose faster than post-bloom brown leaves. The rate constants of abiotic decomposition are significantly higher in post-bloom leaves as compared with pre-bloom leaves, while microbial decomposition is significantly higher in pre-bloom leaves. After 30 days, the dry mass loss by abiotic and microbial decomposition is 15% and 55%, respectively, in pre-bloom leaves, 33% and 19% in post-bloom green leaves, and 24% and 6% in post-bloom brown leaves.

Leaching losses during decomposition of mangrove leaf litter

Two experiments were conducted in the laboratory to determine leaching losses from submerged mangrove leaves: the first, on freshly-picked and air-dried senescent Avicennia marina (Forrsk.) Vierh. leaves submerged in water of different salinities (16 and 32‰) for up to 14 days; the second, on freshly-picked senescent leaves of A. marina and Bruguiera gymnorrhiza (L.) Lam. submerged in water of 16‰ for up to 7 days. In both experiments, loss of dry mass and changes in nitrogen, phosphorus, potassium and tannins of the leaves were monitored. In the initial experiment there was a mean loss in dry mass of 24.6% after 14 days. The chemical analyses revealed that, although there was no significant decline in nitrogen concentration, there were sharp decreases in the other constituents. The greatest total loss relative to the amount initially present in the litter was in potassium (83 – 95%), while the losses for phosphorus and tannins were 57 – 87% and 74 – 85%, respectively. In general, losses were greater at 16‰ than at 32‰, and air-dried leaves showed greater initial losses than fresh leaves. In the second experiment, trends in leaching losses of both species were similar to those of the first experiment. With the exception of nitrogen, the concentrations of phosphorus and potassium (expressed as percentage oven-dry mass) had decreased significantly after 6 h in both species, while the concentrations of tannins showed a significant decrease only after 24 and 48 h in A. marina and B. gymnorrhiza, respectively. This work has confirmed that significant losses take place in the leaf litter as a result of leaching. It is suggested that those losses could have important consequences for the estuarine ecosystem. Twee eksperimente is in die laboratorium uitgevoer om die logingsverliese uit ondergedompelde manglietblare te bepaal: die eerste, op varsgeplukte en luggedroogde verouderende blare van Avicennia marina (Forssk.) Vierh. wat tot 14 dae lank in water van verskillende soutgehaltes (16 en 32‰) gedompel was; die tweede, op varsgeplukte verouderende blare van A. marina en Bruguiera gymnorrhiza (L.) Lam. wat tot 7 dae lank in water met ‘n soutgehalte van 16‰ gedompel was. Die verlies aan droë massa en veranderings in stikstof, fosfor, kalium en tanniene van die blare is in albei eksperimente gemonitor. In die eerste eksperiment was daar na 14 dae ‘n gemiddelde verlies van 24% aan droë massa. Die chemiese ontledings het getoon dat hoewel daar geen betekenisvolle afname in stikstofpersentasies was nie, van die ander bestanddele skerp gedaal het. Die grootste totale verlies met betrekking tot die hoeveelheid wat aanvanklik in die afval teenwoordig was, was aan kalium (83 – 95%), terwyl die verliese vir fosfor en tanniene onderskeidelik 57 – 87% en 74 – 85% was. In die algemeen was die verliese groter by 16‰ as by 32‰ soutgehalte, en luggedroogde blare het groter aanvanklike verliese as vars blare getoon. In die tweede eksperiment was die neigings in logingsverliese by albei spesies soortgelyk aan die van die eerste eksperiment. Met doe uitsondering van stikstof, wat nie betekenisvolle verskille getoon het nie, het die konsentrasies van fosfor en kalium (uitgedruk as persentasie oondgedroogde massa) na 6 h betekenisvol afgeneem by albei spesies, terwyl die tannienkonsentrasies slegs na 24 h en 48 h by A. marina en B. gymnorrhiza, onderskeidelik, ‘n betekenisvolle afname getoon het. Hierdie werk bevestig dat betekenisvolle verliese as gevolg van loging in die blaarafval plaasvind. Hierdie verliese kan moontlik belangrike gevolge vir die ekosisteem van die riviermonding hê.

Potential Carbon Losses From Peat Profiles: Effects of Temperature, Drought Cycles, and Fire.

Global warming and the resultant increase in evapotranspiration might lead to lowered water tables in peatlands and an increase in fire frequency. The objective of this study was to investigate some of the potential effects of these changes on peat decomposition. Dry mass losses and emissions of CO2 and CH4 from peat samples taken from three depth layers (0-10, 10-20, and 30-40 cm) of a black spruce peatland were measured in the laboratory at 8°, 16°, and 24°C under two moisture treatments. Effects of deep peat fire on decomposition were also simulated by burning the upper layer (0-10 cm) of peat and adding the ash to peat samples from the 10-20 cm layer. CH4 release averaged <1% of total carbon loss in flooded samples. Release of CO2 was 4-9 times greater from the 0-10 cm layer than from the 30-40 cm layer. After 120 d, the 30-40 cm layer had lost <1% of its original dry mass in all treatments. Higher temperatures strongly promoted decomposition of samples exposed to drying cycles but had little effect on decomposition of continuously flooded samples. Ash addition had variable effects on CO2 emissions but may have promoted CH4 production. It is suggested that in certain situations, global warming may not cause appreciable increases in carbon loss from peat deposits. The results indicate that some deeper peats are resistant to decay even when exposed to warm, aerobic conditions. However, further experimental work is needed to predict the long-term response of peat deposits to changes in water levels in different peatland types.

Relative contribution of different decay processes to the decomposition of Eichhornia crassipes (Mart.) solms

The relative contribution of different decay processes were determined for Eichhornia crassipes (Mart.) solms. The dry weight loss in the initial 4 days of decay was solely due to non-microbial processes and thereafter, the contribution of microbial processes increased and that of non-microbial processes decreased exponentially. The green litter recorded significantly higher raye constants of non-microbial and microbial decay than the brown litter. In 30 days of decay, the dry mass loss due to physical, autolytic and microbial leachings was 27%, 5% and 20%, respectively, in the green litter, and 18%, 2% and 7% respectively, in the brown litter. The non-microbial decomposition solely caused 31–33% dry mass loss in the E. crassipes litter.

Energetics of early development for the sea urchinsStrongylocentrotus purpuratus andLytechinus pictus and the crustaceanArtemia sp.

Embryos and larvae of two species of sea urchin,Strongylocentrotus purpuratus andLytechinus pictus, and larvae of the brine shrimpArtemia sp. (San Francisco brand) were cultured to investigate the contribution of dissolved organic material in seawater to the energetics of early development. When embroys ofS. purpuratus were reared in artificial seawater, a net loss in dry organic mass was observed. In contrast, when sibling embryos were reared to Day 2 under identical conditions in natural seawater, there was either a net increase in dry organic mass or no change. A net decrease in mass was observed in only one of five cultures reared in filtered natural seawater. Energy budgets for each species were determined by giving energy equivalents to the changes in carbohydrate, lipid and protein, and to the rate of oxygen consumption for each day of development. In the case ofS. purpuratus, the use of endogenous reserves accounted for either 0 or 38% of the metabolic demand for two independent cultures reared from Days 0 to 2. For larvae ofL. pictus, reared to 8 d, only 66% of the metabolic demand could be accounted for by the use of endogenous reserves. Sea urchins are capable of transporting dissolved organic material from seawater. Calculations revealed that the energy deficit during the early development of sea urchins (S. purpuratus) could be accounted for by the uptake of dissolved organic matter from seawater. However, for a species that cannot use this resource (Artemia sp.), the metabolic needs during development are supplied through the use of endogenous reserves.

Effect of Dikegulac Sodium on Water Stress-induced Changes in Vigna sinensis (L.) Walp.

Summary Imposition of water deficit stress by withholding watering in the field, increased water saturation deficit (WSD), reduced leaf water potential (Ψ L), enhanced conductivity of tissue effusates, increased proline level and decreased the levels of chlorophyll and protein in Vigna sinensis (L.) Walp. cv. Pusa Phalguni. Feeding of 0.5 g 1-1 dikegulac sodium through the roots, followed by folliar spraying of 15days old seedling (twice at an interval of 15 d), prevented loss of shoot and root dry mass but increased root: shoot ratio of water stressed Vigna plants. This treatment also caused stunted growth by shortening internodes and also increased the number of xylem elements in stressed plants. Improved water status, as increased by WSD and ΨL, decreased conductivity of tissue effusates, increased levels of chlorophyll and protein and reduced accumulation of proline in DK-treated stressed Vigna plants, suggest that DK is a potentially useful hardening agent against water deficit stress.

Degenerative changes in the epidermal cell wall of Allium cepa caused by Botrytis allii: Loss of dry mass, pectin, and cellulose in halos

Halos detected using interference microscopy (even- and fringle-field modes with monoand poly-chromatic light) around penetration sites of Botrytis allii in cell walls of normal and protoplast-free outer epidermal tissue of white, yellow, and red onions were alike. Halos in protoplast-free cell walls contained 33% less dry mass than areas of these walls adjacent to halos (quantitative interference miscroscopy with 546 nm light in the even-field mode). Halos were significantly larger in the white onion than in the yellow and red varieties. The loss of cell wall dry mass during the production of halos involved the loss of pectin and cellulose. We infer that this is caused by enzymes released from the pathogen. Cuticle degradation at penetration sites was not observed.

Phenology of stranded kelp degradation by the kelp fly Paractora dreuxi mirabilis (Helcomyzidae) at Marion island

During heavy seas, bull-kelp Durvillaea antarctica (Cham.) Har. plants are stranded either singly or in wrack beds on sub-Antarctic Marion Island's (46°54′S, 37°45′E) few pebbled beaches. In the supralittoral zone, Durvillaea wrack is consumed chiefly by kelp fly larvae (the endemic Paractora dreuxi mirabilis Seguy), whilst two marine amphipods attack wrack in the eulittoral and sometimes in the supralittoral zone. During the summer of 1984 on Marion Island, artificial Durvillaea deposits were established in the supralittoral zone of a beach close to the meteorological station and were closely monitored for six weeks thereafter. Eight days after deposition, temperatures inside the protected wrack bed reached 10°C above ambient, and P. dreuxi larvae attained a maximum biomass of 27 g/kg (dry mass) of kelp in the bed. After 30 days, wrack strings and a protected wrack bed had lost 80 and 65%, respectively, of their original dry mass. A bed left exposed to trampling by seals had disappeared. Over 30 days, P. dreuxi larvae accounted for 35% of the dry mass loss in the wrack bed. P. dreuxi has an opportunistic and flexible ecological strategy, facilitated by a stable, interstitial biotope of particulate kelp detritus from which it colonizes fresh wrack.

Food chemical analysis of tempeh prepared from South African-grown soybeans

Tempeh was prepared from locally grown soybeans of the cultivars Hutton and Prima, using the mould strain Rhizopus oligosporus NRRL 2549. The purpose of this food chemical study was to investigate the nutritionally beneficial changes which are brought about during fermentation, pending the probable introduction of the product to the South African market. Tempeh, fermented for 24, 48 and 72 h, together with unfermented controls and whole soybeans, were analysed for the proximate composition, phytic acid, specific carbohydrate materials including starch, mono- and oligosaccharides, minerals, thiamine, riboflavin and nicotinic acid; losses in dry mass occurring during fermentation were determined for tempeh made from Prima soybeans. Processing of soybeans into tempeh brought about favourable nutritional changes including reduction in the levels of phytic acid, starch and the flatulence-causing oligosaccharides stachyose and raffinose; whereas thiamine concentrations were reduced, riboflavin and nicotinic acid contents increased during fermentation. Brief comment is made on toxicological investigations concerning R. oligosporus. Tempeh was found to be an acceptable product that could be employed to promote greater utilisation of soybeans for human consumption in this country.

The influence of invertebrates on the breakdown ofPotamogeton pectinatus L. in a coastal marina (Zandvlei, South Africa)

The influence of invertebrates upon the decomposition ofPotamogeton pectinatus L. in a coastal Marina system was examined over 112 days using litter bags. Invertebrate inclusion bags (2 mm mesh, 5 mm holes) registered a dry mass loss of 1% d−1, while exclusion litter bags (80 µm mesh) produced a 0.4% mass loss d−1 (a 2.5 fold difference). Losses of ash and N from inclusion bags were greater than those from exclusion bags (p < 0.05). There was a three fold difference between the two treatments in the time taken for litter to breakdown to half the initial stock: T1/2 for inclusion bags = 43 d, exclusion bags = 130 d. In both treatments, minerals showed an expected rapid loss, due to leaching, with a subsequent slow increase relative to the dry material remaining. A total of nine invertebrate taxa was recorded from inclusion bags, with a peak biomass of 64 mg g−1 dry massPotamogeton bag−1 reached at 64 days after immersion. Grazing amphipods,Melita zeylanica Stebbing andAustrochiltonia subtenuis (Barnard), numerically dominated the litter bag fauna, whileM. zeylanica and nymphs of the zygopteran predatorIschnura senegalensis (Rambur) formed most of the biomass. Scanning Electron Microscopy indicated heavy grazing of micro-organisms by invertebrates, with major qualitative differences occurring 112 days after immersion. Invertebrates significantly accelerated the rate of litter breakdown through their feeding activities, assisting fragmentation and thus contributing to plant losses and also by increasing the surface area for microbial colonisation and attack.