Net Biomass Loss Research Articles

Inhibition limits by undissociated acids in mixed culture fermentation and strategies to elevate process capacity

Using high substrate concentrations in mixed culture fermentation increases the products concentration achieved, making more cost-effective and sustainable its subsequent extraction. However, elevated levels of organic acids also result in inhibition by undissociated acids. This study investigates the concentration limits of undissociated acids that inhibit a lab-scale mixed culture carbohydrate fermenter operated under constant conditions (pH 5.4; HRT 20 h; 30 °C). Under these conditions, the conversion capacity was consistently inhibited at undissociated acids concentrations above 24.9 mM and substrate concentrations over 18.5 gCOD LFeed−1. This is attributed to the high maintenance costs incurred to maintain cell homeostasis at neutral intracellular pH in the presence of acids. This inhibition leads to lower yields and net biomass loss from the system, resulting in incomplete glucose conversion. Operating at a higher pH of 6 and utilizing granules proved to be effective strategies for expanding the conversion capacity.

Net loss of biomass predicted for tropical biomes in a changing climate

Net loss of biomass predicted for tropical biomes in a changing climate

On the ecology of Cystophora spp. forests.

Cystophora is the second largest genus of fucoids worldwide and, like many other forest-forming macroalgae, is increasingly threatened by a range of anthropogenic impacts including ocean warming. Yet, limited ecological information is available from the warm portion of their range (SW Western Australia), where severe range contractions are predicted to occur. Here, we provide the first insights on the abundance, diversity, productivity, and stand structure of Cystophora forests in this region. Forests were ubiquitous over more than 800 km of coastline and dominated sheltered and moderately-exposed reefs. Stand biomass and productivity were similar or greater than that of kelp forests in the temperate reef communities examined, suggesting that Cystophora spp. play a similarly important ecological role. The stand structure of Cystophora forests was, however, different than those of kelp forests, with most stands featuring an abundant bank of sub-canopy juveniles and only a few plants forming the canopy layer. Stand productivity followed an opposite seasonal pattern than that of kelps, with maximal growth in late autumn through early winter and net biomass loss in summer. Annually, stands contributed between 2.2 and 5.7 kg · m-2 (fresh biomass) to reef productivity depending on the dominant stand species. We propose that Cystophora forests play an important and unique role in supporting subtidal temperate diversity and productivity throughout temperate Australia, and urge a better understanding of their ecology and responses to anthropogenic threats.

Massive loss and microbial decomposition in reproductive biomass of Zosteramarina

The biomass of Zostera marina in the temperate coastal zone has seasonal variations in their dry weight, with a peak during the spring season when a large section of the shoots develops reproductive organs. However, the period of high biomass is only short-term, after which large numbers of reproductive shoots drastically disappeared. Dislodgement is an important fate of the reproductive biomass. The fraction of biomass that reaches the deep sea contributes to carbon sequestration, however the processes of dislodgement and transportation of reproductive shoots of Z. marina has been rarely studied. Here, based on a monitoring survey of two Z. marina meadows, we estimated the net loss of biomass, including their reproductive one. In addition, microbial decomposition was assessed by dark incubation to evaluate the fate of the dislodged biomass. The apparent loss of biomass from the Z. marina meadows in the “Declining Period”, defined with the most rapid decrease in biomass, accounted for 82–100% of the biomass at the initial time-point of this period. By subtracting the biomass production from the apparent loss, we calculated the net loss of biomass in the Declining Period, accounting for 14–81% of the annual production. Approximately half of the biomass loss in the Declining Period was attributed to reproductive biomass, suggesting that dislodgement of reproductive shoots is an important fate of photosynthetic products of Z. marina. The carbon to nitrogen (CN) ratio of the reproductive shoots was found to be significantly higher than that of vegetative shoots. Since nitrogenous materials are relatively labile, we expected a lower bioavailability of reproductive shoots. However, microbial decomposition did not reflect the CN ratio, probably due to the heterogeneity of nitrogenous materials and/or due to the contribution of carbohydrates consisting mostly of non-nitrogenous compounds.

Metabolic Responses of Subtropical Microplankton After a Simulated Deep-Water Upwelling Event Suggest a Possible Dominance of Mixotrophy Under Increasing CO2 Levels

In the autumn of 2014, nine large mesocosms were deployed in the oligotrophic subtropical North-Atlantic coastal waters off Gran Canaria (Spain). Their deployment was designed to address the acidification effects of CO2 levels from 400 to 1,400 μatm, on a plankton community experiencing upwelling of nutrient-rich deep water. Among other parameters, chlorophyll a (chl-a), potential respiration (Φ), and biomass in terms of particulate protein (B) were measured in the microplankton community (0.7–50.0 μm) during an oligotrophic phase (Phase I), a phytoplankton-bloom phase (Phase II), and a post-bloom phase (Phase III). Here, we explore the use of the Φ/chl-a ratio in monitoring shifts in the microplankton community composition and its metabolism. Φ/chl-a values below 2.5 μL O2 h−1 (μg chl-a)−1 indicated a community dominated by photoautotrophs. When Φ/chl-a ranged higher, between 2.5 and 7.0 μL O2 h−1 (μg chl-a)−1, it indicated a mixed community of phytoplankton, microzooplankton and heterotrophic prokaryotes. When Φ/chl-a rose above 7.0 μL O2 h−1 (μg chl-a)−1, it indicated a community where microzooplankton proliferated (>10.0 μL O2 h−1 (μg chl-a)−1), because heterotrophic dinoflagellates bloomed. The first derivative of B, as a function of time (dB/dt), indicates the rate of protein build-up when positive and the rate of protein loss, when negative. It revealed that the maximum increase in particulate protein (biomass) occurred between 1 and 2 days before the chl-a peak. A day after this peak, the trough revealed the maximum net biomass loss. This analysis did not detect significant changes in particulate protein, neither in Phase I nor in Phase III. Integral analysis of Φ, chl-a and B, over the duration of each phase, for each mesocosm, reflected a positive relationship between Φ and pCO2 during Phase II [α = 230·10−5 μL O2 h−1 L−1 (μatm CO2)−1 (phase-day)−1, R2 = 0.30] and between chl-a and pCO2 during Phase III [α = 100·10−5 μg chl-a L−1 (μ atmCO2)−1 (phase-day)−1, R2 = 0.84]. At the end of Phase II, a harmful algal species (HAS), Vicicitus globosus, bloomed in the high pCO2 mesocosms. In these mesocosms, microzooplankton did not proliferate, and chl-a retention time in the water column increased. In these V. globosus-disrupted communities, the Φ/chl-a ratio [4.1 ± 1.5 μL O2 h−1 (μg chl-a)−1] was more similar to the Φ/chl-a ratio in a mixed plankton community than to a photoautotroph-dominated one.

Extraction and milking of astaxanthin from Haematococcus pluvialis cultures

Natural astaxanthin can be recovered from Haematococcus pluvialis culture without any cell pre-treatment by using human-compatible solvents, and can be re-synthesized by cells if algae-compatible solvents are applied in a milking mode, avoiding a net biomass loss.

Consequence of litter removal on pedogenesis: A case study in Bachs and Irchel (Switzerland)

In forests, soils contain at least twice as much carbon than plants that mostly grow in the upper layers. Litter at the interface between soils and the atmosphere regulates a variety of biogeochemical cycles, which are important for both plants and soils and have possible implications for other environmental components. We have compared leachates collected during an incubation experiment on: a) two deciduous leaves; b) organic and mineral horizons; c) treated with litter removal (and untreated) plots, to assess the changes in the chemical composition of the litter layers and leachates during weathering and their influence on the underlying horizons. Two different types of broadleaves – beech and oak – become indistinguishable when they experience weathering. As a litter horizon is altered, it becomes more stable and loses fewer elements, both in gaseous and liquid forms. The annual removal of litter represents a net loss of biomass from the system. Nevertheless, the effect on soil in the medium term is not significant. Leaves and litter horizons were incubated in micro-lysimeters, leached, and characterised by different analytical approaches, from elementary analyses (dissolved organic carbon, CO2 production, nitrogen forms, UV absorptivity) to solid state NMR spectroscopy. The results reveal that the removal of the litter does not degrade the underlying soils, in direct contrast to what was thought to be the case previously. Moreover, it extends previous knowledge that litter removal promotes an increase in fulvic acid activity in underlying horizons. The results demonstrate how this human disturbance, if not combined with other degradation factors, could promote podzolisation. In a wider outlook, if managed properly (for example, by burying litter removed after its use in animal husbandry), even the repeated removal of forest biomass contribute not negatively to the genesis of these soils.

The effect of light and nutrient availability on growth, nitrogen, and pigment contents of Saccharina latissima (Phaeophyceae) grown in outdoor tanks, under natural variation of sunlight and temperature, during autumn and early winter in Denmark

Late summer harvest of cultivated Saccharina latissima, prior to seasonally determined negative length growth, is considered advantageous in North Atlantic waters to optimize biomass yields. We hypothesized that seasonal increase in tissue protein and pigments over autumn and early winter would counterbalance the loss of biomass, and increase the absolute harvestable amount of protein and pigments. The hypothesis was tested in a land-based, factorial-designed, pilot-scale experiment using whole algae individuals exposed to naturally relevant high or low availability of nutrients and light. The experiment was conducted during fall/early winter in Grenaa, Denmark, in outdoor tanks, exposed to ambient light and temperature variations. With high nutrient availability, the absolute harvestable amounts of nitrogen, fucoxanthin, and chlorophyll a increased by 50.1–60.1, 21.7–53.7, and 47.0–73.5 %, respectively, despite a loss of biomass of 16.2–18.7 %. Under low nutrient availability, there was a net loss of biomass (8.1–9.5 %), tissue nitrogen (10.7–44.1 %), and fucoxanthin (7.1–17.2 %), and a minor increase in chlorophyll a (2.5–22.8 %). Nutrient availability had a significant negative impact on the biomass growth, but a positive control on the tissue concentration of nitrogen, chlorophyll a, and fucoxanthin. Our results, from a land-based experiment, indicate that early winter harvest of S. latissima biomass grown under high nutrient availability in Denmark, fulfills a higher degree of nutrient bioremediation, and has an improved biomass quality in regards of increased concentrations of pigments and nitrogen rich compounds.

Feeding behavior and trophic relationship of earthworms and other predators in vermifiltration system for liquid-state sludge stabilization using fatty acid profiles

The sludge reduction capability (VSS reduction) of vermifilter (VF) was 14.7% higher than that of conventional biofilter (BF) due to the fact that there was a net loss of biomass and energy when the food web in VF is extended. Therefore, feeding behavior and trophic relationship of earthworms and other predators (leeches, lymnaeidaes and limaxes) in VF were investigated using fatty acid (FA) profiles for the first time. Compared with BF biofilm, microbial community structure of VF biofilm got optimized by earthworms that the percentage of protozoa increased from 14.2% to 20.4%. Furthermore, analysis of specific microbial FAs composition in each predator suggested different trophic level of predators resulted from their selective ingestion of different microorganisms, and earthworms were at the second high trophic level in VF food web. Overall findings indicated earthworms modified microbial community and extended the food web of VF and thus enhanced the sludge reduction.

The age of managed heathland communities: implications for carbon storage?

Shrublands are ecosystems vulnerable to climate changes, with key functions such as carbon storage likely to be affected. In dwarf shrublands dominated by Calluna vulgaris, the aboveground carbon allocation is associated with community age and phase of development. As the Calluna community grows older, a shift to net biomass loss occurs and it was hypothesized this would result in carbon stock increases within the soil. The interaction of community age with ecosystem carbon stocks was investigated through a chronosequence study on three Calluna communities, aged 11, 18 and 27 years. Aboveground Calluna carbon stock increased significantly from the 11 year community (0.73 kg C m−2) to the 18 year community (1.11 kg C m−2) but did not significantly change from 18 to 27 years (1.0 kg C m−2), indicating a net carbon gain that corresponded with the growth phase of the Calluna plants. Moss was also found to be a relatively large contributor to aboveground carbon stock (e.g. 30 % in the Young community). Moss has often been excluded in aboveground assessments on Calluna heathlands which may have led to previous stock underestimation. Belowground carbon stocks to 25 cm were six to nine times greater than in the aboveground pools. For example in the Young community, 8 % of the carbon stock was located aboveground, 35 % in the organic layer and 55 % in the mineral soil. Increased heathland age resulted in increased aboveground carbon stock until peak production was reached at approximately 18 years of age. However, the proportionally large belowground carbon stock eclipsed any aboveground effect when total carbon stocks were considered. The investigation emphasized both the importance of including the mineral soil in sampling programs and of consider all major species, such as bryophytes, and vegetation age in carbon stock assessments.

The ability of aquatic macrophytes to increase root porosity and radial oxygen loss determines their resistance to sediment anoxia

Radial oxygen loss (ROL) has been suggested to be a major process to protect plants exposed to root anaerobic stress. In the present study, we aimed to test the importance of root porosity and radial oxygen loss on the aquatic macrophyte resistance to sediment anoxia. We expected that species living in eutrophic environments characterized by anaerobic conditions in sediments exhibited higher root porosity and radial oxygen loss than species restrained to oligotrophic environments. In this way, we compared the responses to sediment anoxia of two hydrophyte species growing under meso-eutrophic conditions in the field (Myriophyllumspicatum L. and Vallisneriaspiralis L.) and three species growing under oligotrophic conditions (Potamogeton coloratus Horne, Elodeacanadensis Michx and Sparganiumemersum Michx.). Under laboratory conditions, ROL, root porosity, plant metabolism (aerobic respiration, photosynthesis, root fermentative activity) and plant growth were analysed after 3 months of acclimation in anaerobic sediments and compared with control values obtained from aerobic sediments. The results showed that two meso-eutrophic species (M. spicatum and V. spiralis) survived in anaerobic sediments and maintained similar photosynthesis rates than those measured under aerobic conditions. In contrast, the three oligotrophic species (P. coloratus, E. canadensis and S. emersum) suffered net biomass loss and depressed their photosynthesis rates under anaerobic conditions. All variables associated with plant tolerance to anaerobic conditions (maintenance of photosynthesis, aerobic respiration and growth rate, and limitation of root fermentative activity) were positively linked to root porosity and ROL. According to our hypothesis, species that could survive to anaerobic conditions were the species able to increase their root porosity and ROL under these conditions. Thus, in ecological studies, it would be useful to use the root porosity and ROL plasticity as biological traits in order to model the distribution of macrophytes in river floodplains.

Quantifying small‐scale deforestation and forest degradation in African woodlands using radar imagery

AbstractCarbon emissions from tropical land‐use change are a major uncertainty in the global carbon cycle. In African woodlands, small‐scale farming and the need for fuel are thought to be reducing vegetation carbon stocks, but quantification of these processes is hindered by the limitations of optical remote sensing and a lack of ground data. Here, we present a method for mapping vegetation carbon stocks and their changes over a 3‐year period in a > 1000 km2 region in central Mozambique at 0.06 ha resolution. L‐band synthetic aperture radar imagery and an inventory of 96 plots are combined using regression and bootstrapping to generate biomass maps with known uncertainties. The resultant maps have sufficient accuracy to be capable of detecting changes in forest carbon stocks of as little as 12 MgC ha−1 over 3 years with 95% confidence. This allows characterization of biomass loss from deforestation and forest degradation at a new level of detail. Total aboveground biomass in the study area was reduced by 6.9 ± 4.6% over 3 years: from 2.13 ± 0.12 TgC in 2007 to 1.98 ± 0.11 TgC in 2010, a loss of 0.15 ± 0.10 TgC. Degradation probably contributed 67% (96.9 ± 91.0 GgC) of the net loss of biomass, but is associated with high uncertainty. The detailed mapping of carbon stock changes quantifies the nature of small‐scale farming. New clearances were on average small (median 0.2 ha) and were often additions to already cleared land. Deforestation events reduced biomass from 33.5 to 11.9 MgC ha−1 on average. Contrary to expectations, we did not find evidence that clearances were targeted towards areas of high biomass. Our method is scalable and suitable for monitoring land cover change and vegetation carbon stocks in woodland ecosystems, and can support policy approaches towards reducing emissions from deforestation and degradation (REDD).

Arboreal forage lichens in partial cuts – a synthesis of research results from British Columbia, Canada

The mountain ecotype of the woodland caribou (Rangifer tarandus caribou) is highly dependent on the arboreal hair lichens Bryoria spp. and Alectoria sarmentosa during winter. In parts of British Columbia, partial-cutting silvicultural systems have been used in an effort to provide continuously usable winter habitat for mountain caribou, while allowing some timber removal. We reviewed available information about the changes in hair lichens after partial cutting in Engelmann spruce (Picea engelmannii) – subalpine fir (Abies lasiocarpa) forests of British Columbian and Idaho. Generally, abundance of Bryoria spp. in the lower canopy of individual residual trees increases with increased exposure after partial cutting, until the new regeneration begins to shelter the lower canopy of the residuals. Heavy basal area removal, however, results in low lichen availability at the stand level for many years. Abundance of Bryoria on the regeneration is low, and appears to be limited largely by the structure of the young trees, not by lichen dispersal, although dispersal capability may be limiting in Alectoria. Both distributional and physiological data suggest that Bryoria is intolerant of prolonged wetting, and that increased ventilation, rather than increased light, accounts for enhanced Bryoria abundance in the partial cuts. Alectoria sarmentosa reaches its physiological optimum in the lower canopy of unharvested stands; its growth rates are somewhat reduced in the more exposed environment of partial cuts. Both genera are capable of rapid growth: over a 7-year period, individual thalli of A. sarmentosa and Bryoria spp. (excluding those with a net biomass loss due to fragmentation) in an unlogged stand more than tripled their biomass. Calculated growth rates, as well as dispersal potential, are influenced by fragmentation. Bryoria produces more abundant, but smaller, fragments than Alectoria, and fragmentation in both genera increases in partial cuts. In subalpine mountain caribou habitat, partial-cutting prescriptions that enhance exposure of residual trees while keeping basal area removal low will maintain forage best. Regeneration management should focus on maintaining ventilation in the lower canopy of the residual stand.

Growth and architecture of small honey mesquites under jackrabbit browsing: overcoming the disadvantage of being eaten.

Browsing is an important mortality factor in seedlings and small plants. However, the induced changes in the architecture of plant survivors may influence subsequent browsing, opening the possibility of compensating for the damage done. How jackrabbit (Lepus californicus) browsing affects the growth and architecture of small individuals of honey mesquite, Prosopis glandulosa var. torreyana, a tree/shrub that produces spines at every node, was explored. Naturally established mesquites of unknown age were selected in one site, and 2-year-old mesquites were transplanted in another site. In both cases, half of them were exposed to jackrabbits and the other half were excluded as controls. After 4 years, shoot production (height, length and number of derived shoots) and plant growth (height and cover) increased 1.4-2.5-fold in naturally established controls relative to exposed plants, depending on the measured variable. In the transplant experiment, the increases were 2.8-7.1-fold in controls relative to exposed plants 2 years after initiation of the experiment. The net loss of biomass in treatment vs. control plants in these experiments suggests a negative response to browsing which has been defined as under-compensation. Alternative architectures in honey mesquites were evident at the end of the exclusion experiments: controls had long branches and an extended crown cover, while exposed plants had short branches and a compact crown cover. Results indicated that mesquites were able to grow under browser pressure by packing many stems in a compact matrix armed with spines and producing one or more shoots tall and wide enough to escape from jackrabbits.

Collembola populations in an organic crop rotation: Population dynamics and metabolism after conversion from clover-grass ley to spring barley

Summary Population dynamics of earthworms, enchytraeids, mites and collembolans were assessed over two years as part of a collaborative research project in an organic crop rotation at the agricultural Research Centre Foulum, Jutland, Denmark. The Collembola study presented here is restricted to the first growth season of a two-year study, i.e from just before conversion of a two year old clover-grass ley to seedbed until harvest of the barley crop. The results refer mostly to the four most abundant species. The project included experimental reductions of earthworm populations to test the effects on interactions between earthworms and mesofauna. Expulsion by electro-shocking resulted in modest reductions in earthworm density and biomass. No significant effect of the reduction was observed on the collembolan populations. Total collembolan density and density, mean weight per specimen, biomass and population metabolism of the four most abundant species decreased markedly between the first and second sampling date as an effect of the mechanical disturbance, and inversion of soil layers caused by soil preparation. The depth distribution for all Collembola species was inverted from highest concentration in the 0–10 cm layer to highest concentration in the 10–20 cm soil layer. After a population minimum in May, the density, mean weight, biomass and metabolism increased more or less regularly according to species. The net loss of biomass after conversion implied a mobilization of 5 mg N.m−2 from dead collembolan tissues. Together with an estimate for nitrogen due to excretion, the contribution of Collembola to nitrogen mobilization through the growth season was estimated tentatively as 10 mg.m−2. This amount was negligible compared with the contribution of earthworms. The possibility that indirect catalytic effects of collembolan activity could have any significant effect on nutrient availability for plants was not resolved but the collembolan population metabolism showed no obvious synchrony with the nutrient requirements of the crop.

Changes in sea-ice phagotrophic microprotists (20–200 μm) during the spring algal bloom, Canadian Arctic Archipelago

Heterotrophic microflagellates and ciliates (i.e., 20–200 μm size fraction) were examined for evidence of their response to the spring accumulation of algal biomass in the bottom of the annual sea ice in Resolute Passage (Canadian High Arctic, 74°N, 95°W). The most abundant heterotrophic microflagellates were dinoflagellates in the water column and cryothe-comonad-type cells in the ice. Ciliates were exclusively represented by typical planktonic species in the water column while the ice community was characterized by the occurrence of benthic-type species. This contrasts with observations in the Antarctic and at the southern limit of sea ice in the northern hemisphere, where annual sea ice seems to serve as a temporary habitat for planktonic communities. Protist biomasses in Resolute Passage were one to two orders of magnitude higher in the ice than in the plankton. In the ice, a seasonal increase in the biomass of phagotrophic microprotists as well as in the number of micrometazoa (from our microprotist samples) followed the spring algal bloom. These observations (1) support previous suggestions of the existence of a functional microbial food web within sea-ice communities and (2) indicate that micrograzers may represent one of the basic levels of the ice food web that responds to the seasonal accumulation of algal biomass. Heterotrophic microprotists growing in the ice accumulated about 4 mg C m−2 d−1, a net production rate that is two to four times higher than those reported for sea-ice bacteria (both Arctic and Antarctic), and represented 1–9% of the net production of ice algea in the early season at resolute. A carbon budget exercise indicated that the required energy for microprotozoan growth in the later season, when algal biomass was declining, corresponded to 1–8% of the net biomass loss from the ice algal populations. The specific growth rates of microprotozoan populations within the ice (0.04–0.18 d−1) appeared to increase significantly with decreasing algal productivity. This may be critical for the protracted heterotrophic food web in multi-year ice and to many consumers during the long polar winter.

Sources of Energy for Increased Metabolic Demand During Metamorphosis of the Abalone Haliotis rufescens (Mollusca).

Pelagic, lecithotrophic (nonfeeding) larvae of the red abalone (Haliotis rufescens) settle and subsequently metamorphose into benthic juveniles capable of feeding on particulate food. Thus, metamorphosis must be fueled by either endogenous reserves or a nonparticulate food source such as dissolved organic material (DOM) in seawater. The metabolic rates (measured as oxygen consumption) of abalone larvae were found to increase by an average of 3- to 5-fold from the larva to early juvenile stage. The total cost of development from embryo to juvenile measured for three cultures ranged from 41.6 mJ to 55.0 mJ. Meeting this cost would require 1.3 to 1.7 {mu}g of biomass (ash-free dry mass), which is similar to the initial biomass of the spawned oocyte at 1.36 +/- 0.04 {mu}g (mean of four cultures). However, there was no net loss of biomass during development from the oocyte to the juvenile. The uptake of alanine and glucose from seawater by larvae and juveniles could provide one-third of the organic material required to supply metabolism, even if the transporters were only operating at 20% of their maximum capacity throughout development. For larvae undergoing metamorphosis (between 6- and 9-days-old) the proportion of total metabolic demand supplied using aerobically catabolized biomass was only 39%. The higher metabolic rates of metamorphosis are met only in part by consuming stored endogenous reserves. Concomitant with an increase in mass-specific metabolic rate during metamorphosis, the maximal capacity (Jmax) for the transport of dissolved alanine from seawater increased 3-fold, from 61.2 +/- 1.9 (SE) to 182.0 +/- 49 pmol alanine individual-1 h-1. The majority (range: 61% to 100%) of the energy requirements of larval and early juvenile development of H. rufescens could be supplied by input of DOM from the environment. Measurements of transport rates of amino acids and sugars by these animals, and calculations of the energy input from these substrates, indicate that the cumulative transport of DOM from seawater during development to the early juvenile stage could supply an amount of energy equivalent to the initial maternal endowment of energy reserves to the oocyte of this lecithotrophic species.

Reports of other scientific meetings

Population dynamics of earthworms, enchytraeids, mites and collembolans were assessed over two years as part of a collaborative research project in an organic crop rotation at the agricultural Research Centre Foulum, Jutland, Denmark. The Collembola study presented here is restricted to the first growth season of a two-year study, i.e from just before conversion of a two year old clover-grass ley to seedbed until harvest of the barley crop. The results refer mostly to the four most abundant species. The project included experimental reductions of earthworm populations to test the effects on interactions between earthworms and mesofauna. Expulsion by electro-shocking resulted in modest reductions in earthworm density and biomass. No significant effect of the reduction was observed on the collembolan populations. Total collembolan density and density, mean weight per specimen, biomass and population metabolism of the four most abundant species decreased markedly between the first and second sampling date as an effect of the mechanical disturbance, and inversion of soil layers caused by soil preparation. The depth distribution for all Collembola species was inverted from highest concentration in the 0–10 cm layer to highest concentration in the 10–20 cm soil layer. After a population minimum in May, the density, mean weight, biomass and metabolism increased more or less regularly according to species. The net loss of biomass after conversion implied a mobilization of 5 mg N.m−2 from dead collembolan tissues. Together with an estimate for nitrogen due to excretion, the contribution of Collembola to nitrogen mobilization through the growth season was estimated tentatively as 10 mg.m−2. This amount was negligible compared with the contribution of earthworms. The possibility that indirect catalytic effects of collembolan activity could have any significant effect on nutrient availability for plants was not resolved but the collembolan population metabolism showed no obvious synchrony with the nutrient requirements of the crop.

Encapsulated development of the marine prosobranch gastropod Nucella lapillus

Nucella (=Thais) lapillus (L.) develops to the juvenile stage within an egg capsule. This study was undertaken to investigate nutritive and bacteriostatic properties of the intracapsular fluid for this species. Capsules were collected intertidally at Nahant, Massachusetts, USA, in the summers of 1982 and 1983. The average capsule contained only 1.1 μl of intracapsular fluid per embryo. A statistically significant correlation was observed between capsule height and number of developing embryos contained therein, although the number of embryos per capsule was more closely related to capsule volume. Total dry weight of encapsulated, shelled embryos increased exponentially as a function of shell length. However, weight increases may be entirely due to shell calcification; the average dry tissue weight of shelled embryos was significantly below that for pre-shelled individuals, suggesting a net loss of biomass during development. Aliquots of intracapsular fluid failed to inhibit the growth of the 13 bacterial strains tested. Despite the above results, pre-shelled embryos generally survived only several days following their premature removal from egg capsules at 12°C. Shelled veligers were reared outside of the capsules with no apparent ill effects. An explanation for these survivorship results is elusive.