Drought impact on stream detritivores: experimental effects on leaf litter breakdown and life cycles

Predictions of effects of global climate change include decreased runoff for many parts of the world, which will result in drying of streams. Information of the effects of drought on aquatic ecosystems is limited and little is known of the effects on ecosystem functions. Our main objective was to measure the direct effects of drought on leaf litter breakdown by invertebrate shredders in a controlled laboratory experiment. We hypothesized a decreased breakdown at high drought level. Single-species and multi-species treatments with three shredder species (Asellus aquaticus, Limnephilus bipunctatus, and L. flavicornis) were set up in an experiment with three drought level treatments, control, medium, and high drought (6 cm water level, 1 cm water level, and water level below sediment surface, respectively). Breakdown measured as leaf litter loss was significantly lower in both medium and high drought treatments compared to the control. Previously, decreased breakdown due to drying has been reported, but attributed to low densities of invertebrate shredders. We show that even when shredders are present, drought decreases the breakdown. Drought treatments also induced earlier pupation for the caddisfly L. flavicornis. Shifts in species phenology due to drought, e.g., earlier emergence, may affect species ability to adult survival and reproduction. Shifts in timing of emergence may also affect terrestrial food webs, where emerging aquatic insects may constitute an important food subsidy. Our knowledge of the complex effects of droughts in aquatic systems is limited with an urgent need of extended knowledge of the ecological effects of droughts on freshwater ecosystem functioning.     

The role of litter in an old-field community: impact of litter quantity in different seasons on plant species richness and abundance

Summary We studied the effect of removing and adding plant litter in different seasons on biomass, density, and species richness in a Solidago dominated old-field community in New Jersey, USA. We removed all the naturally accumulated plant litter in November (658 g/m²) and in May (856 g/m²) and doubled the amount of litter in November and May in replicated plots (1 m²). An equal number of plots were left as controls. Litter removal and addition had little impact on total plant biomass or individual species biomass in the growing season following the manipulations. Litter removal, however, significantly increased plant densities but this varied depending upon the season of litter removal, species, and life history type. Specifically, the fall litter removal had a much greater impact than the spring litter removal suggesting that litter has its greatest impact after plant senescence in the fall and prior to major periods of early plant growth in spring. Annual species showed the greatest response, especially early in the growing season. Both spring and fall litter removal significantly increased species richness throughout the study. Litter additions in both spring and fall reduced both plant densities and species richness in June, but these differences disappeared near the end of the growing season in September. We concluded than in productive communities where litter accumulation may be substantial, litter may promote low species richness and plant density. This explanation does not invoke resource competition for the decline in species richness. Finally, we hypothesize that there may be broad thresholds of litter accumulation in different community types that may act to either increase or decrease plant yield and diversity.     

The effects of collembola grazing on microbial activity in decomposing leaf litter

Summary Ground leaf litter was inoculated with the fungus Coriolus versicolor and incubated in respirometers for 6 days (fresh cultures) or 33 days (senescent cultures) before different number of Folsomia candida were added. Grazing by 5 animals stimulated O₂ consumption in both series of cultures but 10, 15 or 20 animals inhibited microbial respiration. The stimulatory effect was less marked in the senescent cultures. Bacterial and fungal standing crops increased in fresh cultures during the course of the experiment but grazing by collembola increased bacterial and reduced fungal standing, crops in proportion to the grazing intensity. Microbial standing crops were not determined for senescent cultures. Microarthropod feeding activities can therefore exert a strong differential effect on fungal and bacterial populations which has not been previously recognised.     

山杨林地枯落物层对溅蚀的影响

天然降雨下３０年生山杨林内溅蚀试验结果表明,当Ｉ＿（３０）（最大３０分钟雨强）为０．０７６ｍｍ／ｍｉｎ或Ｐ＿ｏ（林内降雨量）为３．３ｍｍ时,清除枯落物层林地发生溅蚀,在Ｉ＿（３０）为０．３５ｍｍ／ｍｉｎ或Ｐ＿ｏ为２５．５６ｍｍ时具１ｃｍ枯落物层的林地不发生溅蚀;从溅蚀月动态看出７、８月份占全年溅蚀量的６０％以上;在同一土壤和坡度条件下,Ｉ＿（３０）、Ｐ＿ｏ、Ｈ＿１（枯落物层厚度）是溅蚀发生的主要因素,且溅蚀量（Ｓ＿ｔ）与其呈二次多项式回归关系,但当枯落物层具有一定厚度时溅蚀与其他因素无关。溅蚀主要发生在清除枯落物层的林下,随枯落物层厚度增加,溅蚀量剧减,当枯落物层积累到１ｃｍ时防止土壤溅蚀量达９７．５０％。     

Interacting effects of leaf litter species and macrofauna on decomposition in different litter environments

The leaf litter environment (single species versus mixed species), and interactions between litter diversity and macrofauna are thought to be important in influencing decomposition rates. However, the role of soil macrofauna in the breakdown of different species of leaf litter is poorly understood. In this study we examine the multiple biotic controls of decomposition – litter quality, soil macrofauna and litter environment and their interactions. The influence of soil macrofauna and litter environment on the decomposition of six deciduous tree species (Fraxinus excelsior L., Acer pseudoplatanus L., Acer campestre L., Corylus avellana L., Quercus robur L., Fagus sylvatica L.) was investigated in a temperate forest, Wytham Woods, Southern England. We used litterbags that selectively excluded macrofauna to assess the relative importance of macrofauna versus microbial, micro and mesofauna decomposition, and placed single species bags in either conspecific single species or mixed species litter environments. The study was designed to separate plant species composition effects on litter decomposition rates, allowing us to evaluate whether mixed species litter environments affect decomposition rates compared to single species litter environments, and if so whether the effects vary among litter species, over time, and with regard to the presence of soil macrofauna. All species had faster rates of decomposition when macrofauna were present, with 22–41% of the total mass loss attributed to macrofauna. Macrofauna were most important for easily decomposable species as soon as the leaves were placed on the ground, but were most important for recalcitrant species after nine months in the field. The mass loss rates did not differ between mixed and single species litter environments, indicating that observed differences between single species and mixed species litterbags in previous field studies are due to the direct contact of neighbouring species inside the litterbag rather than the litter environment in which they are placed.     

The use of in vitro procedures in teratology.

The capabilities of investigators in the fields of teratology and toxicology are greatly enhanced by the use of tissue culture procedures in unraveling the mechanisms of drug action. Techniques currently available for the culture of postimplantation mammalian embryos permit evaluation of their metabolic responses to potential teratogens even when the length of time embryos survive and develop in culture is too short to allow a conventional teratologic survey of malformations. A simple procedure for culturing mouse embryos during early organogenetic stages is described in this report that will be of value to teratologists; it avoids the requirements of special glassware and equipment by using ordinary capped test tubes which are rotated tomaintain and efficient nutritional and gaseous evnironment. Some studies concucted with this procedure to monitor the metabolism of embryo during the first 24 h of culture are summarized. Another aspect of tissue culture, organ culture, provides further manipulative capability by which embryonic organs can be maintained for long periods of time during which they develop and differentiate to an extent that their morphological and biochemical responses to a teratogen can usually be made. Comparative effects of several teratogenic agents and the relative concentration of each that produces a similar degree of response are summarized. It is concluded that organs are more sensitive to teratogens in culture than they are in vivo, and that different teratogens possess enough specificity to isolate their simple growth-retarding effect from the role they play in distrubing other specific developmental events.     

Potential impact of invasive amphipods on leaf litter recycling in aquatic ecosystems

The impact of biological invasions on local biodiversity is well established, but their impact on ecosystem functioning has only been sketchily documented. However, biological invasions may impede services provided by aquatic ecosystems, such as, for example, the decomposition of organic matter, a key process in most small streams. To address this question, we experimentally quantified the leaf litter breakdown activity of native and invasive amphipod species, which are keystone species in aquatic ecosystems. The breakdown rate of each species was used to estimate the potential leaf litter recycling in the Rhône and Meurthe Rivers in sites occupied solely by native species and sites dominated by invasive species. We found that invaders were not able to compensate for the activity of native species and that the replacement of native species led to a decrease of at least 66% in the rate of leaf litter recycling. Our approach provides empirical evidence of the functional impact of non-indigenous species on leaf litter recycling, using standard protocols and literature data.     

The effects of feeding broiler litter on microbial contamination of beef carcasses

Two experiments were conducted to test the effects of feeding broiler litter, either directly in the diet or indirectly through pasture-fertilization, to beef cattle on the incidence of Salmonella typhimurium (S) and Escherichia coli O157:H7 (EC) contamination of carcasses and ground beef. In Experiment 1, beef cows (n = 32) were allotted either ad libitum access to grass hay or a formulated diet (80% deep-stacked broiler litter and 20% corn). In Experiment 2, beef cows (n = 32) were assigned to graze on pastures fertilized with a commercial fertilizer or fresh broiler litter. Cows in Experiment 1 were harvested following a 56-d feeding period; whereas, cows in Experiment 2 were harvested after 5, 10, 20, and 40 d of grazing pastures. All samples of muscle, purge, and ground beef were culture-negative for S and EC, suggesting that beef cattle may consume properly handled deep-stacked broiler litter, or pastures fertilized with fresh litter, without increasing the likelihood of carcass/meat contamination with S and (or) EC.     

The effects of natural zeolite on salinity level of poultry litter compost

The aim of this study was to investigate the salinity uptake by natural zeolite when used as an ingredient during the composting process. The amounts of 5% and 10% of natural zeolite were applied to poultry litter as volume and compared with the compost made with no amendment. The results clearly showed that the salinity level of poultry litter was too high. It was found that the salinity level in the end compost decreases with increasing the amount of natural zeolite used. Salinity uptake efficiencies were 66.64% and 88.92% for end product containing 5% and 10% natural zeolite, respectively. Significantly, the addition of natural zeolite to poultry litter compost was found to have a beneficial effect on the characteristics of the end product.     

Fish farming impact on decomposition of Posidonia oceanica litter

Fish farming impact on decomposition and loss of carbon, nitrogen and phosphorus fixed in seagrass litter were studied in a Posidonia oceanica meadow (Aegean Sea, Greece) using in situ incubation of senescent seagrass leaves collected under (station: cages) and away (station: control) from fish cages and deployed in a cross design of origin/station. Decomposition rate and loss of carbon and nitrogen fixed in seagrass litter were pronounced under the cages while loss of phosphorus was less evident. Decomposition was related to nutrient availability in seagrass tissue and pore water, sediment organic matter and origin of seagrass litter. When incubated under the cages, litter originated from the control decomposed faster than litter originated from the cages since the former was qualitatively better substrate for decomposers and the nutrient conditions in that station were enriched in the pore water and sediment. The lower decomposition of litter originated from cages suggests that seagrass tissues under the cages accumulate chemical deterrents, possibly in order to confront high grazing pressure, which on the other hand reduces the rate of decomposition.     

Conspecific versus heterospecific litter effects on seedling establishment

Plant litter is an important determinant of seed germination and seedling establishment. Positive effects of litter have received considerable attention, but few studies have explicitly tested whether seedlings are more facilitated by conspecific litter compared to heterospecific litter. In order to contrast conspecific and heterospecific facilitative effects on seedling establishment, we used Anthriscus sylvestris, Angelica sylvestris, Pimpinella saxifraga and different combinations of their seeds and litter seedbeds as a model system. Although litter had a significant species-specific effect on seedling emergence, we found no evidence of strictly conspecific facilitation. Anthriscus sylvestris displayed a positive response to all types of litter. In contrast, there was a clear negative effect of conspecific litter in Pimpinella saxifraga. Activated carbon did not modify the negative effect, indicating that chemical compounds were not the cause. Our study suggests a high level of idiosyncrasy in response to litter at the species level.