The direct effects of UV-B radiation on Betula pubescens litter decomposing at four European field sites

A co-ordinated series of field experiments were conducted to consider the effects of elevated UV-B radiation applied directly to decomposing plant litter. Betula pubescens was decomposed under ambient and elevated UV-B (simulating a 15% ozone depletion) using outdoor irradiation facilities at Adventdalen, Norway (78° N), Abisko, Sweden (68° N), Amsterdam, The Netherlands (52° N,) and Patras, Greece (38° N). There was no significant effect of treatment on mass loss for samples collected after 2, 12 and 14 months decomposition at Amsterdam, or after 4 months decomposition at Adventdalen. Significant reductions in the mass loss of litter decomposing under elevated UV-B compared to ambient were found at the other 2 sites. The only effect of treatment on litter chemistry during decomposition was a significant reduction in the N concentration of material at Abisko and a significant increase in C:N at Patras for litter decomposing under elevated UV-B. Significant differences were found in the structure of the fungal community decomposing litter in Sweden, the only site to be tested. These data, and the few published studies of the response of decomposition to UV-B incident on litter suggest that, in the ecosystems and climates that have been studied, such direct effects are typically confined to the initial stages of decomposition, and are rather small in magnitude.     

Growth inhibitory activity of ABA-β-<Emphasis Type="SmallCaps">d</Emphasis>-glucopyranosyl ester and ABA-β-<Emphasis Type="SmallCaps">d</Emphasis>-glucosidase

Exogenously applied ABA-β-d-glucopyranosyl ester (ABA-GE) inhibited shoot growth of alfalfa (Medicago sativa L.), cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), Digitaria sanguinalis L., timothy (Pheleum pratense L.) and ryegrass (Lolium multiflorum Lam.) seedlings at concentrations greater than 0.1 μM. The growth inhibitory activity of ABA-GE on these shoots was 26–40% of that of (+)-ABA. ABA-β-d-glucosidase activities in these seedlings were 11–31 nmol mg⁻¹ protein min⁻¹. These results suggests that exogenously applied ABA-GE may be absorbed by plant roots and hydrolyzed by ABA-β-d-glucosidase, and liberated free ABA may induce the growth inhibition in these plants. Thus, although ABA-GE had been thought to be physiologically inactive ABA conjugate, ABA-GE may have important physiological functions rather than an inactive conjugated ABA form.     

Litter decomposition promotes differential feedbacks in an oligotrophic southern Everglades wetland

The differential accumulation or loss of carbon and nutrients during decomposition can promote differentiation of wetland ecosystems, and contribute to landscape-scale heterogeneity. Tree islands are important ecosystems because they increase ecological heterogeneity in the Everglades landscape and in many tropical landscapes. Only slight differences in elevation due to peat accumulation allow the differentiation of these systems from the adjacent marsh. Hydrologic restoration of the Everglades landscape is currently underway, and increased nutrient supply that could occur with reintroduction of freshwater flow may alter these differentiation processes. In this study, we established a landscape-scale, ecosystem-level experiment to examine litter decomposition responses to increased freshwater flow in nine tree islands and adjacent marsh sites in the southern Everglades. We utilized a standard litterbag technique to quantify changes in mass loss, decay rates, and phosphorus (P), nitrogen (N) and carbon (C) dynamics of a common litter type, cocoplum (Chrysobalanus icaco L.) leaf litter over 64 weeks. Average C. icaco leaf degradation rates in tree islands were among the lowest reported for wetland ecosystems (0.23 ± 0.03 yr⁻¹). We found lower mass loss and decay rates but higher absolute mass C, N, and P in tree islands as compared to marsh ecosystems after 64 weeks. With increased freshwater flow, we found generally greater mass loss and significantly higher P concentrations in decomposing leaf litter of tree island and marsh sites. Overall, litter accumulated N and P when decomposing in tree islands, and released P when decomposing in the marsh. However, under conditions of increased freshwater flow, tree islands accumulated more P while the marsh accumulated P rather than mineralizing P. In tree islands, water level explained significant variation in P concentration and N:P molar ratio in leaf tissue. Absolute P mass increased strongly with total P load in tree islands (r ² = 0.81). In the marsh, we found strong, positive relationships with flow rate. Simultaneous C and P accumulation in tree island and mineralization in adjacent marsh ecosystems via leaf litter decomposition promotes landscape differentiation in this oligotrophic Everglades wetland. However, results of this study suggest that variation in flow rates, water levels and TP loads can shift differential P accumulation and loss leading to unidirectional processes among heterogeneous wetland ecosystems. Under sustained high P loading that could occur with increased freshwater flow, tree islands may shift to litter mineralization, further degrading landscape heterogeneity in this system, and signaling an altered ecosystem state.     

Immobilization of α-amylase from mung beans (Vigna radiata) on Amberlite MB 150 and chitosan beads: A comparative study

α-Amylase from mung beans (Vigna radiata) was immobilized on two different matrices, Amberlite MB 150 and chitosan beads. Maximum immobilization obtained was 72% and 69% in case of Amberlite and chitosan beads, respectively. The pH optima of soluble α-amylase were 5.6, whereas that for immobilized amylase on chitosan and Amberlite was 7.0. Soluble amylase and Amberlite immobilized amylase showed maximum activity at 65 °C, whereas chitosan immobilized amylase showed maximum activity at 75 °C. α-Amylase immobilized on Amberlite showed apparent K_m of 2.77 mg/ml, whereas α-amylase immobilized on chitosan showed an apparent K_m of 5 mg/ml. The Amberlite-amylase and chitosan-amylase showed a residual activity of 43% and 27%, respectively, after 10 uses. The loss of activity for free amylase after 100 days of storage at 4 °C was 70%, whereas that for Amberlite- and chitosan-amylases, under the same experimental conditions, the losses were 45% and 55%, respectively. The easy availability of mung bean α-amylase, the ease of its immobilization on low-cost matrices and good stability upon immobilization in the present study makes it a suitable product for further use in industrial applications.     

Comparison of some novel polyculture and traditional monoculture vermicomposting reactors to decompose organic wastes

Efforts were made to evaluate the decomposition potentials of traditional monoculture and some novel polyculture vermireactors. Three earthworm species, i.e. Eisenia fetida (E. f.), Perionyx excavatus (P. ex.) and Lampito mauritii (L. m.), representing two different ecological categories: epigeic (E. fetida and P. excavatus) and anecic (L. mauritii), were used to design seven different vermireactors, i.e. Mono-(E. f.), Mono-(P. ex.), Mono-(L. m.), Poly-(E. f. + P. ex.), Poly-(P. ex. + L. m.), Poly-(E. f. + L. m.) and Poly-(E. f. + P. ex. + L. m.). The microbial load of vermireactors was evaluated through measuring dehydrogenises activities (DH-ase) and microbial biomass-N, while mineralization rate was measured in respect to changed level of some important nutrients in vermicomposted substrate. The vermicomposting caused decrease in pH (67.0–15.0%), organic C (46.1–28.4%) and C:N ratio (72.2–57.1%) and increase in total N (137.7–67.8%) as well as available P (107.9–16.9%) contents, at the end. The carbon and nitrogen mineralization rate showed the order: Poly-(E. f. + P. ex. + L. m.) > Poly-(E. f. + L. m.) > Poly-(P. ex. + L. m.) > Poly-(E. f. + P. ex.) > Mono-(E. f.) > Mono-(P. ex.) > Mono-(L. m.) for this study. The Poly-(E. f. + P. ex. + L. m.) vermireactor showed the maximum level of DH-ase activity 1926 ± 245 μg g⁻¹ substrate 24 h as well as microbial biomass-N 3059.1 ± 242.3 mg N g⁻¹ substrate, during experimentation. This study clearly suggests that burrowing earthworms in vermireactor not only promote the microbial colonization, but at the same time also accelerate the mineralization rate in decomposing waste. The polyculture vermicomposting, using burrowing earthworms with epigeics, could be more efficient than traditional monoculture vermireactors to decompose organic waste resources.     

Decomposition and nutrient release from logging residues after clear-cutting of mixed boreal forest

Elevated dissolved carbon (C), nitrogen (N) and phosphorus (P) concentrations are frequently observed in surface water soon after clear-cutting of boreal coniferous forests. It has been suggested that they originate from the fine logging residues whose decomposition may be accelerated as a result of changes in soil temperature and moisture conditions. In the present study, the decomposition rate and release of C, N, and P from Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karsten) and silver birch (Betula pendula Roth.) logging residues (fine roots 2 mm, branches 10 mm and foliage) were investigated during three years with the litterbag method in a clear-cut area and in an adjacent Norway spruce dominated, mixed boreal forest in eastern Finland (63°51 N, 28°58 E, 220 m asl). The mass loss of the logging residues decreased in the order: foliage > roots > branches. Birch leaves were the only fraction that showed significantly higher losses of mass and C at the clear-cut plot than at the forest plot; otherwise there was no tendency for accelerated decomposition or mineralization at the clear-cut plot. After three years the initial C pool in the logging residues had declined by 33% and that of P by 49% but there was no net release of N as more N accumulated in roots and branches than was released from foliage. The results indicate that 1) logging residues release relatively large and rapid fluxes of CO₂ to the atmosphere 2) are potential source of elevated P in surface waters soon after clear-cutting 3) are not a net source of N immediately after clear-cutting.     

The effects of wind and temperature on cuticular transpiration of Picea abies and Pinus cembra and their significance in dessication damage at the alpine treeline

Summary The importance of high winter winds and plant temperatures as causes of winter desiccation damage at the alpine treeline were studied in the Austrian Alps. Samples of 1- and 2-year twigs of Picea abies and Pinus cembra were collected from the valley bottom (1,000 m a.s.l.), forestline (1,940 m a.s.l.), kampfzone (2.090 m a.s.l.), wind-protected treeline (2,140 m a.s.l.), and wind-exposed treeline (2,140 m a.s.l.). Cuticular transpiration was measured at three different levels of wind speed (4, 10, and 15 ms^-1) and temperature (15°, 20°, and 25° C). At elevated wind speeds slight increases in water loss were observed, whereas at higher temperatures much greater increases occurred. Studies on winter water relations show a significant decline in the actual moisture content and osmotic potentials of twigs, especially in the kampfzone and at treeline. The roles of high winds and temperatures in depleting the winter water economy and causing desiccation damage in the alpine treeline environment are discussed.     

Disproportionately high N-mineralisation rates from green manures at low temperatures – implications for modeling and management in cool temperate agro-ecosystems

We examined the decomposition of Medicago lupulina, Melilotus alba and Poa pratensis at 3, 9, and 25 °C during 4 weeks. There was a strong temperature effect on the rate of CO₂ evolution, and thus the extent of energy exhaustion from the added substrates. However, there was no concomitant retardation of N mineralisation at low temperatures. In the analysis of variance of mineralized N the residue type gave a 10 times larger contribution to the regression than the temperature (T), whereas for CO₂ evolution residue type and temperature were equally important contributors. This indicates that although the temperature has a statistically significant effect on N-mineralisation it is substantially less than compared with the effect on carbon mineralisation in the materials examined. The retardation of carbon mineralisation was least strong in Melilotus alba that had a relatively low cellulose content, and a higher content of low molecular compounds. Though more research will be necessary to consolidate and explain this phenomena, it is likely that an important factor is a decrease in the bioavailability of C-rich polymers at low temperatures, and thus a preferential utilization of N-rich low molecular substances. Nitrification was not effectively deterred at 3 °C. Thus, in terms of management, it is pertinent to reconsider the timing of green manure and catch crop incorporation in cool temperate climate regions, since the rapid release of nitrogen, coupled with the relatively undeterred nitrification may result in a high N leaching risk by early incorporation, but a low risk for N immobilization at late incorporation, if N rich residues are used.     

Thermostability of immobilized plant microsomes

Microsomes from grapewine (V. vinifera L. cv. Camay Fréaux) cell homogenates were immobilized in calcium alginate beads. Cinnamic acid-4-hydroxylase activities for both freely suspended and immobilized microsomes were compared, resulting in a decrease of 30–40% of the initial activity as a consequence of immobilization. This decrease was probably due to both protein denaturation and microsomal mass losses during the gelation process. Nevertheless, immobilized microsomes showed an enhanced thermostability. Only 35% of the initial activity was lost when immobilized microsomes were incubated at 45°C for 10 minutes, whereas a 68% activity loss was observed when dealing with free microsomes.     

Influence of selected fruit tree pollen on life history of Euseius stipulatus (Acari: Phytoseiidae)

Euseius stipulatus (Athias-Henriot) is a predatory mite widespread in the Mediterranean region considered to be important for the biological control of spider mites in citrus orchards. Development, survival and reproduction of this phytoseiid mite feeding on seven commercially obtained pollen were studied under constant laboratory conditions (20 ± 1°C, RH 65 ± 5%, photoperiod 16L: 8D h). Mites were kept individually at rearing units with ample quantity of almond (Prunus amygdalus Batch), apple (Malus domestica Borkh), apricot (Prunus armeniaca L.), cherry (Prunus avium L.), pear (Pyrus communis L.), plum (Prunus domestica L.) and walnut (Juglans regia L.) pollen as food source. Developmental time from egg to adult varied between the several pollen tested from 8.38 ± 0.08 to 9.58 ± 0.11 days for females and from 8.23 ± 0.12 and 9.07 ± 0.12 days for males. Female longevity varied from 11.53 ± 1.22 to 51.38 ± 2.45 days, while fecundity ranged from 22.84 ± 2.30 to 43.61 ± 3.78 eggs/female. The predator was unable to reproduce when feeding on walnut pollen. Data were submitted to life table analysis and values of the intrinsic rate of increase were derived, ranging from 0.079 to 0.146 (day⁻¹). The cumulative Weibull function that was used to describe the age specific survival of females produced excellent fits to the survival data. Results show that almond, plum, cherry and apricot pollen possess higher nutritional value for E. stipulatus than pear and apple pollen and thus may contribute in sustaining and increasing the predator population in field conditions. Walnut pollen can be utilized by the predator only to survive during short periods of time when principal or alternative food sources are scarce.     

Contribution of Oxidative Stress to the Development of Cold-Induced Damage to Leaves of Chilling-Sensitive Plants: 3. Injury of Cell Membranes by Chilling Temperatures

Changes in permeability of cell membranes (judged from electrolyte leakage) were examined on leaves of 7- to 11-day-old seedlings of maize (Zea mays L.), cucumber (Cucumis sativus L.), millet (Panicum miliaceum L.), and on etiolated shoots of potato (Solanum tuberosum L.) immediately after cooling plants for 1–24 h at 2°C and one day after a 24-h chilling treatment. A gradually increasing leakage of ions from the cells was observed upon prolongation of chilling exposure, with the maximum attained by the end of 24-h chilling treatment. The leakage of electrolyte was slightly reduced in the post-treatment period but it was still higher than the electrolyte leakage from the control samples (untreated plants). The cold treatment of chilling-sensitive plants (but not of potato) revealed a positive correlation between the rates of lipid peroxidation, indicative of chilling injury, and the electrolyte efflux (r = 0.61–0.96). The evaluation of plant susceptibility to injury showed that millet and potato plants recovered from the chilling damage in 24 h after the treatment, whereas maize and cucumber plants did not show such a recovery.     

Combined Effects of Food Concentration and Temperature on Competition Among Four Species of <Emphasis Type="Italic">Brachionus </Emphasis>(Rotifera)

We evaluated the effect of algal food density (1.5 × 10⁶, 3.0 × 10⁶ and 4.5 × 10⁶ cells ml⁻¹ of Chlorella) and temperature (22° and 28 °C) on competition among the rotifers Brachionus calyciflorus, Brachionus havanaensis, Brachionus patulus and Brachionus rubens, based on population growth experiments for 24 days. The growth experiments were conducted seperately for each individual rotifer species (i.e., controls), and in mixtures of all four species in equal initial proportions (i.e., under competition). The population growth of B. calyciflorus, B. havanaensis, B. patulus and B. rubens grown separately at two temperatures and at three algal food densities showed typical patterns of lag, exponential and retardation phases in the controls. This pattern differed considerably under competition. In general, we observed that in all of the test species, the highest growth rates were observed at higher food levels and in the absence of congenerics. At 22 °C, under the lowest food level, the differences in the population abundances of B. havanaensis, B. patulus and B. rubens grown alone and in the presence of competition were large. However, these differences reduced as food density was increased from 0.5 × 10⁶ to 4.5 × 10⁶ cells ml⁻¹. At 28 °C and at the lowest food level, all of the other rotifer species eliminated B. havanaensis in mixed cultures. Each brachionid species had a higher rate when grown alone than when cultured with other species. The highest r (mean ± standard error: 0.54 ± 0.01 day⁻¹) was recorded for B. havanaensis at 28 °C under 4.5 × 10⁶ cells ml⁻¹ of algal food density. At 28 °C at low algal food density, the presence of competitors resulted in negative population growth rates for three of the four rotifer species tested.     

Allelopathy and the allelothathic activity of a phenylpropanol from cucumber plants

The growth inhibitory effect of cucumber (Cucumis sativus L.) plants after crop harvested was investigated. Aqueous methanol extracts of the cucumber plants inhibited the growth of roots and shoots of cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), alfalfa (Medicago sativa L.), ryegrass (Lolium multiflorum L.), timothy (Pheleum pratense L.), crabgrass (Digitaria sanguinalis L.), Echinochloa crus-galli (L.) Beauv and Echinochloa colonum (L.) Link, and increasing the extract concentration increased the inhibition. These results suggest that cucumber plants may possess allelopathic activity. The aqueous methanol extract of cucumber plants was divided into ethyl acetate and aqueous fractions, and the growth inhibitory activity of ethyl acetate fraction was greater than that of aqueous fraction. Thus, ethyl acetate fraction was further purified and a main allopathically active substance in the fraction was isolated and determined as (S)-2-benzoyloxy-3-phenyl-1-propanol by spectral data. This substance inhibited root and shoot growth of cress seedlings at concentrations greater than 10 μM, and the concentration required for 50% inhibition of root and shoot growth was 21 and 23 μM, respectively. These results suggest that (S)-2-benzoyloxy-3-phenyl-1-propanol may contribute to the growth inhibitory effect of cucumber plants and may play an important role in cucumber allelopathy. Thus, cucumber plants may be potentially useful for weed management in a field setting. An erratum to this article can be found at     

Effects of hot ground water on a small swamp-stream in Nova Scotia,Canada

We examined the effects of hot spring water (35–45 °C) on the ecology of a small, intermittant swamp-stream in Nova Scotia, Canada. Temperatures diminished quickly with distance downstream from the hot spring because of abundant inflow of cold ground water (<10 °C), but elevated temperature effects were detectable 130 m downstream. The brook below the hot spring supported a dense mat of the cyanobacterium Oscillatoria (10 m) followed by the green alga Vaucheria taylorii (40 m). Herbaceous vegetation below the algal zones was also altered by the hot water inflow, even where the temperature increase was slight. The structure of the sparse community of benthic invertebrates was sharply different at sites of different stream temperature: only oligochaete worms, ostracods, chironomids, and a single species of snail thrived at the warmest sites; cold downstream sites supported a typical headwater stream community. Mass loss from decomposing leaves of speckled alder was fast at all sites and strongly correlated with water temperature. The changes in community composition and decomposition rate in response to added heat persisted even where the temperature increase was small, indicating a tight coupling of ecosystem structure and function with the physical environment.     

香樟凋落叶分解对辣椒及土壤氮营养的限制作用

香樟(Cinnamomum camphora)凋落叶分解能够明显干扰受体植物的生长、生殖、光合生理和活性氧代谢。该研究继续采用盆栽试验,探讨了不同量[0(对照)、25、50和100g]的香樟凋落叶添加到土壤(10kg/盆)中对受体植物辣椒(Capsicum annuum)及其土壤氮营养状况的影响,外源氮(尿素)输入对凋落叶分解的交互作用,以及凋落叶分解效应的产生是否因为其较高的C/N比而导致微生物争氮。结果显示:(1)各剂量(25~100g/盆)凋落叶处理下,辣椒幼苗硝态氮、可溶性蛋白和全氮含量均在至少2个月内大幅显著降低。(2)土壤硝态氮与辣椒硝态氮、全氮间均具有极显著的协同下降趋势;土壤微生物生物量氮则在总体上高于对照,而土壤全氮和铵态氮的响应较小。(3)施氮不仅使辣椒各氮组分和土壤硝态氮含量整体提升,还使凋落叶分解在这些指标上的抑制作用显著减弱。(4)香樟凋落叶的初始C/N为125.61±4.89,其在土壤中分解48~137d后的C/N始终远高于Hodge假说指出的可导致微生物争氮的临界值,但经过分解120d和135d的凋落叶添加到土壤中并不抑制辣椒的生长。研究认为,香樟凋落叶分解初期可能释放了不利于土壤硝化过程的物质,造成土壤硝态氮匮乏,以致受体植物的氮素吸收和积累减少,而凋落叶较高的C/N比及土壤微生物争氮并非主导因素。     

Asymbiotic Nitrogen Fixation and Litter Decomposition on a Long Soil-Age Gradient in Hawaiian Montane Rain Forest1

We determined rates of decomposition and asymbiotic nitrogen fixation in the leaf litter of Cheirodendron spp. on the Hawaiian Islands. Leaf litter was collected from four sites on a long soil-age gradient (300 yr to 4.1 M yr) and decomposed at two sites that differed widely in substrate age and nutrient availability. Rates of decomposition were higher in litter decomposed at the older site, where nutrient availability was greater. A substantial amount of nitrogen and phosphorus immobilization occurred in litter decomposed at the older site, with more immobilization occurring in litter with lower initial nitrogen and phosphorus concentrations, suggesting both supply and demand controls on nutrient immobilization. Potential rates of nitrogen fixation were very low in the first 25 d (0–5 nmol acetylene/gdw/h), rose to much higher rates by 70 d (20–45 nmol), and then declined by 140 d. We found no significant difference in rates of potential nitrogen fixation between sites of decomposition, but there was a strong substrate effect, with higher rates in litter with low lignin, low nitrogen, and high phosphorus. Where significant immobilization of nitrogen occurred for decomposing Cheirodendron, nitrogen fixation could have comprised no more than 10 percent of immobilized nitrogen. Overall, rates of nitrogen fixation were dependent on the source of the decomposing substrate but not on the site of decomposition, while short-term decomposition and nutrient immobilization were strongly dependent on the site of decomposition but not as much on the source of the decomposing substrate.     

Decomposition and nutrient release of grass and tree fine roots along an environmental gradient in southern Patagonia

Decomposition of fine roots is a fundamental ecosystem process that relates to carbon (C) and nutrient cycling in terrestrial ecosystems. However, this important ecosystem process has been hardly studied in Patagonian ecosystems. The aim of this work was to study root decomposition and nutrient release from fine roots of grasses and trees (Nothofagus antarctica) across a range of Patagonian ecosystems that included steppe, primary forest and silvopastoral forests. After 2.2 years of decomposition in the field all roots retained 70–90% of their original mass, and decomposition rates were 0.09 and 0.15 year^?1 for grass roots in steppe and primary forest, respectively. For N. antarctica roots, no significant differences were found in rates of decay between primary and silvopastoral forests (k = 0.07 year^?1). Possibly low temperatures of these southern sites restricted decomposition by microorganisms. Nutrient release differed between sites and root types. Across all ecosystem categories, nitrogen (N) retention in decomposing biomass followed the order: tree roots > roots of forest grasses > roots of steppe grasses. Phosphorus (P) was retained in grass roots in forest plots but was released during decomposition of tree and steppe grass roots. Calcium (Ca) dynamics also was different between root types, since trees showed retention during the initial phase, whereas grass roots showed a slow and consistent Ca release during decomposition. Potassium (K) was the only nutrient that was rapidly released from both grass and tree roots in both grasslands and woodlands. We found that silvopastoral use of N. antarctica forests does not affect grass or tree root decomposition and/or nutrient release, since no significant differences were found for any nutrient according to ecosystem type. Information about tree and grass root decomposition found in this work could be useful to understand C and nutrient cycling in these southern ecosystems, which are characterized by extreme climatic conditions.     

Litter decomposition contrasts in second- and old-growth Douglas-fir forests of the Pacific Northwest, USA

Litterfall and its subsequent decomposition are important feedback mechanisms in the intrasystem cycling of nutrients in forest ecosystems. The amount of litterfall and the rate of decomposition are expected to vary with stand age and climate. Over a 2-year period, decomposition of five litter types were measured in two second-growth forest stands and one old-growth stand in the Cascade Mountains of southern Washington state, USA. Both second-growth stands were dominated by Douglas-fir [Pseudotsuga menziesii (Mirb.,) Franco] but one had a significant proportion of red alder (Alnus rubra Bong.), a nitrogen (N) fixer. The old-growth stand was dominated by Douglas-fir and western hemlock [Tsuga heterophylla (Raf.) Sarg.]. All stands had a relatively shallow layer of forest floor mass. The five litter types were placed in each stand to evaluate decomposition patterns. Despite significant differences in stand age, microclimate and mean residence times for carbon (C) and N, the rates of litter mass loss varied only slightly between sites. The relative order of species litter mass loss was: vine maple ≫ salal = western hemlock > Douglas-fir (from the youngest stand) > Douglas-fir (from the N rich stand with red alder). The initial litter lignin concentration, not lignin:N, was the primary determinant of decomposition rates, although the initial N concentration was the predictor for mass loss after 2 years in the N rich Douglas-fir-alder stand. All litter types showed immobilization of N for nearly 2 years. Data for Douglas-fir litter suggest that higher levels of N may retard decomposition of tissues with greater amounts of lignified material. The retention of N by the litter appeared influenced by the nutrient capital of the stands as well as the forest floor C:N ratio. Decomposition was minimal during the cold winter months, but displayed a definitive peak period during early Fall with wet weather, warm soils, and fungal activity. Thus, long-term climatic change effects on forest floor C storage may depend more on changes in seasonality of precipitation changes than just temperature changes.     

The Effects of Root Treatment with Various Stress Agents on Plant Cold- and Heat-Tolerance

The root systems of cucumber (Cucumis sativus L.), wheat (Triticum aestivum L.), and barley (Hordeum vulgare L.) plants were subjected to a short-term (6–7-h-long) treatment with low and high temperatures, sodium chloride, and lead nitrate, and the effect of these treatments on the changes in the cold- and heat-tolerance of leaf cells was determined. It was established that chilling of cucumber and wheat seedling roots at 10 and 2°C, respectively, or their heating at 38°C and 40°C, respectively, induced an increase in both cold- and heat-tolerance of leaf cells. An increase in the cold- and heat-tolerance was also observed in roots treated with sodium chloride at concentrations of 0.15 M (cucumber) and 0.2 M (wheat), as well as with lead nitrate at a concentration of 0.1 mM (barley, wheat). The tolerance increase induced by these stress agents was accompanied by a considerable increase in the ABA concentration in leaves. The effect of physical and chemical stress agents is suggested to induce the same nonspecific changes in the aboveground organs. These changes bring about, directly or indirectly, an increase in the cold- and heat-tolerance and are related to an increase in the ABA content.     

Effects of litter size and quality on processing by decomposers in a tropical savannah stream

Litter fragment size and quality can have profound effects on ecosystem functioning and global biogeochemical cycling due to differential utilization by decomposers. Here we study the influence of these factors on decomposers from two guilds found in a tropical savannah stream: invertebrate shredders of the genus Phylloicus and microorganisms. Containers (16 × 16 × 12 cm, ~ 3L) with either Phylloicus (cases removed; N = 16) or stream water containing microorganisms (N = 16) were supplied with litter from the species Inga laurina, Maprounea guianensis, and Richeria grandis, and cut into disks of 18.7, 13.2, and 8.1 mm in diameter (3 sizes × 3 species = 9 disks per container). Relative decomposition was greater for smaller leaf disks and disks of higher quality in microbial‐only cultures. Phylloicus preferentially harvested large fragments for case building, also preferring the leaves of M. guianensis and R. grandis, likely due increased robustness for case formation. Microbial decomposition resulted in ~20% litter mass loss compared to 30% in Phylloicus (of which 8% was used for case building and 24% for food). Thus, changes to input litter size, such as a decrease in leaf size after drought, may alter microbial decomposition and potentially affect shredder populations by limiting the availability of casing material.