Variability in temperature regulation of CO2 fluxes and N mineralization from five Hawaiian soils: implications for a changing climate

We examined the possibility that microbial adaptation to temperature could affect rates of CO₂, N₂O and CH₄ release from soils. Laboratory incubations were used to determine the functional relationship between temperature and CO₂, N₂O and CH₄ fluxes for five soils collected across an elevational range in Hawaii. Initial rates of CO2 production and net N mineralization increased exponentially from 15 °C to 55 °C; initial rates of CH₄ and N₂O release were more complex. No optimum temperature (in which rates decline at higher and lower temperatures) was apparent for any of the gases, but respiration declined with time at higher temperatures, suggesting rapid depletion of readily available substrate. Mean Q₁₀S for respiration varied from 1.4 to 2.0, a typical range for tropical soils. The functional relationship between CO₂ production and temperature was consistent among all five soils, despite the substantial differences in mean annual temperature, soils, and land-use among the sites. Temperature responses of N₂O and CH₄ fluxes did not follow simple Q₁₀ relationships suggesting that temperature functions developed for CO₂ release from heterotrophic respiration cannot be simply extrapolated. Expanding this study to tropical heterotrophic respiration, the flux is more sensitive to changes in Q₁₀ than to changes in temperature on a per unit basis: the partial derivative with respect to temperature is 2.4 Gt C ·° C^?1 with respect to Q₁₀, it is 3.5 Gt C · Q₁₀ unit^?1. Therefore, what appears to be minor variability might still produce substantial uncertainty in regional estimates of gas exchange.     

Field experiments on the mobility of benthic invertebrates in a southern English stream

1. In each of twenty-six week-long experiments, the colonization by macroinvertebrates of boxes of natural sediment in a stony stream was measured. The experiments took place between February and November 1992 and environmental conditions prevailing during the weeks (particularly discharge and temperature) differed widely.
2. Colonization rate also varied widely between the weekly experiments and was sensitive to discharge, temperature and background benthic density, depending on the taxa considered.
3. A 'mobility index' measured colonization rate independently of background benthic density. This index was most strongly and positively correlated with discharge for the abundant stonefly Leuctra nigra, the net-spinning caddis Plectrocnemia conspersa and the Chironomidae, perhaps indicating that their mobility is physically driven by the influence of flow on drift.
4. Mobility in a second stonefly ( Nemurella pictetii ) was greatest in summer, when flows were low but temperature was high. Peak mobility in this species occurred during an ochreous bloom on the stream bed. It is likely the mobility of N. pictetii is more active than the other taxa.
5. There were thus differences among taxa in their mobility at baseflow and in their susceptibility to flow fluctuations. The population consequences of differences in mobility among taxa are discussed.     

Modelling the ecosystem effects of nitrogen deposition: Simulation of nitrogen saturation in a Sitka spruce forest,Aber, Wales,UK

A new model for simulating nitrogen leaching fromforested ecosystems has been applied to data from anexperimentally manipulated 30-year-old Sitka sprucestand. The manipulation experiment (at Aber, in north-western Wales, UK) was part of the European NITREXproject and involved five years of additions ofinorganic nitrogen to the spruce stand. The model(MERLIN) is a catchment-scale, mass-balance model thatsimulates both biotic and abiotic processes affectingnitrogen in ecosystems.The structure of MERLIN includes representationsof the inorganic soil, one plant compartment and twosoil organic compartments. Fluxes in and out of thesimulated ecosystem and transfers between compartmentsare regulated by atmospheric deposition, hydrologicaldischarge and biological processes such as plantuptake, litter production, immobilization,mineralization, nitrification and denitrification.Rates of nitrogen uptake, cycling and release amongpools are regulated by carbon productivity, inorganicnitrogen availability and the C:N ratios of theorganic pools. Inputs to the model are temporalsequences of carbon fluxes and pools, hydrologicaldischarge and external sources of nitrogen.The NITREX experiment at Aber began in 1990 withweekly additions of ammonium nitrate(NH4NO3) at a rate of 35 kg N ha-1 yr-1.Data were collected from both control andtreatment plots within the stand. The site-intensivedata from the control plots at Aber were augmented bydata taken from a chronosequence of 20 Sitka sprucestands and data from a survey of 5 moorland catchmentsin the same region to providecalibration data for the model. The data were used toestablish current conditions at the Aber site and toreconstruct historical sequences of carbon fluxes andpools from 1900 to the present day with which to drivethe model. The reconstructed sequences included anincrease in nitrogen deposition and a vegetationchange from moorland to plantation forest in 1960. Thecalibrated model was then used to predict the effectsof the experimental nitrogen additions begun in 1990.MERLIN successfully reproduced the observedincrease in NO3 leaching from aging spruce standsthat results from forest maturation and increasednitrogen deposition (as inferred from thechronosequence and forest survey data in the region).MERLIN also correctly predicted the increases insoilwater NO3 concentrations, the changes innitrogen content of tree and soil organic matterpools, and the changes in nitrogen fluxes that occurin spruce stands in response to increased nitrogeninputs (as observed in the nitrogen additionexperiment).     

Salt tolerance in Eucalyptus spp.: identity and response of putative osmolytes

In four species of salt-tolerant eucalypts (Eucalyptus raveretiana, E. spathulata, E. sargentii and E. loxophleba), we found substantial concentrations of quercitol – a cyclitol known for its accumulation in seeds of Quercus. Quercitol was absent in old foliage of E. globulus, a species noted for greater susceptibility to salinity, and also absent in the moderately tolerant E. camaldulensis, but, relative to other species, both had higher foliar concentrations of inositol. Simple sugars and cyclitols accumulated to osmotically significant concentrations in all species. The osmotic potential of expressed sap was always less than that of the external ‘soil’ solution and increasing salinity produced predictable reductions in growth and increases in ion concentrations in foliage of saplings of four eucalypt species. The more salt-tolerant species, E. spathulata, E. loxophleba and E. sargentii, were able to maintain well-regulated leaf Na⁺ concentrations even at 300 mol m⁻³ NaCl. These more salt-tolerant species also showed an apparent increase in net selectivity for K⁺ over Na⁺ as salinity increased, irrespective of the Na⁺ : Ca²⁺ ratio of the external medium (range 25 : 1 to 75 : 1; Ca²⁺ always ≥ 4.0 mol m⁻³). By contrast, E. globulus was unable to exclude Na⁺ when exposed to higher NaCl concentrations (e.g. 200 and 300 mol m⁻³). Carbon isotope signatures of foliage reflected imposed salinity but were not strongly enough correlated with growth to support previous suggestions that isotope discrimination be a means of evaluating salt tolerance. On the other hand, patterns of sugar and cyclitol accumulation should be further explored in eucalypts as traits contributing to salt tolerance, and with potential use as markers in breeding programmes.     

Behavioural and toxic effects of termite defensive secretions on ants

ABSTRACT. The toxicity and biological activity of the defensive secretions of ten species of neotropical termites were examined by bioassay on two species of predatory ant. Pseudomyrmex termitarius (F. Smith) (Pseudomyrmecinae) was more susceptible to the effects of the secretions than Ectatomma sp. (Ponerinae). The bioassay results show a progression in the nature of termite chemical weaponry and in the potency of defensive secretions. The tacky secretions used by Coptotermes and Ruptitermes are simply adhesive, entangling agents with no apparent toxic or pheromonal properties. The secretion of Syntermes calvus Emerson serves as a wound-active poison with little topical activity, while those of Armitermes spp. are repellent to ants and show activity as topical poisons. The secretions used by Nasutitermes spp. combine adhesive, entangling properties with the toxicity of a topically-active poison, and are effective also as ant-repellents.     

Wind Flow Characteristics on a Soybean Leaf Compared with a Leaf Model

The purpose of this paper is to describe momentum boundary layer flow parameters on a soybean leaf [Glycine max (L.) Merrill] at various velocities of the bulk air stream and these data are compared with similar measurements on an artificial leaf. The wind structure is measured at three different bulk air velocitìes (u_∞= 39, 148 and 271 centimeters per second) on an individual soybean leaf and is compared to structural effects on an artificial leaf (flat metal plate) in a small closed-circuit wind tunnel. The boundary layers were homogeneous for the metal plate, but only at the lower velocity for the soybean leaf. The boundary layer thicknesses decrease with increasing bulk air velocity for laminar flow regimes, whereas in the turbulent flow regime the boundary layer thickness greatly increases. The effect of turbulence on the soybean leaf boundary layer made the eddy diffusivities at least three times greater than in the laminar flow regime at the calculated roughness height above the leaf surface. The structure of the leaf boundary layer flow is comparable to that of the metal plate only at the lower bulk air velocity.     

Inhibition of Respiration in Protoplasts from Meristematic Tissues3

Owen, J. H., Hetherington, A. M. and Wellburn, A. R. 1986. Inhibitionof respiration in protoplasts from meristematic tissues by abscisicacid in the presence of calcium ions.—J. exp. Bot. 38:498–505. A study was made of the influences of abscisic acid (ABA) andcalcium ions on mitochondrial respiration in protoplasts fromcells close to the basal intercalary meristem of light-grownbarley (Hordeum vulgare L. cv. Patty) seedlings. This respirationwas inhibited by ABA only when calcium ions were present. Thecalcium channel agonist BAY K8644 caused a significant inhibitionof protoplast dark respiration, similar to that observed usingABA and calcium, presumably because it imitated the action ofABA by increasing calcium influx into protoplasts. These resultssuggest that ABA increases the permeability of the plasmamembraneto calcium and that calcium acts as a second messenger to regulatemitochondrial respiratory activity and thus the very early eventsassociated with plastid and meristematic cell development. Key words: Abscisic acid, calcium, meristematic respiration     

Some Biochemical Effects of Glyphosate on Plant Meristems

Glyphosate promoted the activity of phenylalanine ammonia lyase(PAL) in both single node rhizome buds of Agropyron repens androot tips of wheat seedlings, in the latter case correlatinginversely with decline in respiratory activity. Differentialrates of ¹⁴C-amino acid incorporation suggest that glyphosatedepleted the phenylalanine protein precursor pool with resultantinhibition of protein synthesis, as evidenced by a rapid declinein the level of ‘soluble’ protein. Promotion ofPAL is assumed to occur by derepression through decline in end-productlevels. Activities of shikimate: NADP oxidoreductase (SORase),chorismate mutase, and polyphenol oxidase (PPO) were also elevated,but to lesser extents than for PAL.