Physiological ecology of frillneck lizards in a seasonal tropical environment

The frillneck lizard, Chlamydosaurus kingii, is a conspicuous component of the fauna of the wetdry tropics of northern Australia during the wet season, but it is rarely seen in the dry season. Previous studies have demonstrated that during the dry season the field metabolic rate (FMR) is only about one-quarter of the wet-season rate, and one factor involved in this seasonal drop is a change in the behavioural thermoregulation of the species such that lower body temperatures (T _bs) are selected during dry-season days. Here we examine other factors that could be responsible for the seasonal change in FMR: standard metabolic rates (SMR) and activity. Samples from stomach flushing revealed that the lizards in the dry season continued to feed, but the volume of food was half as much as in the wet season. SMR in the laboratory was 30% less in the dry season. During the dry season, the energy expended by the lizards is 60.4 kJ kg^-1 day^-1 less than during the wet season. Combining laboratory and field data, we determined the relative contribution of the factors involved in this energy savings: 10% can be attributed to lower nighttime T _b, 12% is attributable to lower daytime T _b, 12% is attributable to decreased metabolism, and the remaining 66% is attributable to other activities (including e.g. locomotion, reproductive costs, digestion). Calculations indicate that if FMR did not drop in the dry season the lizards would not survive on the observed food intake during this season. Seasonal analysis of blood plasma and urine indicated an accumulation of some electrolytes during the dry season suggesting modest levels of water stress.     

Energetics of bluetongue lizards (<Emphasis Type="Italic">Tiliqua scincoides</Emphasis>) in a seasonal tropical environment

We studied the physiological ecology of bluetongue lizards (Tiliqua scincoides) on the Adelaide River floodplain in tropical Australia to determine the seasonal patterns of energy expenditure and to determine the mechanisms by which seasonal differences were achieved. Field metabolic rates (FMR) were significantly lower in the dry season (37.6 kJ kg(-1) day(-1); n=9) than in the wet (127.3 kJ kg(-1) day(-1); n=7). Water flux was also lower in the dry season (6.8 ml kg(-1) day(-1); n=9) than in the wet (39.4 ml kg(-1) day(-1); n=7). Measurements of body temperatures (T(b)) and movements of free-ranging animals, and standard metabolic rate (SMR) of recently caught animals, allowed a detailed analysis of energy budgets for wet and dry seasons. In the dry, bluetongue lizards expended 90 kJ kg(-1) day(-1) less energy than in the wet season. Unlike some other lizards of the wet-dry tropics, SMR did not differ between seasons. About 5% of the seasonal difference in FMR was due to lower night time T(b) during the dry season, and about 7% was due to lower diurnal T(b). The remaining 88% of the decrease in energy expended in the dry season was due to a substantial decrease in other costs that may include reproduction, growth, digestion and activity. If we assume the animals fed daily and the costs of digestion are taken into account, the estimates are: 14% of the savings result from lower T(b) at night, 20% from lower T(b) in the day, and 66% result from decreased activity. It is therefore apparent that, unlike some agamid and varanid lizards that use a combination of behavioural and physiological mechanisms to conserve energy when food and water are limited, bluetongue lizards primarily use behavioural mechanisms to achieve a dramatic reduction in energy expenditure in the dry season.     

Energetics and water flux of the marbled velvet gecko (Oedura marmorata) in tropical and temperate habitats

The gecko Oedura marmorata was studied in two different climatic zones: the arid zone of central Australia and in the wet-dry tropics of northern Australia. Doubly labelled water was used to measure field metabolic rate (FMR) and water flux rates of animals in the field during the temperate seasons of spring, summer and winter, and during the tropical wet and dry seasons. FMRs were highest in the tropical wet season and lowest in the temperate winter. The geckos in central Australia expended less energy than predicted for a similarly sized iguanid lizard, but geckos from the tropics expended about the same amount of energy as predicted for an iguanid. Water flux rates of geckos from the arid zone were extremely low in all seasons compared to other reptiles, and although water flux was higher in tropical geckos, the rates were low compared to other tropical reptiles. The standard metabolic rates (SMRs) of geckos were similar between the two regions and among the seasons. Geckos selected higher body temperatures (T _bs) in a laboratory thermal gradient in the summer (33.5°C) and wet (33.8°C) seasons compared to the winter (31.7°C) and dry (31.4°C) seasons. The mean T _bs selected in the laboratory thermal gradient by geckos from the two regions were not different at a given time of year. The energy expended during each season was partitioned into components of resting metabolism, T _b and activity. Most of the energy expended by geckos from central Australia could be attributed to the effects of temperature on resting lizards in all three seasons, but the energy expended by tropical geckos includes a substantial component due to activity during both seasons. This study revealed variability in patterns of ecological energetics between populations of closely related geckos, differences which cannot be entirely attributed to seasonal or temperature effects. Received: 14 November 1997 / Accepted: 4 May 1998     

Net nitrogen mineralization,nitrification and CO2 production in alternating moisture conditions in an unfertilized low-humus sandy soil from the Sahel

In this study the rates of net mineralization, net immobilization and net nitrification have been quantified under laboratory conditions in a sandy low-humus soil from a semi-arid region, in absence of plant growth. Incubation experiments were carried out under constant humidity and under alternating wet and dry conditions to simulate field conditions during the rainy season. The ammonium and nitrate content of the incubates were determined and their CO₂ production measured.The rate of net mineralization at field capacity was 0.6 kg N ha^–1d^–1 during the first 40 days and decreased to 0.06 kg N ha^–1d^–1 after 400 days. This rate was twice as high on wet days under alternating wet and dry conditions. The rate of net nitrification during alternating wet and dry conditions was also higher (1.9 kg N ha^–1d^–1) than at constant field capacity (1.3 kg N ha^–1d^–1) until the ammonium was almost completely depleted. These rates of net mineralization and net nitrification are in agreement with field observations.Net immobilization did not occur in the experiments, unless glucose was added to the soil.The data on CO₂ production and net mineralization showed that the C/N ratio of the degraded material was around 9 or below. It is much lower than the ratio of total carbon over total nitrogen in the soil. This indicates that microorganisms and compounds high in nitrogen were mineralized. Certainly after about 30 days the only growth taking place is based on turnover of material of the microbial biomass itself.A decrease in the amount of inorganic nitrogen was observed upon drying of the soil, while it returned to the original content after rewetting. It is postulated that this might be due to temporary uptake of nitrogen in an inorganic form in microorganisms as part of their osmoregulation.     

Effect of varying periods of inoculation ofAzolla pinnata R. Brown on its growth,nitrogen fixation and response to rice crop

Summary Inoculation of water fernAzolla pinnata R. Brown (Bangkok isolate) at the rate of 500kg fresh weight ha⁻¹ in rice fields at weekly intervals after planting in addition to 30 kg N ha⁻¹ as urea showed a decrease in its growth and N₂-fixation with delay in application. Use of Azolla up to 3 weeks after planting (WAP) during wet and 4 WAP during dry season produced significantly more grain yield than 30 kg N ha⁻¹, whereas its application upto one WAP produced more grain yield than 60 kg N ha⁻¹. Grain yield with Azolla applied at the time of planting was similar to that of 60 kg N treatment during the wet season. Higher grain yields in zero and one WAP Azolla treatments resulted due to increase in both number of panicles m⁻² and number of grains/panicle while the subsequent Azolla inoculations increased grain yield mainly by producing more number of grains/panicle. Dry matter and total N yields at maturity of rice crop were more with Azolla application upto 3 WAP during wet and 2 WAP during dry season while the reduction in sterility (%) was observed upto one WAP over 30 kg N ha⁻¹ during both seasons. Number of tillers m⁻² and dry matter production at maximum tillering and flowering were more than 30 kg N ha⁻¹ with the use of Azolla upto one WAP. Increased grain N yield was observed with the use of Azolla upto 4 WAP during two seasons whereas straw N yield increased upto one WAP during wet and 2 WAP during dry season.     

Effects of climatic variation on field metabolism and water relations of desert tortoises

We used the doubly labeled water method to measure the field metabolic rates (FMRs, in kJ kg^?1?day^?1) and water flux rates (WIRs, in ml H₂O?kg^?1?day^?1) of adult desert tortoises (Gopherus agassizii) in three parts of the Mojave Desert in California over a 3.5-year period, in order to develop insights into the physiological responses of this threatened species to climate variation among sites and years. FMR, WIR, and the water economy index (WEI, in ml H₂O?kJ^?1, an indicator of drinking of free water) differed extensively among seasons, among study sites, between sexes, and among years. In high-rainfall years, males had higher FMRs than females. Average daily rates of energy and water use by desert tortoises were extraordinarily variable: 28-fold differences in FMR and 237-fold differences in WIR were measured. Some of this variation was due to seasonal conditions, with rates being low during cold winter months and higher in the warm seasons. However, much of the variation was due to responses to year-to-year variation in rainfall. Annual spring peaks in FMR and WIR were higher in wet years than in drought years. Site differences in seasonal patterns were apparently due to geographic differences in rainfall patterns (more summer rain at eastern Mojave sites). In spring 1992, during an El Niño (ENSO) event, the WEI was greater than the maximal value obtainable from consuming succulent vegetation, indicating copious drinking of rainwater at that time. The physiological and behavioral flexibility of desert tortoises, evident in individuals living at all three study sites, appears central to their ability to survive droughts and benefit from periods of resource abundance. The strong effects of the El Niño (ENSO) weather pattern on tortoise physiology, reproduction, and survival elucidated in this and other studies suggest that local manifestations of global climate events could have a long-term influence on the tortoise populations in the Mojave Desert.     

Seasonal metabolism of a small, arboreal monitor lizard, Varanus scalaris, in tropical Australia

The field metabolic rates (FMR) and water fluxes of Varanus scalaris were measured during the wet and dry seasons by the doubly-labelled water technique. Seasonal measurements of standard (night-time) metabolism (SMR) and resting (daytime) metabolism (RMR) were made in the laboratory at 18, 24, 30 and 36°C, and maximal oxygen consumption was measured at 36°C on a motorized treadmill. This population was active throughout the year. In the wet season, the mean FMR was 7.8 kJ day⁻¹ (128.0 kJkg⁻¹ day⁻¹; mean mass = 66.4 g, n = 13), and during the dry season the mean was 5.0 kJ day⁻¹ (67.6 kJ kg⁻¹ day⁻¹; mean mass = 77.4 g, n = 17). The mean water flux rates for these animals were 3.6 and 1.2 ml day⁻¹, respectively (60.4 and 16.6 ml kg⁻¹ day⁻¹). The seasonal means of FMR and water flux were significantly different by ANCOVA ( P < 0.0001). Measurements of SMR and RMR were significantly higher in the wet season (ANCOVA: P < 0.0001), but we found no difference in the maximal oxygen consumption between seasons (ANCOVA: P = 0.6). The maximal oxygen consumption of the lizards on the treadmill (2.9 ml min⁻¹= 1.8 ml g⁻¹ h⁻¹), mean mass = 97.4 g, n = 16) was 20 times that of the SMR at the same temperature during the dry season, and 11 times that of the SMR during the wet season. The seasonal differences in FMR were attributable to: changes in SMR (12.2%) and RMR (16.4%); differences in night-time body temperatures (11.3) and daytime body temperatures (16.4%); and activity (broadly defined to include locomotion, digestion, and reproductive costs (43.7%).     

Fluxes of carbon, water and energy over Brazilian cerrado: an analysis using eddy covariance and stable isotopes

We present the energy and mass balance of cerrado sensu stricto (a Brazilian form of savanna), in which a mixture of shrubs, trees and grasses forms a vegetation with a leaf area index of 1·0 in the wet season and 0·4 in the dry season. In the wet season the available energy was equally dissipated between sensible heat and evaporation, but in the dry season at high irradiance the sensible heat greatly exceeded evaporation. Ecosystem surface conductance g_s in the wet season rose abruptly to 0·3 mol m^?2 s^?1 and fell gradually as the day progressed. Much of the total variation in g_s was associated with variation in the leaf-to-air vapour pressure deficit of water and the solar irradiance. In the dry season the maximal g_s values were only 0·1 mol m^?2 s^?1. Maximal net ecosystem fluxes of CO₂ in the wet and dry season were –10 and –15 μmol CO₂ m^?2 s^?1, respectively (sign convention: negative denotes fluxes from atmosphere to vegetation). The canopy was well coupled to the atmosphere, and there was rarely a significant build-up of respiratory CO₂ during the night. For observations in the wet season, the vegetation was a carbon dioxide sink, of maximal strength 0·15 mol m^?2 d^?1. However, it was a source of carbon dioxide for a brief period at the height of the dry season. Leaf carbon isotopic composition showed all the grasses except for one species to be C₄, and all the palms and woody plants to be C₃. The CO₂ coming from the soil had an isotopic composition that suggested 40% of it was of C₄ origin.     

Growth and physiological responses of cotton (Gossypium hirsutum L.) to elevated carbon dioxide and ultraviolet-B radiation under controlled environmental conditions

Better understanding of crop responses to projected changes in climate is an important requirement. An experiment was conducted in sunlit, controlled environment chambers known as soil–plant–atmosphere–research units to determine the interactive effects of atmospheric carbon dioxide concentration [CO₂] and ultraviolet‐B (UV‐B) radiation on cotton (Gossypium hirsutum L.) growth, development and leaf photosynthetic characteristics. Six treatments were used, comprising two levels of [CO₂] (360 and 720 µmol mol^?1) and three levels of 0 (control), 7.7 and 15.1 kJ m^?2 d^?1 biologically effective UV‐B radiations within each CO₂ level. Treatments were imposed for 66 d from emergence until 3 weeks after the first flower stage. Plants grown in elevated [CO₂] had greater leaf area and higher leaf photosynthesis, non‐structural carbohydrates, and total biomass than plants in ambient [CO₂]. Neither dry matter partitioning among plant organs nor pigment concentrations was affected by elevated [CO₂]. On the other hand, high UV‐B (15.1 kJ m^?2 d^?1) radiation treatment altered growth resulting in shorter stem and branch lengths and smaller leaf area. Shorter plants at high UV‐B radiation were related to internode lengths rather than the number of mainstem nodes. Fruit dry matter accumulation was most sensitive to UV‐B radiation due to fruit abscission. Even under 7.7 kJ m^?2 d^?1 of UV‐B radiation, fruit dry weight was significantly lower than the control although total biomass and leaf photosynthesis did not differ from the control. The UV‐B radiation of 15.1 kJ m^?2 d^?1 reduced both total (43%) and fruit (88%) dry weights due to smaller leaf area and lower leaf net photosynthesis. Elevated [CO₂] did not ameliorate the adverse effects of UV‐B radiation on cotton growth and physiology, particularly the boll retention under UV‐B stress.     

Seasonal activity and energetics of two species of varanid lizards in tropical Australia

The field metabolic rates (FMR) and rates of water flux were measured in two species of varanid lizards over five periods of the year in tropical Australia. The energetics of these species were further investigated by directly measuring activity (locomotion) and body temperatures of free-ranging animals by radiotelemetry, and by measuring standard metabolic rate (over a range of body temperatures) and activity metabolism in the laboratory. Seasonal differences in the activity and energetics were found in these goannas despite similar, high daytime temperatures throughout the year in tropical Australia. Periods of inactivity were associated with the dry times of the year, but the onset of this period of inactivity differed with respect to habitat even within the same species. Varanus gouldii, which inhabit woodlands only, were inactive during the dry and late dry seasons. V. panoptes that live in the woodland had a similar seasonal pattern of activity, but V. panoptes living near the floodplain of the South Alligator River had their highest levels of activity during the dry season when they walked long distances to forage at the receding edge of the floodplain. However, during the late dry season, after the floodplain had dried completely, they too became inactive. For V. gouldii, the rates of energy expenditure were 196 kJ kg^–1 day^–1 for active animals and 66 kJ kg^–1 day^–1 for inactive animals. The rates of water influx for these groups were respectively 50.7 and 19.5 ml kg^–1 day^–1. For V. panoptes, the rates of energy expenditure were 143 kJ kg^–1 day^–1 for active animals and 56 kJ kg^–1 day^–1 for inactive animals. The rates of water influx for these two groups were respectively 41.4 and 21.0 ml kg^–1 day^–1. We divided the daily energy expenditure into the proportion of energy that lizards used when in burrows, out of burrows but inactive, and in locomotion for the two species during the different seasons. The time spent in locomotion by V. panoptes during the dry season is extremely high for a reptile (mean of 3.5 h/day spent walking), and these results provide an ecological correlate to the high aerobic capacity found in laboratory measurements of some species of varanids.     

Fluxes of nitrogen and phosphorus in a gallery forest in the Cerrado of central Brazil

The Gallery forests of the Cerrado biome play a critical role in controlling stream chemistry but little information about biogeochemical processes in these ecosystems is available. This work describes the fluxes of N and P in solutions along a topographic gradient in a gallery forest. Three distinct floristic communities were identified along the gradient: a wet community nearest the stream, an upland dry community adjacent to the woodland savanna and an intermediate community between the two. Transects were marked in the three communities for sampling. Fluxes of N from bulk precipitation to these forests resulted in deposition of 12.6 kg ha^?1 y^?1 of total N of which 8.8 kg ha^?1 was as inorganic N. The throughfall flux of total N was generally <8.4 kg ha^?1 year^?1. Throughfall NO₃?CN fluxes were higher (7?C32%) while NH₄?CN and organic N fluxes were lower (54?C69% and 5?C46%) than those in bulk precipitation. The throughfall flux was slightly lower for the wet forest community compared to other communities. Litter leachate fluxes differed among floristic communities with higher NH₄?CN in the wet community. The total N flux was greater in the wet forest than in the dry forest (13.5 vs. 9.4 kg ha^?1 year^?1, respectively). The stream water had total N flux of 0.3 kg ha^?1 year^?1. The flux of total P through bulk precipitation was 0.7 kg ha^?1 year^?1 while the mean fluxes of total P in throughfall (0.6 kg ha^?1 year^?1) and litter leachate (0.5 kg ha^?1 year^?1) declined but did not differ between communities. The low concentrations presented in soil solution and low fluxes in stream water (0.3 and 0.1 kg ha^?1 year^?1 for N and P, respectively) relative to other flowpaths emphasize the conservative nutrient cycling of these forests and the importance of internal recycling processes for the maintenance and conservation of riparian and stream ecosystems in the Cerrado.     

High rates of net ecosystem carbon assimilation by Brachiara pasture in the Brazilian Cerrado

To investigate the consequences of land use on carbon and energy exchanges between the ecosystem and atmosphere, we measured CO₂ and water vapour fluxes over an introduced Brachiara brizantha pasture located in the Cerrado region of Central Brazil. Measurements using eddy covariance technique were carried out in field campaigns during the wet and dry seasons. Midday CO₂ net ecosystem exchange rates during the wet season were ?40 μmol m^?2 s^?1, which is more than twice the rate found in the dry season (?15 μmol m^?2 s^?1). This was observed despite similar magnitudes of irradiance, air and soil temperatures. During the wet season, inferred rates of canopy photosynthesis did not show any tendency to saturate at high solar radiation levels, with rates of around 50 μmol m^?2 s^?1 being observed at the maximum incoming photon flux densities of 2200 μmol m^?2 s^?1. This contrasted strongly to the dry period when light saturation occurred with 1500 μmol m^?2 s^?1 and with maximum canopy photosynthetic rates of only 20 μmol m^?2 s^?1. Both canopy photosynthetic rates and night‐time ecosystem CO₂ efflux rates were much greater than has been observed for cerrado native vegetation in both the wet and dry seasons. Indeed, observed CO₂ exchange rates were also much greater than has previously been reported for C₄ pastures in the tropics. The high rates in the wet season may have been attributable, at least in part, to the pasture not being grazed. Higher than expected net rates of carbon acquisition during the dry season may also have been attributable to some early rain events. Nevertheless, the present study demonstrates that well‐managed, productive tropical pastures can attain ecosystem gas exchange rates equivalent to fertilized C₄ crops growing in the temperate zone.     

Fluxes of nitrous oxide, methane and carbon dioxide during freezing–thawing cycles in an Inner Mongolian steppe

Combined measurements of nitrification activity and N₂O emissions were performed in a lowland and a montane tropical rainforest ecosystem in NE-Australia over a 18 months period from October 2001 until May 2003. At both sites gross nitrification rates, measured by the BaPS technique, showed a strong seasonal pattern with significantly higher rates of gross nitrification during wet season conditions. Nitrification rates at the montane site (1.48?±?0.24–18.75?±?2.38 mg N kg^?1 day^?1) were found to be significantly higher than at the lowland site (1.65?±?0.21–4.54?±?0.27 mg N kg^?1 day^?1). The relationship between soil moisture and gross nitrification rates could be described best by O’Neill functions having a soil moisture optimum of nitrification at app. 65% WFPS. At the lowland site, for which continuous measurements of N₂O emissions were available, nitrification was positively correlated with N₂O emission. Nitrification contributed significantly to N₂O formation during dry season (app.85%) but less (app. 30%) during wet season conditions. In average 0.19‰ of the N metabolized by nitrification was released as N₂O. The N₂O fraction loss for nitrification was positively correlated with changes in soil moisture and varied slightly between 0.15 and 0.22‰. Our results demonstrate that combined N₂O emission and microbial N turnover studies covering prolonged observation periods are needed to clarify and quantify the role of the microbial processes nitrification and denitrification for annual N₂O emissions from soils of terrestrial ecosystems.     

Gross Primary Productivity of a High Elevation Tropical Montane Cloud Forest

For decades, the productivity of tropical montane cloud forests (TMCF) has been assumed to be lower than in tropical lowland forests due to nutrient limitation, lower temperatures, and frequent cloud immersion, although actual estimates of gross primary productivity (GPP) are very scarce. Here, we present the results of a process-based modeling estimate of GPP, using a soil–plant–atmosphere model, of a high elevation Peruvian TMCF. The model was parameterized with field-measured physiological and structural vegetation variables, and driven with meteorological data from the site. Modeled transpiration corroborated well with measured sap flow, and simulated GPP added up to 16.2 ± SE 1.6 Mg C ha^?1 y^?1. Dry season GPP was significantly lower than wet season GPP, although this difference was 17% and not caused by drought stress. The strongest environmental controls on simulated GPP were variation of photosynthetic active radiation and air temperature (T _air). Their relative importance likely varies with elevation and the local prevalence of cloud cover. Photosynthetic parameters (V _cmax and J _max) and leaf area index were the most important non-environmental controls on GPP. We additionally compared the modeled results with a recent estimate of GPP of the same Peruvian TMCF derived by the summing of ecosystem respiration and net productivity terms, which added up to 26 Mg C ha^?1 y^?1. Despite the uncertainties in modeling GPP we conclude that at this altitude GPP is, conservatively estimated, 30–40% lower than in lowland rainforest and this difference is driven mostly by cooler temperatures than changes in other parameters.     

Land use and season affect fluxes of CO2, CH4, CO,N2O,H2 and isotopic source signatures in Panama: evidence from nocturnal boundary layer profiles

Conversion of tropical rainforests to pastures and plantations is associated with changes in soil properties and biogeochemical cycling, with implications for carbon cycling and trace gas fluxes. The stable isotopic composition of ecosystem respiration (δ¹³C_R and δ¹⁸O_R) is used in inversion models to quantify regional patterns of CO₂ sources and sinks, but models are limited by sparse measurements in tropical regions. We measured soil respiration rates, concentrations of CO₂, CH₄, CO, N₂O and H₂ and the isotopic composition of CO₂, CH₄ and H₂ at four heights in the nocturnal boundary layer (NBL) above three common land‐use types in central Panama, during dry and rainy seasons. Soil respiration rates were lowest in Plantation (average 3.4 μmol m^?2 s^?1), highest in Pasture (8.3 μmol m^?2 s^?1) and intermediate in Rainforest (5.2 μmol m^?2 s^?1). δ¹³C_R closely reflected land use and increased during the dry season where C₃ vegetation was present. δ¹⁸O_R did not differ by land use but was lower during the rainy than the dry season. CO₂ was correlated with other species in approximately half of the NBL profiles, allowing us to estimate trace gas fluxes that were generally within the range of literature values. The Rainforest soil was a sink for CH₄ but emissions were observed in Pasture and Plantation, especially during the wet season. N₂O emissions were higher in Pasture and Plantation than Rainforest, contrary to expectations. Soil H₂ uptake was highest in Rainforest and was not observable in Pasture and Plantation during the wet season. We observed soil CO uptake during the dry season and emissions during the wet season across land‐use types. This study demonstrated that strong impacts of land‐use change on soil–atmosphere trace gas exchange can be detected in the NBL, and provides useful observational constraints for top‐down and bottom‐up biogeochemistry models.     

Soybean residues sequestration affected by different tillage practices and the impacts on soil microbial characteristics and enzymatic activities

A large quantity of leaf litter was left on soil surface after soybean (Glycine max) harvest in the black soil region, northeast of China, where soybean was planted with the largest area. This paper investigated the effects of different fall tillage practices on soybean leaf litter sequestration into soil, and the subsequently durative effects on soil biological and biochemical properties during the next growing season. Two practices were investigated, fall tillage (T) and no fall tillage (NT) after soybean harvest in autumn. Results showed that the residue biomass on soil surface and in subsoil profile (0–20 cm) after soybean harvest was about 1450 kg ha^?1 and 340 kg ha^?1, respectively in October 2006. The residue biomass on soil surface and in subsoil profile was about 84 kg ha^?1, 1581 kg ha^?1 for T, and 423 kg ha^?1, 340 kg ha^?1 for NT respectively in May 2007. It was obvious that T practice can more effectively sequester leaf litter into soil compared to NT. Results also showed that T practices after soybean harvest eminently improved soil microbial carbon biomass and nitrogen biomass contents, and significantly improved soil urease and acid phosphate activities than NT. No significant difference of dehydrogenase activity was found between N and NT. The positive effects of T treatment on Soil microbial properties and soil enzymes activities among the next growing season due to soybean residues sequestration performed durative profit.     

Factors Affecting Methylmercury Levels in Surficial Tailings from Historical Nova Scotia Gold Mines

Large quantities of Hg remain in tailings dumps from historical Nova Scotian gold mines. Depth profiles of total Hg (Hg_T) and methylmercury (MeHg) were compared with geochemical and microbiological variables, to identify factors influencing MeHg levels in tailings. Hg_T and MeHg were highly variable in tailings (0.2–73.5 μ mol kg^{? 1} and < dl-56.4 nmol kg^{? 1}, respectively), and were influenced by a complex set of in situ factors. Elevated MeHg was linked with > 5 μ mol kg^?1 Hg_T, organic matter, hydrology, abundance and activity of sulfate reducing bacteria, and demethylation processes. Methylmercury levels in tailings from a wet, bog-like site appeared to undergo seasonal fluctuations, with higher concentrations measured in September and October, and lower concentrations in May. Evaluations of amalgamation tailings should examine MeHg and Hg_T transport out of low-lying, saturated tailings dumps after snowmelt and major rainfall events, and should take into account the possibility of seasonal variation in MeHg levels in northern regions.     

Site specific and regional estimates of methane uptake by tropical rainforest soils in north eastern Australia

Methane flux from rainforest soils in northeast Queensland, Australia, was investigated using a combination of laboratory, field and simulation modelling. In aerobic laboratory incubations, CH₄ uptake in the top 0.1 m of the soil (?2.5 to ?7.3 μg CH₄ kg^?1 SDW day^?1) is approximately one order of magnitude higher than CH₄ production under anaerobic conditions. The highest CH₄ uptake, as well as potential CH₄ production is found in the uppermost C rich soil layers. Detailed measurements from three contrasting rainforest sites identified the soils to be functioning as sinks for atmospheric CH₄. Fifteen months continuous measurement at one of the lowland rainforest sites showed that the seasonality of CH₄ uptake was mainly driven by changes in soil moisture rather than by temperature changes. Maximum CH₄ uptake (109 μg CH₄ m^?2 h^?1) was observed during dry season conditions, whereas during the wet season, CH₄ uptake decreased significantly to near zero. Based on our laboratory experiments and on published literature we developed a semi-empirical CH₄ module for the biogeochemical model ForestDNDCtropica. Tests at several sites showed the robustness of our modelling approach with mean simulated values within 12% of observed values. To estimate regional CH₄ uptake by rainforest soils in the region of the ‘Wet Tropics’, Queensland, Australia, we linked CH₄ uptake and production algorithms to a regional GIS database. We estimated that the lowland and montane rainforest soils in northeast Queensland, Australia, were a net sink for CH₄ with a mean uptake rate of ?2.89 kg CH₄ ha^?1 year^?1 during July 1996 to June 1997 period.     

Growth and maintenance respiration in leaves of northern red oak seedlings and mature trees after 3 years of ozone exposure

A two-component model of growth and maintenance respiration is used to study the response of northern red oak (Quercus rubra L.) seedlings and 32-year-old trees to sub-ambient (10 μmol h; cumulative dose based on 7 h daily mean), ambient (43 μmol h), and twice-ambient (85 μmolh) ozone. The relative growth rates (RGR) of leaves sampled from seedlings and trees were similar across treatments, as were specific leaf respiration rates (SRR). Growth coefficients estimated from the SRR versus RGR relationship averaged 25-3 mol CO2 kg^?1 leaf dry mass produced for seedlings and 21-5 mol kg^?1 for trees. Maintenance coefficients ranged from 0-89 to 1-07 mol CO₂ kg^?1 leaf dry mass d^?1 for seedlings and from 0-64 to 0-84 mol kg-1 d^?1 for trees. Neither coefficient was affected by ozone. Leaves sampled throughout the growing season also showed little response of respiration to ozone. This occurred despite a 30% reduction in net photosynthesis for trees grown at twice-ambient ozone. These results suggest that growth and maintenance respiration in young northern red oak leaves are not affected by ozone and that in older leaves injury can occur without a parallel increase in so-called ‘maintenance’ respiration.     

Water flux and energy use in wild house mice (Mus domesticus) and the impact of seasonal aridity on breeding and population levels

Summary Water turnover rate (WTR), urine concentration and field metabolic rate (FMR) were examined in house mice, Mus domesticus, permanently inhabiting roadside verge areas and seasonally invading crops in semi-arid wheatlands in South Australia. FMR was approximately proportional to body mass^0.5 and mean values varied from 4.8 ml CO₂ g^–1h^–1 (2.9 kJ g^–1d^–1) in autumn and winter, to 7.0 ml CO₂ g^–1h^–1 (4.2 kJ g^–1d^–1) in maturing crops during spring. WTR was independent of body mass, indicating that larger mice were selecting a diet containing moister foods. WTR was low in summer and high in winter, and in mice from crops varied from 165 ml l^–1 body water d^–1 (122 ml kg^–1d^–1) to 1000 ml l^–1d^–1 (725 ml kg^–1d^–1). Seasonal changes in WTR were less extreme on the roadside, where a greater diversity of food was available. In the crops, breeding occurred throughout summer during two of three years, but the population increased only in the one summer when mice had marginally higher WTR. On the roadside breeding and population growth were continuous during summer, except in a drought year. Avcrage urine concentration was inversely related to WTR, and varied from 2.0 to 4.8 Osm l^–1. The data indicate that the water conserving abilities of mice equal those of many desert rodents. The water conserving abilities of mice living in crops during summer were fully extended, and in some years aridity limited breeding success and population levels. The degree of moisture stress to which mice are exposed during summer appears to depend not only on rainfall but also on other factors such as availability of food and shelter, and the level of weed infestation in crops.