Dry Season Conditions Research Articles

Bare Surface Soil Moisture Estimation Using Double-Angle and Dual-Polarization L-Band Radar Data

Based on today's most widely used surface scattering model, the advanced integral equation model (AIEM), this study proposes a novel soil moisture inversion model that estimates bare surface soil moisture using double-incidence angle and dual-polarized L-band radar data. Compared with previous studies at L-/C-band, the proposed method provides the estimation of soil moisture without referring to the measured soil roughness and eliminates the requirement of an initial dry season condition. The root-mean-square error (rmse) of volumetric soil moisture varies from 0.8% to 3.2% at different incidence-angle combinations validated by simulated solving and from 4.0% to 7.9% by field measurements when the paired incidence angles are not both large. In case the paired angels are both large, not particularly suitable for soil moisture estimation, the rmse increases to 10.3%. Therefore, this method is applicable to bare surface soil moisture retrieval when at least one of the incidence angles is not large.

Dynamics of copper and zinc sedimentation in a lagooning system receiving landfill leachate

This study characterises the sediment dredged from a lagooning system composed of a settling pond and three lagoons that receive leachates from a municipal solid waste (MSW) landfill in France. Organic carbon, carbonate, iron oxyhydroxides, copper (Cu) and zinc (Zn) concentrations were measured in the sediment collected from upstream to downstream in the lagooning system. In order to complete our investigation of sedimentation mechanisms, leachates were sampled in both dry (spring) and wet (winter) seasonal conditions. Precipitation of calcite and amorphous Fe-oxyhydroxides and sedimentation of organic matter occurred in the settling pond. Since different distributions of Zn and Cu concentrations are measured in sediment samples collected downstream in the lagooning system, it is suggested that these elements were not distributed in a similar way in the leachate fractions during the first stage of treatment in the settling pond, so that their sedimentation dynamics in the lagooning system differ. In the lagoons, it was found that organic carbon plays a major role in Cu and Zn mobility and trapping. The presence of macrophytes along the edges provided an input of organic matter that enhanced Cu and Zn scavenging. This edge effect resulted in a two-fold increase in Cu and Zn concentrations in the sediment deposited near the banks of the lagoons, thus confirming the importance of vegetation for the retention of Cu and Zn in lagooning systems.

Influence of Vertisol development on sauropod egg taphonomy and distribution at the Auca Mahuevo locality, Patagonia, Argentina

At the Auca Mahuevo locality in the Upper Cretaceous Anacleto Formation in Patagonia, Argentina pedogenic processes associated with Vertisol development affected changes in both individual titanosaur egg morphology and three-dimensional egg distribution. These changes resulted primarily from vertical and lateral movement within fluvial overbank sediments due to clay mineral expansion and contraction in alternating wet and dry seasonal conditions. At the scale of individual sauropod eggs, pedogenic sediment movement produced egg shearing, eggshell fracture and displacement, mechanical abrasion of egg ornamentation, and alteration of egg size and shape. Movement of either individual eggs or subsets of eggs along slickensided surfaces (1) modified the number and relative position of eggs within individual clutches, (2) combined eggs of one of more clutches produced by different females, and (3) combined eggs from one or more nesting horizons, producing a time-averaged fossil assemblage. These mechanisms of egg rearrangement suggest that accurate interpretation of dinosaur reproductive behavior using fossil egg assemblages preserved in fine-grained fluvial overbank deposits require careful assessment of pedogenic processes.

Modeling Groundwater Level Fluctuation in the Tropical Peatland Areas under the Effect of El Nino

Abstract This research aimed to model groundwater level (GWL) fluctuation in the tropical peatland areas under the effect of El Nino Southern Oscillation (ENSO). The focus of the study was the peatland area between Sebangau River and Kahayan River, Central Kalimantan Province Indonesia. One-dimensional GWL model was developed using Excel in order to simulate the GWL fluctuation of 4 GWL observation wells which were Swtr2, Swtr3, Swtr4, and Swtr6. The model was calibrated for the dry season 2011 and, after that, was used to model GWL fluctuation in El Nino year of 1997 and 2002. The model showed very good performance in simulating GWL fluctuation of 4 observation wells in the dry season condition where the GWL were under the ground level elevation. The model indicated that in the El Nino years of 1997 and 2002, the GWL in the observed area in the dry season dropped significantly due to the absence of rainfall in the area. Based on the model, the fire risk in the tropical peatland areas can be measured and predicted.

Sheep grazing bladder clover (Trifolium spumosum L.) had similar productivity and meat quality to sheep grazing subterranean clover (Trifolium subterraneum L.)

An accession of bladder clover, a new species to agriculture, was selected for commercial release in Australia with the cultivar name of AGWEST Bartolo. As part of a duty-of-care assessment, we tested the hypothesis that sheep grazing the bladder clover cultivar will have similar liveweight, condition scores and wool production to sheep grazing a widely adopted subterranean clover cultivar (cv. Dalkeith). Further, we hypothesised that sheep grazing bladder clover and subterranean clover will have similar meat quality (after 48 days of grazing) and health as indicated by muscle, liver and kidney panel analysis. The data supported the hypotheses. While there were significant initial differences in liveweight between the two groups of sheep, there were no significant differences in liveweight at later time points during the grazing period and no significant differences in mean daily growth rate between weighing times. There were no differences in wool growth between sheep grazing the bladder or subterranean clover cultivars. Sheep in the subterranean clover plots had significantly higher condition scores after the first 24 days of grazing; however, these differences were not apparent after another 24 days of grazing. There were some differences in indications of animal health; however, there were no significant detrimental effects associated with bladder clover and sheep grazing both species had mean plasma indicators that were deemed ‘healthy’. There were no differences in meat eating quality as estimated by a consumer panel for tenderness, juiciness or flavour. Dry seasonal conditions limited biomass growth and the sheep were removed from the subterranean clover plots on Day 48 of grazing. The sheep grazing the bladder clover plots remained on the plots for a further 26 days. The data indicate that, for the conditions of this experiment, the clovers had the same relative feeding value. Laboratory analysis of herbage from across the clover plots (bulked before analysis) suggest that the bladder clover had higher in vitro digestibility, crude protein and lower fibre than the herbage sample from the subterranean clover plots. The biomass data indicate that the bladder clover cultivar can support more grazing days per ha in a relatively dry season than the subterranean clover cultivar.

Spatial distribution and seasonal variation of polycyclic aromatic hydrocarbons (PAHs) contaminations in surface water from the Hun River, Northeast China

The objectives of this study were to investigate the levels, dispersion patterns, seasonal variation, and sources of 16 priority polycyclic aromatic hydrocarbons (16 EPA-PAHs) in the Hun River of Liaoning Province, China. Samples of surface water were collected from upstream to downstream locations, and also from the main tributaries of the Hun River in dry period, flood period, and level period, respectively. After appropriate preparation, all samples were analyzed for 16 EPA-PAHs. Total PAHs concentrations varied from 124.55 to 439.27 ng l(-1) in surface water in dry period, 1,615.75 to 5,270.04 ng l(-1) in flood period, and 2,247.42 to 7,767.9 ng l(-1) in level period. The 16 EPA-PAHs concentrations were significantly increased in the order of level period > flood period > dry period. The composition pattern of PAHs in surface water was dominated by low molecular weight PAHs, in particular two- to three-ring PAHs. In addition, two-ring PAH accounted for 39.33 to 88.27 % of the total PAHs in level period. Low molecular weight PAHs predomination together with higher levels of PAHs in flood and level period suggested a relatively recent local source of PAHs. Special PAHs ratios such as phenanthrene/anthracene and fluoranthene/pyrene indicated that under dry weather season conditions, the PAHs found in surface water were primarily from petrogenic source, while under wet weather season conditions they were from mixed source of both petrogenic inputs and combustion sources. The comparison of PAHs contamination among different types of areas in China suggested that atmospheric depositions might be the most important approaches of PAHs into water system. Although the Hun River exists low PAHs ecological risk now, potential toxic effects will be existed in the future especially in flood and level period.

Water Use Efficiency and Physiological Response of Rice Cultivars under Alternate Wetting and Drying Conditions

One of the technology options that can help farmers cope with water scarcity at the field level is alternate wetting and drying (AWD). Limited information is available on the varietal responses to nitrogen, AWD, and their interactions. Field experiments were conducted at the International Rice Research Institute (IRRI) farm in 2009 dry season (DS), 2009 wet season (WS), and 2010 DS to determine genotypic responses and water use efficiency of rice under two N rates and two water management treatments. Grain yield was not significantly different between AWD and continuous flooding (CF) across the three seasons. Interactive effects among variety, water management, and N rate were not significant. The high yield was attributed to the significantly higher grain weight, which in turn was due to slower grain filling and high leaf N at the later stage of grain filling of CF. AWD treatments accelerated the grain filling rate, shortened grain filling period, and enhanced whole plant senescence. Under normal dry-season conditions, such as 2010 DS, AWD reduced water input by 24.5% than CF; however, it decreased grain yield by 6.9% due to accelerated leaf senescence. The study indicates that proper water management greatly contributes to grain yield in the late stage of grain filling, and it is critical for safe AWD technology.

Major and trace metal mobility during weathering of mine tailings: Implications for floodplain soils

Mine tailings discharged to river systems have the potential to release significant quantities of major and trace metals to waters and soils when weathered. To provide data on the mechanisms and magnitudes of short- and long-term tailings weathering and its influence on floodplain environments, three calendar year-long column leaching experiments that incorporated tailings from Potosí, Bolivia, and soil from unaffected downstream floodplains, were carried out. These experiments were designed to model 20 cycles of wet and dry season conditions. Two duplicate columns modeled sub-aerial tailings weathering alone, a third modeled the effects of long-term floodplain tailings contamination and a fourth modeled that of a tailings dam spill on a previously contaminated floodplain. As far as was practical local climatic conditions were modeled. Chemical analysis of the leachate and column solids, optical mineralogy, XRD, SEM, EPMA, BCR and water-soluble chemical extractions and speciation modeling were carried out to determine the processes responsible for the leaching of Al, Ca, Cu, K, Na, Mg, Mn, Sn, Sr and Ti. Over the 20 cycles, the pH declined to a floor of ca. 2 in all columns. Calcium, Cu, Mg, Mn and Na showed significant cumulative losses of up to 100%, 60%, 30%, 95% and 40%, respectively, compared to those of Al, K, Sr, Sn and Ti, which were up to 3%, 1.5%, 5%, 1% and 0.05%, respectively. The high losses are attributed to the dissolution of relatively soluble minerals such as biotite, and oxidation of chalcopyrite and Cu-sulfosalts, while low losses are attributed to the presence of sparingly soluble minerals such as svanbergite, cassiterite and rutile. These results strongly suggest that the release of tailings to floodplains should be limited or prohibited, and that all tailings should be removed from floodplains following dam spills.

Environmental impacts of irrigated sugarcane production: Herbicide run-off dynamics from farms and associated drainage systems

Irrigation is vital to most of the sugarcane produced in Australia's ecologically sensitive Great Barrier Reef catchment area, although little is known regarding pesticide losses under irrigated sugarcane production. This study determined the dynamics of off-site paddock-scale pesticide movement and subsequent concentrations in local receiving environments in fully irrigated sugarcane farming systems of the lower Burdekin floodplain region, the largest sugar producing area in Australia. Chemical movement (both mass and concentration) in paddock surface run-off followed a similar pattern across sites in the region for several of the commonly applied herbicides such as diuron, atrazine and ametryn. Highest losses (loads and event concentrations) occurred in the first irrigation run-off events following application, with subsequent irrigation losses tailing off rapidly. Significant losses could also occur during wet season rainfall run-off events from paddocks with recent pesticide applications. There was a strong seasonal signal evident in catchment monitoring results. Pesticide concentrations in nearby receiving creek systems were invariably an order of magnitude or more lower than values collected at paddock-scale, highlighting the considerable dilution that takes place over relatively short distances. While the concentrations found in receiving creek systems were considerably lower than direct paddock run-off, they regularly exceeded some ecological guidelines and results of pesticide risk modeling suggested concentrations, particularly under dry season conditions, posed considerable ecological risk to aquatic ecosystems.

Using Trichogramma Westwood (Hymenoptera: Trichogrammatidae) for insect pest biological control in cotton crops: an Australian perspective

Trichogramma Westwood egg parasitoids alone generally fail to suppress heliothine pests when released in established cotton-growing regions. Factors hindering their success include indiscriminate use of detrimental insecticides, compensation for minimal pest larval hatch due to their activity via reduced larval cannibalism or mortality in general, singly laid heliothine eggs avoiding detection and asynchronous development benefiting host over parasitoid. Yet, despite these limitations, relatively large Trichogramma pretiosum Riley populations pervade and effectively suppress Helicoverpa (Hardwick) pests in Australian Bt (Bacillus thuringiensis Berliner)-transgenic cotton, Gossypium hirsutum L., crops, especially in the Ord River Irrigation Area (ORIA) of tropical northern Australia, where their impact on the potentially resistant pest species, Helicoverpa armigera (Hübner), is considered integral to the local insecticide resistance management (IRM) strategy for continued, sustainable Bt-transgenic cotton production. When devoid of conventional insecticides, relatively warm and stable conditions of the early dry season in ‘winter’ grown ORIA Bt-transgenic cotton crops are conducive to Trichogramma proliferation and biological control appears effective. Further, there is considerable scope to improve Trichogramma's biological control potential, in both the ORIA and established cotton-growing regions, via habitat manipulation. It is proposed that Trichogramma may prove equally effective in developing agricultural regions of monsoonal northern Australia, and that environmental constraints on Trichogramma survival, and those of other natural enemies, require due consideration prior to their successful application in biological control programs.

Evaluation of case-based design principles in the design of Soche wastewater treatment plant, Blantyre, Malawi

This paper evaluates case-based design principles in the design of Soche wastewater treatment works (WWTW) in the city of Blantyre, Malawi. According to the Case Study Manager in the ED-WAVE tool, a similar case to both dry season and wet season conditions of Soche plant is Municipal Case 6 in Greece. The raw material at Municipal Case 6 in Greece is raw municipal sewage where the typical wastewater parameters are BOD5, and TSS. The treatment target is BOD5, and TSS reduction. The study confirmed the practical use of case-based design principles in the design of wastewater treatment systems, where after encountering a new situation; already collected decision scenarios (cases) are invoked and modified in order to arrive at a particular design alternative. What is necessary, however, is to appropriately modify the case arrived at through the Case Study Manager in order to come up with a design appropriate to the local situation taking into account technical, socio-economic and environmental aspects.

The influence of flow and season upon leaf-litter breakdown in monsoonal Hong Kong streams

We investigated the effects of water extraction and flow regime on leaf litter breakdown in 10 Hong Kong streams experiencing varying degrees of extraction: five with severe extraction (>85% downstream flow removed), four with moderate extraction (20–85% removed), and one without extraction (~0% removed). Breakdown rates, macroinvertebrate assemblages and nutrients were compared in upstream (reference) reaches and downstream reaches with reduced flow in each stream during high-flow (wet season) and low-flow (dry season) conditions to determine whether responses to flow were influenced by Hong Kong’s monsoonal climate. Litter breakdown was slower in downstream reaches during the wet season, and discharge was the main determinant of breakdown rate in both reaches across the 10 study streams. In contrast, inter-reach differences in breakdown during the dry season were small and unrelated to flow. Instead, breakdown rates among streams were influenced by the abundance of detritivorous shredders and chironomids (Chironominae), as well as phosphate concentrations, indicating the importance of biological processing of litter under low-flow conditions. Although litter breakdown rates appear to offer a promising functional indicator of flow-reduction impacts during the wet season, the pattern seen reflected the physical effects of flow rather than any underlying biological processes, and the lack of response to flow reduction during the dry season was notable.

Incongruent weathering of Cd and Zn from mine tailings: A column leaching study

The weathering of discharged mine tailings can contaminate groundwaters, rivers and floodplains with potentially toxic Cd and Zn, depending on tailings mineralogy, storage, dispersal and climatic conditions. The mechanisms of long-term tailings weathering and its influence on waste piles and floodplain environments were assessed by a column leaching experiment that incorporated tailings and soil from Potosí, Bolivia, and modelled 20 cycles of wet and dry season conditions over three calendar years. Chemical analysis of the leachate and column solids, optical mineralogy, XRD, SEM, EPMA, BCR and water-soluble chemical extractions and speciation modelling were carried out to determine the processes responsible for the leaching of Cd, Fe, S and Zn. Over this period, approximately 50 to 95% of the original Cd and 50 to 60% of the Zn were leached from the columns. Large amounts of leached Cd and Zn at the beginning of the experiment are attributed to the dissolution of soluble sulphate minerals present in the original tailings and formed after the first wetting of the columns. The Zn/Cd mass ratios of the tailings and soil, initially 429 and 400, respectively, vary considerably over the course of the experiment. Low values (between 220 and 300) in the early cycles are attributed to preferential weathering of Cd-rich wurtzite [Zn,Fe)S] and sequestration of Zn in preference to Cd in secondary Fe phases forming in the columns. In the middle cycles, dissolution of secondary Fe(OH)3 under low pH (<3) conditions, and of ferroan (Cd-poor) sphalerite [Zn,Fe)S], releases Zn and raises the Zn/Cd ratio to 550–600 in the tailings-only columns and up to 1500 in the mixed tailings-soil columns. The very high ratios in the latter are also ascribed to the formation of low molecular weight organic ligands that have high affinity for Zn over Cd. In the later column-cycles, Zn/Cd ratios return to near-initial values, due to the weathering of Fe-poor sphalerite and secondary Fe phases, and the declining preference of Zn over Cd in the soil organic acids under the strongly acidic conditions prevailing in the columns. The formation and dissolution of secondary soluble sulphate minerals also play a role in Cd and Zn cycling, especially at the beginning of the experiment.

ED-WAVE tool design approach: case of Limbe wastewater treatment works, Blantyre, Malawi

The ED-WAVE tool is a PC based package for imparting training on wastewater treatment technologies. The system consists of four modules viz. Reference Library, Process Builder, Case Study Manager, and Treatment Adviser. The principles of case-based design (CBD) and case-based reasoning (CBR) as applied in the ED-WAVE tool are utilised in this paper to evaluate the design approach of Limbe wastewater treatment works (Limbe WWTW) in Malawi. The plant has an average dry weather flow rate of 1,800 m3/d. The study established that a similar case to both the dry season and wet season conditions of Soche wastewater treatment works has similarities to Municipal Case 1 in Sri Lanka, with a flow rate of 1,700 m3/d. The study further established that that there are certain unit treatment processes that are important in wastewater treatment. These include a primary sedimentation process, achieved through the imhoff tank at the plant in Sri Lanka, chemical precipitation followed by sedimentation as suggested by the dr...

Middle and late Cenomanian oceanic anoxic events in shallow and deeper shelf environments of western Morocco

The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep-water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in δ13Corg for mid-Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 δ13C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea-level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow-water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid-Cenomanian event 1b and the Cenomanian–Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north-east trade winds in tropical areas.

Annual wood production in a tropical rain forest in NE Costa Rica linked to climatic variation but not to increasing CO2

AbstractIncreased atmospheric [CO2] could theoretically lead to increased forest productivity (‘CO2 fertilization’). This mechanism was hypothesized as a possible explanation for biomass increases reported from tropical forests in the last 30+ years. We used unique long‐term records of annually measured stands (eighteen 0.5 ha plots, 10 years) and focal tree species (six species, 24 years) to assess the effects of rainfall, temperature, and atmospheric [CO2] on annual wood production in a neotropical rain forest. Our study area was a meso‐scale section (600 ha) of old‐growth Tropical Wet Forest in NE Costa Rica. Using the repeated remeasurements we directly assessed the relative effects of interannual climatic variation and increasing atmospheric [CO2] on wood production. A remarkably simple two‐factor model explained 91% of the interannual variance in stand‐level tree growth; the statistically independent factors were total dry season rainfall (positive effect, r2=0.85) and night‐time temperature (negative effect, r2=0.42). Stand‐level tree mortality increased significantly with night‐time temperature. After accounting for dry season rainfall and night‐time temperature, there was no effect of annual [CO2] on tree growth in either the stand or focal species data. Tree growth in this Tropical Wet Forest was surprisingly sensitive to the current range of dry season conditions and to variations in mean annual night‐time temperature of 1–2°. Our results suggest that wood production in the lowland rainforests of NE Costa Rica (and by extension in other tropical regions) may be severely reduced in future climates that are only slightly drier and/or warmer.

Impact of subsoil physicochemical constraints on crops grown in the Wimmera and Mallee is reduced during dry seasonal conditions

Subsoil physicochemical constraints can limit crop production on alkaline soils of south-eastern Australia. Fifteen farmer paddocks sown to a range of crops including canola, lentil, wheat, and barley in the Wimmera and Mallee of Victoria and the mid-north and Eyre Peninsula of South Australia were monitored from 2003 to 2006 to define the relationship between key abiotic/edaphic factors and crop growth. The soils were a combination of Calcarosol and Vertosol profiles, most of which had saline and sodic subsoils. There were significant correlations between ECe and Cl– (r = 0.90), ESP and B (r = 0.82), ESP and ECe (r = 0.79), and ESP and Cl– (r = 0.73). The seasons monitored had dry pre-cropping conditions and large variations in spring rainfall in the period around flowering. At sowing, the available soil water to a depth of 1.2 m (θa) averaged 3 mm for paddocks sown to lentils, 28 mm for barley, 44 mm for wheat, and 92 mm for canola. Subsoil constraints affected canola and lentil crops but not wheat or barley. For lentil crops, yield variation was largely explained by growing season rainfall (GSR) and θa in the shallow subsoil (0.10–0.60 m). Salinity in this soil layer affected lentil crops through reduced water extraction and decreased yields where ECe exceeded 2.2 dS/m. For canola crops, GSR and θa in the shallow (0.10–0.60 m) and deep (0.60–1.20 m) layers were important factors explaining yield variation. Sodicity (measured as ESP) in the deep subsoil (0.80–1.00 m) reduced canola growth where ESP exceeded 16%, corresponding to a 500 kg/ha yield penalty. For cereal crops, rainfall in the month around anthesis was the most important factor explaining grain yield, due to the large variation in rainfall during October combined with the determinant nature of these crops. For wheat, θa in the shallow subsoil (0.10–0.60 m) at sowing was also an important factor explaining yield variation. Subsoil constraints had no impact on cereal yield in this study, which is attributed to the lack of available soil water at depth, and the crops’ tolerance of the physicochemical conditions encountered in the shallow subsoil, where plant-available water was more likely to occur. Continuing dry seasonal conditions may mean that the opportunity to recharge soil water in the deeper subsoil, under continuous cropping systems, is increasingly remote. Constraints in the deep subsoil are therefore likely to have reduced impact on cereals under these conditions, and it is the management of water supply, from GSR and accrued soil water, in the shallow subsoil that will be increasingly critical in determining crop yields in the future.

Diverging temperature response of tree stem CO2 release under dry and wet season conditions in a tropical montane moist forest

It is commonly presumed that plant respiratory CO2 release increases with increasing temperature. However, we report on very contrasting stem CO2 release (R S)–temperature relationships of trees in a species-rich tropical montane forest of southern Ecuador under dry and wet season conditions. Rates of R S were low and completely uncoupled from the dial temperature regime during the humid season. In contrast, during the dry season, R S was generally higher and temperature sensitivity of R S differed greatly in degree and even in the direction of response, indicating that temperature might not be the only determinant of R S. In order to explain the heterogeneity of R S, we related R S to vapour pressure deficit, wind speed and solar radiation as important abiotic drivers influencing transpiration and photosynthesis. Stepwise multiple regression analyses with these meteorological predictors either were biased by high collinearity of the independent variables or could not enhance the ability to explain the variability of R S. We assume maintenance respiration to dominate under humid conditions unfavourable for energy acquisition of the tree, thus explaining the pronounced uncoupling of R S from atmospheric parameters. In contrast, the drier and hotter climate of the dry season seems to favour R S via enhanced assimilatory substrate delivery and stem respiratory activity as well as elevated xylem sap CO2 imports with increased transpiration. In addition, tree individual differences in the temperature responses of R S may mirror diverging climatic adaptations of co-existing moist forest tree species which have their distribution centre either at higher or lower elevations.

Patterns of wood carbon dioxide efflux across a 2,000-m elevation transect in an Andean moist forest

During a 1-year measurement period, we recorded the CO2 efflux from stems (R S) and coarse woody roots (R R) of 13–20 common tree species at three study sites at 1,050, 1,890 and 3,050 m a.s.l. in an Andean moist forest. The objective of this work was to study elevation changes of woody tissue CO2 efflux and the relationship to climate variation, site characteristics and growth. Furthermore, we aim to provide insights into important respiration–productivity relationships of a little studied tropical vegetation type. We expected R S and R R to vary with dry and humid season conditions. We further expected R S to vary more than R R due to a more stable soil than air temperature regime. Seasonal variation in woody tissue CO2 efflux was indeed mainly attributable to stems. At the same time, temperature played only a small role in triggering variations in R S. At stand level, the ratio of C release (g C m−2 ground area year−1) between stems and roots varied from 4:1 at 1,050 m to 1:1 at 3,050 m, indicating the increasing prevalence of root activity at high elevations. The fraction of growth respiration from total respiration varied between 10 (3,050 m) and 14% (1,050 m) for stems and between 5 (1,050 m) and 30% (3,050 m) for roots. Our results show that respiratory activity and hence productivity is not driven by low temperatures towards higher elevations in this tropical montane forest. We suggest that future studies should examine the limitation of carbohydrate supply from leaves as a driver for the changes in respiratory activity with elevation.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-009-1438-2) contains supplementary material, which is available to authorized users.

Long-term effects of lime on earthworm abundance and biomass in an acidic soil on the south-western slopes of New South Wales, Australia

Earthworm populations were monitored annually over 10 years in an acidic soil on the south-western slopes of New South Wales, Australia. The Typic Fragiochrept soil at the experimental site has a strong texture-contrast profile with a soil pH of 4.0–4.2 in 0.01 M CaCl 2 in the 0–20 cm horizon. We found that the site was dominated by two native species, the megascolecids Spenceriella macleayi and Spenceriella montana, and accompanied by three exotic species, the lumbricid Aporrectodea trapezoides, and the acanthodrilids Microscolex dubius and Microscolex phosphoreus. Total earthworm abundance varied from 61 to 188 m −2. Lime, applied as a treatment, favoured all exotic earthworm species; their abundance was 3 times greater in limed soil than in unlimed soil. This strongly indicated that severe soil acidity was the most likely factor limiting, directly and indirectly, these species at this site. In contrast, the responses of the two native species to lime varied from negative ( S. montana) to non-responsive ( S. macleayi), suggesting that these native species are well adapted to acidic soil conditions, and perhaps to the dry seasonal conditions experienced during 5 of the 10 years the site was sampled.