Foraging behaviour and habitat use by Antechinus flavipes and Sminthopsis murina (Marsupialia: Dasyuridae) in response to predation risk in eucalypt woodland

We examined the foraging behaviour and habitat use of two species of small Australian mammal (Antechinus flavipes and Sminthopsis murina) in response to predation risk in remnant eucalypt woodland. Predation risk was manipulated by providing refuge in the form of ground level wire netting to reduce risks from avian and mammalian predators. Giving-up-densities (GUD) using artificial food trays (20 mealworms in 1.5 l vermiculite) quantified the foraging behaviour in response to predation risk, by measuring the quitting harvest rate. Both A. flavipes and S. murina had lower GUDs (number of mealworms remaining) under the netting than in the open, most likely because these areas have lower predation risk. Animals also made greater visits to tracking tunnels under the netting compared to in the open. Tracking animal movements using fluorescent pigments also revealed preference for natural microhabitats that were structurally complex with animals moving most where logs and rock crevices were present. These results suggest that small mammals may use habitat structure to reduce their risks of predation. If future studies are able to demonstrate commensurate population-level responses, manipulation of habitat may be a useful management option to complement the direct control of exotic predators such as foxes and feral cats.     

Pathogen exposure in endangered island fox (Urocyon littoralis) populations: Implications for conservation management

Island fox (Urocyon littoralis) populations on four California Channel Islands have declined severely since 1994. Canine distemper (CDV) was suspected to be responsible for the decline of the Santa Catalina Island fox, so knowledge of infectious disease exposure in the remaining island fox populations was urgently needed. This study reviewed previous pathogen exposure in island foxes and investigated the current threat by conducting a serologic survey of foxes on all islands and sympatric feral cats on three islands from 2001 to 2003 for antibodies against canid pathogens. Before the decline, foxes had evidence of exposure to CDV, canine adenovirus (CAV), canine parvovirus (CPV), and Toxoplasma, with exposure to these five pathogens differing greatly by island. Exposure to canine coronavirus (CCV), canine herpesvirus (CHV), and Leptospira was rare. In 2001-2003, wild-born foxes had evidence of exposure to CDV (5.2-32.8%) on 5 of 6 islands, CPV (28-100%) and CAV (4.7-100%) on five islands, and Toxoplasma gondii (2.3-15.4%) on four islands. Exposure to CCV, CHV and Leptospira was less common. Sharing of infectious agents between sympatric foxes and feral cats appeared minimal, but CDV exposure was detected in two cats on Santa Catalina Island. Domestic dogs have historically been present on the islands, but it is not known if canine diseases can be maintained in fox populations without the continual presence of dogs. Targeted vaccination programs against the most virulent pathogens and continued intensive disease surveillance may help protect the critically small remaining fox populations from disease outbreaks that could threaten the success of ongoing conservation efforts.     

Compaction effects on soil macropore geometry and related parameters for an arable field

Soil compaction decreases soil pores are important for root growth as well as infiltration of water and nutrients. A study was conducted to evaluate the effects of soil compaction on macropore parameters measured using X-ray computed tomography (CT). Macropore parameters included number of pores, number of macropores (> 1000 μm diam.), number of coarse mesopores (200 to 1000 μm diam.), porosity, macroporosity, coarse mesoporosity, area of largest pore, pore circularity, and fractal dimension of macroporosity. A field experiment was conducted on Mexico silt loam (fine, smectitic, mesic Vertic Epiaqualfs) with field treatments including four replicates of uniformly Compacted (C) and Non-Compacted (NC) plots arranged in a randomized complete block design. Soil cores (76.2 mm diam. by 76.2 mm long) were removed from three selected depths (0 to 10 cm, 10 to 20 cm, and 20 to 30 cm). Cores were scanned using a medical X-ray CT scanner with four scans taken in each sample at 15 mm spacing starting at 25 mm from the core surface. Images were analyzed using Image-J software. The C treatment was found to increase bulk density by 8% (1.34 to 1.45 g cm⁻³) and decrease saturated hydraulic conductivity by 69% (47.1 to 14.6 cm hr^− 1). CT-measured number of pores decreased by 71%, number of macropores by 69%, and coarse mesopores by 75% with the C treatment used in the study. Compaction was also found to significantly decrease CT-measured porosity and macroporosity by 64%. Differences between treatments for the parameters were most pronounced in the upper 10 cm; differences between treatments were not significant below 20 cm. A regression equation with CT-measured macroporosity, area of largest pore and porosity explained most of the variability in saturated hydraulic conductivity (R² = 0.79). Efforts should be made to minimize soil compaction due to its harmful effects on soil pores and subsequent challenges for plant root growth and enhanced runoff of water and nutrients.     

Surplus killing by introduced predators in Australia—evidence for ineffective anti-predator adaptations in native prey species?

Australian examples of surplus killing by mammalian predators were collated. These included surplus killing of native mammals and birds by foxes (Vulpes vulpes) and stock, native mammals and native birds by dingoes (Canis lupus dingo). We found no examples of surplus killing by feral cats (Felis catus). Incidents collated include historical anecdotes of surplus killing by foxes as they colonised the Australian mainland, recent examples where foxes killed threatened native species at sites despite intensive management to exclude foxes, and recent examples of the killing of native species on formerly fox-free islands to which foxes gained entry. Episodes of surplus killings by foxes, other than predation on captive or closely confined animals, appeared different in kind and frequency to those documented for co-evolved predator-prey systems on the large continental landmasses. They did not appear to be uncommon events associated with synchronised births of prey species, unusual or extreme weather that disadvantaged prey species, or seasonal food caching by a predator. Rather, surplus killing events appeared to reflect ineffective anti-predator defences by prey species when encountering a novel and efficient predator to which they have had no evolutionary exposure. We suggest that surplus killing by foxes may have been a feature of, and major contributor to, the rapid mainland extinction or contraction in range of many native species in Australia. In contrast to foxes, examples of surplus killing by dingoes relate mostly to domestic stock (calves and sheep). The arrival of dingoes to the Australian continent preceded that of foxes by 3500-4000 years, but they appear not to have had the dire impact on native mammals that we attribute to foxes. This may be due to fundamental differences in hunting styles and prey size and to their sparse populations in pre-European Australia. Active persecution of non-commensal dingoes by Aborigines, the lack of free-water, and the absence of European rabbits (Oryctolagus cuniculus) as an alternative food supply would have limited their numbers and their impact on native mammals.     

Microbial biomass and activity at various soil depths in a Brazilian oxisol after two decades of no-tillage and conventional tillage

The advantages of no-tillage (NT) over conventional tillage (CT) systems in improving soil quality are generally accepted, resulting from benefits in soil physical, chemical and biological properties. However, most evaluations have only considered surface soil layers (maximum 0-30 cm depth), and values have not been corrected to account for changes in soil bulk density. The objective of this study was to estimate a more realistic contribution of the NT to soil fertility, by evaluating C- and N-related soil parameters at the 0-60 cm depth in a 20-year experiment established on an oxisol in southern Brazil, with a soybean (summer)/wheat (winter) crop succession under NT and CT. At full flowering of the soybean crop, soil samples were collected at depths of 0-5, 5-10, 10-20, 20-30, 30-40, 40-50 and 50-60 cm. For the overall 0-60 cm layer, correcting the values for soil bulk density, NT significantly increased the stocks of C (18%) and N (16%) and microbial biomass C (35%) and N (23%) (MB-C and -N) in comparison to CT. Microbial basal respiration and microbial quotient (qMic) were also significantly increased under NT. When compared with CT, NT resulted in gains of 0.8 Mg C ha⁻¹ yr⁻¹ (67% of which was in the 0-30 cm layer) and 70 kg N ha⁻¹ yr⁻¹ (73% in the 0-30 cm layer). In the 0-5-cm layer, MB-C was 82% higher with NT than with CT; in addition, the 0-30 cm layer accumulated 70% of the MB-C with NT, and 58% with CT. In comparison to CT, the NT system resulted in total inputs of microbial C and N estimated at 38 kg C ha⁻¹ yr⁻¹ and 1.5 kg N ha⁻¹ yr⁻¹, respectively. Apparently, N was the key nutrient limiting C and N stocks, and since adoption of NT resulted in a significant increase of N in soils which were deficient in N, efforts should be focused on increasing N inputs on NT systems.     

Rabbit and fox introductions in tierra del fuego: history and assessment of the attempts at biological control of the rabbit infestation

Four European rabbits Oryctolagus cuniculus were introduced in the Chilean side of Tierra del Fuego island in 1936. At the height of the rabbit infestation (1953) they numbered about 30 million. Twenty-four foxes Dusicyon griseus were released in Tierra del Fuego in 1951, three years before the myxoma virus decimated the rabbit populations. We document the history of the introductions of both rabbits and foxes in Tierra del Fuego, and evaluate the role of foxes as biological-control agents for the rabbits.     

Effects of long-term organic and mineral fertilizers on bulk density and penetration resistance in semi-arid Mediterranean soil conditions

Soil aggregation is of great importance in agriculture due to its positive effect on soil physical properties, plant growth and the environment. A long-term (1996-2008) field experiment was performed to investigate the role of mycorrhizal inoculation and organic fertilizers on some of soil properties of Mediterranean soils (Typic Xerofluvent, Menzilat clay-loam soil). We applied a rotation with winter wheat (Triticum aestivum L.) and maize (Zea mays L.) as a second crop during the periods of 1996 and 2008. The study consisted of five experimental treatments; control, mineral fertilizer (300-60-150 kg N-P-K ha⁻¹), manure at 25 t ha⁻¹, compost at 25 t ha⁻¹ and mycorrhiza-inoculated compost at 10 t ha⁻¹ with three replicates. The highest organic matter content both at 0-15 cm and 15-30 cm soil depths were obtained with manure application, whereas mineral fertilizer application had no effect on organic matter accumulation. Manure, compost and mycorrhizal inoculation + compost application had 69%, 32% and 24% higher organic matter contents at 0-30 cm depth as compared to the control application. Organic applications had varying and important effects on aggregation indexes of soils. The greatest mean weight diameters (MWD) at 15-30 cm depth were obtained with manure, mycorrhiza-inoculated compost and compost applications, respectively. The decline in organic matter content of soils in control plots lead disintegration of aggregates demonstrated on significantly lower MWD values. The compost application resulted in occurring the lowest bulk densities at 0-15 and 15-30 cm soil depths, whereas the highest bulk density values were obtained with mineral fertilizer application. Measurements obtained in 2008 indicated that manure and compost applications did not cause any further increase in MWD at manure and compost receiving plots indicated reaching a steady state. However, compost with mycorrhizae application continued to significant increase (P < 0.05) in MWD values of soils. Organic applications significantly lowered the soil bulk density and penetration resistance. The lowest penetration resistance (PR) at 0-50 cm soil depth was obtained with mycorrhizal inoculated compost, and the highest PR was with control and mineral fertilizer applications. The results clearly revealed that mycorrhiza application along with organic fertilizers resulted in decreased bulk density and penetration resistance associated with an increase in organic matter and greater aggregate stability, indicated an improvement in soil structure.     

Concentration and stock of carbon in the soils affected by land uses and climates in the western Himalaya,India

Soils are the third biggest sink of carbon on the earth. Hence, suitable land uses for a climatic condition are expected to sequester optimum atmospheric carbon in soils. But, information on how climatic conditions and land uses influence carbon accumulation in the soils on the Himalayan Mountains is not known. This study reports the impact of four climatic conditions (sub-tropical, altitude: 500–1200 m; temperate 1200–2000 m; lower alpine 2000–3000 m; upper alpine, 3000–3500 m) and four land uses (forest, grassland, horticulture, agriculture) on the concentrations and stocks of soil organic carbon (SOC) in upper (0–30 cm) and deeper (30–100 cm) soil depths on the western Himalayan Mountains of India. The study also explored the drivers which influenced the SOC stock build up on the mountains. Rainfall and soil moisture showed quadratic relations, whereas temperature declined linearly with the altitude. SOC stock as well as concentration was the highest (101.8 Mg ha^− 1 in 0–30 cm, 227.97 Mg ha^− 1 in 0–100 cm) in temperate and the lowest in sub-tropical climate (37 Mg ha^− 1 in 0–30 cm, 107.04 Mg ha^− 1 in 0–100 cm). Pattern of SOC stock build up across the altitude was: temperate > lower alpine > upper alpine > sub-tropical. SOC stocks in all land uses across the climatic conditions, except agriculture in lower alpine, was higher (0.7 to 41.6%) in the deeper than upper soil depth. SOC stocks in both the depths showed quadratic relations with soil temperature and soil moisture. Other factors like fine soil particles, land-use factor and altitude influenced positively whereas slope and pH, negatively to the SOC stocks. In all climatic conditions, other than temperate, SOC stocks were greater in natural ecosystems like forests and pastures (112.5 to 247.5 Mg ha^− 1) than agriculture (63 to 120.4 Mg ha^− 1). In temperate climate, SOC stock in agriculture (253.6 Mg ha^− 1) on well formed terraces was a little higher than forest (231.3 Mg ha^− 1) on natural slope. These observations, suggest that land uses on temperate climate may be treated as potential sinks for sequestration of the atmospheric carbon. However, agriculture in subtropical climate need to be pursued with due SOC protection measures like the temperate climate for greater sequestration of the atmospheric carbon.     

Organic matter status and the size, activity and metabolic diversity of the soil microbial community in the row and inter-row of sugarcane under burning and trash retention

The concentrations of organic C, labile organic fractions and the size and activity of the microbial community were measured to a depth of 30 cm below the plant row and at distances of 30 and 60 cm into the inter-row area under sugarcane under pre-harvest burning or green cane harvesting with retention of a crop residue (trash) mulch. Total root mass was similar under burning and trashing but under trashing there was a redistribution of roots towards the surface 0-10 cm in the inter-row space as roots proliferated beneath the trash mulch. Soil organic C content decreased in response to both increasing distance from the plant row (to a depth of 20 cm) and burning rather than trashing (to a depth of 10 cm). Declines in K₂SO₄-extractable C, light fraction C, microbial biomass C, basal respiration and aggregate stability in response to distance and burning were much more marked than those for organic C and occurred to a depth of 30 cm. Bulk density was greater under burnt than trashed sugarcane and was greater in the inter-row than row, particularly under burning. Heterotrophic functional diversity (measured by analysis of catabolic response profiles to 36 substrates) was also investigated. Principal component analysis of response profiles demonstrated that soils below the row and those under trashing at 30 cm out from this row were separated from the other soils on PC1 and the sample from the inter-row centre (60 cm out) under burning was separated from the others on PC2. Catabolic evenness was least for the latter soil. It was concluded that soil in the inter-row of burnt sugarcane receives few inputs of organic matter and that conversion to green cane harvesting with retention of a trash mulch greatly improves the organic matter, microbial and physical status of the inter-row soil.     

Long-term tillage effects on the distribution patterns of microbial biomass and activities within soil aggregates

The effects of tillage on the interaction between soil structure and microbial biomass vary spatially and temporally for different soil types and cropping systems. We assessed the relationship between soil structure induced by tillage and soil microbial activity at the level of soil aggregates. To this aim, organic C (OC), microbial biomass C (MBC) and soil respiration were measured in water-stable aggregates (WSA) of different sizes from a subtropical rice soil under two tillage systems: conventional tillage (CT) and a combination of ridge with no-tillage (RNT). Soil (0–20 cm) was fractionated into six different aggregate sizes (> 4.76, 4.76–2.0, 2.0–1.0, 1.0–0.25, 0.25–0.053, and < 0.053 mm in diameter). Soil OC, MBC, respiration rate, and metabolic quotient were heterogeneously distributed among soil aggregates while the patterns of aggregate-size distribution were similar among properties, regardless of tillage system. The content of OC within WSA followed the sequence: medium-aggregates (1.0–0.25 mm and 1.0–2.0 mm) > macro-aggregates (4.76–2.0 mm) > micro-aggregates (0.25–0.053 mm) > large aggregates (> 4.76 mm) > silt + clay fractions (< 0.053 mm). The highest levels of MBC were associated with the 1.0–2.0 mm aggregate size class. Significant differences in respiration rates were also observed among different sizes of WSA, and the highest respiration rate was associated with 1.0–2.0 mm aggregates. The C_mic/C_org was greatest for the large-macroaggregates regardless of tillage regimes. This ratio decreased with aggregate size to 1.0–0.25 mm. Soil metabolic quotient (qCO₂) ranged from 3.6 to 17.7 mg CO₂ g^− 1 MBC h^− 1. The distribution pattern of soil microbial biomass and activity was governed by aggregate size, whereas the tillage effect was not significant at the aggregate scale. Tillage regimes that contribute to greater aggregation, such as RNT, also improved soil microbial activity. Soil OC, MBC and respiration rate were at their highest levels for 1.0–2.0 mm aggregates, suggesting a higher biological activity at this aggregate size for the present ecosystem.     

Soil organic matter and land degradation in semi-arid area,Israel

Soil organic matter (SOM) was monitored at five research sites along a climatic transect extending from the Judean Mountains (mean annual rainfall 700 mm; annual mean temperature 17 °C) to the Dead Sea (mean annual rainfall < 100 mm; annual mean temperature 23 °C) in Israel. At four sites, representing four climatic regions, Mediterranean (site GIV), semi-arid (site MAL), mildly arid (site MIS) and arid (site KAL), four to eight soil samples were taken four times a year, in January, March, May and September, from 1992 through 1993 and 1994 and in April and August 2000. In the last 2 months soil samples were also taken from another site (MAB) in the semi-arid area. Comparison between the sites along the climatic transect shows that, except for site MAB, SOM increased significantly in both 0–2 cm and 2–10 cm, from the arid site, through the mildly arid site and the semi-arid site, to the Mediterranean site. Analysis of SOM temporal patterns of the two semi-arid sites (MAL and MAB) shows significant change from the normal SOM pattern in both the regional scale and the soil profile scale in one site (MAB). The a-normal pattern of SOM and the low soil aggregate stability at MAB indicates land degradation and it is attributed to overgrazing.     

Hydrolase activities, microbial biomass and bacterial community in a soil after long-term amendment with different composts

The use of composts in agricultural soils is a widespread practice and the positive effects on soil and plants are known from numerous studies. However, there have been few attempts to compare the effects of different kinds of composts in one single study. The aim of this paper is to investigate to what extent and to which soil depth four major types of composts would affect the soil and its microbiota.In a crop-rotation field experiment, composts produced from (i) urban organic wastes, (ii) green wastes, (iii) manure and (iv) sewage sludge were applied at a rate equivalent to 175 kg N ha⁻¹ yr⁻¹ for 12 years. General (total organic C (C_org), total N (N_t), microbial biomass C (C_mic), and basal respiration), specific (enzyme activities related to C, N and P cycles), biochemical properties and bacterial genetic diversity (based on DGGE analysis of 16S rDNA) were analyzed at different depths (0-10, 10-20 and 20-30 cm).Compost treatment increased C_org at all depths from 11 g kg⁻¹ for control soil to 16.7 g kg⁻¹ for the case of sewage sludge compost. Total N increased with compost treatment at 0-10 cm and 10-20 cm depths, but not at 20-30 cm. Basal respiration and C_mic declined with depth, and the composts resulted in an increase of C_mic and basal respiration. Enzyme activities were different depend on the enzyme and among compost treatments, but in general, the enzyme activities were higher in the upper layers (0-10 and 10-20 cm) than in the 20-30 cm layer. Diversity of ammonia oxidizers and bacteria was lower in the control than in the compost soils. The type of compost had less influence on the composition of the microbial communities than did soil depth.Some of the properties were sensitive enough to distinguish between different compost, while others were not. This stresses the need of multi-parameter approaches when investigating treatment effects on the soil microbial community. In general, with respect to measures of activity, biomass and community diversity, differences down the soil profile were more pronounced than those due to the compost treatments.     

Do domestic cats impose an unsustainable harvest on urban bird populations?

We assessed the impact of domestic cats on population persistence of native and exotic urban bird populations using a model adjusted for habitat-specific catch rates, cat ownership and hunting activity data. GPS-derived home ranges of 32 cats and resource selection indices demonstrated the degree of penetration and preference for native vegetation fragments. Owners reported on prey brought back by 144 domestic cats in Dunedin, New Zealand, during 12 months. One third of cats never brought back prey, and 21% returned more than one item/month. Cats brought back a mean of 13.4 prey items/year (median = 4), with cats aged <1 year returning more prey than older cats. Birds were the most common prey, followed by rodents. Although cats penetrated adjacent vegetation fragments they did not catch more birds and preferred garden habitat, suggesting that predation pressure may be reduced in fragments. Cat home range size appears to be constrained by cat density while the number of birds caught depends on the density of available prey. Estimates of city-wide catch for six bird species were either more than total urban population size estimates or close to lower confidence intervals. Modelling of three species indicated low likelihood of population persistence with cat predation. The observed persistence of these prey species suggests a meta-population structure with urban populations acting as sinks with source populations located on the city fringe.     

Spatial distribution of fungal communities in a coastal grassland soil

In grasslands, saprotrophic fungi, including basidiomycetes, are major decomposers of dead organic matter, although spatial distributions of their mycelial assemblages are little described. The aim of this study was to characterise the scale and distribution of saprotrophic fungal communities in a coastal grassland soil using terminal restriction fragment length polymorphism (T-RFLP).Soil fungi were sampled at Point Reyes, California, USA, by taking forty-five 26 mm diam. cores in a spatially defined manner. Within each sampled core, complete core sections at 1-2 cm and 14-15 cm depths were removed and sub-sampled for DNA extraction and amplification using the primer pairs ITS1F-FAM/ITS4 (general fungi) or ITS1F-FAM/ITS4B (basidiomycete-specific).Nonmetric Multidimensional Scaling showed that general fungal communities could be clearly separated by depth, although basidiomycete communities could not. There were no strong patterns of community similarity or dissimilarity for general or basidiomycete fungal communities at horizontal geographical distances from 25 cm to 96 m in the upper horizon. These results show considerable vertical, but little horizontal, variability in fungal community structure in a semi-natural grassland at the spatial scales measured here.     

Do fences create an edge-effect on the movement patterns of a highly mobile mega-herbivore?

Physical barriers, such as rivers and roads, constrain the movement of animals, usually by preventing access to adjacent habitats and impeding dispersal. Fences are artificial barriers that are commonly used as a conservation tool to intentionally restrict movements of animals to within protected reserves. However, the potential edge-effect of fences on the behaviour of animals within reserves is poorly understood. We examined the effect of fences on the movement patterns of African elephant (Loxodonta africana), an ecosystem modifier, in Pilanesberg National Park, South Africa. We used linear and non-linear models to determine the relationship between minimum distance from fence and seasonal daily net displacement of six GPS-collared female elephant. Elephant movement patterns were best explained by a piecewise regression that showed a strong negative relationship between minimum distance from fence and daily net displacement up to a “breakpoint” distance of 2551 m in the dry season and 3829 m in the wet season. The effect of the fence dissipated beyond this distance in both seasons. The increased tortuosity in movement patterns of elephant in the central area of the reserve suggested that they used this area more intensively for foraging compared to the peripheral area, as confirmed by differences in habitat selection. This occurs despite there being no difference in habitat composition between these areas. The decreased use of areas near the fence and more intensive foraging in the central areas constitute an important edge-effect of fences. Since elephant are ecosystem engineers, such edge-effects could potentially cascade throughout the reserve, adversely altering ecologically processes, particularly in reserves with a high edge-to-area ratio.     

Soil carbon turnover and sequestration in native subtropical tree plantations

Approximately 30% of global soil organic carbon (SOC) is stored in subtropical and tropical ecosystems but it is being rapidly lost due to continuous deforestation. Tree plantations are advocated as a C sink, however, little is known about rates of C turnover and sequestration into soil organic matter under subtropical and tropical tree plantations. We studied changes in SOC in a chronosequence of hoop pine (Araucaria cunninghamii) plantations established on former rainforest sites in seasonally dry subtropical Australia. SOC, δ¹³C, and light fraction organic C (LF C<1.6 g cm⁻³) were determined in plantations, secondary rainforest and pasture. We calculated loss of rainforest SOC after clearing for pasture using an isotope mixing model, and used the decay rate of rainforest-derived C to predict input of hoop pine-derived C into the soil. Total SOC stocks to 100 cm depth were significantly (P<0.01) higher under rainforest (241 t ha⁻¹) and pasture (254 t ha⁻¹) compared to hoop pine (176-211 t ha⁻¹). We calculated that SOC derived from hoop pine inputs ranged from 32% (25 year plantation) to 61% (63 year plantation) of total SOC in the 0-30 cm soil layer, but below 30 cm all C originated from rainforest. These results were compared to simulations made by the Century soil organic matter model. The Century model simulations showed that lower C stocks under hoop pine plantations were due to reduced C inputs to the slow turnover C pool, such that this pool only recovers to within 45% of the original rainforest C pool after 63 years. This may indicate differences in soil C stabilization mechanisms under hoop pine plantations compared with rainforest and pasture. These results demonstrate that subtropical hoop pine plantations do not rapidly sequester SOC into long-term storage pools, and that alternative plantation systems may need to be investigated to achieve greater soil C sequestration.     

Effects of diatomite on soil physical properties

Organic and inorganic soil amendments are commonly added to soil for improving its physical and chemical characteristics which promote plant growth. Although many inorganic amendments are extensively used for this purpose, diatomite (DE) is not commonly used. This study was conducted to determine effects of diatomite applications (10, 20, and 30% v/v) on physical characteristics of soils with different textures (Sandy Loam, Loam, and Clay), under laboratory conditions. The results indicated that diatomite application protects large aggregate (> 6.4 mm) formation in clay-textured soils, however it reduced the mean weight diameter in sand-textured soil. 30% diatomite reduced mean weight diameter in sand-textured soils from 1.74 to 1.49 mm. Diatomite applications significantly increased aggregate stability of all the experimental soils in all aggregate size fractions. In overall, aggregate stability increased from 28.04% to 45.70% with the application rate of 30%. Diatomite application also significantly increased soil moisture content at field capacity in SL textured soil. 30% diatomite increased field capacity in sand-textured soil in the percent of 43.78 as compared with control. Therefore it is suggested that diatomite may be considered as a soil amendment agent for improving soil physical characteristics. However, its effectiveness in enhancing soil properties depends on initial soil factors and texture. Moreover, since its protective effect against large aggregate (> 6.4 mm) formation and reducing effect on soil penetration resistance in clay textured soils, diatomite might be an alternative soil amendment agent in soil tillage practices and seedling.     

The dynamics of water extractable organic matter (WEOM) in common arable topsoils: II. Influence of mineral and combined mineral and manure fertilization in a Haplic Chernozem

Data on the dynamics of dissolved or water extractable organic matter (DOM, WEOM) in soils are often contradicting, which is especially true for arable soils. Since a complex set of soil inherent and environmental factors affects these dynamics, there is still a great need for additional data. Especially DOM results from (arable) field studies and long-term trials are scarce. We sampled the WEOM of the soils under three fertilization treatments in a Haplic Chernozem differing in fertilization intensity for over 90 years: (i) no fertilization (Control), (ii) mineral fertilization (NPK), and (iii) mineral plus additional farmyard manure fertilization (NPK + FYM). We sampled the WEOM from 0-40 cm at 10 cm intervals over a three year period during three seasons (spring, summer, and fall). We measured WEOM quantity (WEOC and WEON concentrations) and investigated the quality of WEOM with UV (absorptivity) and fluorescence (humification index, HIX) as well as biodegradability (BWEOC). The total soil organic carbon (SOC) and nitrogen (TN) were also quantified. The overall results indicated that NPK did not affect SOC and TN but did increase WEOC and WEON even though NPK does not contain organic matter, implying that fertilization affected WEOM via the biomass. The more aromatic and condensed compound of WEOM were especially increased. The NPK + FYM treatment also increased SOC and TN and had a stronger effect on WEOM than NPK alone. However, BWEOC was not significantly affected by fertilization practices. The three sampled years varied strongly in total precipitation and in crop type. Nevertheless, with the exception of WEON and HIX, no significant overall annual fluctuations could be detected. A seasonal pattern was found in WEOM concentration and quality but, except for WEON and HIX, fertilization treatments did not influence this seasonal pattern. The effects of fertilization did not vary as a function of depth for the parameters WEOC, WEON, and BWEOC, presumably because of their mobile nature. For the immobile SOC and TN depth had an effect. The values in the plough layer (0-30 cm) were significantly higher than in the region below it (30-40 cm). Absorptivity and HIX also showed such a pattern, indicating that more aromatic and condensed compounds are either preferentially retained or not as well metabolized in the plough layer.     

Soil organic carbon distribution in relation to land use and its storage in a small watershed of the Loess Plateau, China

Soil organic carbon (SOC) is an important component in agricultural soil, and its stock is a major part of global carbon stocks. Estimating the SOC distribution and storage is important for improving soil quality and SOC sequestration. This study evaluated the SOC distribution different land uses and estimated the SOC storage by classifying the study area by land use in a small watershed on the Loess Plateau. The results showed that the SOC content and density were affected by land use. The SOC content for shrubland and natural grassland was significantly higher than for other land uses, and cropland had the lowest SOC content. The effect of land use on the SOC content was more significant in the 0-10 cm soil layer than in other soil layers. For every type of land use, the SOC content decreased with soil depth. The highest SOC density (0-60 cm) in the study area was found in shrublandII (Hippophae rhamnoides), and the other land uses decreased in the SOC density as follows: natural grassland > shrublandI (Caragana korshinskii) > abandoned cropland > orchard > level ground cropland > terrace cropland > artificial grassland. Shrubland and natural grassland were the most efficient types for SOC sequestration, followed by abandoned cropland. The SOC stock (0-60 cm) in this study was 23,584.77 t with a mean SOC density of 4.64 (0-60 cm).     

Influence of water table levels on CO2 emissions in a Colorado subalpine fen: an in situ microcosm study

We quantified the relationship between water table position and CO₂ emissions by manipulating water table levels for two summers in microcosms installed in a Colorado subalpine fen. Water levels were manipulated in the microcosms by either adding water or removing water and ranged from +10 cm above the soil surface to 40 cm below the soil surface, with ambient water levels in the fen averaging +3 and +2 cm above the soil surface during 1998 and 1999, respectively. Microcosm installation had no significant effect on CO₂ efflux; the 2 year means of natural and reference CO₂ efflux were 205.4 and 213.9 mg CO₂-C m⁻² h⁻¹, respectively (p=0.80). Mean CO₂ emissions were lowest at the highest water tables (water +6 to +10 cm above the soil surface), averaging 133.8 mg CO₂-C m⁻² h⁻¹, increased to 231.3 mg CO₂-C m⁻² h⁻¹ when the water table was +1 to +5 cm above the soil surface and doubled to 453.7 mg CO₂-C m⁻² h⁻¹, when the water table was 0-5 cm below the soil surface. However, further lowering of the water table had little additional effect on CO₂ emissions, which averaged 470.3 and 401.1 mg CO₂-C m⁻² h⁻¹ when the water table was 6-10 cm, and 11-40 cm beneath the soil surface, respectively. The large increase in CO₂ emissions as we experimentally lowered the water table beneath the soil surface, coupled with no increase in CO₂ emissions as we furthered lowered water tables beneath the soil surface, suggest the presence of an easily oxidized labile carbon pool near the soil surface.