Measuring the effects of reduced snow cover on Australia's alpine arthropods

Snow is one of the most important factors in the ecology of alpine ecosystems. In Australia, both the depth and duration of snow cover have declined significantly in recent decades and this trend is projected to continue with global warming. Many small arthropods remain active throughout the winter, within a space beneath the snowpack (subnivean) where the snow's insulation creates a thermally stable environment. Using field surveys and experimental manipulation of snow depth at two locations in the Australian alpine region, we explored the diversity of winter‐active arthropods and their response to reduced snow. Individuals from 18 arthropod Orders were detected beneath the snow during winter, with Collembola, Araneae, Acari and Coleoptera accounting for 95–98% of the individuals collected. The subnivean taxa represented a distinct subset of those active outside the winter months. Removal of the snow layer increased daily temperature fluctuations, increased the number of days below freezing and raised the mean surface temperatures. Community composition was altered by snow removal, driven by changes in the numbers of two abundant springtail taxa at each location. We found a strong reduction in the abundances of both taxa at one study site, and contrasting responses (one strong positive and one strong negative) to snow removal at the second study site. Subnivean arthropod communities in Australia thus appear sensitive to snow conditions at small spatial scales.     

Deepened winter snow cover enhances net ecosystem exchange and stabilizes plant community composition and productivity in a temperate grassland

Global warming has greatly altered winter snowfall patterns, and there is a trend towards increasing winter snow in semi‐arid regions in China. Winter snowfall is an important source of water during early spring in these water‐limited ecosystems, and it can also affect nutrient supply. However, we know little about how changes in winter snowfall will affect ecosystem productivity and plant community structure during the growing season. Here, we conducted a 5‐year winter snow manipulation experiment in a temperate grassland in Inner Mongolia. We measured ecosystem carbon flux from 2014 to 2018 and plant biomass and species composition from 2015 to 2018. We found that soil moisture increased under deepened winter snow in early growing season, particularly in deeper soil layers. Deepened snow increased the net ecosystem exchange of CO₂ (NEE) and reduced intra‐ and inter‐annual variation in NEE. Deepened snow did not affect aboveground plant biomass (AGB) but significantly increased root biomass. This suggested that the enhanced NEE was allocated to the belowground, which improved water acquisition and thus contributed to greater stability in NEE in deep‐snow plots. Interestingly, the AGB of grasses in the control plots declined over time, resulting in a shift towards a forb‐dominated system. Similar declines in grass AGB were also observed at three other locations in the region over the same time frame and are attributed to 4 years of below‐average precipitation during the growing season. By contrast, grass AGB was stabilized under deepened winter snow and plant community composition remained unchanged. Hence, our study demonstrates that increased winter snowfall may stabilize arid grassland systems by reducing resource competition, promoting coexistence between plant functional groups, which ultimately mitigates the impacts of chronic drought during the growing season.     

Differential ecophysiological response of deciduous shrubs and a graminoid to long-term experimental snow reductions and additions in moist acidic tundra, Northern Alaska

Changes in winter precipitation that include both decreases and increases in winter snow are underway across the Arctic. In this study, we used a 14-year experiment that has increased and decreased winter snow in the moist acidic tussock tundra of northern Alaska to understand impacts of variation in winter snow depth on summer leaf-level ecophysiology of two deciduous shrubs and a graminoid species, including: instantaneous rates of leaf gas exchange, and δ¹³C, δ¹⁵N, and nitrogen (N) concentrations of Betula nana, Salix pulchra, and Eriophorum vaginatum. Leaf-level measurements were complemented by measurements of canopy leaf area index (LAI) and depth of thaw. Reductions in snow lowered summer leaf photosynthesis, conductance, and transpiration rates by up to 40 % compared to ambient and deep snow conditions for Eriophorum vaginatum, and reduced Salix pulchra conductance and transpiration by up to 49 %. In contrast, Betula nana exhibited no changes in leaf gas exchange in response to lower or deeper snow. Canopy LAI increased with added snow, while reduced winter snow resulted in lower growing season soil temperatures and reduced thaw depths. Our findings indicate that the spatial and temporal variability of future snow depth will have individualistic consequences for leaf-level C fixation and water flux by tundra species, and that these responses will be manifested over the longer term by changes in canopy traits, depth of thaw, soil C and N processes, and trace gas (CO₂ and H₂O) exchanges between the tundra and the atmosphere.     

Winter CO2 flux from soil and snow surfaces in a cool-temperate deciduous forest, Japan

We measured diurnal and wintertime changes in CO₂ fluxes from soil and snow surfaces in a Japanese cool-temperate Quercus/Betula forest between December 1994 and May 1995. To evaluate the relationship between these winter fluxes and temperature, flux measurements were made with the open-flow infrared gas analyzer (IRGA) method rather than with the more commonly used closed chamber method or the snow CO₂ profile method. The open-flow IRGA method proved to be more successful in measurements of winter CO₂ fluxes than the two standard methods. Despite colder air temperatures, soil temperature profiles were greater than 0°C because of the thermal insulation effect of deep snowpack. This reveals that soil temperature is satisfactory for microbial respiration throughout the winter. Unfrozen soils under the snowpack showed neither diurnal nor wintertime trends in CO₂ fluxes or in soil surface temperature, although there was a daily snow surface CO₂ flux of 0.18–0.32 g m^–2. By combining this with other reference data, Japanese cool-temperate forest soils in snowy regions can be estimated to emit < 100 g m^–2 carbon over an entire winter, and this value accounts for < 15% of the annual emission. In the present study, when data for all winter fluxes were taken together, fluxes were most highly correlated with deep soil temperatures rather than the soil surface temperature. Such a high correlation can be attributed to the relatively increased respiration of the deep soil where the temperature was higher than the soil surface temperature. Thus, deeper soil temperature is a better predictor of winter CO₂ fluxes in cold and snowy ecosystems.     

Seasonal abundance of soil-surface arthropods in relation to some meteorological and edaphic variables of the grassland and tree-planted areas in a tropical semi-arid savanna

Seasonality of relative population abundance in different groups of soil-surface arthropods was investigated monthly by pit-fall traps during a 2-year period in the grassland and tree-planted areas of a tropical semi-arid savanna at Warangal (south India). Densities of most groups were lowest during summer and highest during the rainy season. They were less abundant during winter. Arthropods were recorded in higher numbers in tree-planted compared to grassland areas. Certain arthropods that were found only during part of the year were recorded for a longer period in the tree-planted area. Formicidae,Monomorium indicum Forel,Crematogaster sp. andPachycondyla? tesserinoda (Emery), and Coleoptera,Pachycera sp. reached maximum densities in the rainy season and minimum numbers during winter and summer in the grassland area. However, these species had lower densities during the rainy season and reached maximum densities during winter and summer in the tree-planted area. The seasonal abundance of arthropods showed significant linear correlations with different abiotic environmental variables such as rainfall, soil moisture, organic matter, soil and air temperatures, soil pH, relative humidity at the soil surface, and potassium and phosphorus of surface soil. Soil moisture and rainfall were generally the strongest correlates with densities, particularly in the grassland area.     

Short-term responses of winter soil respiration to snow removal in a Picea asperata forest of western Sichuan

Aims Seasonal snow cover is one of the most important factors that control winter soil respiration in the cold biomes. The warming-induced decreases in snowpack could affect winter soil respiration of subalpine forests. The aim of this study was to explore the effects of snow removal on winter soil respiration in a Picea asperata forest.Methods A snow removal experiment was conducted in a P. asperata forest stand in western Sichuan during the winter of 2015/2016. The snow removal treatment was implemented using wooden roof method. Soil temperatures, snow depth and soil respiration rate were simultaneously measured in plots of snow removal and controls during the experimental period.Important findings Compared to the control, snow removal increased the fluctuations of soil temperatures. The average daily temperature of the soil surface and that at 5 cm depth were 1.12 °C and 0.34 °C lower, respectively, and the numbers of freeze-thaw cycles of the soil surface and that at 5 cm depth were increased by 39 and 12, respectively, in plots of snow removal than in the controls. The average rate of winter soil respiration and CO₂ efflux were 0.52 μmol·m^-2·s^-1 and 88.44 g·m^-2, respectively. On average, snow removal reduced soil respiration rate by 21.02% and CO₂ efflux by 25.99%, respectively. More importantly, the snow effect mainly occurred in the early winter. The winter soil respiration rate had a significant exponential relationship with soil temperature. However, snow removal significantly reduced temperature sensitivity of the winter soil respiration. Our results suggest that seasonal snow reduction associated with climate change could inhibit winter soil respiration in the subalpine forests of western Sichuan, with significant implications for the carbon dynamics of the subalpine forests.     

Snow cover manipulations alter survival of early life stages of cold‐temperate tree species

Projections of future climate suggest increases in global temperatures that are especially pronounced in winter in cold‐temperate regions. Thermal insulation provided by snow cover to litter, soil, and overwintering plants will likely be affected by changing winter temperatures and might influence future species composition and ranges. We investigated effects of changing snow cover on seed germination and sapling survival of several cold‐temperate tree species using a snow manipulation approach. Post‐winter seed germination increased or decreased with increasing snow cover, depending on species; decreased seed germination was found in species that characteristically disperse seed in summer or fall months prior to snowfall. Post‐winter sapling survival increased with increasing snow cover for all species, though some species benefitted more from increased snow cover than others. Sapling mortality was associated with root exposure, suggesting the possibility that soil frost heaving could be an important mechanism for observed effects. Our results suggest that altered snow regimes may cause re‐assembly of current species habitat relationships and may drive changes in species’ biogeographic range. However, local snow regimes also vary with associated vegetation cover and topography, suggesting that species distribution patterns may be strongly influenced by spatial heterogeneity in snow regimes and complicating future projections.     

Long‐term increase in snow depth leads to compositional changes in arctic ectomycorrhizal fungal communities

Many arctic ecological processes are regulated by soil temperature that is tightly interconnected with snow cover distribution and persistence. Recently, various climate‐induced changes have been observed in arctic tundra ecosystems, e.g. shrub expansion, resulting in reduction in albedo and greater C fixation in aboveground vegetation as well as increased rates of soil C mobilization by microbes. Importantly, the net effects of these shifts are unknown, in part because our understanding of belowground processes is limited. Here, we focus on the effects of increased snow depth, and as a consequence, increased winter soil temperature on ectomycorrhizal (ECM) fungal communities in dry and moist tundra. We analyzed deep DNA sequence data from soil samples taken at a long‐term snow fence experiment in Northern Alaska. Our results indicate that, in contrast with previously observed responses of plants to increased snow depth at the same experimental site, the ECM fungal community of the dry tundra was more affected by deeper snow than the moist tundra community. In the dry tundra, both community richness and composition were significantly altered while in the moist tundra, only community composition changed significantly while richness did not. We observed a decrease in richness of Tomentella, Inocybe and other taxa adapted to scavenge the soil for labile N forms. On the other hand, richness of Cortinarius, and species with the ability to scavenge the soil for recalcitrant N forms, did not change. We further link ECM fungal traits with C soil pools. If future warmer atmospheric conditions lead to greater winter snow fall, changes in the ECM fungal community will likely influence C emissions and C fixation through altering N plant availability, fungal biomass and soil‐plant C‐N dynamics, ultimately determining important future interactions between the tundra biosphere and atmosphere.     

The terrestrial arthropods of Sør Rondane in eastern Dronning Maud Land,Antarctica, with biogeographical notes

Five species of terrestrial arthropods have been found in Sør Rondane inland nunataks of eastern Dronning Maud Land, Antarctica, so far almost a biologically unexplored region. These arthropods comprised one collembolan and four mite species (one oribatid mite and three prostigmatic mite). Their occurrence was restricted to the nunataks in the central and western parts of the region. The same was also observed for the visible vegetation, such as algae and mosses, near nesting-bird colonies. The maximum reorded population density was 859 arthropods/100 ml soil at the nest of snow petrel at Tanngarden, in the northwestern part of the region. The arthropod fauna of Sør Rondane is very similar to that of central Dronning Maud Land, particularly in Gjelsvikfjella and Mühlich-Hofmannfjella. The fauna is, however, different from that of the eastern region, e.g. at Syowa Station and Enderby Land. Different species of collembolans and oribatid mites occur at locations separated by the Lüitzow-Holm Bay and Shirase Glaciers, whereas prostigmatic mites do not show such a difference.     

Efflux of carbon dioxide from snow-covered forest floors

The release of CO₂ from the snow surface in winter and the soil surface in summer was directly or indirectly measured in four cool-temperate deciduous broadleaved and evergreen needle forests. The closed chamber method (CC-method) and Fick's diffusion model (DM-method) were used for the direct and indirect measurements, respectively. The winter soil temperatures from the soil surface to 10 cm depth were between 0 and 2°C. The concentration of CO₂ within snowpack increased linearly with increasing snow depth. The average effluxes of CO₂ calculated from the gradients of CO₂ concentration in the snow using the DM-method ranged from 20 to 75 mg CO₂ m⁻² h⁻¹, while the CC-method showed the average effluxes of 20 to 50 mg CO₂m⁻²h⁻¹. These results reveal that the snow thermally insulates the soil, allowing CO₂ production to continue at soil temperatures a little above freezing throughout the winter. Carbon dioxide formed in the soil can move across snowpack up to the atmosphere. The winter/summer ratio of CO₂ emission was estimated to be higher than 7%. Therefore, the snow-covered soil served as a source of CO₂ in the winter and the effluxes represent an important part of the annual CO₂ budget in snowy regions.     

Effects of experimentally imposed climate scenarios on flowering phenology and flower production of subarctic bog species

Climate scenarios for high‐latitude areas predict not only increased summer temperatures, but also larger variation in snowfall and winter temperatures. By using open‐top chambers, we experimentally manipulated both summer temperatures and winter and spring snow accumulations and temperatures independently in a blanket bog in subarctic Sweden, yielding six climate scenarios. We studied the effects of these scenarios on flowering phenology and flower production of Andromeda polifolia (woody evergreen) and Rubus chamaemorus (perennial herb) during 2 years. The second year of our study (2002) was characterized by unusually high spring and early summer temperatures. Our winter manipulations led to consistent increases in winter snow cover. As a result, average and minimum air and soil temperatures in the high snow cover treatments were higher than in the winter ambient treatments, whereas temperature fluctuations were smaller. Spring warming resulted in higher average, minimum, and maximum soil temperatures. Summer warming led to higher air and soil temperatures in mid‐summer (June–July), but not in late summer (August–September). The unusually high temperatures in 2002 advanced the median flowering date by 2 weeks for both species in all treatments. Superimposed on this effect, we found that for both Andromeda and Rubus, all our climate treatments (except summer warming for Rubus) advanced flowering by 1–4 days. The total flower production of both species showed a more or less similar response: flower production in the warm year 2002 exceeded that in 2001 by far. However, in both species flower production was only stimulated by the spring‐warming treatments. Our results show that the reproductive ecology of both species is very responsive to climate change but this response is very dependent on specific climate events, especially those that occur in winter and spring. This suggests that high‐latitude climate change experiments should focus more on winter and spring events than has been the case so far.     

Food resources and foraging habits of the common shrew,Sorex araneus: does winter food shortage explain Dehnel's phenomenon?

It is widely assumed that winter is a critical time for homeotherms because of decreased ambient temperatures coupled with reduced food supply. Shrews are excellent models for investigating overwintering strategies, not only because of their particularly small size, high energy requirements relative to their size and short fasting endurance, but also the dramatic reduction in body size (Dehnel's phenomenon) exhibited by soricine shrews in northern temperate winters. The cause of Dehnel's phenomenon is poorly understood but food supply is implicated. To test the hypothesis that winter at higher latitudes is a period of food shortage for small homeotherms, we compared feeding habits of common shrews, Sorex araneus, and abundance and biomass of their prey in winters and summers in northeastern Poland using scat analysis combined with pitfall and ground core sampling for invertebrates. Ground‐surface activity and numbers of invertebrates in pitfall traps were greatly reduced in winter but, contrary to prediction, no significant differences between winter and summer were found in total numbers and biomass of prey invertebrates in ground core samples. However, certain prey types changed seasonally with respect to numbers, biomass and distribution in the soil profile, which was reflected in shrews’ food composition and foraging behaviour. Dehnel's phenomenon appears not to be caused by reduction in total prey numbers and biomass, at least in our study area. Smaller body mass coupled with lowering of absolute food requirements may have important survival value in winter with its reduced numbers of certain major prey coupled with increased difficulty of locating and extracting invertebrates within the soil profile resulting in higher energetic costs of foraging.     

The redistribution of soil water by tree root systems

Plant roots transfer water between soil layers of different water potential thereby significantly affecting the distribution and availability of water in the soil profile. We used a modification of the heat pulse method to measure sap flow in roots of Grevillea robusta and Eucalyptus camaldulensis and demonstrated a redistribution of soil water from deeper in the profile to dry surface horizons by the root system. This phenomenon, termed “hydraulic lift” has been reported previously. However, we also demonstrated that after the surface soils were rewetted at the break of season, water was transported by roots from the surface to deeper soil horizons – the reverse of the “hydraulic lift” behaviour described for other woody species. We suggest that “hydraulic redistribution” of water in tree roots is significant in maintaining root viability, facilitating root growth in dry soils and modifying resource availability. Received: 26 January 1998 / Accepted: 15 April 1998     

Spatial Distribution,Food and Activity of Gomphus pulchellus SELYS 1840 (Insecta; Odonata; Gomphidae) from a Still Water Habitat

Distribution patterns of Gomphus pulchellus larvae in different sediments with different density of prey organisms were studied in the field in a small gravel pit lake in the south of Germany. Larval burrowing behaviour at different temperatures as well as food preference, consumption rates and activity were studied in laboratory experiments. In the study lake G. pulchellus larvae lived exclusively in places where macrophytes were present and in fine sediments (mean grain size <3 mm) with detritus cover. There was a significant positive correlation between larval density and density of food organisms suggesting that abundance of food is one of the determinants of larval distribution. In late autumn larvae migrated to deeper places probably to survive the winter. Low temperatures simulated in laboratory experiments did not induce larvae to burrow deeper. Larvae were always found in a sediment depth of 0.59–0.74 cm. Experiments with mixed prey showed that G. pulchellus larvae preferred tubificid worms and chironomid larvae over gammarids and ephemerid larvae. However, chironomid larvae which stayed in their tubes had a higher survival rate than those outside of tubes. Single-prey experiments showed that G. pulchellus larvae can prey not only on benthic species but also on Daphnia from the open water. Functional-response experiments showed that one G. pulchellus larva consumes a maximum of 2 to 3 tubificid worms or chironomid larvae per day, which corresponds to a maximum biomass (freshweight) of 5 to 30 mg per day. Video recordings of activity showed that G. pulchellus larvae cover long distances of up to 52 m per night on the substrate surface and that activity on the substrate surface started after midnight and ceased before sunrise. Consumption of Zooplankton prey and high activity above the substrate is interpreted as an adaptation of G. pulchellus larvae to the life in still water habitats.     

Cover Caption

Snow cover is an important environmental component which facilitates migration and as a stage of sexual behaviour for some aquatic Chironomidae of a winter emerging strategy. A community of at least 35 species active on the snow was found during a long‐term study of adult non‐biting midges in temperate areas of Poland. The fully‐wings as well as brachypterous forms were documented to swarm on the snow and use the searching mating behaviour within some narrow temperature range of mid and late winter. (See pages 754–770). Photo provided by Agnieszka SoszyDska‐Maj.     

Release and uptake of volatile inorganic and organic gases through the snowpack at Niwot Ridge,Colorado

Whole air drawn from four heights within the high elevation (3,340 m asl), deep, winter snowpack at Niwot Ridge, Colorado, were sampled into stainless steel canisters, and subsequently analyzed by gas chromatography for 51 volatile inorganic and organic gases. Two adjacent plots with similar snow cover were sampled, one over bare soil and a second one from within a snow-filled chamber where Tedlar/Teflon-film covered the ground and isolated it from the soil. This comparison allowed for studying effects from processes in the snowpack itself versus soil influences on the gas concentrations and fluxes within and through the snowpack. Samples were also collected from ambient air above the snow surface for comparison with the snowpack air. Analyzed gas species were found to exhibit three different kinds of behavior: (1) One group of gases, i.e., carbon dioxide (CO₂), chloroform (CHCl₃), dimethylsulfide (CH₃)₂S, carbondisulfide (CS₂), and dichlorobromomethane (CHBrCl₂), displayed higher concentrations inside the snow, indicating a formation of these species and release into the atmosphere. (2) A second group of compounds, including carbon monoxide (CO), carbonyl sulfide (COS), the hydrocarbons methane, ethane, ethyne, benzene, and the halogenated compounds methylchloride (CH₃Cl), methylbromide (CH₃Br), dibromomethane (CH₂Br₂), bromoform (CHBr₃), tetrachloromethane (CCl₄), CFC-11, CFC-12, HCFC-22, CFC-113, 1,2-dichloroethane, methylchloroform, HCFC-141b, and HCFC-142b, were found at lower concentrations in the snow, indicating that the snow and/or soil constitute a sink for these gases. (3) For 21 other gases absolute concentrations, respectively concentration gradients, were too low to unequivocally identify their uptake or release behavior. For gases listed in the first two groups, concentration gradients were incorporated into a snowpack gas diffusion model to derive preliminary estimates of fluxes at the snow-atmosphere interface. The snowpack gradient flux technique was found to offer a highly sensitive method for the study of these surface gas exchanges. Microbial activities below this deep, winter snowpack appear to be the driving mechanism behind these gas sources and sinks. Flux results were applied to a simple box model to assess the potential contribution of the snowpack uptake rates to atmospheric lifetimes of these species.     

The importance of cuticular permeability, osmolyte production and body size for the desiccation resistance of nine species of Collembola

Euedaphic collembolans have recently been shown to actively regulate internal osmotic pressure by means of sugars and polyols in response to desiccation. In contrast, studies of cuticular permeability have shown that some, especially epedaphic, species of collembolans may primarily rely on a low cuticular permeability to survive desiccation. To elucidate to what extent these strategies are important for desiccation resistance, the survival of 7-day acute desiccation stress (LRH(50)), the cuticular water conductance constant and osmolyte production were investigated in nine species of collembolans, covering euedaphic, hemiedaphic and epedaphic species. The LRH(50) values ranging from 98.8% to 95.2% RH showed no correlation with the vertical distribution of species, since both the highest and lowest values were found in epedaphic species. The water conductance varied from 698+/-141 to 41+/-13 microg h(-1) cm(-2) mmHg(-1) and showed good agreement with the vertical distribution of species in their natural habitats. Modelling the drying curves showed that, in addition to cuticular permeability and osmolyte production, body size also plays an important role in the survival of short-term severe desiccation stress. Furthermore, the model pointed to the need for behavioural responses to desiccation, particularly in epedaphic species. Thus, in keeping with expected humidity regimes in their respective microhabitats, euedaphic species rely on small body size, high cuticular permeability and the ability to actively regulate the osmotic pressure of their body fluids, hemiedaphic species have similar strategies but with reduced cuticular permeability, whereas in epedaphic species, active regulation of osmotic pressure is replaced by combinations of greatly reduced cuticular permeability or greatly reduced surface area to volume ratio combined with behavioural responses to desiccation.     

Entomopathogenic fungi isolated from suspended-soil-inhabiting arthropods in East Kalimantan,Indonesia

As a preliminary survey to develop suspendedsoil arthropods as a new isolation source of entomopathogenic fungi, we investigated the entomopathogenic fungi of these arthropods. Fifty-five suspended-soil arthropods were collected from lowland tropical rainforests in East Kalimantan, and ten fungal isolates belonging to seven entomopathogenic species, including two undescribed species, were isolated from nine of the arthropods. Only two of the seven entomopathogenic species were commonly found from the arthropods inhabiting the ground soil in the same forests. The percentage of entomopathogenic fungi-positive arthropods from suspended soil was similar to that from ground soil of the same and another forest of the region, and lower than that from ground soil of Japan. However, the number of entomopathogenic species isolated from the suspended-soil arthropods was larger than that from ground-soil arthropods. This result suggests that suspended-soil arthropods can be a new isolation source of entomopathogenic fungi.     

Effect of deep and shallow root systems on the dynamics of soil inorganic N during 3-year crop rotations

Unused inorganic nitrogen (N_inorg) left in agricultural soils will typically leach to deeper soil layers. If it moves below the root zone it will be lost from the system, but the depth of the root zone depends on the crop species grown. In this experiment we studied the effect of 3-year crop sequences, with different combinations of deep-rooted and shallow-rooted crops, on soil N_inorg dynamics to 2.5 m soil depth and the possibility of crop utilization of N leached to deep soil layers. We grew ten different crop sequences for 3 years. The crops and catch crops grown were selected to allow different sequences of deep-rooted and shallow-rooted crops. Very different rooting depths were obtained, from only 0.5 m (leek), to ∼1.0 m (ryegrass and barley), 1.5 m (red beet), 2.0 m (fodder radish and white cabbage) and more than 2.5 m by the chicory catch crop. The results showed a significant retention of N_inorg within the 2.5 m soil profile from one year to the next, but the retained N had leached to deeper parts of the profile during the winter season. Only little N_inorg was retained over two winter seasons. The retention in the deeper soil layers allowed N_inorg to be taken up by succeeding deep-rooted main crops or catch crops. The effects of crop rooting depth on N_inorg in the subsoil layers from 1.0 to 2.5 m were striking. White cabbage reduced N_inorg below 1.0 m with up to 113 kg N ha^-1 during its growth. Grown after catch crops, leek and red beet left on average 60 kg N ha⁻¹ less below 1.0 m than leek and red beet grown without a preceding catch crop. We conclude that it is possible to design crop rotations with improved nitrogen use efficiency by using the differences in crop rooting patterns; deep-rooted crops or catch crops can be used to recover N_inorg leached after previous crops, and catch crops can be grown before shallow-rooted crops to lift the deep N_inorg up to layers where these crops have their roots.     

Large variation of suction sampling efficiency depending on arthropod groups,species traits,and habitat properties

Suction sampling is widely used to estimate arthropod abundance and diversity. To test the reliability of abundance data derived from suction sampling, we examined sampling efficiency across a wide range of arthropod groups and tested for effects of species traits, vegetation density, and differences between sites. Suction sampling efficiency was quantified by vacuuming an enclosed meadow area and subsequent removal of the turf, which was treated with heat extraction to collect the remaining arthropods. We obtained 250 pairs of suction and turf samples from seven grasslands with variable vegetation density. High suction sampling efficiencies between 49 and 86% were obtained for Auchenorrhyncha, Heteroptera, Araneida, Curculionoidea, Hymenoptera, and Diptera. In contrast, efficiencies were below 30% for Aphidae, Thysanoptera, Staphylinidae and other Coleoptera, and for soil arthropods such as Collembola, Isopoda, Diplopoda, and Formicidae. Efficiency varied significantly among habitats (sites) for most groups, often more than two‐fold. Surprisingly, sampling efficiency for Hymenoptera, Diplopoda, and Collembola increased with vegetation density, probably because aboveground activity of these taxa was higher in dense vegetation. Suction sampling was nearly twice as efficient for spiders living in the vegetation than for spiders living near the soil surface, and cursorial and large‐bodied spider species were more efficiently sampled than web‐builders and small species. Depending on the sampling effort, suction sampling missed between 49% (one sample) and 31% (250 samples) of the spider species present. Suction sampling efficiency varied more strongly among sites and among arthropod groups than previously recognized. Abundance data derived from suction sampling are strongly underestimated, especially for arthropods living near the soil surface. Thus, comparisons of abundance and diversity between sites should be restricted to vegetation‐dwelling species of the most efficiently sampled groups. The positive relationship of sampling efficiency with vegetation density demonstrates that variation in efficiency is mediated by arthropod behaviour.