Metal accumulation strategies in saprophagous and phytophagous soil invertebrates: a quantitative comparison

To quantitatively reveal accumulation patterns of environmentally relevant heavy metals in selected saprophagous or phytophagous soil invertebrates, adults of the species Porcellio scaber (Isopoda), Tetrodontophora bielanensis (Collembola), Julus scandinavius (Diplopoda), and Deroceras reticulatum (Gastropoda) were exposed to lead-, cadmium-, or zinc-contaminated food and soil for three weeks. The heavy metal concentrations in the food, the substrate, and the bodies of the invertebrates were measured by atomic absorption spectrophotometry (AAS). The investigated species were found to differ in their metal accumulation strategies, which is interpreted as a consequence of different detoxification mechanisms.     

Secondary succession, soil formation and development of a diverse community of oribatids and saprophagous soil macro-invertebrates

Investigations into different stages of secondary succession (from a wheat field to a beechwood on Threstone; Northern Germany) demonstrated the formation of a carbon rich top soil in later successional stages. Parallel to changes in plant species and soil formation, there were also changes in species composition and diversity of saprophagous macro-invertebrates (Lumbricidae, Diplopoda, Isopoda) and oribatid mites (Acari: Oribatida). Diversity of diplopod and isopod species increased after cessation of cultivation, but in a late successional stage (ca 50 y-old fallow, ash-dominated wood) species number of diplopods and isopods declined strongly. In comparison with the other soil invertebrate groups, species composition of earthworms among the sites was more similar. Accumulation of soil C was assumed to be related to wood formation and occurrence of woody debris and recalcitrant leaf litter of beech trees. Incorporation of recalcitrant litter materials by earthworm species living in the upper mineral soil presumably contributed significantly to accumulation of soil C. Accumulation of soil C was accompanied by the development of an oribatid mite community rich in species. In early successional stages oribatids predominantly colonized the litter layer, while most oribatid mites of the beechwood inhabited the upper mineral soil. Maximum diversity of oribatid mites in the beechwood is assumed to be related to instability of the mineral soil caused by earthworm activity. Changes in species composition and diversity are discussed considering succession theory. Even soil invertebrates of similar trophic groups appear to respond very differently to successional changes. It is concluded that conservation strategies to maintain high diversity of soil invertebrates are most likely to be successful if a wide range of habitats of different successional stages is included.     

Short-term incorporation of freshly fixed plant carbon into the soil animal food web: field study in a spruce forest

We analyzed the dynamics of the short-term incorporation of recently fixed carbon into the below-ground food web in a boreal forest. Five young spruce trees (Picea abies) were pulse-labeled with ¹³CO₂ and the isotopic label was traced in soil invertebrates during 5 weeks. The freshly fixed plant carbon quickly entered both litter-located and soil-located compartments of the detrital food web. Among invertebrates inhabiting the mineral soil layers, a trophic link to the root-derived C was most pronounced in species with higher δ ¹⁵N values, suggesting this energy source to be more important in deeper mineral soil horizons. The label appeared faster in saprophagous animals than in predators (the median time lag after labeling was 6 and 12 days, respectively), but the difference was not significant. The label was recovered in 15 of 38 species of saprophagous animals and in 20 of 63 species of predators. Among saprophages, the frequency and intensity of the label was relatively high in endogeic collembolans and in bibionid larvae, but earthworms and enchytraeids were not labeled. Several groups of predators, lithobiid centipedes in particular, quickly acquired the root-derived carbon, possibly indicating the feeding on live roots or mycorrhizal mycelium. In total, only 35 % of species or genera examined acquired the label. This suggests that majority of invertebrate taxa in the decomposer food web are unlikely to depend heavily on freshly fixed plant carbon provided by roots and root-associated microorganisms.     

Positive correlation of trophic level and proportion of sexual taxa of oribatid mites (Acari: Oribatida) in alpine soil systems

We investigated community structure, trophic ecology (using stable isotope ratios; ¹⁵N/¹⁴N, ¹³C/¹²C) and reproductive mode of oribatid mites (Acari, Oribatida) along an altitudinal gradient (2,050–2,900 m) in the Central Alps (Obergurgl, Austria). We hypothesized that (1) the community structure changes with altitude, (2) oribatid mites span over four trophic levels, (3) the proportion of sexual taxa increases with altitude, and (4) the proportion of sexual taxa increases with trophic level, i.e. is positively correlated with the δ¹⁵N signatures. Oribatid mite community structure changed with altitude indicating that oribatid mites occupy different niches at different altitudes. Oribatid mites spanned over 12 δ¹⁵N units, i.e. about four trophic levels, which is similar to lowland forest ecosystems. The proportion of sexually reproducing taxa increased from 2,050 to 2,900 m suggesting that limited resource availability at high altitudes favors sexual reproduction. Sexual taxa more frequently occurred higher in the food web indicating that the reproductive mode is related to nutrition of oribatid mites. Generally, oribatid mite community structure changed from being decomposer dominated at lower altitude to being dominated by fungal and lichen feeders, and predators at higher altitude. This supports the view that resources from dead organic material become less available with increasing altitude forcing species to feed on living resources such as fungi, lichens and nematodes. Our findings support the hypothesis that limited resource accessibility (at high altitudes) favors sexually reproducing species whereas ample resource supply (at lower altitudes) favors parthenogenetic species.     

Ecosystem Linkages Between Lakes and the Surrounding Terrestrial Landscape in Northeast Iceland

Despite a recent emphasis on understanding cross-habitat interactions, few studies have examined the ecological linkages between lakes and surrounding terrestrial habitats. The current paradigm of land–lake interactions is typically unidirectional: the view is that nutrients and matter are transported downslope from the surrounding watershed to their ultimate lacustrine destination. Emergent aquatic insects, which spend their larval stages in lake sediments and emerge as adults to mate over land, can act as vectors of material, energy and nutrients from aquatic to terrestrial habitats. In this study, we document a gradient of midge (Diptera: Chironomidae) infall rates into terrestrial habitats (measured as g dw midges m^?2 d^?1) surrounding eight lakes in Northern Iceland (≈66°N latitude). Lakes ranged from having virtually no midge infall (for example, Helluvaðstjörn, 0.03 g m^?2 d^?1) to extreme levels (for example, Mývatn, 19 g m^?2 d^?1) with abundances of midges decreasing logarithmically with distance from shore. Annual midge input rates are estimated as high as 1200–2500 kg midges ha^?1 y^?1. As midges are approximately 9.2% total N, this can result in a significant fertilization effect of terrestrial habitats with consequences for plant quality and community structure. In addition, we used naturally-occurring δ¹³C and δ¹⁵N isotopes to examine food web structure and diet sources of terrestrial arthropod consumers surrounding lakes with differing amounts of midge input. Terrestrial arthropods showed increased utilization of aquatic-derived (that is, midge) C relative to terrestrial sources as midge infall increased. This pattern was particularly pronounced for predators, such as spiders and opiliones, and some detritivores (Collembola). These findings suggest that, despite being largely ignored, aquatic-to-terrestrial linkages can be large and midges can fuel terrestrial communities by directly serving as resources for predators and decomposers.     

Linking aboveground and belowground food webs through carbon and nitrogen stable isotope analyses

Carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) have been used for more than two decades in analyses of food web structure. The utility of isotope ratio measurements is based on the observation that consumer δ¹³C values are similar (<1‰ difference) to those of their diet, while consumer δ¹⁵N values are about 3‰ higher than those of their diet. The technique has been applied most often to aquatic and aboveground terrestrial food webs. However, few isotope studies have examined terrestrial food web structure that includes both above- and belowground (detrital) components. Here, we review factors that may influence isotopic signatures of terrestrial consumers in above- and belowground systems. In particular, we emphasize variations in δ¹³C and δ¹⁵N in belowground systems, e.g., enrichment of ¹³C and ¹⁵N in soil organic matter (likely related to soil microbial metabolism). These enrichments should be associated with the high ¹³C (~3‰) enrichment in belowground consumers relative to litter and soil organic matter and with the large variation in δ¹⁵N (~6‰) of the consumers. Because such enrichment and variation are much greater than the trophic enrichment generally used to estimate consumer trophic positions, and because many general predators are considered dependent on energy and material flows from belowground, the isotopic variation in belowground systems should be taken into account in δ¹³C and δ¹⁵N analyses of terrestrial food webs. Meanwhile, by measuring the δ¹³C of key predators, the linkage between above- and belowground systems could be estimated based on observed differences in δ¹³C of primary producers, detritivores and predators. Furthermore, radiocarbon (¹⁴C) measurements will allow the direct estimation of the dependence of predators on the belowground systems.     

Water chemistry,landscape, and spatial controls of δ13C and δ15N of zooplankton taxa in boreal lakes: One size does not fit all

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Free‐living nematodes as prey for higher trophic levels of forest soil food webs

Nematodes are the most abundant invertebrates in soils and are key prey in soil food webs. Uncovering their contribution to predator nutrition is essential for understanding the structure of soil food webs and the way energy channels through soil systems. Molecular gut content analysis of consumers of nematodes, such as soil microarthropods, using specific DNA markers is a novel approach for studying predator–prey interactions in soil. We designed new specific primer pairs (partial 18S rDNA) for individual soil‐living bacterial‐feeding nematode taxa (Acrobeloides buetschlii, Panagrellus redivivus, Plectus velox and Plectus minimus). Primer specificity was tested against more than 100 non‐target soil organisms. Further, we determined how long nematode DNA can be traced in the gut of predators. Potential predators were identified in laboratory experiments including nine soil mite (Oribatida, Gamasina and Uropodina) and ten springtail species (Collembola). Finally, the approach was tested under field conditions by analyzing five mite and three collembola species for feeding on the three target nematode species. The results proved the three primer sets to specifically amplify DNA of the respective nematode taxa. Detection time of nematode DNA in predators varied with time of prey exposure. Further, consumption of nematodes in the laboratory varied with microarthropod species. Our field study is the first definitive proof that free‐living nematodes are important prey for a wide range of soil microarthropods including those commonly regarded as detritivores. Overall, the results highlight the eminent role of nematodes as prey in soil food webs and for channelling bacterial carbon to higher trophic levels.     

Isotopic signature (<Superscript>15</Superscript>N/<Superscript>14</Superscript>N and <Superscript>13</Superscript>C/<Superscript>12</Superscript>C) confirms similarity of trophic niches of millipedes (Myriapoda,diplopoda) in a temperate deciduous forest

The species composition, abundance, and isotopic signature of millipedes (Myriapoda, Diplopoda) were investigated in seven biotopes of Kaluzhskie Zaseki State Nature Reserve. Nine Diplopoda species were found in total, and the local species diversity (within a sampling plot) reached seven species. The Diplopoda tissues were similar to the plant litter in the isotopic composition of nitrogen (δ¹⁵N was by 0.4‰ higher, on average), but were strongly enriched in heavy carbon (δ¹³C was by 4‰ higher, on average). Removal of mineral carbon from the cuticle reduced δ¹³C of Diplopoda by about 1.4‰ on average. Differences in the δ¹⁵N and δ¹³C values between the species did not exceed 2.5‰. Differences in the isotopic compositions of the considered species were small, and, it is impossible to distinguish particular trophic guilds in the Diplopoda community. Analysis of the published data confirmed that isotopic differentiation of millipedes was much less pronounced than in other investigated groups of soil animals. Hence, millipedes of the deciduous forest form a uniform trophic group.     

Fertilization alters nitrogen isotopes and concentrations in ectomycorrhizal fungi and soil in pine forests

To assess how nitrogen (N) availability affected ectomycorrhizal functioning and to test a theoretical model of ectomycorrhizal ¹⁵N partitioning, we measured C/N and δ¹⁵N in soils and nine fungal taxa in two Swedish N addition experiments. Sporocarp C/N and soil C/N decreased with fertilization, implying that N uptake per unit fungal growth increased. The S horizon was more responsive than the F and H horizons to changes in N addition, with N turnover for these horizons of 24, 57, and 57 y, respectively. Fungal and soil δ¹⁵N patterns identified fungal N sources, with N acquisition primarily from the S, F, or H horizon for two, five, and two taxa, respectively. With increasing N availability, sporocarp ¹⁵N enrichment increased in five taxa, in agreement with our model of fungal-plant N partitioning. However, it decreased in Lactarius rufus and Russula aeruginea, perhaps indicating shifts towards greater inorganic N uptake in these two taxa. This may relate to the generally lower sensitivity of these taxa to N deposition compared to the Cortinarius and Suillus taxa that fit our model of ¹⁵N partitioning.     

Non-omnia moriantur—toxicity of mancozeb on dead wood microarthropod fauna

The effect of Dithane M-45 (dithiocarbamate fungicide; active substance: mancozeb) was studied on microarthropod fauna inhabiting dead wood. Although the exposure was almost never 100% lethal for the majority of observed taxa, almost all (Mesostigmata, Oribatida, some Uropodina, Actinedida, Collembola and Diplopoda) showed very high correlation between concentration of the fungicide and mortality (r > 0.86). Only Stigmaeidae showed low correlation (r = 0.293). For the majority of taxa LC₅₀ values were close to the concentrations used during agrochemical activities in woods. Only Trachytes aegrota showed full susceptibility to the fungicide within the range of recommended field concentrations used in forestry (characterised by the low LC₉₅ value). Tolerance of mesostigmatid and oribatid mites was found to differ between juveniles and adults, but not consistently. Related Uropodina species varied in susceptibility to the fungicide.     

Functional differences between woodland savannas and seasonally dry forests from south‐eastern Brazil: Evidence from 15N natural abundance studies

Nitrogen availability and N‐cycling dynamics across ecosystems play a critical role in plant functioning and species distribution. Measurements of ¹⁵N natural abundance provides a way to assess ecosystem N dynamics, and the range of nitrogen stable isotope values (δ¹⁵N) for plants in an ecosystem can indicate divergent strategies for N uptake. We tested the hypotheses that the N‐rich seasonally dry forest would have higher soil and leaf δ¹⁵N and a smaller range of leaf δ¹⁵N values compared to the N‐poor cerradão (savanna woodland). We measured N concentration and δ¹⁵N in two soil depths and leaves of 27 woody species in cerradão and 26 in seasonally dry forest. As expected, total soil N concentration decreased while soil δ¹⁵N value increased with soil depth. Regardless of soil depth, seasonally dry forest soils had higher δ¹⁵N and total N concentration compared to cerradão soils. Foliar δ¹⁵N values varied from ?6.4‰ to 5.9‰ in cerradão and from ?2.3‰ to 8.4‰ in seasonally dry forest plants. Phylogenetically independent contrasts analysis and comparisons of δ¹⁵N mean values of the most abundant species and species co‐occurring in both sites confirmed the hypothesis of higher δ¹⁵N for seasonally dry forest in comparison to cerradão. These results corroborate the expectation of higher soil and leaf δ¹⁵N values in sites with higher soil N availability. However, except for the most abundant species, no across‐site leaf–soil (δ¹⁵N leaf –δ¹⁵N soil) differences (Δδ¹⁵N) were found suggesting that differences in leaf δ¹⁵N between cerradão and seasonally dry forest are driven by differences in soil δ¹⁵N. Variation of leaf δ¹⁵N was large in both sites and only slightly higher in cerradão, suggesting high diversity of N use strategies for both cerradão and seasonally dry forest communities.     

Is the high 15N natural abundance of trees in N-loaded forests caused by an internal ecosystem N isotope redistribution or a change in the ecosystem N isotope mass balance?

High δ¹⁵N of tree foliage in forests subject to high N supply has been attributed to ¹⁵N enrichment of plant available soil N pools after losses of N through processes involving N isotope fractionation (ammonia volatilization, nitrification followed by leaching and denitrification, and denitrification in itself). However, in a long-term experiment with high annual additions of NH₄NO₃, we found no change in the weighted average δ¹⁵N of the soil, but attributed the high δ¹⁵N of trees to loss of ectomycorrhizal fungi and their function in tree N uptake, which involves redistribution of N isotopes in the ecosystem (Högberg et al. New Phytol 189:515–525, 2011), rather than a loss of isotopically light N. Here, we compare the effects of additions of urea and NH₄NO₃ on the δ¹⁵N of trees and the soil profile, because we have previously found higher δ¹⁵N in tree foliage in trees in the urea plots. Doing this, we found no differences between the NH₄NO₃ and urea treatments in the concentration of N in the foliage, or the amounts of N in the organic mor-layer of the soil. However, the foliage of trees receiving the highest N loads in the urea treatment were more enriched in ¹⁵N than the corresponding NH₄NO₃ plots, and, importantly, the weighted average δ¹⁵N of the soil showed that N losses had been associated with fractionation against ¹⁵N in the urea plots. Thus, our results in combination with those of Högberg et al. (New Phytol 189:515–525, 2011) show that high δ¹⁵N of the vegetation after high N load may be caused by both an internal redistribution of the N isotopes (as a result of change of the function of ectomycorrhiza) and by losses of isotopically light N through processes fractionating against ¹⁵N (in case of urea ammonia volatilization, nitrification followed by leaching and denitrification).     

Historical Small‐Scale Surface Structures as a Model for Post‐Mining Land Reclamation

Historical land use provides long‐term field experiments that give valuable clues for ecosystem management and habitat restoration. We hypothesized that remnants of a small‐scale charcoal‐ore industry that ceased more than a century ago still affect soil properties and the litter‐dwelling fauna of a beech forest on rendzina soil (pH 4–6.5). We sampled the remains of charcoal kilns, small mining pits, and mounds of dugout material. Soils from kilns displayed increased carbon and nutrient contents and soils from kilns and in pits tended to be moister than that from all other locations. Leaf litter accumulated in the pits. Most mesofauna taxa occurred independent of the modifications, whereas larger‐sized Collembola and many macrofauna taxa (Aranea, Chilopoda, Diplopoda, Isopoda, Coleoptera, and Gastropoda) were more abundant in the pits. Snails are highly sensitive to microclimatic fluctuations and structural changes and thus were used to compare man‐made structures with natural ones: assemblages from kilns equaled those from the unmodified forest floor, assemblages from pits resembled those from adjacent to coarse woody debris (CWD), and assemblages from mounds resembled those from outcrops and tree bases. The outcrops were the local keystone structure, but mining pits and CWD added to species richness as they provided shelter for hygrophilous species. We thus recommend maintaining or creating a diversified soil surface structure in post‐mining land reclamation to accumulate organic matter and nutrients and to buffer microclimatic extremes.     

Spatial heterogeneity of trophic pathways in the invertebrate community of a temperate bog

Summary 1. To examine spatial heterogeneity of trophic pathways on a small scale (<5 m diameter), we conducted dual stable isotope (δ¹³C and δ¹⁵N) analyses of invertebrate communities and their potential food sources in three patchy habitats [sphagnum lawn (SL), vascular‐plant carpet (VC) and sphagnum carpet] within a temperate bog (Mizorogaike Pond, Kyoto, Japan). 2. In total, 19 invertebrate taxa were collected from the three habitats, most of which were stenotopic, i.e. collected from a single habitat. Amongst the habitats, significant variation was observed in the isotopic signatures of dominant plant tissues and their detrital matter [benthic particulate organic matter (BPOM)], both of which were potential organic food sources for invertebrates. Site‐specific isotopic variation amongst detritivores was found in δ¹³C but not in δ¹⁵N, reflecting site‐specificity in the isotopic signatures of basal foods. The eurytopic hydrophilid beetle Helochares striatus was found in all habitats, but showed clear site variation in its isotopic signatures, suggesting that it strongly relies on foods within its own habitat. 3. The most promising potential foods for detritivores were the dead leaf stalks of a dominant plant in the VC and BPOM in the SL and carpet. An isotopic mixing model (IsoSource version 1.3.1) estimated that aquatic predators rely on unknown trophic sources with higher δ¹³C than detritus, whereas terrestrial predators forage on allochthonous as well as autochthonous prey, suggesting that the latter predators might play key roles in coupling between habitats. 4. Our stable isotope approach revealed that immobile detritivores are confined to their small patchy habitats but that heterogeneous trophic pathways can be coupled by mobile predators, stressing the importance of habitat heterogeneity and predator coupling in characterising food webs in bog ecosystems.     

Patterns of soil and plant nitrogen isotope composition and their relationships with climate factors in Xilingol League,Inner Mongolia,China

Background: Plant and soil nitrogen stable isotope (δ¹⁵N) can integrate several fundamental biogeochemical processes in ecosystem nitrogen dynamics, and reflect characteristics of ecosystem nitrogen cycling.

Aims: We investigated how climate change influenced plant-soil nitrogen cycling by relating soil δ¹⁵N, plant δ¹⁵N and Δδ¹⁵N (difference between soil and plant δ¹⁵N) with climatic factors.

Methods: Field investigation was conducted in temperate grasslands in Inner Mongolia during August 2015. Plant δ¹⁵N, soil δ¹⁵N and Δδ¹⁵N were determined, and their relationships with climatic factors were examined by simple regression analyses and general linear models.

Results: Soil δ¹⁵N was significantly higher than plant δ¹⁵N, and there was a positive linear correlation between them. Soil and plant δ¹⁵N were negatively related with mean annual precipitation (MAP) and positively with mean annual temperature (MAT); conversely, Δδ¹⁵N was positively related with MAP and negatively with MAT.

Conclusion: Soil δ¹⁵N was dominantly controlled by MAT, while it was MAP for plant δ¹⁵N. Climate factors influenced plant δ¹⁵N not only through their effects on soil nitrogen dynamics but also strategies of plant nitrogen acquisition. Thus, compared with plant δ¹⁵N, soil δ¹⁵N can more accurately reflect soil nitrogen dynamics, while plant δ¹⁵N may integrate soil nitrogen dynamics and plant nitrogen acquisition.     

Assimilation dynamics of soil carbon and nitrogen by wheat roots and Collembola

It has been demonstrated that plant roots can take up small amounts of low-molecular weight (LMW) compounds from the surrounding soil. Root uptake of LMW compounds have been investigated by applying isotopically labelled sugars or amino acids but not labelled organic matter. We tested whether wheat roots took up LMW compounds released from dual-labelled (¹³C and ¹⁵N) green manure by analysing for excess ¹³C in roots. To estimate the fraction of green manure C that potentially was available for root uptake, excess ¹³C and ¹⁵N in the primary decomposers was estimated by analysing soil dwelling Collembola that primarily feed on fungi or microfauna. The experimental setup consisted of soil microcosm with wheat and dual-labelled green manure additions. Plant growth, plant N and recoveries of ¹³C and ¹⁵N in soil, roots, shoots and Collembola were measured at 27, 56 and 84 days. We found a small (<1%) but significant uptake of green manure derived ¹³C in roots at the first but not the two last samplings. About 50% of green manure C was not recovered from the soil-plant system at 27 days and additional 8% was not recovered at 84 days. Up to 23% of C in collembolans derived from the green manure at 56 days (the 27 days sampling was lost). Using a linear mixing model we estimated that roots or root effluxes provided the main C source for collembolans (54−79%). We conclude that there is no solid support for claiming that roots assimilated green manure derived C due to very small or no recoveries of excess ¹³C in wheat roots. During the incubation the pool of green manure derived C available for root uptake decreased due to decomposition. However, the isotopic composition in Collembola indicated that there was a considerable fraction of green manure derived C in the decomposer system at 56 days thus supporting the premise that LMW compounds containing C from the green manure was released throughout the incubation. Responsible Editor: A. C. Borstlap.     

Iron supply prevents Cd uptake in Arabidopsis by inhibiting IRT1 expression and favoring competition between Fe and Cd uptake

Background

Anthropogenic nitrogen (N) addition has dramatically increased and significantly affected global nitrogen cycling. The natural abundance of stable N isotope ratios (δ¹⁵N) has been used as an indicator of the N status of an ecosystem. However, how plant and soil δ¹⁵N signatures would respond to N addition is still unclear.

Methods and aims

Herein, we synthesized the data of 951 observations from 48 individual studies associated with responses of plant and soil δ¹⁵N values to N addition and conducted a meta-analysis to explore a general pattern of N addition effects on δ¹⁵N values of plant and soil.

Results

Our results showed that δ¹⁵N values of plant, soil total N, and soil NO₃ ^? were significantly increased by N addition, while δ¹⁵N value of soil N₂O was significantly decreased and δ¹⁵N value of soil NH₄ ⁺ was not significantly changed. The δ¹⁵N value of soil total N of different ecosystems showed similar responses to N addition, whereas δ¹⁵N values of different plant types showed different responses. Increasing treatment duration significantly increased the effects of inorganic N addition on δ¹⁵N values of shrubs and soil NH₄ ⁺ but did not affect the responses of δ¹⁵N values of soil total N and NO₃ ^?. With increasing inorganic N addition rate, only δ¹⁵N value of plant was significantly increased, but no significant relationship was found between the effect of N addition on other components and N addition rate because of the input of isotopically depleted sources.

Conclusions

Our study revealed a comprehensive picture of the effects of N addition on δ¹⁵N signatures in terrestrial ecosystems and could help us understand how plant and soil δ¹⁵N signatures change with N addition and how these signatures can be used as an indicator of ecosystem N status under increasing N deposition or fertilization.

     

Spruce monoculture establishment affects functional traits of soil microarthropod communities

Structure and density of soil microarthropod communities (Oribatida and Collembola) were studied in one natural beech forest and one spruce monoculture planted on a former beech stand in South Bohemia (Czech Republic). The spruce monoculture establishment increased microarthropod densities (93,000 ind. m^?2 in the natural beech forest vs. 400,540 ind. m^?2 in the spruce monoculture for Oribatida; 66,360 ind. m^?2 in the natural beech forest vs. 136,360 ind. m^?2 in the spruce monoculture for Collembola); additionally, it changed greatly the community structure in terms of species composition and functional traits. In the spruce monoculture, groups susceptible to disturbance were suppressed. The oribatid trophic structure changed as well with opportunistic herbifungivorous species increasing in the monoculture at the expense of fungivorous species. Similarly, hemiedaphic collembolans increased in the monoculture at the expense of euedaphic species. We conclude that the “functional approach” seems to be fruitful in revealing soil fauna response to environmental change.     

Environmental and species‐specific controls on δ13C and δ15N in dominant woody plants from central‐western Argentinian drylands

Spatial variation in mean annual precipitation is the principal driver of plant water and nitrogen status in drylands. The natural abundance of carbon stable isotopes (δ¹³C) in photosynthetic tissues of C3 plants is an indicator of time‐integrated behaviour of stomatal conductance; while that of nitrogen stable isotopes (δ¹⁵N) is an indicator of the main source of plant N (soil N vs. atmospheric N₂). Previous studies in drylands have documented that plant δ¹³C and δ¹⁵N values increase with decreasing mean annual precipitation due to reductions in stomatal conductance, and soil enriched in ¹⁵N, respectively. However, evidence for this comes from studies focused on stable isotopes measurements integrated at the plant community level or on dominant plants at the site level, but little effort has been made to study C and N isotope variations within a species growing along rainfall gradients. We analysed plant δ¹³C, δ¹⁵N and C/N values of three woody species having different phenological leaf traits (deciduous, perennial and aphyllous) along a regional mean annual precipitation gradient from the central‐western Argentinian drylands. Noticeably, plant δ¹³C and δ¹⁵N values in the three woody species did not increase towards sites with low precipitation or at the start of the growing season (drier period), as we expected. These results suggest that environmental factors other than mean annual precipitation may be affecting plant δ¹³C and δ¹⁵N. The short‐term environmental conditions may interact with species‐specific plant traits related to water and nitrogen use strategies and override the predictive influence of the mean annual precipitation on plant δ¹³C and δ¹⁵N widely reported in drylands.