Soil microbial communities regulate global biogeochemical cycles and respond rapidly to changing environmental conditions. However, understanding how soil microbial communities respond to climate ...change, and how this influences biogeochemical cycles, remains a major challenge. This is especially pertinent in alpine regions where climate change is taking place at double the rate of the global average, with large reductions in snow cover and earlier spring snowmelt expected as a consequence. Here, we show that spring snowmelt triggers an abrupt transition in the composition of soil microbial communities of alpine grassland that is closely linked to shifts in soil microbial functioning and biogeochemical pools and fluxes. Further, by experimentally manipulating snow cover we show that this abrupt seasonal transition in wide-ranging microbial and biogeochemical soil properties is advanced by earlier snowmelt. Preceding winter conditions did not change the processes that take place during snowmelt. Our findings emphasise the importance of seasonal dynamics for soil microbial communities and the biogeochemical cycles that they regulate. Moreover, our findings suggest that earlier spring snowmelt due to climate change will have far reaching consequences for microbial communities and nutrient cycling in these globally widespread alpine ecosystems.
Soil-dwelling pests inflict considerable economic damage in agriculture but are hard to control. A promising strategy to reduce pest pressure on crops is to increase the plant diversity in ...agroecosystems. This approach, however, demands a sound understanding of species' interactions, which is widely lacking for subterranean herbivore-plant systems. Here, we examine the effects of plant diversification on wireworms, the soil-dwelling larvae of click beetles that threaten crops worldwide. We conducted a field experiment employing plant diversification by adding either wheat or a mix of six associated plants (grasses, legumes, and forbs) between rows of maize to protect it from
Agriotes
wireworms. Wireworm feeding behavior, dispersal between crop and associated plants, as well as maize damage and yield were examined. The former was assessed combining molecular gut content and stable isotope analysis. The pests were strongly attracted by the associated plants in August, when the crop was most vulnerable, whereas in September, shortly before harvest, this effect occurred only in the plant mix. In maize monoculture, the larvae stayed in the principal crop throughout the season. Larval δ
13
C signatures revealed that maize feeding was reduced up to sevenfold in wireworms of the vegetationally diversified treatments compared to those of the maize monoculture. These findings were confirmed by molecular analysis, which additionally showed a dietary preference of wireworms for specific plants in the associated plant mix. Compared to the monoculture, maize damage was reduced by 38% and 55% in the wheat and plant mix treatment, which translated into a yield increase of 30% and 38%, respectively. The present findings demonstrate that increasing the plant diversity in agroecosystems provides an effective insurance against soil pests. The underlying mechanisms are the diversion of the pest from the principle crop and a changed feeding behavior. The deployment of diverse mixes of associated plants, tailored to the specific preferences of the soil herbivores, provides a promising strategy for managing subterranean pests while maintaining crop yield.
Plant roots represent an important food source for soil‐dwelling animals, but tracking herbivore food choices below‐ground is difficult. Here, we present an optimized PCR assay for the detection of ...plant DNA in the guts of invertebrates, using general plant primers targeting the trnT‐F chloroplast DNA region. Based on this assay, we assessed the influence of plant identity on the detectability of ingested plant DNA in Agriotes click beetle larvae. Six different plant species were fed to the insects, comprising a grass, a legume and four nonlegume forbs. Moreover, we examined whether it is possible to amplify DNA of decaying plants and if DNA of decayed plant food is detectable in the guts of the larvae. DNA of the ingested roots could be detected in the guts of the larvae for up to 72‐h post‐feeding, the maximum digestion time tested. When fed with living plants, DNA detection rates differed significantly between the plant species. This may be ascribed to differences in the amount of plant tissue consumed, root palatability, root morphology and/or secondary plant components. These findings indicate that plant identity can affect post‐feeding DNA detection success, which needs to be considered for the interpretation of molecularly derived feeding rates on plants. Amplification of plant DNA from decaying plants was possible as long as any tissue could be retrieved from the soil. The consumption of decaying plant tissue could also be verified by our assay, but the insects seemed to prefer fresh roots over decaying plant material.
Climate change was already shown to increase species numbers in high elevations. In contrast, grazing might interfere with climate change effects. To disentangle both the effects remains a major ...challenge of alpine ecology. The present study investigated both the effects on species diversity along an elevation gradient in the Austrian Central Alps. We aimed to answer the following questions: How do species diversity and frequency of subalpine–alpine–subnival plant communities change in grazed sites with time? Do competitive plant species increase in the communities? How does grazing exclusion affect species diversity, functional groups, and strategy types? Are environmental changes (temperature, sunshine duration, precipitation) responsible for diversity changes or does grazing override climate effects? The study was carried out for 18 years along an elevation gradient from 1,958 to 2,778 m a.s.l. at Obergurgl (Tyrol, Austria), including six different plant communities. A total of 11 grazing exclusions were established. At each community, the frequency of the species was counted in 1 m
2
plots yearly or at least every 3–4 years. Environmental data were obtained from the weather station Obergurgl. Changes of the community parameters and the species composition were analyzed by partial redundancy analyses and mixed-effect models. Species diversity increased with time at all grazed sites, but this increase was suppressed under grazing exclusion. Grazing exclusion effects became pronounced after 5 years. The most consistent result was the increase of bryophytes throughout. At the subalpine grassland, tall-growing species expanded in the exclosures; at the upper alpine
Carex curvula
grassland, snow bed species decreased with grazing exclusion. Among the environmental factors, sunshine duration of the previous year’s autumn quartal was found to be the essential variable for the changes. We concluded that diversity increases in grazed communities of the Austrian Central Alps can be attributed to climate change. An indication of slightly reduced and altered weather effects under grazing exclusion was found.
Plant identity and diversity influence herbivore communities in many different ways. While it is well known how they affect the feeding preferences of aboveground herbivores, this information is ...lacking for soil ecosystems, where examining plant-herbivore trophic interactions is difficult. We performed a mesocosm experiment assessing how plant identity and diversity affect the food choice of
Agriotes
larvae, which are soil-living generalist herbivores. We offered four plant species, (maize, a grass, a legume, and a forb) at varying combinations and diversity levels to these larvae, and analyzed their feeding behavior using stable isotopes. We hypothesized that (1) their food choice is driven by preference for certain plant species rather than by root abundance and that (2) the preference for specific plants changes with increasing plant diversity. We found that larvae preferred the grass and legume but avoided maize and the forb. Whether a plant was preferred or avoided was independent of diversity, but the extent of avoidance or preference changed with increasing plant diversity. Our findings reveal that the dietary choice of soil-living generalist herbivores is determined by plant-specific traits rather than root abundance. Our data also suggest that soil herbivore feeding preferences are modulated by plant diversity.
To understand soil food webs, empirically generated data on the trophic connections and the feeding ecology of the major below-ground animal taxa are needed. Here we used stable isotope analysis to ...assess the trophic ecology of wireworms, the larvae of click beetles, in Central European arable land. Wireworms are amongst the major soil macroinvertebrates and are of practical importance in arable soils. Besides feeding on crops, they are thought to feed on weeds, soil organic matter (SOM), and even animal prey, but their feeding ecology is poorly studied under natural conditions. Elaterid larvae and their putative feeding substrates—plant roots, SOM, and litter—were sampled at 17 locations in Austria, Germany, and Italy and their isotope ratios of carbon (
12C/
13C) and nitrogen (
14N/
15N) measured to determine the wireworms’ trophic level, the importance of SOM and weeds within the diet of
Agriotes larvae, as well as the individual diet variation in
Agriotes obscurus larvae.
δ
15N signatures suggested that
Agriotes larvae are predominately herbivorous, whereas the other wireworm species primarily fed on animal prey. In contrast to SOM, weeds were readily eaten by
Agriotes larvae: their dietary contribution ranged between 28% and 67% in weedy maize fields. Most
A. obscurus larvae fed on a mixed diet of weeds and maize, although ∼15% of the larvae fed primarily on one of the two food sources only.
δ
15N signatures indicated that ∼10% of the “herbivorous”
A. obscurus larvae fed primarily on animal prey, revealing high intraspecific trophic plasticity in these soil insects. Wireworm feeding behaviour is apparently complex at the individual level: the population consists of types A and B generalists, a phenomenon which needs further assessment.
Plant identification is challenging when no morphologically assignable parts are available. There is a lack of broadly applicable methods for identifying plants in this situation, for example when ...roots grow in mixture and for decayed or semi-digested plant material. These difficulties have also impeded the progress made in ecological disciplines such as soil- and trophic ecology. Here, a PCR-based approach is presented which allows identifying a variety of plant taxa commonly occurring in Central European agricultural land. Based on the trnT-F cpDNA region, PCR assays were developed to identify two plant families (Poaceae and Apiaceae), the genera Trifolium and Plantago, and nine plant species: Achillea millefolium, Fagopyrum esculentum, Lolium perenne, Lupinus angustifolius, Phaseolus coccineus, Sinapis alba, Taraxacum officinale, Triticum aestivum, and Zea mays. These assays allowed identification of plants based on size-specific amplicons ranging from 116 bp to 381 bp. Their specificity and sensitivity was consistently high, enabling the detection of small amounts of plant DNA, for example, in decaying plant material and in the intestine or faeces of herbivores. To increase the efficacy of identifying plant species from large number of samples, specific primers were combined in multiplex PCRs, allowing screening for multiple species within a single reaction. The molecular assays outlined here will be applicable manifold, such as for root- and leaf litter identification, botanical trace evidence, and the analysis of herbivory.
1 The dispersal abilities of agrioted beetles, serious pests on a variety of crops, are poorly known under natural conditions. This hampers their control. We used, for the first time, a stable ...isotope approach to assess dispersal of adult Agriotes obscurus in arable land.
2 After a diet switch from a C3‐ to a C4‐plant, carbon isotope ratios of A. obscurus larvae significantly changed towards the isotopic signature of the new diet. Moreover, the larval δ13C signatures were transferred to the wing covers of the adult beetles with little distortion.
3 To assess the dispersal abilities under natural conditions, pheromone traps, lured for Agriotes sp., were installed at two study sites in Western Austria. Each site comprised a maize field (= C4‐plant) and adjacent C3‐grasslands with traps established along a transect of increasing distance to the maize.
4 δ13C signatures of wing covers revealed that adult male A. obscurus were able to migrate at least 80 m, which was the maximum distance that dispersal could be traced in the present study. The dispersal behaviour might have been influenced by site‐specific factors.
5 The results obtained demonstrate a higher potential of adult male Agriotes to disperse than previously assumed. Moreover, the combination of pheromone trapping and stable isotope analysis proved to be an effective approach to study insect movement and dispersal in arable systems harbouring C3‐ and C4‐crops.
Although a significant proportion of plant tissue is located in roots and other below-ground parts of plants, little is known on the dietary choices of root-feeding insects. This is caused by a lack ...of adequate methodology which would allow tracking below-ground trophic interactions between insects and plants. Here, we present a DNA-based approach to examine this relationship. Feeding experiments were established where either wheat (Triticum aestivum) or maize (Zea mays) was fed to Agriotes larvae (Coleoptera: Elateridae), allowing them to digest for up to 72 h. Due to the very small amount of plant tissue ingested (max = 6.76 mg), DNA extraction procedures and the sensitivity of polymerase chain reaction (PCR) had to be optimized. Whole-body DNA extracts of larvae were tested for the presence of both rbcL and trnL plastid DNA using universal primers. Moreover, based on cpDNA sequences encoding chloroplast tRNA for leucine (trnL), specific primers for maize and wheat were developed. With both, general and specific primers, plant DNA was detectable in the guts of Agriotes larvae for up to 72 h post-feeding, the maximum time of digestion in these experiments. No significant effect of time since feeding on plant DNA detection success was observed, except for the specific primers in maize-fed larvae. Here, plant DNA detection was negatively correlated with the duration of digestion. Both, meal size and initial mass of the individual larvae did not affect the rate of larvae testing positive for plant DNA. The outcomes of this study represent a first step towards a specific analysis of the dietary choices of soil-living herbivores to further increase our understanding of animal–plant feeding interactions in the soil.
► We identified ingested plant material by molecular means from Agriotes larvae, which are amongst the most important soil pests in arable land. ► Whole-body DNA extracts of larvae were tested for the presence of both rbcL and trnL plastid DNA using universal primers and specific primers. ► Plant DNA was detectable in the guts of Agriotes larvae for up to 72 h post-feeding. ► Time since feeding, meal size and initial mass of the individual larvae did not affect the rate of larvae testing positive for plant DNA. ► This work will facilitate future studies on soil food web ecology.
Belowground herbivores impact plant performance, thereby inducing changes in plant community composition, which potentially leads to cascading effects onto higher trophic levels and ecosystem ...processes and productivity. Among soil‐living insects, external root‐chewing generalist herbivores have the strongest impact on plants. However, the lack of knowledge on their feeding behaviour under field conditions considerably hampers achieving a comprehensive understanding of how they affect plant communities. Here, we address this gap of knowledge by investigating the feeding behaviour of Agriotes click beetle larvae, which are common generalist external root‐chewers in temperate grassland soils. Utilizing diagnostic multiplex PCR to assess the larval diet, we examined the seasonal patterns in feeding activity, putative preferences for specific plant taxa, and whether species identity and larval instar affect food choices of the herbivores. Contrary to our hypothesis, most of the larvae were feeding‐active throughout the entire vegetation period, indicating that the grassland plants are subjected to constant belowground feeding pressure. Feeding was selective, with members of Plantaginaceae and Asteraceae being preferred; Apiaceae were avoided. Poaceae, although assumed to be most preferred, had an intermediate position. The food preferences exhibited seasonal changes, indicating a fluctuation in plant traits important for wireworm feeding choice. Species‐ and instar‐specific differences in dietary choice of the Agriotes larvae were small, suggesting that species and larval instars occupy the same trophic niche. According to the current findings, the food choice of these larvae is primarily driven by plant identity, exhibiting seasonal changes. This needs to be considered when analysing soil herbivore–plant interactions.
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