Harsh Abiotic Conditions Research Articles

Incorporating biotic interactions to better model current and future vegetation of the maritime Antarctic

Maritime Antarctica's harsh abiotic conditions forged simple terrestrial ecosystems, mostly constituted of bryophytes, lichens, and vascular plants. Though biotic interactions are, together with abiotic factors, thought to help shape this ecosystem, influencing species' distribution and, indirectly, mediating their response to climate, the importance of these interactions is still fairly unknown. We modeled current and future abundance patterns of bryophytes, lichens, and vascular plants, accounting for biotic interactions and abiotic drivers, along a climatic gradient in maritime Antarctica. The influence of regional climate and other drivers was modeled using structural equation models, with and without biotic interactions. Models with biotic interactions performed better; the one offering higher ecological support was used to estimate current and future spatial distributions of vegetation. Results suggest that plants are confined to lower elevations, negatively impacting bryophytes and lichens, whereas at higher elevations both climate and other drivers influence bryophytes and lichens. Our findings strongly support the use of biotic interactions to predict the spatial distribution of Antarctic vegetation.

Recruitment responses of shade‐tolerant and heliophilous trees in degraded areas: The necessity of knowing the recruitment autecology of species for effective reforestation decisions

AbstractDirect seeding is a reforestation technique that allows introducing a great variety of tree species in degraded areas with less logistics, but tree establishment rates are usually low because developing plants do not tolerate the high sun exposure, extreme temperatures, and low soil moisture that prevail in these habitats. This leads to the proposal that seeds should be planted beneath shrubs or herbaceous plants that ameliorate harsh abiotic conditions, although this can also trigger interspecific competition and impair the performance of developing trees. This study aimed to test these proposals in dry forests in northwest Argentina. For this, seeds of two shade‐tolerant trees and a heliophilous tree, native to this region, were sowed beneath the canopy of pioneer shrubs and in open spaces with and without herbaceous plants. After 2 years, our findings indicated that shade‐tolerant trees performed better beneath shrub canopies, while the heliophilous tree achieved higher establishment rates in the open spaces. Nevertheless, it seems that herbaceous plants compete with the tree seedlings and, therefore, they should be removed before conducting reforestation programs. Thus, we propose that direct seeding could be an efficient reforestation strategy, but the regeneration autecology of the tree species selected for this task, as well as their competitive ability in the face of the pioneer vegetation, must be carefully evaluated before seeding.

Impacts of behaviour and acclimation of metabolic rate on energetics in sheltered ectotherms: a climate change perspective.

Many ectothermic organisms counter harsh abiotic conditions by seeking refuge in underground retreats. Variations in soil hydrothermal properties within these retreats may impact their energy budget, survival and population dynamics. This makes retreat site choice a critical yet understudied component of their strategies for coping with climate change. We used a mechanistic modelling approach to explore the implications of behavioural adjustments and seasonal acclimation of metabolic rate on retreat depth and the energy budget of ectotherms, considering both current and future climate conditions. We used a temperate amphibian, the alpine newt (Ichthyosaura alpestris), as a model species. Our simulations predict an interactive influence of different thermo- and hydroregulatory strategies on the vertical positioning of individuals in underground refuges. The adoption of a particular strategy largely determines the impact of climate change on retreat site choice. Additionally, we found that, given the behavioural thermoregulation/hydroregulation and metabolic acclimation patterns considered, behaviour within the retreat has a greater impact on ectotherm energetics than acclimation of metabolic rate under different climate change scenarios. We conclude that further empirical research aimed at determining ectotherm behavioural strategies during both surface activity and inactivity is needed to understand their population dynamics and species viability under climate change.

Diurnal Rhythms in the Red Seaweed Gracilariopsis chorda are Characterized by Unique Regulatory Networks of Carbon Metabolism.

Cellular and physiological cycles are driven by endogenous pacemakers, the diurnal and circadian rhythms. Key functions such as cell cycle progression and cellular metabolism are under rhythmic regulation, thereby maintaining physiological homeostasis. The photoreceptors phytochrome and cryptochrome, in response to light cues, are central input pathways for physiological cycles in most photosynthetic organisms. However, among Archaeplastida, red algae are the only taxa that lack phytochromes. Current knowledge about oscillatory rhythms is primarily derived from model species such as Arabidopsis thaliana and Chlamydomonas reinhardtii in the Viridiplantae, whereas little is known about these processes in other clades of the Archaeplastida, such as the red algae (Rhodophyta). We used genome-wide expression profiling of the red seaweed Gracilariopsis chorda and identified 3,098 rhythmic genes. Here, we characterized possible cryptochrome-based regulation and photosynthetic/cytosolic carbon metabolism in this species. We found a large family of cryptochrome genes in G. chorda that display rhythmic expression over the diurnal cycle and may compensate for the lack of phytochromes in this species. The input pathway gates regulatory networks of carbon metabolism which results in a compact and efficient energy metabolism during daylight hours. The system in G. chorda is distinct from energy metabolism in most plants, which activates in the dark. The green lineage, in particular, land plants, balance water loss and CO2 capture in terrestrial environments. In contrast, red seaweeds maintain a reduced set of photoreceptors and a compact cytosolic carbon metabolism to thrive in the harsh abiotic conditions typical of intertidal zones.

Micromonospora parastrephiae sp. nov. and Micromonospora tarensis sp. nov., isolated from the rhizosphere of a Parastrephia quadrangularis plant growing in the Salar de Tara region of the Central Andes in Chile.

Two novel Micromonospora strains, STR1-7T and STR1S-6T, were isolated from the rhizosphere of a Parastrephia quadrangularis plant growing in the Salar de Tara region of the Atacama Desert, Chile. Chemotaxonomic, cultural and phenotypic features confirmed that the isolates belonged to the genus Micromonospora. They grew from 20 to 37 °C, from pH7 to 8 and in the presence of up to 3 %, w/v NaCl. The isolates formed distinct branches in Micromonospora gene trees based on 16S rRNA gene sequences and on a multi-locus sequence analysis of conserved house-keeping genes. A phylogenomic tree generated from the draft genomes of the isolates and their closest phylogenetic neighbours showed that isolate STR1-7T is most closely related to Micromonospora orduensis S2509T, and isolate STR1S-6 T forms a distinct branch that is most closely related to 12 validly named Micromonospora species, including Micromonospora saelicesensis the earliest proposed member of the group. The isolates were separated from one another and from their closest phylogenomic neighbours using a combination of chemotaxonomic, genomic and phenotypic features, and by low average nucleotide index and digital DNA-DNA hybridization values. Consequently, it is proposed that isolates STR1-7T and STR1S-6T be recognized as representing new species in the genus Micromonospora, namely as Micromonospora parastrephiae sp. nov. and Micromonospora tarensis sp. nov.; the type strains are STR1-7T (=CECT 9665T=LMG 30768T) and STR1S-6T (=CECT 9666T=LMG 30770T), respectively. Genome mining showed that the isolates have the capacity to produce novel specialized metabolites, notably antibiotics and compounds that promote plant growth, as well as a broad-range of stress-related genes that provide an insight into how they cope with harsh abiotic conditions that prevail in high-altitude Atacama Desert soils.

Wood density is related to aboveground biomass and productivity along a successional gradient in upper Andean tropical forests.

Wood density (WD) is a key functional trait related to ecological strategies and ecosystem carbon dynamics. Despite its importance, there is a considerable lack of information on WD in tropical Andean forests, particularly regarding its relationship with forest succession and ecosystem carbon cycling. Here, we quantified WD in 86 upper Andean tree and shrub species in central Colombia, with the aim of determining how WD changes with forest succession and how it is related to productivity. We hypothesized that WD will increase with succession because early successional forests will be colonized by acquisitive species, which typically have low WD, while the shaded understory of older forests should favor higher WD. We measured WD in 481 individuals from 27 shrub and 59 tree species, and quantified aboveground biomass (AGB), canopy height, net primary production (NPP) and species composition and abundance in 14, 400-m2, permanent plots. Mean WD was 0.513 ± 0.114 (g/cm3), with a range between 0.068 and 0.718 (g/cm3). Shrubs had, on average, higher WD (0.552 ± 0.095 g/cm3) than trees (0.488 ± 0.104 g/cm3). Community weighted mean WD (CWMwd) decreased with succession (measured as mean canopy height, AGB, and basal area); CWMwd also decreased with aboveground NPP and stem growth. In contrast, the percentage of NPP attributed to litter and the percent of shrubs in plots increased with CWMwd. Thus, our hypothesis was not supported because early successional forests had higher CWMwd than late successional forests. This was related to a high proportion of shrubs (with high WD) early in succession, which could be a consequence of: 1) a low seed availability of trees due to intense land use in the landscape and/or 2) harsh abiotic conditions early in succession that filter out trees. Forest with high CWMwd had a high %NPP attributed to litter because they were dominated by shrubs, which gain little biomass in their trunks. Our findings highlight the links between WD, succession and carbon cycling (biomass and productivity) in this biodiversity hotspot. Thus, WD is an important trait that can be used to understand upper Andean forest recovery and improve forest restoration and management practices.

The role of chronic anthropogenic disturbances in plant community assembly along a water availability gradient in Brazil’s semiarid Caatinga region

The effects of anthropogenic disturbances on the structure and function of seasonally dry tropical forests (SDTFs) are mediated both by disturbance type and intensity, and the environmental conditions, including climate. In a climate change scenario, the interaction between low water availability and chronic anthropogenic disturbances may potentially have drastic consequences on SDTF dynamics and the ecosystem services it provides. We hypothesized that in these naturally stressed systems, the effects of human disturbance are strongest in the most water-stressed sites, implying a worrisome synergism between harsh abiotic conditions (lower precipitation, higher temperature) and human effects, ultimately resulting in a less developed community structure and reduced diversity. By integrating information for the adult and regenerating vegetation strata in 21 sites distributed across climatic, plant cover and disturbance gradients in the Caatinga (seasonally dry tropical) forest of Brazil, we analyzed the individual and combined effects of chronic anthropogenic disturbances, as measured through the Cattle Pressure Index and the Human Activity Index, along climate gradients, on community structure, diversity, and composition. As expected, the Cattle Pressure Index was negatively related to diameter at ground level, basal area, and diversity in the adult stratum, whereas for the regenerating stratum, litter stock had the strongest effect on vegetation structure. Climatic factors were poor predictors of the variation in the three true diversity measures (0D, 1D, and 2D) of the regenerating community. Our results revealed important cross-site differences in both vegetation strata over a small range of climatic variation. We conclude that the most stressful conditions associated with a very low precipitation regime enhance the effects on chronic disturbances, gradually driving SDTF communities into new alternative states and rendering these environments more prone to desertification.

Volatile responses of dwarf birch to mimicked insect herbivory and experimental warming at two elevations in Greenlandic tundra.

Plants release a complex blend of volatile organic compounds (VOCs) in response to stressors. VOC emissions vary between contrasting environments and increase with insect herbivory and rising temperatures. However, the joint effects of herbivory and warming on plant VOC emissions are understudied, particularly in high latitudes, which are warming fast and facing increasing herbivore pressure. We assessed the individual and combined effects of chemically mimicked insect herbivory, warming, and elevation on dwarf birch (Betula glandulosa) VOC emissions in high-latitude tundra ecosystems in Narsarsuaq, South Greenland. We hypothesized that VOC emissions and compositions would respond synergistically to warming and herbivory, with the magnitude differing between elevations. Warming increased emissions of green leaf volatiles (GLVs) and isoprene. Herbivory increased the homoterpene, (E)-4,8-dimethyl-1,3,7-nonatriene, emissions, and the response was stronger at high elevation. Warming and herbivory had synergistic effects on GLV emissions. Dwarf birch emitted VOCs at similar rates at both elevations, but the VOC blends differed between elevations. Several herbivory-associated VOC groups did not respond to herbivory. Harsher abiotic conditions at high elevations might not limit VOC emissions from dwarf birch, and high-elevation plants might be better at herbivory defense than assumed. The complexity of VOC responses to experimental warming, elevation, and herbivory are challenging our understanding and predictions of future VOC emissions from dwarf birch-dominated ecosystems.

Intraspecific competition in common coastal dune grasses overshadows facilitation on the dune face

Restoration of degraded dunes through revegetation of native dune building species is critical to preserve multiple ecosystem services (i.e., coastal protection, habitat). As dunes exhibit high levels of abiotic stress, it is likely that facilitative interactions among plants occur, reducing stress caused by harsh abiotic conditions, and benefiting restoration efforts. The research was to determine how plant spatial arrangement (clumped vs. dispersed) at the dune slope affects the growth of two dominant dune grasses along the United States Atlantic coast, Ammophila breviligulata (American beachgrass) and Uniola paniculata (sea oats). We determined the local distribution and density of each species through field surveys to inform a manipulative study of planting arrangement and to assess plant growth and survival under different spatial arrangements. Planting arrangement did not influence the survival of U. paniculata, but dispersed plantings had a positive effect on growth parameters (height, stem number, ramet number), compared to the clumped arrangement. No plantings of A. breviligulata survived by the end of the second season, regardless of planting arrangement. Clumped arrangements did not improve growth of U. paniculata or growth and survival of A. breviligulata over the two growing seasons studied; thus, creating clumped arrangements may not be necessary for revegetation efforts. However, observing natural spatial patterns and using this information to guide restoration planting may be beneficial as climate change may impact revegetation results due to increased abiotic stress. Further research focusing on biotic interactions and density of plantings at multiple locations along dunes will contribute to dune restoration planning.

Trends in soil microclimate and modeled impacts on germination timing in the sagebrush steppe

AbstractPast and projected changes in climate affect soil microclimate, impacting seeds that use soil moisture and soil temperature as cues for germination. Seed germination and plant establishment are among the most important processes regulating plant community assembly in response to climate change. Changes in germination timing expose seedlings to new abiotic and biotic risk factors that can affect recruitment success. Species with seed dormancy strategies to avoid harsh winter conditions could experience more mortality if changes in germination timing cause early germination and subsequent exposure to freezing conditions. We analyzed soil microclimate trends in the sagebrush steppe from 1979 to 2017 using a soil physics model (SHAW) and calculated the germination timing of native species used in restoration efforts with wet‐thermal response curves from lab trials. We applied the germination curves to modeled soil microclimate at 10 sites in the sagebrush steppe. Our results indicate that warmer and wetter fall seasons have become more prevalent and will likely lead to accelerated germination of several native restoration species in the sagebrush steppe. Changes to spring soil conditions favor slightly more germination in early spring, but strong trends of earlier onset of spring soil conditions were not evident. Trends in climate have created drier and warmer summer seedbed conditions, likely to increase stress on seedlings. Historic cycles of alternating slow or fast germination appeared less frequently during the last 12 years of the study (2004–2016). Seedbed microclimate trends will likely impact seedling establishment by altering germination timing and exposing seeds to more harsh abiotic conditions, likely resulting in decreased recruitment of native species and increased abundance of invasive annual grasses.

Biological Soil Crusts as Ecosystem Engineers in Antarctic Ecosystem.

Biological soil crusts (BSC) are considered as pivotal ecological elements among different ecosystems of the world. The effects of these BSC at the micro-site scale have been related to the development of diverse plant species that, otherwise, might be strongly limited by the harsh abiotic conditions found in environments with low water availability. Here, we describe for the first time the bacterial composition of BSCs found in the proximities of Admiralty Bay (Maritime Antarctica) through 16S metabarcoding. In addition, we evaluated their effect on soils (nutrient levels, enzymatic activity, and water retention), and on the fitness and performance of Colobanthus quitensis, one of the two native Antarctic vascular plants. This was achieved by comparing the photochemical performance, foliar nutrient, biomass, and reproductive investment between C. quitensis plants growing with or without the influence of BSC. Our results revealed a high diversity of prokaryotes present in these soil communities, although we found differences in terms of their abundances. We also found that the presence of BSCs is linked to a significant increase in soils’ water retention, nutrient levels, and enzymatic activity when comparing with control soils (without BSCs). In the case of C. quitensis, we found that measured ecophysiological performance parameters were significantly higher on plants growing in association with BSCs. Taken together, our results suggest that BSCs in Antarctic soils are playing a key role in various biochemical processes involved in soil development, while also having a positive effect on the accompanying vascular flora. Therefore, BSCs would be effectively acting as ecosystem engineers for the terrestrial Antarctic ecosystem.

The Assembly of Tropical Dry Forest Tree Communities in Anthropogenic Landscapes: The Role of Chemical Defenses.

The effect of anthropogenic disturbance on plant community traits and tradeoffs remains poorly explored in tropical forests. In this study, we aimed to identify tradeoffs between defense and other plant functions related to growth processes in order to detect potential aboveground and edaphic environmental conditions modulating traits variation on plant communities, and to find potential assembly rules underlying species coexistence in secondary (SEF) and old-growth forests (OGF). We measured the foliar content of defense phytochemicals and leaf traits related to fundamental functions on 77 species found in SEF and OGF sites in the Jalisco dry forest ecoregion, Mexico, and we explored (1) the trait-trait and trait-habitat associations, (2) the intra and interspecies trait variation, and (3) the traits-environment associations. We found that phytochemical content was associated with high leaf density and leaf fresh mass, resulting in leaves resistant to drought and high radiation, with chemical and physical defenses against herbivore/pathogen attack. The phytochemicals and chlorophyll concentrations were negatively related, matching the predictions of the Protein Competition Model. The phylogenetic signal in functional traits, suggests that abundant clades share the ability to resist the harsh biotic and abiotic conditions and face similar tradeoffs between productive and defensive functions. Environmental filters could modulate the enhanced expression of defensive phytochemicals in SEF, while, in OGFs, we found a stronger filtering effect driving community assembly. This could allow for the coexistence of different defensive strategies in OGFs, where a greater species richness could dilute the prevalence of pathogens/herbivores. Consequently, anthropogenic disturbance could alter TDF ecosystem properties/services and functioning.

The contribution of intraspecific trait variation to changes in functional community structure along a stress gradient

AbstractQuestionWe considered two possibilities related to the contribution of intraspecific trait variation (ITV) to changes in functional community structure along a stress gradient in tundra vegetation. First, ITV could contribute to the success of plant species across the stress gradient by promoting optimal trait values for each condition along the gradient; thus, ITV enhances convergence toward optimal traits. Second, ITV of only a few dominant species aligns with the optimal trait, and ITV of other species promotes trait diversification within communities.LocationSalluit, Québec, Canada (62°12′N, 75°39′W).MethodsVegetation was surveyed under three different conditions (harsh, intermediate, and competitive) representing an environmental stress gradient. We assessed ITV across the gradient for four plant functional traits: leaf carbon (C) and nitrogen (N) contents, specific leaf area (SLA), and plant height. We assessed community‐weighted means (CWMs) and functional dispersion (FDis) for each of the four traits. These indices were calculated from mean trait values from all individuals across all habitats (mean‐CWM and mean‐FDis), and from each habitat (ITV‐CWM and ITV‐FDis).ResultsFor the four traits, increasing trends (leaf N content, SLA, and plant height) and decreasing trends (leaf C content) in mean‐CWM along the stress gradient were maintained and pronounced for ITV‐CWM. Comparisons between ITV‐FDis and mean‐FDis suggested that, except for leaf C content, ITV tends to reduce and increase FDis values at the abiotically stressful and competitive ends of the environmental stress gradient, respectively.ConclusionsITV along the abiotic stress–competition gradient appears to promote community‐level changes towards optimal traits. In particular, ITV in three traits (with the exception of leaf C content) may contribute to equalization of optimal trait values, and to “passage through environmental filtering” in harsh habitats. However, when species deal with competition for richer resources, only some dominant species may show optimal trait values. Therefore, ITV may allow for trait diversification within communities under competitive rather than harsh abiotic conditions.

Directional selection shifts trait distributions of planted species in dryland restoration

Abstract The match between species trait values and local abiotic filters can restrict community membership. An often‐implicit assumption of this relationship is that abiotic filters select for a single locally optimal strategy, though difficulty in isolating effects of the abiotic environment from those of dispersal limitation and biotic interactions has resulted in few empirical tests of this assumption. Similar constraints have made it difficult to assess whether the type and intensity of abiotic filters shift along gradients of environmental harshness, as predicted by the stress‐dominance hypothesis. We planted 9,216 plants of 29 perennial grass and forb species that had a range of functional trait values and were assigned to a warm, intermediate or cool temperature tolerance pool across eight sites on the Colorado Plateau. We compared the distributions of traits of surviving individuals to null distributions to evaluate whether there were shifts in trait means and variation. Borrowing from phenotypic selection concepts in evolutionary biology, we assessed support for stabilizing, directional and disruptive abiotic filtering of trait distributions and whether these types of filtering varied with initial species pool. Functional composition was significantly different from null distributions for nearly all traits at all sites, with trait variation more restricted in harsher abiotic conditions, supporting the stress‐dominance hypothesis. Contrary to expectations, we primarily found evidence for directional selection, which increased in frequency in warm species pools while disruptive selection was found more often in cool and intermediate species pools. Synthesis. This study provides a controlled experimental approach to test the effect of the abiotic environment on plant trait filtering. We found that opportunistic strategies allowing for rapid water acquisition during favourable periods improved survival at warmer sites. Species with these strategies may be expected to benefit from increasing aridity and may be selected for active management efforts. More generally, the prevalence of directional selection may have important implications for dynamic vegetation models that rely on trait distributions for translating environmental variation into ecosystem processes.

Gene Expression Profiles Suggest a Better Cold Acclimation of Polyploids in the Alpine Species Ranunculus kuepferi (Ranunculaceae).

Alpine habitats are shaped by harsh abiotic conditions and cold climates. Temperature stress can affect phenotypic plasticity, reproduction, and epigenetic profiles, which may affect acclimation and adaptation. Distribution patterns suggest that polyploidy seems to be advantageous under cold conditions. Nevertheless, whether temperature stress can induce gene expression changes in different cytotypes, and how the response is initialized through gene set pathways and epigenetic control remain vague for non-model plants. The perennial alpine plant Ranunculus kuepferi was used to investigate the effect of cold stress on gene expression profiles. Diploid and autotetraploid individuals were exposed to cold and warm conditions in climate growth chambers and analyzed via transcriptome sequencing and qRT-PCR. Overall, cold stress changed gene expression profiles of both cytotypes and induced cold acclimation. Diploids changed more gene set pathways than tetraploids, and suppressed pathways involved in ion/cation homeostasis. Tetraploids mostly activated gene set pathways related to cell wall and plasma membrane. An epigenetic background for gene regulation in response to temperature conditions is indicated. Results suggest that perennial alpine plants can respond to temperature extremes via altered gene expression. Tetraploids are better acclimated to cold conditions, enabling them to colonize colder climatic areas in the Alps.

Patterns and drivers of leaf‐litter ant diversity along a tropical elevational gradient in Mexico

AbstractAimGiven their high environmental variation over relatively short distances, mountains represent ideal systems for evaluating potential factors shaping diversity gradients. Despite a long‐standing interest in ecological gradients, ant diversity patterns and their related mechanisms occurring on mountains are still not well understood. Here, we (i) describe species diversity patterns (α and β) of leaf‐litter ants along the eastern slope of Cofre de Perote in Veracruz, Mexico; and (ii) evaluate climatic and spatial factors in determining these patterns.LocationVeracruz, Mexico.TaxonLeaf‐litter ants.MethodsWe sampled 320 m2 of leaf litter spread across eight equally spaced sites from sea level to 3500 m of elevation. We used regression models to predict α‐diversity patterns with climatic (temperature and precipitation) and spatial (geometric constraints) variables. We also assessed, through multiple regression based on distance matrices (MRM), the relative importance of habitat filtering and dispersal limitations for shaping total dissimilarity (βsor), turnover (βsim) and nestedness (βnes).ResultsA hump‐shaped pattern was observed in the α‐diversity. This pattern is best explained by the temperature gradient. β‐diversity showed a nonlinear pattern along the elevational gradient with total dissimilarity and turnover components better explained by habitat filtering (i.e. temperature distances). Turnover had higher contribution to total dissimilarity rather than the nestedness component.Main conclusionsThe significance effect of temperature on both α‐ and β‐diversity patterns reinforces its widespread importance in shaping litter ant diversity patterns across elevational gradients. The hump‐shaped pattern in species richness is probably the result of harsh abiotic conditions at the base and the top of the mountain combined with biotic attrition in lowland sites. The niche specialization of ant species in their optimal thermal zones may explain total dissimilarity and ant species replacement along the studied gradient. Taken all together, these results suggest a high relevance of temperature‐driven mechanisms in the origin and maintenance of the biodiversity of such insects and probably another ectothermic taxa.

Silicon Amendment Enhances Agronomic Efficiency of Nitrogen Fertilization in Maize and Wheat Crops under Tropical Conditions

Sustainable management strategies are needed to improve agronomic efficiency and cereal yield production under harsh abiotic climatic conditions such as in tropical Savannah. Under these environments, field-grown crops are usually exposed to drought and high temperature conditions. Silicon (Si) application could be a useful and sustainable strategy to enhance agronomic N use efficiency, leading to better cereal development. This study was developed to explore the effect of Si application as a soil amendment source (Ca and Mg silicate) associated with N levels applied in a side-dressing (control, low, medium and high N levels) on maize and wheat development, N uptake, agronomic efficiency and grain yield. The field experiments were carried out during four cropping seasons, using two soil amendment sources (Ca and Mg silicate and dolomitic limestone) and four N levels (0, 50, 100 and 200 kg N ha−1). The following evaluations were performed in maize and wheat crops: the shoots and roots biomass, total N, N-NO3−, N-NH4+ and Si accumulation in the shoots, roots and grain tissue, leaf chlorophyll index, grain yield and agronomic efficiency. The silicon amendment application enhanced leaf chlorophyll index, agronomic efficiency and N-uptake in maize and wheat plants, benefiting shoots and roots development and leading to a higher grain yield (an increase of 5.2 and 7.6%, respectively). It would be possible to reduce N fertilization in maize from 185–180 to 100 kg N ha−1 while maintaining similar grain yield with Si application. Additionally, Si application would reduce N fertilization in wheat from 195–200 to 100 kg N ha−1. Silicon application could be a key technology for improving plant-soil N-management, especially in Si accumulator crops, leading to a more sustainable cereal production under tropical conditions.

Animal migrations and parasitism: reciprocal effects within a unified framework.

Migrations, i.e. the recurring, roundtrip movement of animals between distant and distinct habitats, occur among diverse metazoan taxa. Although traditionally linked to avoidance of food shortages, predators or harsh abiotic conditions, there is increasing evidence that parasites may have played a role in the evolution of migration. On the one hand, selective pressures from parasites can favour migratory strategies that allow either avoidance of infections or recovery from them. On the other hand, infected animals incur physiological costs that may limit their migratory abilities, affecting their speed, the timing of their departure or arrival, and/or their condition upon reaching their destination. During migration, reduced immunocompetence as well as exposure to different external conditions and parasite infective stages can influence infection dynamics. Here, we first explore whether parasites represent extra costs for their hosts during migration. We then review how infection dynamics and infection risk are affected by host migration, thereby considering parasites as both causes and consequences of migration. We also evaluate the comparative evidence testing the hypothesis that migratory species harbour a richer parasite fauna than their closest free-living relatives, finding general support for the hypothesis. Then we consider the implications of host migratory behaviour for parasite ecology and evolution, which have received much less attention. Parasites of migratory hosts may achieve much greater spatial dispersal than those of non-migratory hosts, expanding their geographical range, and providing more opportunities for host-switching. Exploiting migratory hosts also exerts pressures on the parasite to adapt its phenology and life-cycle duration, including the timing of major developmental, reproduction and transmission events. Natural selection may even favour parasites that manipulate their host's migratory strategy in ways that can enhance parasite transmission. Finally, we propose a simple integrated framework based on eco-evolutionary feedbacks to consider the reciprocal selection pressures acting on migratory hosts and their parasites. Host migratory strategies and parasite traits evolve in tandem, each acting on the other along two-way causal paths and feedback loops. Their likely adjustments to predicted climate change will be understood best from this coevolutionary perspective.

Litter and soil characteristics mediate the buffering effect of snow cover on litter decomposition

In cold biomes, snow cover mitigates the harsh winter soil conditions, thereby enhancing overwinter decomposition of organic matter which controls the availability of nutrients for plants and microbial uptake at the beginning of the growing season. Yet, how this buffering effect is modulated by litter traits, soil characteristics and herbivory remains poorly studied. We conducted a litter-bag experiment in four types of subalpine grasslands, two of which being naturally free of snow during most of the winter. Litter bags were filled either by grasses or forbs sampled in plots submitted the preceding summer to grasshopper grazing treatments. Snow cover strongly increased the decomposition of forbs, but not of grasses. Litter quality (low C:N and polyphenols triggering a priming effect) and soil ammonium content were correlated with litter decomposition rate in the presence of snow only, whereas soil organic matter content was positively associated with decomposition rate under both snow regimes. Herbivory did not affect decomposition. Our findings may be explained by the functional differences between copiotrophic and oligotrophic microbes, copiotrophs being more sensitive to harsh abiotic conditions than oligotrophs. As long as copiotrophs are favored by high litter quality and nutrient-rich soils (high ammonium content), litter decomposition is enhanced in the absence of snow only.

Living on the edge: Meoneura obscurella in the ‘Wieliczka’ Salt Mine (southern Poland) exhibits the first case of lecithotrophic ovoviviparity in the family Carnidae (Diptera)

During the studies on the invertebrate fauna of the subterranean part of the “Wieliczka” Salt Mine in Wieliczka, Poland, the presence of many specimens of the dipteran species Meoneura obscurella (Fallén 1823) was observed. Organic remains and faeces related to the presence of mice (Mus musculus) were indicated as a potential food source for the insects. M. obscurella displays lecithotrophic viviparity (ovoviviparity), which has developed due to extremely harsh abiotic conditions and a lack of food. This is the first documented case of lecithotrophic viviparity within the fly family Carnidae. Based on the ability of this species to inhabit and reproduce in the conditions of the subterranean part of the “Wieliczka” Salt Mine, it is proposed to classify the species as a troglophile. The occurrence of Niptus hololeucus (Faldermann 1835), a species of beetle representing the family Ptinidae, was also confirmed in the subterranean part of the “Wieliczka” Salt Mine.