Altitudinal Transect Research Articles

Metabarcoding reveals ecologically distinct fungal assemblages in river and groundwater along an Austrian alpine to lowland gradient.

Biodiversity, the source of origin, and ecological roles of fungi in groundwater are to this day a largely neglected field in fungal and freshwater ecology. We used DNA-based Illumina high-throughput sequence analysis of both fungal gene markers 5.8S and internal transcribed spacers region 2 (ITS2), improving taxonomic classification. This study focused on the groundwater and river mycobiome along an altitudinal and longitudinal transect of a pre-alpine valley in Austria in two seasons. Using Bayesian network modeling approaches, we identified patterns in fungal community assemblages that were mostly shaped by differences in landscape (climatic, topological, geological), and environmental conditions. While river fungi were comparatively more diverse, unique fungal assemblages could be recovered from groundwater, including typical aquatic lineages such as Rozellomycota and Olpidiomycota. The most specious assemblages in groundwater were not linked to the input of organic material from the surface, and as such, seems to be sustained by characteristic groundwater conditions. Based on what is known from closely related fungi, our results suggest that the present fungal communities potentially contribute to mineral weathering, carbon cycling and denitrification in groundwater. Furthermore, we were able to observe the effects of varying land cover due to agricultural practices on fungal biodiversity in groundwater ecosystems. This study contributes to improving our understanding of fungi in the subsurface aquatic biogeosphere.

Differentiated Contributions of Plant Diversity and Soil Parameters to Shifts in Fungal Taxonomic Composition across Three Altitudinal Transects

Differentiated Contributions of Plant Diversity and Soil Parameters to Shifts in Fungal Taxonomic Composition across Three Altitudinal Transects

Selection on the vascular-remodeling BMPER gene is associated with altitudinal adaptation in an insular lizard

Abstract High altitude imposes several extreme constraints on life, such as low oxygen pressure and high levels of ultraviolet radiation, which require specialized adaptations. Many studies have focused on how endothermic vertebrates respond to these challenging environments, but there is still uncertainty on how ectotherms adapt to these conditions. Here, we used whole-genome sequencing of low-altitude (100–600 m) and high-altitude (3,550 m) populations of the wide-ranging Tenerife lizard Gallotia galloti to uncover signatures of selection for altitudinal adaptation. The studied populations show reduced differentiation, sharing similar patterns of genetic variation. Selective sweep mapping suggests that signatures of adaptation to high altitude are not widespread across the genome, clustering in a relatively small number of genomic regions. One of these regions contains BMPER, a gene involved with vascular remodeling, and that has been associated with hypoxia-induced angiogenic response. By genotyping samples across 2 altitudinal transects, we show that allele frequency changes at this locus are not gradual, but rather show a well-defined shift above ca. 1,900 m. Transcript and protein structure analyses on this gene suggest that putative selection likely acts on noncoding variation. These results underline how low oxygen pressure generates the most consistent selective constraint in high-altitude environments, to which vertebrates with vastly contrasting physiological profiles need to adapt in the context of ongoing climate change.

Surface soil phytolith assemblages across an altitudinal transect in the Qilian Mountains of Northwestern China, and their implications for palaeoecologic analysis in arid alpine regions

Reconstructing changes in altitudinal vegetation belts is crucial for comprehending vegetation response to past environmental changes in arid alpine regions, however, proxy data are limited. In this study, we report 51 surface soil phytolith samples from various vegetation types across an altitudinal transect in the arid alpine region of the Qilian Mountains, to elucidate the relationships between vegetation types and phytolith assemblages. Our results show that phytolith morphotypes in surface soil samples could be categorized into 16 classes, with Gobbet, Crenate, Rondel, Elongate entire, and Acutebulbosus being the predominant classes. The characteristics of surface soil phytolith assemblages vary across an altitudinal transect, reflecting differences in local vegetation. Discriminant analysis identifies Cubic, Elongate entire, Crenate, Gobbet, and Rondel as discriminant variables that correlated with five vegetation types (desert vegetation, mountain steppe vegetation, mountain coniferous forest vegetation, subalpine shrub meadow vegetation, and alpine meadow vegetation). We establish five discriminant functions based on the relationships between vegetation types and phytolith assemblages, demonstrating a high accuracy of our method for distinguishing between different vegetation types. These discriminant functions are applicable for distinguishing between diverse vegetation types in the mountains of arid inland regions of Asia. They are also effective in identifying coniferous forest vegetation in mid-latitude mountains. Therefore, these discriminant functions hold significant potential for reconstructing changes in altitudinal vegetation belts in mountainous regions and determining the vegetative types recorded by terminal lakes in arid regions. Our study introduces a new perspective on palaeoecologic analysis in arid alpine regions, advancing our understanding of ecosystem dynamics in response to environmental fluctuations.

Metabolic insights into high-altitude adaptation of Himalayan ‘Horsetails’ [Equisetum diffusum D. Don] with special reference to the fatty acid dynamicity

Equisetum diffusum D. Don, a perennial herb of Equisetaceae, is considered as native to the Himalayan mountain range. This plant has prolific distribution along different altitudes of Eastern Himalayan region. Generally, mountain flora, like E. diffusum, experience a combination of contrasting abiotic stresses and may represent a unique natural model for investigating physiological resilience to address climate change. So, the present study has been framed to compare the metabolic responses in E. diffusum growing at different elevation belts with an aim to understand the underlying basis for their high-altitude adjustment ability. The biochemical profiles of this plant, collected from three different altitudinal transects of Darjeeling hills, were compared. The fatty acid profiles of neutral lipids, membrane phospholipids and glycolipids demonstrated palmitic acid and oleic acid as the predominant fatty acids. The major outcome was the substantial increase of polyunsaturated fatty acids (PUFAs) and unsaturation index in glycolipids of the samples collected from higher altitudes. Major proportion of changes in PUFA content was contributed by arachidonic acid. Therefore, the plants homeostatically control the membrane fluidity by enhancing the unsaturation of glycolipid fatty acids. Moreover, significantly higher antioxidant enzyme activities in higher altitude samples reflect the involvement of these enzymes in coping with the oxidative stress condition and membrane damage. The stress responsive effects may be further augmented by enhanced content of secondary metabolites. Therefore, a combination of biochemical responses along with the changes in membrane plasticity can be predicted as the metabolic adjustment strategies for high-altitude adaptation of E. diffusum.

Biomonitoring of airborne microplastics and microrubbers in Shiraz, Iran, using lichens and moss.

Microplastics (MPs) and microrubbers (MRs) determined in lichens and mosses around Shiraz. In lichens, MPs mainly thin fibres up to 1 MP g-1; MRs were < 0.1 MP g-1. In mosses, abundances were similar but with a greater fraction of larger, non-fibrous particles. Larger MPs and MRs decreased in abundance with distance and elevation from Shiraz. Around Shiraz, the common moss, Grimmia critina, would be the most suitable biomonitor. Lichens and mosses have been employed as biomonitors of atmospheric particulate pollutants, like metals and industrial solids, for many decades. Here, we evaluated the potential of nine species of crustose and foliose lichens and a widely distributed moss (Grimmia critina) to act as biomonitors of airborne microplastics (MPs) and microrubbers (MRs). About 200 lichens and 40 mosses were sampled across different altitudinal transects in the vicinity of Shiraz City, southwest Iran, and MPs and MRs were quantified and characterised after sample peroxidation. In most species of lichen, MP and MR abundance overall was < 1g-1 and < 0.1g-1, respectively, and the majority of plastics were fibres of < 10 µm in diameter and < 1000 µm in length. Respective weight normalised abundances of MPs and MRs were similar in G. critina, but there were greater proportions of both larger (> 1000µm) and non-fibrous particles among the MPs. In both lichens and moss, there was a greater number of larger MPs and MRs at locations closest to and at the same elevation as Shiraz than at more distant and elevated locations, suggesting an inverse relationship between particle size and distance travelled. Among the lichens, members of the genus Acarospora, with their areolated form, appeared to act as the most suitable biomonitors for MPs and MRs. Overall, however, the wide distribution of the moss, G. crinita, and its ability to intercept and accumulate a broader range of sizes and shapes of MPs and MRs make this species a better choice, at least in the type of environment studied.

Unravelling the maternal evolutionary history of the African leopard (Panthera pardus pardus).

The African leopard (Panthera pardus pardus) has lost a significant proportion of its historical range, notably in north-western Africa and South Africa. Recent studies have explored the genetic diversity and population structure of African leopards across the continent. A notable genetic observation is the presence of two divergent mitochondrial lineages, PAR-I and PAR-II. Both lineages appeared to be distributed widely, with PAR-II frequently found in southern Africa. Until now, no study has attempted to date the emergence of either lineage, assess haplotype distribution, or explore their evolutionary histories in any detail. To investigate these underappreciated questions, we compiled the largest and most geographically representative leopard data set of the mitochondrial NADH-5 gene to date. We combined samples (n = 33) collected in an altitudinal transect across the Mpumalanga province of South Africa, where two populations of leopard are known to be in genetic contact, with previously published sequences of African leopard (n = 211). We estimate that the maternal PAR-I and PAR-II lineages diverged approximately 0.7051 (0.4477-0.9632) million years ago (Ma). Through spatial and demographic analyses, we show that while PAR-I underwent a mid-Pleistocene population expansion resulting in several closely related haplotypes with little geographic structure across much of its range, PAR-II remained at constant size and may even have declined slightly in the last 0.1 Ma. The higher genetic drift experienced within PAR-II drove a greater degree of structure with little haplotype sharing and unique haplotypes in central Africa, the Cape, KwaZulu-Natal and the South African Highveld. The phylogeographic structure of PAR-II, with its increasing frequency southward and its exclusive occurrence in south-eastern South Africa, suggests that this lineage may have been isolated in South Africa during the mid-Pleistocene. This hypothesis is supported by historical changes in paleoclimate that promoted intense aridification around the Limpopo Basin between 1.0-0.6 Ma, potentially reducing gene flow and promoting genetic drift. Interestingly, we ascertained that the two nuclear DNA populations identified by a previous study as East and West Mpumalanga correspond to PAR-I and PAR-II, respectively, and that they have come into secondary contact in the Lowveld region of South Africa. Our results suggest a subdivision of African leopard mtDNA into two clades, with one occurring almost exclusively in South Africa, and we identify the potential environmental drivers of this observed structure. We caution that our results are based on a single mtDNA locus, but it nevertheless provides a hypothesis that can be further tested with a dense sample of nuclear DNA data, preferably whole genomes. If our interpretation holds true, it would provide the first genetic explanation for the smaller observed size of leopards at the southernmost end of their range in Africa.

Varied growth response of high alpine Rhododendron myrtifolium and forest zone tree species to climate warming in the Eastern Carpathians, Ukraine

Plants growing along altitudinal transects in alpine and mountainous areas respond differently to climatic conditions. The present study is centred on the unique and ecologically significant species, Rhododendron myrtifolium Schott & Kotschy, an evergreen clump-forming or prostrate dwarf shrub. This high-mountain endemic plant grows at several localities in isolated massifs of the Eastern Carpathians, but the greatest numbers of sites can be found in the subalpine and alpine belts of the Chornohora range. The main objectives of this study were (1) to assess the dendrochronological potential of Rhododendron myrtifolium as a new species in dendrochronological research and (2) to compare the growth response of R. myrtifolium (sampling elevation: 1800–1950 m a.s.l.) with Picea abies Karst. (1350–1500 m a.s.l.) and Abies alba Mill. (950–1050 m a.s.l.) collected from the upper and lower forest belts. Tree-ring material from 97 trees and shrubs enabled the construction of three site chronologies from sites located within the altitudinal transect. The longest chronology, covering the previous 184 years, was developed for fir. The chronology for the rhododendron was the shortest at 66 years. This species is the most sensitive of the three species analysed. The highest positive r-value (r=0.71) was obtained between the rhododendron chronology and the warm-season temperature (from March to July). Also, the growth of this species was significantly positively correlated with the summer temperature (r=0.50). In contrast, fir and spruce demonstrated a similar inverse relationship with August temperatures.

Large Differences in Bud Burst and Senescence between Low- and High-Altitude European Beech Populations along an Altitudinal Transect in the South-Eastern Carpathians

Large Differences in Bud Burst and Senescence between Low- and High-Altitude European Beech Populations along an Altitudinal Transect in the South-Eastern Carpathians

Widespread contamination of soils and vegetation with current use pesticide residues along altitudinal gradients in a European Alpine valley

Pesticides are transferred outside of cropland and can affect animals and plants. Here we investigated the distribution of 97 current use pesticides in soil and vegetation as central exposure matrices of insects. Sampling was conducted on 53 sites along eleven altitudinal transects in the Vinschgau valley (South Tyrol, Italy), in Europe’s largest apple growing area. A total of 27 pesticides (10 insecticides, 11 fungicides and 6 herbicides) were detected, originating mostly from apple orchards. Residue numbers and concentrations decreased with altitude and distance to orchards, but were even detected at the highest sites. Predictive, detection-based mapping indicates that pesticide mixtures can occur anywhere from the valley floor to mountain peaks. This study demonstrates widespread pesticide contamination of Alpine environments, creating contaminated landscapes. As residue mixtures have been detected in remote alpine ecosystems and conservation areas, we call for a reduction of pesticide use to prevent further contamination and loss of biodiversity.

Ecophysiological Behavior of Fagus sylvatica L. Growing at Its Southern Distribution Limit: Insights for Understanding the Fate of the European Beech under Warmer and Dryer Growth Conditions

In the last 20 years, a significant mortality of Fagus sylvatica L. (European beech) has been documented in central and northern European forests. Surprisingly, no beech die off occurred at the southern limit. This fact leads us to hypothesize that European beech populations growing at the southern limit of the distribution might have a significant phenotypic plasticity to better cope with low water availability and rising temperatures. To check this hypothesis, we evaluated the ecophysiological behavior of F. sylvatica growing along an altitudinal transect in Calabria (Italy). We selected three study sites (750 m a.s.l., 976 m a.sl. m a.s.l., 1450 m a.s.l.) showing narrow ranges of temperature, rainfall and air humidity. Trees growing at 976 m a.s.l. showed the highest stomatal conductance values during the entire experimental period. The lowest gas exchange and highest leaf mass area were recorded in plants growing at 750 m a.s.l. In the European beech growing at 1450 m a.s.l., higher vessel density, lower mean vessel diameter and higher vessel grouping index values were recorded. Overall, our results highlighted that the measured populations show a considerable phenotypic plasticity leading them to adjust anatomical and physiological traits in response to narrow ranges of environmental parameters. Despite that, the distribution of F. sylvatica seems to be limited to areas with a growing season rainfall of at least 400 mm and vapor pressure deficit (VPD) values &lt; 3 kPa, which may represent the main environmental thresholds which strongly limit the beech growth and, therefore, influence the ability of this species to cope with future environmental conditions.

Evaluating the application of branched tetraether proxies in surface soils along the altitudinal transect at Mount Dabie, China

Evaluating the application of branched tetraether proxies in surface soils along the altitudinal transect at Mount Dabie, China

Phenological variations of avocado cv. Hass and their relationship with thermal time under tropical conditions

In recent years, the avocado has been one of the most dynamic fruits in the world market. In particular, cv. Hass stands out due to its productivity, nutritional quality, and acceptance. Under tropical conditions, weather elements, especially air temperature, and precipitation, affect the productivity and quality of cv. Hass. However, in tropical environments, many relationships between weather and phenological aspects of this cultivar are still unknown. Given this situation, our aim was to identify the variation and degree of association between the phenology of avocado cv. Hass and thermal time (TT) under low-latitude conditions. Eight commercial fields planted with cv. Hass grafted onto Antillean genotypes, located in an altitudinal transect between 1,700 and 2,500 m, were evaluated. The evaluation was carried out for three years and was focused on determining the differences in avocado phenological patterns associated with different environmental variables monitored by weather stations at each location. Air temperature data were used to calculate the base temperature (BT) using different methods for all phenological stages. Later the TT was determined for each stage and all locations. The results show that the duration of each phenological stage varies as a function of elevation (air temperature) and that the phenological stages overlap at the regional, crop field, and plant levels at different periods of the year, generating a high phenological variability but with specific patterns associated with temperature and precipitation. The BT for each phenological stage varied between 0.3 and 7.5 °C, and TT was found to vary depending on the method of calculation. Our work suggests that the generalization of a BT of 10 °C is not applicable for avocado cv. Hass crops under tropical conditions, specifically in the case of Colombia. Detailed studies of phenological relationships with respect to climatic variables will allow a better approximation of the productive behavior of avocado cv. Hass.

Persistent organic pollutants in global surface soils: Distributions and fractionations

The distribution and fractionation of persistent organic pollutants (POPs) in different matrices refer to how these pollutants are dispersed and separated within various environmental compartments. This is a significant study area as it helps us understand the transport efficiencies and long-range transport potentials of POPs to enter remote areas, particularly polar regions. This study provides a comprehensive review of the progress in understanding the distribution and fractionation of POPs. We focus on the contributions of four intermedia processes (dry and wet depositions for gaseous and particulate POPs) and determine their transfer between air and soil. These processes are controlled by their partitioning between gaseous and particulate phases in the atmosphere. The distribution patterns and fractionations can be categorized into primary and secondary types. Equations are developed to quantificationally study the primary and secondary distributions and fractionations of POPs. The analysis results suggest that the transfer of low molecular weight (LMW) POPs from air to soil is mainly through gas diffusion and particle deposition, whereas high molecular weight (HMW) POPs are mainly via particle deposition. HMW-POPs tend to be trapped near the source, whereas LMW-POPs are more prone to undergo long-range atmospheric transport. This crucial distinction elucidates the primary reason behind their temperature-independent primary fractionation. However, the secondary distribution and fractionation can only be observed along a temperature gradient, such as latitudinal or altitudinal transects. An animation is produced by a one-dimensional transport model to simulate conceptively the transport of CB-28 and CB-180, revealing the similarities and differences between the primary and secondary distributions and fractionations. We suggest that the decreasing temperature trend along latitudes is not the major reason for POPs to be fractionated into the polar ecosystems, but drives the longer-term accumulation of POPs in cold climates or polar cold trapping.

Disentangling the impact of photosynthesis and stomatal conductance on rising water-use efficiency at different altitudes on the Tibetan plateau

Tree intrinsic water-use efficiency (iWUE) has dramatically increased in recent decades in global forests. The rising iWUE can be a result of either enhanced photosynthesis rate (A), or decreased stomatal conductance (gs) or both. The underlying physiological mechanisms are still not well understood. Here, we investigated tree-ring isotopes δ13C and δ18O from two tree species in three altitudinal transects on the southeast Tibetan plateau. We found that the relationship between iWUE and ∆18Olw was negative at lower-altitude forests, whereas it was positive at the treeline, indicating that enhanced photosynthesis was the main driver of the increasing iWUE at the treeline, whereas reduction in stomatal conductance was the prime regulator at lower-altitude forests. Furthermore, vapor pressure deficit (VPD) and precipitation during the main growing season showed the highest and significant correlations with leaf water 18O (Δ18Olw) at lower-altitude forests, suggesting that gs was strongly controlled by moisture conditions in the growing season particularly in the lower-altitude forests. These findings shed light to a better understanding of the regulatory mechanism of iWUE changes under the background of rising atmospheric CO2 and climate change and serve to improve the reliability of ecophysiological modeling.

Multidisciplinary approach to investigate human-forest relationships in southern French Alps: How to estimate the impact of populations on the local mountain wood stock?

This study presents a multidisciplinary approach between palaeoecology and the analysis of historical archives to reconstruct forest history subjected to long-term human activities. We focus on a case study from the southern French Alps (the Bléone Valley), for which a rich historical corpus but little palaeoenvironmental data are available. We compared and contrasted (i) pedoanthracological data obtained along an altitudinal transect (ca 400 m), (ii) dendrochronological data from historical buildings and old living trees, and (iii) historical data from written sources on forest management and land-use change. The aim of this paper is to demonstrate that the comparison between different proxy data to understand the history of mountain forest ecosystems and human-forest interactions is very challenging. We show that the spatial distribution of forest and treeline position have been impacted by human activities, mainly due to agro-sylvo-pastoral practices through the use of fire and forest cutting to maintain open pasture lands and local building purposes. Despite centuries of local agro-sylvo-pastoral activities, the forest composition has remained relatively unchanged since the Middle Ages. Our comparison of historical documents with dendrochronological data on local buildings and soil charcoal data shows that the local demands of wood cannot explain the observed large-scale changes in forest spatial continuity. Curiously, the highest demand for wood by local residents did not occur in pace with modern demographic boom (17th century), as would be expected. Thus, we suggest that supra-regional external regulations and State's control played a more important role in forest management. Royal shipbuilding industry, more lucrative economic stakes, and expanded demand for timber for construction of buildings in urban areas of the lower valleys and plains are among the external factors which impacted forest exploitation during periods when logging was prohibited.

Microbial diversity in Antarctic Dry Valley soils across an altitudinal gradient.

The Antarctic McMurdo Dry Valleys are geologically diverse, encompassing a wide variety of soil habitats. These environments are largely dominated by microorganisms, which drive the ecosystem services of the region. While altitude is a well-established driver of eukaryotic biodiversity in these Antarctic ice-free areas (and many non-Antarctic environments), little is known of the relationship between altitude and microbial community structure and functionality in continental Antarctica. We analysed prokaryotic and lower eukaryotic diversity from soil samples across a 684 m altitudinal transect in the lower Taylor Valley, Antarctica and performed a phylogenic characterization of soil microbial communities using short-read sequencing of the 16S rRNA and ITS marker gene amplicons. Phylogenetic analysis showed clear altitudinal trends in soil microbial composition and structure. Cyanobacteria were more prevalent in higher altitude samples, while the highly stress resistant Chloroflexota and Deinococcota were more prevalent in lower altitude samples. We also detected a shift from Basidiomycota to Chytridiomycota with increasing altitude. Several genera associated with trace gas chemotrophy, including Rubrobacter and Ornithinicoccus, were widely distributed across the entire transect, suggesting that trace-gas chemotrophy may be an important trophic strategy for microbial survival in oligotrophic environments. The ratio of trace-gas chemotrophs to photoautotrophs was significantly higher in lower altitude samples. Co-occurrence network analysis of prokaryotic communities showed some significant differences in connectivity within the communities from different altitudinal zones, with cyanobacterial and trace-gas chemotrophy-associated taxa being identified as potential keystone taxa for soil communities at higher altitudes. By contrast, the prokaryotic network at low altitudes was dominated by heterotrophic keystone taxa, thus suggesting a clear trophic distinction between soil prokaryotic communities at different altitudes. Based on these results, we conclude that altitude is an important driver of microbial ecology in Antarctic ice-free soil habitats.

Holocene forest and land-use history of the Erzgebirge, central Europe: a review of palynological data

Abstract. The ongoing ecological conversion of mountain forests in central Europe from widespread Picea monocultures to mixed stands conceptually also requires a historical perspective on the very long-term, i.e. Holocene, vegetation and land-use dynamics. Detailed sources of information for this are palynological data. The Erzgebirge in focus here, with a maximum height of 1244 m a.s.l., represents an extreme case of extensive historical deforestation since the Middle Ages due to mining, metallurgy, and other industrial activities, as well as rural and urban colonisation. For this regional review we collected and evaluated 121 pollen diagrams of different stratigraphic, taxonomic, and chronological resolution. This number makes this region an upland area in central Europe with an exceptionally high density of palynological data. Using well-dated diagrams going back to the early Holocene, main regional vegetation phases were derived: the Betula–Pinus phase (ca. 11 600–10 200 cal yr BP), the Corylus phase (ca. 10 200–9000 cal yr BP), the Picea phase (ca. 9000–6000 cal yr BP), the Fagus–Picea phase (ca. 6000–4500 cal yr BP), the Abies–Fagus–Picea phase (ca. 4000–1000 cal yr BP), and the anthropogenic vegetation phase (ca. 1000–0 cal yr BP). Some diagrams show the presence or even continuous curves of potential pasture and meadow indicators from around 2000 cal BCE at the earliest. Even cereal pollen grains occur sporadically already before the High Medieval. These palynological indications of a local prehistoric human impact also in the higher altitudes find parallels in the (geo-)archaeologically proven Bronze Age tin placer mining and in the geochemically proven Iron Age metallurgy in the Erzgebirge. The pollen data show that immediately before the medieval clearing, i.e. beginning at the end of the 12th century CE, forests were mainly dominated by Fagus and Abies and complemented by Picea with increasing share towards the highest altitudes. According to historical data, the minimum of the regional forest cover was reached during the 17th–18th centuries CE. The dominance of Picea in modern pollen spectra is caused by anthropogenic afforestation in the form of monocultures since that time. Future palynological investigations, preferably within the framework of altitudinal transect studies, should aim for chronologically and taxonomically high-resolution and radiometrically well-dated pollen diagrams from the larger peatlands.

Abundance of Dendroctonus frontalis and D. mexicanus (Coleoptera: Scolytinae) along altitudinal transects in Mexico: Implications of climatic change for forest conservation.

Bark beetle infestations have historically been primary drivers of stand thinning in Mexican pine forests. However, bark beetle impacts have become increasingly extensive and intense, apparently associated with climate change. Our objective was to describe the possible association between abundance of bark beetle flying populations and the occurrence of given value intervals of temperature, precipitation and their balance, in order to have a better comprehension of the climatic space that might trigger larger insect abundances, an issue relevant in the context of the ongoing climatic change. Here, we monitored the abundance of two of the most important bark beetle species in Mexico, Dendroctonus frontalis and D. mexicanus. We sampled 147 sites using pheromone-baited funnel traps along 24 altitudinal transects in 11 Mexican states, from northwestern Chihuahua to southeastern Chiapas, from 2015 to 2017. Through mixed model analysis, we found that the optimum Mean Annual Temperatures were 17°C-20°C for D. frontalis in low-elevation pine-oak forest, while D. mexicanus had two optimal intervals: 11-13°C and 15-18°C. Higher atmospheric Vapor Pressure Deficit (≥ 1.0) was correlated with higher D. frontalis abundances, indicating that warming-amplified drought stress intensifies trees' vulnerability to beetle attack. As temperatures and drought stress increase further with projected future climatic changes, it is likely that these Dendroctonus species will increase tree damage at higher elevations. Pine forests in Mexico are an important source of livelihood for communities inhabiting those areas, so providing tools to tackle obstacles to forest growth and health posed by changing climate is imperative.

Nematode biomass changes along an elevational gradient are trophic group dependent but independent of body size.

Aboveground, large and higher trophic-level organisms often respond more strongly to environmental changes than small and lower trophic-level organisms. However, whether this trophic or size-dependent sensitivity also applies to the most abundant animals, microscopic soil-borne nematodes, remains largely unknown. Here, we sampled an altitudinal transect across the Tibetan Plateau and applied a community-weighted mean (CWM) approach to test how differences in climatic and edaphic properties affect nematode CWM biomass at the level ofcommunity, trophic group and taxon mean biomass within trophic groups. We found that climatic and edaphic properties, particularly soil water-related properties, positively affected nematode CWM biomass, with no overall impact of altitude on nematode CWM biomass. Higher trophic-level omnivorous and predatory nematodes responded more strongly to climatic and edaphic properties, particularly to temperature, soil pH, and soil water content than lower trophic-level bacterivorous and fungivorous nematodes. However, these differences were likely not (only) driven by size, as we did not observe significant interactions between climatic and edaphic properties and mean biomasses within trophic groups. Together, our research implies a stronger, size-independent trophic sensitivity of higher trophic-level nematodes compared with lower trophic-level ones. Therefore, our findings provide new insights into the mechanisms underlying nematode body size structure in alpine grasslands and highlight that traits independent of size need to be found to explain increased sensitivity of higher trophic-level nematodes to climatic and edaphic properties, which might affect soil functioning.