Origins of an alpine flora The evolution of high mountain floras is strongly influenced by tectonic and climatic history. Ding et al. document the timing, tempo, and mode by which the world's most ...species-rich alpine flora, that of the Tibet-Himalaya-Hengduan region, was assembled. Alpine assemblages in the region are older than previously thought, with lineages tracing their alpine ancestry to the early Oligocene—older than any other modern alpine system. Alpine species diversified faster during periods of orogeny and intensification of the Asian monsoon, and the Hengduan Mountains—the most species-rich area in this region—played a key biogeographic role as the location of the earliest pulse of alpine diversification in the Oligocene. Science , this issue p. 578
Mountain formation and monsoon intensification drove species accumulation in the alpine flora of the Tibet-Himalaya-Hengduan region.
Understanding how alpine biotas formed in response to historical environmental change may improve our ability to predict and mitigate the threats to alpine species posed by global warming. In the world’s richest temperate alpine flora, that of the Tibet-Himalaya-Hengduan region, phylogenetic reconstructions of biome and geographic range evolution show that extant lineages emerged by the early Oligocene and diversified first in the Hengduan Mountains. By the early to middle Miocene, accelerated diversification and colonization of adjacent regions were likely driven jointly by mountain building and intensification of the Asian monsoon. The alpine flora of the Hengduan Mountains has continuously existed far longer than any other alpine flora on Earth and illustrates how modern biotas have been shaped by past geological and climatic events.
Studies of early human settlement in alpine environments provide insights into human physiological, genetic, and cultural adaptation potentials. Although Late and even Middle Pleistocene human ...presence has been recently documented on the Tibetan Plateau, little is known regarding the nature and context of early persistent human settlement in high elevations. Here, we report the earliest evidence of a prehistoric high-altitude residential site. Located in Africa's largest alpine ecosystem, the repeated occupation of Fincha Habera rock shelter is dated to 47 to 31 thousand years ago. The available resources in cold and glaciated environments included the exploitation of an endemic rodent as a key food source, and this played a pivotal role in facilitating the occupation of this site by Late Pleistocene hunter-gatherers.
Mountain regions are unusually biodiverse, with rich aggregations of small-ranged species that form centers of endemism. Mountains play an array of roles for Earth's biodiversity and affect ...neighboring lowlands through biotic interchange, changes in regional climate, and nutrient runoff. The high biodiversity of certain mountains reflects the interplay of multiple evolutionary mechanisms: enhanced speciation rates with distinct opportunities for coexistence and persistence of lineages, shaped by long-term climatic changes interacting with topographically dynamic landscapes. High diversity in most tropical mountains is tightly linked to bedrock geology-notably, areas comprising mafic and ultramafic lithologies, rock types rich in magnesium and poor in phosphate that present special requirements for plant physiology. Mountain biodiversity bears the signature of deep-time evolutionary and ecological processes, a history well worth preserving.
Contamination by plastic debris has been documented in most regions of the world, but their occurrence in high mountain areas has not been investigated to date. Here we present the first report of ...the occurrence and amount of microplastic in any terrestrial glacier environment. In the supraglacial debris of the Forni Glacier (Italian Alps), we observed the occurrence of (mean ± standard error) 74.4 ± 28.3 items kg−1 of sediment (dry weight). This amount is within the range of variability of microplastic contamination observed in marine and coastal sediments in Europe. Most plastic items were made by polyesters, followed by polyamide, polyethylene and polypropylene. We estimated that the whole ablation area of Forni Glacier should host 131–162 million plastic items. Microplastic can be released directly into high elevation areas by human activities in the mountain or be transported by wind to high altitude. The occurrence of microplastic on Forni Glacier may be due to the gathering of debris coming from the large accumulation area into the relatively smaller ablation area of the glacier, as a consequence of its flow and melting.
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•We report the first evidence of microplastic contamination on an alpine glacier.•Mean amount of 74.4 ± 28.3 (SE) items kg−1 of sediment was found.•Microplastic contamination was in the same range of marine and coastal sediments.•We estimated 131–162 million plastic items on the glacier ablation area.
Capsule: We present the first evidence of the occurrence of microplastic contamination on an Alpine glacier.
Groundwater discharge in alpine headwaters sustains baseflow in rivers originating in mountain ranges of the world, which is critically important for aquatic habitats, run‐of‐river hydropower ...generation, and downstream water supply. Groundwater storage in alpine watersheds was long considered negligible, but recent field‐based studies have shown that aquifers are ubiquitous in the alpine zone with no soil and vegetation. Talus, moraine, and rock glacier aquifers are common in many alpine regions of the world, although bedrock aquifers occur in some geological settings. Alpine aquifers consisting of coarse sediments have a fast recession of discharge after the recharge season (e.g., snowmelt) or rainfall events, followed by a slow recession that sustains discharge over a long period. The two‐phase recession is likely controlled by the internal structure of the aquifers. Spatial extent and distribution of individual aquifers determine the groundwater storage‐discharge characteristics in first‐ and second‐order watersheds in the alpine zone, which in turn govern baseflow characteristics in major rivers. Similar alpine landforms appear to have similar hydrogeological characteristics in many mountain ranges across the world, suggesting that a common conceptual framework can be used to understand alpine aquifers based on geological and geomorphological settings. Such a framework will be useful for parameterizing storage‐discharge characteristics in large river hydrological models.
Article Impact Statement: This article presents a synthesis of current knowledge on alpine groundwater providing critical baseflow to major rivers of the world.
Parallel local adaptation, that is, when distinct genetic lineages independently adapt to the same selective environment, provides strong evidence for the action of natural selection. A few cases of ...parallel local adaptation were reported in plants but underlying mechanisms promoting or preventing the parallel response, such as the balance between migration and selection, were rarely quantified. Here, we conducted a transplant experiment to test whether distinct foothill–alpine population pairs of Arabidopsis arenosa exhibited similar adaptive responses to a contrasting alpine environment. We further investigated selection and migration patterns in these populations.
Seedlings of 16 foothill and alpine populations of A. arenosa from four distinct mountain regions (one occupied by diploid and three by tetraploid populations) were transplanted into one low‐ and one high‐elevation site. We recorded fitness proxies over two growing seasons to test whether the elevation‐of‐origin advantage was manifested in the same way across the four regions of origin. Then, we quantified the strength of selection on the traits at each transplantation site and used coalescent simulations to estimate past gene flow intensity between each pair of foothill and alpine populations in each region.
We demonstrated that the four pairs of populations exhibited similar adaptive responses to elevation difference in terms of survival, number of flowering plants, stem height and accumulation of above‐ground dry biomass; the other traits (rosette size, number of leaves, stems and flowers) exhibited rather regional‐specific patterns. In addition, we found minor effects of ploidy level on the fitness proxies recorded. Our selection and migration analysis revealed that parallel local adaptation was probably achieved by differential selective pressure at low versus high elevation in combination with lack or limited gene flow between foothill and alpine populations.
Synthesis. We show that the previously documented strong morphological and genetic distinctness of alpine A. arenosa compared to their foothill counterparts, which has been hypothesized to be driven by natural selection, is indeed mirrored in fitness differences consistent with parallel local adaptation. Our results provide experimental support for the repeatability of adaptive evolution and highlight the prominent role of divergent selection.
We demonstrated that distinct pairs of foothill–alpine populations exhibited similar adaptive responses to elevation providing evidence for parallel local adaptation. This was probably achieved by differential selective pressure at low versus high elevation combined with lack or limited gene flow. Our results provide experimental support for the repeatability of adaptive evolution and highlight the prominent role of natural selection.
Although important for riverine solute and nutrient fluxes, the connections between biogeochemical processes and subsurface hydrology remain poorly characterized. We investigate these couplings in ...the East River, CO, a high‐elevation shale‐dominated catchment in the Rocky Mountains, using concentration‐discharge (C‐Q) relationships for major cations, anions, and organic carbon. Dissolved organic carbon (DOC) displays a positive C‐Q relationship with clockwise hysteresis, indicating mobilization and depletion of DOC in the upper soil horizons and emphasizing the importance of shallow flow paths during snowmelt. Cation and anion concentrations demonstrate that carbonate weathering, which dominates solute fluxes, is promoted by both sulfuric acid derived from pyrite oxidation in the shale bedrock and carbonic acid derived from subsurface respiration. Sulfuric acid weathering dominates during base flow conditions when waters infiltrate below the inferred pyrite oxidation front, whereas carbonic acid weathering plays a dominant role during snowmelt as a result of shallow flow paths. Differential C‐Q relationships between solutes suggest that infiltrating waters approach calcite saturation before reaching the pyrite oxidation front, after which sulfuric acid reduces carbonate alkalinity. This reduction in alkalinity results in CO2 outgassing when waters equilibrate to surface conditions, and reduces the riverine export of carbon and alkalinity by roughly 33% annually. Future changes in snowmelt dynamics that control the balance of carbonic and sulfuric acid weathering may substantially alter carbon cycling in the East River. Ultimately, we demonstrate that differential C‐Q relationships between major solutes can provide unique insights into the complex subsurface flow and biogeochemical dynamics that operate at catchment scales.
Key Points
C‐Q relationships for multiple stream solutes highlight couplings between hydrologic flow regime and biogeochemical reaction fronts
Balance of carbonate weathering from carbonic acid (soil respiration) versus sulfuric acid (pyrite oxidation) shaped by subsurface flow paths
Data advance a conceptual model for transport and transformation of carbon and alkalinity from the watershed
Abstract
Arbuscular mycorrhizal (AM) fungi can benefit plants under environmental stress, and influence plant adaptation to warmer climates. However, very little is known about the ecology of these ...fungi in alpine environments. We sampled plant roots along a large fraction (1941–6150 m asl (above sea level)) of the longest terrestrial elevational gradient on Earth and used DNA metabarcoding to identify AM fungi. We hypothesized that AM fungal alpha and beta diversity decreases with increasing elevation, and that different vegetation types comprise dissimilar communities, with cultured (putatively ruderal) taxa increasingly represented at high elevations. We found that the alpha diversity of AM fungal communities declined linearly with elevation, whereas within-site taxon turnover (beta diversity) was unimodally related to elevation. The composition of AM fungal communities differed between vegetation types and was influenced by elevation, mean annual temperature, and precipitation. In general, Glomeraceae taxa dominated at all elevations and vegetation types; however, higher elevations were associated with increased presence of Acaulosporaceae, Ambisporaceae, and Claroideoglomeraceae. Contrary to our expectation, the proportion of cultured AM fungal taxa in communities decreased with elevation. These results suggest that, in this system, climate-induced shifts in habitat conditions may facilitate more diverse AM fungal communities at higher elevations but could also favour ruderal taxa.
Plant-symbiotic fungal diversity and community composition are influenced by vegetation and the abiotic environment along an extended elevational gradient in the Himalayan Mountains.
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