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1. Increasing phylogenetic stochasticity at high elevations on summits across a remote North American wilderness

   https://doi.org/10.1002/ajb2.1328  

   Marx, Hannah E. ; Richards, Melissa ; Johnson, Grahm M. ; Tank, David C. ( July 2019 , American Journal of Botany)

   At the intersection of ecology and evolutionary biology, community phylogenetics can provide insights into overarching biodiversity patterns, particularly in remote and understudied ecosystems. To understand community assembly of the high alpine flora in the Sawtooth National Forest,USA, we analyzed phylogenetic structure within and between nine summit communities.

   We used high‐throughput sequencing to supplement existing data and infer a nearly completely sampled community phylogeny of the alpine vascular flora. We calculated mean nearest taxon distance (MNTD) and mean pairwise distance (MPD) to quantify phylogenetic divergence within summits, and assessed whether maximum elevation explains phylogenetic structure. To evaluate similarities between summits, we quantified phylogenetic turnover, taking into consideration microhabitats (talus vs. meadows).

   We found different patterns of community phylogenetic structure within the six most species‐rich orders, but across all vascular plants phylogenetic structure was largely not different from random. There was a significant negative correlation between elevation and tree‐wide phylogenetic diversity (MPD) within summits: overdispersion degraded as elevation increased. Between summits, we found high phylogenetic turnover driven by greater niche heterogeneity on summits with alpine meadows.

   Our results provide further evidence that stochastic processes may also play an important role in the assembly of vascular plant communities in high alpine habitats at regional scales. However, order‐specific patterns suggest that adaptations are still important for assembly of specific sectors of the plant tree of life. Further studies quantifying functional diversity will be important in disentangling the interplay of eco‐evolutionary processes that likely shape broad community phylogenetic patterns in extreme environments.

    

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2. Taxonomic decomposition of the latitudinal gradient in species diversity of North American floras

   https://doi.org/10.1111/jbi.13131  

   Weiser, Michael D. ; Swenson, Nathan G. ; Enquist, Brian J. ; Michaletz, Sean T. ; Waide, Robert B. ; Zhou, Jizhong ; Kaspari, Michael ( November 2017 , Journal of Biogeography)

   To test the latitudinal gradient in plant species diversity for self‐similarity across taxonomic scales and amongst taxa.

   North America.

   We used species richness data from 245 local vascular plant floras to quantify the slope and shape of the latitudinal gradients in species diversity (LGSD) across all plant species as well as within each family and order. We calculated the contribution of each family and order to the empiricalLGSD.

   We observed the canonicalLGSDwhen all plants were considered with floras at the lowest latitudes having, on average, 451 more species than floras at the highest latitudes. When considering slope alone, most orders and families showed the expected negative slope, but 31.7% of families and 27.7% of orders showed either no significant relationship between latitude and diversity or a reverseLGSD. Latitudinal patterns of family diversity account for at least 14% of thisLGSD. Most orders and families did not show the negative slope and concave‐down quadratic shape expected by the pattern for all plant species. A majority of families did not make a significant contribution in species to theLGSDwith 53% of plant families contributing little to nothing to the overall gradient. Ten families accounted for more than 70% of the gradient. Two families, the Asteraceae and Fabaceae, contributed a third of theLGSD.

   The empiricalLGSDwe describe here is a consequence of a gradient in the number of families and diversification within relative few plant families. Macroecological studies typically aim to generate models that are general across taxa with the implicit assumption that the models are general within taxa. Our results strongly suggest that models of the latitudinal gradient in plant species richness that rely on environmental covariates (e.g. temperature, energy) are likely not general across plant taxa.

    

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3. Ectomycorrhizal fungi and soil enzymes exhibit contrasting patterns along elevation gradients in southern Patagonia

   https://doi.org/10.1111/nph.15714  

   Truong, Camille ; Gabbarini, Luciano A. ; Corrales, Adriana ; Mujic, Alija B. ; Escobar, Julio M. ; Moretto, Alicia ; Smith, Matthew E. ( March 2019 , New Phytologist)

   The biological and functional diversity of ectomycorrhizal (ECM) associations remain largely unknown in South America. In Patagonia, theECMtreeNothofagus pumilioforms monospecific forests along mountain slopes without confounding effects of vegetation on plant–fungi interactions.

   To determine how fungal diversity and function are linked to elevation, we characterized fungal communities, edaphic variables, and eight extracellular enzyme activities along six elevation transects in Tierra del Fuego (Argentina and Chile). We also tested whether pairingITS1rDNAIllumina sequences generated taxonomic biases related to sequence length.

   Fungal community shifts across elevations were mediated primarily by soilpHwith the most species‐rich fungal families occurring mostly within a narrowpHrange. By contrast, enzyme activities were minimally influenced by elevation but correlated with soil factors, especially total soil carbon. The activity of leucine aminopeptidase was positively correlated withECMfungal richness and abundance, and acid phosphatase was correlated with nonECM fungal abundance. Several fungal lineages were undetected when using exclusively paired or unpaired forwardITS1 sequences, and these taxonomic biases need reconsideration for future studies.

   Our results suggest that soil fungi inN. pumilioforests are functionally similar across elevations and that these diverse communities help to maintain nutrient mobilization across the elevation gradient.

    

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4. Species origin affects the rate of response to inter‐annual growing season precipitation and nutrient addition in four Australian native grasslands

   https://doi.org/10.1111/jvs.12450  

   Morgan, John_W ; Dwyer, John_M ; Price, Jodi_N ; Prober, Suzanne_M ; Power, Sally_A ; Firn, Jennifer ; Moore, Joslin_L ; Wardle, Glenda_M ; Seabloom, Eric_W ; Borer, Elizabeth_T ; et al ( August 2016 , Journal of Vegetation Science)

   Predicted increases in temperature and changes to precipitation are expected to alter the amount of plant available nutrients, in turn, altering rates of primary production and exotic plant invasions. However, it remains unclear whether increased responses occur in wetter than average years, even in low fertility and low rainfall regions.

   Four Australian grasslands, including sites in arid Western Australia, semi‐arid Victoria, alpine Victoria and sub‐tropical Queensland.

   Using identical nutrient addition experiments, we use 6‐years of biomass, cover and species richness data to examine how rates of biomass production and native and exotic cover and richness are affected by growing season precipitation [proportion of yearly growing season precipitation (GSP) to long‐term meanGSP] and nutrient (N, P, K and micronutrients) addition.

   Rates of grassland productivity strongly increased with increasingGSP.GSPincreased rates of native cover but not native or exotic richness, nor rates of exotic cover change. We detected no significantNPKeffect on rates of grassland productivity, exotic cover or exotic richness change. In contrast,NPKaddition decreased rates of native cover change and fertilized plots had significantly fewer native species. We did not detect a significant interaction betweenNPKandGSP_.

   Grassland productivity was more strongly predicted by variation in growing season precipitation than by nutrient addition, suggesting it will vary with future changes in rainfall. Response to nutrients, however, depend on species origin, suggesting that increasing soil nutrient availability due to anthropogenic activities is likely to lead to negative effects on native species richness and cover.

    

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5. Bryophytes in fir waves: Forest canopy indicator species and functional diversity decline in canopy gaps

   https://doi.org/10.1111/jvs.12718  

   Berdugo, Monica B. ; Dovciak, Martin ; Nakashizuka, ed., Tohru ( March 2019 , Journal of Vegetation Science)

   Bryophytes can cover three quarters of the ground surface, play key ecological functions, and increase biodiversity in mesic high‐elevation conifer forests of the temperate zone. Forest gaps affect species coexistence (and ecosystem functions) as suggested by the gap and gap‐size partitioning hypotheses (GPH,G_SPH). Here we test these hypotheses in the context of high‐elevation forest bryophyte communities and their functional attributes.

   Spruce–fir forests on Whiteface Mountain, NY,USA.

   We characterized canopy openness, microclimate, forest floor substrates, vascular vegetation cover, and moss layer (cover, common species, and functional attributes) in three canopy openness environments (gap, gap edge, forest canopy) across 20 gaps (fir waves) (n = 60); the functional attributes were based on 16 morphologic, reproductive, and ecological bryophyte plant functional traits (PFTs). We testedGPHandG_SPHrelative to bryophyte community metrics (cover, composition), traits, and trait functional sensitivity (functional dispersion;FDis) using indicator species analysis, ordination, and regression.

   Canopy openness drove gradients in ground‐level temperature, substrate abundance and heterogeneity (beta diversity), and understory vascular vegetation cover. TheGPHwas consistent with (a) the abundance patterns of forest canopy indicator species (Dicranum fuscescens,Hypnum imponens, andTetraphis pellucida), and (b)FDisbased on threePFTs (growth form, fertility, and acidity), both increasing with canopy cover. We did not find support forGPHin the remaining species or traits, or forG_SPHin general; gap width (12–44 m) was not related to environmental or bryophyte community gradients.

   The observed lack of variation in most bryophyte metrics across canopy environments suggests high resistance of the bryophyte layer to natural canopy gaps in high‐elevation forests. However, responses of forest canopy indicator species suggest that canopy mortality, potentially increased by changing climate or insect pests, may cause declines in some forest canopy species and consequently in the functional diversity of bryophyte communities.

    

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