Gradient Of Nutrient Availability Research Articles

Water use segregation among plants with contrasting root depth and distribution along gypsum hills

AbstractAimsPlant communities growing along gypsum hills in NE Spain show a distinct zonation that may depend on water table depth, salt and nutrient availability gradients between hilltops and saline depressions. We analysed the main sources of water used by woody species in these communities. Specifically, we assessed whether hydrological niche segregation occurred among dominant woody species with different root depth and plant location along gypsum hills during spring and summer.LocationMiocene gypsum formations of NE Spain, Middle‐Ebro depression.MethodsWe analysed the oxygen and hydrogen isotope composition of the xylem water of ten dominant woody species growing along gypsum hills and compared it to water extracted from the top 20 cm of the soil, gypsum crystallization water and groundwater, both in spring and summer. Bayesian isotope mixing models were used to estimate the proportion of each water source used by different species.ResultsThere was a clear segregation in the sources of water used by dominant woody species from plant communities co‐existing on gypsum hills, and such segregation responded to their rooting depth and position along the hill. Shallow‐rooted plants growing out of saline depressions exploited superficial free soil water and gypsum crystallization water, and had limited access to groundwater, particularly during summer. In contrast, deep‐rooted plants and shallow‐rooted plants from saline depressions thrived preferentially on the water table. Such differences were noticeable in spring, but became sharper during summer.ConclusionsWoody species from gypsum hills have different hydrological niches. Niche segregation is mainly related to the depth of the root system of plants and to their position along gypsum hills, which determine proximity to the water table. It is accentuated during summer, highlighting the role of summer drought as a structuring factor in gypsum plant communities. The segregation of the water sources used by plants is related to a suite of phenological, functional and anatomical features, indicating adaptation of plant species to their respective hydrological niches.

Foliar nutrient resorption patterns of four functional plants along a precipitation gradient on the Tibetan Changtang Plateau.

Nutrient resorption from senesced leaves as a nutrient conservation strategy is important for plants to adapt to nutrient deficiency, particularly in alpine and arid environment. However, the leaf nutrient resorption patterns of different functional plants across environmental gradient remain unclear. In this study, we conducted a transect survey of 12 communities to address foliar nitrogen (N) and phosphorus (P) resorption strategies of four functional groups along an eastward increasing precipitation gradient in northern Tibetan Changtang Plateau. Soil nutrient availability, leaf nutrient concentration, and N:P ratio in green leaves ([N:P]g) were linearly correlated with precipitation. Nitrogen resorption efficiency decreased, whereas phosphorus resorption efficiency except for sedge increased with increasing precipitation, indicating a greater nutrient conservation in nutrient‐poor environment. The surveyed alpine plants except for legume had obviously higher N and P resorption efficiencies than the world mean levels. Legumes had higher N concentrations in green and senesced leaves, but lowest resorption efficiency than nonlegumes. Sedge species had much lower P concentration in senesced leaves but highest P resorption efficiency, suggesting highly competitive P conservation. Leaf nutrient resorption efficiencies of N and P were largely controlled by soil and plant nutrient, and indirectly regulated by precipitation. Nutrient resorption efficiencies were more determined by soil nutrient availability, while resorption proficiencies were more controlled by leaf nutrient and N:P of green leaves. Overall, our results suggest strong internal nutrient cycling through foliar nutrient resorption in the alpine nutrient‐poor ecosystems on the Plateau. The patterns of soil nutrient availability and resorption also imply a transit from more N limitation in the west to a more P limitation in the east Changtang. Our findings offer insights into understanding nutrient conservation strategy in the precipitation and its derived soil nutrient availability gradient.

Optimal metabolic regulation along resource stoichiometry gradients

Most heterotrophic organisms feed on substrates that are poor in nutrients compared to their demand, leading to elemental imbalances that may constrain their growth and function. Flexible carbon (C)-use efficiency (CUE, C used for growth over C taken up) can represent a strategy to reduce elemental imbalances. Here, we argue that metabolic regulation has evolved to maximise the organism growth rate along gradients of nutrient availability and translated this assumption into an optimality model that links CUE to substrate and organism stoichiometry. The optimal CUE is predicted to decrease with increasing substrate C-to-nutrient ratio, and increase with nutrient amendment. These predictions are generally confirmed by empirical evidence from a new database of c. 2200 CUE estimates, lending support to the hypothesis that CUE is optimised across levels of organisation (microorganisms and animals), in aquatic and terrestrial systems, and when considering nitrogen or phosphorus as limiting nutrients.

Clonal vs leaf-height-seed (LHS) traits: which are filtered more strongly across habitats?

Plant functional traits are now frequently used instead of species identity to identify how plant species co-exist in assemblages. One notion is that species inhabiting the same environment have more characteristics in common than species from different habitats, leading to different prevailing dominant traits along environmental gradients, and also to a lesser diversity of traits in habitats that impose a stronger filter on these traits. Though such patterns have been demonstrated for different environmental drivers and different traits, studies using easily available traits connected to above ground processes (i.e. traits of the leaf-height-seed, or LHS, strategy scheme) are largely overrepresented in these analyses. Here we combined data on clonal and bud bank traits, representing the ability to reproduce and spread vegetatively, with LHS trait data and examined how these traits varied in relation to the vegetational composition of 29 Central-European habitat types. Our analysis focused on determining whether clonal/bud bank or LHS traits play an important role for environmental filtering along gradients approximated by Ellenberg indicator values (EIV) across these habitats. Our results show that clonal and bud bank traits are at least as – if not more – important for the differentiation of the 29 habitat types. Overall, diversity and dominance of clonal and bud bank traits was more strongly correlated with gradients of light availability, temperature, moisture, soil reaction, and nutrient availability across these habitats than it was the case for traits of the leaf-height-seed scheme. Our results call for a stronger integration of belowground traits into the functional traits approach in plant ecology and for an extension of efforts to collect such data.

Functional trait variation and nitrogen use efficiency in temperate coastal phytoplankton

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 563:35-49 (2017) - DOI: https://doi.org/10.3354/meps11974 Functional trait variation and nitrogen use efficiency in temperate coastal phytoplankton Elsa Breton, Urania Christaki, Simon Bonato, Morgane Didry, Luis Felipe Artigas* UMR 8187 LOG, Laboratoire d’Océanologie et de Géosciences, Université du Littoral Côte d’Opale, CNRS, Université Lille, 62930 Wimereux, France *Corresponding author: felipe.artigas@univ-littoral.fr ABSTRACT: This study explored the relevance of the use of a trait-based approach to explain seasonal phytoplankton succession and the underlying mechanisms that structure phytoplankton assemblages and promote nitrogen use efficiency (NUE) in the temperate coastal waters of the eastern English Channel (EEC). A 3 yr time series of phytoplankton abundance assessed by flow cytometry was combined with a selection of traits related to resource utilization (light and inorganic nutrients), grazing resistance, and maximum growth, mainly sourced from the literature. Our results showed that the identified functional groups (FGs) ranged deterministically along a temporal gradient of light and nutrient availability, according to several fundamental trade-offs. These trade-offs, which reflected different ecological strategies, were distributed along 1 axis of niche differentiation. This favoured different FGs through time, and consequently allowed them to partition those available resources. The observed functional divergence of the phytoplankton community deviated from that of the expected, random one. It showed that as light increased, the phytoplankton community assembly was mainly driven by competition and grazing pressure, which eventually favoured those FGs that were fastest growing and less vulnerable to predation. Structural equation modeling evidenced that a phytoplankton community, functionally dominated by FGs that were relatively large, fast-growing, and well-adapted to higher light, promoted NUE. Together, these results confirmed the potential use of laboratory-measured functional traits to explore environment-trait linkages in phytoplankton. They also showed the possibility of further extending this approach to identify the mechanisms driving phytoplankton community assembly, structure, and related ecosystem processes. KEY WORDS: Phytoplankton community · Flow cytometry · Functional traits · Nitrogen use efficiency Full text in pdf format Supplementary material PreviousNextCite this article as: Breton E, Christaki U, Bonato S, Didry M, Artigas LF (2017) Functional trait variation and nitrogen use efficiency in temperate coastal phytoplankton. Mar Ecol Prog Ser 563:35-49. https://doi.org/10.3354/meps11974 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 563. Online publication date: January 20, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Modification of littoral algal assemblages by gardening caddisfly larvae

Summary Sedentary herbivores may improve the food resources available to them by ‘gardening’, and most obviously by fertilising primary producers with excreted nutrients such as nitrogen. In five English lakes, spanning a gradient of nutrient availability, we predicted that fertilisation of the larval retreat by the littoral, gallery‐building caddisfly Tinodes waeneri would result in: (a) a distinct algal assemblage from that in the background epilithon, and that (b) the difference would be greatest in the least productive lakes (where the importance of the nutrient subsidy from larvae should be greatest). Classes of algae present in samples of galleries and epilithon were investigated using chlorophyll and carotenoid pigment analysis and diatoms were identified. Galleries were characterised by a greater content of pigments indicative of diatoms, including fucoxanthin, than the background epilithon (which contained a higher proportion of chlorophyte algae). Redundancy analysis (RDA) of diatom counts indicated a clear separation between gallery and epilithic assemblages in all lakes, supporting hypothesis (a). Furthermore, in agreement with hypothesis (b), the assemblage of diatoms on galleries was most similar to that of the epilithon in the more productive lakes, with the greatest divergence in Windermere and Coniston, mainly due to a much greater relative proportion of Gomphonema in the epilithon than in the galleries, suggesting that fertilisation had a greater impact where background nutrient concentrations were low. Lakes in the RDA triplot were arranged in order of productivity along axis 1, with gallery assemblages in each case located towards the more productive end relative to the epilithon. This sedentary, retreat‐building grazer, probably in common with many other taxa with such traits in aquatic ecosystems, improves its own food resources by gardening. Larvae can modify algal assemblages in their feeding patches by weeding and fertilisation. They create new surfaces for growth of the biofilm via continually adding to the front of their silken galleries and harvesting the biofilm (dominated by diatoms) that has developed on older parts of their galleries to the rear. It is also feasible that the physical structure of the gallery (separately from the effects of nutrients) plays some role in increasing the availability of algae within the territory. This behaviour is likely to extend the range of conditions under which such species can persist, raise the carrying capacity of their habitat, and has possible wider ecosystem consequences for productivity and nutrient cycling.

Leaf traits of dipterocarp species with contrasting distributions across a gradient of nutrient and light availability

Background: Tree species composition at the landscape scale is often tightly associated with underlying soil type in tropical forests. Changes in soil type may have effects on forest structure that drive changes in both light and soil resource availability, since light availability in the understorey tends to be lower in more fertile sites. Plant functional traits may determine species distributions across gradients of light and soil resource availability.Aims: To test whether tree species with contrasting distributions exhibit leaf traits that reflect adaptation to the resources most limiting in their native environment.Methods: We measured foliar nutrient concentrations, stomatal density, leaf δ13C values, leaf mass per area, and leaf lifespan for saplings of nine common dipterocarp species at Sepilok Forest Reserve, Malaysian Borneo, possessing varying associations to soil resource habitats.Results: Species specialised in their adult distribution to nutrient-poor sandstone soils had traits indicative of a nutrient conservation strategy. Species specialised to more fertile alluvial soils had a wider spectrum of leaf N and P concentrations and LL, reflecting greater variance in strategies for resource acquisition and use among species in this habitat.Conclusions: Understorey light regimes co-vary with soil type, and both light and soil resource availability influence leaf trait adaptations that may contribute to species–habitat associations.

Nutrient uptake and use efficiency in co‐occurring plants along a disturbance and nutrient availability gradient in the boreal forests of the southwest Yukon, Canada

AbstractAimIn boreal forest ecosystems plant productivity is typically constrained by mineral nutrient availability. In some boreal regions changes in nutrient availability have led to limited changes in productivity but large changes in plant composition. To determine the impact that a change in nutrient availability has on the plant communities it is important to understand how species use nutrients. Here we explore how plant species and functional types in a cold‐dry boreal forest community use available nutrients by quantifying their respective nutrient utilization and response efficiency.LocationBoreal forests in the southwest corner of the Yukon Territory, Canada.MethodsWe collected soil samples and total plant biomass from 29 plots from nine locations subjected to fire, harvesting or bark beetle disturbances. Nutrient analysis of all vegetation and soil samples were conducted to determine the concentration of macro‐ and micronutrients from both plant biomass and soils collected. Nutrient pools between stands with different disturbance histories are compared. Nutrient uptake, use and response efficiencies were then calculated and nutrient response profiles were developed for each species/functional type.ResultsWe found few differences between nutrient pools in plots with different disturbance histories. A clear separation of species and functional groups in elemental hyperspace suggesting divergent nutrient use in co‐occurring species was identified. The use efficiency analysis highlighted that the species with the highest uptake efficiency have lowest use efficiency and vice versa. Species showed either a monotonic or constant relationship between nutrient response efficiency and N, P, K, reflecting a lack of relationship between plant productivity and resource availability or a linear increase in productivity with increasing nutrient availability, respectively.ConclusionsOur findings indicate that species are maximizing nutrient use along different parts of the resource gradient, which has implications for understanding how species respond to changes in nutrient availability. Our findings also show that nutrient use by some species may be governed more by uptake efficiency than use efficiency, allowing them to respond to increases in resource availability by increasing uptake rather than use.

Effects of defoliation and site quality on growth and defenses of Pinus pinaster and P. radiata

The susceptibility to pests and pathogens is frequently of only minor consideration by foresters when selecting tree species to plant, but growth reductions from pests and pathogens are commonly large relative to productivity differences among tree species. Because the selection of tree species and sites when establishing plantation forests has potential effects on subsequent damage by pests, there is need for consideration of joint effects of tree species, site quality, and risk of pests. We tested here how site quality influences the response of two pines species that differ in their evolutionary history with a primary pest in the system. Our specific research objectives were to (1) measure the growth response of two pine species (the native Pinus pinaster and the introduced P. radiata) to defoliation by the pine processionary moth, across a gradient of nutrient availability and (2) compare the constitutive and delayed defoliation induced chemical defenses of these two pine species on sites of low and high quality. We analyzed variation in foliar nitrogen, terpenes, tannins, total phenols and four defensive proteins. The impact on tree growth from experimentally applied defoliation by PPM was surprisingly low. Even with complete defoliation, large sample sizes, and baseline measurements that accounted for much of the variation among trees, we observed only modest effects on diameter growth and no effects on height growth; volume growth was initially reduced by only 6–8% initially, with full recovery within 3 years of defoliation. Pinus radiata, the faster growing species, had higher concentrations than P. pinaster of foliar N while P. pinaster had up to 12 times higher concentrations of terpenes, these results match with predictions of the resource availability hypothesis (RAH). Pinus radiata foliage was relatively rich in tannins and total phenolics. The pine species also differed in defensive proteins. Pinuspinaster had higher concentrations of peroxidase (POD), polyphenol oxidase (PPO) and chitinase (CHI), while P. radiata had higher concentrations of trypsin inhibitor (TI). Finally there was no evidence for delayed inducible defenses in either pine species following PPM defoliation; both species seem to use other defensive strategies to counter predictable attacks by the herbivore. In our study region, defoliation by PPM may not be a primary consideration in the selection of pine species for production forests, but this conclusion need not hold in regions where pines grow more slowly or are exposed to multiple years of defoliation by PPM.

Marine Primary Productivity Is Driven by a Selection Effect

The number of species of autotrophic communities can increase ecosystem productivity through species complementarity or through a selection effect which occurs when the biomass of the community approaches the monoculture biomass of the most productive species. Here we explore the effect of resource supply on marine primary productivity under the premise that the high local species richness of phytoplankton communities increases resource use through transient selection of productive species. Using concurrent measurements of phytoplankton community structure, nitrate fluxes into the euphotic zone and productivity from a temperate coastal ecosystem, we find that observed productivities are best described by a population growth model in which the dominant species of the community approach their maximum growth rates. We interpret these results as evidence of species selection in communities containing a vast taxonomic repertory. The prevalence of selection effect was supported by open ocean data that show an increase in community dominance across a gradient of nutrient availability. These results highlight the way marine phytoplankton optimize resources and sustain world food stocks. We suggest that the maintenance of phytoplankton species richness is essential to sustain marine primary productivity since it guarantees the occurrence of highly productive species.

The clam Neilonella sulculata in San Jorge Gulf (Argentina, Southwest Atlantic): spatial distribution pattern and inverse relationship between size and density

ABSTRACTNeilonella sulculata is a dominant bivalve on muddy bottoms of the continental shelf and gulfs off Argentina (Southwest Atlantic). Two benthic surveys performed in 2007 and 2009 in San Jorge Gulf, a depositional area characterized by silt/clay sediments, gave us the opportunity to test whether the population of this clam displays a significant spatial structure and to analyse if there is an inverse relationship between size and density. Density, biomass and size–frequency distribution displayed significant spatial structure, being positively autocorrelated at the smallest spatial scales (c. 1.7–14/17 km). Biomass also showed spatial contagion at scales of 25–33 km. A substantial increase in density and biomass occurred between 2007 and 2009. Empty valves in the sediment showed that the maximum size attained by the species may exhibit considerable variation at relatively short temporal scales. Regardless of temporal changes in density and biomass, the spatial structure of these variables remained stable. In densely populated areas, shell size decreased with increasing density, suggesting a density-dependent control of growth. A clear north–south increase in density and biomass was detected, which might be related to a gradient in food availability caused by a thermohaline frontal system associated with wind-related upwelling.

Root Foraging Performance and Life-History Traits.

Plants use their roots to forage for nutrients in heterogeneous soil environments, but different plant species vastly differ in the intensity of foraging they perform. This diversity suggests the existence of constraints on foraging at the species level. We therefore examined the relationships between the intensity of root foraging and plant body traits across species in order to estimate the degree of coordination between plant body traits and root foraging as a form of plant behavior. We cultivated 37 perennial herbaceous Central European species from open terrestrial habitats in pots with three different spatial gradients of nutrient availability (steep, shallow, and no gradient). We assessed the intensity of foraging as differences in root placement inside pots with and without a spatial gradient of resource supply. For the same set of species, we retrieved data about body traits from available databases: maximum height at maturity, mean area of leaf, specific leaf area, shoot lifespan, ability to self-propagate clonally, maximal lateral spread (in clonal plants only), realized vegetative growth in cultivation, and realized seed regeneration in cultivation. Clonal plants and plants with extensive vegetative growth showed considerably weaker foraging than their non-clonal or slow-growing counterparts. There was no phylogenetic signal in the amount of expressed root foraging intensity. Since clonal plants foraged less than non-clonals and foraging intensity did not seem to be correlated with species phylogeny, we hypothesize that clonal growth itself (i.e., the ability to develop at least partly self-sustaining ramets) may be an answer to soil heterogeneity. Whereas unitary plants use roots as organs specialized for both resource acquisition and transport to overcome spatial heterogeneity in resource supply, clonal plants separate these two functions. Becoming a clonal plant allows higher specialization at the organ level, since a typical clonal plant can be viewed as a network of self-sustainable harvesting units connected together with specialized high-throughput connection organs. This may be an effective alternative for coping with spatial heterogeneity in resource availability.

Evaluating aquaponic crops in a freshwater flow-through fish culture system

This study examined the establishment and growth performance of 34 food crops grown in a cool, low nutrient aquaponic system. Process water from a spring-fed flow-through trout raceway, with an average fish biomass of 3630kg, was used as the water and nutrient source for the plant growing operation. Process water temperature entering the plant growing channels was 13°C with average concentrations of 0.35, 0.34 and 0.19mg·L−1 for ammonium, nitrate, and phosphate, respectively. Crop types included lettuce, Asian greens, mustards, other greens, vegetables and herbs. Stand establishment (percent filled cells) and harvest and individual biomass were evaluated under three treatments; low flow (18.9L/min), high flow (75.7L/min), and an amended high flow treatment. The amended high flow treatment consisted of vermiculite planting media amended with composted fish waste and was placed in a channel receiving high flow. These treatments represented a gradient of nutrient availability with low flow receiving the fewest and the amended high flow treatment receiving the most nutrients. Due to space constraints cultivars were sown in two sets. Cultivars in set two were sown as space was made available when cultivars from set one were harvested. Stand establishment was greater than 80% for most cultivars under all treatments. However, the herbs sage, garlic chives, and lovage had poor stand establishment as did the vegetables Swiss chard and beets, which were sown late in the study. For most cultivars, stand establishment was not significantly different among treatments. The majority of cultivars attained the lowest biomass on the low flow treatment. Notable exceptions were cilantro, parsley, and minutina. Eight cultivars, including kohlrabi and the bibb lettuce ‘Rex’, grew best on the high flow treatment. The remaining 21 cultivars realized the greatest biomass on the amended treatment although in many cases the increase in biomass was minor. Additionally, for some cultivars, significant increases in stand establishment offset decreases in growth. Minimal improvements in water quality were observed, probably as a result of nutrient mobilization from accumulated solids within the aquaponic channels. Statement of relevanceMany producers want to produce aquaponic crops but little basic information such as provided in this study is available about stand establishment, expected harvest biomass, or time to harvest making this study extremely relevant to commercial aquaculture.

The influence of the biological pump on ocean chemistry: implications for long-term trends in marine redox chemistry, the global carbon cycle, and marine animal ecosystems.

The net export of organic matter from the surface ocean and its respiration at depth create vertical gradients in nutrient and oxygen availability that play a primary role in structuring marine ecosystems. Changes in the properties of this ‘biological pump’ have been hypothesized to account for important shifts in marine ecosystem structure, including the Cambrian explosion. However, the influence of variation in the behavior of the biological pump on ocean biogeochemistry remains poorly quantified, preventing any detailed exploration of how changes in the biological pump over geological time may have shaped long‐term shifts in ocean chemistry, biogeochemical cycling, and ecosystem structure. Here, we use a 3‐dimensional Earth system model of intermediate complexity to quantitatively explore the effects of the biological pump on marine chemistry. We find that when respiration of sinking organic matter is efficient, due to slower sinking or higher respiration rates, anoxia tends to be more prevalent and to occur in shallower waters. Consequently, the Phanerozoic trend toward less bottom‐water anoxia in continental shelf settings can potentially be explained by a change in the spatial dynamics of nutrient cycling rather than by any change in the ocean phosphate inventory. The model results further suggest that the Phanerozoic decline in the prevalence ocean anoxia is, in part, a consequence of the evolution of larger phytoplankton, many of which produce mineralized tests. We hypothesize that the Phanerozoic trend toward greater animal abundance and metabolic demand was driven more by increased oxygen concentrations in shelf environments than by greater food (nutrient) availability. In fact, a lower‐than‐modern ocean phosphate inventory in our closed system model is unable to account for the Paleozoic prevalence of bottom‐water anoxia. Overall, these model simulations suggest that the changing spatial distribution of photosynthesis and respiration in the oceans has exerted a first‐order control on Earth system evolution across Phanerozoic time.

Integrated molecular, physiological and in silico characterization of two Halomonas isolates from industrial brine.

Two haloalkaliphilic bacteria isolated from industrial brine solutions were characterized via molecular, physiological, and in silico metabolic pathway analyses. Genomes from the organisms, designated Halomonas BC1 and BC2, were sequenced; 16S ribosomal subunit-based phylogenetic analysis revealed a high level of similarity to each other and to Halomonas meridiana. Both strains were moderate halophiles with near optimal specific growth rates (≥60% μ max) observed over <0.1-5% (w/v) NaCl and pH ranging from 7.4 to 10.2. Isolate BC1 was further characterized by measuring uptake or synthesis of compatible solutes under different growth conditions; in complex medium, uptake and accumulation of external glycine betaine was observed while ectoine was synthesized de novo in salts medium. Transcriptome analysis of isolate BC1 grown on glucose or citrate medium measured differences in glycolysis- and gluconeogenesis-based metabolisms, respectively. The annotated BC1 genome was used to build an in silico, genome-scale stoichiometric metabolic model to study catabolic energy strategies and compatible solute synthesis under gradients of oxygen and nutrient availability. The theoretical analysis identified energy metabolism challenges associated with acclimation to high salinity and high pH. The study documents central metabolism data for the industrially and scientifically important haloalkaliphile genus Halomonas.

Salmon nutrients are associated with the phylogenetic dispersion of riparian flowering‐plant assemblages

A signature of nonrandom phylogenetic community structure has been interpreted as indicating community assembly processes. Significant clustering within the phylogenetic structure of a community can be caused by habitat filtering due to low nutrient availability. Nutrient limitation in temperate Pacific coastal rainforests can be alleviated to some extent by marine nutrient subsidies introduced by migrating salmon, which leave a quantitative signature on the makeup of plant communities near spawning streams. Thus, nutrient-mediated habitat filtering could be reduced by salmon nutrients. Here, we ask how salmon abundance affects the phylogenetic structure of riparian flowering plant assemblages across 50 watersheds in the Great Bear Rainforest of British Columbia, Canada. Based on a regional pool of 60 plant species, we found that assemblages become more phylogenetically dispersed and species poor adjacent to streams with higher salmon spawning density. In contrast, increased phylogenetic clumping and species richness was seen in sites with low salmon density, with steeper slopes, further from the stream edge, and within smaller watersheds. These observations are all consistent with abiotic habitat filtering and biotic competitive exclusion acting together across local and landscape-scale gradients in nutrient availability to structure assembly of riparian flowering plants. In this case, rich salmon nutrients appear to release riparian flowering-plant assemblages from the confines of a low-nutrient habitat filter that drives phylogenetic clustering.

Recasting the dynamic equilibrium model through a functional lens: the interplay of trait‐based community assembly and climate

Summary According to the dynamic equilibrium hypothesis (DEH), plant species richness is locally controlled by productivity and disturbance. Given that regional conditions widely affect local environmental variables such as soil nutrient availability, the DEH predictions could be improved by considering how climate influences local controls of species richness. Further, a trait‐based approach to community assembly has the potential to reveal a deeper, mechanistic understanding of species richness variation across environments. Here, we bring together DEH and trait‐based community assembly expectations to examine whether and how local relationships between diversity, disturbance and productivity are affected by habitat filtering and regional climate. We specifically tested how gradients of local nutrient availability and disturbance intensity interact with climatic conditions to drive the species richness of grassland communities. Further, we recast the DEH through a functional lens by exploring how disturbance–diversity and nutrient availability–diversity relationships are shaped by the functional space occupied by species in a community and species packing within this functional space. The functional space occupied by co‐occurring species and the way they are functionally packed are quantified using multi‐trait indices calculated with five core plant functional traits. Working with grassland communities spread across differing regional climatic conditions, we used mixed models to test whether the variation in taxonomic and functional metrics corresponded to the DEH predictions as well as to determine the relationship between those metrics. Contrary to the expectations based on the relation between species richness and the functional components considered, taxonomic and functional metrics did not vary in accordance along environmental gradients. Climate strongly interacted with the local environment to modulate local diversity patterns, sometimes even inversing a given trend and falsifying the DEH predictions. Synthesis. Our findings quantitatively highlight the interplay between regional and local environmental gradients in driving community assembly. We demonstrate that, depending on climatic conditions, observed patterns of both taxonomic and functional community composition can be opposite to expected productivity–diversity and disturbance–diversity relationships. This emphasizes the relevance of multifaceted studies of biodiversity and the need for a more systematic quantification of regional controls in community assembly studies.

Phytoplankton taxonomic compositional shifts across nutrient and light gradients in temperate lakes

Nutrient and light availability, and their balance, can modify community composition and structure in pelagic communities. Previous studies have demonstrated contradictory findings about whether total phosphorus (TP) concentrations alone or the ratio of total nitrogen (TN) to TP concentrations (TN:TP) drive Cyanobacteria dominance in freshwater ecosystems, and influences of light availability are often overlooked. Here, we analyzed a 12 year, 137 lake database to test paradigms of phytoplankton compositional patterns across nutrient (TN, TP, TN:TP) and light availability gradients in an agricultural region. We hypothesized that (1) TN:TP ratios would better predict phytoplankton compositional shifts than TP concentrations alone, (2) Cyanobacteria relative abundance would increase at low TN:TP ratios, and (3) Cyanobacteria biomass fluctuations would be the primary driver of light climate. We found that TN:TP ratios better described phytoplankton compositional patterns than TP concentrations, with Cyanobacteria proportions decreasing with increasing TN:TP while other taxa increased. Contrary to expectations, Cyanobacteria always dominated community composition (≥80% biomass), regardless of TP concentrations. Despite these patterns, N-fixing Cyanobacteria proportions were not correlated to TN:TP, suggesting that shifts toward N-fixation were not solely driving phytoplankton compositional patterns. Although Cyanobacteria biomass decreased with increasing light availability, inorganic particles explained more variance in light than total phytoplankton biomass, suggesting that buoyancy-regulating Cyanobacteria may gain an initial competitive advantage in light acquisition before bloom development in turbid systems. These findings suggest that Cyanobacteria strongly influence pelagic community dynamics in nutrient-enriched lakes, and their ability to manipulate light and nutrient environments enable their persistent dominance across large environmental gradients.

Differences in disturbance type and nutrient availability favour different functional traits across three co-occurring montane wetland systems in eastern Australia

Three co-occurring temperate montane non-riparian freshwater wetland communities of the New England Batholith of eastern Australia were chosen to test differences in resource allocation to select functional traits. Each of the wetlands was tested against inferred gradients of nutrient availability, fire and disturbance frequency. Collated functional trait data on 563 native vascular plant taxa known to occur in bogs, fens and lagoons were used against a centrally weighted means redundancy analysis. Traits included life form, plant height, leaf area, fruit size, seed size, mono- or polycarpy, storage organs, fruit type, vegetative spread and geographic range size. Where disturbances were moderate to low in frequency and habitats persistent, tolerance and in-situ permanence traits were favoured. With high nutrient availability and a low disturbance regime polycarpic species with large leaves that allow for larger fruit development were more common. Under low nutrient availability and a moderate disturbance regime, persistence was shifted to a longer lived polycarpic life history that includes woody taxa with increased seed size and a greater diversity of fruit types. In frequently inundated habitats, with shifting windows of available habitats, avoidance was the best strategy. Here persistence shifts to long-lived soil stored diaspores and a monocarpic life history with rapid vegetative growth to capture above ground spatial resource within temporary habitats.

Trade‐offs in juvenile growth potential vs. shade tolerance among subtropical rain forest trees on soils of contrasting fertility

Summary Plant adaptation to gradients of light availability involves a well‐studied functional trade‐off, as does adaptation to gradients of nutrient availability. However, little is known about how these two major trade‐offs interact, and thus, it remains unclear whether and how the nature of the growth–shade tolerance trade‐off differs on soils of contrasting fertility. We asked whether juvenile growth–shade tolerance trade‐offs differed in slope and elevation between tree assemblages on nutrient‐rich basalt and nutrient‐poor rhyolite soils in an Australian subtropical rain forest. We measured the growth of, and the range of light environments occupied by, juveniles (40–120 cm tall) of eight basalt specialists, six rhyolite specialists, and one generalist that was common on both substrates. In situ minimum light requirements were estimated from the 5th percentile of the distribution of naturally regenerated juveniles in relation to daily light transmittance. Stem growth was measured for 12–16 months across a wide range of light environments to estimate the light compensation point of growth of each species. Light compensation points of growth showed nearly a 1 : 1 correspondence with in situ minimum light requirements of species, indicating that whole‐plant carbon balance is a key driver of ecological success in low light. Minimum light requirements were negatively correlated with relative growth rate in low light, but correlated positively with growth in high light. Soil type had no effect on either the slope or the elevation of this trade‐off, all species aligning around a common growth–shade tolerance trade‐off, but our results do show a wider range of growth rates and shade tolerance on the nutrient‐rich basalt soil than on the nutrient‐poor rhyolite. Our results suggest that adaptation to light availability involves fundamentally similar trade‐offs on these two substrates of differing fertility. However, a wider range of growth rates and shade tolerance on the nutrient‐rich basalt soil than on the nutrient‐poor rhyolite may help to explain the higher species richness and greater structural complexity of forest stands on the former substrate.