Gradient Of Nutrient Availability Research Articles

Deer activity levels and patterns vary along gradients of food availability and anthropogenic development

Animal activity reflects behavioral decisions that depend upon environmental context. Prior studies typically estimated activity distributions within few areas, which has limited quantitative assessment of activity changes across environmental gradients. We examined relationships between two response variables, activity level (fraction of each day spent active) and pattern (distribution of activity across a diel cycle) of white-tailed deer (Odocoileus virginianus), with four predictors—deer density, anthropogenic development, and food availability from woody twigs and agriculture. We estimated activity levels and patterns with cameras in 48 different 10.36-km2 landscapes across three larger regions. Activity levels increased with greater building density, likely due to heightened anthropogenic disturbance, but did not vary with food availability. In contrast, activity patterns responded to an interaction between twigs and agriculture, consistent with a functional response in habitat use. When agricultural land was limited, greater woody twig density was associated with reduced activity during night and evening. When agricultural land was plentiful, greater woody twig density was associated with more pronounced activity during night and evening. The region with the highest activity level also experienced the most deer-vehicle collisions. We highlight how studies of spatial variation in activity expand ecological insights on context-dependent constraints that affect wildlife behavior.

Calcareous dinoflagellate blooms during the Late Cretaceous 'greenhouse' world-a case study from western Ukraine.

The Late Cretaceous was a unique period in the history of the Earth characterized by elevated sea levels, reduced land area, and significantly high concentrations of atmospheric CO2 resulting in increased temperatures across the globe-a 'Greenhouse World'. During this period, calcareous dinoflagellate cysts (c-dinocysts) flourished and became a ubiquitous constituent of calcifying plankton around the world. An acme in calcareous dinocysts during the Albian to the Turonian coincided with the highest recorded seawater surface temperatures and was possibly linked to conditions that favored calcification and a highly oligotrophic system in European shelf seas. This study examines the potential applicability of c-dinocysts as a proxy for paleoenvironmental conditions based on their assemblage changes plotted against foraminiferal occurrences and microfacies analysis. The material was extracted from the upper Turonian chalk of the Dubivtsi region in western Ukraine. An inverse correlation was observed between species diversity and the number of c-dinocyst specimens. Nutrient availability gradients apparently determined important changes in the calcareous dinocysts distribution. These trophic changes were likely caused by the interplay of eustatic sea-level fluctuations and Subhercynian tectonic activity leading to changeable nutrient inputs from the nearby land.

Niche partitioning overrides interspecific competition to determine plant species distributions along a nutrient gradient

Changes in some combination of niche availability, niche overlap and the strength of interspecific interactions are thought to drive changes in plant composition along resource gradients. However, because these processes are difficult to measure in the field, their relative importance in driving compositional change in plant communities remains unclear. In an Australian temperate grassland, we added seeds of three native and three exotic grasses to 1875 experimental plots in a way that allowed us to simultaneously estimate niche availability, niche overlap and the strength of pairwise interspecific interactions along a gradient of nutrient availability, obtained by adding 0, 5 or 20 g m−2 each of nitrogen, phosphorous and potassium jointly to plots. Niche availability (the proportion of microsites suitable for establishment and growth) was generally low and did not vary in response to nutrient addition. Most species co‐occurred along the nutrient gradient by partitioning the available niche space. Where species interacted due to niche overlap, the abundance of one species, the native Chloris truncata, was usually facilitated by other species, with each of the five other species increasing the niche availability to C. truncata under at least one nutrient treatment. Chloris truncata also competitively excluded two species from some but not all sites they could otherwise have occupied. These outcomes did not clearly differ across nutrient treatments. Our results show that fine‐scale spatial heterogeneity in establishment microsites can enable species to co‐occur via niche partitioning, and competitive exclusion is rare. This finding contributes to an emerging picture that niche partitioning is common and frequently a stronger influence on recruitment outcomes than interspecific competition. The importance of competition in structuring plant communities may be overestimated if recruitment processes are overlooked.

Phosphate adsorption by riverborne clay sediments in a southern-Italy Mediterranean reservoir: Insights from a “natural geo-engineering” experiment

This paper reports data from a southern-Italy reservoir (Lake Occhito) characterized by a strong riverborne sediment transport. Main hydrochemical, trophic, and nutrient variables were measured (over a twelve-month period) in both lake and tributaries. Lacustrine sediments were subjected to mineralogical characterization and to phosphorus fractioning, while a 6-day long batch experiment was carried out to evaluate the lake sediment orthophosphate adsorption capacity. A set of algal growth potential tests was also undertaken on the lake and its tributaries. Results highlight the presence of a strong gradient in nutrient availability among the inflows. Most of the nutrient loads were from the main tributary (20.3 t P a−1, ~83 %), that showed the highest trophic potential (average: 56.8 mg L−1) and was nitrogen/phosphorus co-limited. The other inflows were phosphorus limited and characterized by a higher sediment transport. The lake showed the lowest nutrient concentrations (average total phosphorus: 21 μg P L−1) and was strongly phosphorus limited. Clays were the principal minerals in the lake sediments (~51 %), while the main phosphorus fraction was apatite (~78 %). The batch experiment demonstrated the capability of the lake sediments to reduce orthophosphate concentrations in phosphorus-rich waters (initial orthophosphate: 320 μg P L−1; ~80 % reduction). The lake sediment orthophosphate kinetics of abatement was similar to that of a commercially available phosphorus sorbent (lanthanum modified bentonite), although the stability of phosphorus binding was higher for the commercial product. Theoretical average in-lake total phosphorus, chlorophyll-a, and transparency values, estimated through Vollenweider models, were approximately double of the average values measured in the lake. Therefore, the massive presence of riverborne clay sediments seems to markedly reduce the in-lake orthophosphate concentrations (and light penetration), inducing an overall lowering of the lake trophic state, as if the lake ecosystem were permanently subjected to a geo-engineering phosphorus sorbent treatment.

Impacts of nutrient addition on soil carbon and nitrogen stoichiometry and stability in globally-distributed grasslands

Global changes will modify future nutrient availability with implications for grassland biogeochemistry. Soil organic matter (SOM) is central to grasslands for both provision of nutrients and climate mitigation through carbon (C) storage. While we know that C and nitrogen (N) in SOM can be influenced by greater nutrient availability, we lack understanding of nutrient effects on C and N coupling and stability in soil. Different SOM fractions have different functional relevance and mean residence times, i.e., mineral-associated organic matter (MAOM) has a higher mean residence time than particulate organic matter (POM). By separating effects of nutrient supply on the different SOM fractions, we can better evaluate changes in soil C and N coupling and stability and associated mechanisms. To this end, we studied responses of C and N ratios and distributions across POM and MAOM to 6–10 years of N, phosphorus (P), potassium and micronutrients (K+µ), and combined NPK+µ additions at 11 grassland sites spanning 3 continents and globally relevant environmental gradients in climate, plant growth, soil texture, and nutrient availability. We found addition of N and NPK+µ generally reduced C:N in MAOM and POM. However, at low fertility and at warm, sandy sites, nutrient addition promoted higher MAOM and POM C:N, respectively. Addition of NPK+µ also promoted C storage in POM relative to MAOM, and this was consistent across sites. Our results suggest that addition of macro- and micronutrients consistently decrease SOM stabilization, whereas responses of soil C:N stoichiometry were contingent on SOM fraction and environmental conditions.

Changes in forest nitrogen cycling across deposition gradient revealed by δ15N in tree rings

Tree rings provide valuable insight into past environmental changes. This study aimed to evaluate perturbations in tree ring width (TRW) and δ15N alongside soil acidity and nutrient availability gradients caused by the contrasting legacy of air pollution (nitrogen [N] and sulphur [S] deposition) and tree species (European beech, Silver fir and Norway spruce). We found consistent declines of tree ring δ15N, which were temporarily unrelated to the changes in the TRW. The rate of δ15N change in tree rings was related to the contemporary foliar carbon (C) to phosphorus (P) ratio. This observation suggested that the long-term accumulation of 15N depleted N in tree rings, likely mediated by retained N from deposition, was restricted primarily to stands with currently higher P availability. The shifts observed in tree-ring δ15N and TRW suggest that acidic air pollution rather than changes in stand productivity determined alteration of N and C cycles. Stable N isotopes in tree rings provided helpful information on the trajectory of the N cycle over the last century with direct consequences for a better understanding of future interactions among N, P and C cycles in terrestrial ecosystems.

Soil fertility and water availability effects on trait dispersion and phylogenetic relatedness of tropical terrestrial ferns.

Analysis of plant functional traits and their phylogenetic relationships has shed light on the processes structuring the occurrence patterns of angiosperm taxa across environmental gradients. In montane tropical forests, angiosperms coexist with diverse communities of terrestrial ferns, with distinct evolutionary histories, leaf morphology, and reproductive systems. Here we examined the functional traits, functional dispersion, and phylogenetic diversity of ferns across a well-described gradient of moisture and soil nutrient availability in a premontane tropical rainforest in western Panama. We measured 15 functional traits from 33 terrestrial fern species occurring in 12 one-ha plots. We applied RLQ and fourth-corner analyses to assess relationships between trait and environmental variables and used beta regression to evaluate how functional dispersion responds to environmental factors. In addition, we analyzed trait distributions with respect to fern phylogeny. We found that functional composition was predicted by soil variables and dry season rainfall. Leaf phosphorus (P) increased and leaf carbon (C) to nitrogen (N) ratio decreased with increasing soil total N:P ratio. Functional dispersion decreased with increasing soil total N:P in wet sites and with increasing manganese in dry sites, suggesting that low soil fertility and dry season moisture stress both tend to reduce functional diversity. Traits exhibited phylogenetic clustering primarily at deep nodes associated with tree versus herbaceous fern clades. Our results indicate that environmental filtering of functional traits affects ferns in a similar way to angiosperms and highlight the association of the early tree fern clade with low fertility soils.

Abstract P1-05-07: Spatially-resolved single-cell tumor heterogeneity captured by TumorScope biophysical modeling software using MR Imaging

Abstract Background: Dysregulated cellular metabolism is a hallmark of breast cancer, and targeting it has promising implications for improving care and patient outcomes. Specifically, heterogeneity in tumor metabolism is thought to play a role in determining chemotherapy response, the development of resistance, and promoting metastastasis. Despite this, metabolic tumor heterogeneity for individual breast cancer patients has not been characterized completely. Methods: In this study, we used state-of-the-art techniques to characterize metabolic heterogeneity within individual patient tumors by integrating single cell RNA-seq data with genome-scale metabolic modeling. Using SimBioSys’ TumorScope - a commercially available biophysical modeling platform, we compared intra-tumoral metabolic heterogeneity from experimental single cell RNA-seq data to simulated intra tumoral heterogeneity. Results: Using single cell RNA-seq data, we found that intra-tumoral gradients in nutrient availability are widely present within patient tumors (for a single luminal A patient, glucose import flux ranged from 0.19 - 1.25 g/gDW/day, while glutathione import ranged from 0.004 - 0.054 g/gDW/day). We also found that these gradients lead to cellular growth rate gradients within individual tumors (for our representative patient, median SGR = 0.62 %/day +/- 0.33 %/day stdev). Using TumorScope, we found this same gradient behavior within patient tumors. Selecting a similarly growing luminal A patient from our TumorScope simulations resulted in gradients in glucose import (range = 0.17 - 1.26 g/gDW/day), glutathione import (range = 0.024 - 0.058 g/gDW/day), and tumor SGR (median = 0.40 %/day, stdev = 0.42 %/day), which closely match metabolism from single cells (comparing maximum-scaled SGR distributions between single cells and TumorScope yielded a p-value = 0.10). We next examined which nutrients govern heterogeneity in tumor SGR. We found that glucose availability with the tumor microenvironment is more limiting to cell growth than oxygen availability, and this result was consistent between metabolic profiles from both single cell RNA-seq data and TumorScope simulations. TumorScope’s spatially resolved simulations offered the additional insight that gradients in nutrient availability are caused by heterogeneity in the distribution of macro- and micro-vasculature and the composition of the tumor microenvironment. We then used data reduction techniques to compare populations of single cells with differing metabolic phenotypes to identify molecular behavior at the single cells in higher molecular resolution. We found that single cells collected from the clinic co-cluster with single cells from TumorScope simulations, suggesting that a significant amount of intra-tumoral metabolic heterogeneity observed in patients is captured by TumorScope simulations. Conclusion: Accessing tumor heterogeneity has traditionally required specialized equipment, analytic expertise, and invasive procedures, largely limiting its study to large, academic hospitals. Currently, metabolic heterogeneity is only understood in 2D and for few markers (using pathology slides) or in relatively few cells with little or no spatial resolution (for single cell RNA-seq). TumorScope provides a novel approach to simulate metabolic heterogeneity at the single cell scale in 3D across a whole tumor. TumorScope democratizes the study of tumor heterogeneity by making it accessible to clinicians and researchers from MRI data alone. TumorScope has the capability to capture tumor metabolic heterogeneity at a higher scale than previously achievable which will allow for a dramatic increase in our understanding of tumor biology and ultimately improve clinical decision making. Citation Format: Daniel J Cook, John Whitman, Nicole Liadis, John Cole. Spatially-resolved single-cell tumor heterogeneity captured by TumorScope biophysical modeling software using MR Imaging [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-05-07.

Silicon mobilisation by root-released carboxylates.

Plants have evolved numerous strategies to acquire poorly available nutrients from soil, including the release of carboxylates from their roots. Silicon (Si) release from mineral dissolution increases in the presence of chelating substances, and recent evidence shows that leaf [Si] increases markedly in old phosphorus (P)-depleted soils, where many species exhibit carboxylate-releasing strategies, compared with younger P-richer soils. Here, we propose that root-released carboxylates, and more generally rhizosphere processes, play an overlooked role in plant Si accumulation by increasing soil Si mobilisation from minerals. We suggest that Si mobilisation is costly in terms of carbon but becomes cheaper if those costs are already met to acquire poorly available P. Uptake of the mobilised Si by roots will then depend on whether they express Si transporters.

Mycorrhizal status is a poor predictor of the distribution of herbaceous species along the gradient of soil nutrient availability in coastal and grassland habitats.

Plant mycorrhizal status (a trait indicating the ability to form mycorrhizas) can be a useful plant trait for predicting changes in vegetation influenced by increased fertility. Mycorrhizal fungi enhance nutrient uptake and are expected to provide a competitive advantage for plants growing in nutrient-poor soils; while in nutrient-rich soils, mycorrhizal symbiosis may be disadvantageous. Some studies in natural systems have shown that mycorrhizal plants can be more frequent in P and N-poor soils (low nutrient availability) or Ca and Mg-high (high pH) soils, but empirical support is still not clear. Using vegetation and soil data from Scottish coastal habitats, and Latvian and Czech grasslands, we examined whether there is a link between plant mycorrhizal status and plant-available P, N, Ca and Mg. We performed the max test analysis (to examine the central tendency) and a combination of quantile regression and meta-analysis (to examine tendencies in different quantiles) on both community and plant species data combined with plant phylogenies. We consistently found no changes in mycorrhizal status at the community and species levels along the gradients of plant-available P, N, Ca and Mg in the central tendency and in almost all quantiles across all datasets. Thus, we found no support for the hypotheses that herbaceous species which are able to form mycorrhizas are more frequent in nutrient-poor and high pH environments. Obligatory, facultatively and non-mycorrhizal herbaceous species appear to assemble randomly along the gradients of nutrient availability in several European herbaceous habitats, suggesting that all these strategies perform similarly under non-extreme soil nutrient conditions.

Fine root production in a chronosequence of mature reforested mangroves.

Mangroves are among the world's most carbon-dense ecosystems, but have suffered extensive deforestation, prompting reforestation projects. The effects of mangrove reforestation on belowground carbon dynamics are poorly understood. In particular, we do not know how fine root production develops following mangrove reforestation, despite fine root production being a major carbon sink and an important control of mangrove soil accretion. Using minirhizotrons, we investigated fine root production and its depth variation along a chronosequence of mature Vietnamese mangroves. Our results showed that fine root production decreases strongly with stand age in the uppermost 32cm of our soil profiles. In younger mangrove stands, fine root production declines with depth, possibly due to a vertical gradient in soil nutrient availability; while root production in the oldest stand is low at all depths and exhibits no clear vertical pattern. A major fraction of fine root production occurs deeper than 30cm, depths that are commonly omitted from calculations of mangrove carbon budgets. Younger mangroves may accrue shallow soil organic matter faster than older mangroves. Therefore, root productivity and forest stand age should be accounted for when forecasting mangrove carbon budgets and resistance to sea-level rise.

Resolving whole‐plant economics from leaf, stem and root traits of 1467 Amazonian tree species

It remains unclear how evolutionary and ecological processes have shaped the wide variety of plant life strategies, especially in highly diverse ecosystems like tropical forests. Some evidence suggests that species have diversified across a gradient of ecological strategies, with different plant tissues converging to optimize resource use across environmental gradients. Alternative hypotheses propose that species have diversified following independent selection on different tissues, resulting in a decoupling of trait syndromes across organs. To shed light on the subject, we assembled an unprecedented dataset combining 19 leaf, stem and root traits for 1467 tropical tree species inventoried across 71 0.1‐ha plots spanning broad environmental gradients in French Guiana. Nearly 50% of the overall functional heterogeneity was expressed along four orthogonal dimensions, after accounting for phylogenetic dependences among species. The first dimension related to fine root functioning, while the second and third dimensions depicted two decoupled leaf economics spectra, and the fourth dimension encompassed a wood economics spectrum. Traits involved in orthogonal functional strategies, five leaf traits in particular but also trunk bark thickness, were consistently associated with a same gradient of soil texture and nutrient availability. Root traits did not show any significant association with edaphic variation, possibly because of the prevailing influence of other factors (mycorrhizal symbiosis, phylogenetic constraints). Our study emphasises the existence of multiple functional dimensions that allow tropical tree species to optimize their performance in a given environment, bringing new insights into the debate around the presence of a whole plant economic spectrum in tropical forest tree communities. It also emphasizes the key role that soil heterogeneity plays in shaping tree species assembly. The extent to which different organs are decoupled and respond to environmental gradients may also help to improve our predictions of species distribution changes in responses to habitat modification and environmental changes.

Nutrient‐use strategy and not competition determines native and invasive species response to changes in soil nutrient availability

Non‐native invasive plants often outcompete native species under high resource availability. Restoration techniques that lower resources may, therefore, create favorable conditions for resource conservative native species over resource exploitative invasive species. Research on this topic has focused on temperate grass and forb‐dominated ecosystems and has rarely been tested for woody species or tropical vegetation. We evaluated growth, resource‐use efficiency (RUE), ecophysiology, and competition (i.e. a relative interaction index based on biomass) of four woody native and two dominant invasive species from Hawaiian wet and dry tropical ecosystems in a greenhouse experiment. Density of plants was constant and species were grown with either a conspecific or the invasive species from that ecosystem type across a gradient of soil nutrient availability. Instantaneous photosynthetic rates varied minimally across nutrient availability. However, both invasive and one native species increased leaf area as nutrients increased, providing more photosynthetic area and increasing total biomass. Nitrogen RUE decreased with increasing nutrient availability for all but one native species, while phosphorus RUE remained constant for all but one native species. Competitive interactions were weak, variable, and not significantly impacted by soil nutrients. Overall, plants categorized as invasive or resource exploitative had larger changes in response variables with increasing soil nutrients compared to those categorized as native or resource conservative. These results suggest that manipulating soil nutrient availability is a potentially viable restoration tool for at least some woody species in tropical ecosystems. However, predicting restoration success requires understanding species‐specific ecophysiological traits determining response to altered environmental conditions.

A comparison of the functional traits of Phragmites australis in Lake Burullus (a Ramsar site in Egypt): Young vs. old populations over the nutrient availability gradient

This research was performed in order to compare the functional traits (morphology, density and biomass) of Phragmites australis (common reed): young vs. old populations which were analyzed along nutrient availability gradient in Lake Burullus (Egypt) every month for a year. The samples were gathered from six sites distributed equally along the northern and southern parts of this lake. The present study indicated that, water N, P, Ca and Mg concentrations of the southern sites were higher than those of the northern sites. Shoot height, stem diameter, number of leaves, flowering ratio, leaf area, and leaf area index (LAI) were significantly lower in young populations compared with old populations. However, shoot density was significantly higher in young populations compared with old populations. The above-ground biomass increased from February until it reached its maximum during August and then decreased again, while a decrease in below-ground biomass in spring to support the rapid shoot growth, followed by an increase in summer due to the shoot translocations in the reverse direction was indicated. The CR (common reed) exhibited a slower relative growth rate (RGR) during cooler months, September–December, while highest RGR was achieved during spring months, March–May. In Lake Burullus the results from this field work indicated that shoot height, stem diameter, number of leaves, flowering ratio, leaf area, LAI, and biomass of CR increased with increasing nutrients along north-south direction in Lake Burullus, where lake eutrophication influenced CR growth positively. Thus, the theory that the biomass and morphology of this macrophyte is determined by the water trophic content is reinforced. The collection of this data is valuable to further comprehend the growth cycle of CR and to contribute to the future management and utilization of CR in the Egyptian wetlands.

Nutrient resource availability mediates niche differentiation and temporal co-occurrence of soil bacterial communities

Nutrient resource availability is a crucial environmental factor in determining soil bacterial community assembly. However, the effects of nutrient availability on niche differentiation and temporal co-occurrence patterns of bacterial communities remain elusive. Here, we retrieved sequencing datasets (105 amplicon samples of bacterial 16S rRNA genes and 60 bacterial metagenomic samples) from a laboratory incubation experiment and a coastal wetland study, to elucidate the effects of nutrient availability on niche differentiation and co-occurrence patterns of bacterial communities. Niche differentiation within bacterial communities, indicated by nearest taxon index and niche breadth of bacterial communities, did not significantly correlate with nutrient availability gradients in either environment, even though deterministic processes dominated bacterial community assembly. Network analyses revealed that co-occurrence patterns of bacterial OTUs over incubation time changed across nutrient availability gradients, and were likely to be mediated by environmental selection. There were more co-occurrences of metabolic genes under higher nutrient levels. This study revealed the non-significant correlation between nutrient availability gradients and niche differentiation within bacterial communities, not only in a natural environment but also in a laboratory modified environment where the nutrient availability gradient was the sole environmental variable. These findings boost the understanding of bacterial community assembly along environmental nutrient availability gradients.

Microfluidics for Single-Cell Study of Antibiotic Tolerance and Persistence Induced by Nutrient Limitation.

Nutrient limitation is one of the most common triggers of antibiotic tolerance and persistence. Here, we present two microfluidic setups to study how spatial and temporal variation in nutrient availability lead to increased survival of bacteria to antibiotics. The first setup is designed to mimic the growth dynamics of bacteria in spatially structured populations (e.g., biofilms) and can be used to study how spatial gradients in nutrient availability, created by the collective metabolic activity of a population, increase antibiotic tolerance. The second setup captures the dynamics of feast-and-famine cycles that bacteria recurrently encounter in nature, and can be used to study how phenotypic heterogeneity in growth resumption after starvation increases survival of clonal bacterial populations. In both setups, the growth rates and metabolic activity of bacteria can be measured at the single-cell level. This is useful to build a mechanistic understanding of how spatiotemporal variation in nutrient availability triggers bacteria to enter phenotypic states that increase their tolerance to antibiotics.

Diatom communities differ among Antarctic moss and lichen vegetation types

AbstractContinental Antarctica is a polar desert containing sparse pockets of vegetation within ice-free areas. Despite the recognized association between lichens, mosses and epiphytic diatoms, the environmental factors controlling diatom community structure are poorly understood. We investigated the association between diatom communities and host vegetation characteristics by experimentally adding nutrients and/or water to two bryophyte (healthy and moribund) and two lichen (crustose andUsnea) vegetation types in the Windmill Islands. Diatom communities were morphologically characterized, diversity indices calculated and differences between treatments, vegetation type and vegetation characteristics tested. We identified 49 diatom taxa, 8 of which occurred with > 1% relative abundance. Bryophyte and lichen vegetation harboured significantly different diatom communities, both in composition and diversity indices. Specifically,Luticola muticopsiswas more prevalent in moribund bryophytes and crustose lichens, andUsnealichens showed lower species richness than other types. While nutrient and water additions did not significantly alter diatom communities, diversity indices and some species showed relationships with vegetation physiological characteristics, notably %N and δ13C, suggesting the importance of ambient gradients in water and nutrient availability. Collectively, this work suggests that future conditions favouring the dominance of a particular vegetation type may have a homogenizing effect on the terrestrial diatom communities of East Antarctica.

Compositional variation in understorey fern and palm communities along a soil fertility and rainfall gradient in a lower montane tropical forest

AbstractQuestionsFerns and palms are key components of tropical wet forest understories. The distributions of these groups are influenced by variation in rainfall and soil properties, although the degree to which their resource requirements overlap remains unclear. Palms and ferns also represent extremes in a spectrum of reproductive traits, which may impact habitat requirements and compositional turnover. We asked whether: (a) environmental variables influence fern and palm distributions in a similar manner across a gradient in soil nutrient availability; and (b) larger propagule size and lower reproductive output in palms result in greater spatial aggregation of populations and, consequently, greater distance–decay rates in community similarity in palms than ferns.LocationOld‐growth premontane forest, Fortuna, western Panama.MethodsAll ferns and palms were sampled in fifteen 5 m × 5 m subplots in each of 12 one‐hectare plots. The plots span a strong gradient in soil nutrient availability related to parent material. Light, precipitation and soil variables were measured in each subplot. Species associations were analyzed using ordination and regression, as well as Procrustes and Mantel tests.ResultsParent material significantly impacted compositional similarity of both ferns and palms, with fern compositional variation related to total soil N:P ratio and red:far red (R:FR), and palms with bulk density (p < 0.05). Palm and fern abundances were not correlated; however, tree fern abundances showed an opposing abundance relationship with total soil N:P and R:FR compared to herbaceous ferns and palms. Distance–decay rates in compositional similarity were slightly higher for palms than ferns.ConclusionsFerns and palms show similar patterns of compositional variation in response to resource availability but were related to distinct environmental factors. Soil fertility and light availability emerged as key factors in predicting the abundance of plant groups, with clear partitioning of environmental gradients only apparent when tree ferns were compared with other groups.

Understanding stoichiometric mechanisms of nutrient retention in wetland macrophytes: stoichiometric homeostasis along a nutrient gradient in a subtropical wetland

Nutrient homeostasis relates ambient stoichiometric conditions in an environment to the stoichiometry of living entities of that ecosystem. Plant nutrient sequestration in wetland ecosystems is a key process for downstream water quality. However, few studies have examined stoichiometric homeostasis of aquatic vegetation despite the importance of stoichiometry to plant nutrient uptake efficiency. This study investigated stoichiometric homeostasis of dominant emergent and submerged aquatic vegetation (EAV and SAV, respectively) within two treatment flow-ways of Everglades Stormwater Treatment Area 2 (STA-2). These flow-ways encompass a large gradient in plant nutrient availability. This study hypothesizes that wetland vegetation is homeostatic relative to ambient nutrients and consequently nutrient resorption does not vary along the nutrient gradient. We developed a framework to investigate how vegetation uptake and resorption of nutrients contribute separately to homeostasis. Overall, we determined that the wetland vegetation in this study was non-homeostatic with respect to differential uptake of nitrogen (N) versus phosphorus (P). In EAV, P resorption was relatively high and N resorption was moderate, and resorption efficiency did not vary significantly along the gradient. In separating the proportional contribution of resorption and uptake to the degree of homeostasis, resorption did not affect overall homeostatic status in EAV.

Salty, mild, and low plant biomass grasslands increase top‐heaviness of invertebrate trophic pyramids

AbstractAimMultiple hypotheses predict how gradients of nutrient availability, plant biomass, and temperature shape trophic pyramids. We aim to disentangle the simultaneous influence of those factors and their indirect effects on trophic structure and individual trophic levels.LocationUnited States.Time period2017.Major taxa studiedInvertebrates.MethodsTo examine differences in trophic pyramid shape and abundance within trophic levels and across ecological gradients, we conducted 54 standardized surveys of invertebrate communities in North American grasslands. We tested for the direct and indirect effects of plant biomass, temperature, sodium (Na), other essential elements (e.g. N, P, and K), and toxic heavy metals, (e.g. Ar and Pb) in plant tissue on both individual trophic levels, and trophic pyramid shape, estimated as the community trophic mean (CTM).ResultsPlant sodium increased CTM, indicating that high plant sodium concentrations are associated with top‐heavy invertebrate trophic pyramids. Sites with higher plant biomass had higher proportions of herbivores compared to higher trophic levels. Finally, increasing temperature resulted in more top‐heavy trophic pyramids. Overall, plant biomass, temperature, and plant chemistry directly and indirectly affected the abundances within different trophic levels, highlighting the complexity of factors regulating trophic structure.Main conclusionsTrophic structure of grassland invertebrate communities is strongly influenced by plant sodium, plant biomass, and to a lesser extent, temperature. Grasslands occupy 30% of the Earth’s terrestrial surface and are an imperiled ecosystem due to conversion to row crop agriculture. As biogeochemistry and temperature in the Anthropocene are increasingly modified, our results have considerable implications for the trophic structure of future grassland communities.