Resource Uptake Research Articles

Divergence of functional traits at early stages of development in Stipa tenacissima populations distributed along an environmental gradient of the Mediterranean

Assessing differences in plant functional traits (PFTs) along climatic gradients is potentially useful for understanding variation within and across populations, and for predicting their responses to climate change. This study investigates the intraspecific variability of several PFTs in Stipa tenacissima (Alpha grass) seedlings from different populations distributed across a climatic gradient. Seven populations from Tunisia to Spain within a 100–600 mm/year rainfall range were selected. Seedlings from each population were grown in a common garden. We expected the functional characteristics to differ among seedling populations according to their climatic gradient. The response patterns were helpful to predict acclimation and fitness under future climatic conditions in these populations. The seedling development analysis showed differences in PFTs among S. tenacissima populations. The biomass traits analysis revealed that higher above-ground biomass was related to higher below-ground development. The leaf traits proved that seedlings with longer leaf length would have less sclerophyllous leaves, a trade-off between productivity and drought resistance. The root traits analysis reflects seedling strategies to maximize resource uptake efficiency. PFTs showed several significant relationships with climatic conditions. The less rainfall, the higher plant allocation to root systems exploring soil. Higher mean temperatures were related to reduced root/plant development. The PFT analysis proves that species followed the ‘optimal partitioning theory’, in that plants preferentially allocate biomass to acquire the resource that most limits their development. However, both the environmental conditions and genetic diversity in S. tenacissima populations influenced seedling growth and behaviour to face ongoing climate change.

Ecologically distinct pine species show differential root development after outplanting in response to nursery nutrient cultivation

The capacity to rapidly expand root systems to increase soil foraging is key for the survival of tree seedlings in arid regions. Plants alter root growth dynamics and architecture in response to environmental changes and this plasticity in root development allows plants to maximize soil resource uptake. However, how variation in plant physiological status, such as nutrient content, affects root growth dynamics and architecture is poorly understood. We assessed how variation in seedling nutrient status affects root growth dynamics and architecture in three closely related, yet ecologically distinct pine species: Pinus nigra J.F. Arnold, Pinus pinaster Ait., and Pinus pinea L. Seedlings were cultivated under contrasting fertilization regimes to promote different levels of mineral nutrient content. Seedlings were then transplanted into rhizotrons to evaluate root growth dynamics and architecture over 10 weeks. Overall, increased seedling nutrient content enhanced root development, but species showed distinct root growth patterns and architecture. Pinus pinaster, which inhabits moderate climatic stress environments, showed the greatest root growth plasticity with variation in seedling nutrient content. In contrast, root development was less plastic in the pines adapted to more stressful environments, P. pinea, which occurs in sites with long and strong summer drought and P. nigra, which inhabits cold winter areas. High nutrient-content seedlings developed larger root systems by maintaining a greater number of growing roots rather than by increasing the elongation rate of individual roots, reflecting a strategy that likely improves soil foraging capacity. Nitrogen use efficiency for root growth (new root growth per unit of plant nitrogen content at planting) increased with increasing nutrient content in P. pinaster, yet the opposite effect occurred in the other two species. New roots of high nutrient-content seedlings had lower specific root length than low content seedlings in all species, suggesting that internal seedling nutrient status determines specific root length. The means by which increased seedling nutrient content affects root development after transplanting in pine species seems to be related to species ecology and stress resistance physiology. With a surplus of mineral nutrients during nursery cultivation, pine species from high stressful environments have low flexibility in modifying root development, while species from moderate climatic stress environments prioritize root development.

Invasive knotweed has greater nitrogen-use efficiency than native plants: evidence from a 15N pulse-chasing experiment.

Habitats with fluctuating resource conditions pose specific challenges to plants, and they often favor a small subset of species that includes exotic invaders. These species must possess a superior ability to capitalize on resource pulses through faster resource uptake or greater resource-use efficiency. We addressed this question in an experiment with invasive knotweed, a noxious invader of temperate ecosystems that is known to benefit from nutrient fluctuations. We used stable isotopes to track the uptake and use efficiency of a nitrogen pulse in competition pairs between knotweed and five native competitors. We found that nitrogen pulses indeed promoted knotweed invasion and that this is explained by a superior efficiency in turning the taken-up extra nitrogen into biomass, rather than capturing an overproportional share of the nitrogen. Thus, temporary increases in nutrient availability might help knotweed to invade natural environments, such as river banks or nitrogen-polluted margins and wastelands, where nutrient fluctuations occur. Our experiment shows that resource-use efficiency can drive invasion under fluctuating resource conditions, and that stable isotopes help to understand these processes.

Phenological responses to climate change in communities of plants species with contrasting functional strategies

Understanding why co-occurring plant species show differential phenological sensitivities to climate fluctuations, and more specifically to the joint variation in temperature and precipitation, is critical to make accurate predictions on how climate change could alter community dynamics and ecosystem functioning. However, the role that some relevant functional traits involved in resource uptake and/or stress tolerance could play on these inter-specific differences in phenological sensitivity remains largely unknown. In this study we evaluated experimentally how five co-occurring herbaceous species with contrasting functional strategies respond to current and ongoing climatic scenarios of increased temperature, decreased water availability and both abiotic changes acting interactively. To decompose the direct effect of climate change and the indirect effect of neighbors on plant performance and reproductive phenology, each of the five species was exposed to a density gradient of competitor species. Although the study species were more sensitive to changes in temperature than in water availability, the combined effect of both abiotic cues triggered very heterogeneous responses. Species with higher SLA values were particularly sensitive to climate change, delaying their reproduction and lengthening their flowering period under warmer scenarios while maintaining a high plant growth rate. In contrast, the species with the lowest SLA values exhibited less phenological variability to climate alterations, but they were more strongly affected by neighbor density compared to species with opposite trait values. These species-specific responses to climatic shifts altered the synchrony of phenological events at the community level. The most important changes appeared under the two scenarios of increased temperature, where 4 out of 5 species overlapped their flowering periods. Our findings indicate that the ongoing scenarios of increasing temperature and aridity could disrupt the phenological asynchrony within communities, and highlight the necessity of considering the interactive effects of temperature and precipitation to obtain an overall picture of climate change predictions on plant phenology and population dynamics.

Conservative allocation strategy of multiple nutrients among major plant organs: From species to community

Abstract Nutrient allocation is an important aspect of plant resource uptake and use, which is related to life‐history strategies. Although to date considerable attention has focused on plant allocation of nitrogen and phosphorus, comparatively little information is available on the allocation of various other nutrients and their up‐scaling from the species to community level. We measured 10 nutrient elements in the leaves, branches and fine roots of 551 plant species growing in eight forest ecosystems in China, ranging from cold temperate to subtropical forests. We estimated the scaling relationship of multiple nutrients among plant organs at the species level and scaled‐up the relationship to the community level by combining this information with that of community structure. Nutrient allocation among plant organs was conserved in different functional groups and biomes across broad environmental gradients. Nutrient partitioning between organs with similar function tended to be isometric, whereas partitioning between organs with distinct functions tended to be allometric. The scaling relationship between above‐ and below‐ground organs remained consistent, whereas the scaling relationship within above‐ground organs changed after scaling up from the species to the community level, with the relative change in nutrients being consistently smaller in the more active organs. Synthesis. The pattern of multiple nutrient allocation among organs showed a degree of conservatism across plant functional groups and biomes, with disproportional changes in nutrient content between functionally distinct organs and a lower relative change in more active organs. This conservative strategy implies the existence of general rules that constrain plant nutrient allocation.

Inter‐specific differences in invader and native fish functional responses illustrate neutral effects on prey but superior invader competitive ability

AbstractInter‐specific interactions are key factors in the structuring and functioning of ecological communities. Therefore, it is necessary to assess species interactions, such as predator–prey dynamics and competitive exclusion, within the context of continuing global species introductions. The aim of the present study was to assess ecological impacts and competitive exclusion dynamics involving co‐occurring introduced and native fish species, using the multiple predator functional response (FR) approach.We use comparative FR analysis (resource uptake as a function of resource density) to assess inter‐specific interactions between the invasive western mosquitofishGambusia affinisand the native freshwater river gobyGlossogobius callidustowards chironomid larvae. The FR was derived for each fish species as individuals and when in heterospecific pairings. Data from single individuals were used to predict the expected FR of individuals when in heterospecific multiple predator combinations. Expected FRs were then compared to the observed FRs of each predator in combination trials, enumerated using prey items in their gut contents.Both fish species displayed TypeIIFRs, however, in single fish trials, invasive mosquitofish had significantly higher FRs (curve asymptotes; i.e. shorter handling times and higher maximum feeding rates) than native river gobies. Heterospecific mosquitofish‐river goby combinations revealed that the FR of the river goby was reduced (i.e. longer handling times and lower maximum feeding rates) by the presence of mosquitofish, whereas this combination greatly enhanced mosquitofish FR magnitudes (i.e. shorter handling times and higher maximum feeding rates). The heterospecific treatments resulted in neutral impacts on prey and there were clear inter‐species interference in favour of the non‐native mosquitofish.This study demonstrates how multiple predators can alter the shape of individualFRs, with neutral effects on prey but superior invader competitive ability. This has implications for predicting the naturalisation success of invasive predators, as predatory and competitive interactions with native predators and prey may facilitate rather than impede establishment.

Effects of morphology and stand structure on root biomass and length differed between absorptive and transport roots in temperate trees

Absorptive and transport roots (diameter ≤ 2 mm) are closely related to soil resource uptake for plant growth, carbon budget and nutrient cycling in forest ecosystems, but how and why the relative share of root biomass or root length for both root functional types changes with tree species is not well understood. Our aims were to examine the inter-specific variations of root biomass and length per unit area of absorptive and transport roots, and their relationships with stand structure and soil characteristics, root morphological and architectural traits. We measured root biomass and length per unit area, diameter, specific root length (SRL), root tissue density (RTD), and branching ratio of the first five order roots, stand and soil characteristics in seven forests consisting of different tree species at a common site. The first order roots were classified as absorptive roots and the other orders as transport roots based on our earlier work. Biomass ratios of absorptive to transport roots varied from 1:5.56 to 1:1.12 among species, and length ratios ranged from 1:1.56 to 1:0.29. Root biomass was not influenced by root morphology or architecture, nor by stand or soil characteristics. Absorptive root length was significantly correlated with SRL, RTD, and branching ratio of the first to second order roots among species, whereas transport root length was significantly correlated with stem density. The relative share of biomass and length for absorptive and transport roots differed among tree species, which may influence belowground carbon allocation and resource competition.

Spatial Distribution of Roots across Three Dryland Ecosystems and Plant Functional Types

Roots play a critical role in carbon storage, carbon cycling, and resource acquisition in dryland ecosystems, yet their distribution and production patterns are poorly understood. We aimed to compare the vertical and horizontal distribution of roots of the dominant plant functional types across 3 dryland ecosystems in the western Great Plains of the United States. We collected consecutive soil cores from directly under plants to 29 cm away from the center of plant individuals (horizontal plane), to a 20-cm depth (vertical plane). Across the 3 ecosystem types, grass root biomass decreased with depth and, for the sagebrush steppe, at a distance beyond 6.5 cm from the center of the plant. At the 10–20 cm depth increment, there was no horizontal pattern in root biomass. Uniformity in root biomass in the 10–20 cm depth and at distances >6.5 cm from the plant center is best explained by the overlap of roots of individual and neighboring plants to maximize belowground resource uptake. There was much lower root biomass in the surface 20 cm adjacent to shrubs than adjacent to grasses in the sagebrush steppe, and while grass root biomass decreased significantly with depth and distance as described above, shrub roots were uniform in both planes. Our study confirms that root distribution in drylands differs among plant functional types, with grasses exploiting surface soils both horizontally and vertically to capitalize on surface resources, and shrubs capitalizing less on those resources.

A few Ascomycota taxa dominate soil fungal communities worldwide

Despite having key functions in terrestrial ecosystems, information on the dominant soil fungi and their ecological preferences at the global scale is lacking. To fill this knowledge gap, we surveyed 235 soils from across the globe. Our findings indicate that 83 phylotypes (<0.1% of the retrieved fungi), mostly belonging to wind dispersed, generalist Ascomycota, dominate soils globally. We identify patterns and ecological drivers of dominant soil fungal taxa occurrence, and present a map of their distribution in soils worldwide. Whole-genome comparisons with less dominant, generalist fungi point at a significantly higher number of genes related to stress-tolerance and resource uptake in the dominant fungi, suggesting that they might be better in colonising a wide range of environments. Our findings constitute a major advance in our understanding of the ecology of fungi, and have implications for the development of strategies to preserve them and the ecosystem functions they provide.

Asynchrony in shoot and root phenological relationships in hybrid walnut

Understanding the processes driving plant phenology is crucial for assessing how shifts in climate affect plant productivity and species’ distribution. Despite the key role of fine roots in carbon and nutrient cycling, root phenology is less well characterized than shoot phenology, due largely to methodological problems when measuring root systems at depths > 1.0 m. Fine root demography is also poorly related to the better established patterns of aboveground primary and secondary growth. We examined the influence of climatic factors on the dynamics of fine root elongation rate (RER), to a depth of 4.7 m, and assessed relationships with shoot phenology of walnut trees (Juglans nigra × J. regia) in a Mediterranean agroforestry system. Rhizotrons and minirhizotrons were installed for 21 months to monitor RER. Dendrometers were used to measure trunk and lateral root radial growth during the same period. Results showed that RER was not synchronous with budbreak and leaf unfolding (occurring from April to May) at any soil depth. However, during phase 2 of the growing season (June–November), daily RER in the upper soil (0.00–1.70 m) was synchronous with both trunk and lateral root radial growth, which were themselves positively correlated with the mean monthly soil and air temperatures and the mean monthly solar irradiance. Mean daily RER was not correlated to mean monthly soil and air temperatures at any soil depth during phase 2 of the growing season. However, during this period, mean daily RER of very shallow roots (0.00–0.85 m) was significantly and positively correlated with both mean monthly soil water content and solar irradiance. Maximal daily RER occurred during phase 2 of the growing season for the three upper soil layers (June–October), but peaked during the aerial dormant season (December) in the deepest soil layer (4.00–4.70 m). We conclude that drivers of phenology for different tree organs and between shallow and deep roots are not the same. This spatial plasticity in growth throughout a tree enables it to maximize resource uptake, even throughout the winter months, and thus is a highly useful mechanism for increasing tree resistance to abiotic stresses.

Water and nutrient uptake capacity of leaf-absorbing trichomes vs. roots in epiphytic tank bromeliads

The water and nutrient uptake mechanisms used by vascular epiphytes have been the subject of a few studies. While leaf absorbing trichomes (LATs) are the main organ involved in resource uptake by bromeliads, little attention has been paid to the absorbing role of epiphytic bromeliad roots. This study investigates the water and nutrient uptake capacity of LATs vs. roots in two epiphytic tank bromeliads Aechmea aquilega and Lutheria splendens. The tank and/or the roots of bromeliads were watered, or not watered at all, in different treatments. We show that LATs and roots have different functions in resource uptake in the two species, which we mainly attributed to dissimilarities in carbon acquisition and growth traits (e.g., photosynthesis, relative growth rate, non-structural carbohydrates, malate), to water relation traits (e.g., water and osmotic potentials, relative water content, hydrenchyma thickness) and nutrient uptake (e.g., 15N-labelling). While the roots of A. aquilega did contribute to water and nutrient uptake, the roots of L. splendens were less important than the role played by the LATs in resource uptake. We also provide evidenced for a synergistic effect of combined watering of tank and root in the Bromelioideae species. These results call for a more complex interpretation of LATs vs. roots in resource uptake in bromeliads.

A note on the complexity of evolutionary dynamics in a classic consumer-resource model

We study how the complexity of evolutionary dynamics in the classic MacArthur consumer-resource model depends on resource uptake and utilization rates. The traditional assumption in such models is that the utilization rate of the consumer is proportional to the uptake rate. More generally, we show that if these two rates are related through a power law (which includes the traditional assumption as a special case), then the resulting evolutionary dynamics in the consumer is necessarily a simple hill-climbing process leading to an evolutionary equilibrium, regardless of the dimension of phenotype space. When utilization and uptake rates are not related by a power law, more complex evolutionary trajectories can occur, including the chaotic dynamics observed in previous studies for high-dimensional phenotype spaces. These results draw attention to the importance of distinguishing between utilization and uptake rates in consumer-resource models.

Abyssal Deposit‐Feeding Rates Consistent with the Metabolic Theory of Ecology

The metabolic theory of ecology (MTE) posits that metabolic rate controls ecological processes. Metabolic rate is a function of organism body mass. We tested a fundamental assumption of MTE, whether resource uptake scales to metabolism, using a temperature-adjusted model of ingestion for aquatic deposit feeders, and deposit-feeding rates of abyssal invertebrates estimated from time-lapse photos. Ingestion was significantly related to body mass, with a mass-scaling coefficient near the MTE-predicted value. Our results suggest that after temperature correction, all marine invertebrates might be summarized into a single mass-scaled ingestion rate, and provide insight into the potential mechanism for this assumption. This photograph illustrates the article “Abyssal deposit-feeding rates consistent with the metabolic theory of ecology” by Jennifer M. Durden, Brian J. Bett, Christine L. Huffard, Henry A. Ruhl, and Kenneth L. Smith published in Ecology. https://doi.org/10.1002/ecy.2564

Experimental and Computational Methods for the Study of Cerebral Organoids: A Review.

Cerebral (or brain) organoids derived from human cells have enormous potential as physiologically relevant downscaled in vitro models of the human brain. In fact, these stem cell-derived neural aggregates resemble the three-dimensional (3D) cytoarchitectural arrangement of the brain overcoming not only the unrealistic somatic flatness but also the planar neuritic outgrowth of the two-dimensional (2D) in vitro cultures. Despite the growing use of cerebral organoids in scientific research, a more critical evaluation of their reliability and reproducibility in terms of cellular diversity, mature traits, and neuronal dynamics is still required. Specifically, a quantitative framework for generating and investigating these in vitro models of the human brain is lacking. To this end, the aim of this review is to inspire new computational and technology driven ideas for methodological improvements and novel applications of brain organoids. After an overview of the organoid generation protocols described in the literature, we review the computational models employed to assess their formation, organization and resource uptake. The experimental approaches currently provided to structurally and functionally characterize brain organoid networks for studying single neuron morphology and their connections at cellular and sub-cellular resolution are also discussed. Well-established techniques based on current/voltage clamp, optogenetics, calcium imaging, and Micro-Electrode Arrays (MEAs) are proposed for monitoring intra- and extra-cellular responses underlying neuronal dynamics and functional connections. Finally, we consider critical aspects of the established procedures and the physiological limitations of these models, suggesting how a complement of engineering tools could improve the current approaches and their applications.

Cover Crop Biomass Production Is More Important than Diversity for Weed Suppression

Biotic resistance theory suggests that diverse cover crop mixes may be more effective at weed suppression than a cover crop monoculture. However, evidence for this has so far been inconsistent. To investigate, we designed a trial to explicitly test the role of cover crop diversity in weed suppression by comparing eight cover crop mixes that varied in species diversity, functional diversity, and composition. Mixes contained either one, four, or eight species, in equal proportions. Three mixes contained only cereal species, three contained only legumes, and two contained a mix of cereals, legumes, and brassicas. Research was conducted on two farms in South Africa's winter rainfall region, replicated over 2 yr. Indicators of resource uptake by each mix in terms of light, soil N, and water were measured at three time points throughout the season, approximately 50, 85, and 110 d after emergence (DAE). Aboveground biomass (dry weight) of cover crops and weeds within each mix was measured twice, at approximately 70 and 120 DAE. Regression analyses indicated that cover crop biomass was key to resource uptake and weed suppression, and that early‐season N and later‐season light availability had the strongest influence on weed biomass. Neither species diversity nor functional diversity affected resource uptake or weed suppression by cover crops. These results indicate that it is important to consider the competitiveness of individual species when designing cover crop mixes. Diverse mixes remain valuable to perform multiple functions but may contribute to weed problems if composed of poorly competitive species.

Interactions in self-assembled microbial communities saturate with diversity

How the diversity of organisms competing for or sharing resources influences community function is an important question in ecology but has rarely been explored in natural microbial communities. These generally contain large numbers of species making it difficult to disentangle how the effects of different interactions scale with diversity. Here, we show that changing diversity affects measures of community function in relatively simple communities but that increasing richness beyond a threshold has little detectable effect. We generated self-assembled communities with a wide range of diversity by growth of cells from serially diluted seawater on brown algal leachate. We subsequently isolated the most abundant taxa from these communities via dilution-to-extinction in order to compare productivity functions of the entire community to those of individual taxa. To parse the effect of different types of organismal interactions, we defined relative total function (RTF) as an index for positive or negative effects of diversity on community function. Our analysis identified three overall regimes with increasing diversity. At low richness (<12 taxa), positive and negative effects of interactions were both weak, while at moderate richness (12–26 taxa), community resource uptake increased but the carbon use efficiency decreased. Finally, beyond 26 taxa, the effect of interactions on community function saturated and further diversity increases did not affect community function. Although more diverse communities had overall greater access to resources, on average individual taxa within these communities had lower resource availability and reduced carbon use efficiency. Our results thus suggest competition and complementation simultaneously increase with diversity but both saturate at a threshold.

“Unifying” the Concept of Resource Use Efficiency in Ecology

Resource use efficiency (RUE) is an ecological concept that measures the proportion of supplied resources, which is converted into new biomass, i.e. it relates realized to potential productivity. It is also commonly perceived as one of the main mechanisms linking biodiversity to ecosystem functioning based on the assumption that higher species numbers lead to more complementary and consequently more efficient use of the available resources. While there exists a large body of literature lending theoretical and experimental support to this hypothesis, there are a number of inconsistencies regarding its application: First, empirical tests use highly divergent approaches to calculate RUE. Second, the quantification of RUE is commonly based on measures of standing stock instead of productivity rates and total pools of nutrients instead of their bioavailable fractions, which both vary across systems and therefore can introduce considerable bias. Third, conceptual studies suggest that the relationship between biodiversity, productivity and RUE involves many more mechanisms than complementary resource use, resulting in variable magnitude and direction of biodiversity effects on productivity. Moreover, RUE has mainly been applied to single elements, ignoring stoichiometric or metabolic constraints that lead to co-limitation by multiple resources. In this review we illustrate and discuss the use of RUE within and across systems and highlight how the various drivers of RUE affect the diversity-productivity relationship with increasing temporal and spatial scales as well as under anthropogenic global change. We illustrate how resource supply, resource uptake and RUE interactively determine ecosystem productivity. In addition, we illustrate how in the context of biodiversity and ecosystem functioning, the addition of a species will only result in more efficient resource use and consequently higher community productivity if the species’ traits related to resource uptake and RUE are positively correlated.

Abyssal deposit-feeding rates consistent with the metabolic theory of ecology.

The Metabolic Theory of Ecology (MTE) posits that metabolic rate controls ecological processes, such as the rate of resource uptake, from the individual‐ to the ecosystem‐scale. Metabolic rate has been found empirically to be an exponential function of whole organism body mass. We test a fundamental assumption of MTE, whether resource uptake scales to metabolism, by examining detritivores accessing a single common resource pool, an ideal study case. We used an existing empirical model of ingestion for aquatic deposit feeders adjusted for temperature to test whether ingestion by abyssal deposit feeders conforms to MTE‐predicted feeding rates. We estimated the sediment deposit‐feeding rates of large invertebrates from two abyssal study sites using time‐lapse photography, and related those rates to body mass, environmental temperature, and sediment organic matter content using this framework. Ingestion was significantly related to individual wet mass, with a mass‐scaling coefficient of 0.81, with 95% confidence intervals that encompass the MTE‐predicted value of 0.75, and the same pattern determined in other aquatic systems. Our results also provide insight into the potential mechanism through which this fundamental assumption operates. After temperature correction, both deep‐ and shallow‐water taxa might be summarized into a single mass‐scaled ingestion rate.

Why microbes secrete molecules to modify their environment: the case of iron-chelating siderophores.

Many microorganisms secrete molecules that interact with resources outside of the cell. This includes, for example, enzymes that degrade polymers like chitin, and chelators that bind trace metals like iron. In contrast to direct uptake via the cell surface, such release strategies entail the risk of losing the secreted molecules to environmental sinks, including 'cheating' genotypes. Nevertheless, such secretion strategies are widespread, even in the well-mixed marine environment. Here, we investigate the benefits of a release strategy whose efficiency has frequently been questioned: iron uptake in the ocean by secretion of iron chelators called siderophores. We asked the question whether the release itself is essential for the function of siderophores, which could explain why this risky release strategy is widespread. We developed a reaction-diffusion model to determine the impact of siderophore release on iron uptake from the predominant iron sources in marine environments, colloidal or particulate iron, formed due to poor iron solubility. We found that release of siderophores is essential to accelerate iron uptake, as secreted siderophores transform slowly diffusing large iron particles to small, quickly diffusing iron-siderophore complexes. In addition, we found that cells can synergistically share their siderophores, depending on their distance and the size of the iron sources. Our study helps understand why release of siderophores is so widespread: even though a large fraction of siderophores is lost, the solubilization of iron through secreted siderophores can efficiently increase iron uptake, especially if siderophores are produced cooperatively by several cells. Overall, resource uptake mediated via release of molecules transforming their substrate could be essential to overcome diffusion limitation specifically in the cases of large, aggregated resources. In addition, we find that including the reaction of the released molecule with the substrate can impact the result of cooperative and competitive interactions, making our model also relevant for release-based uptake of other substrates.

Turbulence‐mediated facilitation of resource uptake in patchy stream macrophytes

AbstractMany landscapes are characterized by a patchy, rather than homogeneous, distribution of vegetation. Often this patchiness is composed of single‐species patches with contrasting traits, interacting with each other. To date, it is unknown whether patches of different species affect each other's uptake of resources by altering hydrodynamic conditions, and how this depends on their spatial patch configuration. Patches of two contrasting aquatic macrophyte species (i.e., dense canopy‐forming Callitriche and sparse canopy‐forming Groenlandia) were grown together in a racetrack flume and placed in different patch configurations. We measured 15NH4+ uptake rates and hydrodynamic properties along the centerline and the lateral edge of both patches. When the species with a taller, denser canopy (Callitriche) was located upstream of the shorter, sparser species (Groenlandia), it generated turbulence in its wake that enhanced nutrient uptake for the sparser Groenlandia. At the same time, Callitriche benefited from being located at a leading edge where it was exposed to higher mean velocity, as its canopy was too dense for turbulence to penetrate from upstream. Consistent with this, we found that ammonium uptake rates depended on turbulence level for the sparse Groenlandia and on mean flow velocity for the dense Callitriche, but Total Kinetic Energy was the best descriptor of uptake rates for both species. By influencing turbulence, macrophyte species interact with each other through facilitation of resource uptake. Hence, heterogeneity due to multispecific spatial patchiness has crucial implications for both species interactions and aquatic ecosystem functions, such as nitrogen retention.