Nutrient Foraging Research Articles

Salinity Tolerance and Competition Drive Distributions of Native and Invasive Submerged Aquatic Vegetation in the Upper San Francisco Estuary

Both abiotic and biotic factors govern distributions of estuarine vegetation, and experiments can reveal effects of these drivers under current and future conditions. In upper San Francisco Estuary (SFE), increased salinity could result from sea level rise, levee failure, or water management. We used mesocosms to test salinity effects on, as well as competition between, the native Stuckenia pectinata (sago pondweed) and invasive Egeria densa (Brazilian waterweed), species with overlapping distributions at the freshwater transition in SFE. Grown alone at a salinity of 5, E. densa decreased fivefold in biomass relative to the freshwater treatment and decomposed within 3 weeks at higher salinities. In contrast, S. pectinata biomass accumulated greatly (~4× initial) at salinities of 0 and 5, doubled at 10, and was unchanged at 15. When grown together in freshwater, S. pectinata produced 75 % less biomass than in monoculture and significantly more nodal roots (suggesting increased nutrient foraging). At a salinity of 5, a decline in E. densa performance coincided with a doubling of S. pectinata shoot density. Additional experiments on E. densa showed elevated temperature (26 and 30 °C) suppressed growth especially at higher salinities (≥5). We conclude that salinity strongly influences distributions of both species and that competition from E. densa may impose limits on S. pectinata abundance in the fresher reaches of SFE. With a salinity increase of 5, S. pectinata is likely to maintain its current distribution while spreading up-estuary at the expense of E. densa, especially if increased temperature also reduces E. densa biomass.

Live substrate positively affects root growth and stolon direction in the woodland strawberry, Fragaria vesca.

Studies of clonal plant foraging generally focus on growth responses to patch quality once rooted. Here we explore the possibility of true plant foraging; the ability to detect and respond to patch resource status prior to rooting. Two greenhouse experiments were conducted to investigate the morphological changes that occur when individual daughter ramets of Fragaria vesca (woodland strawberry) were exposed to air above live (non-sterilized) or dead (sterilized) substrates. Contact between daughter ramets and substrate was prohibited. Daughter ramet root biomass was significantly larger over live versus dead substrate. Root:shoot ratio also increased over live substrate, a morphological response we interpret as indicative of active nutrient foraging. Daughter ramet root biomass was positively correlated with mother ramet size over live but not dead substrate. Given the choice between a live versus a dead substrate, primary stolons extended preferentially toward live substrates. We conclude that exposure to live substrate drives positive nutrient foraging responses in F. vesca. We propose that volatiles emitted from the substrates might be effecting the morphological changes that occur during true nutrient foraging.

Marsh plants mediate the influence of nitrogen fertilization on degradation of oil from the Deepwater Horizon spill

Coastal wetlands are commonly exposed to hydrocarbon pollutants derived from extraction disasters like the Deepwater Horizon oil spill. Naturally occurring microbes can degrade oil, but the rate of oil degradation depends heavily on the key chemical and biological factors. The goal of this study was to determine the influence of interactions between marsh plants and nitrogen (N) on the degradation of oil from the Deepwater Horizon oil spill. Oil disappearance was measured with gas chromatography (GC) focusing on the change in C18 n‐alkane‐to‐phytane ratio of oil, and instantaneous oil degradation rates were measured using an instantaneous carbon isotopic partitioning method. N addition often stimulates oil decomposition in soil slurries, but the effect of N in our mesocosms depended on plant species. N addition accelerated oil degradation in Spartina alterniflora mesocosms but slowed oil degradation in Spartina patens mesocosms. Across all plant and N treatments, oil degradation related to plant root growth. In many ecosystems including marshes, N addition has been shown to diminish root growth by reducing the need for nutrient foraging. Where N addition reduces root growth, N may ultimately exacerbate oxygen scarcity in marsh soils possibly negating or reversing the positive, direct effects that N has on oil degradation. Based on these findings, fertilization strategies that maximize marsh plant root growth will be the most effective at increasing the microbial degradation of oil and will have the greatest potential to mitigate the impacts of oil in marsh ecosystems.

Linking root traits to nutrient foraging in arbuscular mycorrhizal trees in a temperate forest.

The identification of plant functional traits that can be linked to ecosystem processes is of wide interest, especially for predicting vegetational responses to climate change. Root diameter of the finest absorptive roots may be one plant trait that has wide significance. Do species with relatively thick absorptive roots forage in nutrient-rich patches differently from species with relatively fine absorptive roots? We measured traits related to nutrient foraging (root morphology and architecture, root proliferation, and mycorrhizal colonization) across six coexisting arbuscular mycorrhizal (AM) temperate tree species with and without nutrient addition. Root traits such as root diameter and specific root length were highly correlated with root branching intensity, with thin-root species having higher branching intensity than thick-root species. In both fertilized and unfertilized soil, species with thin absorptive roots and high branching intensity showed much greater root length and mass proliferation but lower mycorrhizal colonization than species with thick absorptive roots. Across all species, fertilization led to increased root proliferation and reduced mycorrhizal colonization. These results suggest that thin-root species forage more by root proliferation, whereas thick-root species forage more by mycorrhizal fungi. In mineral nutrient-rich patches, AM trees seem to forage more by proliferating roots than by mycorrhizal fungi.

Complementarity in nutrient foraging strategies of absorptive fine roots and arbuscular mycorrhizal fungi across 14 coexisting subtropical tree species.

In most cases, both roots and mycorrhizal fungi are needed for plant nutrient foraging. Frequently, the colonization of roots by arbuscular mycorrhizal (AM) fungi seems to be greater in species with thick and sparsely branched roots than in species with thin and densely branched roots. Yet, whether a complementarity exists between roots and mycorrhizal fungi across these two types of root system remains unclear. We measured traits related to nutrient foraging (root morphology, architecture and proliferation, AM colonization and extramatrical hyphal length) across 14 coexisting AM subtropical tree species following root pruning and nutrient addition treatments. After root pruning, species with thinner roots showed more root growth, but lower mycorrhizal colonization, than species with thicker roots. Under multi-nutrient (NPK) addition, root growth increased, but mycorrhizal colonization decreased significantly, whereas no significant changes were found under nitrogen or phosphate additions. Moreover, root length proliferation was mainly achieved by altering root architecture, but not root morphology. Thin-root species seem to forage nutrients mainly via roots, whereas thick-root species rely more on mycorrhizal fungi. In addition, the reliance on mycorrhizal fungi was reduced by nutrient additions across all species. These findings highlight complementary strategies for nutrient foraging across coexisting species with contrasting root traits.

Root nutrient foraging.

During a plant's lifecycle, the availability of nutrients in the soil is mostly heterogeneous in space and time. Plants are able to adapt to nutrient shortage or localized nutrient availability by altering their root system architecture to efficiently explore soil zones containing the limited nutrient. It has been shown that the deficiency of different nutrients induces root architectural and morphological changes that are, at least to some extent, nutrient specific. Here, we highlight what is known about the importance of individual root system components for nutrient acquisition and how developmental and physiological responses can be coupled to increase nutrient foraging by roots. In addition, we review prominent molecular mechanisms involved in altering the root system in response to local nutrient availability or to the plant's nutritional status.

Using root form to improve our understanding of root function.

Using root form to improve our understanding of root function.

Root and rhizosphere processes-high time to dig deeper.

Root and rhizosphere processes-high time to dig deeper.

Tropical forest responses to increasing atmospheric CO2: current knowledge and opportunities for future research.

Elevated atmospheric CO2 concentrations (ca) will undoubtedly affect the metabolism of tropical forests worldwide; however, critical aspects of how tropical forests will respond remain largely unknown. Here, we review the current state of knowledge about physiological and ecological responses, with the aim of providing a framework that can help to guide future experimental research. Modelling studies have indicated that elevated ca can potentially stimulate photosynthesis more in the tropics than at higher latitudes, because suppression of photorespiration by elevated ca increases with temperature. However, canopy leaves in tropical forests could also potentially reach a high temperature threshold under elevated ca that will moderate the rise in photosynthesis. Belowground responses, including fine root production, nutrient foraging and soil organic matter processing, will be especially important to the integrated ecosystem response to elevated ca. Water use efficiency will increase as ca rises, potentially impacting upon soil moisture status and nutrient availability. Recruitment may be differentially altered for some functional groups, potentially decreasing ecosystem carbon storage. Whole-forest CO2 enrichment experiments are urgently needed to test predictions of tropical forest functioning under elevated ca. Smaller scale experiments in the understorey and in gaps would also be informative, and could provide stepping stones towards stand-scale manipulations.

Global Gene Deletion Analysis Exploring Yeast Filamentous Growth

The dimorphic switch from a single-cell budding yeast to a filamentous form enables Saccharomyces cerevisiae to forage for nutrients and the opportunistic pathogen Candida albicans to invade human tissues and evade the immune system. We constructed a genome-wide set of targeted deletion alleles and introduced them into a filamentous S. cerevisiae strain, Σ1278b. We identified genes involved in morphologically distinct forms of filamentation: haploid invasive growth, biofilm formation, and diploid pseudohyphal growth. Unique genes appear to underlie each program, but we also found core genes with general roles in filamentous growth, including MFG1 (YDL233w), whose product binds two morphogenetic transcription factors, Flo8 and Mss11, and functions as a critical transcriptional regulator of filamentous growth in both S. cerevisiae and C. albicans.

The Behavioral Ecology of Nutrient Foraging by Plants

Foraging for resources influences ecological interactions among individuals and species, regardless of taxonomic affiliation. Here we review studies of nutrient foraging in plants, with an emphasis on how nutritious and non-nutritious cues in the soil alter behavioral decisions and patterns of root placement. Three patterns emerge: (a) Plants alter root placement in response to many diverse cues; (b) species respond differently to these cues; and (c) there are nonadditive responses to multiple cues, indicating that plants exhibit complex multidimensional root foraging strategies. We suggest that this complexity calls for novel approaches to understanding nutrient foraging by plants. Resource selection functions are commonly used by animal behaviorists and may be useful to describe plant foraging strategies. Understanding such approaches may allow researchers to link individual behavior to population and community dynamics.

Sedimentological evidence for rooting structures in the Early Devonian Anglo-Welsh Basin (UK), with speculation on their producers

Rooting structures preserved as casts in alluvial deposits of the Lower Devonian Lower Old Red Sandstone occur more extensively than previously thought in the Anglo-Welsh Basin. Two rooting structure morphotypes are identified: morphotype 1 being predominantly horizontal, and morphotype 2 comprising vertical forms. Both morphotypes taper along their length, are oval in cross-section, branch, and can be linear or sinuous. Fills are heterolithic in nature. The rooting structures are observed in sediments deposited in a wide variety of environments including both low-sinuosity within-channel bar-tops and accretionary bar surfaces (inclined-heterolithic stratification); accretionary banks of sinuous ephemeral channels (inclined-heterolithic stratification); floodplains (including margins of shallow floodplain ponds) of both ephemeral and perennial river channels, and well-developed calcic Vertisols. Although a vascular plant origin to the rooting structures cannot be discounted, there is circumstantial evidence that the structures were produced by the enigmatic Prototaxites, recently reinterpreted as a giant fungus. It is possible that they represent underground aggregates (rhizomorphs or cords) of hyphae involved in anchorage and nutrient foraging. Organic matter associated with biofilms and crusts is hypothesized as a source of nutrients for the presumed saprotroph.

Radial Growth and Ring Formation Process in Clonal PlantEriophorum angustifoliumon Post-Mined Peatland in the Šumava Mts., Czech Republic

Eriophorum angustifolium (Cyperaceae) is a pioneer clonal sedge colonizing bare peat surface of harvested peatlands in central Europe. It forms circular patches of densely aggregated ramets, followed by central die-back and ring formation as circles develop. This study experimentally tested the importance of inter-ramet competition, interference with litter, soil nutrient depletion, and architectural constraints for radial clonal spread and ring formation process. Effects of fertilization, litter addition and competition of neighbor ramets on growth and survival of tillers transplanted into four distinct zones within individual circle were detected only in the first zone (green band) with high ramet density. This suggested that both above-ground competition for light and below-ground competition for soil nutrients can play an important role in population dynamics of E. angustifolium. A field study of clonal growth has shown that rhizomes orient preferentially towards the periphery. As the old ramets within the interior of the tussock died due to senescence and inter-ramet competition, disproportionately more ramets are recruited on the periphery, which reduce axillary bud availability within the interior of the tussocks. We also explored the soil nutrient content (NH4-N, NO3-N and PO4-P). High values of NO3-N outside the circles and low values inside patches might partly explain why Eriophorum rhizomes are oriented into open space. High accumulation of phosphorus (PO4-P) in the centre of the patches was attributed to the leaching of phosphorus from decaying Eriophorum plants. We suggest that processes of nutrient foraging and utilization are responsible for development of circular patches of E. angustifolium in the harsh environment of cut-away peatland.

Response of three floodplain tree species to spatial heterogeneity in soil oxygen and nutrients

1. Plant responses to nutrient heterogeneity may be influenced by spatial heterogeneity in other soil-based resources. We investigated how heterogeneity in two resources, nutrients and oxygen, affected root system morphology and biomass of three floodplain tree species, which differ in waterlogging tolerance from highly tolerant (Nyssa aquatica L.) to intermediate (Fraxinus pennsylvanica Marsh.) to less tolerant (Liquidambar styraciflua L.). 2. We predicted that heterogeneity in soil oxygen would affect the well-known root proliferation response to nutrient-rich patches, and biomass, of the least tolerant species, L. styraciflua, but would not influence biomass or proliferation of the more tolerant species, F. pennsylvanica and N. aquatica. To test this prediction, we grew seedlings in pots where we manipulated the spatial distribution of oxygen (via waterlogging) and nutrients. 3. All species were precise foragers (i.e. they displayed preferential proliferation of roots in nutrient-rich patches) in uniformly drained and waterlogged conditions. When waterlogging and nutrients were both heterogeneous, roots of L. styraciflua avoided waterlogged patches and did not precisely forage for nutrients. In contrast, waterlogging had no negative effects on nutrient foraging of either F. pennsylvanica or N. aquatica; however, these species did not precisely forage for nutrients when nutrient-rich and waterlogged patches were spatially separate. 4. Waterlogging reduced biomass of L. styraciflua, did not significantly affect biomass of F. pennsylvanica, and enhanced biomass of N. aquatica. In pots where waterlogging and nutrients were simultaneously heterogeneous, the spatial position of waterlogging relative to that of nutrients influenced the biomass response of F. pennsylvanica and N. aquatica to nutrient heterogeneity, but did not influence L. styraciflua. For F. pennsylvanica and N. aquatica, nutrients may have been easier to acquire in waterlogged patches due to faster diffusion rates. 5. Synthesis. Our results suggest that root system and biomass responses to nutrient heterogeneity can be affected by heterogeneity in another soil-based resource (i.e. soil oxygen availability). We believe ecologists should consider the effects of spatial heterogeneity in other soil-based resources when attempting to link nutrient heterogeneity to plant population or community attributes.

Root system size and precision in nutrient foraging: responses to spatial pattern of nutrient supply in six herbaceous species

1 An experiment was carried out to test the hypotheses that in heterogeneous environments: (i) the size of species’ root systems will be negatively correlated with their ability to place roots precisely in nutrient-rich patches; (ii) precision of root placement will be less affected by distance to nutrient patches in species with large root systems; (iii) species with greater precision in root placement will show greater variation in biomass (sensitivity) in response to heterogeneity in nutrient supply; and (iv) plants will be less precise in root placement, and will invest more biomass in above-ground structures or in fitness-related attributes, when in association with mycorrhizas. 2 Single plants of six herbaceous species (Arrhenatherum elatius, Festuca ovina, Plantago lanceolata, Campanula rotundifolia,Papaver rhoeas and Sonchus oleraceus) were grown in pots with mycorrhizas either present or absent. The same amount of nutrients was supplied either homogeneously or heterogeneously at different distances from the plants. Pots received the same quantity of nutrients in all treatments. 3 There was a significant negative correlation between species’ root system biomass and precision. Several species, including some with large root systems, showed small but highly significant differences in precision between the various treatments. Only the high-precision species Papaver and the low-precision species Campanula exhibited sensitivity in biomass produced in response to different patterns of heterogeneity. 4 The precision with which roots were placed in nutrient-rich patches was affected by distance from patches in Papaver, the smallest-rooted species used in the experiment, and in Plantago, one of the larger-rooted species. There was no evidence to support the hypothesis that precision would be affected more by distance from nutrient patches in small-rooted species than in large-rooted species. 5 The presence of mycorrhizas did not affect precision of root placement in any species. However, allocation of biomass to roots was significantly lower in Arrhenatherum, and allocation to reproductive structures was significantly higher in Campanula, when mycorrhizas were present. 6 This study confirms that there are differences between species in precision of nutrient foraging that are related to root system size. It also shows that there is variation in precision within species in response to the location of nutrient-rich patches, and that the ability of a species to display precision in nutrient foraging is dependent on its environmental setting.

Root system size and precision in nutrient foraging: responses to spatial pattern of nutrient supply in six herbaceous species

Root system size and precision in nutrient foraging: responses to spatial pattern of nutrient supply in six herbaceous species

An Equalization Control Strategy for Activated Sludge Process Control

Fluctuations in hydraulic and organic loads cause wastewater treatment plant operating problems, necessitating some form of process control to ensure attainment of design objectives. A comparison of in–plant control with equalization control indicates that the latter is more appropriate for the case of long sludge age nutrient removal activated sludge processes which include anaerobic, anoxic and aerobic zones. A microprocessor-based control strategy is presented for the operation of an equalization tank upstream of the process to reduce, optimally, diurnal fluctuations in both flow and organic load rates. Results from implementation on a 150 Mℓ.d−1 plant with an in-line equalization tank (4,5 hour mean retention time) demonstrate the successful performance of the control strategy.