Community Structure In Ecosystems Research Articles

Multidimensional response of China’s grassland stability to drought

Drought usually affects the normal functioning of grassland ecosystems. Due to sustained global warming, the frequency and intensity of drought have significantly increased, leading to greater impacts on many aspects of grassland ecosystem functions, such as soil moisture, vegetation physiological structure and ecosystem community structure. Ecosystem stability dimension can help us better understand the changes induced by drought occurred within ecosystems. Using the Normalized Vegetation Index (NDVI), climate and biodiversity data, we quantified resistance, resilience and temporal stability of grassland ecosystems under long term drought in northern China and calculated the ecosystem stability dimension based on the correlation between the three stability indicators. The results indicated that Qinghai Tibet Plateau and Inner Mongolian Plateau showed strong resistance to drought, while Loess Plateau region presented rapid recovery after drought. The resistance, compared to resilience and temporal stability, exhibited stronger sensitivity to drought in space. Drought promoted the transformation of grassland ecosystems into multidimensional structures. The reduction of aboveground biomass caused by frequent droughts accelerated the transformation in grassland ecosystems. Our findings provide the new insights for guiding the response mechanism of drought on grassland ecosystems.

Effects of overgrazing on the functional diversity of rodents in desert areas.

Environmental stressors and disturbances can cause changes in an ecosystem's community structure, which can be reflected in its functional diversity. As grazing intensity increases, this causes changes in the environment that inevitably lead to changes in the community structure, which can especially affect rodents due to their sensitivity to the environment. The effects of grazing prohibition and overgrazing on the functional diversity of desert rodent communities in Alxa were studied in April, July, and October of 2018-2020. The trap-day method was used to study rodent communities in disturbed habitats. Five functional traits were selected and quantified: nutrition, life history, physiology, morphology, and activity rhythm. The results showed that: (1) The species composition of rodent communities in the Alxa Desert in spring and autumn was significantly correlated with the functional traits of the hibernation, reproductive cycle, and feeding habits. The species composition in the summer was only significantly correlated with the functional traits of reproductive cycle and diet. (2) The effects of overgrazing on the functional diversity of rodents in desert areas have significant temporal and spatial characteristics. (3) In spring and summer, overgrazing made the Functional Richness index of the rodent community lower than that of areas where grazing is prohibited, but the Functional Evenness index was higher than that of grazing-prohibition areas. In autumn, overgrazing increased the Functional Richness index of the rodent community and decreased the Functional Evenness index. The Functional Divergence index was higher in overgrazing areas than in grazing-prohibited ones. These results suggest that, in spring and summer, overgrazing reduced the ecological space utilization ability of rodent communities; however, the impact on the degree of utilization of community resources is more comprehensive. In autumn, overgrazing increases the ability of rodent communities to use ecological space but reduces resource efficiency. Overgrazing makes the niche differentiation of rodent communities higher, the degree of overlap lower, and the competition between species weaker. Therefore, overgrazing will affect the functional diversity of the community through the utilization of ecological space, resource utilization, interspecific competition, and niche.

A Short Review on Various Biodiversity Indices

A multidimensional assessment of biodiversity can provide insights into the relationships between changes in biodiversity in ecosystem functioning and ecosystem services. The Biodiversity Index is widely used because it is a quick way to distinguish between different places, ecosystems or populations of organisms. This is a count of the total number of species at a given location. Different species have different ecological requirements that allow them to thrive in their ecological niches, which determine the patterns and extent of ecosystem community structure. Various indices were used to assess core community structure, species distribution and interactions to gain insight into overall ecosystem health. In this article, our main goal is to give a brief overview of various biodiversity indices and their applications in various areas related to the environment.

Insights from the Niger Delta Region, Nigeria on the impacts of urban pollution on the functional organisation of Afrotropical macroinvertebrates

Anthropogenic activities, including urbanisation and industrialisation threaten stream ecological integrity, ecosystem community structure and ecosystem functioning of rivers and streams worldwide. However, developing sustainable monitoring strategies for ecological health remains a critical challenge in Africa. We examined the effects of urban disturbance on macroinvertebrate Functional Feeding Groups in selected streams in the Niger Delta Region of Nigeria. We sampled 11 sites between 2008 and 2012 and grouped into three site groups (Site groups 1 > 2 > 3). The groups represent an increasing gradient of urban pollution. Our result showed that urban-induced disturbances affected physicochemical variables in the study area (PERMANOVA; p < 0.05), with nutrients NO2-N, PO4-P, and electrical conductivity being significantly higher in impacted Site group 3 (ANOVA, p < 0.05). Predators and gatherers were the most dominant Functional Feeding Group recorded in the study area, while shredders were the least abundant macroinvertebrate Functional Feeding Groups. The multivariate RLQ analysis revealed that shredders, predators, and scrapers were tolerant of urban pollution, whereas gatherers were sensitive to increasing urban pollution. Overall, macroinvertebrates Functional Feeding Groups responded differentially to urban pollution in the Niger Delta Region. Identifying pollution indicator Functional Feeding Groups is seen as an important step towards developing a reliable, low-cost tool for riverine monitoring of urban pollution effects in Africa.

Dietary niche breadth of endemic and introduced anurans (Amphibia: Anura) in Lombok, Lesser Sunda Islands– Indonesia

Anurans are important organisms as components of faunal community structure in ecosystems because of their roles as secondary and tertiary consumers in food webs. Anurans are opportunistic organisms that will consume any resources in their habitat. In this study, we dissected thirty-nine specimens of anurans from Museum Universitas Mataram (MUM) reference collection, it consists by three endemic (Ingerophrynus biporcatus, Limnonectes dammarmani and L. kadarsani) and one introduced species (Duttaphrynus melanostictus) of anurans. These reference collections were collected by authors during herpetofauna survey at Pusuk Forest, western Lombok in 2018. Based on stomach content analysis, both endemic and introduced anurans are generalist arthropod predators where hymenoptera, coleoptera, orthoptera and chilopoda are the most important food. In this study, we found positive correlations between body size and dietary niche breadth in which each anuran species has a high overlap of dietary niches. Anurans with large body size have a variety of prey than the small one.

Implications of unreliable species identification methods for Neotropical deer conservation planning

Deer species play a key role in processes that maintain ecosystem community structure and composition. However, several of the species are considered at risk of extinction. One of the strategies for their conservation is the maintenance of legally protected areas in which administration is prescribed by a management plan. Species inventories form the basis of this instrument as it allows to identify key resources and taxons. We reviewed the management plans of Brazilian protected areas to assess the suitability of methods employed to identify deer species. We reviewed 118 management plans (covering 298,000 km2 of protected area) and checked each occurrence record for information regarding detection methods, which we classified according to their suitability for species-level identification. We found that 38% of the records did not report the species detection method used. Specific identifications were obtained through seven different methodologies, of which 12% were considered suitable, 28% were suitable with caveats, and 60% were unsuitable for species identification. We conclude it is necessary to improve the scientific rigor applied to inventories and data collection to avoid producing further inconsistent information, as this might affect management actions and risks the exclusion of threatened species from public policies on conservation planning.

Patterns of Longleaf Pine (Pinus palustris) Establishment in Wiregrass (Aristida beyrichiana) Understories

Ecosystem community structure and function is shaped in part by intra- and inter-specific interactions among plants. Facilitative interactions, wherein one plant benefits another's fitness, can strongly influence plant community dynamics. We investigated the potential of an endemic, perennial bunchgrass, wiregrass (Aristida beyrichiana), to function as a nurse plant for longleaf pine (Pinus palustris) seedlings in fire-maintained pine savannas of the southeastern U.S.A. We documented significantly more pine seedlings growing close to established wiregrass bunchgrasses in a site burned one year prior to sampling. Pine seedlings growing close to wiregrass were also significantly taller than those growing further away. This positive spatial association between wiregrass and pine seedlings suggests that wiregrass facilitates early longleaf pine establishment in flatwoods environments, at least within the first year after fire.

Influence of occupation history and habitat on Washington sea otter diet

AbstractHabitat characteristics are primary determinants of nearshore marine communities. However, biological drivers like predation can also be important for community composition. Sea otters (Enhydra lutris ssp.) are a salient example of a keystone species exerting top‐down control on ecosystem community structure. The translocation and subsequent population growth and range expansion of the northern sea otter (Enhydra lutris kenyoni) in Washington State over the last five decades has created a spatio‐temporal gradient in sea otter occupation time and density, and acts as a natural experiment to quantify how sea otter population status and habitat type influence sea otter diet. We collected focal observations of sea otters foraging at sites across the gradient in varying habitat types between 2010 and 2017. We quantified sea otter diet composition and diversity, and long‐term rates of energy gain across the gradient. We found that sea otter diet diversity was positively correlated with cumulative sea otter density, while rate of energy gain was negatively correlated with cumulative density. Additionally, we found that habitat type explained 1.77 times more variance in sea otter diet composition than sea otter cumulative density. Long‐term diet studies can provide a broader picture of sea otter population status in Washington State.

Quantifying the ecological stability of artificial aquatic ecosystems: a case study of an artificial lake in Chengdu, China

An urban artificial lake is generally constructed as a macrophytic lake ecosystem; it has a simple ecosystem structure that results in a fragile ecosystem and weak stability. The ecosystem stability obviously changes with the water quality and the season, especially in summer and autumn. The purpose of this study was to establish a stability evaluation system for an artificial lake ecosystem and verify the system applicability using Lake Luxe as a case study. The system was established by the following three steps: (1) select reference period; (2) establish seasonal and annual evaluation methods by determining the ecological units by an “ecological checklist” (the populations and communities of phytoplankton, zooplankton, and benthos) and then calculating the seasonal stability indices (SIs) and annual stability indices (SIy) of each ecological unit; calculating each seasonal or annual ecosystem stability index using these calculated SI and ecological units attributes; and calculating the ecosystem stability index for many years; (3) obtain the evaluation results. The results obtained by the seasonal evaluation method showed that the ecosystem community structure was unstable in spring and the total ecosystem biomass was unstable in summer. The redundancy analysis results between phytoplankton stability values and environmental variables showed that dissolved oxygen (DO), total nitrogen (TN), and chlorophyll a (Chla) were the main driving variables that could be used as indicators for the sustainable management of artificial lakes.

Missing in action: Species competition is a neglected predictor variable in species distribution modelling.

The central role of species competition in shaping community structure in ecosystems is well appreciated amongst ecologists. However species competition is a consistently missing variable in Species Distribution Modelling (SDM). This study presents results of our attempt to incorporate species competition in SDMs. We used a suit of predictor variables including Soil Adjusted Vegetation Index (SAVI), as well as distance from roads, settlements and water, fire frequency and distance from the nearest herbivore sighting (of selected herbivores) to model individual habitat preferences of five grazer species (buffalo, warthog, waterbuck, wildebeest and zebra) with the Ensemble SDM algorithm for Gonarezhou National Park, Zimbabwe. Our results showed that distance from the nearest animal sighting (a proxy for competition among grazers) was the best predictor of the potential distribution of buffalo, wildebeest and zebra but the second best predictor for warthog and waterbuck. Our findings provide evidence to that competition is an important predictor of grazer species’ potential distribution. These findings suggest that species distribution modelling that neglects species competition may be inadequate in explaining the potential distribution of species. Therefore our findings encourage the inclusion of competition in SDM as well as potentially igniting discussions that may lead to improving the predictive power of future SDM efforts.

Alpine soil carbon is vulnerable to rapid microbial decomposition under climate cooling.

As climate cooling is increasingly regarded as important natural variability of long-term global warming trends, there is a resurging interest in understanding its impact on biodiversity and ecosystem functioning. Here, we report a soil transplant experiment from lower to higher elevations in a Tibetan alpine grassland to simulate the impact of cooling on ecosystem community structure and function. Three years of cooling resulted in reduced plant productivity and microbial functional potential (for example, carbon respiration and nutrient cycling). Microbial genetic markers associated with chemically recalcitrant carbon decomposition remained unchanged despite a decrease in genes associated with chemically labile carbon decomposition. As a consequence, cooling-associated changes correlated with a decrease in soil organic carbon (SOC). Extrapolation of these results suggests that for every 1 °C decrease in annual average air temperature, 0.1 Pg (0.3%) of SOC would be lost from the Tibetan plateau. These results demonstrate that microbial feedbacks to cooling have the potential to differentially impact chemically labile and recalcitrant carbon turnover, which could lead to strong, adverse consequences on soil C storage. Our findings are alarming, considering the frequency of short-term cooling and its scale to disrupt ecosystems and biogeochemical cycling.

A supplementary tool to existing approaches for assessing ecosystem community structure

Measures of biological or species diversity are central to ecology and conservation biology. Although there are several commonly used indices, each has shortcomings and all vary in the relative emphasis they place on the number of species and their relative abundance. We propose utilizing Fisher Information, not as a replacement for existing indices, but as a supplement to other indices because it is sensitive to community structure. We demonstrate how Shannon’s and Simpson’s diversity indices quantify the diversity of two different systems and how Fisher Information can enhance the analyses by comparing, as example, body size, and phylogenetic diversity of the different communities. Fisher Information is sensitive to the order in which species are entered into the analysis, and therefore, it can detect differences in community structure. Thus, the Fisher Information index can be useful in helping understand and analyze biodiversity of ecosystems and in comparing ecological communities.

Predation and competition effects on the size diversity of aquatic communities

Body size has been widely recognised as a key factor determining community structure in ecosystems. We analysed size diversity patterns of phytoplankton, zooplankton and fish assemblages in 13 data sets from freshwater and marine sites with the aim to assess whether there is a general trend in the effect of predation and resource competition on body size distribution across a wide range of aquatic ecosystems. We used size diversity as a measure of the shape of size distribution. Size diversity was computed based on the Shannon-Wiener diversity expression, adapted to a continuous variable, i.e. as body size. Our results show that greater predation pressure was associated with reduced size diversity of prey at all trophic levels. In contrast, competition effects depended on the trophic level considered. At upper trophic levels (zooplankton and fish), size distributions were more diverse when potential resource availability was low, suggesting that competitive interactions for resources promote diversification of aquatic communities by size. This pattern was not found for phytoplankton size distributions where size diversity mostly increased with low zooplankton grazing and increasing nutrient availability. Relationships we found were weak, indicating that predation and competition are not the only determinants of size distribution. Our results suggest that predation pressure leads to accumulation of organisms in the less predated sizes, while resource competition tends to favour a wider size distribution.

Sorption and desorption of dissolved organic phosphorus onto iron (oxyhydr)oxides in seawater

Sorption of phosphorus (P) onto particulate surfaces significantly influences dissolved P concentrations in aquatic environments. We present results of a study contrasting the sorption behavior of several dissolved organic phosphorus (DOP) compounds and phosphate onto three commonly occurring iron (oxyhydr)oxides (Fe ox): ferrihydrite, goethite, and hematite. The DOP compounds were chosen to represent a range of molecular weights and structures, and include: adenosine triphosphate (ATP), adenosine monophosphate (AMP), glucose-6-phosphate (G6P), and aminoethylphosphonic acid (AEP). All P compounds displayed decreasing sorption as a function of crystallinity of the Fe ox substrate, with ferrihydrite adsorbing the most, hematite the least. In general, maximum sorption density decreased with increasing molecular weight of P compound; sorption of G6P onto goethite and hematite excepted. P compound size and structure, and the nature of the Fe ox substrate all appear to play a role dictating relative sorption capacity. Failure of a simple, 1-step sorption–desorption model to describe the data suggests that P sorption cannot be explained by a simple balance between sorption and desorption. Instead, the data are consistent with a 2-step sorption model consisting of an initial rapid surface sorption, followed by a slow, solid-state diffusion of P from surface sites into particle interiors. Desorption experiments provide additional support for the 2-step sorption model. Without exception, DOP compounds showed less efficient sorption than did orthophosphate. This suggests that in aquatic systems enriched in reactive Fe ox, whether as suspended particulates in the water column or in benthic sediments, DOP bioavailability may exceed that of orthophosphate. Since biological uptake of P from DOP requires enzymatic cleavage of orthophosphate, a system enriched in DOP relative to orthophosphate may impact ecosystem community structure.

Variation in woody plant mortality and dieback from severe drought among soils, plant groups, and species within a northern Arizona ecotone

Vegetation change from drought-induced mortality can alter ecosystem community structure, biodiversity, and services. Although drought-induced mortality of woody plants has increased globally with recent warming, influences of soil type, tree and shrub groups, and species are poorly understood. Following the severe 2002 drought in northern Arizona, we surveyed woody plant mortality and canopy dieback of live trees and shrubs at the forest-woodland ecotone on soils derived from three soil parent materials (cinder, flow basalt, sedimentary) that differed in texture and rockiness. Our first of three major findings was that soil parent material had little effect on mortality of both trees and shrubs, yet canopy dieback of trees was influenced by parent material; dieback was highest on the cinder for pinyon pine (Pinus edulis) and one-seed juniper (Juniperus monosperma). Ponderosa pine (Pinus ponderosa) dieback was not sensitive to parent material. Second, shrubs had similar mortality, but greater canopy dieback, than trees. Third, pinyon and ponderosa pines had greater mortality than juniper, yet juniper had greater dieback, reflecting different hydraulic characteristics among these tree species. Our results show that impacts of severe drought on woody plants differed among tree species and tree and shrub groups, and such impacts were widespread over different soils in the southwestern U.S. Increasing frequency of severe drought with climate warming will likely cause similar mortality to trees and shrubs over major soil types at the forest-woodland ecotone in this region, but due to greater mortality of other tree species, tree cover will shift from a mixture of species to dominance by junipers and shrubs. Surviving junipers and shrubs will also likely have diminished leaf area due to canopy dieback.

Assessing spatial and temporal variations in surface soil moisture in fire-disturbed black spruce forests in Interior Alaska using spaceborne synthetic aperture radar imagery — Implications for post-fire tree recruitment

Recent studies [Bourgeau-Chavez, L.L., Kasischke, E.S., Riordan, K., Brunzell, S.M., Nolan, M., Hyer, E.J., Slawski, J.J., Medvecz, M., Walters, T., and Ames, S. (in press). Remote monitoring of spatial and temporal surface soil moisture in fire disturbed boreal forest ecosystems with ERS SAR imagery. Int. J. Rem. Sens.] demonstrated that ERS SAR imagery can be used to estimate surface soil moisture in recently burned black spruce forests in interior Alaska. We used this relationship to analyze the intra- and inter-annual variations surface soil moisture in two burned black spruce forests in Alaska. The results of this study showed distinct seasonal and longer-term trends in soil moisture in the two sites, with the site that burned in 1994 having higher soil moisture than the site that burned in 1999. The differences in soil moisture between the sites were related to landscape-scale variations in soil drainage and seasonal permafrost thawing. Finally, we found that the 1999 site had dramatically lower levels of tree recruitment (both aspen and black spruce) than the 1994 site as a result of the lower soil moisture levels. These results show that the ERS SAR and similar systems can be used to monitor a site characteristic that is important to understanding changes in the ecosystem community structure that result from variations in climate and the fire regime in the boreal region.

Putting floodplain hyperdiversity in a regional context: an assessment of terrestrial–floodplain connectivity in a montane environment

Abstract Aim and location Alluvial flood plains support higher levels of vascular plant species richness than other terrestrial ecosystems. Whereas the spatial and temporal heterogeneity of these ecosystems has been considered the local determinant of high plant richness, regional influences, such as regional species pools have received little attention. In this study we surveyed plant species richness across the entire Nyack catchment (c. 21,000 ha), in Glacier National Park, USA, to determine the relation of upland ecosystem community structure to biodiversity patterns on montane floodplains that are relatively extensive and flood‐scoured ecosystems.Method We surveyed floodplain and other terrestrial ecosystems within the Nyack catchment using 50 × 2 m plots to record species present and visual estimates of percentage cover. Species pools from flood plains and three other terrestrial ecosystems (low elevation forests, sub‐Alpine forests and alpine) were analysed with nested subset analysis, detrended correspondence analysis (DCA), and an index of beta diversity to identify dissimilarity in species composition and richness, and the separate contributions of generalists (species occurring in more than one ecosystem) and specialists to richness in each ecosystem. Analysis of variance and post hoc Tukey–Kramer tests were used to identify where in the Nyack catchment each species was most abundant. Species life form and dispersal strategies were analysed to better understand influences on beta diversity.Results Our data show that in this pristine system, floodplain ecosystems host 202 (63%) of the 320 vascular plants identified within Nyack catchment. Of these species, the nested subset analysis showed that 146 (72%) are found in at least one adjacent upland ecosystem. While the DCA ordination scatter plots show statistically significant separations of ecosystems on the first two axes, values of beta diversity showed that substantial similarity exists between floodplain and all upland species pools. Further, of the 146 floodplain species shared with upland ecosystems, 61% were more frequent in upland ecosystems, whereas 55% were more abundant in uplands than flood plains (Tukey–Kramer P ≤ 0.05). Significant numbers of specialists were found on flood plains (24% of floodplain species), but also within upland ecosystems, where 23% and 40% of low elevation forest and alpine species were found to be specialists, respectively. Whereas 83% of herb generalists were wind dispersed, &lt;70% of specialists were animal dispersed, indicating that similarity in species pools may be driven by wind dispersal.Main conclusions These results suggest a re‐evaluation of the contribution of floodplain ecosystems to regional plant species richness. While flood plains host specialists, other ecosystems had equal or higher levels of regional ‘endemism’. Furthermore, these data suggest that conservation of high levels of biodiversity on floodplain ecosystems may require consideration of upland ecosystems throughout the catchment as the majority of species were relatively rare on flood plains, indicating they may be sink habitats for some species.

Sources of variability in geographical and seasonal differences in particulate fluxes from short-term sediment trap deployments, east of New Zealand

Free-floating sediment traps were used to measure total mass and particulate phosphorus fluxes from the upper ocean (>100–550 m) at two stations in each of three water types (subantarctic, Subtropical Convergence and subtropical), east of New Zealand, in winter and spring 1993. Despite marked changes in ecosystem community structure and function between water types and occasionally between stations, there were no significant differences in export flux either across water masses, between stations or with increasing water depth. One exception was in the Subtropical Convergence where significant increases in particulate flux with depth at one station in spring are inferred to be caused by tidal current resuspension of bottom sediments on the crest of the Chatham Rise. High degrees of variation between mass fluxes calculated from individual cylinders observed in winter (coefficients of variation ranging from 10 to 123%) may have been due to inter-trap hydrodynamic interactions or sample processing errors. In spring, overall coefficients of variation of mass flux were smaller than in winter (6–87%), but variations due solely to sub-sampling procedures were significant (<1–83%). The ranges of variability for the New Zealand traps are similar to other published sediment trap studies, suggesting that the use of single, free-floating sediment trap arrays to characterise fluxes for specific oceanic provinces is unlikely to be valid statistically. Based on the results from east of New Zealand, more than two arrays would be required to improve the power of the chosen statistical test in order to determine significant differences in particulate flux between physically and biologically distinctive oceanic water masses.

Ecological effects of river ice break‐up: a review and perspective

SUMMARY1. Abiotic disturbances strongly modify spatial and temporal patterns of lotic ecosystem community structure and function. Such effects are produced because disturbances alter organic matter, nutrient and contaminant dynamics and the distribution and abundance of bacterial, algal, macroinvertebrate and fish communities.2. River ice break‐up is a seasonal disturbance in rivers at high altitudes and latitudes world‐wide and is characterized, in part, by large increases in current velocity, stage, water temperature, concentrations of suspended materials and substrate scouring.3. These abiotic factors are likely to have important effects on primary producers, consumers, and food‐web dynamics of river biota. Despite the potential importance of river ice break‐up on community structure and function, detailed information describing the magnitude of their effects and underlying causal mechanisms is scarce.4. The objective of this paper is to provide a hydrological and ecological review and perspective on the potential effects of ice break‐up on lotic ecosystems. Specifically, the potential importance of break‐up on water temperature, river sediments and geomorphology, riverine energy sources, contaminants, and its effects on river biota and food‐web dynamics are evaluated.

Influence of Dissolved Organic Matter On the Bio-Availability and Toxicity of Metals in Soils and Aquatic Systems

Abstract Cations in soil are essential for the growth of plants and micro-organisms. Their availability is dependent on soil organic matter. Soil organic matter (SOM) is heterogeneous comprising amino, aliphatic and phenolic acids, but particularly humic substances. All these substances can complex cations selectively. Mechanisms of complexation with dissolved organic matter are discussed. Such complexation can lead to the apparently contradictory observations that dissolved organic matter (DOM) can either increase the concentration of some less soluble nutrients, making them more available for plant uptake, or make them less available and hence less toxic. the importance of DOM is discussed in relation to soil solution, particularly the rhizosphere, and also in relation to aquatic systems. the latter systems contain mainly dissolved humic substances whereas in the soil, non-humic substances assume a greater importance. SOM in the rhizosphere is derived from plant, microbial and animal remains but much, especially the water-soluble compounds, are acquired through root exudation. Exudation has important consequences for enhanced nutrient availability as a result of the production of non-humic substances such as amino, aliphatic and phenolic acids. in future, the role of root exudation in relation to DOM and nutrient availability should be investigated more fully, particularly as predicted elevated CO2 levels are likely to have a major impact on root exudation, nutrient availability, and possibly ecosystem community structure and functioning. It is likely that more information will become available on aquatic systems as more highly sensitive techniques and equipment capable of dealing with low concentrations of DOM in these systems become available.