Ecosystem

About: Ecosystem is a research topic. Over the lifetime, 25460 publications have been published within this topic receiving 1291375 citations. The topic is also known as: ecological system & Ecosystem.

Landscape-Level Patterns of Microbial Community Composition and Substrate Use in Upland Forest Ecosystems

Abstract: northern Wisconsin, Christensen (1969) found evidence for such a relationship, wherein communities of soil The composition and diversity of biotic communities are controlled microfungi were correlated with the occurrence of forest by the availability of growth-limiting resources. Resource availability for microbial populations in soil is controlled by the amount and types vegetation (also see Christensen et al., 1962; Tresner et of organic compounds entering soil from plant litter. Because plant al., 1954). Notwithstanding these observations, we have communities differ in the amount and type of substrates entering a limited understanding of the manner in which the soil, we reasoned that the composition and function of soil microbial broader soil microbial community varies with plant comcommunities should differ with the dominant vegetation. We tested munity composition at a landscape-level scale. this idea by studying two sugar maple (Acer saccharum Marsh.)- Temporal patterns of root and leaf litter production, dominated and one oak (Quercus spp.)-dominated forest ecosystems combined with variation in the chemical composition in northern Lower Michigan that differ in rates of soil N cycling. We of these tissues, could influence the composition and used phospholipid fatty acid (PLFA) analysis to gain insight into function of soil microbial communities. Root litter typimicrobial community composition, and we used a subset of Biolog cally contains more N and lignin than leaf litter (Aber GN substrates found in root exudate to assess the metabolic capabilities soil microbial communities. Although microbial biomass did not et al., 1990; Vogt et al., 1986). The fact that roots and differ among ecosystems, principal components analysis of bacterial, leaves differ chemically could lead to changes in microactinomycetal, and fungal PLFAs clearly separated the microbial com- bial community composition and function, depending munities of the three ecosystems. Similarly, principal components on temporal variation in the proportion of leaf vs. root analysis separated microbial communities by differences in growth on litter entering soil. In sugar maple‐dominated forests, carbohydrates, organic acids, and amino acids. Discrimination among the greatest addition of root litter to soil occurs when microbial communities in the three ecosystems by PLFAs and sub- fine-root mortality peaks in early autumn (Hendrick and strate use occurred in spring, summer, and fall, but the individual Pregitzer, 1992), but substantial inputs also can occur PLFAs and substrates contributing to discrimination changed during throughout the growing season. Unlike the continuous the growing season. Our results indicate that floristically and edaphiinput of dead fine roots to mineral soil, the majority of cally distinct forest ecosystems also differ in microbial community composition and substrate use. This pattern was consistent across aboveground litter is deposited in late autumn. Seasonal the growing season and repeatedly occurred across relatively large variation in above- and belowground litter production land areas. could influence microbial community composition and function, depending on the types of substrates available for microbial metabolism.

Denitrification in aquatic environments: a cross-system analysis

Abstract: A meta-analysis was conducted on 136 data sets of denitrification rates (DR) recorded both during the period of highest water temperature and monthly in five types of aquatic ecosystems: oceans, coastal environments, estuaries, lakes and rivers. There was a gradual increase of DR from the ocean to rivers and lakes at both scales, with the rivers showing the highest DR variability. Denitrification peaked during summertime and showed highest seasonal variability in lakes and rivers. High concentrations of nitrate and interstitially-dissolved organic carbon as well as low oxygen concentration in the overlying water enhanced DR both during summer and at a seasonal scale whereas total phosphorus did at the seasonal scale only. There was a positive linear relationship between overlying nitrate and DR over the range of 1–970 µmol NO3 (r2 = 0.86, P = 0.001). DR in lakes and rivers might reach values doubling those in the more denitrifying terrestrial ecosystems (e.g. agrosystems). Discrepancies in DR and its controlling factors between site-specific studies and this meta-analysis may arise from environmental variability at two, often confounded, scales of observation: the habitat and the ecosystem level. Future studies on denitrification in aquatic environments should address the topic of spatial heterogeneity more thoroughly.

The implications of predicted climate change for insect pests in the UK, with emphasis on non‐indigenous species

Abstract: Recent estimates for global warming predict increases in global mean surface air temperatures (relative to 1990) of between 1 and 3.5 °C, by 2100. The impact of such changes on agricultural systems in mid- to high-latitude regions are predicted to be less severe than in low-latitude regions, and possibly even beneficial, although the influence of pests and diseases is rarely taken into account. Most studies have concluded that insect pests will generally become more abundant as temperatures increase, through a number of inter-related processes, including range extensions and phenological changes, as well as increased rates of population development, growth, migration and over-wintering. A gradual, continuing rise in atmospheric CO2 will affect pest species directly (i.e. the CO2 fertilization effect) and indirectly (via interactions with other environmental variables). However, individual species responses to elevated CO2 vary: consumption rates of insect herbivores generally increase, but this does not necessarily compensate fully for reduced leaf nitrogen. The consequent effects on performance are strongly mediated via the host species. Some recent experiments under elevated CO2 have suggested that aphids may become more serious pests, although other studies have discerned no significant effects on sap-feeding homopterans. However, few, if any of these experiments have fully considered the effects on pest population dynamics. Climate change is also considered from the perspective of changes in the distribution and abundance of species and communities. Marked changes in the distribution of well-documented species – including Odonata, Orthoptera and Lepidoptera – in north-western Europe, in response to unusually hot summers, provide useful indications of the potential effects of climate change. Migrant pests are expected to respond more quickly to climate change than plants, and may be able to colonize newly available crops/habitats. Range expansions, and the removal of edge effects, could result in the increased abundance of species presently near the northern limits of their ranges in the UK. However, barriers to range expansions, or shifts, may include biotic (competition, predation, parasitism and disease), as well as abiotic, factors. Climatic phenomena, ecosystem processes and human activities are interactive and interdependent, making long-term predictions extremely tenuous. Nevertheless, it appears prudent to prepare for the possibility of increases in the diversity and abundance of pest species in the UK, in the context of climate change.

What is a healthy ecosystem

Abstract: Rapid deterioration of the world’s major ecosystems has intensified the need for effective environmental monitoring and the development of operational indicators of ecosystem health. Ecosystem health represents a desired endpoint of environmental management, but it requires adaptive, ongoing definition and assessment. We propose that a healthy ecosystem is one that is sustainable ‐ that is, it has the ability to maintain its structure (organization) and function (vigor) over time in the face of external stress (resilience). Various methods to quantify these three ecosystem attributes (vigor, organization, and resilience) are discussed. These attributes are then folded into a comprehensive assessment of ecosystem health. A network analysis based ecosystem health assessment is developed and tested using trophic exchange networks representing several different aquatic ecosystems. Results indicate the potential of such an ecosystem health assessment for evaluating the relative health of similar ecosystems, and quantifying the effects of natural or anthropogenic stress on the health of a particular ecosystem over time.

Pacific Salmon Carcasses: Essential Contributions of Nutrients and Energy for Aquatic and Terrestrial Ecosystems

Abstract: Pacific salmon and other anadromous salmonids represent a major vector for transporting marine nutrients across ecosystem boundaries (i.e., from marine to freshwater and terrestrial ecosystems). Salmon carcasses provide nutrients and energy to biota within aquatic and terrestrial ecosystems through various pathways. In this paper we review and synthesize the growing number of studies documenting this process in different localities. We also discuss the implications for maintaining the nutrient feedback system. Our findings show that future management will need to view spawning salmon and their carcasses as important habitat components for sustaining the production of fish as well as other salmon-dependent species within watersheds.