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.

Effects of plant composition and diversity on nutrient cycling

Abstract: We evaluated the effects of plant functional group richness on seasonal patterns of soil nitrogen and phosphorus cycling, using serpentine grassland in south San Jose, California. We established experimental plots with four functional types of plants: early-season annual forbs (E), late-season annual forbs (L), nitrogen-fixers (N), and perennial bunchgrasses (P). These groups differ in several traits relevant to nutrient cycling, including phenology, rooting depth, root:shoot ratio, size, and leaf C:N content. Two or three species of each group were planted in single functional group (SFG) treatments, and in two-, three-, and four-way combinations of functional groups. We analyzed available nutrient pool sizes, microbial biomass nitrogen and phosphorus, microbial nitrogen immobilization, nitrification rates, and leaching losses. We used an index of “relative resource use” that incorporates the effects of plants on pool sizes of several depletable soil resources: inorganic nitrogen in all seasons, availabl...

Shifts in Lake N:P Stoichiometry and Nutrient Limitation Driven by Atmospheric Nitrogen Deposition

Abstract: Human activities have more than doubled the amount of nitrogen (N) circulating in the biosphere. One major pathway of this anthropogenic N input into ecosystems has been increased regional deposition from the atmosphere. Here we show that atmospheric N deposition increased the stoichiometric ratio of N and phosphorus (P) in lakes in Norway, Sweden, and Colorado, United States, and, as a result, patterns of ecological nutrient limitation were shifted. Under low N deposition, phytoplankton growth is generally N-limited; however, in high-N deposition lakes, phytoplankton growth is consistently P-limited. Continued anthropogenic amplification of the global N cycle will further alter ecological processes, such as biogeochemical cycling, trophic dynamics, and biological diversity, in the world's lakes, even in lakes far from direct human disturbance.

Genetic diversity enhances the resistance of a seagrass ecosystem to disturbance

Abstract: Motivated by recent global reductions in biodiversity, empirical and theoretical research suggests that more species-rich systems exhibit enhanced productivity, nutrient cycling, or resistance to disturbance or invasion relative to systems with fewer species. In contrast, few data are available to assess the potential ecosystem-level importance of genetic diversity within species known to play a major functional role. Using a manipulative field experiment, we show that increasing genotypic diversity in a habitat-forming species (the seagrass Zostera marina) enhances community resistance to disturbance by grazing geese. The time required for recovery to near predisturbance densities also decreases with increasing eelgrass genotypic diversity. However, there is no effect of diversity on resilience, measured as the rate of shoot recovery after the disturbance, suggesting that more rapid recovery in diverse plots is due solely to differences in disturbance resistance. Genotypic diversity did not affect ecosystem processes in the absence of disturbance. Thus, our results suggest that genetic diversity, like species diversity, may be most important for enhancing the consistency and reliability of ecosystems by providing biological insurance against environmental change.

Methane fluxes show consistent temperature dependence across microbial to ecosystem scales

Abstract: Methane (CH4) is an important greenhouse gas because it has 25 times the global warming potential of carbon dioxide (CO2) by mass over a century. Recent calculations suggest that atmospheric CH4 emissions have been responsible for approximately 20% of Earth's warming since pre-industrial times. Understanding how CH4 emissions from ecosystems will respond to expected increases in global temperature is therefore fundamental to predicting whether the carbon cycle will mitigate or accelerate climate change. Methanogenesis is the terminal step in the remineralization of organic matter and is carried out by strictly anaerobic Archaea. Like most other forms of metabolism, methanogenesis is temperature-dependent. However, it is not yet known how this physiological response combines with other biotic processes (for example, methanotrophy, substrate supply, microbial community composition) and abiotic processes (for example, water-table depth) to determine the temperature dependence of ecosystem-level CH4 emissions. It is also not known whether CH4 emissions at the ecosystem level have a fundamentally different temperature dependence than other key fluxes in the carbon cycle, such as photosynthesis and respiration. Here we use meta-analyses to show that seasonal variations in CH4 emissions from a wide range of ecosystems exhibit an average temperature dependence similar to that of CH4 production derived from pure cultures of methanogens and anaerobic microbial communities. This average temperature dependence (0.96 electron volts (eV)), which corresponds to a 57-fold increase between 0 and 30°C, is considerably higher than previously observed for respiration (approximately 0.65 eV) and photosynthesis (approximately 0.3 eV). As a result, we show that both the emission of CH4 and the ratio of CH4 to CO2 emissions increase markedly with seasonal increases in temperature. Our findings suggest that global warming may have a large impact on the relative contributions of CO2 and CH4 to total greenhouse gas emissions from aquatic ecosystems, terrestrial wetlands and rice paddies.

Fishes as integrators of benthic and pelagic food webs in lakes

Abstract: Studies of lake ecosystems generally focus on pelagic food chains and processes. Recently, there has been an emerging recognition of the importance of benthic production and processes to whole-lake ecosystems. To examine the extent to which zoobenthos contribute to higher trophic level production in lakes, we synthesized diet data from 470 fish populations (15 species) and stable isotope data from 90 fish populations (11 species), all of which are common inhabitants of north-temperate lakes. Across all species considered, zoobenthos averaged 50% of total prey consumption. Indirect consumption of zoobenthos (i.e., feeding on zoobenthos-supported fishes) contributed another 15%, for a total of 65% reliance on benthic secondary production. Stable isotopes provided estimates of mean zoobenthivory ranging from 43% to 59%. For most fish species, consumption of zoobenthos was highly variable among populations. The overwhelming concern of ecologists with pelagic food chains and processes contrasts sharply with our finding that benthic secondary production plays a central role in supporting higher trophic level production. This extensive zoobenthivory can subsidize fish populations, leading to apparent competition and otherwise altering trophic dynamics and ecosystem processes in the pelagic zone. We argue for a more integrated view of lake ecosystems that recognizes the duality of benthic and pelagic production pathways. Food web models that explicitly consider energy flow from pelagic and benthic sources will provide a more realistic energy flow template for understanding the regulation of lake ecosystem functioning.