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.

Pulse dynamics and microbial processes in aridland ecosystems

Abstract: Summary 1 Aridland ecosystems cover about one-third of terrestrial environments globally, yet the extent to which models of carbon (C) and nitrogen (N) cycling, developed largely from studies of mesic ecosystems, apply to aridland systems remains unclear. 2 Within aridland ecosystems, C and N dynamics are often described by a pulse-reserve model in which episodic precipitation events stimulate biological activity that generate reserves of biomass, propagules and organic matter that prime the ecosystem to respond rapidly to subsequent precipitation events. 3 The role of microbial C and N processing within the pulse-reserve paradigm has not received much study. We present evidence suggesting that fungi play a critical and underappreciated role in aridland soils, including efficient decomposition of recalcitrant C compounds, N-transformations such as nitrification, and nutrient storage and translocation of C and N between plants and biotic soil crusts. While fungi may perform some of these functions in other ecosystems, this ‘fungal loop’ assumes particular importance in the N cycle in aridlands because water availability imposes even greater restrictions on bacterial activity and physicochemical processes limit accumulation of soil organic matter (SOM). 4 We incorporate these findings into a Threshold-Delay Nutrient Dynamics (TDND) model for aridland ecosystems in which plant responses to pulsed precipitation events are mediated by a fungal loop that links C and N cycling, net primary production (NPP) and decomposition in aridland soils. 5 Synthesis. Arid ecosystems are highly sensitive to global environmental change including N deposition and altered precipitation patterns; yet, models from mesic ecosystems do not adequately apply to aridland environments. Our ‘fungal loop’ N cycle model integrates spatial structure with pulse dynamics and extends the pulse-reserve paradigm to include the key role of microbial processes in aridland ecosystem dynamics.

Impacts of climate warming on lake fish community structure and potential effects on ecosystem function

Abstract: Fish play a key role in the trophic dynamics of lakes, not least in shallow systems. With climate warming, complex changes in fish community structure may be expected owing to the direct and indirect effects of temperature, and indirect effects of eutrophication, water-level changes and salinisation on fish metabolism, biotic interactions and geographical distribution. We review published and new data supporting the hypotheses that, with a warming climate, there will be changes in: fish community structure (e.g. higher or lower richness depending on local conditions); life history traits (e.g. smaller body size, shorter life span, earlier and less synchronised reproduction); feeding mode (i.e. increased omnivory and herbivory); behaviour (i.e. stronger association with littoral areas and a greater proportion of benthivores); and winter survival. All these changes imply higher predation on zooplankton and macroinvertebrates with increasing temperatures, suggesting that the changes in the fish communities partly resemble, and may intensify, the effects triggered by eutrophication. Modulating factors identified in cold and temperate systems, such as the presence of submerged plants and winter ice cover, seem to be weaker or non-existent in warm(ing) lakes. Consequently, in the future lower nutrient thresholds may be needed to obtain clear-water conditions and good ecological status in the future in currently cold or temperate lakes. Although examples are still scarce and more research is needed, we foresee biomanipulation to be a less successful restoration tool in warm(ing) lakes without a strong reduction of the nutrient load.

Dissolved organic carbon and nutrients as regulators of lake ecosystems: Resurrection of a more integrated paradigm

Abstract: The primary interpretive paradigm used to study lakes is their trophic status. Oligotrophic lakes have low nutrient loading and low productivity, while eutrophic lakes have high nutrients and high productivity. The strong empirical relationship between nutrient loading and productivity is a valuable tool for teaching, for research, and for management of lakes. In order to incorporate the variety of other known anthropogenic impacts on lakes, however, lake characterization needs to extend beyond the nutrient-productivity paradigm. For example, acid precipitation, heavy metal and toxic organic contaminants, increases in UV radiation, and global warming are all recognized threats to lake ecosystems. One of the key characteristics of lakes that determines how they respond to disturbances such as these is their concentration of colored dissolved organic carbon (CDOC). Here we argue that a paradigm that includes CDOC (using the absorption coefficient at 320 nm as a proxy) as well as nutrients will be useful in predicting and understanding the response of lake ecosystems to multiple stressors. We propose to resurrect the CDOC axis that was proposed by investigators earlier this century and to extend it by adding some operational definitions to permit placing some of the major lake types on the axes in a way that will help us to better understand the structure, function, and response to disturbance of lake ecosystems that are subject to natural and anthropogenic environmental changes at the local, regional, and global scales. Data from a few diverse lakes and a successional sequence in Glacier Bay, Alaska, are used to illustrate the potential utility of the 2-axis model in separating lake types.