Integration of ecosystem science into radioecology: A consensus perspective.

In the Fall of 2016 a workshop was held which brought together over 50 scientists from the ecological and radiological fields to discuss feasibility and challenges of reintegrating ecosystem science into radioecology. There is a growing desire to incorporate attributes of ecosystem science into radiological risk assessment and radioecological research more generally, fueled by recent advances in quantification of emergent ecosystem attributes and the desire to accurately reflect impacts of radiological stressors upon ecosystem function. This paper is a synthesis of the discussions and consensus of the workshop participant's responses to three primary questions, which were: 1) How can ecosystem science support radiological risk assessment? 2) What ecosystem level endpoints potentially could be used for radiological risk assessment? and 3) What inference strategies and associated methods would be most appropriate to assess the effects of radionuclides on ecosystem structure and function? The consensus of the participants was that ecosystem science can and should support radiological risk assessment through the incorporation of quantitative metrics that reflect ecosystem functions which are sensitive to radiological contaminants.

Resource Concentration Modulates the Fate of Dissimilated Nitrogen in a Dual-Pathway Actinobacterium.

Respiratory ammonification and denitrification are two evolutionarily unrelated dissimilatory nitrogen (N) processes central to the global N cycle, the activity of which is thought to be controlled by carbon (C) to nitrate (NO ) ratio. Here we find that C5, a novel dual-pathway denitrifier/respiratory ammonifier, disproportionately utilizes ammonification rather than denitrification when grown under low C concentrations, even at low C:NO ratios. This finding is in conflict with the paradigm that high C:NO ratios promote ammonification and low C:NO ratios promote denitrification.

Plant species effects on soil nutrients and chemistry in arid ecological zones.

The presence of vegetation strongly influences ecosystem function by controlling the distribution and transformation of nutrients across the landscape. The magnitude of vegetation effects on soil chemistry is largely dependent on the plant species and the background soil chemical properties of the site, but has not been well quantified along vegetation transects in the Great Basin. We studied the effects of plant canopy cover on soil chemistry within five different ecological zones, subalpine, montane, pinyon-juniper, sage/Mojave transition, and desert shrub, in the Great Basin of Nevada all with similar underlying geology.

Earthworm effects on native grassland root system dynamics under natural and increased rainfall.

Earthworms (EWs) can modify soil structure and nutrient availability, and hence alter conditions for plant growth through their burrowing and casting activities. However, few studies have specifically quantified EW effects by experimentally manipulating earthworm densities (EWDs). In an earlier field study in native grassland ecosystems exposed to ambient and experimentally elevated rainfall (+280 mm year(-1), projected under some climate change scenarios), we found no effects of EWDs (37, 114, 169 EW m(-2)) and corresponding EW activity on aboveground net primary productivity (ANPP), even though soil nutrient availability likely increased with increasing EWDs.

Do increased summer precipitation and N deposition alter fine root dynamics in a Mojave Desert ecosystem?

Climate change is expected to impact the amount and distribution of precipitation in the arid southwestern United States. In addition, nitrogen (N) deposition is increasing in these regions due to increased urbanization. Responses of belowground plant activity to increases in soil water content and N have shown inconsistent patterns between biomes.

Loss of plant biodiversity eliminates stimulatory effect of elevated CO2 on earthworm activity in grasslands.

Earthworms are among the world's most important ecosystem engineers because of their effects on soil fertility and plant productivity. Their dependence on plants for carbon, however, means that any changes in plant community structure or function caused by rising atmospheric CO2 or loss of plant species diversity could affect earthworm activity, which may feed back on plant communities. Production of surface casts measured during three consecutive years in field experimental plots (n = 24, 1.

Concurrent and lagged impacts of an anomalously warm year on autotrophic and heterotrophic components of soil respiration: a deconvolution analysis.

*Partitioning soil respiration into autotrophic (R(A)) and heterotrophic (R(H)) components is critical for understanding their differential responses to climate warming. *Here, we used a deconvolution analysis to partition soil respiration in a pulse warming experiment. We first conducted a sensitivity analysis to determine which parameters can be identified by soil respiration data.

On the consequences of the energy imbalance for calculating surface conductance to water vapour.

The Penman-Monteith combination equation, which is most frequently used to derive the surface conductance to water vapour (G), implicitly assumes the energy balance to be closed. Any energy imbalance (positive or negative) will thus affect the calculated G. Using eddy covariance energy flux data from a temperate grassland and a desert shrub ecosystem we explored five possible approaches of closing the energy imbalance and show that calculated G may differ considerably between these five approaches depending on the relative magnitudes of sensible and latent heat fluxes, and the magnitude and sign of the energy imbalance.

Prolonged suppression of ecosystem carbon dioxide uptake after an anomalously warm year.

Terrestrial ecosystems control carbon dioxide fluxes to and from the atmosphere through photosynthesis and respiration, a balance between net primary productivity and heterotrophic respiration, that determines whether an ecosystem is sequestering carbon or releasing it to the atmosphere. Global and site-specific data sets have demonstrated that climate and climate variability influence biogeochemical processes that determine net ecosystem carbon dioxide exchange (NEE) at multiple timescales. Experimental data necessary to quantify impacts of a single climate variable, such as temperature anomalies, on NEE and carbon sequestration of ecosystems at interannual timescales have been lacking.

Atmospheric mercury exchange with a tallgrass prairie ecosystem housed in mesocosms.

This study focused on characterizing air-surface mercury Hg exchange for individual surfaces (soil, litter-covered soil and plant shoots) and ecosystem-level flux associated with tallgrass prairie ecosystems housed inside large mesocosms over three years. The major objectives of this project were to determine if individual surface fluxes could be combined to predict ecosystem-level exchange and if this low-Hg containing ecosystem was a net source or sink for atmospheric Hg. Data collected in the field were used to validate fluxes obtained in the mesocosm setting.

Divergence of reproductive phenology under climate warming.

Because the flowering and fruiting phenology of plants is sensitive to environmental cues such as temperature and moisture, climate change is likely to alter community-level patterns of reproductive phenology. Here we report a previously unreported phenomenon: experimental warming advanced flowering and fruiting phenology for species that began to flower before the peak of summer heat but delayed reproduction in species that started flowering after the peak temperature in a tallgrass prairie in North America. The warming-induced divergence of flowering and fruiting toward the two ends of the growing season resulted in a gap in the staggered progression of flowering and fruiting in the community during the middle of the season.

Net carbon exchange and evapotranspiration in postfire and intact sagebrush communities in the Great Basin.

Invasion of non-native annuals across the Intermountain West is causing a widespread transition from perennial sagebrush communities to fire-prone annual herbaceous communities and grasslands. To determine how this invasion affects ecosystem function, carbon and water fluxes were quantified in three, paired sagebrush and adjacent postfire communities in the northern Great Basin using a 1-m3 gas exchange chamber. Most of the plant cover in the postfire communities was invasive species including Bromus tectorum L.

Influence of elevated CO on canopy development and red:far-red ratios in two-storied stands ofRicinus communis.

Vertical structure of plant stands and canopies may change under conditions of elevated CO due to differential responses of overstory and understory plants or plant parts. In the long term, seedling recruitment, competition, and thus population or community structure may be affected. Aside from the possible differential direct effects of elevated CO on photosynthesis and growth, both the quantity and quality of the light below the overstory canopy could be indirectly affected by CO-induced changes in overstory leaf area index (LAI) and/or changes in overstory leaf quality.