Ecosystems integrity and services are threatened by anthropogenic global changes. Mitigating and adapting to these changes require knowledge of ecosystem functioning in the expected novel ...environments, informed in large part through experimentation and modelling. This paper describes 13 advanced controlled environment facilities for experimental ecosystem studies, herein termed ecotrons, open to the international community. Ecotrons enable simulation of a wide range of natural environmental conditions in replicated and independent experimental units while measuring various ecosystem processes. This capacity to realistically control ecosystem environments is used to emulate a variety of climatic scenarios and soil conditions, in natural sunlight or through broad‐spectrum lighting. The use of large ecosystem samples, intact or reconstructed, minimizes border effects and increases biological and physical complexity. Measurements of concentrations of greenhouse trace gases as well as their net exchange between the ecosystem and the atmosphere are performed in most ecotrons, often quasi continuously. The flow of matter is often tracked with the use of stable isotope tracers of carbon and other elements. Equipment is available for measurements of soil water status as well as root and canopy growth. The experiments ran so far emphasize the diversity of the hosted research. Half of them concern global changes, often with a manipulation of more than one driver. About a quarter deal with the impact of biodiversity loss on ecosystem functioning and one quarter with ecosystem or plant physiology. We discuss how the methodology for environmental simulation and process measurements, especially in soil, can be improved and stress the need to establish stronger links with modelling in future projects. These developments will enable further improvements in mechanistic understanding and predictive capacity of ecotron research which will play, in complementarity with field experimentation and monitoring, a crucial role in exploring the ecosystem consequences of environmental changes.
Experimentation and modelling are necessary to predict ecosystem functioning under future environments and to develop mitigating and adapting strategies. This paper describes 13 advanced controlled environment facilities, called ecotrons, open to the international community. An ecotron comprises a set of replicated enclosures designed to host ecosystems samples and enable realistic simulations of above‐ and belowground environmental conditions, while simultaneously and automatically measuring ecosystem processes. The characteristics of these infrastructures are given as well as examples of collaborative projects hosted so far.
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. This derives from an inability of field studies to avoid the confounding effects of natural intra-annual and interannual variability in temperature and precipitation. Here we present results from a four-year study using replicate 12,000-kg intact tallgrass prairie monoliths located in four 184-m3 enclosed lysimeters. We exposed 6 of 12 monoliths to an anomalously warm year in the second year of the study and continuously quantified rates of ecosystem processes, including NEE. We find that warming decreases NEE in both the extreme year and the following year by inducing drought that suppresses net primary productivity in the extreme year and by stimulating heterotrophic respiration of soil biota in the subsequent year. Our data indicate that two years are required for NEE in the previously warmed experimental ecosystems to recover to levels measured in the control ecosystems. This time lag caused net ecosystem carbon sequestration in previously warmed ecosystems to be decreased threefold over the study period, compared with control ecosystems. Our findings suggest that more frequent anomalously warm years, a possible consequence of increasing anthropogenic carbon dioxide levels, may lead to a sustained decrease in carbon dioxide uptake by terrestrial ecosystems.
Arid ecosystems, which occupy about 35% of the Earth's terrestrial surface area, are believed to be among the most responsive to elevated CO2. Net ecosystem CO2 exchange (NEE) was measured in the ...eighth year of CO2 enrichment at the Nevada Desert Free‐Air CO2 Enrichment (FACE) Facility between the months of December 2003–December 2004. On most dates mean daily NEE (24 h) (μmol CO2 m−2 s−1) of ecosystems exposed to elevated atmospheric CO2 were similar to those maintained at current ambient CO2 levels. However, on sampling dates following rains, mean daily NEEs of ecosystems exposed to elevated CO2 averaged 23 to 56% lower than mean daily NEEs of ecosystems maintained at ambient CO2. Mean daily NEE varied seasonally across both CO2 treatments, increasing from about 0.1 μmol CO2 m−2 s−1 in December to a maximum of 0.5–0.6 μmol CO2 m−2 s−1 in early spring. Maximum NEE in ecosystems exposed to elevated CO2 occurred 1 month earlier than it did in ecosystems exposed to ambient CO2, with declines in both treatments to lowest seasonal levels by early October (0.09±0.03 μmol CO2 m−2 s−1), but then increasing to near peak levels in late October (0.36±0.08 μmol CO2 m−2 s−1), November (0.28±0.03 μmol CO2 m−2 s−1), and December (0.54±0.06 μmol CO2 m−2 s−1). Seasonal patterns of mean daily NEE primarily resulted from larger seasonal fluctuations in rates of daytime net ecosystem CO2 uptake which were closely tied to plant community phenology and precipitation. Photosynthesis in the autotrophic crust community (lichens, mosses, and free‐living cyanobacteria) following rains were probably responsible for the high NEEs observed in January, February, and late October 2004 when vascular plant photosynthesis was low. Both CO2 treatments were net CO2 sinks in 2004, but exposure to elevated CO2 reduced CO2 sink strength by 30% (positive net ecosystem productivity=127±17 g C m−2 yr−1 ambient CO2 and 90±11 g C m−2 yr−1 elevated CO2, P=0.011). This level of net C uptake rivals or exceeds levels observed in some forested and grassland ecosystems. Thus, the decrease in C sequestration seen in our study under elevated CO2– along with the extensive coverage of arid and semi‐arid ecosystems globally – points to a significant drop in global C sequestration potential in the next several decades because of responses of heretofore overlooked dryland ecosystems.
The Penman–Monteith combination equation, which is most frequently used to derive the surface conductance to water vapour (
G
s), implicitly assumes the energy balance to be closed. Any energy ...imbalance (positive or negative) will thus affect the calculated
G
s. 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
s 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. Based on our limited understanding of the nature of the energy imbalance, we tend to favour an approach which preserves the Bowen-ratio and closes the energy balance on a larger time scale.
•Chihuahuan, Sonoran and Mojave Deserts vary in precipitation amount and seasonal distribution.•Due to hydrologic losses, ET was a better metric of ecosystem-available water than ...precipitation.•Ecosystem water use efficiency (GEP/ET) did not differ between winter and summer.•Due to lower respiration, winter seasons were critical for net carbon uptake.•Reduced 21st century winter precipitation reduced the carbon sink ∼6.8TgCyr1 in these 3 deserts.
Global-scale studies suggest that dryland ecosystems dominate an increasing trend in the magnitude and interannual variability of the land CO2 sink. However, such model-based analyses are poorly constrained by measured CO2 exchange in open shrublands, which is the most common global land cover type, covering ∼14% of Earth’s surface. Here we evaluate how the amount and seasonal timing of water availability regulate CO2 exchange between shrublands and the atmosphere. We use eddy covariance data from six US sites across the three warm deserts of North America with observed ranges in annual precipitation of ∼100–400mm, annual temperatures of 13–18°C, and records of 2–8 years (33 site-years in total). The Chihuahuan, Sonoran and Mojave Deserts present gradients in both mean annual precipitation and its seasonal distribution between the wet-winter Mojave Desert and the wet-summer Chihuahuan Desert. We found that due to hydrologic losses during the wettest summers in the Sonoran and Chihuahuan Deserts, evapotranspiration (ET) was a better metric than precipitation of water available to drive dryland CO2 exchange. In contrast with recent synthesis studies across diverse dryland biomes, we found that NEP could not be directly predicted from ET due to wintertime decoupling of the relationship between ecosystem respiration (Reco) and gross ecosystem productivity (GEP). Ecosystem water use efficiency (WUE=GEP/ET) did not differ between winter and summer. Carbon use efficiency (CUE=NEP/GEP), however, was greater in winter because Reco returned a smaller fraction of carbon to the atmosphere (23% of GEP) than in summer (77%). Combining the water-carbon relations found here with historical precipitation since 1980, we estimate that lower average winter precipitation during the 21st century reduced the net carbon sink of the three deserts by an average of 6.8TgC yr1. Our results highlight that winter precipitation is critical to the annual carbon balance of these warm desert shrublands.
1. The occurrence and intensity of climate extremes, such as extremely warm years, are expected to continue to increase with increasing tropospheric radiative forcing caused by anthropogenic ...greenhouse gas emissions. 2. Responses of terrestrial ecosystem processes and services - such as above-ground net primary productivity (ANPP) and maintenance of plant species diversity - to these extreme years for multiple years post-perturbation are poorly understood but can have significant feedback effects on net ecosystem CO₂ uptake and ecosystem carbon sequestration. 3. We exposed six 12 000-kg intact natural tallgrass prairie monoliths to an extremely warm year (+4 °C in 2003) in the second year of a 4-year study (2002-2005) using the EcoCELL whole-ecosystem controlled-environment, gas exchange facility. Six control monoliths were not warmed in the second year but were maintained under average field conditions. Natural diel and seasonal patterns in air temperature were maintained in both treatments throughout the study. Thus, with the exception of the second year in the 'warmed' treatment, we created 4 years of nearly identical climate in all EcoCELLs. 4. Interannual ANPP (10 cm clipping height) responses of the entire plant community to the extreme year were largely determined by responses of the dominant C₄ grasses. These included large decreases in ANPP in 2003 followed by complete recovery to levels observed in the control ecosystems in the year following warming. Species richness and productivity of the nitrogen-fixing plant functional group appeared to play a role in defining overall plant community ANPP, however, even though this richness and productivity could not explain the decrease in community ANPP observed in warmed ecosystems in the second year (2003) of the study or its recovery in the year after (2004). Surprisingly, very few of the 67 species present in plant communities during the 4-year study responded to the warm year at any time during or after the treatment. 5. Synthesis. Results from this study indicate that as extreme climate years become more prevalent, their immediate and lagged impacts on collective ecosystem processes, such as whole-community ANPP, may be very pronounced, but effects on component ecosystem processes may be limited to the dominant plant functional group (ANPP).
The endocrinology regulating ovulation of the desired number of oocytes in the ovarian cycle is well described, particularly in mono-ovulatory species. Less is known about the characteristics that ...make one follicle suitable for ovulation while most other follicles die by atresia. Bromodeoxyuridine (BrdU) injection was used to characterize granulosa cell proliferation rates in developing ovarian follicles in the estrous cycle of mice. This methodology allowed identification of follicle diameters of secondary (80–130 µm), follicle-stimulating hormone (FSH)-sensitive (130–170 µm), FSH-dependent (170–350 µm), and preovulatory (>350 µm) follicles. Few preovulatory-sized follicles were present in the ovaries of mice at estrus, the beginning of the cycle. Progressive increases were seen at metestrus and diestrus, when full accumulation of the preovulatory cohort (∼10 follicles) occurred. BrdU pulse-chase studies determined granulosa cell proliferation rates in the 24–48 h before the follicle reached the preovulatory stage. This showed that slow-growing follicles were not able to survive to the preovulatory stage. Mathematical modeling of follicle growth rates determined that the largest follicles at the beginning of the cycle had the greatest chance of becoming preovulatory. However, smaller follicles could enter the preovulatory follicle pool if low numbers of large antral follicles were present at the beginning of the cycle. In this instance, rapidly growing follicles had a clear selection advantage. The developing follicle pool displays heterogeneity in granulosa cell proliferation rates, even among follicles at the same stage of development. This parameter appears to influence whether a follicle can ovulate or become atretic. Summary Sentence Bromodeoxyuridine pulse-chase labeling revealed that only fast-growing follicles survived to ovulation and follicle growth modeling determined that initial follicle size or follicle growth rate can be advantageous for follicle survival. Graphical Abstract
The effects of hydroponic nutrient solution composition and pH on growth and mineral content of green onions was evaluated. Three onion varieties Allium cepa L. ('Deep Purple' and 'Purplette') and A. ...fistulosum L. ('Kinka') were propagated in three nutrient solutions (Peter's Hydro-Sol, modified Hoagland's, and half-strength modified Hoagland's) at two pH levels (5.8 and 6.5) in a three-by-two factorial design applied in a randomized block with three replications. Seeds were germinated in Cropking's Oasis Horticubes under greenhouse conditions and irrigated with tap water. Once the seedlings reached the flag stage, the plants were placed into hydroponic units within the greenhouse and grown under ambient conditions. Plants were harvested 30 d after transplanting to the hydroponic units. The results indicated nutrient solution, pH, and variety significantly affected several plant physiological variables. Total biomass and edible biomass production was as high for plants grown in half-strength Hoagland's nutrient solution as for those grown in the other solutions. Total biomass was greatest for plants grown at a solution pH of 6.5. 'Deep Purple' produced a significantly greater overall total biomass than did 'Purplette' or 'Kinka.' Hydro-Sol tended to produce onions with highest mineral content. Due to the fact that biomass production was as great in the half-strength Hoagland's as in the more concentrated solution and that a pH of 6.5 produced greater total biomass, the half-strength Hoagland's solution at pH 6.5 was the preferred nutrient solution evaluated in this research. Selection of an appropriate nutrient solution must consider both edible biomass production and mineral content. In the research reported here, the solution that produced the greatest biomass did not produce plant material with the highest mineral content.
Summary 1. The occurrence and intensity of climate extremes, such as extremely warm years, are expected to continue to increase with increasing tropospheric radiative forcing caused by anthropogenic ...greenhouse gas emissions. 2. Responses of terrestrial ecosystem processes and services – such as above‐ground net primary productivity (ANPP) and maintenance of plant species diversity – to these extreme years for multiple years post‐perturbation are poorly understood but can have significant feedback effects on net ecosystem CO 2 uptake and ecosystem carbon sequestration. 3. We exposed six 12 000‐kg intact natural tallgrass prairie monoliths to an extremely warm year (+4 °C in 2003) in the second year of a 4‐year study (2002–2005) using the EcoCELL whole‐ecosystem controlled‐environment, gas exchange facility. Six control monoliths were not warmed in the second year but were maintained under average field conditions. Natural diel and seasonal patterns in air temperature were maintained in both treatments throughout the study. Thus, with the exception of the second year in the ‘warmed’ treatment, we created 4 years of nearly identical climate in all EcoCELLs. 4. Interannual ANPP (10 cm clipping height) responses of the entire plant community to the extreme year were largely determined by responses of the dominant C 4 grasses. These included large decreases in ANPP in 2003 followed by complete recovery to levels observed in the control ecosystems in the year following warming. Species richness and productivity of the nitrogen‐fixing plant functional group appeared to play a role in defining overall plant community ANPP, however, even though this richness and productivity could not explain the decrease in community ANPP observed in warmed ecosystems in the second year (2003) of the study or its recovery in the year after (2004). Surprisingly, very few of the 67 species present in plant communities during the 4‐year study responded to the warm year at any time during or after the treatment. 5. Synthesis . Results from this study indicate that as extreme climate years become more prevalent, their immediate and lagged impacts on collective ecosystem processes, such as whole‐community ANPP, may be very pronounced, but effects on component ecosystem processes may be limited to the dominant plant functional group (ANPP).
The efficient and highly stereoselective syntheses of a variety of (Z)‐configured, substituted α‐(hydroxymethyl)‐β‐iodo‐acrylates from prop‐2‐ynoate and various aldehydes was achieved. The synthetic ...protocol involves a simple one‐pot coupling reaction under mild conditions, promoted by MgI2, which serves both as a Lewis acid and iodine source for a BaylisHillman‐type reaction. All adducts were generated in good‐to‐excellent yields, the (Z)‐isomers being formed in high selectivity (>98%). The conversion of methyl prop‐2‐ynoate into an active ‘β‐iodo allenolate’ intermediate, which then nucleophilically attacks an aldehyde, is proposed as a plausible reaction mechanism.
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