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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. A double precipitation treatment did not significantly affect flowering and fruiting phenology. Variation among species in the direction and magnitude of their response to warming caused compression and expansion of the reproductive periods of different species, changed the amount of overlap between the reproductive phases, and created possibilities for an altered selective environment to reshape communities in a future warmed world.

Ecosystem CO 2 uptake: Prolonged after-effects of an extremely warm year Earth's terrestrial ecosystems strongly modulate levels of CO2 in the atmosphere through seasonal changes in net plant productivity (CO2 absorbance) and soil microbial respiration (CO 2 release). It has been known for decades that these processes respond to seasonal shifts in climate, especially temperature, resulting in the zig-zag form of the global CO 2 curve, but the data necessary to quantify impacts of a single climate variable at interannual timescales have been lacking. A four-year study using intact tallgrass prairie ecosystems in controlled environment chambers (like the one on the cover, showing plant communities a few weeks after summer mowing) now provides some of the missing data. The results show that one anomalously warm year reduces net ecosystem CO 2 exchange for that year and the year after. Carbon sequestration in ecosystems exposed to high temperatures for a year is a third of that in controls. These findings suggest that more frequent anomalously warm years, a possible consequence of rising anthropogenic CO 2 levels, could lead to a sustained decrease in CO 2 uptake by terrestrial ecosystems. Terrestrial ecosystems control carbon dioxide fluxes to and from the atmosphere 1 , 2 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 1 , 3 , 4 , 5 and site-specific 6 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-m 3 enclosed lysimeters 7 . We exposed 6 of 12 monoliths to an anomalously warm year in the second year of the study 8 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 9 , a possible consequence of increasing anthropogenic carbon dioxide levels 10 , may lead to a sustained decrease in carbon dioxide uptake by terrestrial ecosystems.

We quantified the temporal trend and climatic sensitivity of vegetation phenology in dryland ecosystems in the US Great Basin during 1982–2011. Our results indicated that vegetation greenness in the Great Basin increased significantly during the study period, and this positive trend occurred in autumn but not in spring and summer. Spatially, increases in vegetation greenness were more apparent in the northwestern, southeastern, and eastern Great Basin but less apparent in the central and southwestern Great Basin. In addition, the start of growing season (SOS) was not advanced while the end of growing season (EOS) was delayed significantly at a rate of 3.0 days per decade during the study period. The significant delay in EOS and lack of earlier leaf onset caused growing season length (GSL) to increase at a rate of 3.0 days per decade. Interestingly, we found that the interannual variation of mean vegetation greenness calculated for the period of March to November (spring, summer, and autumn – SSA) was not significantly correlated with mean surface air temperature in SSA but was strongly correlated with total precipitation. On a seasonal basis, the variation of mean vegetation greenness in spring, summer, and autumn was mainly attributable to changes in pre-season precipitation in winter and spring. Nevertheless, climate warming appeared to play a strong role in extending GSL that, in turn, resulted in the upward trend in mean vegetation greenness. Overall, our results suggest that changes in wintertime and springtime precipitation played a stronger role than temperature in affecting the interannual variability of vegetation greenness, while climate warming was mainly responsible for the upward trend in vegetation greenness we observed in Great Basin dryland ecosystems during the 30-year period from 1982 to 2011.

AIMS: Climate (precipitation and temperature) and vegetation cover strongly influence surface soil chemical and nutrient properties. The objectives of our study were to quantify the responsiveness of soil chemical properties to climate gradients and how the presence of plant canopies modulates this responsiveness in the arid ecosystems of the Great Basin of Nevada, U.S.A. METHODS: We measured chemical properties of surface soils sampled from between- and under-canopy microsites along a latitudinal-elevational climate gradient with similar underlying geology to quantify responses to climate alone (between-canopy) and to climate and vegetation combined (under-canopy). RESULTS: Only half of the ten soil chemical properties measured (pH, NH₄-N, P, Mg²⁺, and K⁺) responded significantly to the large climate gradients without the influence of canopy cover. The presence of plant canopies significantly amplified both the climate responses and caused significant responses in additional soil chemical properties to climate gradients, especially for nitrate-N, calcium, total organic C, and total N. CONCLUSIONS: Our results suggest that vegetation canopy is a driving factor in defining how soil chemical properties of Great Basin ecosystems respond to climate and anthropogenic climate change.

Semi-arid and arid ecosystems dominated by shrubs (“dry shrublands”) are an important component of the global C cycle, but impacts of climate change and elevated atmospheric CO₂ on biogeochemical cycling in these ecosystems have not been synthetically assessed. This study synthesizes data from manipulative studies and from studies contrasting ecosystem processes in different vegetation microsites (that is, shrub or herbaceous canopy versus intercanopy microsites), to assess how changes in climate and atmospheric CO₂ affect biogeochemical cycles by altering plant and microbial physiology and ecosystem structure. Further, we explore how ecosystem structure impacts on biogeochemical cycles differ across a climate gradient. We found that: (1) our ability to project ecological responses to changes in climate and atmospheric CO₂ is limited by a dearth of manipulative studies, and by a lack of measurements in those studies that can explain biogeochemical changes, (2) changes in ecosystem structure will impact biogeochemical cycling, with decreasing pools and fluxes of C and N if vegetation canopy microsites were to decline, and (3) differences in biogeochemical cycling between microsites are predictable with a simple aridity index (MAP/MAT), where the relative difference in pools and fluxes of C and N between vegetation canopy and intercanopy microsites is positively correlated with aridity. We conclude that if climate change alters ecosystem structure, it will strongly impact biogeochemical cycles, with increasing aridity leading to greater heterogeneity in biogeochemical cycling among microsites. Additional long-term manipulative experiments situated across dry shrublands are required to better predict climate change impacts on biogeochemical cycling in deserts.

PurposeTo study the efficacy and efficiency of a “universal warming protocol” for vitrified human embryos, based on subsequent steps with 1 and 0.5 M concentration of extracellular cryoprotectant (ECCP).MethodTwo studies on patients undergoing fertility treatments via ICSI: a prospective randomized controlled trial (RCT) and a retrospective cohort study (CS). Setting: Private assisted reproductive (AR) center.RCT: duration 01/03/2017–01/10/2017; 315 embryos at blastocyst stage obtained from 169 patients. Each patient’s embryos were first randomized for vitrification with two different kits: Vitrification Kit (Kitazato, Japan) and Sage Vitrification Kit (Origio, Denmark). The embryos were randomly warmed with either Kitazato (K) or Sage (S) warming kits, specifically: group A (KK), group B (KS), group C (SK), and group D (SS). Primary outcome measure: survival rate (number of embryos surviving per number of embryos warmed). Secondary: implantation rate (number of embryos implanted per number of embryos transferred).CS: duration 01/01/2013–31/12/2015 embryos from patients’ own oocytes; 10/04/2015–31/07/2017 embryos from donors’ oocytes. A total of 1055 embryos vitrified at cleavage stage obtained from 631 warming cycles: 847 of these obtained from patients’ own oocytes, 208 egg-donation-derived embryos. Each patient’s embryos were vitrified and warmed in various combinations of three different vitrification/warming kits: Kitazato (K), Sage (S), or made in-house in our laboratory (H). Vitrification/warming kits from different manufacturers are routinely used in our AR center, and the warming procedures are randomly performed with any available kit on a “first-in-first-out” basis, irrespective of the kit used for vitrification. Group names: KK, KS, SK, SS, SH, HK, HS, HH (embryos from patients’ own oocytes); eKK, eKS, eSK, eSS (egg-donation-derived embryos).ResultsCryo-survival rates were comparable in all study groups.RCT. Group A 99.0% (96/97), group B 98.8% (83/84), group C 98.4% (61/62), and group D 98.6% (71/72).CS. Embryos from patients’ own oocytes: KK 96.4% (54/56), KS 100.0% (13/13), SK 98.8% (80/81), SS 97.2% (174/179), SH 97.6% (40/41), HK 95.2% (20/21), HS 99.5% (187/188), and HH 97.4% (261/268). Egg-donation-derived embryos: eKK 100.0% (91/91), eKS 98.4% (60/61), eSK 100.0% (26/26), and eSS 96.7 (29/30).Implantation was generally comparable in all study groups—exceptions were in CS: KS vs. SK (P = 0.049), SS (P = 0.012), HS (P = 0.010), HH (P = 0.025); and SH vs. SS (P = 0.042), HS (P = 0.035).ConclusionWorldwide, millions of embryos have been cryopreserved using different vitrification kits; these studies establish that it is possible to combine different kits for vitrification and warming using a universal warming protocol. This can optimize costs, simplify lab routines, and favor embryo exchange between IVF centers.RCT registration numberISRCTN12342851.

For many years, wind turbine blade experts have based their designs on airfoil polars obtained with panel methods. These are quick to be set and sufficiently robust. On the other hand, their accuracy intrinsically decreases after stall, where simple post-stall extrapolation functions are introduced. Also, the complex shapes of wind turbine blade airfoils, especially the thick ones for use near the hub, introduce challenging simulation requirements at low Reynolds (Re) numbers. Both these issues are now coming at hand in many modern wind energy applications, like for example in stall-controlled small turbines or in utility-scale rotors experiencing extreme loading in parked conditions. Overall, it is acknowledged that higher-accuracy airfoil polars are needed to keep the reliability of engineering design methods high. The present study aims at numerically investigating the potential impact of high-fidelity, Computational Fluid Dynamics (CFD) techniques in predicting the near and post-stall behavior of a typical wind turbine blade airfoil in comparison to both state-of-the-art panel methods and RANS CFD approaches. To this end, the ubiquitous S809 test case has been selected, as it is known to be particularly challenging and for which experimental data have been available from the literature. More specifically, an extended analysis has been first carried out using a RANS approach (both steady and unsteady) to assess the sensitivity on the main simulation settings, with particular focus on turbulence closure. Then, a few high-fidelity simulations based on both the traditional DDES and the innovative LBM approaches have been performed to investigate the rate of improvement in modeling the underlying physics when the airfoil operates in the post-stall regime. Finally, a critical analysis of the different approaches is carried out and the prospects for wind energy applications are discussed.

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. The lack of effects of EWDs on ANPP suggested that EWs may have adversely affected root systems in that study in some way. The objective of the present study was to quantify responses of root length density (RLD), using data collected from the same grassland plots during the earlier study. RLDs were highest in plots with low EWDs and decreased in plots with higher EWDs. Elevated rainfall primarily increased RLDs in the low EWD treatment (by almost +40%). Reductions in RLDs resulting from increased EWDs did not affect ANPP. Our results indicate that elevating EWDs above ambient levels may limit root growth through large increases in soil bioturbation, but concurrent increases in cast production and nutrient availability may compensate for the suppression of root nutrient absorbing surface area leaving ANPP unchanged, but with shifts in growth (biomass) allocation toward shoots. Similarly, reductions in EWDs appeared to promote higher RLDs that increased soil nutrient foraging in soil with lower amounts of nutrients because of reduced casting activity. Amplified responses observed when rainfall during the growing season was increased suggest that EWDs may mainly affect RLDs and above- vs. belowground growth (biomass) allocation under climate changes that include more frequent wetter-than-average growing seasons.

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. Although plant species differed in their effects on soil chemistry, the desert shrubs Sarcobatus vermiculatus, Atriplex spp., Coleogyne ramosissima, and Larrea tridentata typically exerted the most influence on soil chemistry, especially amounts of K⁺ and total nitrogen, beneath their canopies. However, the extent to which vegetation affected soil nutrient status in any given location was not only highly dependent on the species present, and presumably the nutrient requirements and cycling patterns of the plant species, but also on the background soil characteristics (e.g., parent material, weathering rates, leaching) where plant species occurred. The results of this study indicate that the presence or absence of a plant species, especially desert shrubs, could significantly alter soil chemistry and subsequently ecosystem biogeochemistry and function.

Carbon, nutrient, and water balance as well as key plant and soil processes were simultaneously monitored for humid tropical plant communities treated with CO$_2$-enriched atmospheres. Despite vigorous growth, no significant differences in stand biomass (of both the understory and overstory), leaf area index, nitrogen or water consumption, or leaf stomatal behavior were detected between ambient and elevated CO$_2$ treatments. Major responses under elevated CO$_2$ included massive starch accumulation in the tops of canopies, increased fine-root production, and a doubling of CO$_2$ evolution from the soil. Stimulated rhizosphere activity was accompanied by increased loss of soil carbon and increased mineral nutrient leaching. This study points at the inadequacy of scaling-up from physiological baselines to ecosystems without accounting for interactions among components, and it emphasizes the urgent need for whole-system experimental approaches in global-change research.