Open-top Field Chambers Research Articles

Belowground Response of a Bahiagrass Pasture to Long-Term Elevated [CO2] and Soil Fertility Management.

Effects of rising atmospheric CO2 concentration [CO2] on pastures and grazing lands are beginning to be researched, but these important systems remain understudied compared to other agronomic and forest ecosystems. Therefore, we conducted a long-term (2005-2015) study of bahiagrass (Paspalum notatum Flüggé) response to elevated [CO2] and fertility management. The study was conducted at the USDA-ARS, National Soil Dynamics Laboratory open-top field chamber facility, Auburn, AL. A newly established bahiagrass pasture was exposed to either ambient or elevated (ambient + 200 µmol mol-1) [CO2]. Following one year of pasture establishment, half the plots received a fertilizer treatment [N at 90 kg ha-1 three times yearly plus P, K, and lime as recommended by soil testing]; the remaining plots received no fertilization. These treatments were implemented to represent managed (M) and unmanaged (U) pastures; both are common in the southeastern US. Root cores (0-60 cm depth) were collected annually in October and processed using standard procedures. Fertility additions consistently increased both root length density (53.8%) and root dry weight density (68.2%) compared to unmanaged plots, but these root variables were generally unaffected by either [CO2] or its interaction with management. The results suggest that southern bahiagrass pastures could benefit greatly from fertilizer additions. However, bahiagrass pasture root growth is unlikely to be greatly affected by rising atmospheric [CO2], at least by those levels expected during this century.

Elevated O3 concentrations alter the compartment-specific microbial communities inhabiting rust-infected poplars.

Elevated ozone (O3 ) can affect the susceptivity of plants to rust pathogens. However, the collective role of microbiomes involved in such interaction remains largely elusive. We exposed two cultivated poplar clones exhibiting differential O3 sensitivities, to non-filtered ambient air (NF), NF + 40 ppb or NF + 60 ppb O3 -enriched air in field open-top chambers and then inoculated Melampsora larici-populina urediniospores to study their response to rust infection and to investigate how microbiomes inhabiting four compartments (phyllosphere, rhizosphere, root endosphere, bulk soil) are involved in this response. We found that hosts with higher O3 sensitivity had significantly lower rust severity than hosts with lower sensitivity. Furthermore, the effect of increased O3 on the diversity and composition of microbial communities was highly dependent on poplar compartments, with the microbial network complexity patterns being completely opposite between the two clones. Notably, microbial source analysis estimated that phyllosphere fungal communities predominately derived from root endosphere and vice versa, suggesting a potential transmission mechanism between plant above- and below-ground systems. These promising results suggest that further investigations are needed to better understand the interactions of abiotic and biotic stresses on plant performance and the role of the microbiome in driving these changes.

Carbon dioxide enrichment effects on concentration, partitioning and uptake of metallic micronutrient elements in soybean under varied nitrogen application rates

Information on the fate of micronutrients in plant tissue and total uptake from soil upon exposure to elevated carbon dioxide (CO2) is meager. Hence, this field study was conducted in open top field chambers to investigate the effects of elevated CO2 and applied nitrogen (N) on partitioning and uptake of zinc (Zn), copper (Cu), iron (Fe), and manganese (Mn) in soybean crop under two CO2 and four N levels during 2016 and 2018 crop seasons. The two CO2 concentrations were ambient and elevated (∼550 µmol mol−1). Nitrogen treatments included application at 0, 50, 100, and 150% of the recommended dose. Significant effects of CO2 and N were observed on grain yield, biomass and uptake of the four micronutrients. Seed Fe concentration was significantly increased by 12% under CO2 enrichment. Tukey’s post-hoc test revealed significantly higher grain yield, biomass and uptake of micronutrients in seed and straw under CO2 elevation and at higher N application. Uptake of Fe, Zn, Cu, and Mn increased by 53, 42, 36, and 41%, respectively, in seed and by 25, 26, 31, and 18% in straw under elevated CO2. Total uptake of Fe, Zn, Cu, and Mn increased by 39, 38, 34, and 29%, respectively. Nitrogen at 100% level enhanced uptake of Fe, Zn, Cu, and Mn by 25, 20, 32, and 28%. The study bears implications in micronutrient management for sustaining soil health under changing climate.

Yield and Seed Chemical Composition under Elevated CO<sub>2</sub> and Temperature Based on the RCP 4.5 Scenario of Important Thai Rice

This research aimed to examine the effects of combining increased temperature and carbon dioxide (CO₂) under RCP 4.5 scenarios on yield and seed chemical composition of Thai rice cultivars; Chinat1, Phathumthani1, and Phitsanulok2. The field warming experiment was conducted at Phitsanulok from 2018 to 2020. Sixteen field-open top chambers (OTCs) were applied to simulate the expected future climate situation under RCP 4.5 (the elevated temperature at 2℃ and CO₂ up to 800 ppm, respectively). The results revealed that the single factor of elevated temperature at 2℃ led to statistically significant grain size reductions of 2 rice cultivars; Chinat1 and Phitsanulok2. We also found that the combination of elevated temperature and CO₂ induced a significant grain yield loss (ton.ha-1) by 68% in Phitsanulok2 but an increase of 38% appeared in Chainat1. Considering results in seed chemicals, the statistically significant decrease trends in Amylose and Brix values were shown in 3 cultivars. These results suggest that elevated temperature and CO₂ caused the imbalance in seed nutrient contents and an increase in yield loss in some Thai rice cultivars.

Effects of elevated ozone on bacterial communities inhabiting the phyllo- and endo-spheres of rice plants

To explore the effects of elevated ozone (O3) on microbial communities inhabiting phyllo- and endo-spheres of Japonica rice leaves, cultivars Nangeng 5055 (NG5055) and Wuyujing 27 (WYJ27) were grown in either charcoal-filtered air (CF) or elevated O3 (ambient O3 + 40 ppb, E-O3) in field open-top chambers (OTCs) during a growing season. E-O3 increased the values of the Shannon (43–80%) and Simpson (34–51%) indexes of the phyllo-and endo-spheric bacterial communities in NG5055. E-O3 also increased the values of the phyllosphere Simpson index by 58% and the endosphere Shannon index by 54% in WYJ27. Both diversity indexes positively correlated with the contents of nitrogen, phosphorus, magnesium, and soluble sugar, and negatively correlated with the contents of starch and condensed tannins. The leaf-associated bacterial community composition significantly changed in both rice cultivars under E-O3. Moreover, the leaf-associated bacterial communities in NG5055 were more sensitive to E-O3 than those in WYJ27. The chemical properties explained 70% and 98% of variations in the phyllosphere and endosphere bacterial communities, respectively, suggesting a predominant role of chemical status for the endospheric bacterial community. Most variation (57.3%) in the endosphere bacterial community assembly was explained by phosphorus. Gammaproteobacteria and Pantoea were found to be the most abundant class (63–76%) and genus (38–48%) in the phyllosphere and endosphere, respectively. E-O3 significantly increased the relative abundance of Bacteroidetes in the phyllosphere bacterial community and decreased the relative abundance of Gammaproteobacteria in the endophytic community. In conclusion, elevated O3 increased the diversity of bacterial communities of leaf phyllosphere and endosphere, and leaf chemical properties had a more pronounced effect on the endosphere bacterial community.

Field-grown soybean shows genotypic variation in physiological and seed composition responses to heat stress during seed development

An average temperature increase between 2.6 and 4.8 °C, along with more frequent extreme temperatures, will challenge crop productivity by the end of the century. To investigate genotypic variation in soybean response to elevated temperature, six soybean ( Glycine max ) genotypes were subjected to elevated air temperature of + 4.5 °C above ambient for 28 days in open-top field chambers. Gas exchange and chlorophyll fluorescence were measured before and during heating and yield as well as seed composition were evaluated at maturity. Results show that long-term elevated air temperature increased nighttime respiration, increased the maximum velocity of carboxylation by Rubisco, impacted seed protein concentration, and reduced seed oil concentration across genotypes. The genotypes in this study varied in temperature responses for photosynthetic CO 2 assimilation, stomatal conductance, photosystem II operating efficiency, quantum efficiency of CO 2 assimilation, and seed protein concentration at maturity. These diverse responses among genotypes to elevated air temperature during seed development in the field, reveal the potential for soybean heat tolerance to be improved through breeding and underlines the importance of identifying efficient selection strategies for stress-tolerant crops. • Six soybean genotypes were exposed to elevated air temperature in the field. • Several physiological responses to elevated temperature varied among genotypes. • Elevated temperature increased nighttime respiration across genotypes. • Elevated temperature reduced seed oil concentration across genotypes. • Seed protein concentration response to temperature varied among genotypes.

Mercury accumulation response of rice plant (Oryza sativa L.) to elevated atmospheric mercury and carbon dioxide

New observations and updated models now suggest terrestrial ecosystems are net sink of atmospheric mercury (Hg), and the critical constrained process to identify the strengths of terrestrial sink is whether the large amount of Hg stored in vegetation originates from the soil as well as from the atmosphere. In this study, field open top chambers (OTCs) experiments reveal that rice plant can assimilate gaseous elemental mercury (GEM, Hg0) from the atmosphere through stomata, and Hg concentrations in rice leaves, upper and bottom stalks and grains increased with Hg0 levels in air, showing significantly quadratic linear relationships. Coupling field stable isotope soil amendment experiments, atmospheric source of Hg in rice plant is quantified with more than 90% of Hg accumulation in rice aboveground biomass from air and approximately 80% of rice root Hg from soil. Furthermore, elevated atmospheric carbon dioxide (CO2) exposure led to lower Hg concentration in rice tissues through reduction stomatal conductance of rice leaf, and subsequently impact the capacity of Hg storage in rice aboveground parts from the atmosphere. The findings from experiments provide a foundation for future quantification of atmospheric sink of crops in local and larger scales and comprehensive evaluation atmosphere - terrestrial processes and exposure risks in the global Hg cycling.

Elevated temperature and low nitrogen partially offset the yield, evapotranspiration, and water use efficiency of winter wheat under carbon dioxide enrichment

Atmospheric carbon dioxide (CO2) concentration, temperature and nitrogen (N) are the key regulators of productivity and water use of plants under the changing climate. However, field scale studies on the interactive effect of the three above critical inputs are limited. Hence, this field study was conducted with three climate treatments (ambient (AC), elevated CO2 (eC, ~550 µmol mol−1) and co-elevation of both CO2 and temperature (eCeT, ~550 µmol mol−1 and temperature ~2 °C above ambient)) and four N treatments (0%, 50%, 100% and 150% of recommended N dose of 120 kg N ha−1). The experiment was carried out in open top field chambers to study the effects of climate and N application on grain yield, evapotranspiration (ET) and water use efficiency (WUE) in wheat crop. Crop ET was estimated by field water balance method and WUE by taking the ratio of grain yield to crop ET. Elevation of CO2 showed 9% yield gain over ambient (averaged across N levels), whereas, co-elevation of temperature reduced the yield gain to 4%. Further, N application significantly altered the level of CO2 response. Under CO2 enriched environment, the yield gain was 15% with N100 as compared to 2% and 4% under N0 and N50, respectively, indicating CO2 enrichment benefits in grain yield was N dependent. The three years’ pooled data showed significant effect of climate, N and their interaction on profile water storage, evapotranspiration and WUE. Elevation of CO2 alone or with co-elevation of temperature resulted in significant decline in crop ET by 4–11 mm and significant increase in profile soil moisture and WUE. The WUE improved significantly, by 12% under eC and by 4% under eCeT, respectively, with the increase, more attributed to gain in grain yield. Quantitative derivation from the three years’ field experimentation could establish that under elevated CO2 scenario (550 µmol mol−1), an additional 1 °C rise in temperature would result in enhanced crop ET by 5 mm and yield loss of about 4%. This study thus revealed that limited N and increased temperature would potentially restrict the CO2 mediated benefits in wheat yield and water use under the changing climate.

Carbon dioxide and/or temperature elevation effect on yield response, nutrient partitioning and use efficiency of applied nitrogen in wheat crop in central India

Despite several implications of excessive nitrogen (N) use on environment, information on effect of elevated carbon dioxide (CO2) and/or temperature on recovery and use efficiency of applied N are limited. Hence, this field study was carried out for three consecutive seasons of wheat crop during 2016−17 to 2018−19 in Open Top Field chambers (OTCs) under four climate conditions, viz. ambient, elevated CO2 (∼550 μmol mol−1), elevated temperature (∼ 2.0 °C above ambient) and co-elevation of both CO2 and temperature. Interaction of climate and year was found non-significant (P > 0.05) for the studied parameters, but, significant effect of climate was observed in most of the parameters except straw N uptake. Pooled data analysis of three consecutive crop years indicated CO2 elevation significantly enhancing above ground biomass and grain yield and also N uptake in grain. The CO2 mediated grain yield response was to the extent of 15% (P < 0.0001) as compared to ambient, however, the yield advantage was partly offset with co-elevation of temperature. Elevation in CO2 produced 16% higher total N uptake than ambient. Co-elevation of CO2 and temperature showed a higher N uptake by about 10% as compared to ambient. In absolute terms, 25 and 15 kg ha−1 of additional N uptake was observed under elevation of CO2, and with co-elevation of temperature, respectively. Agronomic (AEN) and physiological N use efficiency (PEN), recovery of applied fertilizer N (REN) and partial factor productivity (PFPN) were significantly higher under CO2 elevation. Co-elevation of temperature caused significant depletion in REN and PFPN compared to CO2 elevation. The three years’ study clearly indicated significant advantage in yield and recovery of applied fertilizer N with CO2 elevation, at the cost of significantly higher N uptake. Significantly higher N removal and trend of declining soil mineral N content under elevated CO2 indicates possible N mining and N limitations may constrain the long-term plant response to CO2 elevation. The study has significance in N management for sustaining productivity and maintaining soil nutrient pool under changing climate.

Temporal Changes in Ozone Concentrations and Their Impact on Vegetation

Tropospheric concentrations of phytotoxic ozone (O3) have undergone a great increase from preindustrial 10–15 ppbv to a present-day concentration of 35–40 ppbv in large parts of the industrialised world due to increased emissions of O3 precursors including NOx, CO, CH4 and volatile organic compounds. The rate of increase in O3 concentration ranges between 1 ppbv per decade in remote locations of the Southern hemisphere and 5 ppbv per decade in the Northern hemisphere, where largest sources of O3 precursors are located. Molecules of O3 penetrating into the leaves through the stomatal apertures trigger the formation of reactive oxygen species, leading thus to the damage of the photosynthetic apparatus. Accordingly, it is assumed, that O3 increase reduces the terrestrial carbon uptake relative to the preindustrial era. Here we summarise the results of previous manipulative experiments in laboratory growth cabinets, field open-top chambers and free-air systems together with O3 flux measurements under natural growth conditions. In particular, we focus on leaf-level physiological responses in trees, variability in stomatal O3 flux and changes in carbon fluxes and biomass production in forest stands. As the results reported in the literature are highly variable, ranging from negligible to severe declines in photosynthetic carbon uptake, we also discuss the possible interactions of O3 with other environmental factors including solar radiation, drought, temperature and nitrogen deposition. Those factors were found to have great potential to modulate stomata openness and O3 fluxes.

Influences of high-level atmospheric gaseous elemental mercury on methylmercury accumulation in maize (Zea mays L.)

Maize (Zea mays L.) leaves play an important role in stomatal uptake and surface adsorption of atmospheric mercury (Hg). However, the influence of atmospheric gaseous elemental mercury (GEM) on methylmercury (MeHg) accumulation in maize plants is poorly understood. In this study, we conducted a field open-top chambers (OTCs) experiment and a soil Hg-enriched experiment to investigate the response of MeHg accumulation in maize tissues to different GEM levels in the air. Maize upper leaves had a higher average MeHg concentration (0.21 ± 0.08 ng g−1) than bottom leaves (0.15 ± 0.05 ng g−1) in the OTCs experiment, which was inconsistent with that in the soil Hg-enriched experiment (maize upper leaves: 0.41 ± 0.07 ng g−1, maize bottom leaves: 0.60 ± 0.05 ng g−1). Additionally, significantly positive correlations were found between MeHg concentrations in maize leaves and air Hg levels, suggesting that elevated air Hg levels enhanced MeHg accumulation in maize leaves, which was possibly attributed to methylation of Hg on leaf surfaces. Mature maize grains from the OTCs experiment had low MeHg concentrations (0.12–0.23 ng g−1), suggesting a low accumulation capability of MeHg by maize grains. Approximately 93–96% of MeHg and 51–73% of total Hg in maize grains were lost from the grain-filling stage to the grain-ripening stage at all GEM level treatments, implying that self-detoxification in maize grains occurred. MeHg concentrations in maize roots showed a significant linear relationship (R2 = 0.98, p < 0.01) with soil Hg levels, confirming that MeHg in maize roots is primarily from soil. This study provides a new finding that elevated air GEM levels could enhance MeHg accumulation in maize leaves, and self-detoxification may occur in maize grains. Further studies are needed to clarify these mechanisms of Hg methylation on maize leaf surfaces and self-detoxification of Hg by maize grains.

Elevated CO2 offsets the alteration of foliar chemicals (n-icosane, geranyl acetate, and elixene) induced by elevated O3 in three taxa of O3-tolerant eucalypts

Eucalypts are important forest resources in southwestern China, and may be tolerant to elevated ground-level ozone (O3) concentrations that can negatively affect plant growth. High CO2 may offset O3-induced effects by providing excess carbon to produce secondary metabolites or by inducing stomatal closure. Here, the effects of elevated CO2 and O3 on leaf secondary metabolites and other defense chemicals were studied by exposing seedlings of Eucalyptus globulus, E. grandis, and E. camaldulensis × E. deglupta to a factorial combination of two levels of O3 (< 10 nmol mol−1 and 60 nmol mol−1) and CO2 (ambient: 370 μmol mol−1 and 600 μmol mol−1) in open-top field chambers. GC-profiles of leaf extracts illustrated the effect of elevated O3 and the countering effect of high CO2 on compounds in leaf epicuticular wax and essential oils, i.e., n-icosane, geranyl acetate and elixene, compounds known as a first-line defense against insect herbivores. n-Icosane may be involved in tolerance mechanisms of E. grandis and the hybrid, while geranyl acetate and elixene in the tolerance of E. globulus. Elevated O3 and CO2, singly or in combination, affected only leaf physiology but not biomass of various organs. Elevated CO2 impacted several leaf traits, including stomatal conductance, leaf mass per area, carbon, lignin, n-icosane, geranyl acetate and elixene. Limited effects of elevated O3 on leaf physiology (nitrogen, n-icosane, geranyl acetate, elixene) were commonly offset by elevated CO2. We conclude that E. globulus, E. grandis and the hybrid were tolerant to these O3 and CO2 treatments, and n-icosane, geranyl acetate and elixene may be major players in tolerance mechanisms of the tested species.

O3-Induced Priming Defense Associated With the Abscisic Acid Signaling Pathway Enhances Plant Resistance to Bemisia tabaci.

Elevated ozone (O3) modulates phytohormone signals, which subsequently alters the interaction between plants and herbivorous insects. It has been reported that elevated O3 activates the plant abscisic acid (ABA) signaling pathway, but its cascading effect on the performance of herbivorous insects remains unclear. Here, we used the ABA-deficient tomato mutant notabilis (not) and its wild type, Ailsa Craig (AC), to determine the role of ABA signaling in mediating the effects of elevated O3 on Bemisia tabaci in field open-top chambers (OTCs). Our results showed that the population abundance and the total phloem-feeding duration of B. tabaci were decreased by O3 exposure in AC plants compared with not plants. Moreover, elevated O3 and B. tabaci infestation activated the ABA signaling pathway and enhanced callose deposition in AC plants but had little effect on those in not plants. The exogenous application of a callose synthesis inhibitor (2-DDG) neutralized O3-induced resistance to B. tabaci, and the application of ABA enhanced callose deposition and exacerbated the negative effects of elevated O3 on B. tabaci. However, the application of 2-DDG counteracted the negative effects of O3 exposure on B. tabaci in ABA-treated AC plants. Collectively, this study revealed that callose deposition, which relied on the ABA signaling pathway, was an effective O3-induced priming defense of tomato plants against B. tabaci infestation.

Carbon dioxide and temperature elevation effects on crop evapotranspiration and water use efficiency in soybean as affected by different nitrogen levels

Rising concentration of atmospheric carbon dioxide (CO2) is reported to cause fertilization effect resulting in enhanced crop biomass and yields and may alter the water use of plants. However, factors like air temperature and nitrogen (N) management could modify the feedbacks of CO2 on crop water use. Hence, this field study was carried out in open top field chambers (OTC) for two crop seasons to investigate the interactive effects of climate and N on evapotranspiration, yield and water use efficiency in soybean (Glycine max L.). Soybean crop was grown under three climate conditions (ambient : AC, elevated CO2 : eC, and co-elevation of both CO2 and temperature : eCeT) and four N treatments during July to October 2016 and 2018. Elevation of CO2 was done to the level of 535–540 μmol mol−1, and temperature was elevated by about 2 °C above ambient. The four N levels were N0, N50, N100 and N150 referring to 0, 50, 100 and 150% of recommended N dose (30 kg N ha−1). Crop evapotranspiration (ET) was computed by soil water balance method. The two years’ field study indicated eC and eCeT showed significant yield advantage to the extent of 32-47% over ambient. Significant effect (P < 0.05) of climate was observed on crop ET, profile water storage and water use efficiency (WUE) during both the study years. The effect of N application on these three parameters was significant only in 2016 crop year. Averaged across N treatments, profile soil water storage at harvest was higher by about 5% in 2016 and by 9% in 2018 crop season under eC and eCeT treatments as compared to AC. The crop ET was significantly lower under eC and eCeT in both the years, with significantly higher WUE. The WUE varied from 2.99 to 4.48 kg ha−1 mm−1 in 2016 and from 4.62 to 6.42 kg ha−1 mm−1 in 2018 crop year. Stomatal conductance during major growth period reduced by 21–42% under eC and by 19–31% under eCeT, though it did not reflect in reduced transpiration. The study indicated significantly higher leaf area contributing to reduced soil water evaporation is the major mechanism explaining higher soil water profile under eC and eCeT. Over ambient, the WUE was higher by 48-50% in 2016 and by 37-39% in 2018 under eC and eCeT treatments, which was mostly attributed to higher grain yield.

Roles of heat shock protein and reprogramming of photosynthetic carbon metabolism in thermotolerance under elevated CO2 in maize

Our previous published results demonstrated that elevated CO2 can reprogram photosynthetic carbon metabolism (PCM) during sudden heat stress (SHS) treatments. However, the mechanism explaining how elevated CO2 could regulate the metabolites through SHS-induced proteins is poorly understood. Here, we combined metabolism and transcriptomes analysis to elucidate the differential genes expression of key heat shock proteins (HSPs) under SHS in presence of elevated CO2. Our results show strong positive correlation in terms of carbon assimilation rates (A) between both field open top chamber (OTCs) and growth chamber conditions. The decline in A during SHS is ascribable to a metabolic reprogramming rather than stomatal-limitation. We recorded an increase by about 3 ˜ 4 times in the expression levels of small HSPs, especially Cpn2 and Hsp1 following elevated CO2. This study underlines the beneficial effects of elevated CO2 in the thermotolerance process through amplifying small HSPs in maize. Our current investigation suggests a potential mechanistic model for the metabolic network reprogramming following combined effect of SHS and elevated CO2. It corroborates as well the involvement of two HSPs genes in the in the adjustment of photosynthetic carbon metabolism pathway to avoid any misfolding in Rubisco subunits proteins.

Long-term response of a bahiagrass pasture to elevated CO2 and soil fertility management

Pastures represent a significant portion of the rural landscape in the southeastern US, yet remain understudied agro-ecosystems in terms of the effects of rising atmospheric CO2 concentration. Therefore, in 2005 we initiated a long-term (10 yr) study of bahiagrass (Paspalum notatum Flüggé) response to elevated CO2 using open top field chambers on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). Plants were exposed to ambient or elevated (ambient + 200 μmol mol−1) CO2. After a one-year establishment period, a management (M) treatment was applied where half of all plots received N [(NH4)2SO4] at 90 kg ha−1 three times yearly plus P, K, and lime as recommended by soil testing; the remaining plots received no fertilization. These two treatments represent managed and unmanaged pastures, both of which are common in the Southeast. Prior to M treatment initiation (establishment phase) biomass production was unaffected by CO2 treatment. Harvests after M treatment initiation (Spring 2006) showed strong effects of fertilizer addition on cumulative forage biomass production (˜231.8% increase); the main effect of CO2 was also significant (˜13.8% increase with elevated CO2). Significant M x CO2 interactions showed that CO2 had no impact on bahiagrass production with no fertilizer added (as observed in establishment year); however, forage production was increased (˜15.3%) under elevated CO2 with fertilizer addition. These findings highlight the importance of soil fertility management to enhance pasture productivity under rising atmospheric CO2 levels.

The fate of 15N labeled urea in a soybean-wheat cropping sequence under elevated CO2 and/or temperature

Changing climate has direct linkage with growth and metabolism in plants and is likely to alter nitrogen (N) uptake from fertilizers. Hence, a field study was conducted using 15N labeled urea in micro-plots to study the effects of elevated CO2 and/or temperature on fertilizer-N use in a soybean-wheat cropping sequence. Crops were grown in open top field chambers (OTCs) under two CO2 (386 and 558–561 ppmv), two temperature (ambient, 1.4-1.5 °C above) and three N levels during 2017-18. The N treatments were 50, 100 and 150% of the recommended dose (N50, N100 and N150). Labeled (15N) urea (10% atom excess) was applied to soybean. Elevated CO2 and/or temperature showed significant effects on seed yield, total N uptake, fertilizer-N uptake, per cent N derived from fertilizer (Ndff) and per cent fertilizer-N use in the soybean-wheat crop sequence. Total N uptake in soybean significantly increased under elevated CO2 and/or temperature treatments, mainly due to higher N uptake in seeds. Effect of climate on fertilizer-N uptake and utilization in the soybean-wheat cropping sequence varied with level of N application. The 15N labeled fertilizer-N uptake and per cent fertilizer-N use was significantly higher under co-elevation of both CO2 and temperature at N100 and N150, but, was mostly similar among the climate treatments at N50. In the soybean-wheat crop sequence, 13–40% of the applied fertilizer was used, with significantly higher use with co-elevation of both CO2 and temperature. Out of the applied fertilizer, 20–51% got retained in the surface soil and 43–73% was traced in the soil-plant system. Significantly higher fertilizer-N use in the soybean-wheat crop sequence under co-elevation of CO2 and temperature indicates increasing role of fertilizer-N to harvest the CO2 mediated enhancement in grain yield under the future climate conditions.

Plant phenolics mediated bottom-up effects of elevated CO2 on Acyrthosiphon pisum and its parasitoid Aphidius avenae.

Elevated concentrations of atmospheric CO2 can alter plant secondary metabolites, which play important roles in the interactions among plants, herbivorous insects and natural enemies. However, few studies have examined the cascading effects of host plant secondary metabolites on tri-trophic interactions under elevated CO2 (eCO2 ). In this study, we determined the effects of eCO2 on the growth and foliar phenolics of Medicago truncatula and the cascading effects on two color genotypes of Acyrthosiphon pisum (pink vs. green) and their parasitoid Aphidius avenae in the field open-top chambers. Our results showed that eCO2 increased photosynthetic rate, nodule number, yield and the total phenolic content of M. truncatula. eCO2 had contrasting effects on two genotypes of A. pisum; the green genotype demonstrated increased population abundance, fecundity, growth and feeding efficiency, while the pink genotype showed decreased fitness and these were closely associated with the foliar genstein content. Furthermore, eCO2 decreased the parasitic rate of A. avenae independent of aphid genotypes. eCO2 prolonged the emergence time and reduced the emergence rate and percentage of females when associated with the green genotype, but little difference, except for increased percentage of females, was observed in A. avenae under eCO2 when associated with the pink genotype, indicating that parasitoids can perceive and discriminate the qualities of aphid hosts. We concluded that eCO2 altered plant phenolics and thus the performance of aphids and parasitoids. Our results indicate that plant phenolics vary by different abiotic and biotic stimuli and could potentially deliver the cascading effects of eCO2 to the higher trophic levels. Our results also suggest that the green genotype is expected to perform better in future eCO2 because of decreased plant resistance after its infestation and decreased parasitic rate.

O3-Induced Leaf Senescence in Tomato Plants Is Ethylene Signaling-Dependent and Enhances the Population Abundance of Bemisia tabaci.

Elevated ozone (O3) can alter the phenotypes of host plants particularly in induction of leaf senescence, but few reports examine the involvement of phytohormone in O3-induced changes in host phenotypes that influence the foraging quality for insects. Here, we used an ethylene (ET) receptor mutant Nr and its wild-type to determine the function of the ET signaling pathway in O3-induced leaf senescence, and bottom-up effects on the performance of Bemisia tabaci in field open-top chambers (OTCs). Our results showed that elevated O3 reduced photosynthetic efficiency and chlorophyll content and induced leaf senescence of plant regardless of plant genotype. Leaf senescence in Nr plants was alleviated relative to wild-type under elevated O3. Further analyses of foliar quality showed that elevated O3 had little effect on phytohormone-mediated defenses, but significantly increased the concentration of amino acids in two plant genotypes. Furthermore, Nr plants had lower amino acid content relative to wild-type under elevated O3. These results provided an explanation of O3-induced increase in abundance of B. tabaci. We concluded that O3-induced senescence of plant was ET signal-dependent, and positive effects of O3-induced leaf senescence on the performance of B. tabaci largely resulted from changes of nutritional quality of host plants.

The effect of simulated warming on root dynamics and soil microbial community in an alpine meadow of the Qinghai-Tibet Plateau

Previous studies have explored the effects of global change on above-ground vegetation in grassland ecosystems. Few, however, have investigated the responses of root dynamics and soil microbes to simulated warming in alpine meadows of the Qinghai-Tibet Plateau. This research used field open top chamber experiment to examine warming's impacts. Root production, mortality, and turnover were observed in situ using minirhizotron tubes, while soil microbial community composition and diversity were assessed by using phospholipid-derived fatty acids (PLFA) and Biolog-Eco plates. The results showed that 1) warming shifted the root standing crop distribution to deeper soil while increasing the accumulated root mortality and root production at 0–10cm soil depth; 2) warming increased the abundance of fungal PLFAs while decreasing the abundance of other functional groups; 3) warming decreased the soil microbial functional diversity at the different soil layers; 4) bacterial and fungal PLFA contents were positively correlated with root mortality and turnover but were negatively correlated with root standing crop; 5) root dynamics significantly affect carbon utilization of the soil microbial community; and warming induced changes in root dynamics are associated with soil microbial community structure and function. Overall, these findings indicate that warming alters root production, mortality, and turnover and the relative abundance of different microorganisms in different soil layers. As a result, warming tended to shift microbial communities from bacteria toward fungi, leading to changes in the microbial community structure in different soil layers.