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VanLoocke A.,University of Illinois at Urbana - Champaign | Betzelberger A.M.,University of Illinois at Urbana - Champaign | Ainsworth E.A.,University of Illinois at Urbana - Champaign | Ainsworth E.A.,Global Change and Photosynthesis Research Unit | And 2 more authors.
New Phytologist | Year: 2012

Here, we investigated the effects of increasing concentrations of ozone ([O 3]) on soybean canopy-scale fluxes of heat and water vapor, as well as water use efficiency (WUE), at the Soybean Free Air Concentration Enrichment (SoyFACE) facility. • Micrometeorological measurements were made to determine the net radiation (R n), sensible heat flux (H), soil heat flux (G 0) and latent heat flux (λET) of a commercial soybean (Glycine max) cultivar (Pioneer 93B15), exposed to a gradient of eight daytime average ozone concentrations ranging from approximately current (c. 40ppb) to three times current (c. 120ppb) levels. • As [O 3] increased, soybean canopy fluxes of λET decreased and H increased, whereas R n and G 0 were not altered significantly. Exposure to increased [O 3] also resulted in warmer canopies, especially during the day. The lower λET decreased season total evapotranspiration (ET) by c. 26%. The [O 3]-induced relative decline in ET was half that of the relative decline in seed yield, driving a 50% reduction in seasonal WUE. • These results suggest that rising [O 3] will alter the canopy energy fluxes that drive regional climate and hydrology, and have a negative impact on productivity and WUE, key ecosystem services. © 2012 New Phytologist Trust.


Ruiz-Vera U.M.,University of Illinois at Urbana - Champaign | Siebers M.,University of Illinois at Urbana - Champaign | Gray S.B.,University of Illinois at Urbana - Champaign | Drag D.W.,University of Illinois at Urbana - Champaign | And 7 more authors.
Plant Physiology | Year: 2013

Extensive evidence shows that increasing carbon dioxide concentration ([CO2]) stimulates, and increasing temperature decreases, both net photosynthetic carbon assimilation (A) and biomass production for C3 plants. However the [CO2]-induced stimulation in A is projected to increase further with warmer temperature.While the influence of increasing temperature and [CO2], independent of each other, on A and biomass production have been widely investigated, the interaction between these two major global changes has not been tested on field-grown crops. Here, the interactive effect of both elevated [CO2] (approximately 585 μmol mol-1) and temperature (+3.5°C) on soybean (Glycine max) A, biomass, and yield were tested over two growing seasons in the Temperature by Free-Air CO2 Enrichment experiment at the Soybean Free Air CO2 Enrichment facility. Measurements of A, stomatal conductance, and intercellular [CO2] were collected along with meteorological, water potential, and growth data. Elevated temperatures caused lower A, which was largely attributed to declines in stomatal conductance and intercellular [CO2] and led in turn to lower yields. Increasing both [CO2] and temperature stimulated A relative to elevated [CO2] alone on only two sampling days during 2009 and on no days in 2011. In 2011, the warmer of the two years, there were no observed increases in yield in the elevated temperature plots regardless of whether [CO2] was elevated. All treatments lowered the harvest index for soybean, although the effect of elevated [CO2] in 2011 was not statistically significant. These results provide a better understanding of the physiological responses of soybean to future climate change conditions and suggest that the potential is limited for elevated [CO2] to mitigate the influence of rising temperatures on photosynthesis, growth, and yields of C3 crops. © 2013 American Society of Plant Biologists. All Rights Reserved.


Hussain M.Z.,University of Illinois at Urbana - Champaign | Vanloocke A.,University of Illinois at Urbana - Champaign | Siebers M.H.,University of Illinois at Urbana - Champaign | Ruiz-Vera U.M.,University of Illinois at Urbana - Champaign | And 6 more authors.
Global Change Biology | Year: 2013

Maize, in rotation with soybean, forms the largest continuous ecosystem in temperate North America, therefore changes to the biosphere-atmosphere exchange of water vapor and energy of these crops are likely to have an impact on the Midwestern US climate and hydrological cycle. As a C4 crop, maize photosynthesis is already CO2-saturated at current CO2 concentrations ([CO2]) and the primary response of maize to elevated [CO2] is decreased stomatal conductance (gs). If maize photosynthesis is not stimulated in elevated [CO2], then reduced gs is not offset by greater canopy leaf area, which could potentially result in a greater ET reduction relative to that previously reported in soybean, a C3 species. The objective of this study is to quantify the impact of elevated [CO2] on canopy energy and water fluxes of maize (Zea mays). Maize was grown under ambient and elevated [CO2] (550 μmol mol-1 during 2004 and 2006 and 585 μmol mol-1 during 2010) using Free Air Concentration Enrichment (FACE) technology at the SoyFACE facility in Urbana, Illinois. Maize ET was determined using a residual energy balance approach based on measurements of sensible (H) and soil heat fluxes, and net radiation. Relative to control, elevated [CO2] decreased maize ET (7-11%; P < 0.01) along with lesser soil moisture depletion, while H increased (25-30 W m-2; P < 0.01) along with higher canopy temperature (0.5-0.6 °C). This reduction in maize ET in elevated [CO2] is approximately half that previously reported for soybean. A partitioning analysis showed that transpiration contributed less to total ET for maize compared to soybean, indicating a smaller role of stomata in dictating the ET response to elevated [CO2]. Nonetheless, both maize and soybean had significantly decreased ET and increased H, highlighting the critical role of elevated [CO2] in altering future hydrology and climate of the region that is extensively cropped with these species. © 2013 Blackwell Publishing Ltd.


Bernacchi C.J.,Global Change and Photosynthesis Research Unit | Bernacchi C.J.,University of Illinois at Urbana - Champaign | Leakey A.D.B.,University of Illinois at Urbana - Champaign | Kimball B.A.,U.S. Department of Agriculture | And 2 more authors.
Environmental Pollution | Year: 2011

Tropospheric ozone is increasing in many agricultural regions resulting in decreased stomatal conductance and overall biomass of sensitive crop species. These physiological effects of ozone forecast changes in evapotranspiration and thus in the terrestrial hydrological cycle, particularly in intercontinental interiors. Soybean plots were fumigated with ozone to achieve concentrations above ambient levels over five growing seasons in open-air field conditions. Mean season increases in ozone concentrations ([O3]) varied between growing seasons from 22 to 37% above background concentrations. The objective of this experiment was to examine the effects of future [O3] on crop ecosystem energy fluxes and water use. Elevated [O3] caused decreases in canopy evapotranspiration resulting in decreased water use by as much as 15% in high ozone years and decreased soil water removal. In addition, ozone treatment resulted in increased sensible heat flux in all years indicative of day-time increase in canopy temperature of up to 0.7 °C. © 2011 Elsevier Ltd. All rights reserved.


Bernacchi C.J.,Global Change and Photosynthesis Research Unit | Bernacchi C.J.,University of Illinois at Urbana - Champaign | Bagley J.E.,University of Illinois at Urbana - Champaign | Serbin S.P.,University of Wisconsin - Madison | And 4 more authors.
Plant, Cell and Environment | Year: 2013

Globally, photosynthesis accounts for the largest flux of CO2 from the atmosphere into ecosystems and is the driving process for terrestrial ecosystem function. The importance of accurate predictions of photosynthesis over a range of plant growth conditions led to the development of a C3 photosynthesis model by Farquhar, von Caemmerer & Berry that has become increasingly important as society places greater pressures on vegetation. The photosynthesis model has played a major role in defining the path towards scientific understanding of photosynthetic carbon uptake and the role of photosynthesis on regulating the earth's climate and biogeochemical systems. In this review, we summarize the photosynthesis model, including its continued development and applications. We also review the implications these developments have on quantifying photosynthesis at a wide range of spatial and temporal scales, and discuss the model's role in determining photosynthetic responses to changes in environmental conditions. Finally, the review includes a discussion of the larger-scale modelling and remote-sensing applications that rely on the leaf photosynthesis model and are likely to open new scientific avenues to address the increasing challenges to plant productivity over the next century. The mechanistically based leaf photosynthesis model has played a major role in defining the path toward scientific understanding of photosynthetic carbon uptake and the role of photosynthesis on regulating the earth's climate and biogeochemical systems. This review summarizes the photosynthesis model, including its continued development and applications. We also review the implications these developments have on quantifying photosynthesis at a wide range of spatial and temporal scales, and discuss the model's role in determining photosynthetic responses to changes in environmental conditions. © 2013 John Wiley & Sons Ltd.


Locke A.M.,Urbana University | Ort D.R.,Urbana University | Ort D.R.,Global Change and Photosynthesis Research Unit
Journal of Experimental Botany | Year: 2014

Photosynthesis requires sufficient water transport through leaves for stomata to remain open as water transpires from the leaf, allowing CO2 to diffuse into the leaf. The leaf water needs of soybean change over time because of large microenvironment changes over their lifespan, as leaves mature in full sun at the top of the canopy and then become progressively shaded by younger leaves developing above. Leaf hydraulic conductance (K leaf), a measure of the leaf's water transport capacity, can often be linked to changes in microenvironment and transpiration demand. In this study, we tested the hypothesis that K leaf would decline in coordination with transpiration demand as soybean leaves matured and aged. Photosynthesis (A), stomatal conductance (g s) and leaf water potential (Ψleaf) were also measured at various leaf ages with both field- and chamber-grown soybeans to assess transpiration demand. K leaf was found to decrease as soybean leaves aged from maturity to shading to senescence, and this decrease was strongly correlated with midday A. Decreases in K leaf were further correlated with decreases in g s, although the relationship was not as strong as that with A. Separate experiments investigating the response of K leaf to drought demonstrated no acclimation of K leaf to drought conditions to protect against cavitation or loss of g s during drought and confirmed the effect of leaf age in K leaf observed in the field. These results suggest that the decline of leaf hydraulic conductance as leaves age keeps hydraulic supply in balance with demand without K leaf becoming limiting to transpiration water flux. © 2014 © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology.


Rosenthal D.M.,Global Change and Photosynthesis Research Unit | Slattery R.A.,Urbana University | Miller R.E.,Monash University | Grennan A.K.,Urbana University | And 5 more authors.
Global Change Biology | Year: 2012

Globally, cassava is the second most important root crop after potatoes and the fifth most important crop overall in terms of human caloric intake. In addition to its growing global importance for feed, fuel, and starch, cassava has long been vital to food security in Sub-Saharan Africa. Climate change is expected to have its most severe impact on crops in food insecure regions, yet little is known about how cassava productivity will respond to climate change. The most important driver of climate change is globally increasing atmospheric CO 2 concentration ([CO 2]). However, the potential for cassava to enhance food security in an elevated [CO 2] world is uncertain as greenhouse and open top chamber (OTC) study reports are ambiguous. Studies have yielded misleading results in the past regarding the effect of elevated [CO 2] on crop productivity, particularly in cases where pots restricted sink growth. To resolve these conflicting results, we compare the response of cassava to growth at ambient (ca. 385 ppm) and elevated [CO 2] (585 ppm) under field conditions and fully open air [CO 2] elevation. After three and half months of growth at elevated [CO 2], above ground biomass was 30% greater and cassava root tuber dry mass increased over 100% (fresh weight increased 89%). High photosynthetic rates and photosynthetic stimulation by elevated [CO 2], larger canopies, and a large sink capacity all contributed to cassava's growth and yield stimulation. Cassava exhibited photosynthetic acclimation via decreased Rubisco capacity early in the season prior to root tuber initiation when sink capacity was smaller. Importantly, and in contrast to a greenhouse study, we found no evidence of increased leaf N or total cyanide concentration in elevated [CO 2]. All of our results are consistent with theoretical expectations; however, the magnitude of the yield increase reported here surpasses all other C 3 crops and thus exceeds expectations. © 2012 Blackwell Publishing Ltd.


Davis A.S.,Global Change and Photosynthesis Research Unit | Hill J.D.,University of Minnesota | Chase C.A.,Iowa State University | Johanns A.M.,Iowa State University | Liebman M.,Iowa State University
PLoS ONE | Year: 2012

Balancing productivity, profitability, and environmental health is a key challenge for agricultural sustainability. Most crop production systems in the United States are characterized by low species and management diversity, high use of fossil energy and agrichemicals, and large negative impacts on the environment. We hypothesized that cropping system diversification would promote ecosystem services that would supplement, and eventually displace, synthetic external inputs used to maintain crop productivity. To test this, we conducted a field study from 2003-2011 in Iowa that included three contrasting systems varying in length of crop sequence and inputs. We compared a conventionally managed 2-yr rotation (maize-soybean) that received fertilizers and herbicides at rates comparable to those used on nearby farms with two more diverse cropping systems: a 3-yr rotation (maize-soybean-small grain + red clover) and a 4-yr rotation (maize-soybean-small grain + alfalfa-alfalfa) managed with lower synthetic N fertilizer and herbicide inputs and periodic applications of cattle manure. Grain yields, mass of harvested products, and profit in the more diverse systems were similar to, or greater than, those in the conventional system, despite reductions of agrichemical inputs. Weeds were suppressed effectively in all systems, but freshwater toxicity of the more diverse systems was two orders of magnitude lower than in the conventional system. Results of our study indicate that more diverse cropping systems can use small amounts of synthetic agrichemical inputs as powerful tools with which to tune, rather than drive, agroecosystem performance, while meeting or exceeding the performance of less diverse systems.


Matlaga D.P.,Susquehanna University | Davis A.S.,Global Change and Photosynthesis Research Unit
Journal of Applied Ecology | Year: 2013

Many species prioritized for bioenergy crop development possess traits associated with invasiveness, necessitating a priori efforts by ecologists to identify species or cultivars with minimal invasive potential. The grass Miscanthus × giganteus Greef et Deu ex Hodkinson et Renvoize is a candidate for biomass production in the northern US maize belt, with both sterile and fertile varieties commercially available in the near future. Prior to widespread deployment, the invasive potential of both varieties must be quantified. Using M. × giganteus demographic and seed dispersal data, we parameterized an age-/stage-structured integrodifference equation model to estimate potential spread rates of sterile and fertile M. × giganteus. We identified thresholds for reproductive parameters, above which population numbers and space occupied are likely to increase. Our simulations considered lateral spread of M. × giganteus but not dispersal of rhizome fragments. When clonal recruitment is absent, population growth rate for sterile M. × giganteus is projected to be slightly <1 (λ = 0·979), indicating gradual population decline over the long term. A sterile M. × giganteus population may increase in numbers and space under certain conditions: annually rhizome sprouting must be >20% and rhizome production must be ≥1 per plant. The relatively slow spread rates (0-0·09 m year-1) estimated for sterile M. × giganteus would not apply in scenarios where rhizomes were dispersed long distance. For a fertile M. × giganteus genotype, even low rates of seed viability and survival, seedling survival and seed germination support rapidly expanding populations. Synthesis and applications. Spatial demographic models offer a powerful tool for quantifying risk of invasive spread by bioenergy crops. Our results suggest that sterile and fertile cultivars of M. × giganteus have markedly different invasive potential and therefore should be considered separately in management and policy decisions. Feral populations of sterile M. × giganteus would need to experience frequent and severe disturbance to pose a significant invasion risk, indicating that they should be grown well away from riparian areas prone to streambank scouring. In contrast, cultivars of M. × giganteus bearing fertile seed may be very difficult, if not impossible, to contain. Spatial demographic models offer a powerful tool for quantifying risk of invasive spread by bioenergy crops. Our results suggest that sterile and fertile cultivars of M. × giganteus have markedly different invasive potential and therefore should be considered separately in management and policy decisions. Feral populations of sterile M. × giganteus would need to experience frequent and severe disturbance to pose a significant invasion risk, indicating that they should be grown well away from riparian areas prone to streambank scouring. In contrast, cultivars of M. × giganteus bearing fertile seed may be very difficult, if not impossible, to contain. © 2013 British Ecological Society.


Davis A.S.,Global Change and Photosynthesis Research Unit
Weed Science | Year: 2010

Termination of cover crops prior to no-till planting of soybean is typically accomplished with burndown herbicides. Recent advances in cover-crop rollercrimper design offer the possibility of reliable physical termination of cover crops without tillage. A field study within a no-till soybean production system was conducted in Urbana, IL, from 2004 through 2007 to quantify the effects of cover crop (cereal rye, hairy vetch, or bare soil control), termination method (chemical burndown or rollercrimper), and postemergence glyphosate application rate (0, 1.1, or 2.2 kg ae ha-1) on soybean yield components, weedcrop interference, and soil environmental variables. Biomass of weeds surviving management within a soybean crop following either a vetch or rye cover crop was reduced by 26 and 56, respectively, in the rolled system compared to the burndown system. Soybean yield loss due to weed interference was unaffected by cover-crop termination method in soybean following a rye cover crop, but was higher in the rolled than burndown treatment in both hairy vetch and bare soil treatments. In soybean following a rye cover crop, regardless of termination method, yield loss to weed interference was unaffected by glyphosate rate, whereas in soybean following a vetch cover crop or bare soil, yield loss decreased with glyphosate rate. Variation in soybean yield among cover crops and cover-crop termination treatments was due largely to differences in soybean establishment, rather than differences in the soil environment. Use of a rollercrimper to terminate a cover crop preceding no-till soybean has the potential to achieve similar yields to those obtained in a chemically terminated cover crop while reducing residual weed biomass. © 2010 Weed Science Society of America.

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