Investigating Forest Photosynthetic Response to Elevated CO2 Using UAV-Based Measurements of Solar Induced Fluorescence

The response of ecosystems to increasing atmospheric CO2 will have significant, but still uncertain, impacts on the global carbon and water cycles. A lot of infounation has been gained from Free Air CO2 Enrichment (FACE) experiments, but the response of mature forest ecosystems remains a significant knowledge gap. One of the challenges in FACE studies is obtaining an integrated measure of canopy photosynthesis at the scale of the treatment ring. A new remote sensing approach for measuring photosynthetic activity is based on Solar Induced Fluorescence (SIF), which is emitted by plants during photosynthesis, and is closely linked to the rates and regulation of photosynthesis. We proposed that UAV-based SIF measurements, that enable the spectrometer field of view to be targeted to the treatment ring, provide a unique opportunity for investigating the dynamics of photosynthetic responses to elevated CO2. We have successfully tested this approach in a new FACE site, located in a mature oak forest in the UK. We flew a series of flights across the experiment arrays, collecting a number of spectra. We combined these with ground-based physiological and optical measurements, and see great promise in the use of UAV-based SIF measurements in FACE and other global change experiments.Peer reviewe

Elevated atmospheric [CO2] can dramatically increase wheat yields in semi-arid environments and buffer against heat waves

Wheat production will be impacted by increasing concentration of atmospheric CO2 [CO2], which is expected to rise from about 400 μmol mol−1 in 2015 to 550 μmol mol−1 by 2050. Changes to plant physiology and crop responses from elevated [CO2] (e[CO2]) are well documented for some environments, but field-level responses in dryland Mediterranean environments with terminal drought and heat waves are scarce. The Australian Grains Free Air CO2 Enrichment facility was established to compare wheat (Triticum aestivum) growth and yield under ambient (~370 μmol−1 in 2007) and e[CO2] (550 μmol−1) in semi-arid environments. Experiments were undertaken at two dryland sites (Horsham and Walpeup) across three years with two cultivars, two sowing times and two irrigation treatments. Mean yield stimulation due to e[CO2] was 24% at Horsham and 53% at Walpeup, with some treatment responses greater than 70%, depending on environment. Under supplemental irrigation, e[CO2] stimulated yields at Horsham by 37% compared to 13% under rainfed conditions, showing that water limited growth and yield response to e[CO2]. Heat wave effects were ameliorated under e[CO2] as shown by reductions of 31% and 54% in screenings and 10% and 12% larger kernels (Horsham and Walpeup). Greatest yield stimulations occurred in the e[CO2] late sowing and heat stressed treatments, when supplied with more water. There were no clear differences in cultivar response due to e[CO2]. Multiple regression showed that yield response to e[CO2] depended on temperatures and water availability before and after anthesis. Thus, timing of temperature and water and the crop's ability to translocate carbohydrates to the grain postanthesis were all important in determining the e[CO2] response. The large responses to e[CO2] under dryland conditions have not been previously reported and underscore the need for field level research to provide mechanistic understanding for adapting crops to a changing climate

Elevated atmospheric [CO₂] can dramatically increase wheat yields in semi-arid environments and buffer against heat waves

Tausz, M ORCiD: 0000-0001-8205-8561Wheat production will be impacted by increasing concentration of atmospheric CO2 [CO2], which is expected to rise from about 400 μmol mol-1 in 2015 to 550 μmol mol-1 by 2050. Changes to plant physiology and crop responses from elevated [CO2] (e[CO2]) are well documented for some environments, but field-level responses in dryland Mediterranean environments with terminal drought and heat waves are scarce. The Australian Grains Free Air CO2 Enrichment facility was established to compare wheat (Triticum aestivum) growth and yield under ambient (~370 μmol-1 in 2007) and e[CO2] (550 μmol-1) in semi-arid environments. Experiments were undertaken at two dryland sites (Horsham and Walpeup) across three years with two cultivars, two sowing times and two irrigation treatments. Mean yield stimulation due to e[CO2] was 24% at Horsham and 53% at Walpeup, with some treatment responses greater than 70%, depending on environment. Under supplemental irrigation, e[CO2] stimulated yields at Horsham by 37% compared to 13% under rainfed conditions, showing that water limited growth and yield response to e[CO2]. Heat wave effects were ameliorated under e[CO2] as shown by reductions of 31% and 54% in screenings and 10% and 12% larger kernels (Horsham and Walpeup). Greatest yield stimulations occurred in the e[CO2] late sowing and heat stressed treatments, when supplied with more water. There were no clear differences in cultivar response due to e[CO2]. Multiple regression showed that yield response to e[CO2] depended on temperatures and water availability before and after anthesis. Thus, timing of temperature and water and the crop's ability to translocate carbohydrates to the grain postanthesis were all important in determining the e[CO2] response. The large responses to e[CO2] under dryland conditions have not been previously reported and underscore the need for field level research to provide mechanistic understanding for adapting crops to a changing climate. © 2016 John Wiley & Sons Ltd

Elevated CO2has concurrent effects on leaf and grain metabolism but minimal effects on yield in wheat

While the general effect of CO2 enrichment on photosynthesis, stomatal conductance, N content, and yield has been documented, there is still some uncertainty as to whether there are interactive effects between CO2 enrichment and other factors, such as temperature, geographical location, water availability, and cultivar. In addition, the metabolic coordination between leaves and grains, which is crucial for crop responsiveness to elevated CO2, has never been examined closely. Here, we address these two aspects by multi-level analyses of data from several free-air CO2 enrichment experiments conducted in five different countries. There was little effect of elevated CO2 on yield (except in the USA), likely due to photosynthetic capacity acclimation, as reflected by protein profiles. In addition, there was a significant decrease in leaf amino acids (threonine) and macroelements (e.g. K) at elevated CO2, while other elements, such as Mg or S, increased. Despite the non-significant effect of CO2 enrichment on yield, grains appeared to be significantly depleted in N (as expected), but also in threonine, the S-containing amino acid methionine, and Mg. Overall, our results suggest a strong detrimental effect of CO2 enrichment on nutrient availability and remobilization from leaves to grains.This work was supported by the Department of Industry, Energy and Innovation of the Government of Navarre (PI040 TRIGOCLIM). The technical support given by Inés Urretavizcaya, Petra Högy, and Jürgen Franzaring in harvesting and sample management is acknowledged. JC was supported by an Australia Awards PhD Scholarship. GT was supported by a Connect Talent Award from the Region Pays de la Loire – Angers Loire Metropole (France). Research at the Australian Grains Free Air CO2 Enrichment (AGFACE) facility was jointly run by the University of Melbourne and Agriculture Victoria with funding from the Grains Research and Development Corporation (under contract no. DAV00137) and the Australian Commonwealth Department of Agriculture and Water Resources (under contract no. FtRG 1193982-41). CAAS-FACE was supported by the National Key Research and Development Project (under contracts 2016YFD0300401 and 2019YFA0607403). The FACE experiment in Italy was supported by the AGER project ‘Durum wheat adaptation to global change: effect of elevated CO2 on yield and quality traits’ and by the collaboration CREA-CNR. Finally, the authors also acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI)

Elevated [CO2 ] effects on crops: Advances in understanding acclimation, nitrogen dynamics and interactions with drought and other organisms

Tausz, M ORCiD: 0000-0001-8205-8561Future rapid increases in atmospheric CO2 concentration [CO2 ] are expected, with values likely to reach ~550 ppm by mid-century. This implies that every terrestrial plant will be exposed to nearly 40% more of one of the key resources determining plant growth. In this review we highlight selected areas of plant interactions with elevated [CO2 ] (e[CO2 ]), where recently published experiments challenge long-held, simplified views. Focusing on crops, especially in more extreme and variable growing conditions, we highlight uncertainties associated with four specific areas: (1) While it is long known that photosynthesis can acclimate to e[CO2 ], such acclimation is not consistently observed in field experiments. The influence of sink-source relations and nitrogen (N) limitation on acclimation is investigated and current knowledge about whether stomatal function or mesophyll conductance (gm ) acclimate independently is summarised. (2) We show how the response of N uptake to e[CO2 ] is highly variable, even for one cultivar grown within the same field site, and how decreases in N concentrations ([N]) are observed consistently. Potential mechanisms contributing to [N] decreases under e[CO2 ] are discussed and proposed solutions are addressed. (3) Based on recent results from crop field experiments in highly variable, non-irrigated, water-limited environments, we challenge the previous opinion that the relative CO2 effect is greater under drier environmental conditions. (4) Finally, we summarise how changes in growth and nutrient concentrations due to e[CO2 ] will influence relationships between crops and weeds, herbivores and pathogens in agricultural systems. This article is protected by copyright. All rights reserved

Photosynthesis, photochemistry and antioxidative defence in response to two drought severities and with re-watering in Allocasuarina luehmannii

Gas exchange, chlorophyll fluorescence and water potentials, together with ascorbate and glutathione concentrations, were studied during moderate and severe drought stress and in response to re-watering in Allocasuarina luehmannii seedlings. Moderate drought stress (MS) decreased stomatal conductance (gs) and net CO2 assimilation rates (A) to ∼40% and ∼60% of control values, respectively, and caused decreases in internal CO2 concentration (Ci) and maximum light use efficiency of light-acclimated photosystem II (PSII) centres (Fv′/Fm′). Severe drought stress (SS) decreased gs and A to ∼5% and ∼15% of the control values, respectively, and caused increases in Ci and PSII excitation pressure (1-qP), as well as decreases in water potentials, effective quantum yield of PSII (ΦPSII), maximum efficiency of PSII (Fv/Fm) and Fv′/Fm′. Ascorbate and glutathione concentrations remained unaffected by drought treatments, but ascorbate became more oxidised under severe stress. MS seedlings recovered within 1day (Ci, Fv′/Fm′) to 1week (A, gs) of re-watering. In comparison, SS seedlings had longer-lasting after-stress effects, with recovery of many variables (gs, water potentials, Fv/Fm, ΦPSII, Fv′/Fm′) taking between 1 and 3weeks from re-watering. We found no indication that interaction with antioxidants played a significant role in recovery. In conclusion, A. luehmannii seedlings appear to function normally under moderate drought, but do not seem to have particular metabolic tolerance mechanisms to endure severe drought, which may have implications for its persistence under climate change at the drier margins of its distribution. © 2009 German Botanical Society and The Royal Botanical Society of the Netherlands

Nutrient use and nutrient use efficiency of crops in a high CO2 atmosphere

Abstract Atmospheric CO2 concentrations [CO2] are continually increasing and are predicted to reach ~550 μmol mol-1 by 2050, about a 40 % increase from 2013 levels. Such a large increase in one of the key resources for plant growth will have significant effects on all plants, as carbon assimilation and, consequently, growth and yield is stimulated by the so-called ‘CO2 fertilisation effect’. The one sided increase in carbohydrate acquisition leads to changes in the chemical composition of plants: despite decreases in nutrient concentrations in plant tissues, the greater biomass developed by crops under elevated [CO2] could lead to increased nutrient demand. Nutrient use efficiency in terms of yield divided by available nutrient may improve, but grains or vegetative plant parts have decreased protein and mineral nutrient concentrations, which can diminish market and nutritious value. A number of hypotheses have been proposed to explain the decreases in nutrient concentra- tions, among them: (1) Dilution by increased biomass, (2) decreased mass flow, (3) changes in root architecture and function, (4) decreased nitrate eduction, and (5) changes in nutrient allocation and remobilisation. In addition, elevated [CO2] is likely to change soil processes, including nutrient supply. The extent to which some or all of these contribute to changes in crop nutrition and yield quality is currently unknown because most have not been sufficiently tested under relevant field conditions. This chapter gives an overview of the changes in plant nutrition and trade-offs under elevated [CO2] to point out that current and future efforts towards improved plant nutrient efficiency should explicitly take into consideration rising [CO2]. In particular, field testing of putative nutrient use efficiency traits and nutrient management strategies should include elevated [CO2] as a relevant factor in suitable exposure systems such as Free Air CO2 Enrichment (FACE) technology

Elevated [CO2 ] effects on crops: Advances in understanding acclimation, nitrogen dynamics and interactions with drought and other organisms

Future rapid increases in atmospheric CO2 concentration [CO2 ] are expected, with values likely to reach ~550 ppm by mid-century. This implies that every terrestrial plant will be exposed to nearly 40% more of one of the key resources determining plant growth. In this review we highlight selected areas of plant interactions with elevated [CO2 ] (e[CO2 ]), where recently published experiments challenge long-held, simplified views. Focusing on crops, especially in more extreme and variable growing conditions, we highlight uncertainties associated with four specific areas: (1) While it is long known that photosynthesis can acclimate to e[CO2 ], such acclimation is not consistently observed in field experiments. The influence of sink-source relations and nitrogen (N) limitation on acclimation is investigated and current knowledge about whether stomatal function or mesophyll conductance (gm ) acclimate independently is summarised. (2) We show how the response of N uptake to e[CO2 ] is highly variable, even for one cultivar grown within the same field site, and how decreases in N concentrations ([N]) are observed consistently. Potential mechanisms contributing to [N] decreases under e[CO2 ] are discussed and proposed solutions are addressed. (3) Based on recent results from crop field experiments in highly variable, non-irrigated, water-limited environments, we challenge the previous opinion that the relative CO2 effect is greater under drier environmental conditions. (4) Finally, we summarise how changes in growth and nutrient concentrations due to e[CO2 ] will influence relationships between crops and weeds, herbivores and pathogens in agricultural systems. This article is protected by copyright. All rights reserved