Growth and yield stimulation under elevated CO2 and drought: A meta-analysis on crops

© 2015 Elsevier B.V. Exposure of plants to elevated CO2(eCO2) has a number of physiological effects, including increased photosynthetic carbon fixation and decreased stomatal conductance, resulting in greater growth and yield and also improved water use efficiency. Therefore, eCO2is considered to ameliorate the adverse effects of drought. To test this assumption in existing literature, we undertook a meta-analysis to study the interactive effects of eCO2and experimentally imposed drought on biomass and yield of crops and pasture grasses. We found that for crop species with C3metabolism, eCO2stimulates biomass accumulation and yield under both well-watered and dry conditions to a similar extent. For C4crops, however, stimulation of biomass accumulation and yield by eCO2occurs only under dry growing conditions. Disentangling other functional groups (annuals vs. perennials, crop species, experimental setups) also showed that plant metabolism greatly determines the overall effect of eCO2and water availability on plant performance. Our results suggest that crops grown in areas with limited water availability will benefit from future eCO2, regardless of their metabolism. Drought leads to stomatal limitation of photosynthesis in both C3and C4crops, which is alleviated when the plants are grown under eCO2

Water use dynamics of dryland canola (Brassica napus L.) grown on contrasting soils under elevated CO2

Background and aims: Increasing atmospheric carbon dioxide concentration ([CO 2 ]) stimulates the leaf-level (intrinsic) water use efficiency (iWUE), which may mitigate the adverse effects of drought by lowering water use in plants. This study investigated the interactive effect of [CO 2 ] and soil type on growth, yield and water use of canola (Brassica napus L.) in a dryland environment. Methods: Two canola cultivars (vigorous hybrid cv. ‘Hyola 50’ and non-hybrid cv. ‘Thumper’) were grown in large intact soil cores containing either a sandy Calcarosol or clay Vertosol under current ambient (a[CO 2 ]) and future elevated [CO 2 ] (e[CO 2 ]), ∼550 μmol mol −1 ). Net assimilation rates (A net ), stomatal conductance (g s ) and leaf area were measured throughout the growing season. Seed yield and yield components were recorded at final harvest. Water use was monitored by lysimeter balances. Results: Elevated [CO 2 ]-stimulation of iWUE was greater than the effect on leaf area, therefore, water use was lower under e[CO 2 ] than a[CO 2 ], but this was further modified by soil type and cultivar. The dynamics of water use throughout the growing season were different between the studied cultivars and in line with their leaf development. The effect of e[CO 2 ] on seed yield was dependent on cultivar; the non-hybrid cultivar benefitted more from increased [CO 2 ]. Although textural differences between soil types influenced the water use under e[CO 2 ], this did not affect the ‘CO 2 fertilisation effect’ on the studied canola cultivars. Conclusion: Elevated [CO 2 ]-induced water savings observed in the present study is a potential mechanism of ameliorating drought effects in high CO 2 environment. Better understanding of genotypic variability in response to water use dynamics with traits affecting assimilate supply and use can help breeders to improve crop germplasm for future climates. © 2019, Springer Nature Switzerland AG

Yield of canola (Brassica napus L.) benefits more from elevated CO2 when access to deeper soil water is improved

This study investigated the interactive effects of atmospheric CO2 concentration ([CO2]) and water availability on yield, root growth and water use of two canola cultivars with contrasting growth and vigour (vigorous hybrid cv. Hyola 50 and non-hybrid cv. Thumper). Plants were grown under ambient [CO2] (a[CO2], ∼400 μmol mol−1) or elevated [CO2] (e[CO2], ∼700 μmol mol−1) in a glasshouse. Two water treatments (well-watered and drought) were established in each [CO2] treatment. During the growing season leaf gas exchange parameters were measured. Leaf area was measured at 80 days after sowing. Aboveground biomass, seed yield, yield components and root biomass in four different soil layers (Layer 1: 0–20 cm, Layer 2: 21–40 cm, Layer 3: 41–60 cm and Layer 4: 61–80 cm depth) were measured at maturity. Weekly water use was determined gravimetrically. Elevated [CO2] stimulated seed yield (38%), aboveground biomass (34%), root biomass (42%), leaf area (42%) and leaf biomass (41%). Whilst e[CO2] stimulated root biomass in all soil layers, this stimulation was greater in the deeper than upper soil layers, and was associated with greater extraction of deeper soil water under e[CO2]. The cultivar with greater stimulation of deeper root biomass under e[CO2] showed greater yield benefit from the ‘CO2 fertilisation effect’. Under well-watered conditions, e[CO2]-induced reductions of stomatal conductance (gs) balanced the effect of increased leaf area on water use, resulting in similar water use compared to a[CO2]. In contrast, under drought conditions, water use was greater under e[CO2] than a[CO2]. The ‘CO2 fertilisation effect’ depended on cultivar and water treatment. Under well-watered conditions, aboveground biomass of the hybrid cultivar benefitted more from the ‘CO2 fertilisation effect’. However, under drought both aboveground biomass and seed yield of the non-hybrid cultivar benefitted more from the ‘CO2 fertilisation effect’. These findings show that interactions between environmental conditions (here experimental water treatments) and expression of genotypic traits (here differences between cultivars) play a decisive role in determining potential yield and growth benefits from rising [CO2]. © 2018 Elsevier B.V

The water use dynamics of canola cultivars grown under elevated CO2 are linked to their leaf area development

The ‘CO2 fertilisation effect’ is often predicted to be greater under drier than wetter conditions, mainly due to hypothesised early season water savings under elevated [CO2] (e[CO2]). However, water savings largely depend on the balance between CO2-induced improvement of leaf-level water use efficiency and CO2-stimulation of transpiring leaf area. The dynamics of water use during the growing season can therefore vary depending on leaf area development. Two canola (Brassica napus L.) cultivars of contrasting growth and vigour (vigorous hybrid cv. Hyola 50 and non-hybrid cv. Thumper) were grown under ambient [CO2] (a[CO2], ∼400 μmol mol−1) or e[CO2] (∼700 μmol mol−1) with two water treatments (well-watered and mild drought) in a glasshouse to investigate the interdependence of leaf area development and water use. Dynamics of water use during the growing season varied depending on [CO2] and cultivars. Early stimulation of leaf growth under e[CO2], which also depended on cultivar, overcompensated for the effect of increased leaf-level water use efficiency, so that weekly water use was greater and water depletion from soil greater under e[CO2] than a[CO2]. This result shows that the balance between leaf area and water use efficiency stimulation by e[CO2] can tip towards early depletion of available soil water, so that e[CO2] does not lead to water savings, and the ‘CO2 fertilisation effect’ is not greater under drier conditions. © 2018 Elsevier Gmb

Trade-offs between water-use related traits, yield components and mineral nutrition of wheat under Free-Air CO2 Enrichment (FACE)

This study investigated trade-offs between parameters determining water use efficiency of wheat under elevated CO2 in contrasting growing seasons and a semi-arid environment. We also evaluated whether previously reported negative relationships between nutrient content and transpiration efficiency among wheat genotypes will be maintained under elevated CO2 conditions. Two cultivars of wheat (Triticum aestivum L.), Scout and Yitpi, purportedly differing in water use efficiency related traits (e.g. transpiration efficiency) but with common genetic backgrounds were studied in a high yielding, high rainfall (2013), and in a low yielding, very dry growing season (2014) under Free-Air CO2 Enrichment (FACE, CO2 concentration of approximately 550 μmol mol-1) and ambient (approximately 390 μmol mol-1) CO2. Gas exchange measurements were collected diurnally between stem elongation and anthesis. Aboveground biomass and nutrient content (sum of Ca, K, S, P, Cu, Fe, Zn, Mn and Mg) were determined at anthesis. Yield, yield components and harvest index were measured at physiological maturity. Cultivar Scout showed transiently greater transpiration efficiency (measured by gas exchange) over cultivar Yitpi under both ambient and elevated CO2 conditions, mainly expressed in the high yielding but not in the low yielding season. Nutrient content was on average 13% greater for the lower transpiration efficiency cultivar Yitpi than the cultivar with higher transpiration efficiency (Scout) in the high yielding season across both CO2 concentrations. Elevated CO2 stimulated grain yield to a greater extent in the high yielding season than in the low yielding season where increased aboveground biomass earlier in the season did not translate into fertile tillers in cultivar Yitpi. Yield increased 27 and 33% in the high yielding and 0 and 19% in the low yielding season for cultivars Yitpi and Scout, respectively. Intraspecific variation in CO2 responsiveness related mechanisms of grain yield were observed. These results suggest CO2-driven trade-offs between traits governing water use efficiency are related to both growing season and intraspecific variations, and under very dry finishes, the trade-offs may even reverse. The negative relationship between nutrient content and transpiration efficiency among wheat genotypes will be maintained under elevated CO2 conditions. © 2016 Elsevier B.V

Can additional N fertiliser ameliorate the elevated CO2-induced depression in grain and tissue N concentrations of wheat on a high soil N background?

© 2017 Blackwell Verlag GmbH. Elevated CO2 stimulates crop yields but leads to lower tissue and grain nitrogen concentrations [N], raising concerns about grain quality in cereals. To test whether N fertiliser application above optimum growth requirements can alleviate the decline in tissue [N], wheat was grown in a Free Air CO2 Enrichment facility in a low-rainfall cropping system on high soil N. Crops were grown with and without addition of 50–60 kg N/ha in 12 growing environments created by supplemental irrigation and two sowing dates over 3 years. Elevated CO2 increased yield and biomass (on average by 25%) and decreased biomass [N] (3%–9%) and grain [N] (5%). Nitrogen uptake was greater (20%) in crops grown under elevated CO2. Additional N supply had no effect on yield and biomass, confirming high soil N. Small increases in [N] with N addition were insufficient to offset declines in grain [N] under elevated CO2. Instead, N application increased the [N] in straw and decreased N harvest index. The results suggest that conventional addition of N does not mitigate grain [N] depression under elevated CO2, and lend support to hypotheses that link decreases in crop [N] with biochemical limitations rather than N supply

Elevated [CO2] mitigates the effect of surface drought by stimulating root growth to access sub-soil water

Through stimulation of root growth, increasing atmospheric CO2 concentration ([CO2]) may facilitate access of crops to sub-soil water, which could potentially prolong physiological activity in dryland environments, particularly because crops are more water use efficient under elevated [CO2] (e[CO2]). This study investigated the effect of drought in shallow soil versus sub-soil on agronomic and physiological responses of wheat to e[CO2] in a glasshouse experiment. Wheat (Triticum aestivum L. cv. Yitpi) was grown in split-columns with the top (0-30 cm) and bottom (31-60 cm; 'sub-soil') soil layer hydraulically separated by a wax-coated, root-penetrable layer under ambient [CO2] (a[CO2], ∼400 μmol mol-1) or e[CO2] (∼700 μmol mol-1) [CO2]. Drought was imposed from stem-elongation in either the top or bottom soil layer or both by withholding 33% of the irrigation, resulting in four water treatments (WW, WD, DW, DD; D = drought, W = well-watered, letters denote water treatment in top and bottom soil layer, respectively). Leaf gas exchange was measured weekly from stem-elongation until anthesis. Above-and belowground biomass, grain yield and yield components were evaluated at three developmental stages (stem-elongation, anthesis and maturity). Compared with a[CO2], net assimilation rate was higher and stomatal conductance was lower under e[CO2], resulting in greater intrinsic water use efficiency. Elevated [CO2] stimulated both above- and belowground biomass as well as grain yield, however, this stimulation was greater under well-watered (WW) than drought (DD) throughout the whole soil profile. Imposition of drought in either or both soil layers decreased aboveground biomass and grain yield under both [CO2] compared to the well-watered treatment. However, the greatest 'CO2 fertilisation effect' was observed when drought was imposed in the top soil layer only (DW), and this was associated with e[CO2]-stimulation of root growth especially in the well-watered bottom layer. We suggest that stimulation of belowground biomass under e[CO2] will allow better access to sub-soil water during grain filling period, when additional water is converted into additional yield with high efficiency in Mediterranean-type dryland agro-ecosystems. If sufficient water is available in the sub-soil, e[CO2] may help mitigating the effect of drying surface soil

Water use and growth responses of dryland wheat grown under elevated [CO 2] are associated with root length in deeper, but not upper soil layer

This study investigated crop water use of wheat grown in a dryland Mediterranean-type environment under elevated atmospheric CO 2 concentrations ([CO 2 ]). Two related cultivars, contrasting in agronomic features (cvs. Scout and Yitpi; Scout has good early vigour and high transpiration efficiency), were grown under ambient [CO 2 ] (a[CO 2 ], ∼400 μmol mol −1 ) and elevated [CO 2 ] (e[CO 2 ], ∼550 μmol mol −1 ) in the Australian Grains Free Air CO 2 Enrichment (AGFACE) facility for two growing seasons. Each year, an irrigation treatment (rainfed versus irrigated) was imposed within the CO 2 -treatments. Normalised difference vegetation index (as surrogate for canopy cover) and root length in the upper (0 cm–32 cm) and deeper (33 cm–64 cm) soil layers were measured at stem-elongation and anthesis. Elevated [CO 2 ] stimulated root length of wheat in both upper and deeper soil layers, and this stimulation was modified by cultivars and irrigation regimes. Across cultivars and all treatments, water use, biomass and grain yield were positively associated with root length in the deeper soil layer but not with root length in the upper soil layer. The ‘CO 2 fertilisation effect’ on biomass and grain yield was of similar magnitude under both irrigated and rainfed conditions. Although e[CO 2 ] did not increase canopy cover in these experiments, the CO 2 effect on water use depended on cultivars and irrigation regimes. Despite greater e[CO 2 ]-induced stimulation of tillers and spikes, the cv. Scout did not receive more biomass or grain yield benefit from the ‘CO 2 fertilisation effect’ compared to cv. Yitpi. © 2018 Elsevier B.V

Effect of a heat wave on lentil grown under free-air CO2 enrichment (FACE) in a semi-arid environment

Atmospheric CO2 concentrations have been increasing from ~280 to 405 mmol mol−1 air from the preindustrial era until now. As this rise is a major driver for global warming and increasing variability in weather patterns, it is predicted that the frequency and duration of heat waves will continue to increase in many arable regions during this century. Lentil (Lens culinaris Medik.) is a cool-season crop whose production has recently expanded into areas where it is subject to high temperature stress during pod filling (e.g., Australia). The objective of this experiment was to determine whether growth at elevated atmospheric CO2 concentrations (e[CO2], imposed by free-air CO2 enrichment [FACE]) is able to compensate for the negative impact of a 3-d heat wave event imposed at the flat pod stage on two lines of lentil. Grain yield under e[CO2] subjected to the heat wave were equivalent to grain yield under ambient without the heat wave event. The heat wave reduced grain yield by 33%, but this was not made more or less severe by e[CO2]. This reduction was attributed to a small decrease in aboveground biomass (6%) and a larger decrease in harvest index (16%) due to the heat wave event. The number of pods and grains per square meter were reduced by the heat wave (29–32%), whereas seed size was not affected. The effects of the heat wave during the event were evident on the foliar canopy temperature measured with an infrared thermometer, which increased by 6°C, and on the electron transport rate calculated from the quantum efficiency of photosystem II obtained with chlorophyll fluorescence measurements. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved

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. © 2016 John Wiley & Sons Ltd