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

Abstract

This study investigated trade-offs between parameters determining water use efficiency of wheat under elevated CO 2 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 CO 2 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 CO 2 Enrichment (FACE, CO 2 concentration of approximately 550 µmol mol-1) and ambient (approximately 390 µmol mol-1) CO 2. 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

Water availability moderates N2 fixation benefit from elevated [CO2]: A 2‐year free‐air CO2 enrichment study on lentil (Lens culinaris MEDIK.) in a water limited agroecosystem

“…Consistent with previous results on wheat from the same site (Houshmandfar et al, ; Tausz‐Posch, Seneweera, Norton, Fitzgerald, & Tausz, ), e[CO 2 ] stimulated net assimilation rates (A sat ) and biomass of lentil in our study (by 25% and 30%). Stimulation of grain yield by e[CO 2 ] was increased more in the high rainfall season (63%) than in the dry season (18%), in line with previous results on wheat and lentil in the same experimental facility (Bourgault et al, ; Fitzgerald et al, ; Houshmandfar et al, ; O'Leary et al, ), but in contrast to a long‐held paradigm that the CO 2 fertilization effect is greater under drier than wetter conditions (Kimball, ; Leakey, Bishop, & Ainsworth, ; McGrath & Lobell, ). That paradigm was challenged by a recent meta‐analysis (van der Kooi et al, ) and also by long‐term results from a FACE site in a high rainfall agroecosystem, demonstrating that severe drought diminished yield stimulation by e[CO 2 ] to zero (Gray et al, ).…”

“…Table 3. Mean values that share no common letters are significantly different from each other (P < 0.05) of grain yield by e[CO 2 ] was increased more in the high rainfall season (63%) than in the dry season (18%), in line with previous results on wheat and lentil in the same experimental facility (Bourgault et al, 2017;Fitzgerald et al, 2016;Houshmandfar et al, 2016;O'Leary et al, 2015), but in contrast to a long-held paradigm that the CO 2 fertilization effect is greater under drier than wetter conditions (Kimball, 2016;Leakey, Bishop, & Ainsworth, 2012;McGrath & Lobell, 2013).…”

The relationship between transpiration and nutrient uptake in wheat changes under elevated atmospheric CO2

“…Stomatal conductance was on average 27% lower under elevated than under ambient CO 2 . This is in agreement with CO 2 ‐driven decreases of between 18 and 30% reported by earlier FACE trials measuring in situ g s in wheat, depending on intraspecific variations and environmental conditions under which plants were grown or g s measurements were collected (Garcia et al , Wall et al , McGrath and Lobell , Houshmandfar et al ).…”

“…in dense forest canopies; de Kauwe et al ), is unlikely. Calculating TE for biomass production with our transpiration estimates resulted in about 4 g dry aboveground biomass per liter of transpiration [using anthesis biomass data for ambient CO 2 reported in Houshmandfar et al ()]. Given that 2013 was a very high rainfall season at the site, this compares well to corresponding values between 4–6 g l −1 determined at anthesis for a number of Australian wheat cultivars under non‐limiting water conditions (Fig.…”

Nitrogen application is required to realize wheat yield stimulation by elevated CO2 but will not remove the CO2‐induced reduction in grain protein concentration

“…The mechanism of the decreased grain/seed protein concentration (often measured as nitrogen (N) converted to an estimate of “crude protein”) of crops and other plants under eCO 2 has been a matter of discussion in the scientific literature (Feng et al, ; Taub et al, ; Tausz‐Posch, Armstrong, & Tausz, ; Uddling et al, ). Four main hypotheses, which may all contribute to varying extents, have been proposed: (1) dilution of N if N uptake does not keep pace with the CO 2 ‐induced increase in carbohydrate production under eCO 2 (Loladze, ), (2) decreased uptake and assimilation of nitrate under eCO 2 (Bloom, Burger, Rubio Asensio, & Cousins, ; Rubio‐Asensio & Bloom, ), (3) reduced soil mass‐flow of water and thus nutrients towards the roots as a consequence of reduced stomatal conductance leading to lower transpiration under eCO 2 (e.g., Housmandfar et al, ; Housmandfar et al, ; Taub et al, ) and (4) reduced N uptake following photosynthetic (RuBisCO) downward regulation under eCO 2 (Sitt & Krapp, ). Feng et al () observed for a wide range of plants including several crops, that an eCO 2 ‐induced reduction of the protein concentration exists also in the absence of a growth/yield stimulation.…”