Intra-specific variation of wheat grain quality in response to elevated [CO2] at two sowing times under rain-fed and irrigation treatments

https://doi.org/10.1016/j.jcs.2013.12.002Get rights and content

Highlights

  • Eight wheat cultivars were grown at elevated CO2, at two water levels, at 2 sown times.

  • Grain nutrient, anti-nutrient and flour rheological properties were analysed.

  • Grain quality response to elevated [CO2] dependent on the timing of heat stress during the grain filling.

  • Cultivar specific response of grain Zn, Mn, Cu and some of flour rheological properties to elevated [CO2] were observed.

  • Genetic variability in response to e[CO2] could be incorporated into future wheat breeding programs.

Abstract

In order to investigate the intra-specific variation of wheat grain quality response to elevated atmospheric CO2 concentration (e[CO2]), eight wheat (Triticum aestivum L.)cultivars were grown at two CO2 concentrations ([CO2]) (current atmospheric, 389 CO2 μmol mol−1 vs. e[CO2], FACE (Free-Air CO2 Enrichment), 550  ±  10% CO2 μmol mol−1), at two water levels (rain-fed vs. irrigated) and at two times of sowing (TOS1, vs. TOS2). The TOS treatment was mainly imposed to understand whether e[CO2] could modify the effects of timing of higher grain filling temperatures on grain quality. When plants were grown at TOS1, TKW (thousand kernel weight), grain test weight, hardness index, P, Ca, Na and phytate were not significantly changed under e[CO2]. On the other hand, e[CO2] increased TKW (16%), hardness index (9%), kernel diameter (6%), test weight (2%) but decreased grain protein (10%) and grain phytate (11%) at TOS2. In regard to grain Zn, Mn and Cu concentrations and some flour rheological properties, cultivar specific responses to e[CO2] were observed at both sowing times. Observed genetic variability in response to e[CO2] in terms of grain minerals and flour rheological properties could be easily incorporated into future wheat breeding programs to enable adaptation to climate change.

Introduction

Since 1959, rapid fossil fuel consumption and deforestation has steadily raised carbon dioxide concentration [CO2] in the atmosphere from 315 μmol mol−1 to approximately 389 μmol mol−1 by 2009 (Keeling and Piper, 2009). Current atmospheric [CO2] (a[CO2]) is expected to increase to 550 μmol mol−1 by 2050 under most emission scenarios (Carter et al., 2007). This increase is likely to affect the global and regional climates and weather patterns. For example, global temperature is predicted to increase by an average of 1.5–4.5 °C with the more frequent occurrence of extreme climatic events such as heat waves and/or drought (Carter et al., 2007). In the light of these predicted challenges of future climates, agronomic and genetic adjustments will be required to consider both the indirect climate effects, as well as the direct effects of increasing [CO2] on plant metabolism to increase the grain yield and quality (Tausz et al., 2013).

Cereal grains and their products are important sources of protein, energy, minerals and vitamins for much of the world's population. Wheat is one of the staple foods of almost half the world's population and plays a significant role in global food security (Cakmak, 2004). For example, cereal grains and products provide 44% of the daily intake of Fe (15% from bread), 27% of Mg (13% from bread), 25% of Zn (11% from bread) and 31% of Cu (14% from bread) to the UK population (Henderson et al., 2003). Deficiencies of micronutrients such as Zn and Fe for those on grain based diets is recognized globally and known as “hidden hunger” and affects about two billion people (FAOSTAT, 2007). Moreover, micronutrient deficiencies have been identified in regions where wheat is the staple food (Cakmak et al., 2004).

Results of several FACE (Free Air CO2 Enrichment) studies have demonstrated that increasing [CO2] adversely affects wheat grain quality and flour rheological properties (Fernando et al., 2012, Högy et al., 2009, Kimball et al., 2001). FACE studies have also reported that elevated atmospheric [CO2] (e[CO2]), has resulted in a decrease in the amount of Fe and Zn in wheat grain (Fernando et al., 2012, Högy et al., 2009). Elevated atmospheric [CO2] is, therefore, likely to exacerbate already existing problems of Fe and Zn deficiencies in human diets. Some modern wheat cultivars released in late 20th century have relatively low grain Zn and Fe concentrations, and this has been attributed to breeding programs focused on yield enhancement (Graham et al., 1999). Genetic variation found within the wheat germplasm indicates that Fe and Zn concentrations in wheat grain could be improved through plant breeding (Zhang, 2010).

Significant intra-specific variation of yield in response to e[CO2] has been observed for a number of crop species, among them cowpea, rice, soybean and wheat (Tausz et al., 2013). Varietal differences of flour protein, protein yield per plant and flour yield per plant has also been reported in response to e[CO2] (Ziska et al., 2004). Most of these studies were conducted under either controlled environment chambers or enclosures systems, where responses to e[CO2] are different from those reported under field conditions (Van Oijen, 1999). Therefore it has been argued that field studies, in particular FACE experiments in major cropping areas, are needed to evaluate the genetic variability of grain quality in response to e[CO2] (Tausz et al., 2013).

This study was conducted within the Australian Grains Free Air CO2 Enrichment (AGFACE) facility in the south-eastern wheat belt of Australia, a dryland cropping area representative of low rainfall, rain-fed wheat production regions around the world. In this experiment, we addressed whether there is intra-specific variation in grain quality response to e[CO2]: specifically in terms of (1) grain physical quality, (2) chemical characteristics and (3) flour rheological properties by growing plants at two different sowing times under rain-fed conditions and with supplementary irrigation.

Section snippets

Experimental conditions and CO2 exposure

The experiment was conducted under field conditions in the AGFACE (Australian Grains Free Air CO2 Enrichment) facility in Horsham, Victoria, Australia (36°45′07″S, 142° 06′52″E; 128 m above sea level) during the 2009 growing season. The soil at the experimental site is a Vertosol (Isbell, 1996) and the region has a ‘Mediterranean’ type climate but with drier, cooler winters and less plant growth compared to the classic Mediterranean climate (Hutchinson et al., 2005). A detailed site description

Grain physical properties

Effect of e[CO2] on grain physical properties of TKW, kernel diameter, test weight and hardness index was significantly different between sowing times (Supplementary data Table S2). At TOS2, e[CO2] significantly increased TKW, test weight, kernel diameter, percentage of >2 mm size grain weight class and hardness index compared to a[CO2] grown grains (Supplementary data Table S2, Supplementary data Table S3). At TOS1, effect of e[CO2] on kernel diameter was different among cultivars

Discussion

In this paper, we report for the first time intra-specific variation in grain quality characteristics and flour rheological properties under e[CO2] in free-air field conditions. Impact of e[CO2] concentration on grain quality traits including chemical, physical and flour rheological properties were significantly varied between TOS treatment. These findings suggest that the impact of e[CO2] on grain quality is highly dependent on the prevailing environmental condition and cultivar. Short periods

Conclusions

The results suggest that grain quality of wheat was altered under e[CO2] but the magnitude of changes are highly dependent on the cultivar and prevailing environmental conditions. In this experiment, late sowing or the TOS2 was used to investigate whether high [CO2] will compensate potential negative effects of higher temperatures at two different times of grain filling on grain quality. Grains produced at TOS2 growing conditions were higher with protein and mineral concentrations under both [CO

Acknowledgement

Research at the AGFACE facility is jointly run by the Victorian State Government Department of Environment and Primary Industries and the University of Melbourne, with funding by the Grains Research and Development Corporation and the Australian Commonwealth Department of Agriculture, Fisheries and Forestry. We also thank Victor Raboy, United States Department of Agriculture for assistance with the phytate measurements.

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