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Intraspecific variation of growth and yield response of wheat to elevated CO2 in Australian Grains Free Air Carbon dioxide Enrichment (AGFACE)

Saman Seneweera1, Sabine Posch1, Rob Norton2,1, Michael Tausz3, Glenn Fitzgerald4, Chris Korte4, Greg Rebetzke5, Mahabubur Mollah4 and Snow Barlow6

1 The University of Melbourne, Private Bag 260, Horsham, Victoria, 3400, Australia Email samans@unimelb.edu.au
2
International Plant Nutrition Institute, 54 Florence St, Horsham, Victoria, 3400, Australia
3
Department of Forest and Ecosystem Science, The University of Melbourne, Creswick, Victoria 3363, Australia
4
Department of Primary Industries, 110 Natimuk Rd., Private Bag 260, Horsham, Victoria, 3400 Australia
5
CSIRO Plant Industry, PO Box 1600, Canberra ACT, 2601, Australia
6
Melbourne School of Land and Environment, The University of Melbourne, Parkville, Victoria 3010, Australia

Abstract

We evaluated eight wheat (Triticum, aestivum L.) cultivars, Janz, Yitpi (high tillering), Silverstar, H45 (synchronous tillering), Drysdale, Gladius, Hartog, and Zebu (medium tillering) under different conditions in the Australian Grains Free Air Carbon dioxide Enrichment (AGFACE) facility. The interacting effects of carbon dioxide (ambient aCO2 ~380 ppm, elevated eCO2 ~550 ppm), water supply (RainFed, irrigated) and higher temperatures during grain filling on plant growth, grain yield and yield components were investigated. Overall, above ground total plant dry mass (DM) increased by 25% at eCO2. The responsiveness to eCO2 was varied during plant development, on an average 25, 19 and 31% (P≤0.05) at tillering (DC30), anthesis (DC65) and maturity (DC90), respectively. Large interspecific variation in growth and yield response to elevated CO2 were observed, cultivar Zebu showed the highest grain yield stimulation eCO2 . Across all the treatments, grain yield was increased by 30% at eCO2. Increase in grain yield at eCO2 was partly due to an increase in tiller number at maturity (16%), single grain weight (9%) and kernels per spike (6%) by eCO2.

Key Words

Climate change, dry matter partitioning, plant growth, tillering

Introduction

Atmospheric carbon dioxide (CO2) concentration has increased from 300 mol mol-1 before the industrial revolution to 387 mol mol-1 by the end of 2009 and is projected to increase to 550 mol mol-1 by the middle of this century (IPCC, 2007). Changes in atmospheric CO2 at the global level will have a moderate or stronger effect on regional climate parameters such as temperature, prevalence of frequency of drought and rainfall pattern (IPCC, 2007). For example, in southern Australia, rainfall will decline by 50–100 mm and annual mean surface temperatures will rise by 1–2oC by 2050 (Moise and Hudson 2008).

Large variations in growth and yield response to eCO2 exist between species (Poorter 1993; Ziska 2008; Shimono et al. 2009). Very littleattention has been given to understand how plants respond to eCO2 within the same species (intraspecific), particularly inconjunction with other environmental parameters. Understanding of the growth and physiological basisof such responses are essentialto select cultivars best suited to the future climate.These findings are valuable for plant breeders in selecting lines for breeding agromomically important crop species.

This paper reports results of the 2009 FACE (Free Air CO2 Enrichment) growth data on the physiologically diverse wheat germplasm response to eCO2, temperature and drought under field conditions.

Materials and methods

FACE Experiment

The Australian Grains FACE (AGFACE) site is located in Horsham, Victoria. AGFACE was designed to simulate atmospheric carbon dioxide levels in the year 2050 (550 ppm) to investigate the interaction of CO2, water and temperature on wheat. The facility has 8 elevated FACE rings and 8 control (ambient) rings, with a 16 m diameter accommodating 26 plots per ring. Each plot is 4 m long and 1.7 m wide. A description of the experimental design and equipment performance is given in Mollah et al. (2009). The AGFACE experiment was carried out for 3 years from 2007, 2008 and 2009 of which the 2009 results are addressed in this paper.

Experimental treatment

The main aim of the experiment is to investigate the interacting effects of carbon dioxide (ambient aCO2 ~380 mol mol-1, eCO2 ~550 mol CO2 mol-1) with variations in water supply (by irrigation), temperature during grain filling (by altering sowing time), nitrogen (by fertilizer addition) and cultivars (having different traits) on crop growth, grain yield and yield components. In 2009, Yipti, Janz (high tillering), Zebu, Drysdale, Gladius and Hartog (moderate-tillering cultivars) and Silverstar and H45 (free-tillering cultivars) were grown in May/early June as TOS1 and late July/early August as TOS2. The two watering regimes were designed to provide an average (~290 mm) and above average (~350 mm) growing season (May to November) rainfall for the region. The agronomic practices of the experiment are described Mollah et al. (2009).

Growth and growth analysis

Destructive plant samplings were carried out at three physiological stages, namely tillering (DC30), anthesis (DC65) and grain maturity (DC90). Plant number, tiller number and spikes numbers were counted. The leaf blades were cut from sheaths and the leaf area was determined by a digital image analyser (Delta-T, Cambridge, UK). All of the fractions were dried at 80C for 48 h before determining their DM. Total grain yield and 1000 grain weight was measured.

Statistical analysis

Results were analysed using ReML mixed models where some data was missing, or by a split plot ANOVA for balanced data sets. Mean separations were carried out using the Duncan Multiple Range Test at P≤0.05 to show main treatment differences using SAS (SAS user Guide 2008).

Results and discussion

On an average across all the treatments, above ground total plant DM was increased by 31% at reproductive maturity under eCO2 (Figure 1, Table 1). However, responsiveness to eCO2 was varied during plant development, on an average by 25, 19 and 31% (P≤0.05) at tillering (DC30), anthesis (DC65) and maturity (DC90), respectively (Table 1). The highest growth response to eCO2 was observed at reproductive maturity (Figure 1, Table 1). TOS and IRRI had no effect on any of the growth parameters at tillering (Table 1). At anthesis, total aboveground DM was significantly increased at TOS 1. At grain maturity, all growth parameters except fertile spike numbers were significantly reduced at the RainFed condition (Table 1). In addition, a delay in sowing (TOS 2) significantly reduced the growth and yield component response. Further, supplementary water had no effect on biomass at maturity but showed a significant interaction between CO2 and TOS.

There were variations in growth response to eCO2 among the cultivars tested though no significant interaction between genotype and CO2 was observed (Table 1, Figure 1). Among the cultivars tested, Zebu showed the highest response to eCO2 and its total aboveground biomass significantly increased at eCO2 but responsiveness largely varied during plant development by 54, 27 and 60%, at tillering, anthesis and grain maturity, respectively (Table 1). Increase in tiller number at eCO2 is suggested to be the key factor for plant growth at eCO2 (Seneweera et al. 2000).

Table 1. Main treatment effects of carbon dioxide (CO2), time of sowing (TOS) and water supply (IRRI) on plant growth, growth analysis, grain yield and yield components of wheat. Values are the means across all other treatments. Treatment mean values with alphabets (a or b) indicate whether the means are statistically different at (p<0.05).

Growth stage

Growth parameter

Main Treatment Effects

   

CO2 Concentration

TOS

IRRI

   

eCO2

aCO2

TOS 1

TOS 2

IRRI

RainFed

Tillering

Above ground biomass (g m-2)

99.8a

79.3b

90.2a

89.0a

87.4a

91.8a

 

Tiller number ( m-2)

547a

479b

490b

535a

521a

504a

 

Tiller number per plant

4.2a

3.7b

4.0a

3.9a

4.0a

3.9a

               

Anthesis

Above ground biomass (g m-2)

653a

548b

763a

447b

599a

602a

 

Tiller number (m-2)

420a

474b

454a

440b

448a

446a

 

Tiller number per plant

4.2a

3.7b

4.4a

3.6b

4.0a

4.0a

 

Spike number ( m-2)

420a

366b

413a

373b

393a

394a

               

Maturity

Grain yield (g m-2)

327a

251b

413a

171b

316a

262b

 

Above ground biomass (g m-2)

721a

549b

854a

425b

678a

592b

 

Spike number (m-2)

405a

349b

399a

355b

391a

362b

 

Fertile spikes per plant

3.9a

3.6b

4.3a

3.2b

3.8a

3.7a

 

Harvest index

0.34a

0.32a

0.33a

0.31b

0.33a

0.31b

 

Kernels per spike

33a

31a

44a

21b

34a

30b

Figure 2. Grain yield for 8 spring wheat cultivars were grown under aCO2 (clear bars) and eCO2 (solid bars). First three panels of the graph indicate the main response across all the treatment, TOS, IRRI and CO2. Error bars are S.E. for each cultivar.

Overall, grain yield increased by 30% at eCO2 but the harvest index was not significantly changed between CO2 treatments (Table 1). Increased grain yield at eCO2 was partly due to increases in tiller number at maturity (16%), single grain weight (9%) and kernels per spike (6%) at eCO2. Among the yield components, spikelet density was the major contributor for an increased grain yield at eCO2 (Table 1). Contribution of increase spikes density on yield enhancement under eCO2 has been reported in rice Kim et al., (2001).

Physiological traits which are linked to the observed differences in intraspecific variations in biomass and yield response to eCO2 are still not well understood. Modern medium tillering wheat cultivars like Zebu, Drysdale and Gladius respond well to eCO2 by allocating more carbon to the tillers at early stages of plant development which then leads to strong tillers at maturity. In contrast, high tillering cultivars respond well to eCO2 during vegetative development, but their survival rates are limited after anthesis possibly because they have limited carbon to support the later part of the reproductive development possibly leading to early tiller death as other environmental factors come to play, for example – high temperature and drought. Our data suggests that modern cultivars having moderate tillering capacity have greater potential to respond to eCO2. In addition, our results suggest a capacity for plasticity among wheat germplasm that could be utilised for selection in the breeding of new wheat varieties to increase their adaptability to rising atmospheric CO2.

Conclusion

Large growth stimulation to eCO2 was observed but the responsiveness varied during plant development. The highest growth stimulation was observed at reproductive maturity. Modern wheat cultivars having moderate tillering capacity respond well to eCO2. Increase in grain yield at eCO2 is partly due to increased tiller number, single kernel weight and grain number per spike.

Acknowledgements

The current study is funded by the Australian Commonwealth Department of Agriculture, Fisheries and Forestry (DAFF), the Grains Research and Development Corporation (GRDC), the Victorian Department of Primary Industries and The University of Melbourne. The authors acknowledge the invaluable technical support of Russel Argall, Justine Ellis, Jason Ellifson and Peter Howie.

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