Change in Components of Yield at Elevated [CO2

The consistent stimulation of economic yield at elevated [CO2] can involve larger seed or grain size, more seeds per pod, ear or panicle, and/or more reproductive structures per plant. The yield benefit for most C3 crops resulted from increased above-ground dry matter production supporting more reproductive structures (Table 7.1). In the FACE experiments with rice, tiller, panicle and spikelet numbers per area increased significantly (Kim et al. 2003; Yang et al. 2006). Those increases in dry matter production were large enough to outweigh negative effects of elevated [CO2] on productive tiller ratio and degenerated spikelets (Kim et al. 2003; Yang et al. 2006).

In C3 oilseed and grain crops, elevated [CO2] also had little effect on individual grain or seed mass (Table 7.1). This may not be unexpected since individual grain weight has not changed with genetic improvement in wheat, rice, or soybean over much of the last century (Morrison et al. 2000; Fischer 2007). All C3 oilseed and

Table 7.1 Average percent change in economic yield, final above-ground biomass, individual seed or grain weight, and harvest index of crops grown at elevated [CO2] (~550 ppm) in FACE experiments. Bold numbers represent statistically significant changes (p < 0.10) reported in primary literature sources

Table 7.1 Average percent change in economic yield, final above-ground biomass, individual seed or grain weight, and harvest index of crops grown at elevated [CO2] (~550 ppm) in FACE experiments. Bold numbers represent statistically significant changes (p < 0.10) reported in primary literature sources

Crop

Economic yield (%)

Above-ground biomass (%)

Individual seed or grain weight (%)

Harvest index (%)

Soybean3

+14

+16

0

-2

Wheat"

+13

+10

-

-

Ricec

+13

+27

+1

-2

Potatod

+34

-5

-

-

Oilseed rapee

+18

+17

+18

-3

Maizef

0

-2

-1

-2

Sorghum®

+4

+9

-1

-2

aMorgan et al. 2005; bPinter et al. 1996, Kimball 2006; cData are averaged from the following studies: Kim et al. 2001, 2003; Pang et al. 2006; Sasaki et al. 2005; Seneweera et al. 2002; Shimono et al. 2007; Yang et al. 2006; dBindi et al. 2006; eFranzaring et al. 2008; fLeakey et al. 2006; gOttman et al. 2001.

aMorgan et al. 2005; bPinter et al. 1996, Kimball 2006; cData are averaged from the following studies: Kim et al. 2001, 2003; Pang et al. 2006; Sasaki et al. 2005; Seneweera et al. 2002; Shimono et al. 2007; Yang et al. 2006; dBindi et al. 2006; eFranzaring et al. 2008; fLeakey et al. 2006; gOttman et al. 2001.

grain crops had a lower harvest index at elevated [CO2]; however, the magnitude of the change was only significant for soybean and the change in all crops was small (Table 7.1). Still, maintaining current levels of harvest index represents one potential area for improving crop responses to elevated [CO2] (Ainsworth et al. 2008c).

Potato differed from the other C3 crops (Table 7.1). Tuber production was significantly increased by elevated [CO2] while aboveground dry matter production was not affected (Bindi et al. 2006). The number of tubers, rather than the size of the tubers, caused the enhancement in yield (Miglietta et al. 1998). Also, the fraction of malformed tubers was not affected by elevated [CO2] (Bindi et al. 2006).

When averaged across all experiments, final yield, grain weight and harvest index of C4 crops was not affected by growth at elevated [CO2] (Table 7.1). When sorghum was grown at elevated [CO2] under conditions with water stress, there was a tendency towards higher yields and greater aboveground biomass (Ottman et al. 2001). This supports the notion that C4 plants will benefit from elevated [CO2] in times and places with drought, but more studies are needed to reduce uncertainty in this prediction (Leakey 2009).

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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