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. 2009 Aug;150(4):2104-15.
doi: 10.1104/pp.109.139162. Epub 2009 Jun 17.

More productive than maize in the Midwest: How does Miscanthus do it?

Frank G Dohleman  1 , Stephen P Long
Affiliations

More productive than maize in the Midwest: How does Miscanthus do it?

Frank G Dohleman et al. Plant Physiol. 2009 Aug.

Abstract

In the first side-by-side large-scale trials of these two C(4) crops in the U.S. Corn Belt, Miscanthus (Miscanthus x giganteus) was 59% more productive than grain maize (Zea mays). Total productivity is the product of the total solar radiation incident per unit land area and the efficiencies of light interception (epsilon(i)) and its conversion into aboveground biomass (epsilon(ca)). Averaged over two growing seasons, epsilon(ca) did not differ, but epsilon(i) was 61% higher for Miscanthus, which developed a leaf canopy earlier and maintained it later. The diurnal course of photosynthesis was measured on sunlit and shaded leaves of each species on 26 dates. The daily integral of leaf-level photosynthetic CO(2) uptake differed slightly when integrated across two growing seasons but was up to 60% higher in maize in mid-summer. The average leaf area of Miscanthus was double that of maize, with the result that calculated canopy photosynthesis was 44% higher in Miscanthus, corresponding closely to the biomass differences. To determine the basis of differences in mid-season leaf photosynthesis, light and CO(2) responses were analyzed to determine in vivo biochemical limitations. Maize had a higher maximum velocity of phosphoenolpyruvate carboxylation, velocity of phosphoenolpyruvate regeneration, light saturated rate of photosynthesis, and higher maximum quantum efficiency of CO(2) assimilation. These biochemical differences, however, were more than offset by the larger leaf area and its longer duration in Miscanthus. The results indicate that the full potential of C(4) photosynthetic productivity is not achieved by modern temperate maize cultivars.

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Figures

Figure 1.
Figure 1.
Accumulated aboveground dry biomass (Wb) of Miscanthus (black circles) and maize (white circles) over the 2007 and 2008 growing seasons. The intercept (Wb = 0) indicates the date of emergence for each crop in each year. Values represent arithmetic means ± 1 se (n = 4).
Figure 2.
Figure 2.
Radiation interception efficiency (εi) and GLAI of Miscanthus (black circles) and maize (white circles) over the 2007 and 2008 growing seasons. X-intercepts represent the dates of crop emergence and completion of senescence for each species in each year. Significant effects of species, date (DOY, day of year), and the species by date interaction are indicated by the P values.
Figure 3.
Figure 3.
The accumulated dry biomass (mean ± 1 se) of Miscanthus (black circles) and maize (white circles) plotted against cumulative intercepted total solar radiation in 2007 (A) and 2008 (B). Lines represent the mean best fit linear slope of least squares regression for each species (n = 4). Two-way ANOVA shows that there is no significant difference in slope between species (P = 0.6892); however, there is a marginally significant effect of year (P = 0.0706), but no effect of the species by year interaction (P = 0.7277).
Figure 4.
Figure 4.
Annual course of the daily integrals of measured CO2 uptake per unit leaf area (A′; A), total annual leaf-level CO2 uptake (Al″) by a single sunlit and single shaded canopy layer (B), and total annual canopy-level CO2 uptake (Ac″; C) for Miscanthus and maize based on measured leaf level photosynthetic rates, and calculated sunlit and shaded GLAI over two growing seasons in the Midwestern United States. Significant effects of species, time, and the species by time interaction are indicated by the P values. S*Y, Species × year.
Figure 5.
Figure 5.
Mean midday leaf-level photosynthetic rate (A; A), stomatal conductance (gs; B), ratio of intercellular [CO2] to atmospheric [CO2] (ci/ca; C), whole-chain electron transport rate (JPSII; D), maximum efficiency of PSII (Fv′/Fm′; E), and operating efficiency of PSII (Fq′/Fm′; F) for field-grown sunlit Miscanthus (black bars) and maize (white bars) leaves averaged over dates where both crops were measured in the 2007 and 2008 growing seasons. Bars represent arithmetic means ± 1 se, and P values represent the mixed-model ANOVA where species, year, and species × year (S*Y) were the main effects.
Figure 6.
Figure 6.
Best fit linear regression analysis of A versus gs for Miscanthus (black circles) and maize (white circles) over the 2007 and 2008 growing seasons. Points represent individual subsamples from diurnal measurements with lines representing best-fit linear regression with all respiration (A < 0) values removed and forced through the origin. The difference in slope between species is statistically significant (P = 0.0267; n = 4).
Figure 7.
Figure 7.
Representative responses of leaf CO2 uptake (A) to incident photon flux (Q; n = 4; A) and intracellular CO2 concentration (ci; B) for field-grown leaves of Miscanthus (black circles) and maize (white circles). Arrows represent supply function for each representative curve. Fitted values for all measurements are given in Table II.
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References

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