Photosynthesis, Productivity, and Yield of Maize Are Not Affected by Open-Air Elevation of CO2 Concentration in the Absence of Drought

Abstract

(A.R.) While increasing temperatures and altered soil moisture arising from climate change in the next 50 years are projected to decrease yield of food crops, elevated CO 2 concentration ([CO 2 ]) is predicted to enhance yield and offset these detrimental factors. However, C 4 photosynthesis is usually saturated at current [CO 2 Global climate change, in the form of rising temperature and altered soil moisture, is projected to decrease the yield of food crops over the next 50 years (Thomson et al., 2005). Meanwhile, the simultaneous increase in CO 2 concentration ([CO 2 ]) is predicted to stimulate crop production and offset these detrimental components of climate change (Thomson et al., 2005). This encouraging projection results from speciesspecific ''CO 2 fertilization'' factors in yield models (Phillips et al., 1996;Brown and Rosenberg, 1999;Parry et al., 2004;Thomson et al., 2005). These simulate the enhancements of net CO 2 assimilation rate (A) and yield observed, for both C 3 (17%-29%) and C 4 crops (6%-10%), under elevated [CO 2 ] in controlled environment studies (Kimball, 1983;Allen et al., 1987).While early projections of ''[CO 2 ] fertilization'' were based on studies in glasshouses and other protected environments, Free-Air Concentration Enrichment (FACE) experiments are fully open-air trials of crop performance. They provide realistic simulations of future growing conditions and provide perhaps the best opportunity to requantify CO 2 fertilization effects and elucidate the mechanism of crop response. FACE experiments on the C 3 crops rice (Oryza sativa), wheat (Triticum aestivum), and soybean (Glycine max) have observed smaller increases in yield than were predicted from the early chamber studies Long et al., 2005;Morgan et al., 2005). Yet the primary response mechanisms of C 3 crops have not been controversial . First, elevated [CO 2 ] directly stimulates A, growth, and yield by decreasing photorespiration and accelerating carboxylation by Rubisco. Second, it decreases stomatal aperture, which can reduce plant water use and indirectly enhance performance by ameliorating water stress. In contrast, the response of C 4 crops to future elevated [CO 2 ] is uncertain. In C 4 plants, Rubisco is

Reduced plant water status under sub-ambientpCO2limits plant productivity in the wild progenitors of C3and C4cereals

“…This hypothesized mechanism is consistent with studies investigating the effects of elevated atmospheric pCO 2 (55-70 Pa) on the water relations of C 4 plants, where reduced g s and E improve plant and soil water status, and extend the active period for photosynthesis and growth (Ghannoum et al, 2000). This indirect effect of elevated pCO 2 is particularly important when C 4 plants experience some kind of water deficit (Conley et al, 2001;Wall et al, 2001;Leakey et al, 2004Leakey et al, , 2006Leakey, 2009). It seems likely that these feedbacks of water status on stomatal conductance, and hence photosynthesis, should be greater at sub-ambient than elevated pCO 2 .…”

“…This means that we cannot exclude the possibility of carry-over effects from one cycle to the next, or ontogenetic effects as the plants developed (Harb et al, 2010;Walter et al, 2011). However, the patterns observed from one cycle to the next were internally consistent overall, and consistent with mechanisms of CO 2 -water interactions observed previously (Conley et al, 2001;Wall et al, 2001;Leakey et al, 2004Leakey et al, , 2006Leakey, 2009). Secondly, because our interest was in how physiological characteristics vary over a short experimental watering cycle, we investigated changes over time and did not use a control on a shorter watering cycle.…”

The mutual responses of higher plants to environment: Physiological and microbiological aspects

“…A major motivation for the above effort is the high rate of human-accelerated environmental change, including elevated atmospheric ozone, CO 2 , nitrogen deposition, climate change and land use/land cover change [33,[41][42][43][44][45][46][47][48][49][50][51][52][53][54][129][130][131][132]. It is a clear fact that these changes can affect mycorrhizal fungal species, but it is also clear that we do not yet have data sets sufficiently saturated, or models sufficiently powerful, to determine the exact nature, timing and spatial pattern of fungal community responses.…”

“…Plants live in soil-plant-atmosphere continuum (SPAC) environment, and they have to coordinate the mechanisms of diverse types to respond to the above changing environment at any time for sustainable survival [4][5][6][7][8][9][21][22][23][24][25][26][27][28][29][47][48][49][50][51][52][53][54][55][56][57][58][59]. Plant production realization is obtained eventually through physiological pathways at least at the level of individual and community [102][103][104][105][106][107][108][109]120,[130][131][132][133][134][135][136][137][138][139][140].…”

Modeling soil organic carbon in corn ( Zea mays L.)-based systems in Ohio under climate change

“…Elevated CO 2 (eCO 2 ) concentration in the atmosphere is an additional factor that is not accounted for in this study, due to the uncertainty of the effects at present. There is substantial evidence that eCO 2 results in increased yield and both above-and belowground biomass in most crops (Dijkstra and Morgan 2012), although this effect appears to vary in maize, showing increases in studies in China and India (Xie et al 2015;Abebe et al 2016), and no response in maize in Illinois unless under drought stress (Leakey et al 2006;Dijkstra and Morgan 2012;Attavanich and McCarl 2014). Another study found increased biomass response in maize under drought stress, but only where there was a sufficient supply of nitrogen (N) (Zong and Shangguan 2014).…”