There is extensive evidence that rising atmospheric carbon dioxide concentration, [CO ] can stimulate rice yields. However, such increases are associated with a ubiquitous decline in nutrition, including protein, iron (Fe) and zinc (Zn). To determine the basis for these declines, we used gmo rice lines to test and compare the quantitative and qualitative metrics relative to their non-gmo counterparts at elevated [CO ] in situ . The gmo / non-gmo paired comparisons were associated with three phenological / metabolomic characteristics: (1) increased stomatal conductance, (2) an enlarged root system, and (3) enhanced nitrate absorption. All gmo lines showed a significantly higher percent stimulation of seed yield relative to their paired non-gmo cultivar at elevated [CO ]. Qualitatively, relative to non-gmos, leaf nitrogen and brown rice protein were not significantly reduced and for (1) and (2) the gmo lines showed no decline in Fe and Zn with elevated [CO ]. These findings do not, de facto , represent a gmo “solution” to [CO ] induced nutritional decay; however they provide the first evidence that gmo lines related to specific traits could be fundamental in selecting qualitative and quantitative responses of global rice to maintain yield and nutritional integrity in response to projected increases in atmospheric [CO ].
Nitrogen (N) has a unique place in agricultural systems with large requirements. To achieve optimal nitrogen management that meets the needs of agricultural systems without causing potential environmental risks, it is of great significance to increase N use efficiency (NUE) in agricultural systems. A chlorophyll meter, for example, the SPAD-502, can provide a simple, nondestructive, and quick method for monitoring leaf N status and NUE. However, the SPAD-based crop leaf’s N status varies greatly due to environmental factors such as CO2 concentration ([CO2]) or temperature variations. In this study, we conducted [CO2] (ambient and enriched up to 500 μmol moL1) and temperature (ambient and increased by 1.5~2.0 °C) controlled experiments from 2015 to 2017 and in 2020 in two Free-Air CO2 Enrichment (FACE) sites. Leaf characters (SPAD readings, chlorophyll a + b, N content, etc.) of seven rice cultivars were measured in this four year experiment. Here, we provide evidence that SPAD readings are significantly linearly correlated with rice leaf chlorophyll a + b content (chl a + b) and N content, while the relationships are profoundly affected by elevated [CO2] and warming. Under elevated [CO2] treatment (E), the relationship between chl a + b content and N content remains unchanged, but SPAD readings and chl a + b content show a significant difference to those under ambient (A) treatment, which distorts the SPAD-based N monitoring. Under warming (T), and combined elevated [CO2] and warming (ET) treatments, both of the relationships between SPAD and leaf a + b content and between leaf a + b content and N content show a significant difference to those under A treatment. To deal with this issue under the background of global climate change dominated by warming and elevated [CO2] in the future, we need to increase the SPAD reading’s threshold value by at least 5% to adjust for applying N fertilizer within the rice cropping system by mid-century.
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