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The Response of Rice to Elevated CO2, Temperature and Drought Stress

Paper Reviewed
Padhy, S.R., Nayak, S., Dash, P.K., Das, M., Roy, K.S., Nayak, A.K., Neogi, S. and Bhattacharyya, P. 2018. Elevated carbon dioxide and temperature imparted intrinsic drought tolerance in aerobic rice system through enhanced exopolysaccharide production and rhizospheric activation. Agriculture, Ecosystems and Environment 268: 52-60.

Multiple researchers continue to study the impact of elevated concentrations of atmospheric CO2 on plants growing under resource-limited and stressful environment conditions. Such was the investigation of Padhy et al. (2018), who grew three cultivars of rice (Oryza sativa) at ambient or elevated (+2°C) temperatures and ambient (394 ppm) or elevated (550 ppm) CO2 concentrations, in conjunction with late-season drought stress.

The work was conducted at an experimental site in India in open-top chambers in the field. In all, there were two treatments: ambient (ambient CO2 and ambient temperature) and elevated (elevated CO2 and elevated temperature, the latter of which was maintained via infrared heaters). Ten days prior to harvest, the authors induced drought in both treatments by reducing soil moisture potential to -40 kPa lower than that recommended for aerobic rice. At four critical physiological growth stages (active tillering, maximum tillering, panicle initiation, and grain filling), Padhy et al. conducted a series of analyses to determine the soil health, functioning and intrinsic drought tolerance, as well as plant growth characteristics.

And what did the measurements reveal?

The authors report the following key findings:

1. Total and colloidal soil exopolysaccharides increased significantly in the elevated CO2 and elevated temperature (eCeT) treatment due to a "significant increase in rice root biomass, higher root exudation (lead[ing] to enhanced carbon allocation in belowground) and higher microbial activities in rice rhizosphere." As a result, exopolysaccharide-producing bacteria were enhanced, which "could lead to higher water holding capacity of [the] rhizosphere soil that helps plants survive under limited water stress conditions."

2. Soil labile carbon pools like microbial biomass carbon and ready mineralizable carbon increased in the eCeT treatment because of "increased accumulation of rhizodeposits and enhanced microbial growth and activities." Consequently, Padhy et al. say that "apart from regulating soil nutrients, microbial biomass carbon also plays a key role in increasing water holding capacity of soil (by soil aggregation) and nutrient cycling."

3. Soil enzymatic activities increased, indicating "greater rhizosphere activation which imparted additional intrinsic drought tolerance" in the rice under eCeT.

4. Relatively smaller amounts of enzyme activity associated with stress were noted in plants in the eCeT treatment as opposed to the ambient treatment, which lack of activity also pointed to enhanced drought tolerance in the rice cultivars.

5. Compared to the ambient treatment, grain yields among the three cultivars were stimulated in the eCeT treatment, increasing by 26%, 30% and 42%.

In summing up these several findings, Padhy et al. write that in the future, "elevated CO2 and temperature (2-3°C rise) could impart additional drought tolerance to aerobic rice," adding "their positive impact would be manifested by enhanced soil water holding capacity by producing higher exopolysaccharides and better mineralization of nutrients in rhizosphere through enhanced labile carbon allocation and enzymatic activities." And that is great news for this key agricultural crop grown and consumed by billions of persons across the world.

Posted 31 October 2019