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The Response of a Grassland Species to Elevated CO2

Paper Reviewed
Kostopoulou, P. and Karatassiou, M. 2017. Lotus corniculatus L. response to carbon dioxide concentration and radiation level variations. Photosynthetica 55: 522-531.

Writing as background for their study, Kostopoulou and Karatassiou (2017) state that Lotus corniculatus L. (birdsfoot trefoil) is a common grassland species found in Greece that thrives under a variety of soil conditions, including hardpan, dry, moist, acid, saline and infertile soils. Agronomically, it is important "because of its high nutritive value, and the nonbloating features when grazed directly by livestock." Given its relative importance as a forage species, the two Greek researchers thus set out to examine how L. corniculatus might respond to future changes in the atmosphere's CO2 concentration.

To accomplish their objective Kostopoulou and Karatassiou measured a number of gas-exchange parameters (net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2 concentration) under ambient (380 ppm) or elevated (800 ppm) CO2 on L. corniculatus plants growing at two separate field sites: a mountain grassland and a lowland grassland.

Results of their analysis revealed that elevated CO2 slightly reduced the transpiration rates of L. corniculatus at both sites (by 15% in the mountains and 3 % in the lowland). In addition, elevated CO2 marginally reduced stomatal conductance, by 4 % in the mountain location and 14% in the lowlands. Intercellular CO2 concentration and net photosynthetic rate, however, both experienced large increases under elevated CO2; intercellular CO2 increased by 90% in the mountains and by 122% in the lowlands, whereas the net photosynthetic rate increased by around 80% at both sites. Plant water use efficiency, calculated as the ratio of net photosynthetic rate over transpiration rate, increased by a whopping 116% for L. corniculatus plants growing in the mountain site and by a respectable 85% for the plants growing in the lowland site, which enhancements Kostopoulou and Karatassiou say will enable the plants "to use more efficiently the available water reserves under drought conditions."

Figure 1. Mean values of water use efficiency and net photosynthetic rate of Lotus corniculatus plants from a mountainous (site 1) and a lowland (site 2) location under ambient (380 µmol(CO2) mol-1] and elevated [800 µmol(CO2) mol-1] CO2 concentration. Source: Kostopoulou and Karatassiou (2017).

All things considered, it would thus appear that this important grassland species will benefit from future increases in the air's CO2 concentration.

Posted 2 August 2017