Responses in tissue water relations and growth in a C<sub>4</sub> and C<sub>3</sub> forage grasses<em> </em>to elevated ambient CO<sub>2</sub> — YRD

Responses in tissue water relations and growth in a C4 and C3 forage grasses to elevated ambient CO2 (950)

Solomon Mwendia 1 2 , Isa Yunusa 1 , Ralph Whalley 1 , Brian Sindel 1 , Innocent Kariuki 2
  1. University of New England, NSW, Australia
  2. Kenya Agricultural Research Institute, Nairobi, Kenya

Rising ambient CO2 is associated with global warming and is known to alter rainfall patterns with increased risk of crop failures. Plant species differ in their response to elevated atmospheric CO2 concentration. We determined leaf water potential (LWP), water use efficiency and biomass yields in Napier grass (Pennisetum purpureum) a C4grass and Reed (Phragmites australis)a C3grass exposed to ambient and 560ppm CO2concentrations in glasshouse bays maintained at 15/25oC for 5 weeks. Napier grass is an important forage in tropics while Reed is occasionally used for forage. The aim was to determine how the two grasses differ in the measured attributes when subjected to water stress under the different CO2concentrations.

Elevated CO2 did not have significant effect on either predawn or midday LWP in both grasses in the first two weeks following withdrawal of watering. Between the grasses, C3 had more negative LWP than C4at predawn or midday under both CO2concentrations. By the third week after water withdrawal, both grasses maintained similar predawn and midday LWP under both COconcentrations, but the midday LWP was less negative in P. purpureum under elevated COthan ambient CO2. Compared with ambient concentration, elevated CO2concentration increased biomass accumulation by 72% in Napier grassand 9% in Reed. The photosynthetic water use efficiency increased by 97% in P. purpureumand by 64% in P. australis. It was concluded that elevated CO2 is more likely to enhance biomass accumulation in the Napier grass than in the Reed.

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