Contrasting strategies to cope with drought conditions by two tropical forage C4 grasses.
Drought severely limits forage productivity of C4 grasses across the tropics. The avoidance of water deficit by increasing the capacity for water uptake or by controlling water loss are common responses in forage C4 grasses. Napier grass (Pennisetum purpureum) and Brachiaria hybrid cv. Mulato II are tropical C4 grasses used for livestock production due to their reputed resistance to drought conditions. However, there is scant information on the mechanisms used by these grasses to overcome water-limited conditions. Therefore, assessments of cumulative transpired water, shoot growth, leaf rolling, leaf gas exchange, dry mass production and a number of morpho-physiological traits were recorded over a period of 21 days under well-watered or drought conditions. Drought reduced shoot dry mass of both grasses by 35 %, yet each grass exhibited contrasting strategies to cope with water shortage. Napier grass transpired most available water by the end of the drought treatment, whereas a significant amount of water was still available for Mulato II. Napier grass maintained carbon assimilation until the soil was fairly dry, whereas Mulato II restricted water loss by early stomatal closure at relatively wet soil conditions. Our results suggest that Napier grass exhibits a 'water-spending' behaviour that might be targeted to areas with intermittent drought stress, whereas Mulato II displays a 'water-saving' nature that could be directed to areas with longer dry periods.
Tropical Forages Program, International Center for Tropical Agriculture (CIAT), Apartado Aéreo 6713, Cali, Colombia j.a.cardoso@cgiar.org.
Juan Andrés
JA
Cardoso
Tropical Forages Program, International Center for Tropical Agriculture (CIAT), Apartado Aéreo 6713, Cali, Colombia Facultad de Ciencias Agrarias, Universidad Nacional de Colombia, Carrera 30 No. 45-03, Bogotá, Colombia.
Marcela
M
Pineda
Tropical Forages Program, International Center for Tropical Agriculture (CIAT), Apartado Aéreo 6713, Cali, Colombia.
Juan de la Cruz
Jde L
Jiménez
Facultad de Ciencias Agrarias, Universidad Nacional de Colombia, Carrera 30 No. 45-03, Bogotá, Colombia.
Manuel Fernando
MF
Vergara
Tropical Forages Program, International Center for Tropical Agriculture (CIAT), Apartado Aéreo 6713, Cali, Colombia.
Idupulapati M
IM
Rao
Anisohydric–isohydric behaviour; biomass allocation; projected shoot areas; root distribution; soil water content; stomatal density