Contrasting strategies to cope with drought conditions by two tropical forage C4 grasses.

Juan Andrés Cardoso,Marcela Pineda,Juan De La Cruz Jiménez,Idupulapati M Rao,Manuel Fernando Vergara

doi:10.1093/aobpla/plv107

Juan Andrés Cardoso, Marcela Pineda + Show 3 more

Open Access

https://doi.org/10.1093/aobpla/plv107

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Abstract

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.

Highlights

Grass-dominated ecosystems occupy 33 % of Earths’ vegetative area (Shantz 1954; Jacobs et al 1999) and provide most of the forage to feed domestic livestock (Morgan et al 2011)
Cumulative transpired water and projected shoot areas (PSAs) were significantly lower at 21 days of growth under drought conditions for Napier grass (P, 0.05, Fig. 1A and C) and from 14 days for Mulato II (P, 0.05, Fig. 1B and D)
Our results showed that two tropical forage C4 grasses (Napier grass and Mulato II) were affected by drought as shown by similar shoot dry masses and a

Summary

Introduction

Grass-dominated ecosystems occupy 33 % of Earths’ vegetative area (Shantz 1954; Jacobs et al 1999) and provide most of the forage to feed domestic livestock (Morgan et al 2011). Across the tropics, cultivated grasses used to sustain livestock are mostly C4 perennials of African origin (Sarmiento 1992; Williams and Baruch 2000; Peters et al 2013). The perennial nature of cultivated tropical forage grasses means that these plants must face water-limiting periods at some point or another (Ludlow 1980). The avoidance of water deficit either by increasing the capacity of water uptake or by controlling water loss are common responses in tropical C4 grasses (Williams and Baruch 2000). With greater root length densities with increasing soil depth, have been generally linked with uptake of stored water in lower layers of soil (Baruch and Fernandez 1993; Guenni et al 2004; Zhou et al 2013, 2014). Reductions of E by stomatal closure can be reflected in lower CO2 assimilation rates (A), and thereby and inevitably, in reduced growth

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