Environmental regulation and modelling of cassava canopy conductance under drying root‐zone soil water

Abstract

Sap flow was measured, with Granier-type sensors, in a crop of field-grown water-stressed cassava (Manihot esculenta Crantz) in Ghana, West Africa. The main objective of this study was to examine the environmental control of canopy conductance (g c ) with a view to modelling the stomatal control of water transport under water-stressed condition. Weather variables measured concurrently with sap flow were: air temperature (T a ), relative humidity (RH ), wind speed (u) and solar radiation (R s ). Relationship between canopy conductance (g c ) and vapour pressure deficit (D ε ) was curvilinear while no specific pattern was observed with R s . Average diurnal g c decreased from 3.0 ± 0.6 to 0.7 ± 0.4 mm s −1 between 0730 and 2000 h local time (= GMT) each day. A Jarvis-type model, based on a set of environmental control functions, was parameterized for the cassava crop in this study. Model results demonstrated that g c was estimated with a high degree of accuracy based on R s , T a , and D ε (r 2 = 0.92; F = 809.2; P < 0.0001). D ε explained about 90% (F = 2129.7; P < 0.0001) of the variations observed in g c , whereas both R s and T a contributed about 2% of the explained variance in g c . The aerodynamic conductance (g a ) was very high compared to g c , leading to a daily average ratio g a /g c > 100 and a decoupling factor< 0.1. Cross-validation analysis revealed a consistent good performance (r 2 > 0.85) of the g c model with D ε as the only independent environmental variable.

Comparative photosynthesis, growth, productivity, and nutrient use efficiency among tall- and short-stemmed rain-fed cassava cultivars

“…40-60% of rates under nonlimiting soil water and high air humidity) (Connor and Palta 1981, Porto 1983, 1986Cock et al 1985, El-Sharkawy 1990, 1993, 2006aDe Tafur 2002, De Tafur et al 1997aOguntunde 2005, Oguntunde andAlatise 2007). This characteristic underlies cassava tolerance to prolonged drought where most cereal and grain legumes crops would probably fail.…”

Physiological characteristics of cassava tolerance to prolonged drought in the tropics: implications for breeding cultivars adapted to seasonally dry and semiarid environments

“…Not only can cassava tolerate long periods of soil water deficits aided with the above-mentioned inherent mechanisms, but it can also react to changes in atmospheric humidity (Figure 7) (Connor and Palta, 1981;, 1986, 1985Cock et al, 1985;Berg et al, 1986;ElSharkawy, 1990ElSharkawy, , 1993ElSharkawy, , 2004ElSharkawy, , 2006aOguntunde, 2005, Oguntunde andAlatise, 2007). Cassava leaf stomata are sensitive to air humidity, irrespective of soil water content; they close rapidly in dry air when evaporation is high under field conditions, which may be translated into high leaf water potential.…”

The response of sap flow in desert shrubs to environmental variables in an arid region of China

“…For example, cassava responds to drought by closing its stomata to reduce transpiration, thereby protecting leaf tissues from turgor loss and desiccation (El‐Sharkawy, 1993; Alves and Setter, 2000). Reductions in transpiration have also been attributed to decreases in leaf conductance in response to an increasing relative humidity (El‐Sharkawy, 2006; Oguntunde, and Alatise, 2007). The increasing intensity of solar radiation and increasing air temperatures during the morning induce stomatal opening, thereby accelerating sap flow due to the high evaporative demand from the canopy (O'Brien et al , 2004).…”