The effect of soil temperature on source–sink economy in peanut ( Arachis hypogaea)

Abstract

Information on the effects of air temperature on the peanut's biomass allocation, water status and gas exchange is common, but we lack information on the effects of soil temperature in the field on the same features. The aim of this study was to determine the effect of soil temperature on the source–sink balance in peanut. Soil temperature ( T soil; 12, 18, 25, 32 and 40 °C) was controlled independently of air temperature (26/20 °C, day/night) with thermostatic water baths. Higher T soil significantly shortened the times to flowering, podding and maturity. Sink (individual pod weight) size increased as T soil fell from 40 to 18 °C. The highest total biomass was produced at soil temperatures of 25, 32 and 40 °C, but the highest pod yield was obtained at 25 and 32 °C. The ratio of pod to total biomass increased almost linearly with decreasing soil temperature to 18 °C. The root-to-shoot ratio was minimum at T soil=25 °C. The concentrations of chlorophyll- a (Chl- a) and Chl- b, CO 2 assimilation rate ( A), quantum yield ( Y Q) and water-use efficiency ( E WU) were highest at 32 °C during pre-flowering and flowering stages and at 25 °C during subsequent pod filling stage. Leaf water potential ( Ψ leaf), hydraulic conductivity ( g h), transpiration rate ( E) and stomatal conductance ( g s) increased with increasing soil temperature. The intercellular CO 2 concentration ( C i) did not respond to T soil. A was positively correlated with Chl- a ( r=0.73, P<0.001) and g s ( r=0.74, P<0.001), and E with g s ( r=0.77, P<0.001). The increased source potential at moderately higher T soil (25–32 °C) in association with the greater sink strength at moderately lower T soil (18–25 °C) indicates that modification of field soil temperature through management practices could improve peanut production by achieving an optimum balance between vegetative and reproductive growth.