Root zone temperature influences growth, partitioning, leaf morphology and physiology of the peach rootstock, Green Leaf Nemaguard

Abstract

This paper examines the hypothesis that root zone temperature (RZT) affects the growth of stone fruit plants. This hypothesis was tested by growing plants of the peach rootstock, Green Leaf Nemaguard (Prunus persica L. Batsch), at a diurnally variable (26/15°C) or at constant (5, 15, 20°C) RZTs; the plants were either actively growing or emerging from dormancy when the treatments were applied. These trials demonstrated that RZT, independently of air temperature and light intensity, influences growth, dry matter partitioning, leaf morphology and physiological processes. The growth of plants emerging from dormancy was more sensitive to RZT than that of actively growing plants, therefore, phenology can influence sensitivity to RZT. The area, numbers and daily rates of expansion of leaves, correlated positively with RZT for both sets of plants. However, plants exposed to a diurnally variable 26/15°C RZT were smaller with respect to overall growth and aspects of leaf morphology than plants exposed to a constant 20°C RZT, despite the daily mean RZTs for both treatments being similar. This could be due to supraoptimal RZTs during the day and/or suboptimal RZTs at night. Root mass ratio, in both actively growing and plants exiting dormancy was highest at 20° RZT. In contrast, the stem mass ratio of actively growing plants was maximised at 5°C, and for plants exiting dormancy, the stem mass ratio was minimised at this RZT. RZTs influence the rate of leaf expansion, which in turn affects the total number of leaves and leaf area and, along with its effect on CO2 assimilation rates, results in reductions in DM production. This research illustrates the importance of RZTs, particularly in the spring, on growth and leaf development and suggests the need to incorporate RZT into development models for peaches.