Effects of Drought and Elevated Soil Temperature on Apple Root Lifespan

Abstract

Root lifespan has important consequences for plant growth and productivity, plant competition, and nutrient cycling. However, compared to aboveground parts, much less is know about root systems. Root dynamics of `Red Chief' Delicious on M26 rootstock trained on a trellis were examined near State College, Pa., using minirhizotrons. Soil was heated 5 °C above ambient at a depth of 5 cm by circulating hot water over a stainless steel grid on the soil surface. Soil temperature (by thermocouples) and soil moisture (by TDR) were monitored to a depth of 1 m. Root birth rate peaked between late May and mid-June, during a period of rapid shoot elongation and fruit expansion. Death rate was highest in July. There was no evidence of alternate growth between roots and shoots. Drought and elevated soil temperature increased root mortality. Median lifespan of fine roots near the soil surface (<20 cm) was least in the heated-drought treatment (30 d) and longest in the unheated-irrigated treatment (56 d). Heating caused substantial increases in root birth rate, thus, causing higher populations in the heated than unheated treatments despite the increased root death rate in the heated soil.