Effects of Soil Temperature and Drought on Root–Soil Respiration in Apple under Field Conditions

Abstract

Root respiration is very important to root efficiency, root lifespan, and carbon cycling in plant ecosystems. Yet, the effects of soil temperature and moisture on root respiration are poorly understood, especially under field conditions. In this study, we manipulated soil temperature and moisture by six bearing `Red Chief' Delicious/M26 trees near State College, Pa. Soil temperature was elevated 5 °C at 5-cm depth using circulating hot water and stainless steel grids. Soil temperature was monitored using thermocouples and a data logger, and soil moisture was monitored using TDR. Root–soil respiration was determined by static trapping at the soil surface. Heating was conducted from 8 May to 28 Oct. Drought was initiated on 21 Aug. and lasted 2 months. Root–soil respiration was lowest in spring and increased from June to late August. After September, respiration decreased until the experiment ended in November. Root-soil respiration was not correlated with root length density. Heating enhanced root–soil respiration about 15% to 20% in spring (May) and 10% in summer (June–August). After the drought treatment began, heating increased root-soil respiration about 42% in wet soil, but did not influence respiration in dry soil. Heating accentuated the effect of the drought treatment on soil moisture. After 2 months of no irrigation and no rain, soil moisture was reduced 5% in unheated soil and 10% in heated soil. Drought slowed root–soil respiration 17% in unheated soil and 36% in heated soil, mainly because heating increased respiration in wet soil, but compared to the unheated treatment, had no effect in dry soil.