Changes in fine-root production, phenology and spatial distribution in response to N application in irrigated sweet cherry trees

Abstract

Factors regulating fine-root growth are poorly understood particularly in fruit tree species. In this context the effects of N addition on the temporal and spatial distribution of fine-root growth and on the fine-root turnover were assessed in irrigated sweet cherry trees. The influence of other exogenous and endogenous factors was also examined. The rhizotron technique was used to measure the length-based fine-root growth in trees fertilized at two N rates (0 and 60 kg ha?1)∗and the above-ground growth∗leaf net assimilation∗and air and soil variables were simultaneously monitored. N fertilization exerted a basal effect throughout the season∗changing the magnitude∗temporal patterns and spatial distribution of fine-root production and mortality. Specifically∗N addition enhanced the total fine-root production by increasing rates and extending the production period. On average∗N-fertilized trees had a length-based production that was 110-180% higher than in control trees∗depending on growing season. Mortality was proportional to production∗but turnover rates were inconsistently affected. Root production and mortality was homogeneously distributed in the soil profile of N-fertilized trees while control trees had 70-80% of the total fine-root production and mortality concentrated below 50 cm depth. Root mortality rates were associated with soil temperature and water content. In contrast∗root production rates were primarily under endogenous control∗specifically through source-sink relationships∗which in turn were affected by N supply through changes in leaf photosynthetic level. Therefore exogenous and endogenous factors interacted to control the fine-root dynamics of irrigated sweet cherry trees.