Learning from the past to improve in the future: tree-ring wood anatomy as retrospective tool to help orchard irrigation management

Tree-ring annual growth and wood anatomical traits were used for the retrospective analysis of the impact of hydro-climatic conditions on the orchard irrigation management. Data were collected in the oldest (20 years), in full-production, orchards of Emilia-Romagna (Italy), one of the most important Italian Region for fruit production. Despite the development of advanced techniques to quantify the effectiveness of irrigation schemes, precise and widely applicable metrics are still lacking. The study of the tree rings of woody fruit crops, can facilitate the understanding of tree response to water availability under increasingly drier climatic conditions. In the selected orchards, irrigation was performed differently over years, according to horticultural extensionists’ suggestions and growers’ experience. Standard dendrochronological methods were used to prepare, date, measure and cross-date tree-ring width series. Quantitative wood anatomy was performed for assessing vessel diameter, vessel density, mean percentage of conductive xylem area and mean hydraulic diameter. Monthly precipitation and air temperature were collected from nearby weather stations. For each year and orchard, tree growth data were compared to meteorological records, using correlation analyses. Anatomical parameters were analyzed to determine if the different amount of spring and summer precipitations had a significant impact on wood anatomy. Results showed how orchard tree-rings and wood anatomical traits were partially influenced by climate. In some orchards tree growth was clearly affected by hydro-climatic conditions, suggesting that the tree water demand was not fully satisfied by irrigation. Vessel size and xylem conductive area, were reduced by drought. The main finding of the study pointed out that differences in ring-width and wood anatomical traits can occur also in irrigated orchards, suggesting irrigation supplies below crop demand. Tree rings and wood anatomical traits could be used as retrospective proxies to investigate the impact of water stress along the orchard lifecycle. The derived information can be used to improve irrigation management.