FROST DAMAGE IN WOOD OF ARAUCARIA ARAUCANA (MOLINA) K. KOCH (ARAUCARIACEAE) TREES FROM NORTHERN PATAGONIA

ARCO MOLINA, JULIETA; HADAD M; ROIG, F

Congreso; XI Congreso Latinoamericano de Botánica /LXV Congresso Nacional de Botânica; 2014

The recent global warming is signaled as a responsible factor of changes in the frequency and intensity of climate extremes such as unseasonably frost events. A frost may cause injuries at tissue (cambial) level leading to the formation of frost rings. These frost rings present different anatomy and morphology, depending on many physical and biological factors. Moreover, the localization of the frost injury within the growth ring allows to classify the frost event in relation to the growing activity. In this study we analyzed the anatomy and the morphology of frost rings on stems of Araucaria araucana (Molina) K. Koch trees from two sites, Primeros Pinos (PP) and Picún Leufú (PL), in northern Patagonia, Argentina. Wood core samples were extracted from 30 trees per site. Growth rings were visually dated and frost rings were anatomically recognized by visual observation. Each frost ring was classified according to the inner position of the frost injury in the growth ring as follows: 1) frost at the early beginning of the earlywood (EWF), 2) frost at the middle of earlywood (MEWF), and 3) frost in the transition between early to latewood (LWF). The characteristic of a frost ring in the xylem was investigated using various microscopic techniques. The results showed that frost damage in A. araucana wood is easily distinguishable as a traumatic ring area where the axial tracheids have collapsed walls and have lost their axial orientation. Moreover, rays appear locally distended and departed from the usual radial course of alignment. Even when the damaged area is characterized by a strong disruption of the tissue, the vascular cambium in A. araucana experiences a relatively rapid recovery, producing new series of normal tracheids after the traumatic tissue. Otherwise, at both sample sites, we analyzed 43428 growth rings, identifying 1009 frost rings. We also observed that MEWF and LWF rings occurred respectively more and less frequently at both sites. Two successive frost injuries within the same growth ring appeared at the PP site. This study showed that frost events during the growing season affect de normal development of the cambium in A. araucana from northern Patagonia. A record of palaeo frosts may allows the analysis of frequency and intensity of cold events, contributing to the discussion of the ecological implications of increasing weather extremes in the context of a warmer global climate.