Different climate sensitivity for radial growth, but uniform for tree ring stable isotopes along an aridity gradient in Polylepis tarapacana, the world?s highest elevation tree species

MILAGROS RODRIGUEZ CATON; LAIA ANDREU HAYLES; MARIANO S. MORALES; VALERIE DAUX; DUNCAN A. CHRISTIE; RAFAEL E. COOPMAN; CLAUDIO ALVAREZ; MUKUND PALAT RAO; DIEGO ALISTE; FELIPE FLORES; RICARDO VILLALBA

TREE PHYSIOLOGY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2021

0829-318X

Tree growth is generally considered to be temperaturelimited at upper elevation treelines. Yet,climate factors controlling tree growth at semiarid treelines are poorly understood. We explored theinfluence of climate on stem growth and stable isotopes for Polyepis tarapacana , the world?shighest elevation tree species found only in the South America n Altiplano. We developed tree ringwidth index (RWI), oxygen ( δ 18 O ) and carbon δ 13 C ) chronologies for the last 60 years at four P.tarapacana stands located above 4,400 meters in elevation, along a 500 km latitude ariditygradient. Total annual precipita tion decreased from 300 to 200 mm from the northern to thesouthern sites. We used RWI as a proxy of wood formation (carbon sink) and isotopic tree ringsignatures as proxies of leaf level gas exchange processes (carbon source). We found distinctclimatic conditions regulating carbon sink processes along the gradient. Current growing seasontemperature regulated RWI at wetter northern sites, while prior growing season precipitationdetermined RWI at arid southern sites. This suggests that the relative impor tance of temperature toprecipitation in regulating tree growth is driven by site water availability . In contrast, warm and drygrowing seasons resulted in enriched tree ring δ 13 C and δ 18 O at all study sites, suggesting thatsimilar climate conditions cont rol carbon source processes. Site level δ 13 C and δ 18 O chronologieswere significantly and positively related at all sites, with the strongest relationships among thesouthern drier stands. This indicates an overall regulation of intercellular carbon dioxid e viastomatal conductance for the entire P. tarapacana network , with greater stomatal control whenaridity increases. The manuscript also highlights a coupling and decoupling of physiologicalprocesses at leaf level versus wood formation depending on their respectively uniform and distinctsensitivity to climate. This study contributes to better u nderstand and predict the response of highelevation Polylepis woodlands to rapid climate changes and projected drying in the Altiplano.