Climate sensitivity for radial growth and tree-ring stable isotopes suggest a decoupling between carbon sink and carbon source processes as aridity increases in the semiarid Central Andes

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

New Orleans

Conferencia; AGU fall meeting; 2021

Tropical and subtropical Andean forests are important carbon sinks. Yet, climate factors controlling carbon sink capacity of forests are poorly understood. We explored the influence of climate on radial growth and stable isotopes for Polyepis tarapacana, the worlds highest elevation tree species growing in the South American Altiplano. We developed tree-ring width (TRW), oxygen (18O) and carbon (13C) chronologies for the last 60 years at four P. tarapacana stands located above 4,400 m a.s.l. across a 500-km north-south aridity gradient (from 300 to 200 mm precipitation). We used TRW as a proxy of wood formation (carbon sink) and isotopic tree-ring signatures as proxies of leaf-level gas exchange processes (carbon source). We found different climate sensitivity for radial growth, but uniform for tree-ring stable isotopes between sites across the gradient. While current-growing season temperature regulated TRW at northern-wetter sites, prior-growing season precipitation determined TRW at southern-drier sites. In contrast, concurrent warm and dry growing seasons resulted in more enriched tree-ring 13C and 18O at all study sites. Further, we found significant correlations between TRW and 13C at the northern sites, which may be related to the synchronous current-climate conditions influencing both wood formation and leaf gas exchange. However, we found non-significant correlations between TRW and 13C at the southern sites, as well as prior-climate driving wood formation and current-climate driving leaf gas exchange, indicating a decoupling between these two processes. The coupling between leaf-level carbon uptake and tree growth at the northern-wetter sites is consistent with increased tree growth with higher carbon availability when water is not limited, while the decoupling at southern-drier sites may indicate a sink limitation under stronger water deficit. These results contribute to understand the carbon sink capacity of high-elevation woodlands under the present climate change scenario of the Central Andes.