Possible climatic response of δ ¹³C in leaf cellulose of pinyon pine in Arizona, U.S.A.

Leaves of pinyon pine (Pinus edulis) were collected from ten living trees at nine sites in Arizona and New Mexico, representing elevations from 1200 to 2200 m. Stable-carbon isotopic analysis was performed on cellulose isolated from the whole leaf material. In spite of the range of conditions, the δ ¹³C response only varies over ~ 1‰ with an average δ ¹³C variance among leaves of the same tree of 0.4‰. The δ ¹³C-values were regressed with elevation and with monthly, seasonal and annual climate data obtained from nearby climatological stations. Linear relations of S with temperature, T, and 5 with precipitation, R, yield mostly positive correlations, not significant at 95%. Because of high δ ¹³C-values of the two highest elevation sites, the regressions improve greatly for second-order polynomials of elevation and temperature (P < 0.05). The mechanism for higher δ ¹³C at higher elevations is not clear, but perhaps related to length of growing season. There may be some potential for reconstructions based on strong linear relations derived for the lower elevation trees.