Latitudinal trends in foliar δ13C and δ15N of Quercus variabilis and their influencing factors.

We aimed to reveal the latitudinal trends in foliar δ¹³C and δ¹⁵N of Quercus variabilis, a widely distributed species in East Asia, associated with two ontogenetic stages (juvenile and mature trees) along a North-South transect (26°-40° N). The results showed that mature trees had higher foliar δ¹³C and δ¹⁵N values than juveniles. Foliar δ¹³C and δ¹⁵ values of trees with both ontogenetic stages were nonlinearly increased and decreased with latitude, respectively. No interaction between ontogenetic stage and latitude for the changes of foliar δ¹⁵N and δ¹³C indicated that both ontogenetic stages across the transect consistently responded to latitudinal environmental variations. Results from the random forest models indicated that foliar δ¹³N of Q. variabilis was mainly affected by soil nutrient contents, e. g., soil organic matter, phosphorus, nitrogen, whereas dominated factors for foliar δ¹³C were related to moisture, such as relative humidity, precipitation of growing season. [ABSTRACT FROM AUTHOR]