The combined analysis of stable carbon and oxygen is a promising way to investigate tree physiological responses to environmental changes. However, there are only few studies that investigated the tree-ring carbon and oxygen isotope variations in subtropical and tropical areas in southwestern China.
Researchers from Xishuangbanna Tropical Botanical garden (XTBG) and University of Erlangen- Nürnbergv analyzed the tree-ring stable carbon (δ13C) and oxygen (δ18O) isotope variations in the earlywood and latewood of two pine species (Pinus kesiya and Pinus armandii) from secondary forest and the natural forest. They aimed to study whether the earlywood and latewood of the two pine species differed in their δ13C and δ18O and investigate whether there were differences in intrinsic water use efficiency (iWUE) of pine species from the secondary forest and the natural forest and their response to elevated CO2.
Theresearchers found a strong carry-over effect for δ13C in both secondary forest pine species P. kesiya and natural forest pine species P. armandii. There was nosignificant difference between earlywood and latewood for either δ13C or δ18O in P. kesiya. Both δ13C and δ18O in the earlywood of P. kesiya were significantly higher than those oflatewood in P. armandii. The results showed that P. armandii had slightly higherintrinsic water use efficiency (iWUE) than that of P. kesiya.
Water use efficiency of both pine species increased, but with a higher rate in P. kesiya. δ13Cvariations in earlywood and latewood represented a site-specific or species-specific climate signals. δ18O variations showed strong coherence. δ18Oin earlywood of both pinespecies was negatively correlated with May relative humidity, whereas δ18Oin latewood of both species had a strong significant autumn precipitation signal.
The results revealed slightly higherintrinsic water use efficiency in natural forest pine species than in secondary forest pine species, and separating earlywood and latewood of for δ18O analyses could provide seasonally distinct climate signals in southwestern China.