[Geographical variation and the response to hydrothermal factor of stable carbon isotope (δC) in Pinus massoniana].

We used 10 representative provenances at different latitudes in two 33-year-old Pinus massoniana provenance test stands (Chun'an Laoshan in Zhejiang and Taizi Mountain Shilong in Hubei) to measure the differences among provenances, study the geographical variation, and identify its responses to hydrothermal factors. The results showed that the δC of the average annual rings was significantly different among the provenances of P. massoniana, being higher in trees from high latitude than from low latitude. The δC of average annual rings showed a zonal variation trend, indicating an adaptation to the original environment. The δC of annual rings was negatively correlated with mean annual temperature (MAT), mean temperature in January (T), annual precipitation (MAP), precipitation from May to September (P) and cumulative temperature above 10 ℃ (CT). It was positively correlated with the aridity index (AI). The response function of AI toδδC annual rings in Chun'an and Taizi Mountain explained 37.5% and 42.5% of the variation, respectively, indicating that AI was the most important limiting factor. The Taizi Mountain test site in Hubei Province located in the central and western region with relatively dry soil and high aridity. Therefore, the δC of the average annual ring was 1.8% higher than that in the Chun'an test site. The δC rings of P. massoniana at the Taizi Mountain and Chun'an were sensitive to the temperature in July and August, respectively. Summer precipitation was the main factor for carbon isotope fractionation with stable rings. The sensitivity of different provenances to future climate changes was different.