Response of intrinsic water-use efficiency to meteorological factors and the relationship between the intrinsic water-use efficiency and the growth of three tree species in Saihanba area

To investigate the relationship between intrinsic water-use efficiency (iWUE) and forest growth of different afforestation species and their response to meteorological factors in the Saihanba area, and to provide a scientific basis for forest management in the context of global warming.

This study took Larix principis-rupprechtii, Pinus sylvestris var. mongolica and Picea meyeri in the Saihanba area as the research objects, and analyzed the relationship between iWUE and BAI and their responses to indicators such as temperature and SPEI, based on the climatology of the annual rings of the tree and stable carbon isotope techniques.

The results of the study showed that the water use efficiency of all three tree species showed a gradual increase over the 43-year period from 1975 to 2018 and had similar interannual trends, but the rate of increase varied, from fastest to slowest were Picea meyeri, Pinus sylvestris and Larix principis-rupprechtii, which rose at rates of 9.70, 5.75 and 4.40 μmol·mol^-1·(10 a)^-1; BAI of Larix principis-rupprechtii showed a significant negative correlation with iWUE (P < 0.01). There was a positive correlation between BAI and WUE_i in Picea meyeri, but it did not reach a significant level (P > 0.05) and there was no significant correlation between BAI and iWUE of Pinus sylvestris; The iWUE of all three species was significantly and positively correlated with the average temperature in July and the growing season of the year, negatively correlated with the rainfall in July and the growing season, and significantly and negatively correlated with the SPEI in all periods.

Combining the changes in iWUE of the three species and their relationship with BAI, Picea meyeri is more adaptable to future warm-drying climate change in the region, and Larix principis-rupprechtii is relatively less adaptable.