Long-term variation of tree growth and intrinsic water-use efficiency in Schrenk spruce with increasing CO2 concentration and climate warming in the western Tianshan Mountains, China

Abstract

We combined dendrochronological methods and interannual d 13 C measurements to investigate radial growth and physiological responses of Schrenk spruce (Picea schrenkiana) in response to rising atmospheric CO 2 concentration (C a ) and changing climate in high-elevation forests in China's western Tianshan Mountains. The mean maximum temperature in May to August, reconstructed from d 13 C, revealed an overall warming trend, with persistent warm periods from 1910 to 1920, and from 1970 to 1980. Intrinsic water use efficiency (iWUE) increased by 28 % over the last 160 years; temporal trends in iWUE were calculated under three theoretical scenarios as a baseline for interpreting the observed gas-exchange at increasing C a . Basal area increment (BAI) increased by 51.4 % since 1850 with two apparent increases and decreases. Trees exhibited sharp declines in BAI along with enhanced iWUE during the warmer periods; this was possibly due to a reduced stomatal conductance which prevented excessive water loss from trees. Conversely, BAI increased at reduced iWUE (-3.6 %, -7.4 %) during two cold-wet periods (e.g., 1880 to 1992, and 1945 to 1960), suggesting that a diminished water stress caused the observed growth pattern. However, BAI increased significantly (49.4 %) from 1965 to 1983 with constant intercellular atmospheric CO 2 concentrations (C i ) response scenario under acute water limitations, indicating the CO 2 stimulation of tree growth. These results showed that even at high elevations, increased iWUE may not lead to longterm enhancement of tree growth, and other factors may counteract CO 2 -fertilization effects, especially those related to a warming-induced drought. The results of this study suggest that the current models may overestimate the sink capacity of temperate forests, and indicate that multi-proxy records are needed to disentangle the role of a limiting factor in modulating the response of the Schrenk spruce forest to current climate change scenarios.

Carbon and Water Use Efficiencies: A Comparative Analysis of Ten Terrestrial Ecosystem Models under Changing Climate

“…Models, with the exception of VEGAS2.1, predicted an increase in WUE due to CO 2 fertilization (Table S4) consistent with observational studies that estimated an increase in WUE ranging from 8% to 35% over the 20 th century 10,12,15,17,26,27 . This suggests a decrease in the models stomatal conductance with CO 2 fertilization similar to observations 15,20,26,28 . Three of the C-N models (CLM4, CLM4VIC, and DLEM) also show a negative CUE response to CO 2 fertilization (Fig.…”

Physiological and Growth Responses to Increasing Drought of an Endangered Tree Species in Southwest China

“…Since the mid-1980s, warmer and drier conditions in our study area seemed to have caused an increase in VPD, a decrease in RH and PDSI, reduced stomatal conductance, thus leading to higher δ 13 C and iWUE. Previous studies in other areas of China, such as the western Tianshan Mountains and Xinglong Mountains, have reached similar conclusions [66].…”

Long-term changes in the tree radial growth and intrinsic water-use efficiency of Chuanxi spruce (Picea likiangensis var. balfouriana) in southwestern China

“…Increasing iWUE levels do not always enhance tree radial growth rates due to the interaction with different growth conditions and tree species (Newberry, 2010;Andreu-hayles et al, 2011;Gyenge et al, 2012;Brito et al, 2016). In China, studies have been performed in water-limited area (Wang et al, 2012;Xu et al, 2013;Wu et al, 2015), and their results show that the tree radial growth rates do not accelerate when iWUE increases significantly. However, the effects on trees growing in humid locations are not fully understood.…”