Effects of artificial warming on stem radial changes in Qinghai spruce saplings in the Qilian Mountains of China

Climate change has been documented in the Qilian Mountains of China, and the response of tree stem growth to environmental factors may be changed, affecting regional estimates of seasonal growth patterns and carbon sequestration. The objective of this study was to provide initial evidence for responses of intra-annual tree stem radial changes of sapling Qinghai spruce (Picea crassifolia) to climate warming in the Qilian Mountains. We monitored stem radial changes of Qinghai spruce in an open-top chamber (OTC) and out of chamber (OC) over three growing seasons (2014–2016) using high-resolution point dendrometers. Statistical analysis indicated that the differences in annual average air temperature between OTC and OC were about 1 °C. Our results showed that the onset of the main growth period in OTC was about one week earlier than in OC, and soil temperature played an important role in controlling the onset of growth in sapling Qinghai spruce. However, the timing of radial growth cessation exhibited large variability in different growth conditions. These results indicated that the end of growth may not be related to environmental factors. Daily average air temperature, vapor pressure deficit, relative air humidity, and precipitation were significantly correlated with daily stem radial increment (SRI) and tree water deficit (TWD). Further, soil water content and TWD were also correlated. SRI in OTC was larger than that in OC, while TWD exhibited no significant differences between the two growth conditions. However, cumulative seasonal growth may not be influenced by air temperature alone, but by interacting environmental factors.