Phenology response of subtropical Chinese fir (Cunninghamia lanceolata) to soil warming, precipitation exclusion and their interaction

Plant phenology plays an important role in nutrient cycling and carbon balance in forest ecosystems, but its response to the interaction of global warming and precipitation reduction remains unclear. In this study, an experiment with factorial soil warming (ambient, ambient +5 °C) and precipitation exclusion (ambient, ambient −50 %) was conducted in a subtropical Chinese fir (Cunninghamia lanceolata) plantation. We investigated the effects of soil warming, precipitation exclusion, and their interactions on Chinese fir phenology involving the timing of tree height and fine root growth. In the meantime, the impact of tree height growth and related climatic factors on fine root production was also assessed. The results showed that: (1) more variable phenology responses were observed in fine root growth than in tree height growth to the climatic treatments; the duration of fine root growth and tree height growth was significantly reduced by the precipitation exclusion and warming treatment, respectively; phenology differences of fine roots and tree heights exerted by the solo warming and precipitation exclusion treatment were further enlarged by the combined treatment; and despite the greater inter-annual phenology stability of tree height growth than fine roots, both of them showed insignificant response to all the climate treatments; (2) asynchrony of phenology between tree height and fine root growth was significantly extended by solo warming and precipitation exclusion treatments, and further extended by the combined treatment; (3) fine root production was significantly and positively correlated with atmospheric, and soil temperature, and tree height growth as well, which was altered by warming and precipitation exclusion treatments. Our results demonstrated that climatic changes significantly and differently enlarge phenology differences for both above and below ground plant components, extend the phenology asynchrony between above and below ground, and also reveal the sensitive and variable nature of root phenology. Overall, these phenology responses to climatic change may contribute to weaken the close link between fine root production and tree height growth, which may result in mismatch between nutrient demand and supply timing in Chinese fir plantation.