Diel patterns of fine root respiration in a dryland shrub, measured in situ over different phenological stages

Fine root (< 2 mm) respiration (R (fr)) may play an important role in carbon cycles in drylands; thus R (fr) in desert ecosystems may have important implications for belowground processes and global carbon cycles. This study aimed to (1) investigate the diel and seasonal changes in R (fr) of a shrub (Caragana microphylla Lam.) in situ during the growing season and to (2) detect the relationship between both photosynthesis and phenology and R (fr). The study was conducted in an even-aged C. microphylla plantation in a semiarid area in the Mu Us Desert of China. Rates of R (fr) and net photosynthesis were measured using a standard chamber equipped with a portable gas analysis system. The data revealed two diel patterns that varied with different phenological stages. Diurnal R (fr) rates were 2.2-fold greater than nocturnal R (fr) rates. Our results showed that diurnal changes in R (fr) strongly correlated with rates of net photosynthesis, suggesting that the diel changes were strongly associated with the current supply of photosynthates. Furthermore, aboveground phenology could partially explain some of the variations in seasonal R (fr). Our results provide basic information on the link between R (fr) and aboveground activities, and enhance our understanding of carbon processes in dryland ecosystems.