There are double functions as "source" and "sink" for plant roots, which are important for substance and energy exchange between plant and soil. Fine roots contribute greatly to such behaviors. Studies on the dynamics of fine root growth and mortality are essential for understanding these behaviors. Caragana korshinskii Kom is a shrub species widely planted in the Loess Plateau, China. The objective of this study was to characterize the fine root dynamics of young (5-year-old) and mature (30-year-old) Caragana korshinskii plantations in Northwest Shanxi (China) using minirhizotron technique.
Based on the data collected in the growing season (from April to September) of 2007, we analyzed the spatial-temporal patterns of fine root growth rate (G, mm cm^-3 d^-1) and fine root death rate (M, mm cm^-3 d^-1) of Caragana korshinskii in these two plantations, and the relationships of G and M with the environment factors such as soil temperature, soil water content, air temperature and precipitation. The results showed that the G and M were 0.1264 mm cm^-3 d^-1 and 0.0354 mm cm^-3 d^-1 in young plantation, while they were 0.0914 mm cm^-3 d^-1, 0.0220 mm cm^-3 d^-1 in mature plantation. In the early growing season (April), the maximum values of G occurred at 40-50 cm and 10-20 cm soil layers in young and mature plantations, respectively. The maximum G occurred at deeper soil layer in the late growing season (May-September) in these two plantations. In the whole growing season, the maximum values of G occurred on average at 50-60 cm and 70-80 cm soil layers in these two plantations, respectively. The M in both plantations were higher in the top soil layer (0-50 cm) than in the bottom layer (50-100 cm) in the early growing season, and then reversed in the late growing season. The change trend of G with the process of growing season was similar for two plantations: the G increased rapidly from April to July and peaked in August, and then decreased in September. The differences were that the value of G was higher in young plantation than in mature plantation from April to August, but it was lower in the former than in the later at the end of growing season. The change trend of M was also similar for two plantations: the M increased continuously from April to the end of the growing season, while, the M was higher in young plantation than in mature plantation during the whole growing season.
Paired-samples t test showed that there was no significant difference in G between these two plantations, while the M in young plantation was significantly higher than that in mature plantation (P<0.05). Pearson correlation coefficients indicated that there were no significant correlations between the vertical distribution of G and these environment factors (P>0.05) in both plantations, while a significant correlation existed between the vertical distribution of M and the soil temperature in young (P<0.01) and mature (P<0.05) plantations. There was a significant relationship between the seasonal changes of G and air / soil temperature (P<0.05) in young plantation, whereas the relationship between the seasonal changes of G and air / soil factor was insignificant (P>0.05) in mature plantation. Meanwhile no significant relationships were found between M and these environment factors (P>0.05) in both plantations.