| Fine roots (diameter<2 mm) play an important role in global biogeochemical cycle. They are core linkage for material and energy exchange between plant and soil. Observation of fine root dynamics could improve our understanding of fine root growth pattern, and thereby guide the vegetation construction. In this study, we used the minirhizotron technique to observe the fine root dynamics of young (5 years) and mature (30 years) Caragana korshinskii plantations in situ in the northwest Shanxi Province. We campared the temporal and spatial patterns of fine root standing crop (SC), production (NPPfr) and mortality (Mfr) between the young and mature plantations based on observational data during 2008-2011. Responses of fine root SC, NPPfr, and Mfr to environmental factors (temperature, precipitation, soil temperature, and soil moisture) were analyzed as well. The results showed that:(1) In the 0-100 cm soil profile, maximum SC, NPPfr, and Mfr in both plantations occured below the depth of 50 cm. However, the most active depths for fine roots in mature and young plantations are not consistent. Fine root SC, NPPfr, and Mfr for the mature plantation were highest in 50-60 cm soil depth, while they were the highest in 90-100 cm soil depth at the beginning of the observation period and in 80-90 cm at the end for the young plantation. From June 2009 to the end of the observation, fine root SC for the mature plantation was higher than the young plantation. This vertical distribution pattern was mainly affected by soil moisture. Fine roots of young plantation were more sensitive to soil moisture than those of mature platation.(2) During 2008-2011, relatively high fine root SC and NPPfr were observed in March and April. Fine root SC, NPPfr, and Mfr in 0-30 cm soil layer exhibited similar seasonal pattern as precipitation. However, in 30-100 cm soil layer, SC, NPPfr, and Mfr dynamics were similar to tempreture variations. In 30-100 cm soil layer, the occurrence of maximum SC and NPPfr in young plantation was earlier than that in mature plantation. In September and October, SC and NPPfr in yong plantation decreased faster than in mature plantation. In 0-20 cm soil depth, a large number of Mfr were observed in March to May or June to August. While in 40-100 cm, a large number of fine roots usually died in the end of the growing season. Even the surface (0-20 cm) maximum Mfr appeared in the early or middle season, much Mfr still appeared in the end of the growing season. The difference among mean annual fine root SC, NPPjr, and Mfr were mainly affected by interannual precipitation variation, while seasonal dynamics within the calandar year were mainly driven by temperature.(3) In the 0-100 cm soil profile, fine root production turnover rates (Tnpp) for young and mature plantations were 0.71 ± 0.05 yr-1 and 0.65 ± 0.04 yr-1, respectively. Fine root mortality turnover rates (Tm) were 0.57±0.04 yr-1 and 0.43±0.04 yr-1 for young and mature platations, respectively.In summary, fine roots of C. korshinskii were mainly distributed below 50 cm soil depth. Fine roots of young plantation distributed in a deeper depth than those of mature one. This pattern was mainly affected by soil moisture. The seasonal changes of fine root dynamics were controlled by soil temperature. The occurrence of maximum SC and NPPfr in young plantation was earlier than that in mature plantation. Comparing to fine roots in mature plantation, fine roots in young plantation were more easily affected by environmental factors such as precipitation, moisture and temperature. Fine root turnover rates of production and mortality were higher in young plantation than mature one. |
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