| Fine roots (≤2 mm) were the main organs for plants in absorbing nutrients and moisture. Fine root longevity determines the cycling speed of carbon and nutrients in plant and soil. It has great influence on carbon balance and nutrient cycling in the terrestrial ecosystem. From 2007 to 2009, we had observed the processes of fine roots’growth in Minirhizotron for 5 a and 30 a Caragana Korshinskii plantations in loess hilly region of northwestern Shanxi Province, in China. The survival rate and MRL of fine roots had been estimated, and made its survival curve by Kaplan-Meier methods for two-aged plants. Meanwhile, Effects of fine root longevity were also analyzed for some factors (soil depth, spatial location and seasonal change) by Log-rank test and the difference was analyzed among different factors for fine root longevity by the Cox proportional hazards regression model. The results showed that:(1) For 5 a Caragana Korshinskii plantation, fine root longevity showed the shortest on the surface soil (0-20 cm), but increasing with the increase of soil depth. It exhibited the longest in 80-100 cm soil layers. The longevity of first order and higher order were also represented the same trend with the increase of soil depth. For seasonal changed, the fine root longevity was the shortest in spring, and the longest in autumn. While soil spatial heterogeneity, it exhibited that the fine root longevity declined with the distance away from the stem. In conclusion, it all showed that the cumulative survival rates of higher order were higher than the first order for all factors, included soil depth, seasonal changing and soil spatial heterogeneity.(2) For 30 a Caragana Korshinskii plantation, fine root longevity increasing with the increase of soil depth in 0-80 cm soil layers, but declined on 80-100 cm soil layers. The longevity of first order was also represented the same trend, while cumulative survival rate of the higher order roots were still above 50% on 40-60 cm and 60-80 cm soil layers in the end of observation period. Affected by the seasonal change, it exhibited that the fine root longevity was the shortest in spring, while its longevity in summer was longer than in autumn. As for soil spatial heterogeneity, the fine root longevity was the longest at 50 cm and was the shortest at 100 cm. In summary, the cumulative survival rates of higher order were higher than the first order for all factors.(3) By comparing the fine root longevity between the 5 a and 30 a Caragana Korshinskii plantations in the same soil depth, it showed that cumulative survival rate of the first order and the higher order roots in 5 a Caragana Korshinskii plantation were higher than that in 30 a Caragana Korshinskii plantation on 0-40 cm soil layers, while it exhibited adverse on 40-80 cm soil layers. For 80-100 cm soil layers, there was no significant difference between them. As for the difference of fine root longevity between two aged Caragana Korshinskii plantations in the same season, it showed no difference (p>0.05) in spring and autumn, but in summer, the fine root longevity of 30 a Caragana Korshinskii plantation was significantly higher than that of 5 a Caragana Korshinskii plantation (p<0.01). Besides, with the variety of soil spatial location, the fine root longevity represented variances between the two aged Caragana Korshinskii plantations. At 0 cm, there was no significant difference; while at 50 cm, the fine root longevity was longer in 30 a Caragana Korshinskii plantation than in 5 a Caragana Korshinskii plantation.(4) By the Cox proportional hazards regression, it showed that the affecting factors on fine root longevity successively performed as soil depth, root sequence, season, plantation age and spatial location in Caragana Korshinskii plantations. |
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