| Fine root (≤2mm in diameter) is one of the most important organs in tree which control the energy and matter exchange between tree and soil. In forest ecosystems, Carbon and nutrient allocated to soil by fine root turnover (formation, senescence, death and decomposition) is an important component of the carbon and nutrient budget. Fine root lifespan is the intrinsic mechanism of fine root turnover, equaling to the time from birth to death. Fine root lifespan determines the amounts of carbon and nutrient allocated to soil each year.In the study, manchurican ash (Fraxinus mandshurica) and davurian larch (Larix gmelinii), two of the important forest trees in northeastern China, were used as the experimental materials. Dynamics of birth, senescence and death of fine roots was monitored in situ by minirhizotron technique. The lifespan data collected from plots were analyzed by survival analysis method. The survivorship and median root lifespan (MRL) were estimated by Kaplan-Meier method. The objectives of this study were to compare the lifespan of fine roots for ash and larch, and to estimate the effects of diameter, order, soil depth, season, and fertilization on fine root lifespan. The main results were below:(1) There was a significant difference in fine root lifespan between tree species. In the same sites, the cumulative survivorship of fine roots in ash was higher significantly than that of in larch (p<0.001) . The results suggested that fine root lifespan of ash was longer than that of larch. MRL of ash was 336 ± 13d, contrasting with 64±3d of larch. The difference of MRL between ash and larch was 272d.(2) There was a positive relationship between fine root survivorship and diameter. The finer root appeared to a shorter lifespan, especially for the fine roots born in 2004. For example, the MRL of roots ≤0.3mm in diameter in ash was 243±44d, and the MRL of roots 0.3 0.6mm in diameter in ash was 415 ± 14d, while survivorship of roots 0.6 1.0mm and >1.0mm in diameter was higher than 60% (respectively, 62.45% and 66.67%) when the experiment was end. Accordingly, MRL of four diameter classes in larch was respectively 48±8d, 95±61d, 332±144d, 400±0d.(3) The study indicated that whether definite order or apparent order, the survivorship of higher-order roots was higher significantly than that of first-order roots for ash and larch in two years (pash-D04<0.001; pash-A04<0.001; plarch-D04<0.001; plarch-A04<0.001; pash-A05<0.05; p1arch-D05<0.001;plarch-A05<0.001), except for definite order of ash in 2005 (pash-D05=0.315), To make a summary, the lifespan of higher-order roots was longer than that of first-order roots.(4) Roots deeper in the soil always had a longer lifespan than roots in shallow soil layers for ash and larch. There was a significant increase in the survivorship of fine roots with depth,... |
