Chin J Plan Ecolo ›› 2007, Vol. 31 ›› Issue (1): 102-109.doi: 10.17521/cjpe.2007.0013
• Research Articles •
YU Shui_Qiang; WANG Zheng_Quan*; SHI Jian_Wei; QUAN Xian_Kui; MEI Li; SUN Yue ; JIA Shu_Xia; YU Li_Zhong
Aims Fine-roots (≤2 mm diameter) are important in controlling energy and matter exchange between tree and soil. Fine-root longevity is a critical determinant of fine-root turnover and therefore carbon allocation and nutrients returned to the soil. However, little is known about variation in fine-root longevity in relation to spatial and temporal heterogeneity in availability of soil resources (such as temperature, moisture and nitrogen). How does availability of soil resources affect fine root longevity? Do different tree species, soil depths and root cohorts have different fine-root longevity in the same forest site? To answer these questions it is important to understand the fate of fine roots in s oil with heterogeneous resource availability. The objectives of this study were to: 1) compare fine-root longevity between ash (Fraxinus mandshurica) and larch (Larix gmelinii) in the same site, 2) define patterns of fine-root longevity in different soil depths and elucidate the effect of availability of soil resources on fine-root longevity and 3) analyze seasonal changes of fine-root longevity for both species.
Methods Mini-rhizotrons (root observation tubes) were used to estimate fine-root longevity. We established three 20 m×30 m plots in an ash and larch plantation, and installed six clear PVC (polyvinyl chloride) mini-rhizotron tubes (90 cm long × 5.5 cm inside diameter) in each plot in October 2003. From 16 April to 30 October in 2004, video images were collected from the mini-rhizotron tubes at approximately two-week intervals and analyzed with an image analysis system (RooTracker software). We compared differences in longevity between tree species , soil depths and seasonal root cohorts using cumulative survival rate and median root longevity (MRL) of fine roots by Kaplan-Meier methods in survival analysis.
Important findings Cumulative survival rate of fine roots decreased gradually with time. Survivorship curves showed that cumulative survival rate of fine roots in ash was significantly higher than that in larch (p<0.001);MRL was 111±7 d in ash and 77±4 d in larch. Higher fine root mortality was found in 0-20 cm soil, as MRL was 62±11 d for larch and 111±6 d for ash, contrasting with 95 ±11 d for larch and 124±20 d for ash in deep soil. This study also indicated longer life spans of fine roots produced in summer (82±6 d for larch) than spring (47 ±13 d). Similar seasonal pattern was found for ash. Fine-root longevity was different between tree species due to different root genetics, physiology and architecture. High soil temperature and high N content can decrease fine root longevity. In summer, photosynthates are allocated to roots and fine roots grow rapidly and have increased longevity. Our results suggested that fine-root longevity is correlated with genetics of the species, physiological status and soil resource availability.
YU Shui-Qiang, WANG Zheng-Quan, SHI Jian-Wei, QUAN Xian-Kui, MEI Li, SUN Yue, JIA Shu-Xia, YU Li-Zhong. ESTIMATING FINE_ROOT LONGEVITY OF FRAXINUS MANDSHURICAAND LARIX GMELINII USING MINI-RHIZOTRONS[J].Chin J Plan Ecolo, 2007, 31(1): 102-109.
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