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Fine Root Longevity of Two Chinese Fir Plantations in Subtropic, China

Author: YuanYiDing
Tutor: YangYuSheng
School: Fujian Normal University
Course: Physical Geography
Keywords: Chinese fir (Cunninghamia lanceolata) Fine root turnover Survival analysis Median root lifespan Root order Minirhizotron
CLC: S718.5
Type: Master's thesis
Year: 2009
Downloads: 42
Quote: 1
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Abstract

Fine root is an important organ in plant which is responsible for absorbing water and nutrient. In terrestrial ecosystem, Fine root turnover plays a vital role to carbon and nutrient cycle. Fine root longevity which determines the quantities of nutrient and carbon allocated to soil each year is the intrinsic mechanism for fine root turnover, Therefore, it affects accurate estimation of potential carbon sequestration in forest ecosystem. Chinese fir （Cunninghamia lanceolata） is one of the most important plantation in China in terms of planting area, yield and timber usage. But, there is still no research on estimating its fine root lifespan in forests of southern China, an important area of Chinese fir, so we can’t compile carbon buget of Chinese fir plantation. We choosed 18- and 90-year old Chinese fir plantations to monitor the processes of growth, senescence and death of fine roots by Minirhzotrons in situ. Also, the influences of fine root diameter, root order, season and soil depth on fine root lifespan were estimated. The lifespan data collected from two stands were analyzed by survival analysis, median root lifespan （MRL） and the survivorship were estimated by Kaplan-Meier method. The results are as follows.Fine root production peaked in the spring and summer and most of fine roots （48% in the 18 year-old and 49% in the 90 year-old Chinese fir plantation） appeared in 0-20 cm soil depth. The mean diameter of fine root for 18- and 90-year old Chinese fir plantations were 0.62±0.29 mm and 0.52±0.24 mm, respectively. Fine roots diameters were mainly less than 0.8mm with the distribution of "left skewed". The number of first-order fine roots were more than that of definite higher-order roots. The cumulative survivorship of fine roots decreased with increasing time of fine root birth. There was no prominent difference in fine root lifespan between 18- and 90- year old Chinese fir plantation, in which median lifespan was 216±14 d and 230±15 d, respectively. Furthermore, fine root lifespan estimated by indirect method （sequentially cores） was higher than that by Minirhzotron. However, the influence of stand age on fine root morphology and lifespan was significant. There was no significant effect of stand age on the lifespan of fine roots with the same diameter and order class, but stand age had significant influence on the lifespan of fine roots in the same seasons and soil depths. Fine root diameter was significantly positive to fine root lifespan (R₁₈²=0.9128, p<0.01; R₉₀²=0.7115, p<0.01) ; first order fine roots died faster than higher order fine roots. The lifespan for fine root produced in the winter was longer than that in the other seasons, and the survivorship for fine root produced in the drought season （May-July） was also higher than that in the rain season （Novermber-January） .Soil depth had a major influence on root survivorship. Generally, fine roots at 0-20 cm soil depth had shorter lifespan than those at deeper soil depth. These results show that fine root lifespan is controlled by many factors and further research on the intrinsic mechanism of fine roots survivorship should be done.

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