樟子松人工林细根寿命估计及影响因子研究

doi:10.3773/j.issn.1005-264x.2010.09.007

摘要/Abstract

摘要：

细根寿命的估计是了解细根生产和死亡的关键, 对了解陆地生态系统碳分配格局和养分循环具有重要意义。该研究采用微根管(minirhizotron)技术, 以23年生樟子松(Pinus sylvestris var. mongolica)人工林为研究对象, 对细根生长和死亡过程进行了连续两年的观测。细根寿命的估计采用Kaplan-Meier方法, 计算细根的平均寿命(mean longevity)、中值寿命(median longevity)和累积存活率(cumulative survival rate), 用对数秩检验(log-rank test)比较单一因素, 包括细根直径、根序、出生季节和土层以及菌根侵染对细根寿命的影响。采用Cox比例风险回归分析方法, 同时分析上述因素对细根存活的影响程度。结果表明, 樟子松细根的生产和死亡具有明显的季节性, 春末和夏季(6月和7月)为生产高峰; 而死亡高峰出现在夏末至秋末, 以及冬季。樟子松细根的平均和中值寿命分别为(322 ± 10)天和(310 ± 15)天, 对数秩检验表明, 仅考虑单一因子时, 细根直径、根序、出生季节和土层以及菌根侵染均对细根寿命有显著影响。Cox回归分析表明, 菌根侵染、细根直径和土层是影响樟子松细根寿命的重要因子。细根直径每增加1 mm, 细根死亡危险率就降低99%, 即相当于寿命延长99%; 细根出生土层每增加1 cm, 其寿命延长5%; 而菌根侵染后, 会导致细根死亡危险率增加175%; 但根序和出生季节的影响不显著。这些发现证实: 林木细根寿命受到内在与外在因素的共同控制, 而多变量回归分析的方法有助于我们全面揭示细根寿命变异的潜在机制。

关键词: Cox比例风险回归, 细根寿命, 细根生产, 细根死亡, 微根管, 樟子松

Abstract:

Aims Fine root longevity plays a key role in the processes of root production and mortality and is important to precisely estimate carbon and nutrient cycling in terrestrial ecosystems. However, few studies have simultaneously examined the influence of multiple factors on fine root longevity. Our objectives were to examine: 1) seasonal patterns of fine root length production and mortality in plantation-grown Pinus sylvestris var. mongolica, 2) effects of fine root diameter, order, season of fine root birth, soil depth and mycorrhizal colonization on fine root longevity, and 3) relative strength of the influences of these factors on fine root survivorship.

Methods Minirhizotrons were used to estimate fine root length production, mortality and longevity. In July 2007, three 20 m × 30 m plots were established in a P. sylvestris plantation, and six minirhizotron tubes (90 cm length, 5.5 cm inside diameter) were installed randomly throughout the plot. Video images were collected at approximately four-week intervals during the growing season from 5 May 2008 to 22 October 2009. Video images were digitized via RooTracker software (NC, USA). Kaplan-Meier method in survival analysis was used to estimate mean longevity, median longevity and cumulative survival rate. The effects on root longevity by single factors, including root diameter, order, season of root birth, soil depth and mycorrhizal colonization, were tested by Log-rank test. The relative strength of the influences of these factors on fine root survivorship was examined by Cox proportional hazards regression analysis.

Important findings Fine root length production and mortality exhibited strong seasonal patterns, in which production peaked in spring and summer and mortality peaked in late summer, autumn and winter. Mean and median fine root longevity were (322 ± 10) d and (310 ± 15) d, respectively. Log-rank test indicated that fine-root longevity was significantly affected by root diameter, order, season of birth, soil depth and mycorrhizal colonization. Cox proportional hazards regression suggested that mycorrhizal colonization, root diameter and soil depth significantly influenced fine root survivorship, controlling for other factors (covariates). The risk of fine root mortality decreased 99% with a 1 mm diameter increase, and fine root longevity increased 5% with a 1 cm increase in soil depth. However, the risk of mortality of mycorrhizal roots was 175% higher than for non-mycorrhizal roots. Root order and season of root birth had no significant effects on fine root longevity. Our findings highlight that fine root longevity is influenced by endogenous and exogenous factors simultaneously, and multi-covariate analysis is an efficient way to reveal variation of fine root longevity.

Key words: Cox proportional hazards regression, fine root longevity, fine root production, fine root mortality, minirhizotron, Pinus sylvestris var. mongolica

邱俊, 谷加存, 姜红英, 王政权. 樟子松人工林细根寿命估计及影响因子研究. 植物生态学报, 2010, 34(9): 1066-1074. DOI: 10.3773/j.issn.1005-264x.2010.09.007

QIU Jun, GU Jia-Cun, JIANG Hong-Ying, WANG Zheng-Quan. Factors influencing fine root longevity of plantation-grown Pinus sylvestris var. mongolica. Chinese Journal of Plant Ecology, 2010, 34(9): 1066-1074. DOI: 10.3773/j.issn.1005-264x.2010.09.007

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影响因子 Effect factors		平均寿命 Mean longevity (d)	中值寿命 Median longevity (d)
细根直径 Fine root diameter	≤0.5 mm	302 ± 11	305 ± 8
细根直径 Fine root diameter	> 0.5 mm	448 ± 19	ND
根序 Root order	1级 1-Order	304 ± 11	305 ± 13
	2级 2-Order	367 ± 29	461 ± 33
	高级 High-order	444 ± 21	ND
细根的出生季节 Season of fine root birth	春季 Spring	283 ± 23	333 ± 84
	夏季 Summer	297 ± 12	305 ± 13
	秋季 Autumn	321 ± 13	ND
土层 Soil depth	0-20 cm	256 ± 13	276 ± 16
土层 Soil depth	20-40 cm	397 ± 14	ND
菌根侵染 Mycorrhizal colonization	有菌根 Mycorrhizal roots	363 ± 23	397 ± 10
菌根侵染 Mycorrhizal colonization	无菌根 Non-mycorrhizal roots	292 ± 12	305 ± 7

影响因子 Effect factors		平均寿命 Mean longevity (d)	中值寿命 Median longevity (d)
细根直径 Fine root diameter	≤0.5 mm	302 ± 11	305 ± 8
细根直径 Fine root diameter	> 0.5 mm	448 ± 19	ND
根序 Root order	1级 1-Order	304 ± 11	305 ± 13
	2级 2-Order	367 ± 29	461 ± 33
	高级 High-order	444 ± 21	ND
细根的出生季节 Season of fine root birth	春季 Spring	283 ± 23	333 ± 84
	夏季 Summer	297 ± 12	305 ± 13
	秋季 Autumn	321 ± 13	ND
土层 Soil depth	0-20 cm	256 ± 13	276 ± 16
土层 Soil depth	20-40 cm	397 ± 14	ND
菌根侵染 Mycorrhizal colonization	有菌根 Mycorrhizal roots	363 ± 23	397 ± 10
菌根侵染 Mycorrhizal colonization	无菌根 Non-mycorrhizal roots	292 ± 12	305 ± 7

影响因子(协变量) Effect factors (Covariate)	df	参数估计 Parameter estimate (β)	标准误 Standard error (SE)	Wald值 (Chi-square)	p	死亡危险率 Hazard ratio
细根直径 Fine root diameter (mm)	1	-4.248	0.690	37.908	< 0.001	0.014
根序(1级根为参考) Root order (1-order for reference)	2	-	-	7.219	0.027	-
2级 2-Order	1	-0.432	0.254	2.883	0.090	0.649
高级 High-order	1	0.768	0.397	3.736	0.053	2.155
季节(春季为参考) Season (Spring for reference)	2	-	-	0.709	0.702	-
夏季 Summer	1	0.010	0.172	0.003	0.954	1.010
秋季 Autumn	1	-0.142	0.219	0.421	0.516	0.867
土层 Soil depth (cm)	1	-0.053	0.008	49.473	< 0.001	0.948
菌根侵染(无菌根侵染为参考) Mycorrhizal colonization (Non-mycorrhizal roots for reference)	1	1.013	0.285	12.601	< 0.001	2.752

影响因子(协变量) Effect factors (Covariate)	df	参数估计 Parameter estimate (β)	标准误 Standard error (SE)	Wald值 (Chi-square)	p	死亡危险率 Hazard ratio
细根直径 Fine root diameter (mm)	1	-4.248	0.690	37.908	< 0.001	0.014
根序(1级根为参考) Root order (1-order for reference)	2	-	-	7.219	0.027	-
2级 2-Order	1	-0.432	0.254	2.883	0.090	0.649
高级 High-order	1	0.768	0.397	3.736	0.053	2.155
季节(春季为参考) Season (Spring for reference)	2	-	-	0.709	0.702	-
夏季 Summer	1	0.010	0.172	0.003	0.954	1.010
秋季 Autumn	1	-0.142	0.219	0.421	0.516	0.867
土层 Soil depth (cm)	1	-0.053	0.008	49.473	< 0.001	0.948
菌根侵染(无菌根侵染为参考) Mycorrhizal colonization (Non-mycorrhizal roots for reference)	1	1.013	0.285	12.601	< 0.001	2.752