Specific root length as an indicator of environmental change

Figures & data

Figure 1. Mean SRL values (±SE) for four fine-root diameter classes per six major tree species. For n, see Appendix.

Figure 2. Mean SRL values (±SE) for ECM (A) and fine roots (<2 mm) (B) in coniferous and deciduous tree species. There is a tenfold difference in the scale of the y-axis, between A and B.

Table I. The coefficients of variation (CV) for random samples and sample means of diameter (D) and root tissue density (RTD) of ECM and fine roots (<2 mm) in different species

Species	Stands	D	RTD	n	r	p
CV of random samples
ECM
Picea abies	Kivalo	15.7	24.1	44		n.s.
	Voore	17.1	29.3	28	−0.60	0.0007
	Kuusnõmme	11.3	15.8	25		n.s.
Pinus sylvestris	Kivalo	11.6	20.1	35		n.s.
	Voore	13.3	21.6	8		n.s.
	Kuusnõmme	15.3	40.1	16	−0.83	0.0001
Betula pendula	Kivalo	21.1	37.5	48		n.s.
	Voore	18.9	31.8	35		n.s.
	Kuusnõmme	11.6	34.5	28		n.s.
CV of means
ECM
Picea abies<2 mm	Withington et al., 2006; Ostonen et al., 2007	10.3	24.1	5		n.s.
Picea abies	Borken et al., 2007	23.1	31.3	16	−0.81	0.0001
Fagus sylvatica	Curt & Prevosto, 2003	13.6	37	6		n.s.
r, correlations between D and RTD are represented by coefficients; n, the number of observations; p, level of significance.

Figure 3. Correlation analysis between SRL and the latitudes of Picea abies and Fagus sylvatica fine roots (<2 mm). Trendline is added only for Picea abies.

Figure 4. Correlation analysis between SRL and soil pH of Picea abies ECM.

Figure 5. Influence of the sampling method on the mean SRL values (±SE; ±1.96 × SE) of three fine-root diameter classes.

Figure 6. Meta-analysis of treatment effects on the SRL response ratio: mean values and 95% CI. The analyses summarize data from deciduous and coniferous trees, all sampling methods in pots and in the field, and root diameter classes <0.5, <1, 1 – 2, and <2 mm.

Table II. Meta-analyses of the treatment effects on SRL, partitioned into classes by type of treatment, group of tree species (coniferous, deciduous), root diameter, length of study, and sampling method.^a

Treatment	Class	R	95% CI	n	Q B	p
Fertilization type	Optimal element ratio^b	0.83	0.68 – 1.00	8	18.49	0.005
N	0.81	0.76 – 0.87	54
Organic N	1.13	0.58 – 2.16	3
Liming + N	1.00	0.03 – 30.48	2
Liming	1.14	0.92 – 1.41	14
Wood ash	0.96	0.80 – 1.14	13
P	1.24	0.08 – 19.28	2
Opt. elem. Ratio, coniferous	0.88	0.58 – 1.32	4	0.56	0.455
Opt. elem. Ratio, deciduous	0.76	0.49 – 1.19	4
N, coniferous	0.82	0.74 – 0.91	31	0.003	0.953
N, deciduous	0.81	0.74 – 0.90	23
Liming, coniferous	1.32	1.00 – 1.76	8	3.13	0.077
Liming, deciduous	0.99	0.75 – 1.32	6
Opt. elem. ratio, <0.5 mm	0.66	0.41 – 1.05	3	4.42	0.035
Opt. elem. ratio, <1 mm	0.98	0.66 – 1.20	4
Wood ash, <1 mm	0.90	0.74 – 1.09	6	0.000	0.994
Wood ash, 1 – 2 mm	0.89	0.72 – 1.11	6
Liming, <1 mm	1.29	0.83 – 2.00	4	3.27	0.195
Liming, 1 – 2 mm	1.43	0.66 – 3.09	4
Liming, <2 mm	0.99	0.75 – 1.32	6
All fertilizations	<0.5 mm	0.65	0.37 – 1.16	3	19.12	<0.001
<1 mm	0.86	0.81 – 0.92	51
1 – 2 mm	0.72	0.63 – 0.83	18
<2 mm diameter	1.00	0.90 – 1.12	24
<0.5 mm deciduous	0.69	0.09 – 5.50	2	41.84	<0.001
<1 mm coniferous	1.01	0.91 – 1.12	31
<1 mm deciduous	0.77	0.71 – 0.84	20
1 – 2 mm coniferous	0.72	0.63 – 0.83	18
<2 mm coniferous	0.91	0.79 – 1.06	11
<2 mm deciduous	1.15	0.97 – 1.37	13
<0.5 year	0.77	0.72 – 0.83	33	32.74	<0.001
0.5 – 1 year	0.77	0.65 – 0.91	9
>1 year	1.03	0.95 – 1.12	54
Field (soil coring, ingrowth core)	1.04	0.95 – 1.13	48	27.26	<0.001
Pots	0.78	0.74 – 0.84	48
Ingrowth core	1.06	1.01 – 1.11	21	12.99	<0.001
Soil coring	0.92	0.85 – 0.98	27
Soil coring, coniferous	0.89	0.83 – 0.96	21	16.52	<0.001
Soil coring, deciduous	1.09	0.84 – 1.41	6
Ingrowth core, coniferous	1.06	1.01 – 1.11	21
Pots, coniferous	0.74	0.66 – 0.84	19	1.61	0.205
Pots, deciduous	0.81	0.74 – 0.89	29
ECM	0.85	0.80 – 0.90	83	3.00	0.223
AM	0.99	0.78 – 1.26	7
Dual (ECM, AM)	0.95	0.73 – 1.23	6
Irrigation	Irrigation	1.09	0.94 – 1.26	6	23.60	<0.001
Irrigation-fertilization	0.79	0.57 – 1.08	3
Irrigation-temperature^c	1.12	0.42 – 2.99	2
Irrigation-fertilization-temperature	0.77	0.29 – 2.07	2
Irrigation	1.09	0.92 – 1.28	6	9.51	0.002
Irrigation-fertilization	0.79	0.55 – 1.13	3
Irrigation	1.08	0.97 – 1.21	6	0.32	0.632
Irrigation-temperature	1.12	0.57 – 2.20	2
Temperature	Temperature	0.95	0.84 – 1.06	9	15.48	<0.001
Temperature-fertilization	0.72	0.65 – 0.81	9
Temperature	0.95	0.86 – 1.05	9	3.97	0.046
Temperature-irrigation	1.12	0.46 – 2.75	2
Temperature	0.95	0.83 – 1.08	9	12.99	<0.001
Temperature-CO2	0.53	0.08 – 3.54	2
Temperature	0.95	0.77 – 1.17	9	6.73	0.009
Temperature-fertilization-irrigation-CO2	0.71	0.62 – 0.81	17
Elevated CO2	<0.5 mm	0.97	0.91 – 1.05	3	13.07	0.001
1 – 2 mm	0.67	0.17 – 2.63	2
<2 mm	0.83	0.53 – 1.31	4
Coniferous	0.70	0.45 – 1.08	3	10.32	0.001
Deciduous	0.97	0.93 – 1.02	6
CO2	0.88	0.73 – 1.05	9	5.69	0.017
CO2-fertilization	0.57	0.07 – 4.59	2
CO2	0.86	0.67 – 1.10	9	12.90	<0.001
CO2-temperature-fertilization	0.47	0.34 – 0.65	6
^aWhen not otherwise specified, the classes summarize all root diameter classes <2 mm, all sampling methods, and both coniferous and deciduous trees. For each class values were calculated for the following: the weighted mean of the response ratio (R), the 95% confidence interval (CI) for R, the number of observations (n), the between-class homogeneity (Q B) and the probability (p) of the model heterogeneity test; ^bOptimal element ratio – standard plant nutrient solutions e.g. Hoagland's solution; ^cElevated temperature.

Table

Species	Diameter class	SRL (m g^−1)	Reference
Picea abies	ECM	30.8 – 47.2	Ostonen et al., 1999, 2007; Withington et al., 2006
	<1 mm	10 – 23	Püttsepp et al., 2006; Persson & Ahlström, 1990/91, 2002; Persson et al., 1998; Majdi & Viebke, 2004; Göransson et al., 2006
	<2 mm	4.5 – 26	Claus & George, 2005; Genenger et al., 2003; Majdi & Persson, 1995; Godbold et al., 2003; Majdi, unpublished data
	1 – 2 mm	1.4 – 2.5	Püttsepp et al., 2006; Majdi & Viebke, 2004
Picea sitchensis	ECM	38.2 – 45.4	Ford & Deans, 1977
Pinus sylvestris	ECM	24.7 – 51.5	Ostonen et al., 2006, in press; Withington et al., 2006
	<1 mm	20	Persson & Ahlström, 1990/91
	<2 mm	6.5 – 15	Curt & Prevosto, 2003
Pinus nigra	ECM	39.9	Withington et al., 2006
Pseudotsuga menziesii	ECM	27.2	Withington et al., 2006
	<1 mm	11 – 16.7	Hendriks & Bianchi, 1995
	<2 mm	8.3 – 14.1	Olsthoorn, 1991; Hendriks & Bianchi, 1995
	1 – 2 mm	2.0 – 2.8	Hendriks & Bianchi, 1995
Abies alba	ECM	26	Withington et al., 2006
Quercus robur	ECM	68.1	Withington et al., 2006
	<1 mm	23 – 33	Göransson et al., 2006
	<2 mm	4.1 – 21.3	Bakker, 1998
Fagus sylvatica	ECM	90.7	Withington et al., 2006
	<1 mm	19.5 – 37.1	Hendriks & Bianchi, 1995; Göransson et al., 2006
	<2 mm	5.7 – 31.5	Hendriks & Bianchi, 1995; Curt & Prevosto, 2003; Claus & George, 2005; Bolte & Villanueva, 2006
	1 – 2 mm	2.3 – 2.8	Hendriks & Bianchi, 1995
Betula pendula	ECM	87 – 196	Ostonen et al., 2006, in press; Uri et al., 2007
	<2 mm	13 – 14.5	Curt & Prevosto, 2003
Alnus incana	ECM	94 – 158	Lõhmus et al., 2006a,b
Alnus glutinosa	ECM	54 – 167	Lõhmus et al., 2006a,b; Ostonen et al., 2006, 2007

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