Root biomass dynamics in a semi-natural grassland exposed to elevated atmospheric CO₂ for five years

Figures & data

Table 1. Average daily temperatures (T, °C at 1.5 m height, monthly mean), monthly precipitation (ΣP, mm month⁻¹) and cumulated potential Penman evapotranspiration (ΣET, mm month⁻¹). Data is from the Ultuna meteorological station about 1 km from the experiment site. Normal values are calculated as means from 1961–1990

	Normal			1996			1997			1998			1999			2000
Month	T	ΣP	ΣET	T	ΣP	ΣET	T	ΣP	ΣET	T	ΣP	ΣET	T	ΣP	ΣET	T	ΣP	ΣET
April	3.9	29.3	45	5.0	14	42	3.5	22	54	3.7	34	43	6.5	83	44	5.6	17	35
May	10.2	32.8	89	7.9	58	72	8.5	58	75	9.9	48	87	9.3	15	87	11.8	40	90
June	15.0	45.9	102	14.4	44	104	15.6	95	104	12.7	99	71	16.3	33	114	13.8	46	97
July	16.3	70.5	100	15.1	62	87	18.1	38	109	15.6	84	86	18.9	12	127	15.6	153	75
August	15.1	66.4	70	17.8	29	78	19.5	59	85	13.7	55	61	15.1	33	73	15.0	19	49

Table 2. Net seasonal production in root numbers dm⁻² (N _r ), i.e. peak root numbers minus initial root numbers. Different capital letters indicate a significant difference between treatments for the particular year at P<0.05. Different lowercase letters indicate significant difference between years for the particular treatments, also at P<0.05

	1996	1997	1998	1999	2000
Elevated	89^Aa	219^Ab	113^Aa	397^Ac	363^Ac
Ambient	70^Aa	173^Ab	83^Ba	220^Bb	204^Bb
Control	105^Aa	245^Ab	108^Aa	350^Ac	259^Cb

Fig. 1 Total root numbers per square decimeter at 0–20 cm depth observed with minirhizotrons. Each point is the mean of four blocks. Error bars are omitted for figure clarity, CV ranged between 6% and 66%. Years 1996, 1997 and 1998 reprinted with permission from Sindhøj et al. (2000).

Table 3. Root ingrowth biomass for 1999 and 2000. Ingrowth cores were installed in April and removed in August each year. Different letters indicate a significant difference at P<0.05. Ingrowth cores from 1999 include total root length measurments, the percentage of root length for three diameter classes, and the specific root length (SRL). Root biomass values are ash corrected. Ash content was 14% with no significant differences between treatments or years

		Elevated	Ambient	Control
1999
Root biomass	g m^−2	81.2^a	39.4^b	63.7^ab
Total root length	km m^−2	8.68^a	4.09^b	6.74^ab
<0.5 mm diam.	%	88.80^a	88.36^a	92.21^a
0.5–2 mm	%	9.46^ab	10.87^a	6.55^b
>2 mm diam.	%	0.74^a	0.77^a	0.70^a
SRL	m g^−1	106.9^a	103.8^a	105.8^a
2000
Root biomass	g m^−2	141.4^a	73.2^b	121.3^a

Fig. 2 A) Root biomass in g m⁻² to 15 cm depth calculated according to R _bio =c _b ·N _r , where c _b is the regression coefficient and N _r is the net change in root numbers (see Results). B) Shoot biomass in g m⁻² sampled in early August each year indicated, years 1996 to 1998 reprinted with permission from Sindhøj et al. (2000). C) Root to shoot biomass ratio for each year indicated. Different letters indicate statistical differences of P<0.05 between treatments for that year.

Sindhøj , E , Hansson , AC , Andrén , O , Kätterer , T , Marissink , M and Pettersson , R . 2000 . Root dynamics in a semi-natural grassland in relation to atmospheric carbon dioxide enrichment, soil water and shoot biomass . Plant Soil. , 223 : 253 – 263 .

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