Modelling below-ground shoot elongation and emergence time of Sonchus arvensis shoots

Figures & data

Table 1. Harvest occasion, planting depths within bucket, number of roots per bucket and harvest day after planting for each of the temperature regimes (4, 8, and 18°C).

Harvest occasion	Planting depths (cm)	Number of roots per bucket	Harvest day at T = 4°C	Harvest day at T = 8°C	Harvest day at T = 18°C
1	3, 10, 17	9	57	20	9
2	3, 10	6	77	24	13
3	3, 17	6	85	37	15
4	10	3	106	45	16
5	17	3	120	57	17

Note: This design was used for each of two root lengths (5, 10 cm), three replicates and three temperature regimes.

Table 2. Slope (a), intercept (b) and R ² for the linear regression of shoot length on time since planting (Equation 1) for each root-weight class and temperature.

Root-weight class	Temperature (T, °C)	Elongation rate (a, mm day^–1)	Intercept (b, mm)	R ^2	Delay (day)
1 (0.044 g)	4	0.798	–7.8	0.80	10.00
1 (0.044 g)	8	2.842	–17.5	0.87	6.16
1 (0.044 g)	18	6.939	–1.8	0.97	0.25
2 (0.079 g)	4	1.156	–14.9	0.89	12.90
2 (0.079 g)	8	2.640	–6.0	0.97	2.64
2 (0.079 g)	18	10.120	–9.4	0.96	0.92
3 (0.163 g)	4	1.437	–14.3	0.90	9.95
3 (0.163 g)	8	3.388	–12.4	0.98	3.66
3 (0.163 g)	18	12.260	–14.8	0.88	1.21

Note: The average initial root weights per root-weight class are given in parentheses. Delay is the number of days from planting to when the observed mean length of the first shoot becomes larger than 0.

Figure 1. Shoot elongation rate (a _T; mm day^–1; y axis) in relation to temperature (°C; x axis) for root-weight classes 1 (rhombus, solid line), 2 (squares, dashed line) and 3 (triangle, dotted line). Points are measurements and lines are regression lines according to Equation 2. a _T(class 1) = 0.436 T–1.02; a _T(class 2) = 0.626 T–1.90; a _T(class 3) = 0.736 T–2.09; R ² range 0.986–1.000 and n = 3.

Figure 2. (a) Calculated time from planting to emergence (no days; y axis) plotted versus the constant temperature during this period (°C; x axis). Planting depth is assumed to be 10 cm. Solid line is root-weight class 1 (small roots), long dashed line is class 2 (medium roots) and dashed line is class 3 (large roots). (b) Accumulated temperature sum from planting to emergence (d°C, y axis) plotted versus the constant temperature during this period (°C; x axis). Conditions and line notations are the same as in Figure 2a, using a threshold value of 2.0°C. In addition, using a threshold value of 2.5°C for weight class 2 and 3, a dashed dotted and dotted line respectively are shown.

Figure 3. Observed soil temperatures at 5-cm depth at Ultuna Meteorological station for 2004–2010 (°C; y axis) versus day number since 1 January (x axis). Day number 61 is March 1. Lines are different years from left to right (at y = 10): 2008, 2010, 2007, 2009, 2004, 2005 and 2006. Dotted line = 2005; Dashed line = 2008.

Figure 4. Calculated length of below-ground shoot of the root-weight class 3 (mm; y axis) versus day number since 1 January (x axis). Lines are different years from left to right (at y = 10): 2008, 2010, 2007, 2009, 2004, 2005 and 2006. Dotted line = 2005; Dashed line = 2008.

Table 3. Time of emergence response to changes (Δ) of temperature and/or root weight.

Root-weight class	Temperature (T, °C)	ΔTime in days
3	ΔT: 7 years in Uppsala 2004–2010	13
ΔRoot weight (1–3)	Uppsala 2005	9
1	ΔT = +2°C added to Uppsala 2008	7
1	ΔT = +4°C added to Uppsala 2008	18
1	ΔT = +6°C added to Uppsala 2008	29
ΔRoot weight (1–3)	Uppsala 2008 +2°C	1–2^a

^aSimilar range was achieved when +2°C was replaced by +4°C or +6°C.