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Germination

There was a significant effect of both organic matter (F2,30=9.25, P<0.001) and water

input (F1,30=63.91, P<0.001) on the total number ofA. myosuroidesseeds germinating

(see Supplementary Table S4.1) with fewest seeds germinating on high organic matter soil and the most on low organic matter soil. Increasing water input increased the

Table 4.2. Parameters and their standard errors of the Gompertz model (Equation 4.2) when fitted to germination data across Experiment 1 and to each treatment separately. In each case, the parameterAwas fixed at zero.

Curve Parameter: B C M

Estimate SE Estimate SE Estimate SE

All data 0.2211 0.023 50.47 1.1 1.655 0.28

Low organic matter, low water input 0.5200 0.102 49.20 1.1 0.658 0.25 Low organic matter, high water input 0.2895 0.039 63.82 1.4 0.961 0.30 Medium organic matter, low water input 0.3032 0.064 43.12 1.4 0.637 0.45 Medium organic matter, high water input 0.1535 0.019 69.31 2.8 4.452 0.46 High organic matter, low water input 0.2275 0.063 28.74 1.7 2.063 0.75 High organic matter, high water input 0.1731 0.025 54.06 2.4 4.104 0.51

number of seeds germinating. There was no significant interaction between organic matter and water input on the total number of seeds germinating.

When we fit a single Gompertz curve (Equation 4.2) to the germination counts we account for 45.1% of the variance in the data set. By fitting a separate curve to each treatment we see a significant improvement (P<0.001, see Supplementary Table S4.2) with this model accounting for 76.1% of the variance in the data set (Table 4.2). We see different shaped curves for each water input and different asymptotes for each organic matter indicating there is some interaction between the two (Figure 4.3).

a b

Figure 4.3.Germination data with separate curves fitted for each level of organic matter and water treatment. (a) shows the data for low water input, (b) shows the data for high water input. Data points are shown as circles. The fitted curve is a solid line. Grey is low organic matter; Yellow is medium organic matter and blue is high organic matter.

When we fitted germination counts from Experiment 1 against hydrothermal time (Figure 4.4), the curves were much more similar in appearance across the three soil types indicating that the different levels of organic matter in each soil were allowing different levels of water retention and so accumulated hydrothermal time at different rates. At the low level of water input, the curves fitted for the low and medium organic matter were similar (Figure 4.4 a) with the germination counts and hydrothermal time not reaching as high a level as in the high watering treatment (Figure 4.4 b). However, on the high organic matter soil with low water input (Figure 4.4 a, blue line) the accumulation of hydrothermal time was particularly slow and germination seemed to exceed the expectation according to the accumulation of hydrothermal time. This may be because of the artificial nature of the soil used here. The calculations used to convert the theta probe measurements to water content were based on reference values for mineral soil and so the combination of a particularly dry watering regime with an artificial soil may have led to inaccurate estimates of the soil moisture in this case.

a b

Figure 4.4. Germination data plotted against hydrothermal time with separate curves fitted for each level of organic matter. (a) shows the low water input, (b) shows the high water input. Data points are averages for each treatment. Grey is low organic matter; Yellow is medium organic matter and blue is high organic matter.

Phenology

There was no significant effect (see Supplementary Table S4.3) of either soil organic matter or water input on the day of first flowering (Table 4.3).

Table 4.3. Summary of data for the day of first flowering. Means and their standard errors are shown for each treatment combination in Experiment 1.

Mean (Julian day) SEM

All data 123.1 0.821

Low organic matter, low water input 123.0 2.000

Low organic matter, high water input 125.0 3.367

Medium organic matter, low water input 122.6 1.571

Medium organic matter, high water input 124.0 2.082

High organic matter, low water input 121.0 1.528

High organic matter, high water input 123.0 12.292

Plant Height

There was a significant effect of both water input (F1,30=21.45, P<0.001) and its

interaction with soil organic matter (F2,30=9.74, P<0.001) on the height of the plant at

maturity (see Supplementary Table S4.4). When water input is high theA. myosuroides plants were significantly taller than when water input was low. The interaction between soil organic matter and water input is particularly interesting because at low water input there is a tendency for plant height to decrease as organic matter increases whereas at high water input this trend is reversed and the shortest plants are found on the low organic matter soil (Figure 4.5).

Seed Production

The total number ofA. myosuroidesseed heads was significantly affected by soil organic matter (F2,30=15.54, P<0.001, Figure 4.6) but not water input (see Supplementary

Table S4.5). However, the dry weight of seed remained unaffected by soil organic matter or water input (see Supplementary Table S4.6).

Biomass

Organic matter affected the dry weight of straw (F2,30=32.15, P<0.001, low organic

matter = 12.9, medium organic matter = 23.6, high organic matter = 32.6). There was no effect of water input on the dry weight of straw (see Supplementary Table S4.7).

Figure 4.5. The height of A. myosuroides plants grown in trial one at two different levels of water input. Plants were grown on soil with three different levels of organic matter; low organic matter is shown in grey, medium organic matter shown in yellow and high organic matter shown in blue. The means of all pots are presented with error bars indicating±1 SEM. Bars labelled with the same letter are not significantly different from one another (P≤0.05).

Figure 4.6. The number of seed heads per A. myosuroidesplant grown in trial one at two different levels of water input. Plants were grown on soil with three different levels of organic matter; low organic matter is shown in grey, medium organic matter shown in yellow and high organic matter shown in blue. The means of all seven pots are presented with error bars indicating±1 SEM. Bars labelled with the same letter are not significantly different from one another (P=0.05).

Table 4.4. Parameters and their standard errors of the Gompertz model (Equation 4.2) when fitted to germination data across Experiment 2 and to each pH treatment separately. In each case, the parameter A was fixed at zero.

Curve Parameter: B C M

Estimate SE Estimate SE Estimate SE All data 0.3452 0.053 38.86 1.6 7.833 0.33 Low pH 0.3781 0.084 40.92 2.2 8.002 0.42 High pH 0.3243 0.073 36.72 2.4 7.730 0.50

Similarly, total plant biomass was significantly affected by organic matter (F2,30=29.40,

P<0.001, low organic matter = 15.2, medium organic matter = 27.8, high organic matter = 36.6) but not water input (see Supplementary Table S4.8).

4.4.2 Experiment 2: pH

Germination

There was no significant effect of soil pH on the total number of seeds germinating (see Supplementary Table S4.9).

When we fit a single Gompertz curve (Equation 4.2) to the germination counts we account for 66.7% of the variance in the data set. By fitting a separate curve to each soil pH we see a marginal improvement (P=0.058, see Supplementary Table S4.10) with this model accounting for 67.1% of the variance in the data set (Table 4.4). These fitted curves indicate that a greater number of seeds germinate at lower pH (Figure 4.7).