Table III.
Model optimization results
Total C or N import into the growth zone (〈IX〉) and first-order rate constants (k10, k12, and k21; numbers refer to donor and receptor pools, respectively) fitted to two- or one-pool models describing the time course of C and N tracer incorporation into substrates supplying leaf growth (Fig. 4). Models were run with a 0.1-d time step, and predicted values integrated to give 1-d averages. Estimated parameters and 〈IC〉 and 〈IN〉 were used to compute pool size (Q1 and Q2), turnover rate (the ratio of atoms passing through relative to the total amount present in each pool), and half-time (t0.5; the average time an atom will reside in a pool = −ln (0.5)/turnover rate), and the contribution of MX to IX [φ = MX/(MX+TX)]. In the two-pool model, the turnover rate of Q1 is k10 + k12, while turnover rate of Q2 is simply k21. In the one-pool model, the turnover rate of the only pool is k10. Means ± se (n = 6). For comparison, Q1 and Q2 are shown as a proportion of tiller mass and of C assimilation and N uptake rates. Growth conditions as for Table I. n.e., Not estimated.
| Carbon
|
Nitrogen
|
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|---|---|---|---|---|---|---|---|---|---|
|
L. perenne
|
P. dilatatum
|
L. perenne
|
P. dilatatum
|
||||||
| 23°C | 15°C | 23°C | 15°C | 23°C | 15°C | 23°C | 15°C | ||
| Subordinate | Dominant | Dominant | Subordinate | Subordinate | Dominant | Dominant | Subordinate | ||
| 〈IX〉 | μg d−1 | 972 ± 75 | 1,136 ± 66 | 3,488 ± 327 | 286 ± 23 | 98 ± 6.5 | 85 ± 5.0 | 278 ± 26.4 | 26 ± 2.6 |
| k10 | d−1 | 2.4 ± 0.29 | 1.7 ± 0.031 | 2.8 ± 0.10 | 1.6 ± 0.19 | 0.23 ± 0.054 | 0.37 ± 0.066 | 0.43 ± 0.034 | 0.071 ± 0.015 |
| k12 | d−1 | 0.91 ± 0.16 | 0.19 ± 0.016 | 0.22 ± 0.031 | n.e. | 0.66 ± 0.24 | n.e. | 0.30 ± 0.051 | 0.22 ± 0.067 |
| k21 | d−1 | 0.028 ± 0.013 | 0.080 ± 0.011 | 0.055 ± 0.020 | n.e. | 0.035 ± 0.023 | n.e. | 0.010 ± 0.013 | 0.020 ± 0.14 |
| Q1 | μg | 401 ± 57 | 681 ± 42 | 1,224 ± 123 | 177 ± 25 | 419 ± 101 | 232 ± 44 | 645 ± 79 | 369 ± 89 |
| Q2 | μg | 12,976 ± 6,771 | 1,628 ± 273 | 4,939 ± 2,008 | n.e. | 7,879 ± 6,147 | n.e. | 19,485 ± 25,853 | 4,037 ± 27,807 |
| t0.5Q1 | d | 0.21 ± 0.02 | 0.37 ± 0.01 | 0.23 ± 0.01 | 0.43 ± 0.05 | 0.77 ± 0.21 | 1.89 ± 0.34 | 0.95 ± 0.08 | 2.39 ± 0.57 |
| t0.5Q2 | d | 25 ± 12 | 9 ± 1.1 | 13 ± 4.7 | n.e. | 20 ± 13 | n.e. | 69 ± 91 | 35 ± 238 |
| φ | % | 27 ± 4.3 | 10 ± 0.8 | 7 ± 1.0 | 4 ± 2.1 | 74 ± 8.4 | 24 ± 3.8 | 41 ± 4.5 | 76 ± 6.9 |
| Q1/tiller | 0.011 | 0.018 | 0.014 | 0.013 | 0.12 | 0.10 | 0.11 | 0.29 | |
| Acquisition/Q1 | 4.2 | 4.6 | 8.0 | 3.4 | 0.14 | 0.23 | 0.37 | 0.01 | |
| Q2/tiller | 0.34 | 0.04 | 0.06 | n.e. | 2.3 | n.e. | 3.4 | 3.2 | |