Leaf mass partitioning as a determinant of dry matter accumulation in Zantedeschia

Dry matter accumulation and partitioning in plants of Zantedeschia Spreng. 'Best Gold' aff. Z. pentlandii (Wats.) Wittm. (syn. Richardia pentlandii Wats.) were quantified under a range of temperature and photosynthetic photon flux (PPF) regimes using plant growth analysis. The relative rate of dry matter accumulation [relative growth rate (RGR(M)), g.g-1.d-1] was highly correlated with the partitioning of the daily increment of dry matter into leaf tissue (leaf matter partitioning (LMP), g.d-1 per g.d-1). In contrast, a poor correlation existed between RGR(M) and net assimilation rate (NAR, g.m-2.d-1). Maximum values of RGR(M) increased linearly with increasing temperature (from 13 to 28 degree C), with a base temperature of 2.1 +/- 2.7 degree C. The optimum temperature for growth was PPF dependent with maximum total plant dry mass occurring under high PPF (694 micromole.m-2.s-1) at 25 degree C. However, as the plant responded to PPF by altering LMP, find total plant dry mass was actually greater under the low PPF regime (348 micromole.m-2.s-1) at temperatures 22 degree C. The optimum temperature for dry matter accumulation was close to the average daily air temperature during the growing season for the natural habitat of the parent species. Similarly, the greater dry matter accumulation under the combination of either low PPF and cooler temperatures or high PPF and warmer temperatures was paralleled by the diversity of PPF habitats in the natural open grassland and forest margin the parent species occupies. It is therefore suggested that Zantedeschia 'Best Gold' is well adapted to optimize growth under these environmental conditions