T. Tani et al., Responses of photosynthesis and biomass allocation of an understorey herb,Pteridophyllum racemosum, to gradual increases in irradiance, ANN BOTANY, 88(3), 2001, pp. 393-402
In wave-regenerating Abies forests in central Japan, light availability on
the forest floor of a mature-tree stand increases gradually over 4 to 5 yea
rs during the senescence of trees. The understorey evergreen perennial Pter
idophyllum racemosum Sieb. et Zucc. (Papaveraceae) is commonly found in suc
h forests. To determine the acclimation characteristics of this species to
gradual changes in light availability, leaf photosynthetic traits and bioma
ss allocation patterns were determined along a transect running from fully
shaded understorey to a canopy gap. Along the transect, the photon flux den
sity on the forest floor relative to full sun (RPFD) varied from 2.3-36.7 %
. The light-saturated net photosynthetic rate of field-grown plants increas
ed as the light environment increased from 2.3-14.1 % RPFD. However, as lig
ht conditions increased from moderate (14.1 %) to high (36.7 %), the light-
saturated net photosynthetic rate decreased to a level comparable to that e
xhibited by low-light grown plants. On the other hand, root mass per unit l
eaf area (RMA) increased with increasing light conditions. A higher RMA con
tributes to a higher water uptake capacity per unit leaf area which in turn
supports higher rates of photosynthesis and transpiration in high light. W
e conclude that in wave-regenerating forests P. racemosum can survive in hi
gh-light environments by avoiding a severe water deficit and heat load by i
ncreasing RMA. (C) 2001 Annals of Botany Company.