Late-stage canopy tree species with extremely low delta C-13 and high stomatal sensitivity to seasonal soil drought in the tropical rainforest of French Guiana
D. Bonal et al., Late-stage canopy tree species with extremely low delta C-13 and high stomatal sensitivity to seasonal soil drought in the tropical rainforest of French Guiana, PL CELL ENV, 23(5), 2000, pp. 445-459
We assessed the daily time-courses of CO2 assimilation rate (A), leaf trans
piration rate (E), stomatal conductance for water vapour (g(s)), leaf water
potential (Psi(w)) and tree transpiration in a wet and a dry season for th
ree late-stage canopy rainforest tree species in French Guiana differing in
leaf carbon isotope composition (delta(13)C). Th, lower sunlit leaf delta(
13)C values found in Virola surinamensis (-29.9 parts per thousand) and in
Diplotropis purpurea (-30.9 parts per thousand), two light-demanding specie
s, as compared to Eperua falcata (-28.6 parts per thousand), a shade-semi-t
olerant species, were clearly associated with higher maximum g(s) values of
sunlit leaves in the two former species. These two species were also chara
cterized by a high sensitivity of g(s), sap flow density (Ju) and canopy co
nductance (g(c)) to seasonal soil drought, allowing maintenance of high mid
day Psi(w) values in the dry season. The data for Diplotropis provided an o
riginal picture of increasing midday Psi(w) with increasing soil drought. I
n Virola, stomata were extremely sensitive to seasonal soil drought, leadin
g to a dramatic decrease in leaf and tree transpiration in the dry season,
whereas midday Psi(w) remained close to -0.3 MPa. The mechanisms underlying
such an extremely high sensitivity of stomata to soil drought remain unkno
wn, In Eperua, g(s) of sunlit leaves was nonresponsive to seasonal drought,
whereas Ju and g(c) were lower in the dry season. This suggests a higher s
tomatal sensitivity to seasonal drought in shaded leaves than in sunlit one
s in this species.