Se. Sultan et al., PHYSIOLOGICAL-RESPONSE TO COMPLEX ENVIRONMENTS IN ANNUAL POLYGONUM SPECIES OF CONTRASTING ECOLOGICAL BREADTH, Oecologia, 115(4), 1998, pp. 564-578
Individual physiological response to complex environments is a major f
actor in the ecological breadth of species. This study compared indivi
dual patterns of both long-term and short-term response to controlled,
multifactorial environments in four annual Polygonum species that dif
fer in field distribution (P. cespitosum, P. hydropiper, P. lapathifol
ium, and P. persicaria). To test long-term response, instantaneous net
photosynthetic rate and stomatal conductance were measured in situ on
one full-sib replicate from five inbred lineages from each of five fi
eld populations per species, raised in all possible combinations of lo
w or high light; dry, moist, or flooded soil; and poor or rich nutrien
t status. Short-term plastic adjustment to changes in light level was
examined by switching individual plants of the four species from one o
f six multifactorial growth environments to the contrasting light envi
ronment, and measuring assimilation rates 1 h after transfer. The Poly
gonum species differed significantly in their patterns of long-term ph
otosynthetic response to particular resources and resource combination
s. The species known to have relatively broad ecological distributions
(P. persicaria and P. lapathifolium) maintained high photosynthetic p
erformance in a variety of moisture and nutrient environments when gro
wn in high light, while the more narrowly distributed P. hydropiper ma
intained such functional levels only if given both high light and ampl
e macronutrients. P. cespitosum, a species limited to shaded habitats,
maintained low photosynthetic rates across the environmental range. C
omplex differences among the species in instantaneous water use effici
ency (WUE) reflected their highly specific and to some extent independ
ent patterns of photosynthetic and stomatal response to the multifacto
rial environments. The species also differed significantly in short-te
rm physiological adjustment to changes in light level. Plants of P. pe
rsicaria and P. cespitosum reached 78% and 98%, respectively, of their
maximum photosynthetic rates 1 h after transfer from low to high ligh
t, but P. hydropiper and P. lapathifolium plants reached only c. 60% o
f their maximum rates. When switched from high to low light, P. persic
aria and P. cespitosum plants maintained 64-76% of their maximum rates
, while P. hydropiper and P. lapathifolium plants decreased photosynth
etic rates sharply to less than 50% of their maximum rates. These resu
lts indicate that the latter two species will be less able to maintain
effective functional levels in variable light environments, a result
consistent with their distributions in the field.