EFFECTS OF A NATURAL SOURCE OF VERY HIGH CO2 CONCENTRATION ON THE LEAF GAS-EXCHANGE, XYLEM WATER POTENTIAL AND STOMATAL CHARACTERISTICS OF PLANTS OF SPATIPHYLUM-CANNIFOLIUM AND BAUHINIA-MULTINERVIA
Md. Fernandez et al., EFFECTS OF A NATURAL SOURCE OF VERY HIGH CO2 CONCENTRATION ON THE LEAF GAS-EXCHANGE, XYLEM WATER POTENTIAL AND STOMATAL CHARACTERISTICS OF PLANTS OF SPATIPHYLUM-CANNIFOLIUM AND BAUHINIA-MULTINERVIA, New phytologist, 138(4), 1998, pp. 689-697
The effect of a very high CO2 mole fraction (27 000-35 000 mu mol mol(
-1)) on photosynthesis and water relations was studied during the dry
and the rainy season in plants of Spatiphylum cannifolium (Dryand.) Sc
hott and Bauhinia multinervia (H.B.K.) DC. growing near natural cold C
O2 springs. Xylem water potential in plants of both species was lowere
d by drought, high CO2 growth-concentration decreasing it further in S
. cannifolium. In plants of both species growing under high CO2 concen
tration photosynthetic rates measured at a CO2 mole fraction of 1000 m
u mol mol(-1) were higher than in plants growing at ambient CO2 mole f
raction and measured at 350 mu mol mol(-1). The response was the resul
t of a direct effect of CO2 on the photosynthetic machinery. Changes i
n carboxylation efficiency in response to high CO2 were found during t
he rainy season, with an increase in S. cannifolium and a decrease in
B. multinervia; a significant interaction between growth CO2 concentra
tion and season in B. multinervia resulted from significant effects of
both factors. An increase in intrinsic water-use efficiency due to hi
gh CO2 was determined in both species by an increase in photosynthetic
rate as well as a decrease in leaf conductance. In high-CO2 plants of
S. cannifolium a 71 % decrease in stomatal density and 73 % in stomat
al index suggested that CO2 affected stomatal initiation, whereas in B
. multinervia an 85 % decrease in stomatal index and a 72 % decrease i
n stomatal density indicated that CO2 influenced stomatal initiation a
s well as epidermal cell expansion. Our results indicate that very hig
h CO2 concentrations did not inhibit photosynthesis in these species,
and that growth under high CO2 allowed plants to attain carbon balance
s higher than those of plants growing under low CO2. This was particul
arly so during the dry season, since the photosynthetic rates at the c
orresponding ambient concentration were higher in plants nearer the sp
rings, and carboxylation efficiency and some stomatal characteristics
of both species apparently acclimated to high CO2, but patterns were n
ot consistent and bore no obvious relationship to photosynthetic capac
ity.