| The influences of water stress on gas exchange and chlorophyll fluorescence parameters of Ammopiptanthus
mongolicus were studied using Li-6400 portable photosynthesis system. The results showed that the relationship between
net photosynthesis rate, transpiration rate, stomatal conductance of A. mongolicus and water potential were stimulated by y=
a+b(1原e-kx), and the relation between chlorophyll fluorescence parameters and water potential were y=ae-bx^k. The net
photosynthesis rate, transpiration rate, stomatal conductance and chlorophyll fluorescence parameters of A. mongolicus
decreased under water stress. The initial water stress potential of net photosynthesis rate, transpiration rate and stomatal
conductance were less than those of chlorophyll fluorescence parameters, and the photosynthetic water potential
compensation point, water potential at transpiration rate critical point and stomatal conductance critical point were similar
to those of chlorophyll fluorescence parameters(NPQ, qP and ETR), but that were much less than initial water stress
potential of Fv/Fm. The water potential at stomatal conductance critical point could be used as the limit of estimating the
photosynthetic stomatal and nonstomatal regulation, and the initial water stress potential of Fv/Fm was used as the critical
value of plant water stress. When the water potential was more than the water potential at stomatal conductance critical
point, it belonged to the water potential of stomatal regulation, however, when the water potential was less than the water
potential at stomatal conductance critical point, it belonged to the water potential of nonstomatal regulation. When the water
potential was more than the initial water stress potential of Fv/Fm, it belonged to the mild or moderate water stress, if it
was less than the initial water stress potential of Fv/Fm, it
belonged to heavy water stress. The result showed that the
water potential at stomatal conductance critical point of A .
mongolicus was between -3.81 and -5.26 MPa, and the
critical point of heavy water stress was between -8.05 and
-14.53 MPa, and they had the seasonal difference. |
