Abstract:
In order to explore the eco-physiological mechanism of Populus euphratica Oliv adapting to the arid desert environment,P.euphratica Oliv.that the key species in the Tarim desert ecosystem was used as material.It was conducted to research the change of photosynthetic gas exchange,antioxidative enzyme activity and osmoregulation substances of P.euphratica grown at different groundwater depths(GWD).The results showed that:(1)the diurnal courses of net photosynthetic rate(P
n),transpiration rate(T
r)and stomatal conductance(G
s)of P.euphratica under different GWD conditions showed the single peak curves respectively,while the diurnal variation of intercellular CO
2mole fraction(C
i)were the“V”curve,the valley value was significantly reduced at GWD=5.5 m(P<0.01)respectively.P
na nd G
s changed synchronously,and the peak value appeared at 12:00,while the T
r peak value lagged 2 hours.The peak values of P
n in different GWD were significantly different(P<0.05),while the peak values of T
r,G
s and C
i valley were significantly reduced in GWD=5.5 m(P<0.01)respectively.P
n,T
r,G
s,C
i,water-use efficiency(WUE)and light utilization efficiency(LUE)decreased with GWD increasing,and the daily mean value of G
s and LUE significantly decreased at GWD=5.5 m(P<0.05)respectively.However,there was no significant difference in the daily mean values of P
n,T
r,C
i and WUE under different GWD conditions(P>0.05)respectively;(2)The decline of P
nin P.euphratica from 12:00-16:00 was mainly restricted by stomatal factors,while the decline of P
nfrom 16:00-20:00 was mainly limited by non-stomatal factors;(3)The relationship between eco-physiological factors and P
n,T
runder different GWD conditions were analyzed with correlation,partial correlation and stepwise regression methods,it was found that G
swas the main factor affecting P
nand T
rof P.euphratica respectively.The correlation degree between P
nand photosynthetically active radiation(PAR),T
r and G
s were enhanced respectively with GWD increasing,indicating that GWD directly regulated the airwater exchange;(4)The malondialdehyde content(MDA),superoxide dismutase activity(SOD),peroxidase activity(POD)and free proline content(Pro)were increased respectively with GWD increasing,but the content of soluble protein(SP),soluble sugar(SS)were both decreased,which indicated that the cell membrane permeability and photosynthetic carbon assimilation were inhibited respectively with GWD increasing.P.euphratica enhanced the protective enzyme activity(POD,SOD)and osmoregulation content(Pro)to cooperate against drought stress caused by GWD increasing,and ensured to maintain the basic normal physiological activities.This was the eco-physiological strategy for P.euphratica to adapt arid desert environment.