A pot experiment was conducted for water control test of spring maize. Three water control levels (normal water supply

moderate drought

severe drought) and two periods (droughting

rewatering) were set up to research the effects of different degrees of drought stress and rewatering during seedling stage on light response curve

CO2 response curve

curve fitting parameters and antioxidant enzymes activities of spring maize. The results showed that the light radiation utilization capacity of spring maize leaves was decreased under drought stress. [1]Along with the increasing drought stress

maximum leaf net-photosynthetic rate (Pnmax)

apparent quantum efficiency (AQY)

light saturation point(LSP)

the maximum electric transportation rate (Jmax)

and even the maximum carboxylation rate (VCmax) of spring maize leaves were all decreased significantly

however

light compensation point (LCP)

the activities of superoxide dismutase (SOD)

peroxidase (POD) and catalase (CAT) in leaves were apparently increased. After rewatering

the Pnmax

AQY

LSP

Jmax and VCmax under moderate drought stress in early stage were generally higher than those of normal water supply and moderate drought. However

the above parameters (except Jmax

VCmax ) under the severe drought did not reach the level of normal water supply

but higher than the severe drought. The SOD

POD and CAT activities had decreased

which still were higher than the normal water supply and drought level

and had a less decrement after severe drought stress. These results implied that a moderate drought hardening at the seedling stage could bring the higher antioxidant enzymes activities and remove the reactive oxygen species. Consequently

the reduced degree of membrane lipid peroxidation would make the membrane easier to be repaired after rewatering. These facts made the photosynthetic efficiency of the leaves produce a super-compensation effect. But after severe drought

the membrane repair was delayed

and the photosynthetic efficiency was just partially compensated. Hence

drought hardening should be limited in the level of medium drought for spring maize production in arid area northwest China

avoiding severe drought.