In order to figure out the effects of mixed sowing and nitrogen applying on leaf chlorophyll
fluorescence parameters of Bothriochloa ischaemum ( Linn．) Keng under drought condition，a pot-culture
method was employed to compare and analyze the changes in leaf chlorophyll fluorescence parameters ofB． ischaemum cultivated under different mixed sowing ratios ( B． ischaemum mixed sowing with Panicum
virgatum Linn． at the ratio of 8 ∶ 0，6 ∶ 2，4 ∶ 4 and 2 ∶ 6，respectively) ，nitrogen applying levels ( no
nitrogen applying and applying 0. 1 g pure nitrogen into 1 kg dry soil) and water supplying conditions
( normal water supplying and rewatering after drought stress for 6 d) ． On this basis，general linear model
was used to analyze the influences of these three factors and their interaction on chlorophyll fluorescence
parameters of B． ischaemum． The results show that there is no obvious change in the maximal
photochemical efficiency ( Fv /Fm
) ，actual photochemical efficiency ( ΦPSⅡ
) ，apparent photosynthetic
electron transport rate ( ETＲ ) ，photochemical quenching coefficient ( qP ) and non-photochemical
quenching coefficient ( NPQ) of B． ischaemum in all treatment groups under normal water supplying
condition． Under drought and rewatering condition，Fv /Fm value of B． ischaemum in no nitrogen applying
treatment group drops to the lowest value at drought stress for 6 d ( when soil relative water content is the
lowest) ，and is back to close level under normal water supplying condition at rewatering for 2 d，while
Fv /Fm value in nitrogen applying treatment group is always near to the level under normal water supplying
condition． Ｒegardless of nitrogen application，ΦPSⅡ
，ETＲ，qP and NPQ values in all treatment groups
basically reach the highest value at drought stress for 6 d，and restore to more than 90% of all values
under normal water supplying condition after rewatering for 2 d． In general，qP and ETＲ values of mixed
sowing B． ischaemum are higher than those of pure sowing B． ischaemum，while NPQ value is lower than
that of the latter． Statistical analysis result shows that interaction among three factors including mixed
sowing ratio，nitrogen application level and water supplying condition has no significant effect on ΦPSⅡ
，
qP and ETＲ values of B． ischaemum，and single action of nitrogen application level on NPQ value，
interaction between nitrogen applying level and mixed sowing ratio on Fv /Fm value，and interaction
between nitrogen applying level and water supplying condition on ETＲ value are also not significant．
However，single action and interaction between two factors of the three factors have significant or
extremely significant effects on other chlorophyll fluorescence parameters of B． ischaemum． In conclusion，
a certain degree of drought stress would be beneficial for enhancing open proportion，photosynthetic
electron transport rate and heat dissipation for excess luminous energy of PSⅡ action center in leaf of B．
ischaemum; under drought stress condition， nitrogen applying helps to maintain activity and
photochemical efficiency of PSⅡ action center in leaf of B． ischaemum; and appropriately mixed sowing
with P． virgatum can improve the photosynthetic performance of leaf of B． ischaemum and increase its
interspecific competitive adaptability．
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