Abstract:

Drought will affect plant nitrogen metabolism， thereby seriously restricting plant growth and forage quality. In order to clarify the changes in nitrogen metabolism indexes of Cynodon dactylon leaves and roots under drought stress， this experiment explored the nitrogen metabolism response mechanism of C. dactylon strains with differing drought resistance to different levels of drought stress， and varieties were screened for the key traits. C. dactylon plants were grown for 10 days under different water gradient treatments， and physiological data such as organic nitrides （proline， soluble protein， free amino acid）， inorganic nitrides （total nitrogen， nitrate nitrogen， ammonium nitrogen）， and the activities of nitrogen metabolism related enzymes ［nitrate reductase （NR）， nitrite reductase （NiR）， glutamine synthetase （GS）， glutamate synthetase （GOGAT）］ were collected for leaves and roots. It was found that with increased intensity of drought stress， total nitrogen of leaf and root decreased， organic nitride increased， the leaf nitrate nitrogen initially decreased and then increased， the root nitrate nitrogen decreased， and the ammonium nitrogen and nitrogen metabolic enzymes in leaves and roots initially increased and then decreased. Under moderate and severe stress， drought resistant materials accelerated the process of nitrogen metabolism due to their high nitrogen metabolism enzyme activity and inorganic nitride content， resulting in the rapid increase of organic nitride content in leaf and root of drought resistant strains to levels significantly higher than those of drought sensitive materials. Under drought， C. dactylon was able to largely overcome negative impacts on leaves by transporting， redistributing and utilising the nitrogen absorbed by the root. Redundancy analysis showed that GOGAT and GS were strongly associated with leaf and root drought resistance traits in drought resistant materials under moderate stress. Meanwhile， under severe stress， drought resistance was correlated proline， free amino acid and soluble protein levels. Path analysis showed that root soluble protein （decision coefficient -0.739）， leaf （0.530） and root free amino acid （0.498） were highly correlated with drought resistance of C. dactylon under drought. The results of this experiment enhance understanding of drought resistance and related nitrogen metabolism responses of C. dactylon， and also provide reference for the breeding of drought resistant resources.

Key words: Cynodon dactylon, drought stress, nitrogen metabolism, nitride content, nitrogen metabolizing enzyme activity