Responses Of Four Spruce Species To Water-Nitrogen Coupling Treatment

Picea is important tree species for afforestation and industrial timber in north and mountainous region of western China,which has important ecological and economic value.The wood of spruce is widely used in construction industry and pulp industry because of its straight stem and excellent wood property.Water and nitrogen are the most critical factors among many environmental factors that affecting the productivity of spruce plantation.Therefore,it is critical to study the effects of different water-nitrogen treatments on photosynthetic parameters and physiological indexes and to reveal the effects of nitrogen on drought response of sprucea,which is beneficial for the cultivation and genetic improvement of spruce plantation.In this study,four spruce varieties(Picea abies,Picea pungens,Picea crassifolia and Picea smithiana)were used as materials,including two clones of Picea abies and Picea pungens,respectively.Four different combinations of water-nitrogen treatments including two levels of water treatments(drought,well-watered)and two levels of N treatments(low nitrogen,normal nitrogen)were set up.The changes of photosynthetic parameters,antioxidant indexes and nitrogen metabolism enzyme activities of different spruce were studied to explore the response of different spruce to water-nitrogen coupling treatment.The main research results are as follows:1.Under drought condition,four spruce species reduced water loss by regulating stomatal opening and reducing gas exchange.Nitrogen application enhanced the adaptive response of gas exchange to drought,promoted WUE_i of four spruce species,thus improved photosynthetic carbon assimilation per unit of transpiration flow.2.The change of free proline content was related to the activity of nitrogen metabolism enzyme under drought stress.Low nitrogen inhibited the activity of GS and GDH,thus blocked the synthesis of Glu and proline.The activity of GDH was increased,thus the synthesis and transformation of Glu was promoted under normal nitrogen condition,which increased the content of free proline and the ability of osmotic adjustment in Picea.3.Under different water-nitrogen treatments,different spruce species response to environmental changes depended on specific antioxidant enzymes.In addition,N nutrient status had different effect on antioxidants for different spruce species.Appropriate nitrogen application effectively improved the antioxidant enzyme activities and enhanced antioxidant defense ability of four spruce species.4.Among four spruce species,Picea pungens had the highest potential for photosynthetic carbon assimilation under well-watered condition,which can be attributed to the adaptation of spruce to the natural distribution environment.However,in terms of WUE_iand osmotic regulation,Picea abies is more sensitive to N application under drought condition.5.The drought tolerance of Picea abies was the highest and that of Picea pungens was the lowest under normal nitrogen application.While the genetic difference in response to drought was greater under low nitrogen condiation,which means the drought tolerance of Picea pungens was the highest,and that of Picea smithiana was the lowest.6.Under drought condition,the N metabolism enzymes activities of Picea pungens genotype1 and Picea pungens genotype 2 were related to nitrogen.Appropriate nitrogen application was beneficial to maintain N metabolic balance,thus promoted the synthesis and transformation of amino acids.The effect of nitrogen on photosynthetic carbon assimilation in two clones of Picea pungens was related to water environment.Appropriate nitrogen application improved their WUE_i under drought condition.Under drought-low nitrogen condition,in terms of WUE_iand antioxidant enzymes,the drought resistance of genotype 1was better than that of genotype 2.