Effects Of Nitrogen Deposition And Biochar On The Growth And Seed Quality Of Torreya Grandis

Torreya grandis‘Merrilli’is an important economic tree species in South China,the yield and quality have decreased obviously under the current increasing nitrogen deposition,which is a troublesome issue for T.grandis industry development.Biochar plays a unique role in soil remediation and crop yield improvement,however,there are few studies on the effects of biochar application on forest soil improvement,tree growth and fruit quality.This experiment uses random complete zone design on the adult plant T.grandis（15 year-old）,including two levels of simulated nitrogen deposition(low nitrogen deposition（NL）:30 kg N ha^-1yr^-1;high nitrogen deposition（NH）:60 kg N ha^-1yr^-1)and two levels of amount of biochar input(BC1:20 t ha^-1;BC2:40 t ha^-1).Leaf photosynthetic indexes,enzyme activities,mineral element contents and the fruit and seed morphological indexes,seed quality indexes of T.grandis under different treatments were measured.Responses and physiological regulation mechanisms of growth and seed quality of T.grandis to simulated nitrogen deposition and biochar input were explored,which provide scientific basis for improving the yield and quality of T.grandis and promoting the healthy development of economic forest industry under the background of increasing atmospheric nitrogen deposition.The main results are the following:（1）The changes in growth traits of T.grandis under simulated nitrogen deposition and biochar input were studied,and the physiological regulation mechanism of T.grandis on response to nitrogen deposition and biochar input was revealed.Under simulated nitrogen deposition,Pn,Y（II）,NPQ and the activity of RuBPC increased under NL and became lower under NH,leaf nitrogen and phosphorus contents had no significant difference,but leaf N:P increased,which was over 20.When biochar was applied,Pn,Y（II）,NPQ,the activity of RuBPC,leaf nitrogen and phosphorus contents raised significantly,but there is no change of leaf N:P.Under the nitrogen deposition,biochar significantly increased Pn,Y（II）,NPQ and the activity of RuBPC of T.grandis,leaf nitrogen contents had no significant change,and the N:P was significantly lower than 20,Pn,Y（II）,NPQ and the activity of RuBPC were higher under BC-1 than BC-2.Besides,it was also found that there was a significant positive correlation between the nitrogen contents and nitrate reductase activity（NR）.This shows that 30 kg N ha^-1yr^-1nitrogen deposition can improve the photosynthetic capacity of T.grandis,increase the stoichiometric ratio and enzyme activities of leaves,however,when the level of nitrogen deposition was beyond 60 kg N ha^-1yr^-1,it may inhibited leaves photosynthetic capacity,relieve phosphorus limitation by decreasing N:P,and alleviate the negative effect of high nitrogen deposition to a certain extent.（2）The effects of simulated nitrogen deposition and the application of biochar on the seed quality of T.grandis were studied,and the response laws of the seed quality of T.grandis to nitrogen deposition and biochar input were revealed.Under the nitrogen deposition,fruit and seed morphological indexes（the fruit and kernel length,width,fresh weight）increased significantly.For the application of biochar,fruit and seed morphological indexes increased significantly with the increase of its application.Simulated nitrogen deposition and biochar input significantly improved seed quality,including nutrient contents（oil content,fatty acid,soluble sugar,starch,soluble protein）,and contents of antioxidant components（tannin and total phenol）,and the low nitrogen deposition was greater than high nitrogen deposition.Under the nitrogen deposition,biochar input improved contents of seed antioxidant components,and BC-1 is superior to BC-2.In conclusion,nitrogen deposition can significantly improve seed quality of T.grandis,biochar has a significant effect on promoting seed quality,and alleviate the negative effects of excessive nitrogen deposition to a certain extent.