Effects of Substrate pH and Ratios of Ammonium to Nitrate on Enzymatic Activities of Nitrogen Metabolism and Nitrogen Content in Cunninghamia lanceolata and Schima superba Seedlings
[Objective]To explore the effects of substrate pH and ammonium to nitrate ratios on the leaf nitrogen(N)metabolism key enzyme activities and N content of the subtropical major coniferous species Cunninghamia lanceolata and the broadleaf species Schima superba.[Method]The culture substrate was set to two distinct pH levels(pH1=4.5 and pH2=6.5)and three ammonium to nitrate ratios(NH4+-N∶NO3--N:10∶0,0∶10,5∶5).Analyzing and comparing the activities of glutamine synthetase(GS),glu-tamine acid synthetase(GOGAT),nitrate reductase(NR),and nitrite reductase(NiR)in the leaves of the two tree species,as well as the N content of roots,stems,and leaves.[Result]①As compared to substrate pH=6.5,pH=4.5 inhibited the leaf N metabolism key enzyme activities of C.lanceolata and S.superba,increased the ammonium N content in the roots,stems and leaves of C.lanceolata,decreased the nitrate N content and total N accumulation in the organs of C.lanceolata and S.superba,and decreased the N accumulation in S.superba leaves under 0∶10 ratio.②The 10∶0 ratio significantly enhanced the N metabolism enzyme activities in C.lanceolata leaves and in S.superba leaves under pH=4.5 treatment,the ammonium N content in S.superba roots and leaves,the nitrate N content in S.superba roots,as well as the total N accumulation in C.lanceolata stems and leaves under pH=6.5 treatment.The 5∶5 ratio sig-nificantly increased the nitrate N content in S.superba roots under pH=4.5 treatment.The 0∶10 ratio sig-nificantly elevated the ammonium N content in C.lanceolata leaves under pH=4.5 treatment,and increased NiR activity in S.superba leaves,as well as the total N accumulation in and of S.superba stems and leaves under pH=6.5 treatment.③Under the same treatment,the N metabolism key enzyme activities in C.lanceolata leaves were lower than those of S.superba,indicating that S.superba had a stronger ability to assimilate N than C.lanceolata.④Correlation analysis results showed that the total N accumulation of C.lanceolata was significantly positively correlated with the N metabolic key enzyme activities and the ni-trate N content in the roots,and significantly negatively correlated with the ammonium N content in the organs,while the total N accumulation of S.superba was significantly negatively correlated with the am-monium N content in the leaves.[Conclusion]The cultivation environment with pH 4.5 is not conducive to the absorption of N by the seedlings of C.lanceolata and S.superba.Ammonium-N added could pro-mote the accumulation of N in C.lanceolata,while nitrate-N added could promote the accumulation of N in S.superba.Therefore,the pH of the substrate and the characteristics of the tree species should be com-prehensively considered in the process of production to select the appropriate ammonium nitrate N ratio for N nutrient management of C.lanceolata and S.superba seedlings and forest land.
culture substrate pHratios of ammonium to nitratenitrogen metabolic key enzyme activitiesnitrogen contentCunninghamia lanceolataSchima superba
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