栽培基质pH和铵硝氮比对杉木木荷氮代谢酶及氮含量的影响

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

【目的】探究栽培基质pH和铵硝态氮配比对亚热带主要针叶树杉木和阔叶树木荷幼苗叶片氮代谢酶活性及植株氮含量的影响。【方法】设置栽培基质为2个pH水平(pH_(1)=4.5和pH_(2)=6.5)和3个铵硝态氮配比(NH_(4)^(+)-N∶NO_(3)^(-)-N分别为10∶0、0∶10、5∶5),分析和比较2个树种幼苗叶片的谷氨酰胺合成酶(GS)、谷氨酸合成酶(GOGAT)、硝酸还原酶(NR)和亚硝酸还原酶(NiR)活性及各器官氮含量差异。【结果】(1)与基质pH=6.5相比,pH=4.5抑制了杉木和木荷叶中氮代谢酶GS、GOGAT、NR和NiR的活性,增加了杉木根、茎、叶中的铵态氮含量,降低了杉木各器官中的硝态氮含量和总氮素积累量,降低了0∶10配比下木荷叶的氮素积累量。(2)10∶0配比显著增加杉木叶中的氮代谢酶活性和pH=4.5处理下木荷叶中的氮代谢酶活性、增加pH=6.5处理下木荷根和叶中的铵态氮含量、木荷根的硝态氮含量及杉木茎叶及总的氮素积累量。5∶5配比显著增加pH=4.5处理下木荷根中硝态氮含量。0∶10配比显著增加pH=4.5处理下杉木叶中的铵态氮含量,增加pH=6.5处理下木荷叶的NiR活性,木荷茎叶和总氮积累量。(3)在同一处理下,杉木叶中的氮代谢酶活性均低于木荷,表明木荷具有比杉木更强的同化氮素的能力。(4)相关性分析表明,杉木总氮素积累量与氮代谢酶活性、根的硝态氮含量呈显著正相关,与器官铵态氮含量呈显著负相关,木荷总氮素积累量与叶铵态氮含量呈显著负相关。【结论】栽培基质pH为4.5的栽培环境不利于杉木和木荷幼苗对氮素的吸收,铵态氮添加可促进杉木的氮素积累,而硝态氮添加可促进木荷的氮素积累。故在生产中应综合考虑栽培基质的pH和树种特性等因素选择适宜的铵硝态氮比例进行杉木和木荷幼苗及林地的氮素营养管理。

【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(pH_(1)=4.5 and pH2=6.5)and three ammonium to nitrate ratios(NH_(4)^(+)-N∶NO_(3)^(-)-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.