氮添加和铵硝态氮配比对杉木幼苗光合特性及叶绿素荧光参数的影响

Effects of nitrogen addition level and NH_(4)^(+)-N to NO_(3)^(-)-N ratio on photosynthetic characteristics and chlorophyll fluorescence parameters in Cunninghamia lanceolata seedling

研究不同氮添加水平和铵硝态氮配比对杉木(Cunninghamia lanceolata)幼苗叶片光合特性和叶绿素荧光参数的影响,从光合生理生态的角度探讨杉木幼苗对氮逆境的短期响应,可以为杉木栽培中氮肥的经营管理提供理论依据。该研究以一年生杉木幼苗为材料,设置3个氮添加水平:0.5(N_(1))、1.0(N_(2))和2.0 mmol·L^(-1)(N_(3))及7个铵态氮:硝态氮的配比:10:0(P_(1))、8:2(P_(2))、6:4(P_(3))、5:5(P_(4))、4:6(P_(5))、2:8(P_(6))和0:10(P_(7))的21个实验处理组,沙培盆栽处理180天后,测定幼苗叶绿素含量、光合特性、叶绿素荧光参数、生物量等指标。结果表明:(1)在N_(1)水平下,叶绿素a和b含量分别在P_(2)和P_(6)配比下最高;在N_(2)水平下,叶绿素a和b及叶绿素(a+b)含量均为P_(4)配比下最高;在N_(3)水平下,叶绿素a和b含量均在P_(3)配比下最高,整体上表现为N_(3)和N_(2)高于N_(1)。(2)叶片净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)和水分利用效率(WUE)均为较高铵态氮浓度的配比处理高于较高硝态氮浓度的配比处理;Pn在N_(3)水平为P_(1)配比最高,但在N_(1)和N_(2)水平为P_(2)配比最高,整体上Pn和WUE均表现为:N_(3)>N_(2)>N_(1)。(3)各处理的最大光化学效率均在0.80-0.85的正常范围内,光系统II潜在光化学活性在P_(2)配比下N_(3)显著高于N_(1)和N_(2);叶片快速叶绿素荧光诱导曲线在N_(1)的P_(1)配比下曲线偏离程度大,N_(2)水平的P_(1)、P_(2)和P_(4)配比和N_(3)水平的P_(1)、P_(2)和P_(5)配比在I、P相逐渐降低,J相逐渐上升;P_(2)和P_(3)配比下单位面积吸收、捕获和传递的光能以及热耗散和反应中心的数量随氮浓度的升高明显增大,而P_(6)配比下单位反应中心吸收、捕获和传递的能力以及耗散掉的能量随氮浓度的升高明显降低,其他配比下差异不显著。最大光化学效率在各处理间无显著差异表明该研究模拟的低氮水平和氮形态异质性配比的环境未对杉木幼苗生长造成胁迫。(4)总生物量和地上生物量均表现为较高铵态氮浓度的配比处理大于较高硝态氮浓度的配比处理,其中N_(2)P_(2)处理下最高,氮添加水平间表现为N_(2)>N_(3)>N_(1)。根冠比在N_(1)和N_(3)水平均为P_(6)配比显著高于其他处理,N_(2)水平为P_(7)显著高于其他处理,且整体上N_(1)水平的根冠比显著高于N_(2)和N_(3)。相对较高的氮添加水平和铵态氮浓度配比的环境能提高杉木幼苗光化学反应效率,优化光系统II反应中心的能量利用,最终促进其光合作用和生物量的积累。

Aims To study the effects of different nitrogen(N)addition levels and NH_(4)^(+)-N to NO_(3)^(-)-N ratios on photosynthetic characteristics and chlorophyll fluorescence parameters of Cunninghamia lanceolata will provid a scientific basis for the management of nitrogen fertilization in C.lanceolata.Methods One-year-old seedlings of C.lanceolata were cultured in sands with three N addition levels of 0.5(N_(1)),1.0(N_(2)),and 2.0 mmol·L^(-1)(N_(3))and seven different N form ratios(NH_(4)^(+)-N to NO_(3)^(-)-N ratios being as 10:0(P_(1)),8:2(P_(2)),6:4(P_(3)),5:5(P_(4)),4:6(P_(5)),2:8(P_(6)),and 0:10(P_(7)).The chlorophyll(Chl)content,photosynthetic characteristics,Chl fluorescence parameters and biomass in C.lanceolata were analyzed after 180 d treatment.Important findings(1)The Chl a and Chl b content of C.lanceolata were the highest at P_(2) and P_(6) under N_(1)level,respectively.The Chl a,Chl b,and Chl(a+b)content were all highest at P_(4) under N_(2)level.Both Chl a and Chl b content were the highest at P_(3) among the seven ratios under N_(3)level.The Chl content showed an overall higher level of N_(3) and N_(2) than that of N_(1) level.(2)The net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),and water use efficiency(WUE)of C.lanceolata were all higher for higher NH_(4)^(+)-N content than for higher NO_(3)^(-)-N content.The Pn was the highest at P_(1) under N_(3) level,but the highest at P_(2) under N_(2) and N_(1) levels.(3)The maximum photochemical efficiency of all treatments was in the normal range of 0.80-0.85,and the potential photochemical activity of photosystem II(PSII)was significantly higher under N_(3) level than that of N_(1) and N_(2) at P_(2).The fast chlorophyll fluorescence induction curve(OJIP)of leaves deviated greatly under N_(1) level at P_(1).P_(1),P_(2),and P_(4) at N_(2) and P_(1),P_(2),and P_(5) at N_(3)gradually decreased at the I and P phases and gradually increased at the J phase.The apparent quantum flux per unit leaf cross-sectional area,heat dissipation capacity,and the number of active reaction centers per unit leaf cross-sectional area with the increase of nitrogen content at P_(2) and P_(3),while the absorption flux per reaction center(RC),electron transport flux per RC,trapped energy flux per RC,and dissipated energy flux per RC at P_(6) decreased significantly with the increase of nitrogen content,the differences were not significant under the other ratios.(4)Total biomass and aboveground biomass of C.lanceolata were higher for higher NH_(4)^(+)-N content than for higher NO_(3)^(-)-N content,and significantly higher under the N_(2)P_(2) treatment than under the other treatments.At the same N form ratio,it showed that N_(2)>N_(3)>N_(1).The root-shoot ratio of N_(1) and N_(3) was significantly higher than that of other treatments,and the ratio of P_(6) at N_(2) level was significantly higher than that of other treatments,and the ratio of P_(7) at N_(2) level was significantly higher than that of N_(2) and N_(3).The photochemical reaction efficiency of C.lanceolata seedlings could be improved and the energy utilization of the PSII reaction center could be optimized by a higher N content and a higher ammonium to nitrate ratios,which would be more beneficial for photosynthesis and biomass accumulation.