不同氮素水平对濒危植物黄檗幼苗光合荧光特性的影响

Effects of nitrogen levels on photosynthetic and fluorescence characteristics in seedlings of endangered plant Phellodendron amurense

为了探讨不同氮素水平对黄檗幼苗光合作用的影响,采用液体培养的方法,研究了4种不同的氮素(以NH_4NO_3计)水平下黄檗幼苗叶绿素含量以及光合和荧光特性的差异。结果显示:随着氮浓度的增加,叶绿素a、叶绿素b、类胡萝卜素和总叶绿素含量都是先升高后降低,都在N8(4 mmol/L的NH_4NO_3)时达到最大值,其次是N16(8mmol/L的NH_4NO_3)、N_4(2 mmol/L的NH_4NO_3)和N1(0.5 mmol/L的NH4NO3),而叶绿素a/b在N_4时最大。N4、N和N处理条件下黄檗幼苗的光响应曲线变化趋势基本一致,其净光合速率(P_n)都随光合有效辐射(PAR)的增加而迅速增大,之后增速明显下降,最后呈平缓的变化趋势,N的最大净光合速率(P_(nmax))最高,其次是N16,最后是N;N的光响应曲线则略有不同,其P_n值达到最大值之后却随PAR的增加而逐渐下降,且N的P_(nmax)值最低。N条件下的光饱合点、气孔导度都最高,表观量子效率和胞间二氧化碳浓度较高且光补偿点和暗呼吸速率较低。随着氮浓度的增加,最大荧光、可变荧光、光化学猝灭系数、光系统Ⅱ原初光能转换效率、PSⅡ量子效率和表观电子传递速率值都是先升高后降低,在N时达到最大值,且在N时最低,初始荧光和非光化学猝灭系数值则是N最高。结果表明,适当增加供氮水平可以显著提高黄檗幼苗的光合能力,但过高的氮素供给反而不利于幼苗生长,N条件最适合幼苗生长。

To investigate the photosynthetic responses of Phellodendron amurense to nitrogen levels,we detected the photosynthetic parameters and chlorophyll fluorescence of liquid-cultured seedlings under four nitrogen（ NH_4NO_3） levels,which are 1 mmol/L（ N1）,4 mmol/L（ N4）,8 mmol/L（ N8）,and 16 mmol/L（ N16）. The results showed that the contents of chlorophyll a,chlorophyll b,carotenoid,and total chlorophyll increased initially,and then decreased with the increasing nitrogen supply. They reached the maximum under N8（ 4 mmol / L NH_4NO_3）,followed by that under N16（ 8 mmol/L NH_4NO_3）,N4（ 2mmol / L NH_4NO_3） and N1（ 0. 5 mmol/L NH_4NO_3）. The chlorophyll a /b reached the maximum under N4. The light response curves of photosynthesis were consistent under N4,N8 and N16,while the net photosynthetic rate（ Pn） increased rapidly,then slowed down significantly,and finally presented gentle changes when photosynthetically active radiation（ PAR） was enhanced gradually. The maximum netphotosynthetic rate（ Pnmax） under N8 condition was the highest,and Pnmaxunder N16 and N4 were lower.However,the light response curve under N1 was slightly different with others. After reaching the peak,Pngradually decreased with the increase of PAR,and Pnmaxunder N1 was the lowest. Under N8,the light saturation point（ LSP） and the stomatal conductance（ Gs） were the highest,the apparent quantum yield（ AQY） and the intercellular CO_2 concentration（ Ci） were relatively higher,while the light compensation point（ LCP） and the dark respiration rate（ Rd） were relatively lower. With the increase of nitrogen concentration,the maximum fluorescence（ Fm）,variable fluorescence（ Fv）,photochemical quenching coefficient（ q P）,original light energy conversion efficiency of optical systemⅡ（ Fv/ Fm）,PSⅡquantum efficiency（ ΦPSⅡ）,and the electron transport rate（ ETR） all increased first and then decreased,and reached the maximum under N8 and the minimum under N1. The initial fluorescence（ Fo） and the nonphotochemical quenching coefficient（ NPQ） under N4 were the highest ones. All these results indicate that increase of nitrogen supply can significantly enhance the photosynthetic capability of P. amurense seedlings,but excessive nitrogen is not conducive to seedling growth,and N8 is the optimal condition for seedling growth.