氮磷供给对长白落叶松叶绿素合成、叶绿素荧光和光合速率的影响

Effects of Different Concentrations of Nitrogen and Phosphorus on Chlorophyll Biosynthesis, Chlorophyll a Fluorescence, and Photosynthetic Rate in Larix olgensis Seedlings

以1年生长白落叶松幼苗为研究对象,采用沙培方式,供给含不同浓度的硝酸铵或磷酸盐的营养液,着重研究氮磷供给水平对其叶绿素生物合成、叶片氮含量及光合速率的影响。结果如下:1)硝酸铵浓度1～8mmol·L-1时,5-氨基酮戊酸(5_aminolevulinicacid,ALA)合成速率增加,而当硝酸铵浓度达到16mmol·L-1时,与8mmol·L-1相比,ALA合成速率反而下降17%。在磷处理下,ALA合成速率变化与之相似。在氮磷处理下,氮磷浓度分别为8和1mmol·L-1时胆色原素(porphobilinogen,PBG)合成酶活性达到最大。2)叶绿素a、叶绿素b、总叶绿素以及类胡萝卜素含量在硝酸铵浓度为8mmol·L-1、磷浓度为0.5mmol·L-1时达到最大。叶片总氮含量随硝酸铵浓度增加而增加。3)磷浓度0.125～1mmol·L-1时,叶片总氮含量只有微量增加,且磷浓度增加到2mmol·L-1时,与1mmol·L-1相比,叶片总氮含量反而下降9%。硝酸铵浓度为1～8mmol·L-1时,叶片中可溶性蛋白含量总体上逐渐增加,硝酸铵浓度增加到16mmol·L-1时,与8mmol·L-1时相比,可溶性蛋白含量下降17%。在磷处理下,可溶性蛋白含量在0.25mmol·L-1时达到最大。4)当硝酸铵浓度为1～8mmol·L-1,总体上FvFm随硝酸铵浓度增加而逐渐增加,而在16mmol·L-1时反而下降。在磷处理下,FvFm的变化趋势与之相似。在硝酸铵浓度1～8mmol·L-1时长白落叶松幼苗净光合速率逐渐增大,但硝酸铵浓度为16mmol·L-1时净光合速率反而下降16%(与8mmol·L-1相比)。在磷处理下,净光合速率在1mmol·L-1时最大,磷浓度过量(2mmol·L-1)则导致光合速率降低。这些结果表明氮供给水平对长白落叶松幼苗叶绿素的生物合成过程中ALA合成速率和PBG酶活性影响较大,从而影响幼苗叶片中叶绿素和类胡萝卜素含量;同时氮供给水平也影响幼苗叶片总氮含量和可溶性蛋白,因而影响净光合速率。磷供给水平对长白落叶松幼苗叶绿素的生物合成过程中ALA合成速率和PBG酶活性影响较大,但对幼苗叶片中叶绿素和类胡萝卜素含量影响则小,同时对净光合速率的影响也小。

In our experiments, one-year-old Larix olgensis seedlings were cultivated in sand, and supplied with solutions with different concentrations of nitrate or phosphate. The effects of nitrogen and phosphorus supply on chlorophyll biosynthesis, total nitrogen content and photosynthetic rate were studied. The experimental results were listed below： 1 ） 5-aminolevulinic acid （ALA） synthetic rate increased as nitrate concentrations supplied to larch seedlings increased from 1 to 8 mmol· L^-1 . But the rate decreased 17 % when nitrate concentration increased to 16 mmol· L^-1 , contrast to the control. Under phosphate treatments,ALA synthetic rates were similar to those under nitrate treatments. The activities of porphobilinogen （PBG） synthase reached maximum when larch seedlings were supplied with 8 mmol· L^- 1 of nitrate or 1 mmol·L^- 1 of phosphate. 2） When larch seedlings were supplied with 8 mmol· L^- 1 of nitrate and 0.5 mmol· L^- 1 of phosphate, the eontents of ehlorophyll a, ehlorophyll b, total chlorophyll and carotenoids reached maximum. The total nitrogen contents in leaves increased as nitrate concentrations increased.3） When phosphate eoneentrations inereased from 0.125 to l mmol· L^- 1 , the total nitrogen contents in leaves slightly increased,however, continuous increase of phosphate concentrations resulted in the decrease in total nitrogen contents in leaves. When nitrate concentrations increased from 1 to 8 mmol·L-L^-1, soluble protein contents in leaves increased in general, and continuous increase of nitrate concentrations induced reduce in soluble protein contents in leaves. 4） Under treatment of 0.25 mmol· L^-1 of phosphate, the soluble protein contents reached maximum. In general, Fv/Fm increased as nitrate concentrations increased from 1 to 8 mmol·L^-1, and continuous increase of nitrate concentrations resulted in reduce in Fv/Fm . The similar changes occurred under phosphate treatments. As nitrate concentrations increased from 1 to 8 mmol· L^-1 photosynthetic rates gradually increased,but when nitrate concentrations increased to 16 mmol· L^-1, photosynthetic rate reduced 16%, contrast to the control.Photosynthetic rates reached maximum when seedlings were supplied with 1 mmol· L^-1 , and oversupply of phosphate （2 mmol·L^-1 ） resulted in reduce in photosynthetic rates. The results suggested that supply levels of nitrogen affected ALA biosynthetic rates, activities of PBG synthase, and affected contents of chlorophyll and earotenoids. Moreover, nitrogen supply levels affected contents of total nitrogen and soluble proteins in leaves, and net photosynthetic rates. ALA biosynthesis rates and activities of PBG synthase were affected by phosphate supply, but contents of chlorophyll and earotenoids were not affected. And net photosynthetic rates were affected little by phosphate supply.