油蒿叶片氮分配对其最大净光合速率季节变异的影响

Effects of leaf nitrogen allocation on seasonal variation in maximum net photosynthetic rate in Artemisia ordosica

植物最大净光合速率的季节变异性及其氮调控机制是近年来植物生理生态领域研究热点,对荒漠植物光合最大净光合速率季节动态及其叶氮影响,特别是叶氮分配对最大净光合速率调控机制的了解仍非常有限。2018年5—10月在宁夏盐池毛乌素沙地,对当地主要建群种油蒿(Artemisia ordosica)进行生长季原位观测,测定其叶光合光响应曲线(A-PAR)、CO_(2)响应曲线(A-Ci)和叶氮含量,结合环境观测数据,分析A-PAR关键参数最大净光合速率(A_(max))的季节变异和叶片氮分配相关参数对A_(max)的调控。结果表明,油蒿叶片A_(max)在生长期季节变异系数(Cv)为14%,在完全展叶中期,光合氮利用效率(PNUE)有最大值11.82μmolCO_(2) gN^(-1) s^(-1),此时叶片氮素在光合系统中的分配比例最大,A_(max)有最大值29.48μmol CO_(2) m^(-2)s^(-1),油蒿光合能力较强。在完全展叶末期,油蒿叶片氮在光合系统中的分配比例(P_(p))有最小值0.21,此时叶氮分配更倾向于非光合系统,A_(max)较小,光合能力较弱,有利于油蒿延长叶片寿命。A_(max)与单位干重叶片氮含量(Nmass)、氮在捕光系统中分配比例(P_(L))、氮在生物力能系统中分配比例(P_(b))正相关(P<0.05),其中,P_(L)对A_(max)产生了最大的直接正向影响,氮在羧化系统中分配比例(P_(c))主要通过P_(b)对A_(max)的产生了间接的正向影响,P_(b)对A_(max)季节动态的解释度最大(R^(2)=0.49,P<0.01)。A_(max)与比叶重(LMA)负相关(P<0.05),即当有较高LMA时油蒿具有较低的光合速率,此时叶片光合能力较弱,叶片机械韧性较强。不同物候时期,油蒿叶片氮素分配的变化及叶片光合能力与结构性状之间的权衡关系,标志着荒漠植物对其生境的适应性调节。研究结果不但可提高荒漠灌木油蒿生态系统生产力预测的准确性,也是对植物光合适应机理认识的补充和深入。

The understanding on the seasonal dynamics of the maximum net photosynthetic rate(A_(max))and its nitrogen regulation in desert plants has been a concern in plant ecology.Understanding of the dynamics of A_(max) and its nitrogen regulation,especially the effect of leaf nitrogen allocation on the regulation mechanism of A_(max) is unusually limited in desert plants.In order to elucidate the mechanism of the seasonal variation in A_(max) in a dominant desert shrub,Artemisia ordosica.Seasonal variation in A_(max) and the effect of leaf nitrogen allocation on A_(max) were analyzed through season-long in-situ measurements of the light response curve(A-PAR),CO_(2) response curve(A-Ci),leaf nitrogen along with simultaneously environmental measurements from May to October,2018 in Mu Us Desert,Yanchi,Northwest China.As a result,A_(max) of Artemisia ordosica varied seasonally,being larger in the middle stage of leaf expansion,with a coefficient of variation(Cv)of 14%.The maximum value of photosynthetic nitrogen use efficiency(PNUE)was 11.82μmolCO_(2) gN^(-1) s^(-1) in the middle stage of leaf expansion.At this time,the distribution proportion of leaf nitrogen in the photosynthetic system was the largest,and A_(max) had the maximum value of 29.48μmol CO_(2) m^(-2)s^(-1).At the end of complete leaf expansion,the distribution proportion of leaf nitrogen in photosynthetic system(P_(p))had a minimum value of 0.21.At this phenological stage,the plants had smaller A_(max) and lower photosynthetic capacity,and leaf nitrogen distribution was more inclined to non-photosynthetic system,which was beneficial to extend the life of plant leaves.The A_(max) was positively related to nitrogen content(Nmass),nitrogen distribution in light capture system(P_(L)),and nitrogen distribution in bioenergy system(P_(b)).P_(L) had the greatest directly positive effect on A_(max)(P<0.05),nitrogen distribution in carboxylation system(P_(c))had indirect positive effect on A_(max) mainly through P_(b),and P_(b) had the greatest explanation for A_(max) seasonal dynamics(R^(2)=0.49,P<0.01).A_(max) of Artemisia ordosica was negatively correlated with leaf mass per unit area(LMA)(P<0.05),indicating that there were higher LMA and lower photosynthetic capacity when leaf photosynthetic rate was lower,and the mechanical toughness of leaves was stronger.The trade-offs between the seasonal variation of leaf nitrogen allocation,and leaf photosynthetic capacity and leaf structure traits,indicated an acclimation of a desert plant to its environmental changes in different phenological periods.The results would contribute to more realistic and accurate prediction of ecosystem response to changing climate,and to deepen understanding of photosynthetic acclimation to biotic and abiotic factors.