氮素形态对高寒人工草地植物群落生物量分配及优势种叶片光合特性的影响

The effects of nitrogen forms on biomass allocation and photosynthetic characteristics of dominant species in alpine artificial grasslands

研究不同氮素形态对高寒人工草地植物群落生物量分配和优势种叶片光合特性的影响,以期筛选出适合高寒人工草地生产力维持的氮素形态。以4龄“青海中华羊茅(Festuca sinensis Qinghai)+青海草地早熟禾(Poa pratensis Qinghai)”混播草地为研究对象,采用随机区组设计,设置对照组(CK)、酰胺态氮(U)、铵态氮(A)和硝态氮(N)4种处理方式,对不同处理方式下的生物量分配特征、优势种叶片光合特性和化学计量特征进行了分析。结果表明,氮添加降低了茎的相对生物量,提高了叶和穗的相对生物量,通过增加15~45 cm高度范围内茎和叶的生物量提高地上总生物量。不同氮素形态对地上生物量的促进作用表现为U>N>A。不同氮素形态不同程度地提高了优势种叶片的光合性能,对净光合速率和水分利用效率的作用效果表现为A>N>U。3种氮素形态对植物叶片碳含量没有显著影响,但显著提高了氮、磷含量,降低了碳氮比和碳磷比,且作用效果均表现为U>N>A。冗余分析表明,胞间CO_(2)浓度、气孔导度和净光合速率是影响植物生产性能的关键光合指标,叶片氮含量、磷含量、碳氮比、碳磷比和氮磷比是影响植物光合作用和生产性能的关键因子。综合而言,酰胺态氮可能更有利于高寒人工草地生产力的维持。

We investigated the effects of different nitrogen forms on biomass allocation and photosynthetic characteristics of dominant species in alpine artificial grasslands,aiming to select nitrogen forms suitable for maintaining productivity.A randomized block design was used to examine biomass allocation pattern,leaf photosynthetic characteristics,and stoichiometric characteristics of dominant species in a 4-year-old mixed grassland of“Festuca sinensis Qinghai+Poa pratensis Qinghai”under four treatments:control(CK),amide nitrogen(U),ammonium nitrogen(A),and nitrate nitrogen(N).The results showed that nitrogen addition decreased the relative biomass of stems,increased that of leaves and ears,and increased the total aboveground biomass by increasing the biomass of stems and leaves within the range of 15-45 cm in plant height.The positive effect of different nitrogen forms on aboveground biomass showed a trend of U>N>A.Different nitrogen forms improved the photosynthetic performance of dominant species to varying degrees,with the effect on net photosynthetic rate and water use efficiency showing a trend of A>N>U.The three nitrogen forms did not affect leaf carbon content,but significantly increased nitrogen and phosphorus content and decreased carbonnitrogen ratio and carbon-phosphorus ratio,with the strength of the effect being U>N>A.Results of redundancy analysis showed that intercellular CO_(2) concentration,stomatal conductance,and net photosynthetic rate were key photosynthetic variables affecting plant productivity,while leaf nitrogen content,phosphorus content,carbon-nitrogen ratio,carbon-phosphorus ratio,and nitrogen-phosphorus ratio were key factors affecting photosynthesis and productivity.Overall,amide nitrogen may be more beneficial for maintaining the productivity of alpine artificial grassland.