以贝加尔针茅草甸草原建群种贝加尔针茅为研究对象,通过一个连续6年氮添加野外控制试验,设置5个氮素处理:N_0(0kg N/hm~2)、N_(30)(30kg N/hm~2)、N_(50)(50kg N/hm~2)、N_(100)(100kg N/hm~2)、N_(150)(150kg N/hm~2),探讨氮沉降变化对贝加尔针茅种群光合特性与叶片功能特性变化规律及其影响因子。结果表明,氮素添加变化显著影响贝加尔针茅的净光合速率等光合特性,氮素添加处理净光合速率(net photosynthetic rate,P_n)、气孔导度(stomatal conductance,G_s)、蒸腾速率(transpiration rate,T_r)、光合氮利用效率(photosynthetic nitrogen use efficiency, PNUE)和光合能量利用效率(photosynthetic energy use efficiency,PEUE)均低于或显著低于无氮素添加处理。氮素添加处理叶片比叶面积(specific leaf area,SLA)、叶片N含量(leaf N content,N_(mass))、建成成本(leaf construction cost,CC_(mass))、叶片N∶P均高于或显著高于无氮素添加处理。相关分析表明,5个氮素处理的P_n与G_s、T_r、 PNUE、PEUE、叶片P含量(leaf P content,P_(mass))、土壤N∶P呈显著正相关,与叶片比叶面积(SLA)、N_(mass)、 CC_(mass)、土壤含水量、土壤pH值呈极显著负相关;叶片N_(mass)与SLA、CC_(mass)、土壤N∶P呈显著正相关,与PNUE、 PEUE、P_(mass)、土壤含水量、土壤pH值呈显著负相关。综合以上研究表明,长期氮添加会降低贝加尔针茅净光合速率、养分利用效率,提高叶片建成成本和叶片N∶P,土壤含水量和土壤pH值是引起这种改变发生的主要因子。
英文摘要:
Atmospheric nitrogen deposition is an important component phenomenon of global change,and induces a series of ecological problems.We conducted a field manipulation experiment to study the photosynthetic response and change in leaf functional traits after long-term nitrogen addition in an S.baicalensis grassland in Inner Mongolia.This study was conducted from 2010-2015.Five treatments including N_0(0kg N/ha),N_(30)(30kg N/ha),N_(50)(50kg N/ha),N_(100)(100kg N/ha)and N_(150)(150kg N/ha)were set up and forty-eight plots, sized 8m*8m,were established with 2 mstrips between each plot.The objective was to determine how photosynthetic characteristics and leaf traits vary with nitrogen addition and what causes these differences.Photosynthetic traits and leaf traits differed among different nitrogen addition treatments.Net photosynthetic rate(P_n),stomatal conductance(G_s),transpiration rate(T_r),photosynthetic nitrogen use efficiency(PNUE), photosynthetic energy use efficiency(PEUE)under N_(30),N_(50),N_(100),and N_(150) treatments were lower or significantly lower than those under N_0.Specific leaf area(SLA),leaf N content(N_(mass)),leaf construction cost(CC_(mass)),leaf N∶P under N_(30),N_(50),N_(100),N_(150) treatments tended to be higher or were significantly higher than those under N_0.Correlation analysis showed that P_n was positively correlated with G_s,T_r,PNUE,PEUE, leaf P content(P_(mass)),N_(mass)and soil N,P while P_nwas negatively correlated with SLA,N_(mass),CC_(mass),soil water content and soil pH;N_(mass)was positively correlated with SLA,CC_(mass)and soil N,P,and N_(mass)was negatively correlated with PNUE,PEUE,P_(mass),soil water content and soil pH.In conclusion,long-term nitrogen addition induced decreases in P_nand nutrient use efficiency of S.baicalensis,and increases in leaf CC_(mass)and N∶ P.Soil water content and pH decreased with nitrogen addition.This suggests that water content and soil pH are two important factors affecting photosynthetic characteristics and leaf traits of S.baicalensis under different nitrogen addition regimes.