氮磷添加对内蒙古温带草原植物功能群氮含量的影响

Effects of nitrogen and phosphorus additions on the nitrogen content of different plant functional groups in the Inner Mongolia temperate grasslands

植物功能群氮含量既是理解氮沉降对生物多样性影响的关键指标,也是生产力过程模型模拟的重要参数,极易受氮素可利用性的影响和磷元素的限制。基于内蒙古温带草原4年氮磷添加试验(N10、N40、P5、P10及其交互,数字代表添加剂量,单位为g m^(-2) a^(-1)),分析氮磷添加对植物群落及三种植物功能群(禾本科、灌木和杂类草)氮含量的影响。结果表明:(1)氮添加显著增加了群落及各功能群的氮含量,同一处理水平下禾本科(N10)和灌木(N10和N40)的氮含量显著高于杂类草,同一功能群不同氮添加剂量间无显著差异;(2)磷添加对群落和三种功能群的氮含量无显著影响;(3)与单独氮添加相比,氮磷同时添加显著增加了群落、禾本科和杂类草氮含量,且高剂量氮磷添加的促进作用更大;(4)与单独氮添加相比,氮磷同时添加显著增加群落和三种功能群磷含量而降低氮磷比,相同处理水平下禾本科和杂类草磷含量增加幅度最大。本研究将为草原生态系统管理和应对全球变化提供科学依据。

The nitrogen(N)content of plant functional groups(PFGs)is vital to understand the nitrogen-induced biodiversity loss under the context of enhanced N deposition globally,and it is also an important parameter in process models that simulated productivity,e.g.,net primary productivity and gross primary productivity in Biome-BGC model.Considering the strong impacts of nitrogen availability and the regulation of phosphorus(P)limitation,we conducted a four-year manipulative experiment to clarify the responses of N content of PFGs to N and P additions(N addition:10 and 40 g N m^(-2) a^(-1),P addition:5 and 10 g P m^(-2) a^(-1))in a temperate steppe of the Inner Mongolia,China.Our results showed that:(1)N addition significantly increased the N content of the community and three PFGs.Grasses(10 g N m^(-2) a^(-1))and shrubs(10 and 40 g N m^(-2) a^(-1))had significantly larger increase of N content than that of forbs with the same rate of N addition.There was no significant difference among different rates of N additions for the same PFG or the whole community.(2)Nomatter what rates of P additions,i.e.5 or 10 g P m^(-2) a^(-1),there was no significant effects of P addition on N content of the community or the three PFGs.However,the P-induced changes of shrubs(5 and 10 g P m^(-2) a^(-1))and grasses(10 g P m^(-2) a^(-1))were significantly higher than that of grasses(10 g P m^(-2) a^(-1)).(3)Compared to N addition,the simultaneous additions of N and P significantly increased the N content of communities,grasses,and forbs but not shrubs,and the increase tended to be larger with the increasing rates of N or P additions.(4)Compared to N addition or the control,the simultaneous additions of N and P significantly increased the P content but decreased the N/P ratios of the communities and the three PFGs.The largest increase in P content was observed in grasses and forbs at the same rate of P addition.Notably,the P-induced increase of P content in grasses was inclined to be greater in the treatments with higher rates of P addition,and it was also the grasses got a lower N/P ratio in the treatments with higher rates of N and P additions.Our findings have important implications for grassland management and provide a better understanding of how grassland ecosystems respond to global changes.