氮素添加对呼伦贝尔草甸草原植物氮钾元素含量和计量比的影响

钾(K)是植物叶片中仅次于氮(N)的第二大营养元素,在调节植物生长发育、稳态维持和胁迫响应等方面具有重要作用。以往关于氮素输入对植物养分状况影响的研究中多关注了氮磷养分,较少关注钾及其与其他元素的计量关系。本研究以内蒙古呼伦贝尔草甸草原为对象,研究氮素添加和刈割对植物功能群水平和群落水平钾含量及计量特征(N∶K)的影响,分析功能群自身养分状况和群落组成改变对群落水平养分状况变化的相对贡献。结果表明: 为期6年的氮素添加提高了所有植物功能群的N含量以及根茎禾草和豆科植物的K含量,刈割降低了根茎禾草和丛生禾草的N含量,而对所有功能群的K含量和N∶K均无显著影响。氮素添加显著提高了群落水平植物N和K含量,刈割仅增加了群落植物的N含量。氮素添加和刈割对功能群和群落水平上的植物N∶K均无显著影响。功能群本身的养分变化情况对群落水平植物养分状况的贡献大于群落组成的贡献。在对群落水平养分特征的影响方面,功能群本身养分变化的贡献与群落组成的贡献具有负的协变关系。呼伦贝尔草甸草原植物具有较高的N∶K内稳性,能够较好地调节自身的氮钾平衡,这对氮沉降背景下维持氮钾元素计量关系具有重要意义。

Effects of nitrogen addition on the contents and stoichiometric ratio of nitrogen and potassium in a meadow steppe of Hulunbuir,China

Potassium (K) is the second most abundant nutrient in plant leaves after nitrogen (N) and the most abundant cation in plant cells. It plays an important role in plant growth regulation, homeostasis maintenance, and stress response. Previous studies on the effects of N input on plant nutrient status mainly focus on N and phosphorus (P), but less on K and its stoichiometry. We examined the effects of N input and mowing on K content and N:K at both plant functional group and community levels. We analyzed the relative contribution of changes in functional groups and community composition to changes of community level nutrition status. The results showed that N input increased N content of each plant functional group and increased K content of rhizomatous grasses and legumes. Mowing reduced N content of rhizomatous grasses and bunchgrass, but did not affect K content and N:K of all functional groups. Nitrogen input significantly increased plant N and K contents at the community level, while mowing significantly increased plant N content. Both N input and mowing did not affect plant N:K at functional group and community levels. The contribution of nutritional changes in plant functional groups to the variation at the community level was greater than that of changes in community composition. For all the three examined nutritional traits, the contribution of nutrients at functional group level and that of community composition showed negative covariation. Our results indicated that plant N:K had high homeostasis in meadow steppe and that plants could regulate N and K balance, which was of great significance for maintaining N:K stoichiometry under the background of increasing N deposition.