图5. 植物N:P阈值假说的提出和再评估。A, Koerselman和Meuleman (1996)提出N:P的14和16阈值可以作为养分限制类型的判断标准, 改自Koerselman和Meuleman (1996)。B, Yan等(2017)参照Koerselman和Meuleman (1996)的数据分析方法, 并扩充样本量来评估N:P阈值适用性的情形, 改自Yan等(2017)。A和B中养分限制类型是基于野外施肥实验结果判断的, 每个点为单个野外控制实验站点数据。

Fig. 5. Original proposition and re-evaluation of the N:P Threshold Hypothesis. A, The N:P threshold values of 14 and 16 as the judgement standard for N and P limitations proposed by Koerselman & Meuleman (1996), redrawn from Koerselman & Meuleman (1996). B, Re-evaluation of the N:P Threshold Hypothesis by Yan et al. (2017) with a larger dataset following the same statistic method as Koerselman & Meuleman (1996), redrawn from Yan et al. (2017). Nutrient limitation here is judged by results of field nutrient fertilization experiments. Each point indicates a field experiment site.