Table 3. The mean and range of root and leaf N, P and N∶P ratio in this study and others.

Data source	N (mg g−1)		P (mg g−1)		N∶P		References
	Mean	Range	Mean	Range	Mean	Range
Root
Northern Tibet	13.05	6.30–27.42	0.60	0.23–1.25	23.40	8.80–47.55	This study
Inner Mongolia Grassland	10.90	—	0.7	—	15.57	—	(Zhou et al. 2010)
Global study	9.8	—	0.78	—	16.0	—	(Yan et al. 2011)
Leaf
Northern Tibet	23.20	11.39–50.13	1.38	0.58–2.93	17.87	7.28–33.09	This study
Chinese grassland	27.6	—	1.9	—	15.3	—	(He et al. 2008)
Chinese flora	20.24***	6.25–52.61	1.45NS	0.05–10.27	16.35NS	3.28–78.89	(Han et al. 2005)
Global flora	20.1***	4.1–59.9	1.77***	0.1–6.99	13.8***	2.6–111.8	(Reich and Oleksyn 2004)

*** Significant differences in leaf N and P concentrations and the N∶P ratio between the northern Tibetan Plateau and other areas at P<0.001, NS represents no significant difference in the leaf P content and the N∶P ratio between the northern Tibetan Plateau and other areas (P>0.05).