Root and leaf N, P concentrations and N∶P ratios for the overall plant in northern Tibet Plateau.

<p>Root and leaf N, P concentrations and N∶P ratios for the overall plant in northern Tibet Plateau.</p

Stoichiometry of Root and Leaf Nitrogen and Phosphorus in a Dry Alpine Steppe on the Northern Tibetan Plateau

<div><p>Leaf nitrogen (N) and phosphorus (P) have been used widely in the ecological stoichiometry to understand nutrient limitation in plant. However,few studies have focused on the relationship between root nutrients and environmental factors. The main objective of this study was to clarify the pattern of root and leaf N and P concentrations and the relationships between plant nitrogen (N) and phosphorus (P) concentrations with climatic factors under low temperature conditions in the northern Tibetan Plateau of China. We conducted a systematic census of N and P concentrations, and the N∶P ratio in leaf and root for 139 plant samples, from 14 species and 7 families in a dry <i>Stipa purpurea</i> alpine steppe on the northern Tibetan Plateau of China. The results showed that the mean root N and P concentrations and the N∶P ratios across all species were 13.05 mg g⁻¹, 0.60 mg g⁻¹ and 23.40, respectively. The mean leaf N and P concentrations and the N∶P ratio were 23.20 mg g⁻¹, 1.38 mg g⁻¹, and 17.87, respectively. Compared to global plant nutrients concentrations, plants distributing in high altitude area have higher N concentrations and N∶P, but lower P concentrations, which could be used to explain normally-observed low growth rate of plant in the cold region. Plant N concentrations were unrelated to the mean annual temperature (MAT). The root and leaf P concentrations were negatively correlated with the MAT, but the N∶P ratios were positively correlated with the MAT. It is highly possible this region is not N limited, it is P limited, thus the temperature-biogeochemical hypothesis (TBH) can not be used to explain the relationship between plant N concentrations and MAT in alpine steppe. The results were valuable to understand the bio-geographic patterns of root and leaf nutrients traits and modeling ecosystem nutrient cycling in cold and dry environments.</p></div

Biomass data

The file contains all the biomass data in the experiment

The relationship between the N and P concentrations (b) and the N∶P ratio (a, c) for roots and leaves across all species on the northern Tibetan Plateau.

<p>The solid line represents the root fitted straight line, the dashed line represents the leaf fitted straight line.</p

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

<p><b>***</b> Significant differences in leaf N and P concentrations and the N∶P ratio between the northern Tibetan Plateau and other areas at <i>P</i><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 (<i>P</i>>0.05).</p><p>The mean and range of root and leaf N, P and N∶P ratio in this study and others.</p

A map of 32 sampling sites of alpine steppe on the northern Tibetan Plateau.

<p>A map of 32 sampling sites of alpine steppe on the northern Tibetan Plateau.</p

The relationship between the leaf N∶P stoichiometry and the MAP and MAT of the northern Tibetan Plateau (a–f), China and global (g–i).

<p>The dashed dot line represents the fitted straight line of the leaf N∶P stoichiometry with the MAT and MAP on the northern Tibetan Plateau, the dashed line represents the fitted straight (curved) line of the global leaf N∶P stoichiometry with MAT from Reich and Oleksyn (2004), the solid line represents the fitted straight line for Chinese leaf stoichiometry N∶P with the MAT from Han et al. (2005). Regression lines are shown only for relationships that were significant at <i>P</i><0.05. * and *** represent relationships that significant at the 0.05 and 0.001, respectively.</p

The relationship between leaf N and the MAT under low temperatures (MAT <10°C), including northern Tibetan Plateau data (this study), global data from Reich and Oleksyn (2004), Chinese data from Han et al. (2005) and eastern Tibetan Plateau data from He et al. (2006 b).

<p>The relationship between leaf N and the MAT under low temperatures (MAT <10°C), including northern Tibetan Plateau data (this study), global data from Reich and Oleksyn (2004), Chinese data from Han et al. (2005) and eastern Tibetan Plateau data from He et al. (2006 b).</p

Correlation coefficients between plant N, P, and N∶P ratio, and climate factors (MAT, MAP) in northern Tibet Plateau.

<p><b>*</b>, <b>**</b>, and <b>***</b> represent correlation that is significant at the 0.05, 0.01 and 0.001 level (2-tailed), respectively.</p><p>Correlation coefficients between plant N, P, and N∶P ratio, and climate factors (MAT, MAP) in northern Tibet Plateau.</p

The relationship between the root N∶P stoichiometry and the MAP and MAT across all species on the northern Tibetan Plateau.

<p>Regression lines are shown only for relationships that were significant at <i>P</i><0.05. * and ** represent relationships that significant at the 0.05 and 0.01, respectively.</p