Stoichiometry of root and leaf nitrogen and phosphorus in a dry alpine steppe on the Northern Tibetan Plateau.

Jiangtao Hong,Xiaodan Wang,Jianbo Wu,Liping Zhu

doi:10.1371/journal.pone.0109052

Abstract

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 Stipa purpurea 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.

Highlights

Nitrogen (N) and phosphorus (P) are two essential elements in plants, both playing a critical role in plant function and most ecosystem processes [1]
Reich and Oleksyn [3] assumed that the global leaf N concentrations generally increased with the mean annual temperature (MAT) when the temperature was below 5–10uC
Wheather the temperaturebiogeochemical hypothesis (TBH) could be used to explain the relationship between leaf N concentrations and MAT in alpine area is still a controversial issue on account of few plant data contained in previous studies [3,4,9]

Summary

Introduction

Nitrogen (N) and phosphorus (P) are two essential elements in plants, both playing a critical role in plant function and most ecosystem processes [1]. Temperature could be an important factor that drive the recirculation of nutrients in terrestrial ecosystems. Shi et al [9] found the similar variation trend that leaf N concentrations increased with MAT under low temperature (MAT , 8.5uC) along an altitudinal gradient of Mount Gongga on the eastern Tibetan Plateau. Other study reported that temperature had no effects on leaf concentrations, but phylogenetic variation was the key factor that affected the leaf N concentrations at the biome scale [5]. Wheather the temperaturebiogeochemical hypothesis (TBH) could be used to explain the relationship between leaf N concentrations and MAT in alpine area is still a controversial issue on account of few plant data contained in previous studies [3,4,9]. The underlying mechanism of temperature on regulating leaf N in cold environment deserves a further discussion

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Conclusion