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

PLOS ONE, Dec 2019

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.

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

Wu J (2014) Stoichiometry of Root and Leaf Nitrogen and Phosphorus in a Dry Alpine Steppe on the Northern Tibetan Plateau. PLoS ONE 9(10): e109052. doi:10.1371/journal.pone.0109052 Stoichiometry of Root and Leaf Nitrogen and Phosphorus in a Dry Alpine Steppe on the Northern Tibetan Plateau Jiangtao Hong 0 Xiaodan Wang 0 Jianbo Wu 0 Liping Zhu, Institute of Tibetan Plateau Research, China 0 1 Institute of Mountain Hazards and Environment, Chinese Academy of Sciences , Chengdu , China , 2 University of Chinese Academy of Sciences , Beijing , China 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 g21, 0.60 mg g21 and 23.40, respectively. The mean leaf N and P concentrations and the N:P ratio were 23.20 mg g21, 1.38 mg g21, 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 temperaturebiogeochemical 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. - Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its Supporting Information files. Funding: This study was supported by the Western Action Plan Project of the Chinese Academy of Sciences (Grant No. KZCX2-XB3-08), the Strategic Pilot Science and Technology Projects of the Chinese Academy of Sciences (Grant No. XDB03030505). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Nitrogen (N) and phosphorus (P) are two essential elements in plants, both playing a critical role in plant function and most ecosystem processes [1]. A number of studies have reported species-specific differences (growth form, physiology, life history, etc.) and site-specific differences (temperature, precipitation, solar radiation, etc.) that account for much of the variability in plantnutrient concentrations on large scales [26]. Temperature could be an important factor that drive the recirculation of nutrients in terrestrial ecosystems. Lower temperatures have depressing effect on microbial decomposition and mineralization of organic matter, which drastically reduce nutrient availability for plant [7,8]. Furthermore, low-temperature supressing of nutrient uptake by root and soil nutrients migration are also well known phenomena [8]. Thus, Reich and Oleksyn [3] assumed that the global leaf N concentrations generally increased with the mean annual temperature (MAT) when the temperature was below 510uC (the temperature-biogeochemical hypothesis). 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. However, 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]. In addition, the underlying mechanism of temperature on regulating leaf N in cold environment also deserves a further discussion. Although ecological stoichiometry has been studied in terrestrial pla (...truncated)


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Jiangtao Hong, Xiaodan Wang, Jianbo Wu. Stoichiometry of Root and Leaf Nitrogen and Phosphorus in a Dry Alpine Steppe on the Northern Tibetan Plateau, PLOS ONE, 2014, 10, DOI: 10.1371/journal.pone.0109052