Leaves and roots may differ in nitrogen (N), phosphorus (P) and N:P stoichiometry, which can influence plant growth and ecosystem functioning. As compared to leaves, however, relatively little is known about the N versus P scaling relationship and N:P stoichiometry in root systems, particularly in fine roots. We used a global dataset comprising 1,890 observations for a total of 763 terrestrial plant species in 123 families (spanning 433 sites world‐wide) to examine live fine root N and P concentrations and stoichiometry, and to determine the scaling of N versus P within and across different plant groups and ecosystems. The global geometric mean values of fine root N and P concentrations and N:P ratios were 10.84 mg/g, 0.94 mg/g and 11.55, respectively. Fine root N and P concentrations and N:P ratios varied both within and across plant groups and ecosystems. A 0.82‐power law described the scaling of fine root N with respect to P across the entire dataset and for major plant phylogenetic and functional groups; however, the numerical value of the N versus P scaling exponent declined from the tropics to higher latitudes and varied significantly at different local sites. Soil nutrient account for much of the variation observed in the scaling of fine root N versus P concentration at different local sites. This study advances our knowledge about limiting resource allocation strategies in below‐ground organs and has important implications for modelling plant growth at local, regional and global levels. A free Plain Language Summary can be found within the Supporting Information of this article.

Aim Fine roots play an important role in biogeochemical cycling in terrestrial ecosystems. However, our understanding of large scale biogeographical patterns and drivers of fine‐root C:N:P stoichiometry is extremely limited. Location China. Methods We compiled data for fine‐root carbon (C), nitrogen (N) and phosphorus (P) concentrations at 165 sites across China to explore large‐scale biogeographical patterns and drivers of fine‐root C:N:P stoichiometry. Results The geometric means of fine‐root C, N, and P concentrations were 448.81, 10.73, and 0.9 mg/g, respectively, whereas C:N, C:P, and N:P ratios were 41.84, 508.32, and 11.73, respectively. The fine‐root elemental concentrations and their ratios varied widely among plant groups and biomes, and showed clear latitudinal and longitudinal trends, as a consequence of differences in climate, soil, and plant type. However, plant type was the largest contributor to the total variance in fine‐root C, N, and P and their ratios compared to climate factors or soil features. Main conclusions The data reveal the existence of broad biogeographical patterns of fine‐root C:N:P stoichiometry in China. These results advance our knowledge about the biogeochemical cycling of fine roots.

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This study was conducted to evaluate the effects of mercury stress on growth, photosynthesis and mercury accumulation in different cultivars of a non-food energy crop, Jerusalem artichoke, and to screen appropriate cultivars for their efficacy in the phytoremediation of mercury (Hg2+) contaminated soil. Cultivars LZJ033 (high above-ground biomass and nutrient content, and strongly sexual reproduction) and LZJ119 (a long period of vegetative growth) exhibited more tolerance to mercury stress than LZJ047 (the highest tuber yield and total sugar content). The lines LZJ119 and LZJ047 showed delays in emergence time of about four weeks, and LZJ047 exhibited the highest mortality rate, 85.19%, under treatment with 10 mg kg-1 mercury. The MDA (malondialdehyde) content increased whereas and the Pn (net photosynthetic rate), Fv∕Fm (the maximum quantum yield of PSII photochemistry) and chlorophyll content decreased in response to mercury stress. The stem diameter, stem biomass and photosynthetic rate of Jerusalem artichoke showed some modest increases in response to mercury stress and exhibited hormesis at least 1 mg kg-1 mercury treatment. Overall, LZJ119 produced more biomass under mercury stress, whereas LZJ033 exhibited a greater capacity for mercury bioaccumulation. Accordingly, LZJ119 may be a good candidate cultivar for use in cases of moderate—low mercury contamination, whereas LZJ033 may be a better candidate under conditions of high mercury contamination. When Jerusalem artichoke was cultivated in mercury contaminated soil, it not only removed the mercury from soil but also produced large amounts of tubers and shoots which could be used as feedstock for the production of bioethanol.