Soil nutrients rather than leaves affect biomass allocation to absorptive fine roots at individual tree level in Populus deltoides

Aims How soil nutrients affect absolute and relative production of major organs and the internal relationships between two resource-acquiring organs (absorptive fine roots (AFR) and leaves) at tree level remain unclear. Methods To address these questions, we assessed soil nutrients, leaf, stem and branch (Stem-Br), coarse root (CR), transport fine root (TFR) and AFR biomass and production, leaf litterfall and AFR and TFR mortality of 12 trees in a young Populus deltoides plantation. Results Biomass, production and mortality of AFRs were significantly related to those of TFRs but were independent of those of leaves, CRs and Stem-Brs. Total production had significant relationships with relative production of AFRs and TFRs. Spatial variations in soil nutrient gradients significantly altered the production of leaves, Stem-Brs and CRs but did not affect AFR and TFR production. By contrast, the relative production of AFRs and TFRs were significantly related to soil nutrients. Conclusions AFR and TFR growth and death are tightly coupled at individual tree level. AFRs do not interact with leaves in a complimentary or inverse fashion in terms of biomass, production and mortality. Lower soil nutrients made Populus deltoides allocate proportionately more biomass to AFRs at the cost of leaf and Stem-Br production. Such a change significantly reduced whole-tree production. The significant relationships between AFRs and TFRs have great potential to accurately estimate C cycling through fine roots.