Lower nodule biomass with increased nitrogenase efficiency in Robinia pseudoacacia seedlings when grown under low soil p
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Lower nodule biomass with increased nitrogenase efficiency in Robinia pseudoacacia seedlings when grown under low soil phosphorus conditions Lindsay A. McCulloch1 · Stephen Porder1 Received: 28 May 2020 / Accepted: 16 September 2020 © The Author(s) 2020 OPEN
Abstract Symbiotic nitrogen (N) fixation is the largest non-anthropogenic N input to many terrestrial ecosystems. The energetic expense of symbiotic N fixation suggests soil phosphorus (P) availability may regulate symbiotic nitrogen fixation directly through nodule development and function, and/or indirectly through plant growth. Since P availability is heterogenous in the landscape, we sought to understand if symbiotic nitrogen fixation responds to both P availability and heterogeneity. To test how P availability affects symbiotic nitrogen fixation, we grew Robinia pseudoacacia seedlings under high −2) conditions. Soil P heterogeneity was simulated by splitting roots into soil patches (8.1 g P m −2) and low (0.2 g P m receiving P or no-P fertilizer. At the whole plant level, P availability limited seedling and nodule biomass. However, the low P treatment had higher nitrogenase efficiency (acetylene reduced (AR) g−1 nodule; a nodule efficiency proxy). High P seedlings had significantly more root and nodule biomass in the patches directly receiving P fertilizer, but patch proliferation was absent in the low P treatment. AR g−1 seedling did not differ between P treatments, suggesting P indirectly limited symbiotic nitrogen fixation through plant growth, rather than directly limiting symbiotic nitrogen fixation. This relatively consistent AR g−1 seedling across treatments demonstrates the ability of seedlings to respond to low P conditions with increased nitrogenase efficiency. Keywords Split-root · nutrient patches · Symbiotic nitrogen fixation · Black locust · P fertilization
1 Introduction The factors that determine when and where symbiotic nitrogen fixation (SNF) occurs have been an area of inquiry for decades, and influence the productivity of both agricultural and natural ecosystems [1–3]. In association with their host plants, symbiotic nitrogen (N)-fixing bacteria convert atmospheric N into a form of readily available N for plant-use, adding reactive N to ecosystems through the plants they help to fertilize.
N-fixing Rhizobia reside in root nodules on plants in the Fabaceae family (hereafter legumes) and receive carbon (C) in exchange for N [4]. While this relationship has been explored for over a century [5], and the rate at which SNF occurs varies widely in response to abiotic factors, such as soil nutrient, light and water availability [6–12]. The availability of these resources in the environment is often heterogenous [13–18]. An understanding how legumes and SNF rates are influenced by this resource
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42452-020-03518-z) contains supplementary material, which is available to authorized users. * Lindsay A. McCulloch, [email protected]
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