Allometric relationships for eight species of 4–5 year old nitrogen-fixing and non-fixing trees

PLOS ONE RESEARCH ARTICLE Allometric relationships for eight species of 4–5 year old nitrogen-fixing and non-fixing trees K. A. Carreras Pereira ID1*, Amelia A. Wolf2, Sian Kou-Giesbrecht1,3,4, Palani R. Akana1, Jennifer L. Funk5, Duncan N. L. Menge ID1 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 1 Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, New York, United States of America, 2 Department of Integrative Biology, University of Texas Austin, Austin, Texas, United States of America, 3 Canadian Centre for Climate Modelling and Analysis, Victoria, British Columbia, Canada, 4 Department of Earth and Environmental Sciences, Dalhousie University, Halifax, Nova Scotia, Canada, 5 Department of Plant Sciences, University of California, Davis, Davis, California, United States of America * Abstract OPEN ACCESS Citation: Carreras Pereira KA, Wolf AA, KouGiesbrecht S, Akana PR, Funk JL, Menge DNL (2023) Allometric relationships for eight species of 4–5 year old nitrogen-fixing and non-fixing trees. PLoS ONE 18(8): e0289679. https://doi.org/ 10.1371/journal.pone.0289679 Editor: Sushanta Kumar Naik, ICAR Research Complex for Eastern Region, INDIA Received: December 15, 2021 Accepted: July 25, 2023 Published: August 21, 2023 Copyright: © 2023 Carreras Pereira et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are in a publicly available repository at DOI 10.5061/ dryad.2bvq83bvk. Funding: This material is based on work supported by the National Science Foundation under grant nos. DEB-1457650, DEB-1457444, and IOS2129542. S.K.-G. was supported by the Natural Sciences and Engineering Research Council. P.R.A. was supported by the National Science Foundation Graduate Research Fellowship Program under grant no. DGE 2036197. The funders had no role in Allometric equations are often used to estimate plant biomass allocation to different tissue types from easier-to-measure quantities. Biomass allocation, and thus allometric equations, often differs by species and sometimes varies with nutrient availability. We measured biomass components for five nitrogen-fixing tree species (Robinia pseudoacacia, Gliricidia sepium, Casuarina equisetifolia, Acacia koa, Morella faya) and three non-fixing tree species (Betula nigra, Psidium cattleianum, Dodonaea viscosa) grown in field sites in New York and Hawaii for 4–5 years and subjected to four fertilization treatments. We measured total aboveground, foliar, main stem, secondary stem, and twig biomass in all species, and belowground biomass in Robinia pseudoacacia and Betula nigra, along with basal diameter, height, and canopy dimensions. The individuals spanned a wide size range (<1–16 cm basal diameter; 0.24–8.8 m height). For each biomass component, aboveground biomass, belowground biomass, and total biomass, we determined the following four allometric equations: the most parsimonious (lowest AIC) overall, the most parsimonious without a fertilization effect, the most parsimonious without canopy dimensions, and an equation with basal diameter only. For some species, the most parsimonious overall equation included fertilization effects, but fertilization effects were inconsistent across fertilization treatments. We therefore concluded that fertilization does not clearly affect allometric relationships in these species, size classes, and growth conditions. Our best-fit allometric equations without fertilization effects had the following R2 values: 0.91–0.99 for aboveground biomass (the range is across species), 0.95 for belowground biomass, 0.80–0.96 for foliar biomass, 0.94–0.99 for main stem biomass, 0.77–0.98 for secondary stem biomass, and 0.88–0.99 for twig biomass. Our equations can be used to estimate overall biomass and biomass of tissue components for these size classes in these species, and our results indicate that soil fertility does not need to be considered when using allometric relationships for these size classes in these species. PLOS ONE | https://doi.org/10.1371/journal.pone.0289679 August 21, 2023 1 / 26 PLOS ONE 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. Allometric relationships for nitrogen-fixing and non-fixing trees 1. Introduction Allometric equations facilitate the estimation of important but labor-intensive tree properties (e.g., total biomass and its components) from easily measured tree properties (e.g., diameter), and therefore are a key tool for ecosystem ecology, forest ecology, forestry, and other fields [1, 2]. Well-calibrated allometric equations are available for numerous species [e.g., 3] but not for many others. They are much more common for aboveground tissues than for belowground tissues and, within aboveground tissues, for total or woody tissues than for foliage or different size classes of woody tissues [4, 5] (but see [6–8]). The relative paucity of biomass data for belowground tissues, foliage, and different size classes of woody tissues likely stems from logistical challenges, but these data are important. For instance, understanding the contribution of roots, which account for a significant fraction of total tree biomass (an average of 20% globally [9]), is critical for quantifying soil carbon stocks [10, 11]. Foliage, twigs, small branches, and main stems have very different nutrient contents [12], so accurately modeling nutrient budgets depends on an ability to estimate them separately. Theory [13–17] suggests that trees allocate biomass differently as nutrient availability declines. Some studies show that plants allocate more to roots in infertile conditions [8, 16, 17], though the details vary. Allometric relationships within aboveground tissues can also change across nutrient conditions. For example, adaptive dynamics theory predicts more allocation to wood as opposed to foliage as fertility increases [17]. Empirically, allometric relationships vary with nutrient availability for some species, but not all. For example, Urban et al. [18] found that Norway spruce trees were shorter for a given diameter in a nutrient-poor site than in a nutrient-rich site, whereas Douglas fir trees had similar height-diameter relationships in both sites. Trees that form symbioses with nitrogen (N)-fixing bacteria (hereafter, “N-fixing trees”) occupy an interesting role in this discussion. Symbiotic N-fixing trees are commonly planted during reforestation efforts, particularly on marginal soils [19, 20], due to their ability to bring newly fixed N into ecosystems. Their rapid growth on marginal sites provides carbon sequestration [21] and soil regeneration [22–25]. Aside from resto (...truncated)