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. 2023 Aug 21;18(8):e0289679.
doi: 10.1371/journal.pone.0289679. eCollection 2023.

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

K A Carreras Pereira  1 , Amelia A Wolf  2 , Sian Kou-Giesbrecht  1   3   4 , Palani R Akana  1 , Jennifer L Funk  5 , Duncan N L Menge  1
Affiliations

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

K A Carreras Pereira et al. PLoS One. .

Abstract

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.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Size distributions of eight tree species.
(a) Aboveground biomass, (b) belowground biomass, (c) basal diameter, and (d) height are shown for each species. Each symbol represents one individual tree. Color and symbol indicate the fertilization treatment, as indicated in the legend. Data were jittered horizontally for visual clarity. Vertical dotted lines separate the points to clarify which points correspond to which species.
Fig 2
Fig 2. Allocation to aboveground biomass across tree size.
(a) Robinia pseudoacacia and (b) Betula nigra. Each symbol represents an individual tree. Colors and symbols indicate treatments, as in Fig 1. Linear regression equations and p values are shown.
Fig 3
Fig 3. Allocation to foliage across tree size.
The fractions of aboveground biomass comprised of foliage are shown for (a) Robinia pseudoacacia, (b) Betula nigra, (c) Gliricidia sepium, (d) Casuarina equisetifolia, (e) Psidium cattleianum, (f) Acacia koa, (g) Morella faya, and (h) Dodonaea viscosa. Each symbol represents one individual tree. Colors and symbols indicate treatments, as in Fig 1. Linear regression equations and p values are shown.
Fig 4
Fig 4. Models for aboveground biomass (AGB) of Robinia pseudoacacia.
(a) The best fit model according to AIC, which models aboveground biomass as a function of the square of basal diameter (D, in cm) multiplied by height (H, in m), with different parameters for each treatment. Colors and symbols of the points indicate treatments, as in Fig 1. Colors of curves are analogous: blue is the control; orange is the +10 g N m−2 y−1 treatment; red is the +15 g N m−2 y−1 treatment; and purple is the +15 g N m−2 y−1 +15 g P m−2 y−1 treatment. (b) Aboveground biomass as a function of basal diameter (D) only. Colors and symbols of the points indicate treatments, as in Fig 1. The fit is shown in black because it does not depend on treatment. The fits shown on the panels are the same as in Tables 3 and 6.
Fig 5
Fig 5. Diameter-driven allometric relationships of species and functional types (Nitrogen-fixing vs. non-fixing tree species).
(a) Aboveground biomass is plotted as a function of diameter (D, in cm) (b) Foliar biomass is plotted as a function of diameter.
Fig 6
Fig 6. Comparison of our allometric equations to other published equations.
We used the input variables (basal diameter, tree height, canopy dimensions) from our trees to estimate biomass components from our equations and from equations from (a) Böhm et al. (2011) for Robinia pseudoacacia, (b) Harrington & Fownes (1993) for Gliricidia sepium, and (c) Xue et al. (2016) for Casuarina equisetifolia. Each symbol represents one (a) Robinia pseudoacacia, (b) Gliricidia sepium, or (c) Casuarina equisetifolia tree from our dataset. The 1:1 line is plotted in each panel (dotted) along with a linear regression (solid; equations and adjusted R2 listed on the figure). See methods for the details of these comparisons.
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Grants and funding

This material is based on work supported by the National Science Foundation under grant nos. DEB-1457650, DEB-1457444, and IOS-2129542. 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 study design, data collection and analysis, decision to publish, or preparation of the manuscript.