Abstract
Key messageSlopes and intercepts of allometric equations for organs’ biomass varied among half-sib families of Norway spruce and between age categories in a family-dependent manner. Genetic variation should be accounted for when applying allometric analysis to mixtures of genetic groups.ContextGenetic variation in relationships among plant biomass components was rarely addressed in trees, though depending on deployment strategies in tree improvement programs, variation among genetic groups in plant organs’ growth rates, and thus biomass allocation, would affect forest growth and carbon balance.AimsWe investigated growth and biomass distribution in Norway spruce (Picea abies [L.] H. Karst) half-sib families. We assumed invariance among families in allometric relationships, and stability in growth rates of different organs between ages 2 and 8 years in the subset of those families. We also tested for ontogenetic trend in allometry using the independent dataset of biomass at age 21 years.MethodsWe analyzed allometric relationships among plant components using standardized major axis regression.ResultsSlopes and intercepts of allometric relationships varied among families, indicating variation in both organs’ growth rates and biomass partitioning at a given plant size. Variation in scaling exponents between age categories was also dependent on the family and plant organ considered.ConclusionVariation in slopes of allometric relationships indicates that a single scaling coefficient should not be applied when different genetic groups are compared. For the interpretation of age effect on biomass partitioning, both slopes and intercepts of allometric relationships should be examined.
Highlights
Studies of biomass partitioning in plants are a way to explore inherent growth patterns and to examine how those growth patterns and biomass allocation vary in response to environmental stimuli
To further our understanding of allometric relationships governing biomass partitioning in trees, we investigated growth and biomass distribution among half-sib families within a single population of Norway spruce
We hypothesized that families would differ in biomass distribution at the same plant size, but not in slopes of allometric relationships relating biomass of different plant components
Summary
Studies of biomass partitioning in plants are a way to explore inherent growth patterns and to examine how those growth patterns and biomass allocation vary in response to environmental stimuli. The allometric equation is more conveniently used with the log-transformed data: log Y = log a + b log X, where log a becomes the Y intercept and b becomes the slope of the log-log relationship The latter equation often takes a linear form and its parameters may be estimated using the appropriate line-fitting procedure (Warton et al 2006; Smith 2009). A useful feature of the allometric approach to biomass partitioning is that it implicitly accounts for differences in plant size. Because the strength of the allometric relationships (R2) depends on the range of plant sizes compared, it has been advocated to combine both approaches in studies of plant biomass partitioning (Poorter and Sack 2012; Poorter et al 2015)
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