6/19/2023 0 Comments Twig and leafTherefore, it is not unreasonable to speculate that total leaf biomass might scale isometrically with respect to total stem biomass at the twig level. For example, an isometric relationship is reported for the scaling of leaf and stem growth (i.e., G L ∝ G S) ( Niklas and Enquist, 2002b). Prior investigations using this formula have focused not only at the whole-plant level ( Enquist and Niklas, 2002 Cheng and Niklas, 2007 Chave et al., 2014 Paul et al., 2016), but also at the level of individual twigs (e.g., Westoby and Wright, 2003 Sun et al., 2006 Xiang et al., 2009a Yang et al., 2015). Generally, the allocation of biomass to leaves, stems, and roots can be described using a scaling function ( Enquist and Niklas, 2002), which takes the general mathematical formula M a = β M b α, where M a and M b are the biomass of different organs, β is the normalization constant, and α is the scaling exponent. Consequently, quantifying the scaling relationships between leaf and stem biomass, and the relationship between stem diameter and length is critical to our understanding of a broad spectrum of important ecological phenomena ( Westoby and Wright, 2003 Niklas and Spatz, 2004 Sun et al., 2006 Olson et al., 2009 Xiang et al., 2009a). The hydraulic architecture of mature twigs also provides for the efflux of photosynthates and influx of water and nutrients. Regardless of their form, size, or longevity, the leaves on current-year shoots (i.e., twigs) provide the photosynthetic machinery that drives annual growth, whereas the stems of twigs sustain the static and dynamic mechanical forces leaves experience by gravity and wind (i.e., self-loading and wind induced drag forces, respectively) ( Niklas, 1992a). We speculate that this rule emerges because stem diameter serves as a proxy for the amount of resources supplied per unit cross section to developing leaves and for the flow of photosynthates from mature leaves to the rest of the plant body. The scaling relationship between leaf biomass and stem diameter in twigs is insensitive to differences in species composition, elevation, or forest type. These results help to identify a general rule that operates at two different levels of biological organization (twigs and whole trees). Across the 64 species, from twigs to individual trees, leaf biomass scaled approximately as the 2.0-power of stem diameter (but not for stem length or leaf number). Our results revealed isometric relationship between leaf and stem biomass on twigs despite differences in forest communities and despite changes in environmental factors along an elevational gradient. We also compared the scaling relationships we observed with biomass allocation patterns reported at the whole tree level. To understand how twig architecture (i.e., current year leaves, and stem diameter and length) affects stem diameter and length, and leaf number and biomass, we examined the twigs of 64 woody species collected from three forest types along an elevational gradient in the Wuyi Mountains, Jiangxi Province, China. The relationship between leaf and stem biomass as well as the relationship between leaf biomass and stem length and diameter are important to our understanding of a broad range of important plant scaling relationship because of their relationship to photosynthesis and thus growth.
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