The lamina is the primary site of photosynthetic activity and carbohydrate synthesis, while the petiole is a cantilevered structure that supports and supplies laminas, additionally playing the role of supporting static gravity and resisting external dynamic tension. The leaf is composed of a lamina and petiole that is an essential component of the twig. The relationship also exists within the leaf. In determining the relationship between twigs and leaves, the thicker the twigs, the larger the components (leaves, inflorescences, and fruits), and larger leaf biomass. Some studies have suggested that the leaf mass scales isometrically with the stem mass (SM) in twigs, and the twig size does not significantly affect the allocation pattern. Twigs and leaves are important transport and material production organs that play a critical role in carbon acquisition, allocation strategy, and water transport efficiency. The trade-off relationship between twig and leaf size is the core phenomenon in the study of plant life-history strategies. Plants invest too many resources in a particular functional trait, and the corresponding traits will be reduced. Because the available resources are limited, plants use resources more efficiently by adjusting traits. Plants are sessile and grow in a specific environment. Therefore, revealing the relationships of the internal components of laminas, petioles, and stems on the current-year twig is vital for understanding the resource allocation strategies of plants under environmental stress. The current-year twig can reflect the response of plants to the environment more accurately than the older parts of the plant. The current-year twig is the most viable part of the plant branching system, its internal nutrient transformation rate is high, and its trait response is easily observed. The allometry estimates how one variable scales against another and tests hypotheses about the nature of this relationship and how it varies across samples.

The allometric function has been applied to describe plant biomass allocation. Research on the effects of heterogeneous habitats on biomass allocation is crucial for understanding the plant life-history strategies. Twig biomass allocation is an important driving factor for capturing the net carbon affecting the phenotype and function of plant leaves and twigs and is sensitive to environmental change. Our results indicated that inhabitats influenced the twig traits and biomass allocation and within-leaf biomass allocation are strategies for plants to adapt to volcanic heterogeneous habitats. However, within the leaf, individual lamina mass (ILM) scaled isometrically with respect to individual petiole mass (IPM) in kipuka and the lava platform, but ILM scaled allometrically to IPM in Shankou lake. TLAM and SM scaled allometrically with respect to TM, while the normalization constants of the lava platform differ significantly between kipuka and Shankou lake, which showed that under certain TM, leaves gain more biomass in the lava platform. The results showed that the leaf number, total lamina mass (TLAM), stem mass (SM), and twig mass (TM) were significantly different between the three habitats and were greatest in kipuka with abundant soil nutrients. platyphylla in Wudalianchi volcanic kipuka, the lava platform, and Shankou lake in northeastern China using standardized major axis analyses. We aimed to test whether twig biomass allocation, within-leaf biomass allocation, and the size-number trade-off of Betula platyphylla would be influenced. Understanding the response of biomass allocation in current-year twigs is crucial for elucidating the plant life-history strategies under heterogeneous volcanic habitats.

Twig and leaf