Biological scarification of <i>Erythrina crista-galli</i> : germination responses, performance costs, and implications for riparian forest restoration

BACKGROUND AND AIMS: Restoration of subtropical riparian forests is frequently constrained by limited seedling recruitment in altered environments, particularly in native legumes with physically dormant seeds. In Erythrina crista-galli, insect seed predation may act as biological scarification, potentially facilitating germination, but at the cost of seed viability and performance. This study compared biological scarification caused by insect predation with controlled mechanical scarification to evaluate their effects on germination, seedling establishment, and reserve mobilization. METHODS: Seeds were subjected to four treatments: intact control, biological scarification (insect-predated seeds), and mechanical scarification by scraping or perforation. Seed viability, imbibition, germination dynamics, membrane integrity, seedling growth under controlled and soil conditions, and carbohydrate and protein reserves were quantified. Multivariate analyses were used to integrate germination, growth, and biochemical responses. KEY RESULTS: Predation was largely detrimental: biologically scarified seeds absorbed water fastest but showed high inviability (∼86%), elevated electrical conductivity (membrane leakage), low germination (∼18%), and frequent abnormal seedlings. In contrast, mechanical scarification broke dormancy efficiently, yielding >90% germination, faster synchronization, and greater biomass. In soil, emergence ranked: scraping (77.7%) > perforation (61.1%) > biological (50%) ≈ control (44%). Protein levels remained stable, but carbohydrate dynamics diverged: biological scarification showed lower starch and final sucrose accumulation, contrasting with the consumption and mobilization in mechanical treatments. PCA clustered mechanical scarification with germination and biomass, whereas biological scarification associated with sucrose. CONCLUSIONS: Biological scarification costs outweigh its benefits in E. crista-galli. This study shows that dormancy release in physically dormant seeds is pathway-dependent, with biological scarification facilitating water entry but compromising physiological integrity and seedling performance. By demonstrating that different scarification routes generate distinct metabolic and developmental outcomes, our findings shift the view of dormancy break from a purely structural process to an integrated physiological filter, with implications for plant regeneration and restoration strategies.