Leaf biomechanical traits predict litter decomposability

Leaf biomechanical strength is important not only in plant defense
strategies but also in "after-life” effects—determining leaf-litter
decomposability. It is a composite metric that can be evaluated by
fracturing a leaf using multiple methods. However, such after-life effects
have not been systematically evaluated. We assessed 40 leaf
functional traits, including 12 biomechanical traits measured through
three standard tests (i.e., punch, tensile, and shearing tests) and
categorized as fracture length-, fracture area-, or mass-based traits, to
predict leaf-litter decomposition dynamics among 186 species from diverse
functional groups. Categorized as fracture length-based traits,
they outcompeted fracture area- and mass-based traits in predicting
decomposition rates, with “force to punch” emerging as the best predictor,
followed by “work to shear”. After incorporating all studied traits into a
multidimensional trait space, the first principal component axis accounted
for 44.3% of the total variation in decomposition rates, whereas excluding
biomechanical traits reduced the variation explained to
31.6%. The leaf’s inherent resistance properties independently
influenced litter decomposability beyond tissue density and lamina
thickness, rendering leaf mass per area an incomplete proxy for
biomechanical traits. Additionally, using the tensile force for leaves
with parallel veins would underestimate leaf-litter decomposition rates.
In contrast, focusing on punch force and shearing work as principal
biomechanical traits offers a promising research avenue for an improved
understanding of how leaf decomposability is determined. Synthesis. Our
results provide the first evaluation of leaf biomechanical traits from
three standard physical resistance tests as predictors of leaf-litter
decomposability. These biomechanical traits complement chemical,
structural, and morphological traits and should be more effectively
integrated into existing models to enhance our comprehension of the
leaf-litter decomposition process.