Background and aims: The “diminishing returns” hypothesis postulates that the scaling exponent governing the lamina area versus lamina mass scaling relationships has, on average, a numerical value less than one. Theoretically, a similar scaling relationship may exist at the twig level. However, this possibility has not been explored empirically. Methods: We tested both hypotheses by measuring the lamina area and mass, petiole mass of individual leaves, and the total foliage area and stem mass of individual current-year shoots (twigs) of 64 woody species growing in three characteristic forest community types: (1) Evergreen broad-leaved, (2) mixed coniferous and broad-leaved, and (3) deciduous. Key results: The results demonstrate that lamina area vs. mass and lamina area vs. petiole mass differ significantly among the three forest types at both the individual leaf and twig levels. Nevertheless, the scaling exponents of lamina area vs. mass were <1.0 in each of the three community types, as were the corresponding exponents for lamina area vs. petiole mass, both within and across the three community types. Similar trends were observed at the individual twig level. The numerical values of the scaling exponent for lamina area vs. petiole mass and total foliage area vs. stem mass per twig decreased with increased elevation. Conclusions: These data support the “diminishing returns” hypothesis at both the individual leaf level and at the individual twig level, phenomena that can inform future inquiries into the mechanistic basis of biomass allocation patterns to physiological (leaf) and mechanical (stem) plant organs.

Leaf respiration in the light (R_light) is crucial for understanding the net CO₂ exchange of individual plants and entire ecosystems. However, R_light is poorly quantified and rarely discussed in the context of the leaf economic spectrum (LES), especially among woody species differing in plant functional types (PFTs) (e.g., evergreen vs. deciduous species). To address this gap in our knowledge, R_light, respiration in the dark (R_dark), light-saturated photosynthetic rates (A_sat), leaf dry mass per unit area (LMA), leaf nitrogen (N) and phosphorus (P) concentrations, and maximum carboxylation (V_cmax) and electron transport rates (J_max) of 54 representative subtropical woody evergreen and deciduous species were measured. With the exception of LMA, the parameters quantified in this study were significantly higher in deciduous species than in evergreen species. The degree of light inhibition did not significantly differ between evergreen (52%) and deciduous (50%) species. R_light was significantly correlated with LES traits such as A_sat, R_dark, LMA, N, and P. The R_light vs. R_dark and N relationships shared common slopes between evergreen and deciduous species, but significantly differed in their y-intercepts, in which the rates of R_light were slower or faster for any given R_dark or N in deciduous species, respectively. A model for R_light based on three traits (i.e., R_dark, LMA and P) had an explanatory power of 84.9%. These results show that there is a link between R_light and the LES, and highlight that PFTs is an important factor in affecting R_light and the relationships of R_light with R_dark and N. Thus, this study provides information that can improve the next generation of terrestrial biosphere models (TBMs).