Functional independence and integration between aboveground and belowground organs across four resource dimensions of...

Resource acquisition, transport, storage and utilization are key determinants of plant performance. Functional coordination and trade-offs are well explored in a conceptual framework of the plant economics spectrum, but how different organs coordinate across these resource dimensions to optimize whole-plant strategies remains largely unclear. We measured 47 functional traits of leaves, stems, coarse roots and fine roots in 33 co-occurring broadleaf tree species from temperate forests in Northeast China, to examine aboveground-belowground coordination across four above-mentioned resource dimensions. We found decoupling between leaves and fine roots in resource acquisition. No significant relationships were observed between leaf and fine root traits associated with acquisition efficiency (leaf photosynthetic rate-specific fine-root length; specific leaf area-specific fine-root area) or spatial occupation (leaf thickness-fine-root diameter; leafing intensity-fine-root branching intensity), supporting functional independence between the two resource-acquiring organs. In contrast, aboveground and belowground organs exhibited coordinated patterns in resource transport. Stem and coarse-root hydraulic efficiency showed positive correlations, and leaf venation density was positively correlated with coarse-root vessel diameters, which also increased with stem vessel diameters. Similar inter-organ relationships were found in resource storage. Nonstructural carbohydrate storage, especially starch, showed synchronized variation between stems and coarse roots, alongside their structural alignments in axial and total parenchyma fractions. As for resource utilization, leaf lamina mechanical resistance (punching force) was positively correlated with coarse-root mechanical strength (modulus of elasticity and rupture), which also positively covaried with corresponding modulus of elasticity and rupture in stems. Additionally, leaf and fine-root tissue density, stem and coarse-root wood density, and stem and coarse-root dry matter content all showed significant positive correlations. These coordinations collectively support the integrated whole-plant strategies in resource transport, storage and utilization. Our work reveals aboveground-belowground specialization and integration patterns, advancing the understanding of whole-plant functioning and its underpinning mechanisms across deciduous broad-leaved species in temperate forests.