The Impact of Light Availability on the Functional Traits of <i>Quercus Robur</i> L. and <i>Acer Platanoides</i> L. First-Year Seedlings by Direct and Indirect Methods

The resource strategy of seedlings is an important aspect for understanding the adaptation of trees at this ontogenetic phase to abiotic changes. In this study, we sought to determine the patterns of response of functional traits of a shade-tolerant (Acer platanoides) and a shade-intolerant (Quercus robur) species along natural environmental light gradients. We conducted trait-based analyses at both individual and community levels using direct (leaf area index [LAI] and diffuse noninterceptance [DIFN]) and indirect (light coefficient, derived from Ellenberg values [LC]) methods in the Arboretum at Kórnik (Poland). Differences between the two species were found for some variables. Analysis of phenotypic plasticity indices of leaf, stem, and root traits of seedlings had high values ​​for both species. The values of plasticity indices of A. platanoides root traits were lower compared to the corresponding traits for Q. robur. Relationships between measures obtained from individual-level trait data were stronger than relationships with measures obtained from community-level trait data. The data obtained from the direct method, which included light measurements both at the community level (experimental plots) and at the individual level (seedlings), revealed the closest relationships between functional traits of seedlings and light changes at the individual level trait data for both species. Correlation links between LAI and leaf (leaf mass per area; specific leaf area) and stem (specific stem length; stem mass fraction) traits were less tight for Q. robur compared to A. platanoides. The indirect Ellenberg indicator analysis revealed relationships between LC and leaf mass per area, and stem-to-root ratio of seedlings based on community-level trait data. Close relationships between LC and leaf mass fraction and specific leaf area were not established, in contrast to LAI and DIFN. The closest relationships, representing among traits within the same organ system, and links, describing interactions between traits of different organ systems, were established at the community-level trait data.