Examples of positive effects of biodiversity on ecosystem functions have kept accumulating in the last two decades, and functional traits are considered suitable tools to explain their underlying mechanisms. However, traits are rarely studied at the scale where these mechanisms (e.g., complementarity) are likely to originate, that is, between two interacting individuals. In an 18-month greenhouse experiment, we investigated how species diversity (i.e., monospecific or heterospecific tree pairs) affects within-individual leaf traits expression and variation and how this effect is modified by soil conditions. While resource addition through phosphorus fertilization partly strengthened the diversity effects, inoculation of soil microbiota (potentially leading to increased resource accessibility) resulted in counter effects. Hence, in contrast to our expectations, we did not find synergistic effects of the two soil treatments, but we found distinct effects on species following an acquisitive or conservative growth strategy. Overall, our study showed that the effect of species diversity on young trees’ adaptability and resource-use strategy needs to be considered alongside soil biotic and abiotic aspects. The influence of soil conditions on species diversity effects is essential to understand mechanisms behind complementarity at the individual level, which ultimately translate to the community scale.
Figure 1. Expected trait acquisitiveness (a) and trait variation (b) of a focal tree in response to increasing species diversity (from mono to heterospecific tree neighbour; dashed line), with inoculation of the native soil microbiota (+ Ino; solid line), phosphorus fertilization (+ P; solid line), or both soil treatments together (+ Ino and + P; double line). (c) Experiment design.
Figure 2. Effect of soil inoculation with microbiota (a, b), phosphorus fertilization (c; d) and the interaction of both soil treatments (e) on leaf traits.
Figure 3.Effect of the tree species pair diversity (mono- or heterospecific TSP; (a) and its interaction with soil inoculation (b), phosphorus fertilization (c, d) and both soil treatments (e) on leaf traits.
Figure 4. Effect of soil inoculation (a, b), phosphorus fertilization (c, d, e) and the interaction of both soil treatments (f, g, h) on leaf trait variation.
Figure 5. Effect of the tree species pair diversity (mono- or heterospecific TSP) interaction with soil inoculation (a, b, c), phosphorus fertilization (d) and both soil treatments (e, f) on leaf trait variation.
Literature:
Andréa Davrinche*, Sylvia Haider. 2024. Soil conditions modify species diversity effects on tree functional trait expression. Scientific Reports. 14(1): 17114. https://www.nature.com/articles/s41598-024-67512-w
