A new study published in Plant, Cell & Environment on July 9 unravels divergent and convergent responses of two sympatric oaks via traits integration and adaptive strategies to climate change. Their distinct trait plasticity and phenotypic integration under unfavorable climate might lead to niche differentiation and complex community assembly.

Exploring the coexistence mechanisms of sympatric closely related species along climate gradients is crucial to predicting shifts in species distribution and community assembly. Previous studies mainly focus on the differentiation of specific functional traits, but scarcely explore trait variability and its coordination with plant trait networks and ecological strategies along climatic gradients, limiting the understanding of coexistence mechanisms in sympatric species with wide geographical ranges.

To address this question, researchers from the Restoration Ecology Group in South China Botanical Garden of the Chinese Academy of Sciences carried out a study on the interspecific and intraspecific variations in plant functional traits, the topology of plant trait networks, and the ecological strategies of two sympatric oak species (Quercus acutissima and Q. variabilis) across temperate and subtropical forests in China.

They found that nine of the 15 studied functional traits differed significantly between the two oak species. Although the two species showed similar levels of intraspecific variability, they exhibited divergent patterns of trait-level variability. Specifically, Q. acutissima showed lower morphological variability but higher physiological variability than Q. variabilis.

The researchers further found that the connectivity and complexity of trait correlation networks in the two oaks changed similarly across favorable temperature ranges but diverged under low and high temperatures and along precipitation gradients. Both species adopted competitive and stress-tolerant ecological strategies; however, Q. variabilis was more competitive but less stress-tolerant than Q. acutissima when growing at their distribution edges.

These findings suggest that sympatric oaks may achieve local divergent and convergent adaptation by modifying trait-level plasticity and trait integration along climate gradients, potentially promoting greater niche differentiation and shaping complex community assembly.

Plant trait networks of Quercus acutissima and Q. variabilis, and variation in edge density and modularity of plant trait network along climate gradients. (Image by LAI Yuan)