Coupled hydrological niche segregation and the leaf economic spectrum explain coexistence of woody species in a natural secondary forest

By contrasting water sources and diverging in leaf economic traits, plants
regulate and balance their use of water, carbon, and nutrient resources,
thereby potentially promoting species coexistence. However, how these
strategies affect species coexistence is unclear. We quantified the
relative contributions of different water sources (topsoil water, 0–20 cm;
subsoil water, 20–200 cm), intrinsic water use efficiency (WUEi), key LES
traits, and the importance value index (a proxy for species dominance),
across the ten coexisting plant species in a natural secondary forest at
Ziwuling Mountains of the Loess Plateau (LP), Northwest China. Our results
showed the large variability in water source utilisation, WUEi, leaf N, P
contents, and specific leaf area (SLA) among species, indicating diverse
resource use strategies. Differences in water sources resulting in varying
degrees of water competition between species, ranging from 47 to 81%. The
water source utilised by plants was coordinated with the LES. Species that
relied on topsoil water, characterised by nutrient-rich but variable water
supply, adopted acquisitive strategies, exhibiting high leaf N, P contents
and SLA. In contrast, species relying on subsoil water, which provides
relatively low-nutrient availability but a stable water supply, adopted
conservative strategies, displaying opposite traits. Notably, species with
conservative strategies dominated in the community. Synthesis. Our
findings highlight a tight coupling between plant water sources and the
LES, which jointly influence species coexistence and dominance. Our study
evaluated the persistence and coexistence strategies of the ten species in
a natural secondary forest, which serves as a reference for the tree
species selection of afforestation in the LP, or similar regions.