Ectomycorrhizal trees enhanced water-holding capacity in forest ecosystems in northeastern China

Improving water-holding functions is an important purpose of sustainable forest management. However, few studies have examined whether there are differences in water-holding capacities between the forests dominated by trees associated with different mycorrhizal types and what are the main factors leading to the differences. Here, we investigated seven parameters of water-holding capacities of soils, litter, and canopy interception in 210 forest plots (10 m × 10 m). The plots were equally divided into three forest types associated with mycorrhizal types, including AM plots (arbuscular mycorrhizal trees > 75% in dominance), ECM plots (ectomycorrhizal trees > 75%), and AM + ECM plots (between 25 and 75%). We calculated tree diversity (richness, Shannon–wiener index, Simpson index, evenness), community structure (diameter at breast height, height, under branch height, density, neighborhood comparison-U, uniform angle index-W, and mingling index-M), and soil physics (soil bulk density and field water content). The results showed that: (1) ECM-dominated communities increased 1.6–2.0-fold in the litter water-holding capacities than those of AM and AM + ECM. The canopy interception of the ECM community was the highest (0.97 mm), significantly higher than that of the AM + ECM community (0.58 mm). (2) The ECM community had lower field soil water-holding capacity (p < 0.05) but 42–78% higher soil non-capillary water capacity than that of AM and AM + ECM (p < 0.05). (3) ECM forests were characterized by low tree species evenness, big-sized trees, and low bulk density, favoring increasing ecosystem water-holding capacities. Moreover, increasing ECM tree dominance enhanced the contribution of community structure to water-holding variations. (4) ECM trees increased ecosystem water-holding functions by direct effects (mainly on the litter) and indirect effects from soil physics (mainly on the soils) or tree size (mainly on the canopy) regulations. This study highlighted that ECM trees enhanced water-holding capacity, providing important information for planting and managing temperate water conservation forests.