Effects of long-term water reduction and nitrogen addition on fine roots and fungal hyphae in a mixed mature Pinus koraiensis forest

The lack of synchronous studies on fine roots and fungal hyphae makes it difficult to gain insight into changes in how mycorrhizal trees search for nutrients under reduced precipitation and increased nitrogen deposition. We applied a modified version of the ingrowth bag approach to estimate the community-level responses of fine roots and fungal hyphae to long-term changes in nitrogen and water availability in a mixed mature forest. Water reduction, nitrogen addition and the two treatments applied in combination decreased root length density, root biomass and fungal hyphal length density, with the lowest values occurring in the combined treatment. Compared with fine roots in the control treatment, fine roots in the water reduction treatment had a thinner diameter, lower branching intensity and a greater specific root length. Fungal hyphae in the combined treatment had significantly greater diameters than in the control treatment at 0–10 cm soil depths. Root length density, root biomass, root branching intensity and hyphal length density significantly decreased with increasing soil depth. In contrast, hyphal diameter increased with increasing soil depth. Fungal hyphal length density was positively related to root length density but negatively related to hyphal diameter. Forest fine roots and fungal hyphae respond plastically to soil water and nitrogen availability. An integrative and simultaneous understanding of both root and hyphal trait plasticity can provide better insights into the resource acquisition strategies of trees experiencing environmental changes.