Japan forest survey finds arbuscular mycorrhizal trees gained ground in 15 years
Researchers comparing more than 13,000 forest plots across Japan found that arbuscular mycorrhizal trees occupied a significantly larger portion of combined trunk cross-section after 15 years. The shift appeared alongside warmer conditions and spreading tree diseases, but the observational data do not establish causation. Dominance of this symbiosis was also linked to a lower ratio between soil carbon and nitrogen stocks.
Science··Night
More than 13,000 plots were compared
Researchers matched trees in more than 13,000 temperate-forest plots across the Japanese archipelago to mycorrhizal types at species or genus level. Mycorrhizas are partnerships between fungi and tree roots that influence nutrient uptake from soil. By comparing two inventory periods, the team calculated the share of total trunk cross-sectional area represented by arbuscular mycorrhizal trees in each plot. Results published in Nature Communications showed a significant increase in that group's dominance within 15 years. The measure is not a simple tree count; it combines the cross-sectional area occupied by trunks of different sizes.[1]
Warming and disease accompanied the shift
The rising share of arbuscular mycorrhizal trees appeared in the same plots as warmer climatic conditions and the spread of tree diseases. The study did not manipulate those factors experimentally; it compared forest composition and environmental indicators recorded across years. The data therefore do not show that warming or disease alone produced the shift. Forestry practices, local disturbance or different regeneration rates among species could also influence composition between inventories. The result identifies a consistent relationship over a broad geography and provides a basis for monitoring that can separate the mechanisms involved.[1]
A link emerged with soil nutrient balance
Because mycorrhizal types acquire and transfer nitrogen differently, the dominant type in a forest can matter for nutrient cycling. In the dataset, dominance of arbuscular mycorrhizal trees declined as the ratio of soil carbon stocks to nitrogen stocks increased. The authors interpret this inverse relationship as a sign that changes in tree partnerships could matter for soil nitrogen availability and retention. The measurements do not directly show how much carbon or nitrogen the soil will hold in the future. What the study establishes is a geographic link between a 15-year change in tree communities and existing soil stocks.[1]
