Elucidation of the process of change in nutrient use by trees due to excess nitrogen

2020 Fiscal Year Final Research Report

• Project/Area Number: 17K07866
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Forest science
• Research Institution: Forest Research and Management Organization
• Principal Investigator: Nagakura Junko 国立研究開発法人森林研究・整備機構, 森林総合研究所, 主任研究員 等 (70353787)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Keywords: 施肥 / 養分バランス / 土壌酸性化

Outline of Final Research Achievements

The effect of excess nitrogen (N) on the nutrient status of trees and soil and the annual change in this status was studied in stands of Monarch birch and Todo fir that have been fertilized continuously for more than 40 years. In the fertilized (F) plots, leaf concentrations of N, P, and K increased in the 2nd year of fertilization; however, such increases were less obvious after the 5th year of fertilization. Leaf Mg concentration in the F plots exhibited a decreasing trend from the 5th year, whereas leaf Al and Mn concentrations increased from the 2nd year. In the F plots, the exchangeable content of Ca and Mg in the surface soil was lower and the exchangeable Al content higher than was the case in the non-F plot. Though excess N changed the nutrient status of both the trees and the soil, it did not reduce tree growth. Analysis of leaf N stable isotope ratios indicated that birch and fir differed in their nitrogen utilization, with fir being more dependent on fertilizer.

Free Research Field

樹木栄養

Academic Significance and Societal Importance of the Research Achievements

人間活動により森林に付加される窒素量が増加し続けた場合、ウダイカンバやトドマツにおいて初期には葉の窒素濃度が高まり乾物生産が促進されるが、長期化すると土壌が酸性化し、樹木の生育に悪影響を及ぼす可能性があることを明らかにした。外部から付加される窒素の利用しやすさが樹種によって異なることや、懸念されていた水ストレスの助長はほとんど見られないという知見が炭素安定同位体比の利用により得られたことの学術的な意義は大きい。