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Abstract Masting, a large interannual variation of reproductive investment spatially synchronized within perennial plants, is an important factor for understanding the use and storage of carbon and nutrient resources in various forest ecosystems. Fine roots play essential roles in water and nutrient uptake but also consume a large amount of net primary production (NPP) during growth. Understanding masting mechanisms requires knowledge of how masting trees succeed in abundant fructification by adjusting resource acquisition via fine roots and how mast seeding influences fine root dynamics. The aims of the present study were to estimate interannual variations in NPP, including belowground production, over several years while evaluating fine root phenology and to suggest possible relationships between fine root growth and the production of nuts, leaves, and woody biomass in mature forest ecosystems. Nut and leaf production was quantified using litter traps in two beech forests located at different altitudes of 550 and 1500 m, and woody biomass increment was estimated using allometric equations. Seasonal and mass‐based annual fine root production was determined using minirhizotrons and soil cores. Correlations between seasonal fine root and aboveground production were analyzed using the state‐space model, which can verify masting effects on fine root production between flower bud formation and mast seeding. NPP estimates exhibited almost biennial or irregular masting behavior. Nut production was positively correlated with fine root production in autumn of the previous year in the lower site but showed negative correlations with that in the early growing season of the same year in the upper site. The former indicated enhanced fine root production to absorb nutrients prior to mast seeding, and the latter suggested the suppression of fine root production due to resource depletion during masting. Fine root production increased with increasing leaf production in the early growing season in both sites, indicating the corresponding water transport between them. Thus, fine root phenology has distinct multiple functions to ensure water and nutrient resources in supporting aboveground vegetative and reproductive growth, resulting in variable seasonal patterns of fine root production. |
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