Biomass and morphology of fine roots of sugi (Cryptomeria japonica) after 3 years of nitrogen fertilization.

Kyotaro Noguchi,Junko Nagakura,Shinji Kaneko

doi:10.3389/fpls.2013.00347

Kyotaro Noguchi, Junko Nagakura + Show 1 more

Open Access

https://doi.org/10.3389/fpls.2013.00347

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Abstract

Increasing nitrogen (N) deposition may affect carbon and nutrient dynamics in forest ecosystems. To better understand the effects of N deposition, we need to improve our knowledge of N effects on fine roots (roots <2 mm in diameter), as they are a key factor in carbon and nutrient dynamics. In this study, we fertilized 1 × 2 m plots in a sugi (Cryptomeria japonica) stand (336 kg ha-1 y-1) for 3 years and evaluated the responses of the fine roots to high N load. After fertilization, the concentration of NO3–N in the soil of N-fertilized (NF) plots was five-times as large as that in the control plots and the effect was more remarkable in the subsurface soil than in the surface soil. The biomass of fine roots <2 mm in diameter appeared to be greater in the NF plots (88 ± 19 g m-2) than in the control plots (56 ± 14 g m-2), but this difference was not statistically significant. In both plots, 76% of the biomass was accounted for by fine roots that were <1 mm in diameter. In the surface soil, the specific root length of fine roots <1 mm in diameter was significantly greater, and the diameter of those fine roots was marginally smaller, in the NF plots than in the control plots. In addition, the concentration of N in fine roots <1 mm in diameter was marginally greater in the NF plots than in the control plots. There may have been increased production of thinner fine roots or increased root branching in the NF plots. This study suggests that, in general, high N load is likely to have positive effects on sugi in terms of fine root characteristics and the effects on fine-root morphology are more evident than the effects on fine-root biomass.

Highlights

Fine roots of forest trees are, in general, defined as roots less than 2 mm in diameter
In November 2006, 19 days after the final fertilization, NO3–N concentrations were significantly greater in the NF plots than in the control plots, but NH4–N concentrations did not significantly differ between NF and control plots (Tables 1 and 2)
After the 3 years of N fertilization, there was a greater concentration of NO3–N in the soil of NF plots than in control plots, whereas NH4–N concentration was not significantly different between the plots

Summary

Introduction

Fine roots of forest trees are, in general, defined as roots less than 2 mm in diameter. Fine roots are recognized as one of the most important components for tree growth and in the carbon and nutrient dynamics of forest ecosystems. Tree roots take up N from the soil in inorganic forms (NH+4 and NO−3 ; Genenger et al, 2003; Hawkins et al, 2008), while recent studies suggested that organic N compounds, such as amino acids, are used in many ecosystems (Näsholm et al, 2009). The amount and spatial distribution of inorganic N in the soil and their chemical forms are likely to affect the biomass and dynamics of fine roots in forest ecosystems (Fujimaki et al, 2004; Tateno et al, 2004)

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