Effects of root zone trenching on soil nitrogen dynamics in Japanese cedar and cypress plantations |
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Authors: | Email author" target="_blank">Tamon?YamashitaEmail author Nobuhiko?Kasuya Sen?Nishimura Hiroshi?Takeda |
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Institution: | (1) Education and Research Centre for Biological Resources, Shimane University, 1060 Nishi-Kawatsu, Matsue 690-8504, Japan;(2) Laboratory of Forest Ecology, Kyoto Prefectural University, Kyoto, Japan;(3) Forest Research Institute Malaysia, KL, Malaysia;(4) Laboratory of Forest Ecology, Kyoto University, Kyoto, Japan |
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Abstract: | The effects of root exclusion and planted tree species on soil nitrogen (N) dynamics were examined at two plantations, one
planted with Japanese cedar and the other with Japanese cypress. We set up ten 1 × 1 × 0.2-m-deep trenched sites and ten untrenched
control sites at each plantation. We measured the pool size and leaching of inorganic N at each site for 2 years and the net
N mineralization 1 and 2 years after trenching. Despite similar soil conditions, the cedar plantation showed higher net N
mineralization than the cypress plantation. Stopped tree uptake of N was expected to cause an increased pool size and leaching
of inorganic N at the trenched sites. Nevertheless, we found no significant increase in those variables at both plantations.
The trenched cypress sites showed no decrease in the net N mineralization during the 2 years after trenching. However, the
net nitrification at the trenched cypress sites increased remarkably at the deeper horizons in comparison with that at the
control sites. Enhanced nitrification might result from improved ammonium availability through root exclusion. Net N mineralization
at the trenched cedar sites decreased more than 60% compared with that at the control sites 2 years after trenching. Higher
nitrification potential at the cedar plantation and enhanced nitrification potential at the trenched cypress sites never resulted
in increased leaching of N, due to added fine root litter which acted as an immobilization agent for excess N, thus preventing
N loss. |
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Keywords: | Coniferous plantation N immobilization Nitrification N mineralization Trenching |
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