Effects of root zone trenching on soil nitrogen dynamics in Japanese cedar and cypress plantations

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 ϫ 1 ϫ 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.

Increased nitrous oxide emissions from a drained organic forest soil after exclusion of ectomycorrhizal mycelia

“…In a spruce forest, the net N mineralisation increased significantly after tree girdling (Zeller et al 2008), which was suggested to be partly caused by decreased plant uptake. However, no effect of root exclusion on inorganic N pool sizes or N leaching was found at two forest sites in Japan (Yamashita et al 2004). Similarly, 13 years after trenching in an old-growth coniferous forest, the annual in-situ rates of net N mineralisation and nitrification did not differ between trenched and untrenched plots (Hart and Sollins 1998).…”

Changes in nitrogen and base cation concentrations in soil water due to the tree cutting in a wetland alder forest in the Kushiro Wetland, northern Japan

“…Especially for (2), an oxidative-reductive condition related to hydrological regime is important for the nitrogen dynamics in the wetland soil, especially in the habitat of alder, an actinorhizal nitrogen-fixing species (Hurd and Raynal 2004). Therefore, we chose the method of trenching the root zone (Vitousek et al 1982;Yamashita et al 2004) of the wetland vegetation, allowing the influence of rainfall and deep groundwater. In mid-July 2004, plastic frames that were 25 cm 9 25 cm with a height of 25 cm were inserted into the soil to 20 cm depth at five hollows in LT and HT to trench the root zone of vegetation (Fig.…”