03812naa a2200157 a 450000100080000000500110000800800410001910000130006024501340007326000090020752030710021670000150328770000140330270000170331677303210333313150562008-10-06       2008    bl uuuu     u00u1 u    #d1 aNIWA, S.  aEffects of fine-scale simulation of deer browsing on soil microfoodweb structure and N mineralization rate in a temperate forest.  c2008  aIn a terrestrial ecosystem, the aboveground and belowground systems depend on each other for resource supply (nutrient and organic matter). Soil microfauna (protozoa, nematode, etc.) is considered to play an important role in nitrogen (N) mineralization process by releasing microbial N. Aboveground herbivory or defoliation on some grass species has found to enhance labile organic carbon (C) supply from roots and N mineralization in rhizosphere soil in the short term possibly due to the activation of soil microorganisms and microfauna. To reveal the relationships between the changes in micro-foodweb (food web with high turnover rate mainly consisting of microorganisms and microfauna; Lavelle, 1997) structure and N mineralization rate shortly after aboveground herbivory and the effects of defoliation intensity on N mineralization, we defoliated a dwarf bamboo (Sasa nipponica)-dominated understory layer in a natural forest at different intensities to realistically simulate sika deer (Cervus nippon) browsing. Defoliation (0?18% leaf removal) was performed three times at approximately 1-week intervals in summer. We measured water-soluble carbon (C) concentration, phospholipid fatty acid (PLFA) profiles as indicators of microbial community structure, a PLFA of 20:4 as an indicator of protozoan abundance, nematode community structure at the family level, and the N mineralization rate in 28 days of incubation. The N mineralization rate in the first 10 days of incubation showed a unimodal response to defoliation intensity, with a peak mineralization rate at a defoliation rate (number of removed leaves/total leaves) of 7.6%, correlating with protozoan PLFA and the abundance of Plectidae (the most dominant family of bacterivorous nematodes). In contrast, the N mineralization rate during the following 18 days of incubation decreased monotonically with increasing defoliation intensity, correlating with the water-soluble C concentration in the soil and the C content of new leaves. These results suggest that removing &lt15% of leaves may have induced a pulse-like release of labile organic matter from roots that lasted for less than 1 week and stimulated N mineralization through microbial loop in soil in the short term (in the first 1?2 weeks after defoliation). N mineralization, however, was reduced with increase of defoliation intensity in the longer term (3?5 weeks after defoliation), possibly because of the reduction in labile organic matter supply from roots 1 week after defoliation. As a result, N mineralization rates over the 28- day incubation period responded to defoliation intensity in a unimodal pattern with a small peak (at a defoliation rate of 4.9%) and were negatively affected by high defoliation rates (&gt10%). This study suggests that browsing on forest floor plants has significant effects on soil N mineralization potential through affecting soil micro-foodweb structure and that the effects are positive or negative depending on browsing intensity level and the length of time that has elapsed since defoliation.1 aKANEKO, N.1 aOKADA, H.1 aSAKAMOTO, K.  tIn: INTERNATIONAL COLLOQUIUM ON SOIL ZOOLOGY, 15; INTERNATIONAL COLLOQUIUM ON APTERYGOTA, 12., 2008, Curitiba. Biodiversity, conservation and sustainabele management of soil animal: abstracts. Colombo: Embrapa Florestas. Editors: George Gardner Brown; Klaus Dieter Sautter; Renato Marques; Amarildo Pasini. 1 CD-ROM.