Effects Of Soil Fauna On Root Biomass, Morphology, Production And Turnover Rate In Larch And Ash Plantations

Fine root turnover is an important component of carbon (C) allocation and nutrient cycles in terrestrial ecosystems. Root herbivores accelerate root death and turnover via consuming root tissues. Therefore research on the effects of soil fauna on fine root eco-physiological processes is important in understanding C and nutrient cycling in forest ecosystems. However, the effects of soil fauna on fine roots have been overlooked in most previous studies. In this study, manchurican ash(Fraxinus mandshurica) and dahurian larch (Larix gmelinii), two important planting species in the Northeast China, were used as experimental stands. This study focuses on the effects of soil fauna on root biomass, morphology, production and turnover rate as well as mycorrhizal colonization under nitrogen (N) and insecticide treatments in both plantations.The results showed that the total density of soil fauna in both plantations was increased at initial period and decreased at later during four sampling seasons in two soil depths under N fertilized treatments, In generally, N fertilization reduced the density of soil detritivores, increased the density of root herbivores, but unchanged the density of soil predators. However, insecticide and N+insecticide treatments significant reduced all soil faunal densities across four sampling seasons and two soil depths. Soil fauna was the highest in autumn, and the lowest in summer, which have close relations with soil temperature, pH, organic matter, available N and P.N fertilization in both plantations significant decreased the biomass of the first five order roots by the method of soil cores in four sampling seasons and two soil depths. Insecticide treatment increased fine root biomass, however, significant increase was only observed in the first two order roots. There was a strong negative correlation between the density of root herbivores and the biomass of the first two order roots, but uncorrelated with higher order roots, and so does in other soil fauna.Fine root diameter and length in both plantations were significant increased under N fertilization, insecticide, and N+insecticide treatments, but specific root length (SRL) and branching roots significant decreased in four sampling seasons. In soil factors, available N was the most important factor in affecting root morphology, root diameter and length increased and SRL decreased with increasing soil N. In addition, mycorrhizal colonization affect fine root morphology, N fertilization and insecticide treatment significant decreased the mycorrhizal colonization in root tips across two soil depths in the two plantations.Fine root biomass production estimated by ingrowth cores were significant increased in the first three order roots for ash and the first two order roots for larch under insecticide treatments, suggesting that root herbivores only graze low order roots in both plantations. Overlooking the effects of root herbivores on fine root growth and mortality, fine root production and turnover rate would be underestimated by about 20% and 10%, respectively, in both plantations.