Fine Root Production, Mortality And Turnover Of Five Tree Species In Maoershan

Fine root is the most important organ for water and nutrient uptakes in woody plants. As a key component in forest ecosystem, dynamic of fine root is important to understand the energy and nutrents cycles. We employed Minirhizotron technique to estimate fine root length production, mortality and turnover in Phellodendron amurense, Juglans mandshurica, Pinus sylvestris var. mongolica, Pinus koraiensis and Picea koraiensis plantations during two years. The results were showed as follows:(1) The results of fine root dynamics indicated:Fine root length or number production and mortality exhibited strong seasonal pattern in five species, in which production peaked at June or July but mortality at August or September and the whole winter. Annual root production is higher than annual root mortality of five species, and annual root production is significantly different among species, but the difference in annual root mortality is not significant. Fine root number productions of coniferous species are all higher than broadleaf species, and fine root number mortality of conifers (except Pinus koraiensis) are also higher than broadleaves.(2) The investigation of fine root dynamics with different diameters and orders suggested: Fine root length production and mortality expressed strong seasonal patterns in five species, in which production peaked at June or July but mortality at August or September and the whole winter. Fine root production is remarkable different between different diameter classes within species (all P<0.05 of five species). Most of fine root production appeared in 0-0.5 mm diameter classes, and the less appeared in more than 1.0 mm diameters classes. Except for Juglans mandshurica (P=0.48), fine root mortality with different diameters is significant different in the other species (all P<0.05). Fine root mortality mainly occored in 0.5～1.0 mm diameters in Philodendrons amurense, but the other three species (Pinus sylvestris var. mongolica, Pinus koraiensis and Picea koraiensis) in 0～0.5 mm diameters,>1.0 mm diameter the least.(3) The results of fine root production and mortality at different soil depths showed:Fine root production and mortality varied significantly in different seasons with depths, in which production peaked at June or July but mortality at August or September and the whole winter. Annual root production is significantly different among soil depths, with most occurred in surface soil (0-20 cm). While there were no significantly different in annual root mortality, although the majority also occurred in surface soil.(4) The results of fine root turnover rate indicated:Turnover rate is the highest in Phellodendron amurense, the lowest in Pinus koraiensis, which were 2.05 a-1 and 1.07 a-1 respectively. Turnover rate decreased with increasing soil depths. Turnover ratealso increased with increasing root diameter in broadleaf species, while the opposite pattern occurred in coniferous species. Except Phellodendron amurense, the other four species showed decreasing turnover with order ascending.In sum, our results showed:(1) Fine root production and mortality had significant seasonal dynamics across all five species, diameter size classes, root orders, soil depths or mycorrhizal colonization status. (2) Diameter, root order and soil depth had important influences on fine root turnover rate, however, which in part depending on the specific species.