Spatio-temporal Dynamics And Influencing Factors Of Fine Roots In Five Chinese Temperate Forest Ecosystems

Production and mortality of fine roots (diameter≤2mm) and influencing factors are important to energy flow and nutrient cycling in forest ecosystems, but remain poorly understood mainly due to the limitation of methodology. In this study, we used a minirhizotron technique to investigate the temporal dynamics in fine root length production (FRP), mortality (FRM) of five representative forest ecosystems in Northeast China during the period between May and October of2010. Soil temperature (Ts), soil moisture (Ms), and leaf area index (LAI) were simultaneously measured for each stand. The stands were aspen-birch forest dominated by Populus davidiana and Betula platyphylla, hardwood forest dominated by Fraxinus mandshurica, Juglans mandshurica), Mongolian oak forest dominated by Quercus mongolica, Korean pine (Pinus Koraiensis) plantation, and Dahurian larch (Larix gmelinii) plantation. The experimental design included five forest types, three20m×30m replicate plots in each forest type.The results showed that the FRP and FRM were significantly (P<0.001) affected by forest types, soil layers and sampling dates. The FRP was13.34±3.44μm·cm-2·d-1(mean±SD),13.04±3.20μm·cm-2·d-1,8.74±2.08μm·cm-2·d-1,8.02±2.39μm·cm-2·d-1, and7.59±2.21μm·cm-2·d-1for the aspen-birch, hardwood, larch, pine, and oak stands, respectively; and the FRM was5.02±0.92μm·cm-2·d-1,6.85±1.27μm·cm-2·d-1,5.05±0.87μm·cm-2·d-1,3.88±0.70μm·cm-2·d-1, and3.88±0.59μm·cm-2·d-1, correspondingly.Both FRP and FRM showed a spatial pattern and decreased with the soil depth increasing for all forests:by the soil layer of0～10cm, the FRP varied from10.51to28.30μm·cm-2·d-1and the FRM varied from5.87to16.23μm·cm-2·d-1; by the soil layer of10～20cm, the FRP varied from7.88to15.02μm·cm-2·d-1and the FRM varied from4.41to8.79μm·cm-2·d-1; by the soil layer of20～30cm, the FRP varied from6.59to14.45μm·cm-2·d-1and the FRM varied from0.56to2.78μm·cm-2·d-1; by the soil layer of30～40cm, the FRP varied from0.63to8.71μm·cm-2·d-1and the FRM varied from0.23to3.39μm·cm-2·d-1.Overall, the FRP showed a unimodal seasonal pattern, with peaks varying with forest types. The FRM increased gradually as the growing season proceeded, and reached its maximum at the end of the growing season for all the stands except for the aspen-birch and hardwood stands where it peaked in middle August.Ts, Ms, and LAI all exerted significant positive effects on FRP and FRM (P<0.01), which, together, explained more than68%and53%of variability in FRP and FRM, respectively. These results illustrated that the temporal dynamics of fine root production and mortality in these temperate forest ecosystems were jointly influenced by changes in soil temperature, moisture and leaf area index.