| Fine root turnover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and may be sensitive to many global change factors. Despite its importance for C allocation and nutrient cycling tremendous research efforts have been made in the past decades, the understanding of fine root turnover remains limited because of the dynamics process of fine roots associated with soil resources availability variation still remains poorly understood. Soil moisture, temperature and available nitrogen are most important components of soil resource availability, impacting fine root growth and mortality at individual root branch and ecosystem level. In temperate forest ecosystem, seasonal changes of soil resource availability will alter the pattern of carbon allocation to below ground, therefore, fine root biomass, root length density (RLD), specific root length (SRL) , production and turnover vary in growing season. Studying seasonal changes of fine root biomass, RLD, SRL and annual production and turnover of fine roots associated with soil resource availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover.This paper, sequential soil coring method was used to get fine root (<2mm in diameter) samples every month from May to October in 2002 in a Larch (Larix olgensis Henry) plantation (17 years old) in Maoershan Experiment Station, Northeast Forestry University. The plot size in larch stand is 25m X 30m(three replicates), and 72 soil cores (inside diameter 60mm; depth interval:0~10cm, ll~20cm, 21~30cm) were sampled randomly to estimate fine root biomass (live and dead), and to calculate RLD, SRL, fine roots production and turnover on an area basis monthly. Soil moisture, temperature, and nitrogen (ammonia and nitrates) in three depth intervals were also observed in these plots. The objective of this study is to know whether seasonal variation of fine root biomass, RLD and SRL are closely associated with soil resource availability, such as moisture, temperature and nitrogen, to understand how these soil components impact fine root dynamics, and further to determine the fine root production and turnover rate in larch plantation.The results showed that the standing fine root biomass (live and dead) was 189.1 g m-2a-1, and 95.4 g m-2 a-1 (50%) was distributed in surface layer (0~10cm), 61.5 g m-2 a-1 (33%) and 32.2 g m-2 a-1 (17%) were distributed in middle (11~20cm) and deep layer (21~30cm) respectively. Both live and dead fine root biomass were monthly higher from May to July, and in September as well, but lower in August and October. The live fine root biomass decreased with the increasing dead biomass during period of growing season. Middle and coarse root showed very different seasonal and deep-related pattern . Annual mean RLD ( 7411.56m m-3a-1) and SRL (10.83m g-1 a-1)in surface layer were greater than those of (1474.68 m m-3 a-1, 8.56 m g-1 a-1 respectively) in bottom layer (21~30cm). RLD and SRL average of three layers in May were much higher (10621.45m.m-3 and 14.83m.g-1) than in other months, and the lower (2198.20 m.m-3 and 3.77 m.g-1) appeared in September (RLD) and October (SRL). The fine root production were mainly occurred in upper layer which holding higher water and nutrient availability. In this paper three methods (Max-Min method, Positive differences method and Compartmental flux method) were used in calculating fine rootproduction and turnover. Fine root production was between 94.4 g m-2 a-1~210.5 g m-2 a-1 and the result calculated with Compartmental flux method were much higher (2.1 times, a and 2.6, b) than those of calculated with other two methods because of including fine root death and decomposition. Despite the difference of the four methods, they show the same trends of fine root production along soil depth, which decreasing with the increasing of soil depth (53.8 g m-2 a-1~123.7 g m-2 a-1 in upper layer and 23.5 g m-2 a-1 47.1g m-2a-1 in deep layer), and the dead fine root production showed the similar variation. While the fin...
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