Fine Root Decomposition And Nutrient Release In Ash And Larch Forests

Fine roots mortality and decomposition are major source of C and nutrient in forest stand. Study on fine root decomposition is crucial in estimating fine root production and turnover. Moreover, it is useful to further understand biogeochemical cycling of forest ecosystems. In this paper, we studied fine root decomposition in an Ash (Fraxinus mandshurica Rupr.) and Larch (Larix olgensis Henry) stand (17 yr) in Northeast region of China with litterbags and intact soil core methods. The results as follows:1 The results of litterbags showed that after 150d, decomposition rate of coarse root (5~10mm) and middle root (2~5mm) of ash were both approximately 25%, and the according proportion of larch was 22%.Fine root (<2mm ) decomposition rate of these two species was about 30%. After 520d, decomposition rates of coarse root (5~10mm), middle root (2~5mm) and fine root(<2mm ) of ash were 48.7%, 46.2% and 42.5% respectively, and the results of larch were 29.5%, 34.9% and 39.4% accordingly. 520 day's decomposition rate data were used to fit equation, we got decomposition constant (k) as follows: the decomposition constants of coarse root (5~10mm), middle root (2~5mm) and fine root(<2mm ) of ash were 0.3649 a-1, 0.4381 a-1 and 0.2720 a-1 respectively, and the results of larch were 0.1967a-1, 0.1955a-1 and 0.2464 a-1 accordingly.2 Fine root decomposition was affected by root litter quality and environment factors. The decomposition constant showed that decomposition constant of coarse root (5~10mm), middle root (2~5mm) of larch were 45% and 54% respectively compaired with ash, and fine root (<2mm decomposition constant of ash was 1.1 times of larch. In all diameter range studied, the coarse root (5~10mm) of ash decomposed fastest, while coarse root (5~10mm) of larch decayed slowest. The decomposition rate of fine root was positive correlated with N concentration, but negative correlated with C/N. The soil temperature and water in forest floor impacted the decomposition rate, although the temperature was low in control stand, its humidity was high and led to rapid decomposition of fine root. Therefore the water was a key factor in regulating decomposition.3 During the course of fine root decomposition ,a large amounts of C and nutrient were released. After 150d decomposition, released soluble sugar amounts of all diameters for both species were above 90%. K release rates of coarse root (5~10mm)and middle root (2~5mm) of ash were both about 40%, and 71% for fine root (<2mm) K released from roots of larch in all diameters was higher than 95%. After 520d, release rate of N for coarse root (5~10mm) and middle root (2~5mm) of both species were 50% approximately and about 40% for P, N and P released from fine root (< 2mm) were above 60%. Release rates of N and P from fine root were positive correlated with initial N and P concentration, while negative correlated with initial C/N and C/P.4, Different study methods influenced the estimation of fine root decomposition rate and nutrient release. In this study, comparing with intact soil core method, decomposition rates of ash and larch using litterbags were underestimated 46% and 25% respectively after 150d decomposition. N and P release of larch were underestimated from 20% to 33% in comparison with those using intact soil core method, but not ash because the initial N concentration were different.5 Fine root decomposition was an important pathway of C and nutrient return. Fine root(<2mm ) weight decayed of ash was 1254.9 kg ha-1 which was as 3.9 times as that of larch. N and P return were 41.67 and 2.81 kg ha-1 respectively which were as 10.9 and 5.5 times as those of larch. Fine root(<2mm ) weight decayed of two species was 73-97% of leaves litter, N returned from fine root(<2mm) decomposition of ash and larch were as 3.6 and 1.1 times as leaves litter respectively. P returned from fine root decomposition of ash was similar to that of leaves litter, but for larch, P return from fine root was 20% lower than that of litter leaves. Weight decayed and N and P return from fine...