Using litterbag method to study Liquidambar formosana root decomposition in different root order and in fresh or dry condition

Background/Question/Methods

Root decomposition plays a vital role in ecosystem C and N cycling. Fine and coarse roots behave differently during the process in terms of decay rates, and one disagreement is on if fine roots decay faster than coarse roots. We carried out a litter bag experiment to examine the decay rates of roots. We planted Liquidambar formosana in greenhouse and collected their roots that were divided into fine (1^st and 2^nd order) and coarse (3^rd and 4^th order) categories. The roots were put into litter bags either in fresh or after oven dried. Then the litter bags were buried into the soil A horizon in a subtropical secondary forest dominated by Liquidambar formosana. The litter bags were harvested at 0, 30, 60, 120, 240, and 360 days, and the mass reduction, C, N and lignin contents of the roots were determined. The decomposition trajectories of fine and coarse roots either freshly started or dry started were statistically compared.

Results/Conclusions

Both fresh and dry roots of the same category had generally similar changing patterns in all measuring variables：mass reduction， C and N contents, as well as soluble C and lignin contents. The fine roots (1^st and 2^nd order) had significant lower mass reduction rates than the coarse roots (3^rd and 4^th order) since the 1^st sampling data (30^th day), and the difference widened until 120^th day, then the decay rates of both root categories slowed and parallel to each other. Total C contents of fine roots decreased continuously while that of coarse roots was kept rather constant. N contents of the fine root generally decreased except during the first 30 day when N contents increased a little, while the N contents of the coarse roots significantly increased, particularly during the first 120 days, suggesting a strong N immobilization. The soluble C reduction rapidly during the first 60 days in roots of both categories, and that of the fine roots went faster. The lignin contents of coarse roots increased faster than fine roots during the first 120 days and leveled off thereafter. Our results indicated that in the subtropical forested ecosystem, the faster N immobilization of coarse roots facilitate the root decay while the lignin contents had little impacts during the first year of decomposition.