Mixed decomposition and interspecific effects during early decomposition of litter mixtures of Pinus tabuliformis Carrière and broadleaved species

In this study, the litter of Pinus tabuliformis Carrière and five broadleaved species was mixed and placed in litterbags for six-month early-stage mixed litter decomposition. The mixed decomposition effects and interspecific impacts of broadleaved and P. tabuliformis species on decomposition were determined. Results indicated that:(1) mixed decomposition of P. tabuliformis and Betula albo-sinensis Burk., Catalpa fargesii Bur., and Populus purdomii Rehd. showed additive effects; however, the decomposition of P. tabuliformis litter was significantly accelerated, whereas the decomposition of broadleaf litter was significantly inhibited. Mixing P. tabuliformis and Eucommia ulmoides Oliver litter inhibited the decomposition of both types of litter, whereas mixing P. tabuliformis and Acer tsinglingense Fang et Hsieh litter showed contrary results. (2) Generally, the activities of sucrase, carboxymethyl cellulase, and polyphenol oxidase in the decomposition medium of mixtures of P. tabuliformis with B. albo-sinensis,C. fargesii, or P. purdomii were significantly higher than those in the decomposition medium (soil) of P. tabuliformis, whereas they were significantly lower than those in the decomposition medium of broadleaf litter. The mixed decomposition of P. tabuliformis and E. ulmoides resulted in significantly lower activities of the above-mentioned enzymes in the decomposition medium of the mixture compared with the activities in both types of single-specific decomposition medium, whereas the mixed decomposition of P. tabuliformis and A. tsinglingense exhibited contrasting impact. Considering the effects of mixed litter decomposition on the material cycling of the ecosystem, B. albo-sinensis,C. fargesii,P. purdomii, and A. tsinglingense could be used for transformation of pure P. tabuliformis forests; however, the inhibitory effects of mixing on litter decomposition of these species should be taken into consideration. As mixed plantation hindered nutrient cycling, E. ulmoides should not be mix-planted with P. tabuliformis.