Effects of different litter compositions on soil microbial biomass carbon and nitrogen contents in Chinese fir plantation

ObjectiveThe responses of soil microbes to decomposition of Chinese fir-Michelia macclurei litter with different compositions were analyzed to provide scientific basis for the sustainable management and development of Chi-nese fir plantations in South China.MethodIn 4-,15-and 32-year Chinese fir plantations in typical southern acid rain region,Shaowu,Fujian,five litter decomposition treatments were set:Chinese fir leaf(C),M. macclurei leaf(M),Chi-nese fir leaf:M. macclurei leaf=2:1(C2M1),Chinese fir leaf:M. macclurei leaf=1:1(C1M1)and Chinese fir leaf:M. macclurei leaf=1:2(C1M2). The difference in soil microbial biomass carbon content(SMBC),soil microbial biomass nitrogen content(SMBN)and soil microbial biomass carbon-to-nitrogen ratio(SMBC/SMBN)of soil at 0-5 cm layer were studied by net bag method.ResultSMBC of 4-and 15-year Chinese fir plantations were at the peak in C2M1 and C1M1 treatments respectiverly,and the contents were significantly higher than single composition treatments C and M(P<0.05, the same below). For 32-year Chinese fir plantation,differences in SMBC among treatmemnts changed as time passed. For 4-, 15-and 32-year Chinese fir plantations, difference of SMBN between mixed litter and single litter altered as time varied. SMBC/SMBN of different plant ages changed greatly at different decomposition periods,and reached the mini-mum on day 120 and 240 of decomposition. Soil temperature and moisture content had significant effects on SMBC and SMBN in the 4- and 15-year Chinese fir plantations,but had insignificant influence on 32-year Chinese fir plantation. SMBC and SMBN of different plant ages were significantly correlated with soil pH. Variance analysis indicated that,in-fluenced by plant age,Chinese fir leaf-M. macclurei litter composition and decomposition time,SMBC and SMBN of each plantation presented wave shape variation during the whole decomposition procedure. SMBC reached the peak on day 60 and 240 after decomposition,and SMBN reached the top on day 120 and 240.ConclusionThe improvement of young and middle age Chinese fir plantation can be mixed with Chinese fir-M. macclurei 2:1 and 1:1 respectively. In actual planting,the selection of Chinese fir-M. macclurei composition should take plant ages,soil pH,soil temperature, moisture content and seasonal variation into consideration.