不同凋落物配比对杉木土壤微生物量碳氮的影响

【目的】探讨土壤微生物对不同配比杉木—火力楠凋落物分解的响应,为促进我国南方杉木人工林的可持续经营与发展提供科学依据。【方法】在我国南方典型酸雨区福建省邵武市4、15和32年生杉木人工林内,设5个凋落物分解试验处理,分别为杉木(C)、火力楠叶(M)、杉木∶火力楠叶=2∶1(C2M1)、杉木∶火力楠叶=1∶1(C1M1)、杉木∶火力楠叶=1∶2(C1M2),采用网袋法分析不同配比处理杉木人工林0~5 cm表层土壤微生物量的碳、氮含量及微生物量碳氮比的差异。【结果】4和15年生杉木人工林中土壤微生物量碳含量最高的处理分别为C2M1和C1M1,显著高于C、M单一配比处理(P0.05,下同),32年生杉木人工林中各处理间土壤微生物量碳含量随时间波动变化;4、15和32年生杉木人工林中,不同混合凋落物与单一凋落物的土壤微生物生物量氮含量差异随时间的变化存在差异。各林龄土壤微生物量碳氮比在凋落物分解的不同时段存在明显波动变化,且分解时间为120和240 d时出现最低值。土壤温度与水分含量对4年生和15年生杉木人工林表层土壤微生物量碳氮的影响显著,对32年生杉木人工林影响不明显;各林龄表层土壤微生物量碳氮含量与土壤pH呈显著相关。方差分析结果表明,受林龄、杉木—火力楠凋落物配比及凋落物分解时间的多重影响,各林分表层土壤微生物量碳氮含量在凋落物整个分解周期内呈波动变化,其中微生物量碳含量的峰值出现在60和240 d,微生物量氮含量的峰值出现在120和240 d。【结论】对纯杉木幼龄林和中龄林的混交改良采用杉木—火力楠以2∶1和1∶1混交效果更佳,而在生产实践中对杉木—火力楠配比的选择还应综合考虑杉木林龄、土壤pH、土壤温度和水分含量等环境因子及季节变化的影响。

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

Objective]The 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.Method]In 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.Result]SMBC 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.Conclusion]The 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.