湘中丘陵区不同演替阶段森林土壤活性有机碳库特征

为了解天然次生林保护对土壤活性有机碳库的影响，采用空间替代时间研究方法，对湘中丘陵区不同演替阶段4种林分类型（杉木人工林、马尾松+石栎针阔混交林、南酸枣落叶阔叶林、青冈+石栎常绿阔叶林）土壤活性有机碳及其与土壤养分相关性进行研究。结果表明：1）各土层总有机碳（TOC）、微生物生物量碳（MBC）、水溶性有机碳（DOC）、易氧化有机碳（EOC）含量均表现为：青冈+石栎常绿阔叶林 > 南酸枣落叶阔叶林 > 马尾松+石栎针阔混交林 > 杉木人工林，在0-30cm土层，马尾松+石栎针阔混交林、南酸枣落叶阔叶林、青冈+石栎常绿阔叶林TOC含量比杉木人工林分别高出13.40%、19.40%和29.91%，MBC含量分别高出15.62%、32.89%和53.33%，DOC含量分别高出8.52%、8.75%和13.76%，EOC含量分别高出32.79%、38.48%和78.30%；2）天然次生林各土层MBC占TOC的比率以南酸枣落叶阔叶林最高，青冈+石栎常绿阔叶林为其次，马尾松+石栎混交林最低，均高于同一土层杉木人工林（除马尾松+石栎混交林15-30cm土层外），天然次生林各土层DOC占TOC的比率随着演替进展而下降，均低于同一土层杉木人工林（除马尾松+石栎混交林0-15cm土层外），天然次生林各土层EOC占TOC的比率随着演替进展而增加，且均高于同一土层杉木人工林；3）土壤MBC、DOC、EOC含量与TOC含量的相关性均达到极显著水平，且天然次生林土壤MBC、DOC、EOC含量与TOC含量的相关系数随着演替进展而增高，均高于杉木人工林；4）4种林分土壤TOC、MBC、DOC、EOC含量与土壤全N、碱解N、全P、有效P、全K、速效K含量之间的相关性均达到显著或极显著水平。

Active pools of soil organic carbon in subtropical forests at different successional stages in Central Hunan, China

Quantification of soil organic carbon as affected by forest succession can facilitate conservation and restoration of the secondary growth forests and increase understanding of the potential for forest ecosystems to sequester carbon. The active pools of soil organic active carbon and its correlations with soil nutrients were investigated for four forest types in central Hunan, China. The four forest types included Cunninghamia lanceolata plantation(PM), Pinus massoniana+ Lithocarpus glaber mixed forests(CL), Choerospondias axillaries deciduous broad leaved forests(CA) and Cyclobalanopsis glauca +Lithocarpus glaber evergreen broad-leaved forests(CG), and the last three forests represent the natural secondary growth forests at different successional stages in the subtropical region.. The results showed that (1) The contents of total organic carbon (TOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC) and easily oxidized organic carbon (EOC) in the same soil layers were in the following order: Cyclobalanopsis glauca and Lithocarpus glaber evergreen broad-leaved forests > Choerospondias axillaries deciduous broad leaved forests > Pinus massoniana+ Lithocarpus glaber mixed forests > Chinese fir plantations at the 0-30cm soil layer. Specifically, the content of TOC was 13.40%, 19.40% and 29.91% higher in Pinus massoniana+ Lithocarpus glaber mixed forests, Choerospondias axillaries deciduous broad leaved forests, Cyclobalanopsis glauca and Lithocarpus glaber evergreen broad-leaved forests than in the Chinese fir plantations, respectively. The corresponding values were 15.62%, 32.89% and 53.33%, 8.52%, 8.75% and 13.76%, and 32.79%, 38.48% and 78.30% for the contents of MBC, DOC and EOC, respectively. (2) In the different soil layers under natural secondary growth forests, the ratio of MBC to TOC displayed the following order: Choerospondias axillaries deciduous broad leaved forests > Cyclobalanopsis glauca and Lithocarpus glaber evergreen broad-leaved forests > Pinus massoniana+ Lithocarpus glaber mixed forests, and all of the values were higher than that in the Chinese fir plantations at the same soil layer, except the ratio of Pinus massoniana+ Lithocarpus glaber mixed forests at the 15-30cm soil layer. The ratio of DOC to TOC decreased with the advanced stages in the succession series, and the values were lower in the secondary growth forests than in the Chinese fir plantations, except the ratio of Pinus massoniana+ Lithocarpus glaber mixed forests at the 0-15cm soil layer. The ratio of EOC to TOC increased with the progress of the successions, and the values were higher in the different successional staged forests than in the Chinese fir plantations. (3) MBC, DOC and EOC were significantly correlated with TOC, and their relative coefficients increased with the advanced succession stages of the studied forests. All the coefficients were higher in the secondary growth forests than in the Chinese fir plantations. (4) In the four forest types, TOC, MBC, DOC and EOC had a significant correlation with soil total N, available N, total P, available P, total K and available K.