不同人工恢复林对退化红壤团聚体组成及其有机碳的影响

研究土壤团聚体的组成及其有机碳的分布,有助于从微观角度理解土壤结构与功能的相互作用.采用于筛法和湿筛法,研究南方红壤退化地实施人工恢复30年后,马尾松与阔叶复层林(PB)、木荷+马尾松混交林(SP)和阔叶林(BF)3种典型林分在0～60 cm土层的团聚体组成及其有机碳分布特征,分析土壤团聚体有机碳与总有机碳相关关系.结果表明:各恢复林分土壤机械稳定性团聚体质量分数,以＞2 mm粒径所占比例最大(均在60％以上),而在水稳性团聚体中,以＜0.05 mm粒径占优势.不同林分土壤团聚体结构破坏率顺序依次为BF(53.38％～84.27％) ＞SP(52.22％ ～70.86％) ＞PB(22.70％ ～47.83％).机械稳定性和水稳性团聚体有机碳质量分数均以PB最高,随着土层深度的增加,各林分土壤团聚体有机碳质量分数呈下降趋势.水稳性大团聚体(＞0.25 mm粒径)有机碳质量分数总体高于相应土层的总有机碳质量分数,而微团聚体的(＜0.25 mm粒径)则低于后者,说明有机碳对于大团聚体的形成和水稳性具有积极作用.土壤团聚体有机碳与总有机碳的相关关系分析表明,土壤团聚体有机碳的增加,对总有机碳的积累具有正面影响.保留密度大、灌木(草)层盖度高的马尾松与阔叶复层林土壤团聚体的数量和质量更高;因此,在红壤侵蚀退化地森林恢复初期,可通过适当密植、增加林下灌草覆盖等措施,增加有机碳的输入,促进团聚体的形成和稳定,从而加速了退化土地的土壤结构改善和功能恢复.该研究可为南方严重红壤退化地生态恢复中的林分类型选择和优化配置提供科学依据.

Effects of different artificially restored forests on aggregate composition and organic carbon in degraded red soil

Background] Research on the composition of aggregates and the distribution of organic carbon in soil will be beneficial for understanding the interaction between soil structure and function at the molecular scale.Methods] Three typical artificially restored forests after a 30-year restoration in degraded red soil were selected in this study,which were Pinus massoniana-multiple layer broadleaf forest (PB),Schima superba-Pinus massoniana mixed forest (SP),and broadleaf forest (BF),respectively.Methods of dry sieve and wet sieve were applied to investigate the composition of aggregates and the distribution of organic carbon in different layers (0-60 cm) of soil in each of the three forests,following which the correlations between soil aggregate organic carbon and soil total organic carbon were also determined.Results] For all three forests,particles larger than 2 mm in diameter constituted more than 60％ of mechanical-stable aggregates in soil,while particles less than 0.05 mm in diameter made up the majority of water-stable aggregates in soil.The broken rate of aggregate structure in the three forests ranked as:BF (53.38％-84.27％) ＞ SP (52.22％-70.86％) ＞ PB (22.0％-47.83％).The organic carbon mass fractions of both mechanical-and water-stable aggregates were the highest in the soil of PB.Along with the increase of soil depth,organic carbon mass fraction of soil aggregates all showed a decreasing trend in the three forests.Compared with the total organic carbon at all soil layers,macro water-stable aggregates (＞0.25 mm in diameter) had higher organic carbon mass fraction,while micro water-stable aggregates (＜ 0.25 mm in diameter) showed lower mass fraction,suggesting that organic carbon may play an active role in the formation and the water-stability of macro aggregates.Furthermore,soil aggregate organic carbon showed a positive correlation with soil total organic carbon.Conculsions] PB had the best quantity and quality of soil aggregates among the three forests,which can be attributed to the high density and coverage of shrubs/herbs.Therefore,to accelerate the improvement of soil structure and the recovery of soil functions in degraded lands,we should increase the input of organic carbon by appropriately creating a higher density and coverage of shrubs/herbs at the early stage of forest restoration,which would promote the formation and the stability of soil aggregates.This may provide a scientific basis for the selection and optimal allocation of forest types in the restoration of degraded red soil in the south of China.