华南退化坡地芒萁层片的“生态筛”功能及其机理

The fern Dicranopteris dichotoma is the most representative pioneer species, dominant species and key species on degraded slopes in South China, and can form dense layer (synusia) fast with single dominant species. D. dichotoma layer would restrain recruitment of most species through competition, while less species can settle down successfully, which are just key and dominant species of the later succession stages. So, D. dichotoma layer was considered as ecological filter theoretically. The process, from layer structure formation, seed retention, seed germination, seedling survivor and growth, to seedling establishment, contains several concept and theory of restoration ecology, including community succession, threshold theory, interspecific association, colonization limit, and so on. This research would disclose the ecological filter function and mechanisms of D. dichotoma layer in south subtropics, and the contribution to ecosystem restoration or succession. Also, suitable species would be screened according the rule of natural succession during the earlier stages of ecological restoration. These species would improve the efficiency of natural restoration and artificial restoration, which provide reference for ecosystem restoration in South China.

芒萁是华南退化坡地上最具代表性的先锋种、优势种和关键种，能够快速形成密集的单优种层片结构。芒萁层片会抑制多数物种的更新，同时通过辅助作用使少数物种成功定居，而这些定居的物种正是后期演替的关键种和建群种。因此，芒萁层片被认为具有“生态筛”功能。从芒萁层片“生态筛”的形成、种子滞留、种子萌发、幼苗存活、生长，直至穿破“生态筛”物种成功定居，涵盖了群落演替、生态恢复阈值、种间关系、定居限制等生态学概念和理论。通过研究华南早期生态恢复过程中芒萁层片的“生态筛”功能，试图阐明其“生态筛”作用和机理，进一步揭示芒萁层片对生态系统恢复/演替过程的贡献；在实践方面，根据自然演替规律，筛选适合早期生态恢复阶段的物种，提高自然恢复和人工恢复的效率，可为华南退化坡地生态系统的恢复与重建提供重要参考。

芒萁是华南退化坡地上最具代表性的先锋种、优势种和关键种，能够快速形成密集的单优种层片结构。芒萁层片会抑制多数物种的更新且同时辅助少数物种定居。芒萁层片的这种“生态筛”效应、机理及其对生态恢复的贡献还不清楚。本项目以广东省鹤山退化坡地为研究对象，通过野外和室内控制实验，研究华南退化坡地早期生态恢复过程中芒萁层片的“生态筛”功能，得出了以下主要结论：（1） 芒萁地下茎纵横交错，形成较大筛孔，而地下根组成了主要的密集筛网，通过足够多的填充物（土壤、凋落物等）形成一个典型的根毯层片结构（大约10 cm左右），且根毯层中土壤养分（土壤有机质、全氮、碱解氮、有效磷、速效钾、交换性钠、交换性钙、交换性镁、阳离子交换量）、土壤水分和土壤微生物多样性均显著高于红壤层；（2） 芒萁根毯层中种子库密度、物种总个体数、物种丰富度、Shannon Wiener指数、Simpson指数均显著大于裸地红壤，说明其种子滞留效应明显；（3） 芒萁根毯层显著降低了种子萌发和幼苗定居，甚至多数乔木种和草本种在芒萁根毯层保留时无法存活，仅少数灌木种（桃金娘、梅叶冬青和野牡丹）可定居；（4）芒萁层片前期通过减少水土流失和固碳、固氮、解磷等作用改善了土壤结构和养分，为突破物理环境阈值奠定了良好基础，又通过生态筛作用使幼苗突破生物阈值。以上结果表明，芒萁层片为华南退化坡地生态恢复早期过程中的最主要群落类型，其生态筛功能是华南退化坡地恢复早期的主要驱动力之一。芒萁层片的生态筛效应主要来自根毯层的定居限制作用，可能是华南森林生态恢复突破生物多样性阈值的关键，为华南退化坡地生态系统的恢复与重建提供了科学依据。