南方红壤强度侵蚀区植被自然更新的建植制约机制

Establishment limitation in degraded ecosystem has been one of the focal point by ecologists. Serious soil erosion makes vegetation natural recruitment and restoration extremely difficult in the red soil region of southern China. However, in the study region with serious soil erosion, it is still not clear whether there are enough available seeds and safe sites for the vegetation natural recruitment and restoration, and however soil erosion effects on establishment limitation is unclear. Based on this situation, the proposed study will use the serious erosion region in Changting as the main study area which was a long-term monitoring sample area of our research group. This study will follow the plant life cycle of available seeds, seed generation, seedling survival, seedling growth and sapling establishment. Based on plot investigation, situ-control, long-term location monitoring, and laboratory simulation experiments, the effects of soil erosion and environmental factor on seed removal, seed generation, seedling survival, seedling growth and sapling establishment were studied. The proposed study reveals the formation process and mechanism of seed limitation, and reveals the key factor hindering the vegetation natural regeneration of serious erosion region in Changting and clarifies their regulation mechanisms. The regulation mechanism of raindrop splash and mechanical erosion limit the natural regeneration in serious erosion region were discussed emphatically. The proposed study will not only contribute to the understanding of the mechanism of establishment limitation in serious erosion region, but also provide scientific evidence for decision-making of vegetation natural regeneration and restoration.

退化生态系统植被更新建植制约是国内外生态学界关注的焦点。南方红壤区严重的土壤侵蚀使植被更新极其困难，但目前尚缺乏红壤强度侵蚀区植被恢复建植制约机制的深入系统研究，特别是强度侵蚀区是否具备充足的有效种子和适宜的生境条件保障植被自然更新顺利进行，以及土壤侵蚀过程对植被建植制约的影响机制尚不清楚。有鉴于此，本项目从植被建植制约机制入手，以课题组长期开展定位研究的长汀强度侵蚀区为研究对象，以更新各环节“有效种子-种子萌发-幼苗存活-生长-定居”为主线，采用野外调查、定位测定、原位控制和室内模拟方法，重点研究土壤侵蚀和环境因子对种子迁移流失-萌发-幼苗存活-生长-定植的影响。探明种子制约的形成过程和机制，筛选关键制约因子并探明其作用机制，探讨雨滴击溅和降雨侵蚀机械冲刷对建植制约的影响机制，为植被自然更新建植制约理论提供实验证据，为南方红壤强度侵蚀区植被恢复与重建决策制定提供科学依据。

南方红壤强度侵蚀区由于长期的土壤侵蚀显著改变了区域地貌以及土壤特性，进而严重制约着红壤侵蚀区的植被更新恢复。本项目通过野外长期的动态监测及控制模拟试验，主要研究了强度侵蚀区不同恢复阶段群落内种源（种子雨和种子库的动态）特征；土壤砂砾化以及环境因子土壤水热变化和光照强度对不同植物种子萌发幼苗存活及时期生长的影响，最后揭示影响红壤强度侵蚀区植被自然更新的障碍机制。本项目取得主要结果如下：.通过连续的种子雨和种子库的监测发现，随着植被退化程度加剧，群落种子雨总密度由次生林的101.9±5.3粒·m-2显著下降到强度侵蚀裸地的3.3±0.8粒·m-2，种子雨种子活力明显不足，侵蚀裸地种子雨种子萌发率仅为3.3%，强度侵蚀区可能存在有效种子输入不足的情况。而土壤种子库密度随着土壤侵蚀强度加重而显著下降，且种子主要分布在5-10cm土壤层内，从而显著降低了强度侵蚀区种子有效性，强度侵蚀区种子雨和种子库相对匮乏，土壤种子库分布呈现深层化，可能是强度侵蚀区植被自然更新的困难的一个重要因素。强度侵蚀区土壤，尤其是浅层土壤水分不足及高温制约了植物种子萌发幼苗存活和早期生长，可能是影响区域内植物成功定殖的重要环境因子；光照过强或过弱均不利于侵蚀区主要造林树种马尾松幼苗出土，弱光环境不利于幼苗生长，侵蚀裸地的强光及植被恢复后浓密生长的芒萁所导致林地弱光下弱光环境可能是马尾松更新能力差的一个主要因素。