莫莫格扁秆藨草恢复湿地土壤种子库对长芒稗入侵的响应

湿地恢复过程中,时常有外来种或本地杂草入侵。土壤种子库作为未来植被的潜在种源,对湿地恢复效果具有重要的指示意义。在莫莫格国家级自然保护区,以恢复白鹤栖息地(扁秆藨草(Scirpus planiculmis)沼泽)为目的,进行了退化湿地的水文恢复;但退化湿地恢复2a后,一年生杂草长芒稗(Echinochloa caudata)在大部分区域成为建群种。以长芒稗入侵湿地和扁秆藨草自然湿地为研究对象,对比分析了长芒稗和扁秆藨草的土壤种子库及生长结实特征。结果表明,在自然湿地扁秆藨草种子库规模是长芒稗的18.42倍,而在恢复湿地长芒稗种子库大小是扁秆藨草的5.04倍。与自然湿地相比,扁秆藨草种子库密度在入侵湿地明显减少,但仍保留了一定量具有活力的种子(664.32±105.98)粒/m~2,这与研究区扁秆藨草较高的种子生产力(9210.4±1513.4)粒/m~2及种子较强的浮力(FP50=39.7d)有关,说明扁秆藨草具备通过种子库或水传播恢复的潜力。长芒稗土壤种子库密度在入侵湿地高达(3345.9±520.3)粒/m~2,明显高于自然湿地种子库规模(P0.01),说明恢复湿地受长芒稗入侵影响严重,这与长芒稗较高的种子生产力(7621.4±376.25)粒/m~2及较弱的种子浮力(FP0=5d)有关,同时也表明长芒稗通过水传播扩散的能力较弱。另外,研究区长芒稗平均高度超过1m,且盖度较大,不仅阻碍扁秆藨草种子的水播,也降低了到达地表的光照水平,从而抑制扁秆藨草更新。因此,在莫莫格受长芒稗入侵湿地,于开花结实前收获长芒稗地上植物体及凋落物应是限制长芒稗扩展、同时促进扁秆藨草恢复的有效措施。

Response of soil seed banks to invasion by Echinochloa caudata in restored Scirpus planiculmis wetlands in the Momoge National Nature Reserve

The wetland restoration process is usually disturbed by the undesirable impacts of invasive plants and ruderal wetland plants. Soil seed banks are usually useful indicators of the efficiency of wetland restoration. The Momoge National Nature Reserve (MNNR) is the largest wetland reserve in Jilin province, China and was established mainly for protecting wetland habitats and rare bird species, including the Siberian white crane (Grus leucogeranus). Tubers of Scirpus planiculmis Fr. Schmidt are the main food source for the Siberian white crane. However, the Scirpus marshes in MNNR have been degraded severely by global climate changes and human activities. Since 2010, the local governement has rewetted many degraded marshes to restore the habitat of the Siberian white crane. In the restored marshes, the dominant species of plant was Echinochloa caudata Roshev., a native ruderal species, which often exhibited over 70% coverage. However, the target plant S. planiculmis has rarely been found in the restored wetlands. In this study, we compared the seed abundances of S. planiculmis and E. caudata in soil seed banks. We also examined the growth and seed setting characteristics for both species. The seed density of S. planiculmis in the soils of natural wetlands was 18.42 times higher than that of E. caudata, while the seed density of E. caudata in restored wetlands was 4.04 times higher than that of S. planiculmis. The high seed productivity of S. planiculmis (9210.4 ± 1513.4) seeds/m² and the relative higher buoyancy of their seeds (FP₅₀ = 39.7 days) supported the potential for restoration via the soil seed bank. Moreover, the density of active seeds in restored wetlands still reached (664.32 ± 105.98)seeds/m², which was still significant lower than that in natural wetlands. The dormant soil seed bank of E. caudata in invaded wetlands (3345.9 ± 520.3)seeds/m² was significantly greater than that in natural wetlands, which indicated that the restored wetlands were heavily encroached by E. caudata. Additionally, the high seed production (7621.4 ± 376.25)seeds/m² and lower seed buoyancy (FP₀ = 5 days) of E. caudata indicated that E. caudata could not expand efficiently through water dispersal. Furthermore, both plant height and vegetation cover of E. caudata were significantly higher than those of S. planiculmis ((110.83±17.57) versus (68.33±10.49) and (75±4.35) versus (30±6.24), respectively), which could affect water dispersal of the buoyant seeds and influence species expansion. The MNNR wetlands, which are located in a mid-temperate zone with long winter days, reduced the decomposition of Echinochloa litter. Additionally, reproductive production of S. planiculmis was significantly reduced because of the increase in shade. Thus, improving the availability of light for S. planiculmis and diminishing the seed bank of Echinochloa by removing live stands and litter before the flowering phase may be an efficient strategy for restoration of S. planiculmis. More studies on the responses of soil seed banks of S. planiculmis to E. caudata removal are needed.