引种樟子松固沙林天然更新的种子限制性研究

The introduction of pinus sylvestris var. mongolica is one of the primary measures in vegetation construction on the northern desertification region in our country. However, the growth has been declined of p. sylvestris plantation, of which the natural regeneration is difficult. The sustainable development of p. sylvestris plantation is limited, which influences the maintain of desertification control benefit. Seed is the material base and key stage of vegetation regeneration. However, there is no report on if natural regeneration of P. sylvestris sand-fixation plantation is limited by seeds. The limitation mechanism from the perspective of seed availability is needed to be clear. In this study, we will select the P. sylvestris sand-fixation plantation in the south of Kerqin Sandy Land as research object and carry out the following studies: We will study seed supply capability of P. sylvestris under different conditions by investigating seed production and testing seed viability of series sample sites. Also, we will reveal seed lose characteristics of seed bank by monitoring seed dispersal characteristics of canopy and soil seed banks of typical adult plants, which will utilize seed burial experiment and seed lose simulation experiment. Moreover, we will explore the availability and mechanism of seed out by combining seed germination experiment with seed addition experiment. Finally, the approach and mechanism of seed limitation of natural regeneration of the P. sylvestris sand-fixation plantation are studied using limitation index, which combine correlation analysis and principal component analysis. The project aims at providing new idea explaining the natural regeneration limitation of P. sylvestris sand-fixation plantation and providing theoretical basis for guiding the artificial promotion of natural regeneration and degraded forest reconstruction for P. sylvestris, which has great signification for the sustainable development of P. sylvestris plantation in desertification region in the north of China.

引种樟子松是我国北方荒漠化地区植被恢复的主要措施之一，但其出现提早衰退、天然更新困难等问题，制约其可持续发展及发挥荒漠化防治效益。种子是植被天然更新的物质基础与关键环节。关于樟子松天然更新障碍是否受种子限制的研究却未见报道。项目以科尔沁沙地南缘引种樟子松固沙林为研究对象，通过系列样地产量的调查和种子活性的测定，阐明不同条件樟子松林种子生产供给特征；通过监测典型结实株植冠种子库和土壤种子库的散布特征，运用种子埋藏与种子损失模拟实验，揭示其种子库的损失特征；采用室内种子萌发控制实验与野外种子补播实验，探明其种子萌发出苗输出有效性及机制；采用限制性指数，结合相关分析、主成分分析等方法，探讨引种樟子松天然更新的种子限制途径及机制。项目旨在为引种樟子松林天然更新限制性的科学解释提供新的思路，成果将为人工促进其天然更新及衰退林改造的实践提供指导，对我国北方荒漠化地区引种樟子松的可持续发展具有重要意义。

樟子松是我国北方荒漠化防治的主要造林树种之一。然而，不同引种区的樟子松林出现提前衰退、天然更新困难等问题，其可持续发展问题亟需解决。关于樟子松天然更新障碍的研究多从幼苗限制角度开展，但其是否受种子的限制却未引起重视。本项目以章古台引种樟子松固沙林为研究对象，通过全面调查研究区不同林龄、不同密度和不同立地樟子松种子生产特征，明确了种子生产特征存在显著的大小年差异，受降水条件影响；密度为800-1000株/hm2、立地为西坡和龄级为21-30 a和31-40 a阶段的林分可为种子输入提供充足、优质的种子保障；林木枝下高、林地土壤表层的全磷含量和碱解氮含量以及深层土壤的全氮含量对樟子松种子产量产生显著影响。通过定位监测与种子埋藏试验，阐明了樟子松种子散布特征及损失途径等，发现种子雨输入可持续一年，在10月份集中脱落，减少了被捕食的风险；大部分球果可宿存植冠至翌年6月份，携带少量种子补给土壤种子库，其散布的时空格局降低了种子的限制性；但土壤库种子寿命不超过一年，在研究区难以形成持久种子库，增加了其更新障碍的种子限制性。采用人工模拟干旱胁迫实验，经综合评价法掌握了密度800-1000株/hm2、平地、林龄21-30 a的樟子松种苗期抗旱性表现最佳，能够为人工促进樟子松天然更新提供优质的种子；利用人工补播试验，探明了樟子松在5月份出苗率最高，在阴坡、小林窗和草地中幼苗的出苗率最高，幼苗存活率则在阴坡、中林窗以及裸地更高，在阴坡、中小林窗及无地表覆盖条件下采用人工补播措施有利于幼苗存活。采用围封林地定位监测，系统探明了人为采种减少48.64%的种子输入，仅有39.12%的种子形成土壤种子库，不良生境与极端天气条件严重制约其有效输出，有效萌发出苗仅占种子总产量的0.83%，有效存活幼苗占种子总产量的0.043%，导致引种樟子松天然更新很难有效进行。研究成果有助于丰富引种樟子松天然更新限制的理论，并为人工促进其天然更新及可持续发展的经营管理提供理论参考。