Zhang Shanshan, Kang Hongmei, Yang Wenzhong
Yunnan Key Laboratory of Forest Plant Cultivation and Utilization, State Forestry Administration Key Laboratory of Yunnan Rare and Endangered Species Conservation and Propagation, Yunnan Academy of Forestry, Kunming, Yunnan, China.
PLoS One. 2017 Aug 1;12(8):e0182012. doi: 10.1371/journal.pone.0182012. eCollection 2017.
Climatic change-induced water stress has been found to threaten the viability of trees, especially endangered species, through inhibiting their recruitment. Nyssa yunnanensis, a plant species with extremely small populations (PSESP), consists of only two small populations of eight mature individuals remaining in southwestern China. In order to determine the barriers to regeneration, both in situ and laboratory experiments were performed to examine the critical factors hindering seed germination and seedling establishment. The results of in situ field experiments demonstrated that soil water potentials lower than -5.40 MPa (experienced in December) had significantly inhibitory effects on seedling survival, and all seedlings perished at a soil water potential of -5.60 MPa (January). Laboratory experiments verified that N. yunnanensis seedlings could not survive at a 20% PEG 6000 concentration (-5.34 MPa) or 1/5 water-holding capacity (WHC; -5.64 MPa), and seed germination was inhibited in the field from September (-1.10 MPa) to November (-4.30 MPa). Our results suggested that soil water potentials between -5.34 and -5.64 MPa constituted the range of soil water potentials in which N. yunnanensis seedlings could not survive. In addition to water deficit, intensified autotoxicity, which is concentration-dependent, resulted in lower seed germination and seedling survival. Thus, seed establishment was probably simultaneously impacted by water deficit and aggravated autotoxicity. Meteorological records from the natural distribution areas of N. yunnanensis indicated that mean annual rainfall and relative humidity have declined by 21.7% and 6.3% respectively over past 55 years, while the temperature has increased by 6.0%. Climate change-induced drought, along with a poor resistance and adaptability to drought stress, has severely impacted the natural regeneration of N. yunnanensis. In conclusion, climate change-induced drought has been implicated as a regulating factor in the natural regeneration of N. yunnanensis through suppressing seed germination and screening out seedlings in the dry season. Based on the experimental findings, habitat restoration and microclimate improvement should both be highlighted in the conservation of this particular plant species.
气候变化引发的水分胁迫已被发现会通过抑制树木的更新来威胁其生存能力，尤其是濒危物种。云南蓝果树是一种极小种群野生植物物种，在中国西南部仅存两个由八株成年个体组成的小种群。为了确定其更新障碍，开展了原位和实验室实验，以研究阻碍种子萌发和幼苗建立的关键因素。原位田间实验结果表明，低于-5.40兆帕（12月出现）的土壤水势对幼苗存活具有显著抑制作用，在-5.60兆帕（1月）的土壤水势下所有幼苗均死亡。实验室实验证实，云南蓝果树幼苗在20%聚乙二醇6000浓度（-5.34兆帕）或1/5持水量（-5.64兆帕）下无法存活，且在9月（-1.10兆帕）至11月（-4.30兆帕）的田间条件下种子萌发受到抑制。我们的结果表明，-5.34至-5.64兆帕的土壤水势范围是云南蓝果树幼苗无法存活的区间。除水分亏缺外，浓度依赖性增强的自毒作用导致种子萌发率和幼苗存活率降低。因此，种子建立可能同时受到水分亏缺和加剧的自毒作用的影响。云南蓝果树自然分布区的气象记录表明，在过去55年中，年平均降水量和相对湿度分别下降了21.7%和6.3%，而气温上升了6.0%。气候变化引发的干旱，加上对干旱胁迫的抗性和适应性较差，严重影响了云南蓝果树的自然更新。总之，气候变化引发的干旱已被认为是云南蓝果树自然更新的调节因素，它通过抑制种子萌发和在旱季筛选淘汰幼苗来发挥作用。基于实验结果，在保护这种特殊植物物种时，应同时强调栖息地恢复和微气候改善。
