Faculty of Science, University of Western Australia, Crawley, Western Australia, 6009, Australia.
Research Institute for the Environment and Livelihoods, National Environmental Science Programme (NESP), Charles Darwin University, Darwin, Northern Territory, 0909, Australia.
Sci Rep. 2018 Apr 26;8(1):6628. doi: 10.1038/s41598-018-24704-5.
Andropogon gayanus Kunth. is a large African tussock grass invading Australia's tropical savannas. Invasion results in more intense fires which increases the mortality rate of adult woody plants. Invasion may also affect community structure by altering the recruitment potential of woody plants. We investigated the effects of A. gayanus invasion on ground-level microclimate, and the carbon assimilation potential and recruitment potential of two Eucalyptus species. We compared microclimatic variables from the early wet-season and into the mid-dry season to coincide with the period of growth of A. gayanus. We assessed Eucalyptus recruitment by monitoring seedling establishment, growth and survival of experimentally sown seed, and estimating seedling density resulting from natural recruitment. A. gayanus invasion was associated with increased grass canopy height, biomass and cover. Following invasion, the understorey microclimate had significantly reduced levels of photon flux density, increased air temperatures and vapour pressure deficit. The conditions were less favourable for woody seedling with aboveground biomass of seedlings reduced by 26% in invaded plots. We estimated that invasion reduced daily carbon assimilation of woody seedlings by ~30% and reduced survivorship of Eucalyptus seedlings. Therefore, A. gayanus invasion reduces recruitment potential, contributing to the transformation of savanna to a grassland ecosystem.
大油芒（Andropogon gayanus Kunth.）是一种入侵澳大利亚热带稀树草原的大型非洲丛生禾草。入侵会导致更频繁的火灾，从而增加成年木本植物的死亡率。入侵还可能通过改变木本植物的繁殖潜力来影响群落结构。我们研究了大油芒入侵对地面小气候以及两种桉树物种的碳同化潜力和繁殖潜力的影响。我们将早湿季和中旱季的小气候变量与大油芒的生长时期进行了比较。我们通过监测实验播种的幼苗的建立、生长和存活率，并估计自然繁殖产生的幼苗密度，来评估桉树的繁殖情况。大油芒入侵与草冠层高度、生物量和盖度的增加有关。入侵后，林下小气候的光子通量密度显著降低，空气温度和蒸气压亏缺增加。这些条件不利于木本幼苗的生长，入侵区的幼苗地上生物量减少了 26%。我们估计，入侵减少了木本幼苗的日碳同化量约 30%，并降低了桉树幼苗的存活率。因此，大油芒入侵降低了繁殖潜力，导致稀树草原向草原生态系统转变。
