Collins L, Boer M M, de Dios V Resco, Power S A, Bendall E R, Hasegawa S, Hueso R Ochoa, Nevado J Piñeiro, Bradstock R A
Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
Department of Ecology, Environment & Evolution, La Trobe University, Bundoora, VIC, 3086, Australia.
Oecologia. 2018 Jul;187(3):811-823. doi: 10.1007/s00442-018-4143-1. Epub 2018 Apr 27.
A trend of increasing woody plant density, or woody thickening, has been observed across grassland and woodland ecosystems globally. It has been proposed that increasing atmospheric [CO] is a major driver of broad scale woody thickening, though few field-based experiments have tested this hypothesis. Our study utilises a Free Air CO Enrichment experiment to examine the effect of elevated [CO] (eCO) on three mechanisms that can cause woody thickening, namely (i) woody plant recruitment, (ii) seedling growth, and (iii) post-disturbance resprouting. The study took place in a eucalypt-dominated temperate grassy woodland. Annual assessments show that juvenile woody plant recruitment occurred over the first 3 years of CO fumigation, though eCO did not affect rates of recruitment. Manipulative experiments were established to examine the effect of eCO on above-ground seedling growth using transplanted Eucalyptus tereticornis (Myrtaceae) and Hakea sericea (Proteaceae) seedlings. There was no positive effect of eCO on biomass of either species following 12 months of exposure to treatments. Lignotubers (i.e., resprouting organs) of harvested E. tereticornis seedlings that were retained in situ for an additional year were used to examine resprouting response. The likelihood of resprouting and biomass of resprouts increased with lignotuber volume, which was not itself affected by eCO. The presence of herbaceous competitors and defoliation by invertebrates and pathogens were found to greatly reduce growth and/or resprouting response of seedlings. Our findings do not support the hypothesis that future increases in atmospheric [CO] will, by itself, promote woody plant recruitment in eucalypt-dominated temperate grassy woodlands.
全球范围内，在草地和林地生态系统中均观察到木本植物密度增加，即木质化加剧的趋势。有人提出，大气中二氧化碳浓度升高是大规模木质化加剧的主要驱动因素，不过很少有实地实验验证这一假设。我们的研究利用了一项自由空气二氧化碳浓度增高实验，来研究二氧化碳浓度升高（eCO）对三种可能导致木质化加剧的机制的影响，即（i）木本植物更新，（ii）幼苗生长，以及（iii）干扰后再萌蘖。该研究在以桉属植物为主的温带草地林地中进行。年度评估表明，在二氧化碳熏蒸的前三年出现了幼年木本植物更新，不过eCO并未影响更新速率。通过移植的细叶桉（桃金娘科）和绢毛哈克木（山龙眼科）幼苗建立了操纵实验，以研究eCO对地上幼苗生长的影响。在接受处理12个月后，eCO对这两个物种的生物量均无积极影响。将收获的细叶桉幼苗的木质块茎（即再萌蘖器官）原地保留一年，用于研究再萌蘖反应。再萌蘖的可能性和再萌蘖的生物量随木质块茎体积增加而增加，而木质块茎体积本身不受eCO影响。结果发现，草本竞争者的存在以及无脊椎动物和病原体造成的落叶极大地降低了幼苗的生长和/或再萌蘖反应。我们的研究结果并不支持以下假设，即未来大气中二氧化碳浓度升高本身将促进以桉属植物为主的温带草地林地中的木本植物更新。
