Buen Lorena López de, Ornelas Juan Francisco
Departamento de Ecología y Comportamiento Animal, Instituto de Ecología, AC, Apartado Postal 63, Km 2.5 Antigua Carretera a Coatepec No. 351, Congregación El Haya, Xalapa, Veracruz 91070, México.
Am J Bot. 2002 Jan;89(1):95-102. doi: 10.3732/ajb.89.1.95.
The consequences of the seed deposition of the parasitic mistletoe Psittacanthus schiedeanus were evaluated in a 32-mo study. We conducted a field seed inoculation experiment to determine variation in seed adhesion, seed germination, seedling establishment, and plant survival to reproduction among five host species and to evaluate whether these post-dispersal processes explain mistletoe prevalence and specificity at the regional scale. Seeds without an exocarp were inoculated onto branches of individuals of the five most common host species identified in nature in central Veracruz, México. Seed fate was monitored for 2 yr, at weekly intervals for the first 2 mo and at 2-mo intervals thereafter. The height and diameter of experimental host branches and canopy cover above them were measured to see if these factors affected mistletoe establishment. Significant differences in seed attachment and seed germination were found among host species. Fewer seeds remained attached on experimental branches of Quercus germana than those of Liquidambar styraciflua, Acacia pennatula, and Platanus mexicana. Although significant differences in seed germination were observed among species (significantly greater on A. pennatula), >70% of mistletoe seeds germinated within the first 5 wk on all host species. Towards the end of the inoculation experiment, more mistletoe seedlings survived, grew, and then flowered on Liquidambar styraciflua than on A. pennatula, P. mexicana, Q. germana, or Q. leiophylla. Host branch initial height and diameter did not affect seedling survival, but seedlings survived better on trees where the canopy was more open. Our results suggest that Liquidambar styraciflua is the most compatible host species with P. schiedeanus in central Veracruz. Not surprisingly, Liquidambar is by far the most common host tree for P. schiedeanus in this area as well. We suggest that the observed local specialization is a result of seed dispersal as consequence of bird foraging and territorial behavior, host abundance, and host species compatibility.
在一项为期32个月的研究中，对寄生槲寄生Psittacanthus schiedeanus种子传播的后果进行了评估。我们开展了一项田间种子接种实验，以确定5种寄主物种在种子附着力、种子萌发、幼苗定植以及植株存活至繁殖阶段等方面的差异，并评估这些种子传播后的过程是否能解释槲寄生在区域尺度上的流行程度和特异性。将没有外果皮的种子接种到墨西哥韦拉克鲁斯中部自然环境中确定的5种最常见寄主物种的个体枝条上。对种子的命运进行了2年的监测，最初2个月每周监测一次，之后每2个月监测一次。测量了实验寄主枝条的高度和直径以及其上方的树冠覆盖度，以观察这些因素是否会影响槲寄生的定植。在寄主物种之间发现了种子附着和种子萌发方面的显著差异。与枫香、羽叶金合欢和墨西哥悬铃木相比，在德国栎的实验枝条上附着的种子更少。虽然在物种间观察到了种子萌发的显著差异（在羽叶金合欢上显著更高），但在所有寄主物种上，超过70%的槲寄生种子在最初5周内发芽。在接种实验接近尾声时，与羽叶金合欢、墨西哥悬铃木、德国栎或平滑栎相比，在枫香上存活、生长并开花的槲寄生幼苗更多。寄主枝条的初始高度和直径并不影响幼苗存活，但在树冠更开阔的树上，幼苗存活得更好。我们的结果表明，在韦拉克鲁斯中部，枫香是与Schiedeanus最相容的寄主物种。毫不奇怪，枫香也是该地区迄今为止Schiedeanus最常见的寄主树。我们认为，观察到的局部专一性是鸟类觅食和领地行为导致的种子传播、寄主丰度以及寄主物种相容性的结果。
