古尔班通古特沙漠土壤种子库和幼苗的空间格局——灌丛的“保护效应”

Spatial Patterns of Soil Seed Bank and Seedlings in the Gurbantunggut Desert: The Nurse Effect of Shrubberies

荒漠生态系统中灌丛通过生境改造而对其周围植物产生＂保护效应＂,这种正交互作用是荒漠植物群落构建的重要驱动力。本文采用室内萌发法观测了古尔班通古特沙漠南缘不同沙丘部位梭梭冠下、冠缘和灌丛间地3种微生境土壤种子库,并调查了相同采样微生境自然条件下幼苗密度及物种组成,以探讨梭梭＂保护效应＂对其周围植物生活史早期阶段的影响。研究结果：（1）土壤种子库和地上幼苗库中以一年生草本和短命植物占绝对优势。（2）土壤种子库密度从梭梭冠下经冠缘至灌丛间地逐渐减小,在冠下、冠缘与灌丛间地分别为（689±67）粒·m-2、（578±58）粒·m-2、（350±48）粒·m-2,梭梭灌丛对植物种子具有明显的聚集效应,但这种聚集效应在沙丘顶部不明显。（3）梭梭冠缘处自然条件下相对萌发率最高,为61%,冠下和灌丛间地则差异不明显,表明灌丛覆盖对种子萌发的影响在灌丛中心至灌丛间地这一小尺度上具有分异,冠缘处植物从梭梭＂保护效应＂中获益最大。土壤种子库和幼苗库的空间格局表明,古尔班通古特沙漠梭梭通过对种子的聚集效应及对种子库萌发成苗的促进作用,对其冠下植物在萌发期这一生活史早期阶段具有明显的＂保护效应＂。研究结果对深入理解荒漠生态系统中种间正交互作用的发生机理具有重要意义。

Known as the＂nurse effect＂,shrubberies in desert ecosystem of ten benefit understory plants through microhabitat amelioration,and they are the typical facilitation structuring plant communities in desert.In this study,the germination method was used to investigate the soil seed bank at three microhabitats relative to the individuals of the dominant shrub species Haloxylon ammodendron,i.e.,under shrubbery,shrubbery periphery and inter-shrubbery open area,across an area between two dunes in the southern marginal zone of the Gurbantunggut Desert.Field seedlings close to the soil seed bank sampled at the microhabitats were also investigated in spring.Our aims were to explore the nurse effect of H.ammodendron on the understory plants at early stage of the life history.The results showed that the soil seed bank and aboveground seedling bank were dominated by annuals and ephemerals.Density of the soil seed bank decreased gradually away from the shrubbery core[（689±67）seed·m-2]to the periphery[（578±58）deed·m-2]and to the inter-shrubbery open area[（350±48）seed·m-2],showing an enrichment effect of shrub seeds.However,this effect was not significant at the dune crest.Germination rate of soil seed bank was the highest at the shrubbery periphery（61%）,but the difference between the shrubbery core and inter-shrubbery open area was not significant,which indicated that there was a fine-scale zonation of the shrubbery effect on germination from shrubbery core to inter-shrubbery open area.Correspondingly,the nurse effect of seedlings from H.ammodendron was the highest at shrubbery periphery.Through aggregating seeds and promoting seedling settling,H.ammodendron has a significant nurse effect on the understory plants in the Gurbantunggut Desert at the early stage of life history.Our findings provide the insights into the occurrence mechanism of interspecific positive interactions in arid ecosystems.