Tchabi Atti, Burger Stefanie, Coyne Danny, Hountondji Fabien, Lawouin Louis, Wiemken Andres, Oehl Fritz
Plant Science Center Zurich-Basel, Institute of Botany, University of Basel, Hebelstrasse 1, CH-4056, Basel, Switzerland.
International Institute of Tropical Agriculture (IITA), 08 BP 0932, Cotonou, Benin.
Mycorrhiza. 2009 Aug;19(6):375-392. doi: 10.1007/s00572-009-0241-6. Epub 2009 Apr 3.
Yam (Dioscorea spp.) is a tuberous staple food crop of major importance in the sub-Saharan savannas of West Africa. Optimal yields commonly are obtained only in the first year following slash-and-burn in the shifting cultivation systems. It appears that the yield decline in subsequent years is not merely caused by soil nutrient depletion but might be due to a loss of the beneficial soil microflora, including arbuscular mycorrhizal fungi (AMF), associated with tropical "tree-aspect" savannas and dry forests that are the natural habitats of the wild relatives of yam. Our objective was to study the AMF communities of natural savannas and adjacent yam fields in the Southern Guinea savanna of Benin. AMF were identified by morphotyping spores in the soil from the field sites and in AMF trap cultures with Sorghum bicolor and yam (Dioscorea rotundata and Dioscorea cayenensis) as bait plants. AMF species richness was higher in the savanna than in the yam-field soils (18-25 vs. 11-16 spp.), but similar for both ecosystems (29-36 spp.) according to the observations in trap cultures. Inoculation of trap cultures with soil sampled during the dry season led to high AMF root colonization, spore production, and species richness (overall 45 spp.) whereas inoculation with wet-season soil was inefficient (two spp. only). The use of D. cayenensis and D. rotundata as baits yielded 28 and 29 AMF species, respectively, and S. bicolor 37 species. AMF root colonization, however, was higher in yam than in sorghum (70-95 vs. 11-20%). After 8 months of trap culturing, the mycorrhizal yam had a higher tuber biomass than the nonmycorrhizal controls. The AMF actually colonizing D. rotundata roots in the field were also studied using a novel field sampling procedure for molecular analyses. Multiple phylotaxa were detected that corresponded with the spore morphotypes observed. It is, therefore, likely that the legacy of indigenous AMF from the natural savanna plays a crucial role for yam productivity, particularly in the low-input traditional farming systems prevailing in West Africa.
山药（薯蓣属）是一种块茎类主食作物，在西非撒哈拉以南的稀树草原地区具有重要意义。在轮作耕种系统中，通常只有在刀耕火种后的第一年才能获得最佳产量。后续年份产量下降似乎不仅是由于土壤养分耗竭，还可能是因为有益土壤微生物群落的丧失，其中包括与热带“树木型”稀树草原和干旱森林相关的丛枝菌根真菌（AMF），而这些是山药野生近缘种的自然栖息地。我们的目标是研究贝宁南部几内亚稀树草原自然稀树草原和相邻山药田的AMF群落。通过对田间土壤以及以高粱和山药（圆果薯蓣和黄肉薯蓣）作为诱饵植物的AMF诱捕培养物中的孢子进行形态学分类来鉴定AMF。根据诱捕培养的观察结果，稀树草原中AMF的物种丰富度高于山药田土壤（18 - 25种对11 - 16种），但两个生态系统的物种丰富度相似（29 - 36种）。用旱季采集的土壤接种诱捕培养物可导致较高的AMF根系定殖、孢子产生和物种丰富度（总共45种），而用雨季土壤接种则效率低下（仅2种）。以黄肉薯蓣和圆果薯蓣作为诱饵分别得到28种和29种AMF物种，以高粱作为诱饵得到37种。然而，山药的AMF根系定殖率高于高粱（70 - 95%对11 - 20%）。经过8个月的诱捕培养，菌根化的山药块茎生物量高于非菌根化对照。还使用一种新颖的田间采样程序对田间实际定殖在圆果薯蓣根系上的AMF进行了分子分析研究。检测到多个系统分类单元，与观察到的孢子形态类型相对应。因此，自然稀树草原中本土AMF的遗留物可能对山药生产力起着关键作用，特别是在西非普遍存在的低投入传统耕作系统中。
