CMY01 Mycorrhizal Colonization and Plant Community Responses to Long-term Suppression of Mycorrhizal Fungi

Twenty replicate permanent 2x2 m plots were established in early 1991 along a randomly located transect, with a 2m space between each plot, on the following watersheds: 1B, 1D, annually burned HQB, 10B, 20D and infrequently burned HQB. Ten of the plots were randomly assigned as long-term mycorrhizal suppression plots. In each of these plots, AM fungi were suppressed by the application of the fungicide benomyl as a soil drench (7.5 liters per plot) at the rate of 1.25 g/m2 (active ingredient). The mycorrhizal suppression plots were treated biweekly throughout each growing season (April through October) beginning in 1991. The control plots each received no fungicide, but an equivalent volume of water (7.5 liters) was applied biweekly. To evaluate the effectiveness of the fungicide, three soil cores (2.5 cm diameter x 14 cm deep) were removed from both fungicide-treated and control plots each October throughout the study. Roots were extracted from the soil, washed free of soil, stained in trypan blue (Phillips and Hayman, 1970), and examined microscopically to assess percentage root colonization by mycorrhizal fungi using a Petri dish scored in 1-cm squares (Daniels et al. 1981). The vegetation within all plots was sampled in May and September of 1991, 1993, and 1995. In each plot, the cover and frequency of each plant species was estimated using a modified point-frame method (Cook and Stubbendieck, 1986). A frame containing ten 1m long vertical pins arranged in parallel at 10 cm apart was placed systematically at 4 locations (each 25 cm apart) within the central 1 m2 of the plot (4 frames=40 pins per plot). Every contact of the aboveground structures of each plant species with each pin was recorded. From the pin-contact data, the relative cover was calculated for each plant species (total number of pin-contacts mad by individual of species x/total number of pin-contacts of all species) for each of the two sample dates each year and for each species the maximum value attained between the two sample dates was retained for analysis. The frequency ( percentage of the 10-pin frames in which species x was encountered) also was estimated for each plant species. The total number of pin contacts of all species was used as an index of total canopy density in each plot. Previous use of this pincontact method on these tallgrass prairie sites showed that the total number of pin contacts of all species is also strongly correlated with total aboveground plant biomass (Hickman, 1996). Plant species richness (mean number of species per plot), species diversity (Shannon’s H’), and evenness were calculated using both types of abundance data (frequency and cover).

1991年初，研究人员沿随机布设的样带，在1B、1D、年度焚烧型HQB、10B、20D以及低频焚烧型HQB流域内建立了20个重复永久2m×2m样方，样方间距为2米。其中10个样方被随机分配为长期菌根抑制样方。在该类样方中，通过以土壤浇灌方式施用杀菌剂苯菌灵（benomyl）（每样方7.5升），以1.25克/平方米（有效成分）的剂量抑制丛枝菌根真菌（Arbuscular Mycorrhizal, AM）。自1991年起，在每个生长季（4月至10月）内，每两周对菌根抑制样方进行一次施药处理。对照样方不施用任何杀菌剂，但每两周喷施等量清水（7.5升/样方）。为评估该杀菌剂的施用效果，在整个研究周期内的每年10月，均从杀菌剂处理样方与对照样方中各采集3个土芯（直径2.5厘米×深度14厘米）。将根系从土壤中分离并清洗去除附着土壤后，采用锥虫蓝（trypan blue）染色法（Phillips与Hayman，1970）进行染色，随后通过镜检，使用刻有1厘米方格的培养皿（Daniels等，1981）估算菌根真菌对根系的侵染百分比。1991、1993与1995年的5月和9月，对所有样方内的植被开展采样调查。每个样方中，采用改良点样框法（Cook与Stubbendieck，1986）估算每种植物的盖度与频度。具体操作为：将由10根长1米、间距10厘米平行排列的垂直针具组成的样框，系统布设至样方中央1平方米区域内的4个彼此间距25厘米的位置，每个样方共设置4个样框，合计40根针具。记录每种植物的地上结构与每根针具的每一次接触事件。基于针具接触数据，计算每年两次采样日期中每种植物的相对盖度（物种x的针具接触总次数/所有物种的针具接触总次数），并保留每种植物在两次采样中达到的最大值用于后续分析。同时估算每种植物的频度（即出现物种x的10针样框占比）。所有物种的针具总接触次数可作为每个样方内总冠层密度的指标。此前在该高草草原样地开展的针具接触法应用研究表明，所有物种的针具总接触次数与植物地上总生物量显著相关（Hickman，1996）。基于盖度与频度两类丰度数据，研究人员计算了植物物种丰富度（每个样方的平均物种数）、物种多样性（香农-威纳指数H’，Shannon’s H’）以及群落均匀度。