Department of Biology, Case Western Reserve University, Cleveland, OH, USA.
PLoS One. 2012;7(11):e48946. doi: 10.1371/journal.pone.0048946. Epub 2012 Nov 8.
Many temperate forests of the Northeastern United States and Europe have received significant anthropogenic acid and nitrogen (N) deposition over the last century. Although temperate hardwood forests are generally thought to be N-limited, anthropogenic deposition increases the possibility of phosphorus (P) limiting productivity in these forest ecosystems. Moreover, inorganic P availability is largely controlled by soil pH and biogeochemical theory suggests that forests with acidic soils (i.e., <pH 5) are particularly vulnerable to P limitation. Results from previous studies in these systems are mixed with evidence both for and against P limitation. We hypothesized that shifts in mycorrhizal colonization and community structure help temperate forest ecosystems overcome an underlying P limitation by accessing mineral and organic P sources that are otherwise unavailable for direct plant uptake. We examined arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) communities and soil microbial activity in an ecosystem-level experiment where soil pH and P availability were manipulated in mixed deciduous forests across eastern Ohio, USA. One year after treatment initiation, AM root biomass was positively correlated with the most available P pool, resin P, while AM colonization was negatively correlated. In total, 15,876 EcM root tips were identified and assigned to 26 genera and 219 operational taxonomic units (97% similarity). Ectomycorrhizal richness and root tip abundance were negatively correlated with the moderately available P pools, while the relative percent of tips colonized by Ascomycetes was positively correlated with soil pH. Canonical correspondence analysis revealed regional, but not treatment, differences in AM communities, while EcM communities had both treatment and regional differences. Our findings highlight the complex interactions between mycorrhizae and the soil environment and further underscore the fact that mycorrhizal communities do not merely reflect the host plant community.
许多美国东北部和欧洲的温带森林在过去一个世纪受到了大量人为酸和氮（N）沉积的影响。尽管温带硬木林通常被认为是 N 限制的，但人为沉积增加了这些森林生态系统中磷（P）限制生产力的可能性。此外，无机 P 的可用性在很大程度上受土壤 pH 值控制，生物地球化学理论表明，土壤酸性（即 pH <5）的森林特别容易受到 P 限制。这些系统之前的研究结果存在矛盾，既有支持也有反对 P 限制的证据。我们假设，菌根定植和群落结构的变化有助于温带森林生态系统通过利用矿物质和有机 P 源来克服潜在的 P 限制，这些源源对于直接植物吸收是不可用的。我们在一个生态系统水平的实验中研究了丛枝菌根（AM）和外生菌根（EcM）群落以及土壤微生物活性，该实验在跨美国俄亥俄州东部的混合落叶林中操纵土壤 pH 值和 P 可利用性。处理开始一年后，AM 根生物量与最可用的 P 库——树脂 P 呈正相关，而 AM 定植呈负相关。共鉴定和分配了 15876 个 EcM 根尖，分为 26 个属和 219 个操作分类单元（97%相似性）。外生菌根丰富度和根尖丰度与中等可用 P 库呈负相关，而被子囊菌纲侵染的根尖相对百分比与土壤 pH 值呈正相关。典范对应分析显示 AM 群落存在区域差异，但不存在处理差异，而 EcM 群落存在处理和区域差异。我们的研究结果突出了菌根与土壤环境之间的复杂相互作用，进一步强调了菌根群落不仅仅反映了宿主植物群落这一事实。
