Parrent Jeri Lynn, Morris William F, Vilgalys Rytas
Biology Department, Duke University, Box 90338, Durham, North Carolina 27708-0338, USA.
Ecology. 2006 Sep;87(9):2278-87. doi: 10.1890/0012-9658(2006)87[2278:canaae]2.0.co;2.
Ectomycorrhizal fungi (EMF), a phylogenetically and physiologically diverse guild, form symbiotic associations with many trees and greatly enhance their uptake of nutrients and water. Elevated CO2, which increases plant carbon supply and demand for mineral nutrients, may change the composition of the EMF community, possibly altering nutrient uptake and ultimately forest productivity. To assess CO2 effects on EMF communities, we sampled mycorrhizae from the FACTS-I (Forest-Atmosphere Carbon Transfer and Storage) research site in Duke Forest, Orange County, North Carolina, USA, where Pinus taeda forest plots are maintained at either ambient or elevated CO2 (200 ppm above ambient) concentrations. Mycorrhizae were identified by DNA sequence similarity of the internal transcribed spacer ribosomal RNA gene region. EMF richness was very high; 72 distinct phylotypes were detected from 411 mycorrhizal samples. Overall EMF richness and diversity were not affected by elevated CO2, but increased CO2 concentrations altered the relative abundances of particular EMF taxa colonizing fine roots, increased prevalence of unique EMF species, and led to greater EMF community dissimilarity among individual study plots. Natural variation among plots in mean potential net nitrogen (N) mineralization rates was a key determinant of EMF community structure; increasing net N mineralization rate was negatively correlated with EMF richness and had differential effects on the abundance of particular EMF taxa. Our results predict that, at CO2 concentrations comparable to that predicted for the year 2050, EMF community composition and structure will change, but diversity will be maintained. In contrast, high soil N concentrations can negatively affect EMF diversity; this underscores the importance of considering CO2 effects on forest ecosystems in the context of background soil chemical parameters and other environmental perturbations such as acid deposition or fertilizer runoff.
外生菌根真菌（EMF）是一个在系统发育和生理上具有多样性的群体，与许多树木形成共生关系，并极大地增强它们对养分和水分的吸收。二氧化碳浓度升高会增加植物的碳供应以及对矿质养分的需求，可能会改变外生菌根真菌群落的组成，进而可能改变养分吸收并最终影响森林生产力。为了评估二氧化碳对外生菌根真菌群落的影响，我们从美国北卡罗来纳州奥兰治县杜克森林的FACTS-I（森林-大气碳转移与储存）研究地点采集了菌根样本，在那里火炬松森林地块被维持在环境二氧化碳浓度或升高的二氧化碳浓度（比环境浓度高200 ppm）下。通过内部转录间隔区核糖体RNA基因区域的DNA序列相似性来鉴定菌根。外生菌根真菌的丰富度非常高；从411个菌根样本中检测到72个不同的系统发育型。总体而言，外生菌根真菌的丰富度和多样性不受二氧化碳浓度升高的影响，但二氧化碳浓度升高改变了定殖在细根上的特定外生菌根真菌类群的相对丰度，增加了独特外生菌根真菌物种的发生率，并导致各个研究地块之间外生菌根真菌群落的差异更大。各地块平均潜在净氮矿化率的自然变化是外生菌根真菌群落结构的关键决定因素；净氮矿化率增加与外生菌根真菌丰富度呈负相关，并对特定外生菌根真菌类群的丰度有不同影响。我们的结果预测，在与2050年预测浓度相当的二氧化碳浓度下，外生菌根真菌群落的组成和结构将会改变，但多样性将得以维持。相比之下，高土壤氮浓度会对外生菌根真菌多样性产生负面影响；这凸显了在背景土壤化学参数以及其他环境扰动（如酸沉降或肥料径流）的背景下考虑二氧化碳对森林生态系统影响的重要性。
