A comprehensive appraisal of the mycorrhizal literature provides data for 336 plant families representing 99% of flowering plants, with regard to mycorrhizas and other nutritional adaptations. In total, arbuscular (AM), orchid, ectomycorrhizas (EM) and ericoid mycorrhizas and nonmycorrhizal (NM) roots occur in 74%, 9%, 2%, 1% and 6% of Angiosperm species respectively. Many families of NM plants have alternative nutritional strategies such as parasitism, carnivory, or cluster roots. The remaining angiosperms (8%) belong to families reported to have both AM and NM species. These are designated as NM-AM families here and tend to occur in habitats considered non-conducive to mycorrhizal fungi, such as epiphytic, aquatic, extremely cold, dry, disturbed, or saline habitats. Estimated numbers of species in each category of mycorrhizas is presented with lists of NM and EM families. Evolutionary trends are also summarised by providing data on all clades and orders of flowering and non-flowering vascular plants on a global scale. A case study of Western Australian plants revealed that plants with specialised nutritional modes such as carnivory, cluster roots, or EM were much more diverse in this ancient landscape with infertile soils than elsewhere. Detailed information on the mycorrhizal diversity of plants presented here is linked to a website (mycorrhizas.info) to allow data to remain current. Over a century of research effort has resulted in data on mycorrhizal associations of >10,000 plant species that are of great value, but also somewhat of a liability due to conflicting information about some families and genera. It is likely that these conflicts result in part from misdiagnosis of mycorrhizal associations resulting from a lack of standardisation in criteria used to define them. Families that contain both NM and AM species provide a second major source of inconsistency, but even when these are excluded there is a ∼10% apparent error rate in published lists of mycorrhizal plants. Arbuscules are linked to AM misdiagnosis since they are used less often than vesicles to recognise AM associations in roots and apparently occur sporadically in NM plants. Key issues with the diagnosis of mycorrhizal plants are discussed using the Cyperaceae as a case study. Detailed protocols designed to consistently distinguish AM from endophytic Glomeromycotan Fungus Colonisation (GFC) are provided. This review aims to stimulate debate and provide advice to researchers delving into root biology.

Mycorrhizal associations and other means of nutrition of vascular plants: understanding the global diversity of host plants by resolving conflicting information and developing reliable means of diagnosis

In the context of potential global warming, it is critical that ecologists bridge the typically local spatial scale of ecology to the regional scale of climatology by linking ecosystem responses to variations in the large-scale synoptic controls of regional climates. In northern Patagonia, Argentina, we related regional-scale tree mortality events over the past -100 years to annual and decadal-scale climatic variations associated with changes in the major synoptic climatic controls of the southeastern Pacific region, including the El Nifio-Southern Oscillation (ENSO). In nine stands of Austrocedrus chilensis, a xeric conifer, we used dendrochronological techniques to date the outermost tree ring on dead-standing and fallen trees to estimate the dates of tree death for 336 trees. To evaluate climatic conditions during periods of high tree mortality, we used regional records of precipitation and temperature from six climate stations and also used a regional set of 24 tree ring chronologies from Austrocedrus. Good preservation of the resinous wood of Austrocedrus allowed relatively precise dating of tree deaths over the past -90 years. Episodes of massive tree mortality coincide with exceptionally dry springs and summers during the 1910s, 1942-1943, and the 1950s. Although there is a general regional synchroneity of tree death associated with drought, intra-regional variations in the intensity of droughts, as interpolated and mapped from the regional network of tree ring chronologies, are also reflected by north-to-south variations in tree mortality patterns. Periods of drought and associated tree mortality during the 20th century in northern Patagonia are strongly associated with above average sea level atmospheric pressure off the coast of Chile at the same latitudes. Temperature and precipitation in northern Patagonia are highly influenced by the intensity and latitudinal position of the southeastern Pacific anticyclone, which, in turn, are greatly affected by ENSO. Tree mortality in northern Patagonia appears to be intensified by extreme events of the Southern Oscillation and is more strongly coincident with El Nifio events along the coast of northern Peru. These results, in combination with previously established climatic influences on fire occurrence and tree seedling establishment, strongly link stand-level and regional-scale forest dynamic processes in northern Patagonia with variations in large-scale atmospheric conditions.

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Influences of large-scale climatic variability on episodic tree mortality in northern patagonia

Most terrestrial plants associate with root-colonising mycorrhizal fungi, which improve the fitness of both the fungal and plant associates. However, exceptions exist both between and within plant families failing to associate with mycorrhizal fungi or in the incidence and the extent of mycotrophy, which may vary greatly. Sedges are important pioneers of disturbed habitats and often dominate vegetations like wetlands, and arctic and alpine vegetations, in which the mycorrhizal inoculum in the soil is often low or absent. In the past, sedges were often designated as non-mycorrhizal, though limited reports indicated the presence of mycorrhiza in certain species. However, studies since 1987 indicate widespread occurrence of mycorrhiza in sedges. Based on these studies, the family Cyperaceae is no longer a non-mycorrhizal family, but the mycorrhizal status of its members is greatly influenced by environmental conditions. Further, sedges appear to have several morphological adaptations to thrive in the absence of mycorrhizal association. Though mycorrhizal associations have been noted in many sedge species, the ecological role of this association is not well documented and no clear generalisation can be drawn. Similarly, the role of mycorrhizal fungi on sedge growth and nutrient uptake or non-nutritional benefits has yet to be fully ascertained. This paper reviews the current information available on the incidence of mycorrhiza in sedges and the possible reasons for low mycotrophy observed in this family.

Mycorrhiza in sedges—an overview

Phosphorus-mobilization ecosystem engineering: the roles of cluster roots and carboxylate exudation in young P-limited ecosystems

Seasonality of arbuscular mycorrhizal symbiosis and dark septate endophytes in a grassland site in southwest China

Despite the recognized importance of arbuscular mycorrhizal (AM) fungi in forest ecosystems, their is little information about their occurrence in natural forest ecosystems of Patagonia. This study investigated root associations in two Austrocedrus forests and the seasonal dynamics of AM of Austrocedrus chilensis. Most of the vascular flora in both forests had arbuscular mycorrhizae (80.5 and 70.5% of species, respectively). The dynamics of mycorrhiza formation and spore number did not differ between these forests but varied with the season. Root colonization was lowest in September at the end of the quarter with the most rain, and spore numbers were highest in September and in December at the beginning of the dry season.

Root associations in Austrocedrus forests and seasonal dynamics of arbuscular mycorrhizas

Austrocedrus chilensis mortality in the Nahuel Huapi National Park (Argentina)

SUMMARY Mortality has been observed in Argentinian Austrocedrus chilensis native forests. This research has been directed towards a systematic analysis of symptoms, their evolution during a period of one year, a search for signs and an evaluation of the spreading of mortality. The symptoms described are uniform and characteristic in all affected forests. No visible signs were found. The causal agent is still unknown and the spreading of mortality is in progress causing losses and damage in Austrocedrus chilensis forests in Argentina.

Pablo H. Rosso

Papers

Root associations in Austrocedrus forests and seasonal dynamics of arbuscular mycorrhizas

Austrocedrus chilensis mortality in the Nahuel Huapi National Park (Argentina)

Austrocedrus chilensis: contribución al estudio de su mortalidad en Argentina

Spatial pattern of Austrocedrus chilensis wilting and the scope of autocorrelation analysis in natural forests

Austrocedrus chilensis: asociación espacial entre individuos sanos y afectados por la mortalidad