Disturbance and Seasonal Dynamics of Mycorrhizae in a Tropical Deciduous Forest in Mexico¹

Abstract

Mycorrhizal fungi were sampled in a deciduous tropical forest on the Pacific coast of Mexico during different seasons and in natural treefall gaps and pastures. All 12 plant species sampled in the forest were arbuscular mycorrhizal. The percent root infection and spore production were closely related to the phenology of the plants. Most tree species and all herbaceous species had the highest infection in the summer rainy season, but two species, Opuntia excelsa and Jacquinia pungens, had highest infection in the dry season. Unusually high rainfall during the dry season was associated with increased infection but not increased spore production. Spore density was low for all species at all sample times, except at the beginning of the July 1993 rainy season in, when we observed up to 28 spores/g soil. The percent cover of shrubs or herbs did not increase in gaps after two years, and we observed no colonizing seedlings. No plant species with cover higher than 2.7 percent occurred exclusively in gaps or forest. The percent mycorrhizal infection did not differ significantly between gaps and forest. Spore counts were as high in the gaps as in the forest in two of the three gaps but lower in the third gap. The lack of significant response of plants in these gaps after two years differed from the rapid response in tropical rainforests. It is likely related to the small size of the gaps and to light infiltration to the forest floor. Pastures were dominated by two species of exotic grasses and one species of mycorrhizal fungus, whereas forests had 15 fungal species. The slow regrowth of vegetation in gaps was not limited by mycorrhizal fungi, since they were still abundant after the treefalls, but recovery in pastures could be affected by low fungal diversity and dominance of grasses.

Potencial de infectividade de fungos micorrízicos arbusculares oriundos de área de caatinga nativa e degradada por mineração, no Estado da Bahia, Brasil

“…Segundo Fischer et al (1994), os FMA podem ser indispensáveis ao estabelecimento e crescimento de algumas plantas em certos ambientes. De acordo com Allen et al (1998), a presença dos FMA em áreas degradadas pode estar relacionada com a cobertura vegetal, ou seja, pode depender das plantas presentes no local. O término das atividades de deposição de rejeito entre uma estação e outra também pode ter propiciado a melhoria das condições do local, facilitando assim a presença dos FMA.…”

“…diferença significativa no número de esporos entre a primeira e a segunda estação. Trabalhando com a dinâmica sazonal de FMA em uma floresta tropical decídua, Allen et al (1998) observaram que a colonização e esporulação durante a estação chuvosa eram maiores do que na estação seca, sugerindo que isso ocorria devido à maior atividade micorrízica naquele período, em conseqüência da maior quantidade de raízes na camada mais superficial do solo nessa estação. Na sub área 6, onde foram registradas nove espécies de plantas, foi encontrado o maior número de propágulos infectivos no solo.…”

Distribution of roots and arbuscular mycorrhizal associations in tropical forest types of Xishuangbanna, southwest China

“…There are however, few experimental investigations on mycorrhizal associations during secondary forest succession. It is well-known that land disturbance may decrease fungal communities (Allen et al, 1998) or affect mycorrhizal propagules (Fischer et al, 1994). These few studies do indicate a fungal succession in which some species of AM fungi persist and dominate presumably due to their ability to tolerate various soil conditions (Abbott and Robson, 1991).…”

Micorriza arbuscular em cupuaçu e pupunha cultivados em sistema agroflorestal e em monocultivo na Amazônia Central

“…Allen et al (1998), em estudo realizado nos trópicos mexicanos, também observaram, em espécies florestais, taxas maiores de colonização na estação chuvosa. Contudo, os autores relacionaram tal característica à maior atividade radicular nessa época do ano, na maioria das espécies estudadas.…”