The Exotic Legume Tree Species Acacia holosericea Alters Microbial Soil Functionalities and the Structure of the Arbuscular Mycorrhizal Community

Abstract

The response of microbial functional diversity as well as its resistance to stress or disturbances caused by the introduction of an exotic tree species, Acacia holosericea, ectomycorrhized or not with Pisolithus albus, was examined. The results show that this ectomycorrhizal fungus promotes drastically the growth of this fastgrowing tree species in field conditions after 7 years of plantation. Compared to the crop soil surrounding the A. holosericea plantation, this exotic tree species, associated or not with the ectomycorrhizal symbiont, induced strong modifications in soil microbial functionalities (assessed by measuring the patterns of in situ catabolic potential of microbial communities) and reduced soil resistance in response to increasing stress or disturbance (salinity, temperature, and freeze-thaw and wet-dry cycles). In addition, A. holosericea strongly modified the structure of arbuscular mycorrhizal fungus communities. These results show clearly that exotic plants may be responsible for important changes in soil microbiota affecting the structure and functions of microbial communities.Forest loss and degradation through human disturbance as well as deterioration of land productivity is a major problem in large areas of arid and semiarid environments. Degraded soils are characterized by loss or disturbance of the vegetation cover, increased soil erosion, decreased in-water infiltration, loss of available nutrients and organic matter, loss of microbial propagules, and/or diminution in microbial activity (25,35,44). Restoration of ecosystem health and productivity was traditionally achieved via abandonment of land and subsequent natural forest succession. In recent decades, management options for acceleration of the recovery and restoration of the productivity and biodiversity of disturbed ecosystems have been considered, since fallow periods have been shortened or eliminated due to increased anthropogenic pressure and agriculture intensification (49). Concerning the techniques used for rehabilitating degraded areas, there is increasing evidence that forest plantations can play a key role in ecosystem rehabilitation or restoration (52). Among candidate plantation species, fast-growing leguminous tree species (e.g., Australian Acacia species) should have preference.

Carbono orgânico e biomassa microbiana do solo em plantios de Acacia mangium no Cerrado de Roraima

“…A introdução de cultivos anuais ou perenes em ecossistemas naturais altera os fluxos de energia e nutrientes no sistema, com conseqüências muitas vezes negativas aos estoques de carbono do solo e na biodiversidade (Luizão et al, 1992;Corazza et al, 1999;Sposito & Zabel, 2003;Remigi et al, 2008).…”

“…Estudos conduzidos em regiões tropicais têm mostrado que a introdução da Acacia mangium e de outras espécies vegetais de rápido crescimento, pode reduzir e alterar a composição, funcionalidade e a diversidade da comunidade microbiana do solo (Andrade, 1999;Remigi et al, 2008), tornando imprescindível a avaliação dos impactos da introdução desta espécie exótica sobre os diferentes componentes do ecossistema.…”

Les forêts au secours de la planète : quel potentiel de stockage du carbone ?

“…Les conséquences en termes de biodiversité sont également fortement discutées. Les travaux menés en Afrique par l'Institut de recherche pour le développement (IRD) (Remigi et al, 2008) soulignent, toujours pour des plantations d'eucalyptus, les effets négatifs sur les communautés de champignons mycorrhiziens indispensables au bon fonctionnement de l'écosystème. Au final, c'est donc bien la pérennité même de ces boisements et leurs impacts sur le milieu qui sont fortement mis en doute.…”

Influence du couvert de <i>Eucalyptus camaldulensis</i> (dehn) sur la diversité spécifique des herbacées dans la zone de Diembéring (Basse Casamance, Sénégal)

“…Cette dégradation aggravée par le contexte socioéconomique et pédoclimatique défavorable, s'est caractérisée par une réduction importante des formations végétales (Remigi et al, 2008). La forte pression anthropique exercée sur le milieu a eu comme corollaire la déforestation, la réduction de la durée des jachères, le surpâturage et la dégradation des ressources naturelles en général (Remigi et al, 2008).…”