Interactions among root colonizing fungi and Persea spp. (Lauraceae): Impact on carbon allocation to plant and fungi.

摘要

Arbuscular mycorrhizal fungi (AMF) are obligate plant symbionts that are capable of altering plant growth and improving soil conditions through growth of hyphae and by producing glomalin. Mexican montane rainforests converted to pasture, shrubland (via burning or non-selective logging) or diverse cornfields (milpas) exhibited contrasting seasonal patterns of AMF species richness, sporulation and composition with no apparent negative impacts on overall AMF sporulation and richness. Glomalin concentrations, an indirect measure of AMF activity, were generally reduced by forest conversion to pasture, shrublands or milpas. In contrast, conversion of diverse forests to Pine did not appear to affect glomalin but did severely reduce AMF sporulation. Reestablished tree species negatively impacted by disturbance would probably be infected by a diverse AMF community in pastures, milpas or shrublands, whereas trees established in Pine forests may be limited by low AMF and non-AMF root colonists.; Chaetomium elatum (Chaetomiaceae) negatively impacted avocado growth under low light and in monoculture but not in the presence of Glomus intraradices (an AMF). Relative to the non-mycorrhizal controls, G. intraradices was only associated with improved avocado performance under high light but light did not impact the positive effect of G. intraradices on avocado investment in leaf area. Glomus intraradices intraspecific density-dependent effects were non-linear predicting that maximum avocado benefit occurs at intermediate levels of inoculum potential. Likewise, maximum G. intraradices sporulation occurred under high light and at intermediate levels of G. intraradices inoculum potential. Interspecific interactions between two AMF, G. intraradices and Scutellospora heterogama , affected avocado growth and avocado carbon allocation. Infection with S. heterogama alone or in mixture with G. intraradices was associated with reduced avocado investment in photosynthetic organs, lower proportion of carbon allocated to stems and greater carbon allocation to glomalin. Phosphorus mediated interactions such that: (i) the negative impact of S. heterogama on avocado growth decreased with increasing phosphorus availability; and (ii) G. intraradices interacted with % leaf phosphorus to positively impact glomalin production. Under phosphorus-limiting conditions, maximum avocado benefit from G. intraradices was acquired in the presence of C. elatum, but not in the presence of the inferior mutualist S. heterogama.