Interactions between plant‐growth‐promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi and Rhizobium spp. in the rhizosphere of Anthyllis cytisoides, a model legume for revegetation in mediterranean semi‐arid ecosystems

Abstract

SUMMARY Arbuscular mycorrhizal (AM) fungi, Rhizobium bacteria and plant‐growth‐promoting rhizobacteria (PGPR) were isolated from a representative area of a desertified semi‐arid ecosystem in the south‐east of Spain. Microbial isolates were characterized and screened for effectiveness by a single‐inoculation trial in soil microcosms. Anthyllis cytisoides L., a mycotrophic pioneer legume, dominant in the target mediterranean ecosystem, was the test plant. Several microbial cultures from existing collections were also included in the screening process. Two AM fungi (Glomus coronatum, native, and Glomus intraradices. exotic), two Rhizobium bacteria (NR4 and NR9, both native) and two PGPR (A2, native, and E, exotic) were selected. A further screening for the appropriate double and triple combinations of microbial inoculants was then performed. The parameters evaluated were biomass accumulation and allocation, N and P uptake, N2‐fixation (15N) and specific root length. Overall, G. coronatum, native in the field site was more effective than the exotic G. intraradices in co‐inoculation treatments. In general, our results support the importance of physiological and genetic adaptation of microbes to the whole environment, thus local isolates must be involved. Many microbial combinations were effective in improving either plant development, nutrient uptake, N2‐fixation or root system quality. Selective and specific functional compatibility relationships in plant response between the microbial inoculants, were observed. Despite the difficulty of selecting a multifunctional microbial inoculum, appropriate microbial combinations can be recommended for a given biotechnological input related to improvement of plant performance. This could be exploited in nursery production of target plant species endowed with optimized rhizosphere/mycorrhizosphere systems that can be tailored to help plants to establish and survive in nutrient‐deficient, degraded habitats. The relevance of this microbial‐based approach in the context of a reclamation strategy addressed to environmental sustainability purposes is discussed.

Some Mediterranean plant species (Lavandula spp. and Thymus satureioides) act as potential ‘plant nurses’ for the early growth of Cupressus atlantica

“…These results are in accordance with other survey studies carried out in Mediterranean areas, that have shown that most of the plant species involved were heavily mycorrhizal (Requena et al 1996(Requena et al , 1997. For example, it has been previously described that lavender plants form arbuscular mycorrhizas and are mycorrhizal-dependent species (Azcon and Barea 1997).…”

Ability of Emericella rugulosa to mobilize unavailable P compounds during Pearl millet [Pennisetum glaucum (L.) R. Br.] crop under arid condition

“…In particular, plant growth promoting fungi have been reported to be key elements for plant establishment under nutrient-imbalance conditions. Use of those fungi use in agriculture can favor a reduction in agro-chemical use and support more crop production 20,21,22 . The availability of phosphorus (P) to plants depends on the activity of microorganisms present in the rhizosphere 23 and the strategies of plant for taking up P 24 .…”

Characterisation of microbial communities colonising the hyphal surfaces of arbuscular mycorrhizal fungi

“…So-called mycorrhiza helper bacteria have been shown to promote mycelial growth and mycorrhiza formation (Garbaye, 1994;Frey-Klett et al, 2007). Several studies have reported interactive effects between plant-growth-promoting bacteria, pathogens, rhizobia and AMF (Azcon-Aguilar and Barea, 1996;Requena et al, 1997;Xavier and Germida, 2002;Wamberg et al, 2003). Moreover, bacteria have been isolated from AMF spores and mycorrhizal cultures that promote or sometimes inhibit AMF spore germination, mycorrhisation and plant growth (Mayo et al, 1986;Budi et al, 1999;Xavier and Germida, 2003).…”