F. Caravaca

Plant-growth-promoting rhizobacteria and arbuscular mycorrhizal fungi modify alleviation biochemical mechanisms in water-stressed plants

This study examined the effect of inoculation with the plant-growth-promoting rhizobacterium (PGPR) Pseudomonas mendocina Palleroni, alone or in combination with an arbuscular mycorrhizal (AM) fungus, Glomus intraradices (Schenk & Smith) or Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe, on antioxidant enzyme activities (superoxide dismutase, catalase and total peroxidase activities), phosphatase and nitrate reductase activities and solute accumulation in leaves of Lactuca sativa L. cv. Tafalla affected by three different levels of water stress. At moderate drought, bacterial inoculation and mycorrhizal inoculation with G. intraradices, alone or in combination, stimulated significantly nitrate reductase activity. At severe drought, fertilisation and P. mendocina inoculation, alone or in combination with either of the selected AM fungi, increased significantly phosphatase activity in lettuce roots and proline accumulation in leaves. Total peroxidase (POX) and catalase (CAT) activities increased in response to drought, whereas superoxide dismutase activity decreased. Inorganic fertilisation and both combined treatments of PGPR and AM fungus showed the highest values of leaf POX activity under severe drought. The highest CAT activity was recorded in the fertilised plants followed by the P. mendocina-inoculated plants grown under severe stress conditions. These results support the potential use of a PGPR as an inoculant to alleviate the oxidative damage produced under water stress.

No-tillage, crop residue additions, and legume cover cropping effects on soil quality characteristics under maize in Patzcuaro watershed (Mexico)

Abstract Intensive maize ( Zea mays L.) cropping based on conventional tillage practices has resulted in soil quality degradation in the Patzcuaro Watershed in central Mexico. A field experiment with seven soil management treatments was implemented on a sandy loam Andisol to evaluate the impact on soil quality of maize cropping with conventional tillage, no-tillage with varying percentages of surface residue coverage (0, 33, 66 and 100%), and no-tillage with 33% residue coverage together with cover crops of either Vicia sp. or Phaseolus vulgaris L. The treatments of no-tillage under crop residue coverage were established in 1995 and the leguminous species were planted in 1998. By 2000, the alternative management treatments had increased soil enzymes, soil organic C, biodegradable C fractions such as water soluble C, water soluble carbohydrates, and microbial biomass C, and soil wet aggregate stability, compared to the CT treatment. Wet aggregate stability was increased by adopting no-tillage and even further by additional residue. Most soil quality characteristics improved in direct proportion to residue inputs. The use of no-tillage management together with a moderate amount of crop residue (33%) and planted to leguminous species rapidly improved some soil quality characteristics. We conclude that conservation tillage practices can provide an alternative technology contributing to sustainable agriculture in the Patzcuaro watershed of Mexico, which can be extrapolated to similar areas elsewhere in Latin America.

Establishment of shrub species in a degraded semiarid site after inoculation with native or allochthonous arbuscular mycorrhizal fungi

The re-establishment of native shrub species in the Mediterranean basin serves to restore the characteristic biodiversity and to prevent the processes of erosion and desertification in semiarid areas. A field experiment was carried out in an abandoned semiarid agricultural Mediterranean area to assess the effectiveness of mycorrhizal inoculation, with a mixture of native arbuscular mycorrhizal (AM) fungi or an allochthonous AM fungus (Glomus claroideum), on the establishment of Olea europaea subsp. sylvestris L., Pistacia lentiscus L., Retama sphaerocarpa (L.) Boissier and Rhamnus lycioides L. seedlings in this area. One year after planting, shoot biomass of inoculated O. europaea and P. lentiscus seedlings was greater, by about 630% and 300%, respectively, than that of non-inoculated plants. Shoot biomass of G. claroideum-colonised R. sphaerocarpa plants was significantly greater than that of seedlings inoculated with the mixed native AM fungi after 12 months. The increase of R. lycioides growth due to inoculation with native AM fungi was significantly greater than that of G. claroideum-colonised seedlings during the same growth period. Inoculation with a mix of native AM fungi was the most effective treatment for increasing shoot biomass and N, P and K contents in shoot tissues of R. lycioides seedlings. The mixture of native AM fungi was the most effective with respect to colonisation of the roots of O. europaea and R. lycioides, but the native AM fungi and G. claroideum achieved similar levels of colonisation in P. lentiscus and R. sphaerocarpa. The use of native mycorrhizal potential as a source of AM inoculum may be considered a preferential inoculation strategy to guarantee the successful re-establishment of native shrub species in a semiarid degraded soil.

Aggregate stability changes after organic amendment and mycorrhizal inoculation in the afforestation of a semiarid site with Pinus halepensis

Abstract The recovery of soil structural stability is a precondition for successful afforestation programmes in semiarid environments. A multifactorial field experiment was carried out in a semiarid rangeland in south-eastern Spain to evaluate the influence of a fresh organic residue addition (first factor), mycorrhizal inoculation with Pisolithus arhizus (second factor), and the rhizosphere of Pinus halepensis (third factor) on soil aggregate stability. A total of 6 years after planting, the addition of residue was seen to increase the levels of stable aggregates to a greater extent than the mycorrhizal inoculation. Both reafforestation methods increased C-fractions and enzyme activities measured (dehydrogenase and phosphatase). The rhizosphere also affected aggregate stability, particularly when P. halepensis was inoculated with P. arhizus. Aggregate stability in the rhizosphere of P. halepensis was strongly correlated (P

Re-establishment of Retama sphaerocarpa as a target species for reclamation of soil physical and biological properties in a semi-arid Mediterranean area

Abstract Re-establishment of the indigenous shrub vegetation is a key step in the restoration of abandoned agricultural semi-arid lands. A field experiment was carried out to evaluate the effect of a composted residue and mycorrhizal inoculation with Glomus intraradices on the viability of Retama sphaerocarpa (L.) Boissier. The influence of the rhizosphere of this shrub legume on the physical–chemical and biological properties of an abandoned semi-arid agricultural area in south-eastern Spain was also assessed. Eighteen months after planting, the combined treatment of mycorrhizal inoculation and composted residue was the most effective for increasing the growth and the N and P contents in shoot tissues of R. sphaerocarpa. There was a highly positive significant correlation between shoot dry weight and the nutrient contents in shoot tissues. Water-soluble C, water-soluble carbohydrates, biomass C contents, and enzyme activities (dehydrogenase, urease, protease–N-α-benzoyl- l -argininamide (BAA), and acid phosphatase) measured in the rhizosphere of R. sphaerocarpa were higher than in the bare soil. Rhizosphere aggregate stability of R. sphaerocarpa was about 47% higher than that of bare soil. These improvements in the physical–chemical and biological properties of the rhizosphere soil of R. sphaerocarpa could facilitate the establishment and development of new plants in the surrounding area, which would aid the revegetation of semi-arid ecosystems.

Assessing the effectiveness of mycorrhizal inoculation and soil compost addition for enhancing reafforestation with Olea europaea subsp. sylvestris through changes in soil biological and physical parameters

A field experiment was carried out in a semiarid area to assess the influence of mycorrhizal inoculation and soil compost addition on establishment of Olea europaea seedlings. Associated changes in soil biological and physical parameters were observed. One year after planting, both reafforestation methods had significantly improved the soil structure. Thus, mycorrhizal inoculation increased soil aggregate stability (AS) and composted residue addition decreased soil bulk density (BD). A significant correlation ( P< 0.05) was found between BD and several biochemical parameters (dehydrogenase, protease and -glucosidase activities), indicating that soil biological agents play an important role in improving soil structure. The growth of O. europaeawas significantly enhanced by both composted organic residue addition and mycorrhizal inoculation treatment. The increase in mycorrhizal O. europaeaseedling growth may be due to the positive influence of mycorrhiza on soil AS. The combination of high fertility levels and low BD also favoured the growth of O. europaea in compost-amended soils. Finally, the positive interaction between the two methods in relation to seedling height growth could be related to the capacity of the fungus to increase nutrient uptake from the composted residue.

Differential response of δ13C and water use efficiency to arbuscular mycorrhizal infection in two aridland woody plant species

During a revegetation field experiment in Southeast Spain, we measured foliar carbon isotope ratios (δ13C) and gas exchange parameters in order to evaluate the influence of arbuscular mycorrhizal (AM) infection on the water use efficiency (WUE) of two semiarid woodland species. WUE during drought was significantly enhanced by inoculation with Glomus intraradices in Olea europaea ssp sylvestris, but not in Rhamnus lycioides. While Olea is a long-lived, slow-growing evergreen tree with a conservative water use strategy, Rhamnus is a drought-deciduous shrub with a shorter lifespan; these differences may explain their dissimilar patterns of physiological response to inoculation with the same AM fungus. Differences in δ13C and WUE between Olea and Rhamnus were larger when comparing AM inoculated than non-inoculated seedlings. This result suggests that some of the interspecific variability in δ13C observed for aridland plant communities may be due to different physiological responses to mycorrhization.

Application of composted urban residue enhanced the performance of afforested shrub species in a degraded semiarid land.

Improvement of physical-chemical soil quality is a key step for carrying out revegetation programs of degraded lands in Mediterranean semiarid areas. Organic residue addition may restore the quality of these areas. A field experiment was conducted in a silt-loam soil (Typic Petrocalcid) from a degraded semiarid Mediterranean area to evaluate the effect of the addition of a composted urban residue on soil aggregate stability, bulk density and chemical properties and on the establishment of Pistacia lentiscus and Retama sphaerocarpa seedlings. The composted residue was applied at a rate of 6.7 kg m(-2) before planting. The nutrient content (NPK), total organic C and water soluble C were increased and bulk density was decreased, in the rhizosphere soil of both shrub species, by the composted residue. The addition of composted residue significantly increased the soil aggregate stability by about 22% for both shrub species. The beneficial effect of the composted residue on soil quality still persisted 18 months after addition. Eighteen months after planting, the addition of composted residue to soil had increased significantly the production of shoot biomass by P. lentiscus and R. sphaerocarpa, by about 160% and 320% respectively, compared to control values. Composted residue addition to soil can be considered an effective preparation method of a degraded area for carrying out successful revegetation programs with Mediterranean shrubs under semiarid conditions.

Increased Diversity of Arbuscular Mycorrhizal Fungi in a Long-Term Field Experiment via Application of Organic Amendments to a Semiarid Degraded Soil

ABSTRACT In this study, we tested whether communities of arbuscular mycorrhizal (AM) fungi associated with roots of plant species forming vegetative cover as well as some soil parameters (amounts of phosphatase and glomalin-related soil protein, microbial biomass C and N concentrations, amount of P available, and aggregate stability) were affected by different amounts (control, 6.5 kg m−2, 13.0 kg m−2, 19.5 kg m−2, and 26.0 kg m−2) of an urban refuse (UR) 19 years after its application to a highly eroded, semiarid soil. The AM fungal small-subunit (SSU) rRNA genes were subjected to PCR, cloning, single-stranded conformation polymorphism analysis, sequencing, and phylogenetic analyses. One hundred sixteen SSU rRNA sequences were analyzed, and nine AM fungal types belonging to Glomus groups A and B were identified: three of them were present in all the plots that had received UR, and six appeared to be specific to certain amendment doses. The community of AM fungi was more diverse after the application of the different amounts of UR. The values of all the soil parameters analyzed increased proportionally with the dose of amendment applied. In conclusion, the application of organic wastes enhanced soil microbial activities and aggregation, and the AM fungal diversity increased, particularly when a moderate dose of UR (13.0 kg m−2) was applied.

Synergistic influence of an arbuscular mycorrhizal fungus and organic amendment on Pistacia lentiscus L. seedlings afforested in a degraded semiarid soil

A field experiment was undertaken to evaluate the effect of mycorrhizal inoculation with Glomus intraradices and added composted residue on the establishment of Pistacia lentiscus L. seedlings in a semiarid area. Composted residue greatly increased macronutrient (NPK) content, soil microbial activity and enzymatic activities, and decreased soil bulk density. There was a significant correlation between soil bulk density and both enzyme activities and labile C fractions (water-soluble C and water-soluble carbohydrates), which are also related to soil microbial activity. The most suitable methodology for revegetating with P. lentiscus seedlings was addition of composted residue to soil in conjunction with a mycorrhizal inoculation pretreatment of seedlings in a nursery, to increase available P uptake from composted residue. One year after planting, such a combined treatment had increased the plant height of P. lentiscus seedlings by 106% with respect to the control.