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Land-use change has drastically reduced the area of pristine forests in tropical and subtropical regions. In NWArgentina, Yungas forests were among the most affected by deforestation for the implementation of agricultural crops. Conversion of forests to croplands modified the structure and function of soil microbial communities, but its effects on soil functionality across time after land-use change are understudied. Therefore, the objective of this study was to analyze the impact of land-use change and time under cultivation on the functionality of microbial communities in these soils. We established a 30- year old chronosequence comprising 4 stages (forest and short-, mid- and long-term agriculture) in 3 independent farms. Together with soil physicochemical properties, we measured microbial biomass carbon, basal respiration, ammonification, acid and alkaline phosphomonoesterase activities, and community-level physiological profiling (CLPP). During the first years of cultivation, the functionality and biomass of soil microbial communities were strongly affected. Compared to forest soils, short-term agricultural soils exhibited a reduction on microbial biomass ( 45%), ammonification ( 67%) and acid phosphomonoesterase activity ( 41%). Moreover, increased basal respiration (up to 94%) and metabolic quotient in those soils suggested radical changes in functionality at the beginning of the chronosequence. However, CLPP evidenced that older agricultural sites had an increased global catabolic response per unit biomass, while it detected no differences in physiological diversity of soil microbial communities along the chronosequence. The lack of differences detected between mid- and long-term agricultural sites, in addition to a reduced inter-site variability, evidences an apparent stabilization and homogenization of soil microbial communities towards the end of the chronosequence. In contrast with physicochemical variables, microbiological variables had a greater performance for characterizing the different stages of the agricultural chronosequence and the impact of land-use change on soil functionality. Fil: Tosi, Micaela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Biología Aplicada y Alimentos. Cátedra de Microbiología Agrícola; Argentina Fil: Correa, Olga Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Biología Aplicada y Alimentos. Cátedra de Microbiología Agrícola; Argentina Fil: Soria, Marcelo Abel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Biología Aplicada y Alimentos. Cátedra de Microbiología Agrícola; Argentina Fil: Vogrig, Jimena Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Biología Aplicada y Alimentos. Cátedra de Microbiología Agrícola; Argentina Fil: Sydorenko, Oksana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Biología Aplicada y Alimentos. Cátedra de Microbiología Agrícola; Argentina Fil: Montecchia, Marcela Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Biología Aplicada y Alimentos. Cátedra de Microbiología Agrícola; Argentina

A B S T R A C T Water stress, with its negative consequences on plant growth and survival, can be mitigated by Azospirillum brasilense inoculation. In tomato, A. brasilense delays wilting caused by a vascular pathogen, Clavibacter michiganensis subsp. michiganensis, by yet unknown mechanisms. We studied morphological, anatomical and physiological changes induced by A. brasilense in tomato that relate to water stress tolerance, which could explain the deferral in symptom expression. For this purpose, tomato seeds were treated or not with A. brasilense BNM65, and 5 weeks later plants were challenged with C. michiganensis subsp. michiganensis or mock inoculated with water. There was a large growth promotion associated to Azospirillum: treated plants had higher total biomass and leaf area. In relation to water stress tolerance, Azospirillum treated plants had larger xylem vessel area, higher stem specific hydraulic conductivity, thicker stems, and lower shoot/root dry matter and specific leaf area. These changes were opposite to those induced by C. michiganensis subsp. michiganensis. We conclude that A. brasilense favoured a better adjustment of plant-water relations by several mechanisms, and thus, transitorily alleviated symptoms expression of a vascular disease.

Land use effects on microbial communities may have profound impacts on agricultural productivity and ecosystem sustainability as they are critical in soil quality and health. The main aim of this study was to characterize the microbial communities of pristine and agricultural soils in the central Yungas region in Northwest Argentina. As a first step in the development of biological indicators of soil quality in this region, a comprehensive approach involving a structural and functional evaluation of microbial communities was used to detect changes in soil as consequence of land use. The sites selected included two pristine montane forest sites (MF1 and MF2), two plots under sugarcane monoculture for 40 and 100 years (SC40 and SC100), one plot under 20 years of soybean monoculture (SB20), a recently deforested and soybean cropped site (RC), and two reference sites of native forest adjacent to the sugarcane and soybean plots (PF1 and PF2). We used three microbial community profiling methods: denaturing gradient gel electrophoresis (DGGE) analysis of PCR amplified 16S rRNA genes, community-level physiological profiling (CLPP) using a BD oxygen biosensor system (BDOBS-CLPP) and phospholipid fatty acid (PLFA) analysis. Deforestation and agriculture caused expected increases in pH and decreases in organic carbon and microbial biomass. Additionally, shifts in the microbial community structure and physiology were detected with disturbance, including reduced diversity based on PLFA data. The higher respiratory response to several carbon substrates observed in agricultural soils suggested the presence of microbial communities with lower growth yield efficiency that could further reduce carbon storage in these soils. Using an integrated multivariate analysis of all data measured in this study we propose a minimum data set of variables (organic carbon, pH, sucrose and valeric acid utilizations, a17:0 and a15:0 PLFA biomarkers and the value of impact on microbial diversity) to be used for future studies of soil quality in Northwest Argentina.

The increase in soybean productivity has contributed to a greater use of agrochemicals, which cause major problems, such as soil and water pollution and reduction of biodiversity, and have a negative impact on non-target species. The development of microbial biocontrol agents for soybean diseases can help to reduce pesticide abuse. Bacillus amyloliquefaciens BNM122 is a potential microbial biocontrol agent able to control the damping-off caused by Rhizoctonia solani when inoculated in soybean seeds, both in a plant growth chamber and in a greenhouse. In this study, we report the effect of soybean seed treatments with strain BNM122 or with two fungicides (thiram and carbendazim) on the structure and function of the bacterial community that colonizes the soybean rhizosphere. Also, soybean root nodulation by Bradyrhizobium japonicum , mycorrhization by arbuscular mycorrhizal fungi and plant growth were evaluated. We used the r - and K -strategist concept to evaluate the ecophysiological structure of the culturable bacterial community, community-level physiological profiles (CLPP) in Biolog™ EcoPlates to study bacterial functionality, and the patterns of 16S RNA genes amplified by PCR and separated by denaturing gradient gel electrophoresis (PCR–DGGE) to assess the genetic structure of the bacterial community. Neither the ecophysiological structure nor the physiological profiles of the soybean rhizosphere bacterial community showed important changes after seed inoculation with strain BNM122. On the contrary, seed treatment with fungicides increased the proportions of r -strategists and altered the metabolic profiles of the rhizosphere culturable bacterial community. The genetic structure of the rhizosphere bacterial community did not show perceptible changes between treated and non-treated seeds. Regarding the bacterial and fungal symbioses, seed treatments did not affect soybean nodulation, whereas soybean mycorrhization significantly decreased ( P It can be concluded that soybean seed treatment with B. amyloliquefaciens BNM122 had a lesser effect on soil microbial community than that with the fungicides, and that these differences may be attributed to the less environmental persistence and toxic effects of the strain, which deserve further studies in order to develop commercial formulations.