| dc.description.abstract | Soil acidity and salinity are major constraints for agricultural productivity around the world. Improving beneficial plant-microbe interactions in the rhizosphere and endosphere could improve plant tolerance to acidity and salinity and increase crop yield and productivity. However, soil acidity and salinity can adversely impact symbiotic interactions of plants with arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria (NFB), which play an important role in plant nutrition. Soil amendments or foliar application of signaling compounds were shown to modulate microbial diversity and composition in the rhizosphere and plant endosphere and could be potential management tools to improve beneficial plant-microbial interactions in acidic and saline soils. However, it is not clear how native microbial community in the rhizosphere and endosphere of a legume crop respond to acidity and salinity stress and soil amendments. It is also not clear whether exogenous application of signaling compounds can significantly modulate rhizosphere and endosphere microbiome structure of a legume crop. Particularly, AMF and NFB responses to soil amendments and signaling compounds needs to be investigated in acidic and saline soils. To address these knowledge gaps, two studies were conducted to evaluate soil and foliar amendments to improve plant-microbe interactions in a legume crop (cowpeas, Vigna unguiculata (L.) Walp.) grown in an acidic and a saline soil. A comprehensive assessment of plant growth and development and microbiome composition in the rhizosphere and endosphere including legume-rhizobia and plant root-AMF symbiosis were evaluated in both studies.
In the first experiment, biochar as a soil amendment and salicylic acid (SA) as a foliar applied stimulant were evaluated for their impacts on soil pH, nutrient uptake, nodulation, AMF colonization, diversity and composition of rhizosphere and endophytic microbiome of cowpea plants grown in acidic soils (pH = 4.8). Results showed that soil acidity reduced nodulation, plant nutrient concentrations, diversity of rhizosphere microbes and pod yield. Biochar (BC) amendment was more effective in improving plant nutrient uptake and pod yields than SA treatment. Soil pH was increased to around 5.8 ± 0.2 in the BC treatment compared to control (5.0 ± 0.2). Similarly, nodulation numbers were higher in BC treatment, which resulted in higher N concentrations in the leaves compared to SA treatment. Percent AMF colonization was also increased significantly in BC treatment, which recorded higher leaf P concentrations. Treatment of SA significantly improved AMF colonization and abundance of AMF taxa in the rhizosphere, however, plant nutrient concentrations and pod yield did not significantly differ from unamended control. Both BC and SA significantly altered the microbial composition in the rhizosphere and plant endosphere. Treatment of BC also significantly increased the relative abundance of several plant beneficial taxa such as Bacillus, Pseudomonas, Penicillium, Rhizobium and Bradyrhizobium compared to control. Based on the results of this study it was concluded that BC application to an acidic soil was effective in improving plant-microbe interactions and pod yields of cowpea plants grown in an acidic soil.
A second greenhouse study was conducted to evaluate compost (CMP) and gypsum (GYP) as soil amendments and foliar application of strigolactones (SL), salicylic acid (SA) and coumarins (COU) for their impacts on plant-microbe interactions of cowpea grown in a saline soil (pH = 8.5). Crop growth and development, diversity and composition of rhizosphere and endophytic microbiome, arbuscular mycorrhizal fungi (AMF) colonization, nodulation, plant nutrient concentrations were estimated from the treatments. Results showed that soil salinity adversely impacted plant nutrient uptake, AMF colonization and pod yields. Among the amendment treatments, SL+SA treatment produced the highest cowpea pod yield followed by CMP amendment. Highest nodulation and root colonization were noted in SL+SA treated plants. Significantly higher relative abundance of several plant beneficial microbes including a Streptomyces species and several AMF (Rhizophagus and Diversispora) were noted in the rhizosphere and roots of SL+SA treated plants compared to control. Based on the results of this study, it was concluded that foliar application of SL+ SA was most effective in improving plant-microbe interactions and pod yield of cowpea plant grown in a saline soil.
It was demonstrated by these two studies that several beneficial microbes in the rhizosphere and endosphere of a legume crop were sensitive to acidity and salinity stress. It was also clear that various soil amendments and exogenous application of signaling compounds significantly altered rhizosphere and endosphere microbiome structure of a legume crop, and improved cowpea interactions with AMF and NFB. Using effective soil amendments such as biochar in acidic soil and foliar application of SL and SA for plants grown in saline soils are potential agriculture management avenues for improving soil health and productivity in acidic and saline soils. | en |
