Exploration of Microbially Inoculated Biochar for Plant Growth Promotion

Abstract

Food security is a big challenge and it is getting more importance due to economic growth, increase in population, and climatic changes. Biochar is a carbon-rich pyrolyzed material widely used in agriculture as soil amendment for enhanced crop production, soil quality improvement, C–sequestration, and mitigation of atmospheric C. Soil microbes are the important component of soil ecosystem which influence ecological components and processes including nitrogen cycling. The presence of the soil microbes establish a symbiotic relationship with the plant roots to assist them in nutrients uptake; ultimately enhancing the plant productivity in limited nutrients condition. Besides the bacterial symbionts, there is another widespread group of symbiont termed ―mycorrhizal association‖ in the plant roots which facilitate in the uptake of nutrients (N, P, K, Ca, Mg, Fe, Cu, Mn, and Zn) from the soil and enhances the plant productivity under limited nutrients condition. Studies in the present thesis were designed by considering a plant-microbe-biochar system for plant growth promotion and heavy metal stress tolerance. In this regard, onion and maize plants system was tested because of their economic importance in the region of Pakistan and Turkey particularly and worldwide in general. Onion and maize plant have an absolute requirement of nutrients (N, P, K) for growth and development. The microbial application can facilitate in addressing limited access to chemical fertilizer concern. Moreover, biochar and phosphorus solubilizing bacteria (PSB) community can contribute together in nutrients availability. Both have the P-supply potential to the soil, but their interaction has been tested less under semi-arid climatic conditions. The purpose of the study was to evaluate the potential of biochemically tested promising PSB strains and biochar for maize plant growth and nutritional status in plant and soil. Therefore, two isolated PSB strains from maize rhizosphere were biochemically tested in vitro and identified by 16S rDNA gene analysis. The experiment was conducted in the greenhouse where the plant growth and nutrient availability to the plants were observed. In this regard, all the treatments such as PSB strains inoculated plants, biochar treated plants and combination of PSBs + biochar treated plants were destructively sampled on day 45 (D45) and day 65 (D65) of sowing with four replications at each time. PSB inoculation, biochar incorporation, and their combinations have positive effects on maize plant height and nutrient concentration on D45 and D65. In particular, plants treated with sawdust biochar + L. fusiformis strain 31MZR inoculation increased N (32.8%), P (72.5%) and K (42.1%) against control on D65. Besides that, only L. fusiformis strain 31MZR inoculation enhanced N (23.1%) and P (61.5%) than control which shows the significant interaction of PSB and biochar in nutrient uptake. PSB and biochar have the potential to be used as a promising amendment in improving plant growth and nutrient absorption besides the conventional approaches. Multifunctionality of BC makes it valuable to use, however, the heterogeneity in its properties raises questions on its suitability in a particular environment. The present study was designed to explore the heterogenic properties of biochar in order to align its use for soil and environment. Biochar was prepared from sludge (S), animal-waste (AW) and plant-derived feedstocks (FS) originated from Mediterranean region. Physical and chemical characterization of BC was performed to evaluate its suitability in the Mediterranean region regarding nutrient availability concentrations to the plants. Considering that, pH, electrical conductivity (EC), proximate, ultimate and nutrient analyses were done. Moreover, Scanning Electron Microscopy (SEM) was performed, and C–stability trend was observed by thermogravimetric analysis. Plant-FS derived biochar possess high moisture content, volatile matrix, fixed and total carbon (TC) as compared to sludge biochar (SBC) and AW derived BC. Higher calcium carbonate (CaCO3) contents were observed in AW derived BC. Furthermore, it is revealed from the porosity of BC that soil microbes can sustain inside the porous structure when used as soil amendment. Different FS-oriented biochar can be used as a soil amendment depending on the soil quality. The AW derived BC and plant-FS derived biochar can be a good source of immediate nutrients release for plant production in agriculture and C–sequestration respectively. Biochar can improve soil properties, plant nutrient uptake by facilitating soil microbes and altering properties of growth media. These studies were further designed to answer that how the biochar interact with soil microbes in different soils for root colonization and plant nutrients uptake. Moreover, to evaluate the incidence of biochar- and microbially induced changes in the plant-soil system with P-application. Onion plant was grown in two soils amended with two types of biochar with (or without) P2O5 application, having three microbially inoculated treatments (and uninoculated control). Shoot and root biomass,macro, and micronutrients concentration, N- and P-uptake and root colonization were analyzed. Moreover, root attributes such as root surface area, root length, and root volume were also evaluated by using WinRhizo. Biochar increased nutrient uptake and plant biomass in the presence of P2O5 and microbial inoculation. Both soils were diversly responsive, and the addition of biochar enhanced their responsiveness. Moreover, without-P addition, soil microbial efficiency enhanced the nutrients uptake in shoot and root while chlorophyll fluorescence was non-significant. Root colonization was also notably increased in B+AM inoculated plants. Biochar types respond differently to varying soil conditions. The P (with- or without-) application significantly influenced soil microbial effectiveness in nutrient uptake and plant growth. Moreover, the root colonization was also influenced by the biochar type and P application. Root attributes were significantly influenced by the microbial inoculation. Cadmium (Cd) toxicity in agricultural crops is a widespread problem. Little is known about the biochar and arbuscular mycorrhizal fungi (AMF) effect, on Cd uptake and translocation in maize plant either applied separately or combined. The current study was performed to demonstrate the effects of biochar and AMF on growth, photosynthesis activity, nutrients and Cd uptake by maize is grown in Cd-spiked soil. The alkaline soil was spiked by three various concentrations of Cd (0, 5, and 10 mg Cd kg-1) for each set of uninoculated control, biochar (Phragmites 1%), AMF (Rhizophagus clarus) and biochar + AMF. Plants were harvested after 70 days, and various morphological and physiological parameters, as well as elemental concentration and root colonization, were recorded. Addition of biochar, AMF, and biochar + AMF enhanced dry plant biomass in Cd-spiked soil. Root colonization decreased proportionally by increasing Cd concentration. Besides that, addition of biochar either separately or with AMF enhanced the root attributes in the Cd-spiked soil. However, biochar + AMF neutralized Cd stress in maize plant for the gaseous attributes (assimilation rate, transpiration rate, intercellular CO2, and stomatal conductance). The AMF enhanced Cd uptake by plant while the addition of biochar phytostabilized the Cd and reduced its uptake by plants. Phosphorus concentration was augmented in shoots and roots of maize plant in biochar-amended soil than control plants. It is concluded that biochar and AMF could ameliorate Cd toxicity effects in maize plant by changing the morphological and physiological attributes along with elemental composition in the Cd-spiked soil.