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Table 2 Effect of co-applied PGPR and biochar on plant productivity and soil quality under environmental stressors

From: Unlocking the potential of co-applied biochar and plant growth-promoting rhizobacteria (PGPR) for sustainable agriculture under stress conditions

Strain

PGPR trait

Biochar production and application rate

Crop

Experimental details

Effect on plant productivity and soil fertility

References

Pseudomonas putida, Planomicrobium chinense

 

Produced from plant leaves

Pyrolyzed at 300–400 °C for 12 h

Soybean (Glycine max)

Pot experiment; Drought applied after 5 weeks of germination, with holding water supply for 4 days

In PGPR + biochar, leaf water content by 9%, root to shoot ratio by 54% and proline content by 65.5% increased over control

Similarly, nitrogen, phosphorus, potassium were increased by 9.5%, 24% and 26%, respectively, than control

[61]

Pseudomonas sp. and Staphylococcus sp.

 

Produced from Morus alba L. wood in oxygen-limited conditions

Brassica napus L.

Field experiment; drought stress applied for 15–30 days

Co-application improved plant antioxidant enzyme activity including ascorbate peroxidase (APX) and catalase (CAT)

Also enhanced the content of photosynthetic pigments such as chlorophyll pigments, anthocyanin content and carotenoids content

[62]

Sphingobacterium pakistanensis, Cellulomonas pakistanensis

 

Produced from Wood residues of mulberry plant (Morus alba L.) combustion at 500–750 °C

Application rate was 5%

Vicia faba

Pot experiment; drought induction was 13 days and 26 days

In PGPR + biochar, relative water content improved by 35.82–54.34%

Similarly, photosynthetic pigments and proline improved by 58.33–173.8% and 46.58–86.62%, respectively

[63]

Azotobacter chroococcum and Pseudomonas koreensis

IAA producing and phosphate solubilizing

Biochar was produced from rice husk and corn stalk at the ratio (1:1)

Pyrolyzed at 350 °C for 3 h

Application level of biochar was: 10 ton/ha

Maize (Zea mays L.)

Field experiment; irrigation with saline water

Plant growth duration was till its maturity

PGPR + biochar treatment increased soil urease and dehydrogenase activity by 26.6% and 33.5%, respectively, than PGPR and biochar treatment. EC decreased by 9% than PGPR treatment and by 5.6% than biochar treatment

Similarly, no. of grains ear−1, 100-grain weight, grain yield and stover yield increased by 1.9%, 17%, 24.60% and 5.23%, respectively, than PGPR treatment, and by 1.1%,13.44%, 9.5% and 4.38%, respectively, than biochar treatment

[64]

Cellulomonas pakistanensis and Sphingobacterium pakistanensis

–

Biochar was produced from wood of Morus alba Pyrolyzed at between 900 and 1100 °C

Applications of biochar level were 0 and 5% w/w

Pea and bean family (Vicia faba)

Pot experiment; Drought applied for 13 and 26 days

Plants were grown for 26 days

PGPR + biochar treatment positively ameliorated fresh and dry weight of leaves by 28.57 and 10.47%, roots 36.36 and 14.28% and shoots by 16 and 10% than sole biochar and PGPR treatments, respectively

[65]

Alcaligenes faecalis, and Bacillus amyloliquefaciens

ACC deaminase producing

Biochar was made from vegetables and fruits

Pyrolyzed at 450 °C for 2 h

Application of biochar level was: 0.5%

Mint (Mentha piperita L.)

Pot experiment: lead stress: 250 mg Pb kg−1soil

Alcaligenes faecalis strain + compost-mixed biochar treatment showed significant results in improving plant chlorophyll content (37%), root dry weight (58%) and nitrogen (46%), phosphorus (39%), and potassium (63%) in leaves of mint than untreated control

Lead (artificially induced) uptake also decreased in spinach roots by 43% and potassium uptake increased by 10.5% over untreated control

[66]

Pseudomonas aeruginosa, Enterobacter cloacae, Achromobacter xylosoxidans and Leclercia adecarboxylata

Drought tolerant and ACC-deaminase producing

Biochar was produced from timber waste

Pyrolyzed at 389 °C for 80 min. Application of biochar levels were: 0.75 and 1.5% w/w

Maize (Zea mays L.)

Drought/moisture conditions: 70% of field capacity (optimum moisture), 50% FC (mild) and 30% FC (severe drought)

Duration of plant growth was 3 months (Harvesting at maturity)

A. xylosoxidans + 1.5% biochar treatment showed 43% and 25 increase in grain yield pot−1 than A. xylosoxidans and 1.5% biochar using alone

A. xylosoxidans + 1.5% biochar showed 19 and 6% higher photosynthetic rate, 30 and 7% higher transpiration rate, and 16% and 7% higher stomatal conductance, respectively, than A. xylosoxidans and 1.5% biochar using alone under severe drought

P. aeruginosa + biochar decreased electrolyte leakage by 28% and 4% than sole application of P. aeruginosa and biochar, respectively

[67]

Burkholderia phytofirmans

Siderophore-producing endophytic

Biochar was produced from tree twigs feedstock

Pyrolyzed at 400 °C for 40 min

Application of biochar level was 1%

Quinoa (Chenopodium quinoa)

Salinity level: EC 20 dS/m

PGPR + biochar treatment showed 2.73 × 105 CFU/g in rhizosphere, 9.92 × 104 CFU/g interior root and 1.9 × 104 CFU/g interior shoots bacterial population than the 5.73 × 105 CFU/g in rhizosphere, 4.53 × 105 CFU/g interior root and 9.92 × 104 CFU/g interior shoots bacterial population found in biochar treatment. Plant height, root dry weight, shoot dry weight, grain yield, photosynthetic rate, stomatal conductance increased by 17, 26, 10, 5, 5, 16 and 12%, respectively, than PGPR only treatment

[68]

Alcaligenes faecalis, and Bacillus amyloliquefaciens

ACC deaminase producing

Biochar was made from vegetables and fruits

Pyrolyzed at 450 °C for 120minuts

Application of biochar level was:0.5%

Spinach (Spinacia oleracea)

Pot experiment: lead stress: 250 mg Pb kg−1 soil

Compost (mixed fruits) mix biochar (vegetable waste) with 1:1

Treatment ACC deaminase producing PGPRs and compost-mixed biochar showed 13.5% less uptake of Pb in leaves of mint plant than the soil without PGPR and biochar under lead stress

[69]

Bacillus sp.

Cd-immobilizing, IAA producing and phosphate solubilizing

Biochar was produced from coconut shell. Pyrolyzed at 800 °C for 6 h

Application of biochar level was: 5 g/100 ml suspension

Ryegrass (Lolium perenne)

Pot experiment; Cd polluted soil was used. Plant growth duration was till at maturity

PGPR + biochar treatment showed Bacillus sp. increased by 7.46% than PGPR only treatment

PGPR + biochar treatment showed dehydrogenase 4.61 times more than biochar treatment 2.47times

HOAc-extractable Cd decreased in soil by 11.34% in than biochar 4.49% and PGPR 6.05% treatments, respectively. PGPR + biochar treatment = ryegrass biomass 1.96 g found than biochar treatment only 0.42 g

Lowest Cd concentration in ryegrass 5.45 mg kg−1 found in PGPR + biochar than biochar, PGPR and soil without PGPR and biochar treatments

[70]

Bacillus sp.

Ni, Pb and Cr tolerant

IAA and ACC deaminase producing

Application level was: 1%

Wheat (Triticum aestivum L.)

Green house pot experiment

K2Cr2O7 solution was applied at the rate of 2.5 mg/Kg with irrigation

PGPR + biochar treatment increased shoot and root length by 22–23.4%, and maximum increase in chlorophyll and SOD was 28–40%. Combined treatment also maintained proline and sugar contents by 20.5% and 9.6%

In dry biomass, Cr concentration was 0.28 ± 1.01 mg/kg than uninoculated control 0.05 ± 1.01 mg/kg

[71]

Enterobacter sp.

Cd tolerant

Biochar was produced from paper and pulp waste

Pyrolyzed at 450 °C

Application of biochar levels were: 0 and 10 g kg−1

Rapeseed (Brassica napus)

Pot experiment;. Soil was spiked with Cd at the at the 2 levels 0 and 80 mg kg−1 dry soil by using Cd (NO3)2

Plant growth duration was 60 days

PGPR + biochar treatment under Cd stress decreased Cd concentration by 45.6% in soil than PGPR and biochar. Bacterial population was 4.5 × 105 in co-applied, whereas it was 1.8 × 105 in biochar only treatment

Under Cd stress, PGPR + biochar treatment decreased Cd by 40.1 and 38.2% in root and shoot than PGPR treatment, by 16.8 and 16.9% than biochar treatment, and by 23.4 and 21.3%, respectively, than control (No PGPR, no biochar)

[16]

Agrobacterium fabrum and Bacillus amyloliquefaciens

ACC deaminase producing

Biochar was produced from timber waste

Pyrolyzed at 389 °C for 1 h and 20 min. Application of biochar levels were: 0 and 1.5%

Wheat (Triticum aestivum L.)

Field experiment; drought stress induced by skiping (4I control, 3I mild and 2I severe drought). Plant growth duration was 120 days.

Bacillus amyloliquefaciens + biochar treatment showed 34% and 24% increase in plant height, 25% and 8% in root length, and 5% and 2% in spike length, respectively, than Bacillus amyloliquefaciens and biochar using alone under severe drought. Agrobacterium fabrum + biochar showed increase in 1000-grain weight by 13% and 2% than Agrobacterium fabrum using alone and with biochar under severe drought

[72]

Pseudomonas koreensis and Bacillus coagulans

IAA producing and inorganic phosphate solubilizing

Biochar was produced from rice husk and corn stalk at the ratio (1:1)

Pyrolyzed at 350 °C

Application of biochar rate was 2 kg m−2

Rice (Oryza sativa L.)

Field Experiment; soil was salt affected, water deficit conditions were created by irrigation every 6, 8 and 10 days

Duration of plant growth was till its maturity

At irrigation after 6 days improved soil moisture content and minimum level of SAR, Na+ and EC were found using combined treatment PGPR + biochar than using PGPR and biochar alone

Grain yield increased by 9.9% and 5.5% and straw yield by 6.68% and 3.78% in PGPR + biochar treatment than PGPR and biochar only treatment. Relative water content and stomatal conductance of rice leaves were enhanced by PGPR + biochar by 8.2% and 12.19% than PGPR and biochar only treatment, respectively. Similarly, 1000-grain weight was increased by 6–22% and proline content in leaves decreased by 38.86% and 22% than PGPR treatment and biochar treatment, respectively

[60]

Leclercia adecarboxylata, Agrobacterium fabrum, Bacillus amyloliquefaciens, Pseudomonas aeruginosa

ACC deaminase producing

Biochar was produced from timber waste

Pyrolyzed at 389 °C for 1 h and 20 min. Application of biochar levels were 0, 1 and 1.5%

Wheat (Triticum aestivum L.)

Pot experiment; drought stress applied by maintaining 50% and 30% of field capacity. Plant growth duration was 50 days

B. amyloliquefaciens + 1.5% biochar treatment under stressed conditions increased the chlorophyll a by 114%,, chlorophyll b by 123%, photosynthetic rate by 118%, transpiration rate by 73%, 100-grain weight by 59%, and grain N, P and K up to 58%, 18% and 23%, respectively, compared to control

[73]

Micrococcus sp. and Arthrobacter sp.

IAA producing and cadmium-resistant bacteria

Biochar was produced from cassava stem (Manihot esculenta L. Crantz). Pyrolyzed at 300 °C for 120 min

Application of biochar level was: 0.2%

Chlorophytum laxum

Green house pot experiment; Cd containing soil (pristine)

Plant growth duration was 9 weeks

Micrococcus sp. + biochar treatment increased root dry weight by 1.2 and 1.1 fold at 6 and 9 weeks of harvesting, respectively, than the PGPR and biochar treatments under Cd stress

[74]

Pseudomonas fluorescens

 

Biochar was produced from azolla biomass

Pyrolyzed at 600 °C under oxygen-limited conditions

Application of biochar level was:0 and 1%

Rosemary (Rosmarinus Officinalis L.)

Green house pot experiment

Calcareous soil was used

Plant growth duration was 6 month

PGPR + biochar treatment increased microbial biomass carbon by 34.9% than control

Nitrogen, phosphorus and potassium content in PGPR + biochar treatment increased by 22%, 10% and 9.5% than PGPR treatment and by 8.6%, 13% and 13.5%, respectively, than biochar treatment

Similarly, PGPR + biochar treatment increased hoot fresh weight increased by 34.7%, fresh weight of roots by 27%, plant height by 18.2% than untreated control

[75]

Serratia odorifera

ACC deainase producing and drought tolerant

Biochar produced from algal biomass. Pyrolyzed at 300 °C for 60 min

Application of biochar level was 4% w/w

Maize (Zea mays L.)

Pot experiment; drought stress induced by maintaining field capacity (FC) at 75% and 50%

Plant growth duration was two months

PGPR + biochar increased pH by 7 and 5%, EC by 34 and 13%, nitrate by 57 and 34%, phosphorus by 54 and 49%, extractable potassium by 30 and 15% and organic matter by 69 and 21% under 50% field capacity than PGPR and biochar treatments using alone. Similarly, plant height increased by 38 and 16%, shoot fresh weight by 29 and 17%, shoot dry weight by 44 and 24%, root fresh weight by 60 and 27%, root dry weight by 84% and 24%, and root length by 47% and 32%, respectively, than PGPR and biochar treatments using alone under 50% field capacity

[76]

Azospirillum

Free-living, mutualistic nitrogen fixators and phosphate solubilizers

Biochar was produced from grain husks and paper fiber sludge. Pyrolyzed at 450–500 °C for 20 min

Application of biochar level was: 3 t ha−1

Maize (Zea mays L.)

Field trial; area was prone to drought

Plant growth duration was 5 months

PGPR + biochar treatment increased substrate induced respiration in acidic soil by up to 100% and 50% in calcareous soil than unamended control (No PGPR, no biochar)

PGPR + biochar treatment increased above ground biomass by 91% than unamended control

[77]

Pseudomonas fluorescens

ACC deaminase, exopolysaccharides and osmolyte producing

Biochar was produced from pine wood

Pyrolyzed at 300 ºC

Application of biochar levels were: 0 and 2% w/w

Cucumber (Cucumis sativus)

Pot experiment; water deficit conditions maintained by maintaining field capacity (FC) at 50, 75, 100%

Duration of plant growth was 35 days. Compost used was 5% level

Pseudomonas fluorescens + biochar at 50% field capacity showed 70% more root colonization in soil than PGPR only treatment

PGPR + biochar treatment at 50% field capacity showed increases in shoot length, shoot fresh weight, root length, and root fresh weight by 10%, 10%, 29% and 16%, respectively, than the 2% biochar only treatment. Also chlorophyll content and relative water content increased by 5% and 6% than 2% biochar only treatment

[59]

Bradyrhizobium japonicum

Nitrogen fixing

Biochar was produced from woody biomass

Produced in closed reactor. Application of biochar levels were: 1, 2.5, and 5%

Mung bean (Vigna mungo)

Green house pot experiment; plant growth duration was 12 weeks

Biochar at 2.5% with PGPR was the most effective treatment that lead to 40% increase in soil microbial biomass carbon, 2.5% biochar with PGPR increased plant height and root length than other treatments

[78]

Pseudomonas sp.

Phosphate solubilizing

Biochar was produced from poplar saw dust

Application of biochar level was: 5 g/Kg of soil

Maize (Zea mays L.)

Pot experiment; in growth chamber with anoxic conditions, induced salinity stress using NaCl at 150 mM rate

Biochar + fertilizer used in ratio (5:1)

PGPR + biochar treatment showed soil moisture content increased almost 20% than in PGPR treatment. Moreover, Pseudomonas sp. + biochar treatment 30% increased calcium and potassium content in aerial part of maize than PGPR treatment under saline conditions

PGPR + biochar treatment increases peroxidase activity by 50% and decreased proline content (leaves) by 20% than PGPR treatment

[79]

Burkholderia phytofirmans and Enterobacter sp.

Endophytic

ACC deaminase and exopolysaccharide producing

Biochar was produced from hard wood (80%) and soft wood (20%) mixture

Pyrolyzed at 500 °C. Application of biochar levels were: 0 and 5%

Maize (Zea mays L.)

Green house pot experiment

Induced salinity: with irrigation water containing 0 and 25 mM NaCl solution, respectively

Duration of plant growth was 2 months

Strain Enterobacter + 5% biochar treatment showed an higher colonizing efficiency (6.0 CUF g–1 DW) in rhizosphere than another strain Burkholderia phytofirmans + biochar in saline soil

Enterobacter + 5% biochar treatment and B. phytofirmans + 5% biochar treatment reduced Na+ uptake by 25% and 8%, respectively, than biochar only treatment

[80]