Lead (Pb) pollution is appearing as an alarming threat nowadays. Excessive Pb concentrations in agricultural soils result in minimizing the soil fertility and health which affects the plant growth and leads to decrease in crop production. Plant growth promoting rhizobacteria (PGPR) are beneficial bacteria which can protect the plants against many abiotic stresses, and enhance the growth. The study aimed to identify important rhizobacterial strains by using the 1-aminocyclopropane-1-carboxylate (ACC) enrichment technique and examine their inoculation effects in the growth promotion of maize, under Pb pollution. A pot experiment was conducted and six rhizobacterial isolates were used. Pb was added to 2 kg soil in each pot (with 4 seeds/pot) using Pb(NO3)2 at the rate of 0, 100, 200, 300, and 400 mg kg(-1) Pb with three replications in completely randomized design. Rhizobacterial isolates performed significantly better under all Pb levels, i.e., 100 to 400 Pb mg kg(-1) soil, compared to control. Comparing the efficacy of the rhizobacterial isolates under different Pb levels, rhizobacterial isolates having both ACC-deaminase and nitrogen-fixing activities (AN8 and AN12) showed highest increase in terms of the physical, chemical and enzymatic growth parameters of maize, followed by the rhizobacterial isolates having ACC-deaminase activity only (ACC5 and ACC8), and then the nitrogen-fixing rhizobia (Azotobacter and RN5). However, the AN8 isolate showed maximum efficiency, and highest shoot and root length (14.2 and 6.1 cm), seedling fresh and dry weights (1.91 and 0.14 g), chlorophyll a, b, and carotenoids (24.1, 30.2 and 77.7 μg/l), protein (0.82 mg/g), proline (3.42 μmol/g), glutathione S-transferase, peroxidase and catalase (12.3, 4.2 and 7.2 units/mg protein), while the lowest Pb uptake in the shoot and root (0.83 and 0.48 mg/kg) were observed under this rhizobial isolate at the highest Pb level (i.e., 400 Pb mg kg(-1) soil). The results revealed that PGPR significantly decreases the deleterious effects of Pb pollution and increases the maize growth under all Pb concentrations, i.e., 100-400 Pb mg kg(-1) soil. PGPR chelate the Pb in the soil, and ultimately influence its bioavailability, release and uptake. The PGPR having both ACC-deaminase and nitrogen-fixing abilities are more effective and resistive against Pb pollution than PGPR having either ACC-deaminase or nitrogen-fixing activity alone. The ACC enrichment technique is an efficient approach to select promising PGPR.

Plant growth promoting rhizobacteria (PGPR) are beneficial bacteria, which can enhance the growth of the plants, when applied to crops. A pot experiment was conducted to examine the effect of six PGPR isolates on the growth of wheat. Inoculation with rhizobacterial isolates increased the all measured physical, chemical and enzymatic growth parameters compared to control (CK). However, the WAN1 isolate had the highest effect, and significantly (P < 0.05) increased the root length (3.51-fold), shoot length (3.22-fold), seedling fresh (3.41-fold) and dry (3.91-fold) weight, chlorophyll a (3.90-fold), chlorophyll b (3.51-fold), carotenoid contents (7.23-fold), plant macronutrient uptake i.e. N (7.20-fold, 6.71-fold), P (7.41-fold, 5.01-fold), K (5.51-fold, 3.91-fold), Ca (6.40-fold, 5.21-fold) and Mg (5.82-fold, 7.11-fold) in shoot and root, plant micronutrient uptake i.e. Zn (6.40-fold, 9.11-fold), Cu (7.31-fold, 7.02-fold), Fe (6.41-fold, 7.52-fold) and Mn (4.57-fold, 5.21-fold) in shoot and root and plant antioxidant enzymes i.e. glutathione S-transferase (7.51-fold), peroxidase (5.21-fold) and catalase (5.01-fold) respectively. Our results revealed that inoculation of agricultural crops with PGPR is a very useful approach to increase the plant growth. The ACC (1-aminocyclopropane-1-carboxylate) enrichment technique is an efficient approach to select promising PGPR. The PGPR containing dual abilities i.e. both ACC-deaminase and nitrogen fixing ability are more effective than PGPR possessing either ACC-deaminase or nitrogen fixing activity alone for growth promotion of crops.

The soils of the world store significantly more carbon than present in the atmosphere. However, there is still no consensus regarding the effects of climate change, i.e. increase in temperature on global soil carbon stocks. An incubation experiment was conducted under a temperature range (5–45°C) and moisture conditions, i.e. U1–U5 (20–100% water‐holding capacity) with the objective to investigate temperature sensitivity of labile and recalcitrant organic carbon pools, total microbial activity, and soil extracellular enzymes, i.e. phenol oxidase and catalase activity in an Ultisol soil. The maximum increase in the labile organic carbon pool, i.e. water soluble organic carbon (3.52‐fold), microbial biomass carbon (2.31‐fold), readily mineralizable carbon (6.16‐fold), permanganate oxidized organic carbon (2.81‐fold), and reducing sugar carbon (3.97‐fold) was observed at 35°C, whereas the effect at other temperatures was in the order 25 > 45 > 15 > 5°C. The total organic carbon (TOC) tended to decrease with the increased temperature (from 5–35°C), therefore, maximum TOC (14.7 g kg−1) was observed at 5°C, and minimum (1.76 g kg−1) at 45°C. Conversely, the highest increase (6.48‐fold) in the recalcitrant organic carbon pool was noticed at 45°C, and the impact of other temperatures was in the order 35 > 25 > 15 > 5°C. The maximum increase in the total microbial activity (13.68‐fold) and soil enzymes, phenol oxidase and catalase (3.94 and 3.98‐fold, respectively) activity was observed at 35°C, while the influence of other temperature ranges was in the order 25 > 45 > 15 > 5°C. The effect of moisture regimes on the temperature sensitivity of organic carbon pools, total microbial and enzymatic activity was in the order U3 > U4 > U2 > U1 > U5.

Increasing cadmium (Cd) pollution in soil is of great concern. A pot experiment was conducted with the aim of assessing the effect of Cd on soil biological indices under potato cultivation. Cadmium was added to 10 kg soil in each pot (6 seeds pot–1) as Cd(NO3)2 at 0, 15, 30, 45 and 60 mg kg–1 with three replications. All soil and plant parameters decreased with all Cd treatments; however, high levels of Cd had a significant (P < 0.05) suppressive effect. The highest Cd level significantly (P < 0.05) decreased microbial biomass carbon (2.16-fold), nitrogen (11.37-fold) and phosphorus (10.3-fold), as well as enzyme activities of dehydrogenase (4.36-fold), phosphatase (9.23-fold), and urease (9.61-fold). The highest Cd level also decreased pH (1.46-fold), potato shoot (3.55-fold) and root (7.43-fold) length, root (10.9-fold) and shoot (6.04-fold) fresh weight, root (7.51-fold) and shoot (13.7-fold) dry weight, chlorophyll content (27.0-fold), carotenoid content (4.08-fold), and plant macronutrient and micronutrient uptake in potato root and shoots. Conversely, the highest level of Cd significantly (P < 0.05) increased the biomass C : N (5.27-fold) and C : P (4.77-fold) ratios, soil extractable Cd (5.38-fold), and Cd uptake in potato root (5.05-fold) and shoot (4.82-fold) at the end of the experiment (day 60). Cadmium contamination substantially affected soil biological indices and growth of potato, and the Cd threshold was strongly associated with the extent of Cd concentration and duration to accumulate. Soil microbial biomass, enzymatic activities, pH and potato physiological parameters could be used as a sensitive indicators to reflect environmental stresses in soil ecosystems.

The soil organic carbon (C) pool is the largest among the terrestrial C pools, and plays a vital role in the exchange of CO2. The increase in CO2 emission from soil to atmosphere has raised concerns about potential global warming. The current study was conducted with the objectives to investigate the relationship between labile organic C fractions and CO2 fluxes in an Alfisol soil treated with green manure (GM) and wheat straw (WS), and moisture regimes namely, W1 (50%) and W2 (100%). The incorporation of GM and WS increased (p < 0.05) the CO2 emission and labile C fractions under both water regimes. The CO2 fluxes showed positive correlation with all measured soil labile organic C fractions, i.e., total organic carbon (TOC), light fraction of organic carbon (LFOC), particulate organic carbon (POC), easily oxidizable carbon (EOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), reducing sugar carbon (RSC), and readily mineralizable carbon (RMC). The overall effect of labile C fractions on the CO2 emission was in the order LFOC > POC > EOC > DOC > MBC > RSC > RMC > TOC. The results demonstrated that LFOC, POC, EOC, DOC, MBC, RSC, and RMC had higher effects on CO2 fluxes as compared to TOC. The LFOC was more suitable and sensitive indicator than POC, EOC, DOC, MBC, WSC, RMC, and RSC for CO2 emissions and change in the soil organic C status.