Deciphering biochar compost co-application impact on microbial communities mediating carbon and nitrogen transformation across different stages of corn development.

Under current climatic conditions, developing eco-friendly and climate-smart fertilizers has become increasingly important.The co-application of biochar and compost on agricultural soils has received considerable attention recently.Unfortunately, little is known about its effects on specific microbial taxa involved in carbon and nitrogen transformation in the soil.Herein, we report the efficacy of applying biochar-based amendments on soil physicochemical indices, enzymatic activity, functional genes, bacterial community, and their network patterns in corn rhizosphere at seedling (SS), flowering (FS), and maturity (MS) stages.The applied treatments were: compost alone (COM), biochar alone (BIOC), composted biochar (CMB), fortified compost (CMWB), and the control (no fertilizer (CNTRL).The non-metric multidimensional scaling (NMDS) indicated total nitrogen (TN), pH, NO3--N, urease, protease, and microbial biomass C (MBC) as the dominant environmental factors driving soil bacteria in this study.The dominant N mediating genes belonged to nitrate reductase (narG) and nitronate monooxygenase (amo), while beta-galactosidase, catalase, and alpha-amylase were the dominant genes observed relating to C cycling.Interestingly, the abundance of these genes was higher in COM, CMWB, and CMB compared with the CNTRL and BIOC treatments.The bacteria network properties of CWMB and CMB indicated robust niche overlap associated with high cross-feeding between bacterial communities compared to other treatments.Path and stepwise regression analyses revealed norank_Reyranellaceae and Sphingopyxis in CMWB as the major bacterial genera and the major predictive indices mediating soil organic C (SOC), NH4+-N, NO3--N, and TN transformation.Overall, biochar with compost amendments improved soil nutrient conditions, regulated the composition of the bacterial community, and benefited C/N cycling in the soil ecosystem.

Enzymatic antioxidant defense in resistant plant: Pennisetum americanum (L.) K. Schum during long-term atrazine exposure.

Plants belonging to the genus Pennisetum have been reported to be resistant to atrazine, a widely used herbicide that also can cause serious pollution of soil and water. To evaluate the enzymatic antioxidant defense mechanism to the oxidative stress of atrazine, experiments focusing on the malondialdehyde (MDA) content and antioxidant enzyme in the leaf and root of Pennisetum americanum (L.) K. Schum (P. americanum) during long-term (68days) atrazine exposure were carried out. The test plant had not suffered obvious lipid membrane peroxidation, which was further confirmed by the result that the MDA content in the root and the leaf of the test plant did not significantly increase when treated with various concentrations of atrazine. The activity of the well-known antioxidases, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidase (POD), was increased when the plants were exposed to atrazine, especially at moderate concentrations (20mgkg-1 or below). These results revealed that antioxidant enzymes played important roles in protecting P. americanum from the oxidative damage induced by atrazine. The increased and more stable SOD activity in the leaf compared to in the root portion of the plant under increasing atrazine concentrations and increasing exposure time indicated that the leaf exhibited more pronounced superoxide radical scavenging ability than the root. Furthermore, correlation analysis showed that the studied antioxidases were positively correlated with the exposure time, suggesting that the antioxidant defense in P. americanum seedlings might become stronger as the plant matures. In conclusion, the increasing antioxidant enzyme activities enable P. americanum seedlings to cope with the oxidative stress induced by moderate concentrations (20mgkg-1 or below) of atrazine.

Exogenous calcium induces tolerance to atrazine stress in Pennisetum seedlings and promotes photosynthetic activity, antioxidant enzymes and psbA gene transcripts.

Calcium (Ca) has been reported to lessen oxidative damages in plants by upregulating the activities of antioxidant enzymes. However, atrazine mediated reactive oxygen species (ROS) reduction by Ca is limited. This study therefore investigated the effect of exogenously applied Ca on ROS, antioxidants activity and gene transcripts, the D1 protein (psbA gene), and chlorophyll contents in Pennisetum seedlings pre-treated with atrazine. Atrazine toxicity increased ROS production and enzyme activities (ascorbate peroxidase APX, peroxidase POD, Superoxide dismutase SOD, glutathione-S-transferase GST); but decreased antioxidants (APX, POD, and Cu/Zn SOD) and psbA gene transcripts. Atrazine also decreased the chlorophyll contents, but increased chlorophyll (a/b) ratio. Contrarily, Ca application to atrazine pre-treated seedlings lowered the harmful effects of atrazine by reducing ROS levels, but enhancing the accumulation of total chlorophyll contents. Ca-protected seedlings in the presence of atrazine manifested reduced APX and POD activity, whereas SOD and GST activity was further increased with Ca application. Antioxidant gene transcripts that were down-regulated by atrazine toxicity were up-regulated with the application of Ca. Calcium application also resulted in up-regulation of the D1 protein. In conclusion, ability of calcium to reverse atrazine-induced oxidative damage and calcium regulatory role on GST in Pennisetum was presented.

Oxidative stress response induced in an atrazine phytoremediating plant: physiological responses of Pennisetum glaucum to high atrazine concentrations.

This research presented here, for the first time, elucidates the responses of several antioxidants in Pennisetum leaves exposed to varying concentrations of atrazine (0 - 200 mg•kg-1). Pennisetum has been reported to be resistant to atrazine; however, its physiological response to high concentrations (≥ 50 mg•kg-1) of atrazine is not well documented. The contents of reduced (AsA) and oxidized (DHA) ascorbate increased significantly with increase in atrazine concentration and exposure time; but the increase was more evident under higher (50 and 100 mg•kg-1) atrazine concentrations. Increase in atrazine concentration to 200 mg•kg-1 significantly decreased AsA, but increased DHA content, throughout the experiment. Seedlings treated with 200 mg•kg-1 atrazine showed significantly lowest reduced glutathione (GSH) content; while oxidized glutathione (GSSG) was not significantly affected, after 68d. Seedlings treated with 100 mg•kg-1 atrazine showed increased Glutathione-S-Transferase (GST) activity after 48 d and 68 d; while treatment with 200 mg•kg-1 atrazine significantly increased Glutathione reductase (GR) after 58d. This result suggests that Pennisetum may tolerate lower atrazine concentrations; However, higher concentrations (≥50 mg•kg-1) which could have longer residency period in the soil, could induce more physiological damage to the plant.