Plant Root Activity Research Articles

Mechanisms underlying salicylic acid on root parameters and antioxidant enzyme activity of potato plant under Lelliottia amnigena stress

Salicylic acid (SA) plays many roles in plant physiology. In addition to pathogenesis-related resistance, SA is involved in the response to biotic stress. There are no adequate studies on mechanism underlying SA-mitigated Lelliottia amnigena infestations in potato (Solanum tuberosum L.) plant. Therefore, this study evaluated the mechanisms of SA on antioxidant enzyme activity of potato plant roots under L. amnigena stress. The bacterial suspension (3.69 × 107 CFU mL-1) at 0.3 mL was inoculated into potato plants through stem injection. After 24 h, different SA concentrations (0.5, 1.0, 1.5 and 2.0 mM) were sprayed to the potato plants, and water as control. The results showed that L. amnigena infestation decreased fresh weight, dry weight, and relative water content of roots by 44.8%, 11.8% and 34.8%, respectively, compared to the control. The potato plant treatment with SA increased fresh weight, dry weight, and relative water content by an average of 34.88%, 10.28% and 13.50%; increased superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) by 35.95%, 32.55%, 33.74%, 33.25%, and 38.90%; decreased malondialdehyde (MDA) and hydrogen peroxide (H2O2) content in potato plant roots by 42.7% and 31.1%, respectively, under L. amnigena stress compared to control. Treatment with SA induced transcriptional levels of the SOD, POD, CAT and glutathione S-transferase (GST) gene expression across the four levels of SA by an average of 3.12-fold, 3.46-fold, 2.93-fold and 3.83-fold, respectively, compared to control. Salicylic acid increased antioxidant enzymes activity in roots of potato plant under L. amnigena stress.

Cold Stress Resistance of Tomato (Solanum lycopersicum) Seedlings Is Enhanced by Light Supplementation From Underneath the Canopy.

Adverse environmental conditions, such as low temperature (LT), greatly limit the growth and production of tomato. Recently, light-emitting diodes (LEDs) with specific spectra have been increasingly used in horticultural production facilities. The chosen spectrum can affect plant growth, development, and resistance, but the physiological regulatory mechanisms are largely unknown. In this study, we investigated the effects of LED light supplementation (W:B = 2:1, light intensity of 100 μmol⋅m–2⋅s–1, for 4 h/day from 9:00 to 13:00) from above and below the canopy on tomato resistance under sub-LT stress (15/8°C). The results showed that supplemental lighting from underneath the canopy (USL) promoted the growth of tomato seedlings, as the plant height, stem diameter, root activity, and plant biomass were significantly higher than those under LT. The activity of the photochemical reaction center was enhanced because of the increase in the maximal photochemical efficiency (Fv/Fm) and photochemical quenching (qP), which distributed more photosynthetic energy to the photochemical reactions and promoted photosynthetic performance [the maximum net photosynthetic rate (Pmax) was improved]. USL also advanced the degree of stomatal opening, thus facilitating carbon assimilation under LT. Additionally, the relative conductivity (RC) and malondialdehyde (MDA) content were decreased, while the soluble protein content and superoxide dismutase (SOD) activity were increased with the application of USL under LT, thereby causing a reduction in membrane lipid peroxidation and alleviation of stress damage. These results suggest that light supplementation from underneath the canopy improves the cold resistance of tomato seedlings mainly by alleviating the degree of photoinhibition on photosystems, improving the activity of the photochemical reaction center, and enhancing the activities of antioxidant enzymes, thereby promoting the growth and stress resistance of tomato plants.

Why and How the Bio-Electric Activity of Plant Roots is Awoken When the Leaves Need Water? A Very Rapid Signal Transmission from Aerial Part to Root

The simplest and scientific method to determine the bioelectric activity of a plant root is the measurement of the Trans-Root Electric Potential (TRP) i.e., the electric potential difference between the xylem apoplast and the earth surrounding the root.

Nd and Sr Isotopes and REE Investigation in Tropical Weathering Profiles of Amazon Region

The exceptional development of lateritic profiles make the Amazon one of the best places to conduct a refined study on the effects of long-term tropical climate on the Earth's surface rocks. Concentrations of Nd and Sr isotopes, as well as rare earth elements (REE), Sr, and other trace elements were determined in six profiles in order to shed new light into element behavior and into the processes controlling the geochemistry and the transfer of these elements among the different compartments of the critical zone. Our investigation indicates natural isotope regional pulse transformations in the Oxisol at the top of all profiles. The ƐNd(t=0) values of the parent rock, mottled horizon, and lateritic duricrust are radiogenic similar to the Amazon craton signature. The thick Oxisol has ƐNd(t=0) values which are much more radiogenic and less variable, whereas it has Zr, Th, Y, and REE in higher concentrations. These issues highlight a complex process for the Nd system, and the following possibilities are proposed to explain this behavior: formation of authigenic cerianite and/or kaolinite, penetration of low-temperature weathering solutions along zircon fractures, and some vegetation uptake. These possibilities allow keeping the more radiogenic Nd isotopes, whereas the less radiogenic Nd is released especially in the Oxisol after REE mineral(s) weathering. The Sr system contrary to that of Nd became less radiogenic along the profiles and relatively to the parent rocks content, because nearly all Sr was removed after K-Rb feldspar and mica weathering. However, a mixture return of less radiogenic Sr from plant, biogenic aerosol, and rainwater may have helped let the weathering profiles become less radiogenic. These characteristics let the Oxisol even less Sr radiogenic but still permitting to identify the general parent rocks signature. In contrast, Nd is highly fractionated in the Oxisol relative to the parent rock. Thus, the REE and Sr behavior, similar in the six profiles, does not necessarily reflect only the parent rock geochemistry, but it also depends on the multiple surficial processes typical of the critical zone: weathering, pedogenesis, plant root activity, and rainwater composition which change the inherited primary minerals isotope signatures.

Polyethylene microplastics interfere with the nutrient cycle in water-plant-sediment systems

Increasing microplastic (MP) pollution and its effects on aquatic systems have become a global issue; however, the impact of MPs on biogeochemical cycles is poorly understood. A simulation study was performed to analyse the influence of polyethylene (PE) microplastics on the morphological, physiological, and stoichiometric (C, N, P) characteristics of submerged plants, and to investigate their effects on the nutrient cycle and microbial community in freshwater sediment. The results showed that PE-MPs treatments significantly decreased leaf nitrogen and carbon contents. Exposure to 1% PE-MPs suppressed the plant height, total biomass, root activity, and relative growth rate of Vallisneria natans. Decrease in dissolved oxygen (DO) concentrations (19.93–40.26%) were observed in the 1% PE-MPs treatment group compared to that in the control between 1 and 6 days. The activities of enzymes (ammonia monooxygenase and nitrate reductase) related to the nitrogen cycle were significantly altered by the addition of PE-MPs. We found that PE-MPs acted as obstacle disruptors, resulting in a reduction in the release of nitrogen and phosphorus from the sediment to the overlying water. This is because PE-MPs significantly alter the composition and metabolic properties of the microbial communities in sediments, the plant growth, and the nutrient cycle. These findings helped evaluate the impacts of PE-MPs on the water-plant-sediment system and on the biogeochemical cycles of the freshwater ecosystems.

Impacts of water deficit and post-drought irrigation on transpiration rate, root activity, and biomass yield of Festuca arundinacea during phytoextraction

Water deficit is a hazardous threat to phytoremediation, while the photosynthetic efficiency of plant leaves can rapidly recover after post-drought irrigation, thereby enhancing the root activity, transpiration rate, and metal accumulation capacity of plants. This study was designed to test whether the phytoextraction effect of drought-stressed Festuca arundinacea could recover to normal levels after post-drought irrigation. Two drought stress levels (D1, slight stress and D2, moderate stress) were carried out at one of five plant growth stages (G1, germinating; G2, tillering; G3, jointing; G4, booting; and G5, flowering). The results showed that drought stress, regardless of level, significantly decreased the transpiration rate of F. arundinacea by 38.9%–85.7%. The degree of reduction of this physiological index was significantly higher in D1G1 and D2G1 than in other treatments. The biomass yield and root activity in D1G3, D1G4, D1G5, D2G3, and D2G4 recovered and even surpassed the normal values after rewatering, suggesting that the detrimental effects of drought stress on F. arundinacea at certain growth stages can be compensated by post-drought irrigation. Drought stress also decreased the Cd uptake capacity of F. arundinacea, and the degree of reduction depended on the stress level and growth stage. Overcompensation for Cd accumulation was observed in D1G3, D1G4, D2G3, and D2G4 after post-drought irrigation. The results indicated that suitable irrigation strategies can improve the phytoextraction effect of F. arundinacea and conserve water resources in practice.

RUSSELL REVIEW Are plant roots only “in” soil or are they “of” it? Roots, soil formation and function

AbstractRoots are near‐ubiquitous components of soils globally but have often been regarded as separate from the soil rather than a substantial factor in determining what soil is and how it functions. The start of rapid soil formation commenced about 400 million years ago with the emergence of vascular plants and the evolution of roots and associated microbes. Roots and associated microorganisms contribute significantly to soil formation by altering rocks and soil minerals through a variety of biogeochemical processes and supply carbon to a depth that can have long residence times. Living root inputs of carbon via rhizodeposits are more efficient than shoot and root litter inputs in forming slow‐cycling, mineral‐associated soil organic carbon pools. The current functionality of soils in providing food and fuel and fibres, supplying plant nutrients, filtering water and flood regulation, and disease suppression are all dependent on the activities of plant roots. Roots are actively communicating and collaborating with other organisms for mutual benefit, and the signals underlying this modulation of the rhizosphere microbiome are being identified. In this review I examine how plant roots (an organ not an organism) affect soil formation and function and conclude that, from several perspectives, roots are not just “in” soil but “of” it and that definitions of soil should recognise this. A possible definition is: “Soils are altered surficial rock or sediment, composed of organic matter, minerals, fluids, and organisms whose formation and functionality are influenced by biogeochemical weathering and interactions of these components with plant roots.”HighlightsPaleoclimatic and paleosoil research shows the key role of roots and mycorrhiza in soil formation.Deep roots and living root inputs are substantial contributors to long‐term C storage.Root/microbe signalling facilitates mutualistic symbioses, nutrient uptake and disease suppression.Definitions of soil should explicitly include roots as an important component of the soil system.

The involvement of abscisic acid in hydrogen gas-enhanced drought resistance in tomato seedlings

Hydrogen gas (H2) regulates plant responses to abiotic and biotic stresses. Abscisic acid (ABA) might alleviate the adverse effects of drought stress. However, the mechanisms by which ABA and H2 ameliorate plant drought stress are unclear. Here, tomato “Micro-Tom” seedlings were used to investigate the interaction between H2 and ABA under drought conditions. The results showed that both hydrogen-rich water (HRW) and ABA increased plant height, stem diameter and root activity of tomato seedlings under drought stress, with optimal concentrations of 75% and 150 μM, respectively. HRW or ABA treatment was able to enhance drought tolerance by increasing photosynthesis, antioxidant enzyme activity and gene expression of antioxidant enzymes under drought stress. Fluridone (FLU), a synthetic inhibitor of ABA, significantly diminished the positive effects of HRW on plant height, stem diameter and root activity under drought stress, suggesting that ABA might play a crucial role in H2-enhanced drought resistance in tomato seedlings. The results revealed that the ABA content in the PEG + HRW treatment was 18% higher than that in the polyethylene glycol (PEG) treatment alone. Furthermore, we found that H2 enhanced endogenous ABA content by increasing zeaxanthin epoxidase (ZEP), 9-cis-epoxycarotenoid dioxygenase (NCED) and abscisic aldehyde oxidase (AAO) activities and the expression of SlZEP, SlNCED, and SlAAO. PEG + HRW treatment increased ZEP and NCED activities, which were 13% and 40% higher than those of PEG treatment, respectively. Meanwhile, the transcription levels of SlSnRK2 and SlAREB were upregulated by HRW or ABA under drought stress, whereas this upregulation was reversed by FLU. Thus, our results demonstrate that H2 was able to enhance drought resistance by regulating ABA biosynthesis and the expression of ABA signal transduction genes in tomato seedlings.

Enhanced phosphorus removal of constructed wetland through plant growth-promoting rhizobacteria (PGPR) addition

Phosphorus (P) removal efficiency of constructed wetland (CW) was limited due to the adsorption saturation on substrate surface along with continuous operation of CW. This study attempted to improve the P removal of CW through introduction of plant growth-promoting rhizobacteria (PGPR). Compared with the control-CW (C-CW), the results of CW with bio-augmentation (B-CW) showed that the total phosphorus (TP) removal efficiency was increased by 36.7% due to the enhanced plant uptake of P. The physiology indicators (height and root activity) of plants in B-CW were significantly improved, and the average P content of plants in B-CW was 0.78 g/kg, which was 85.7% higher than that of C-CW (0.42 g/kg). This was because PGPR addition optimized the P forms adsorbed on substrate surface and increased the proportion of Ca/Mg-P which was bioavailable for plant growth, and then subsequently enhanced plant uptake of P. Through bio-augmentation, the proportion of P removal by plant uptake in B-CW (25.2%) was increased by 2.5 times compared with that of C-CW (7.1%). The outcomes of this study would shed light on intensifying the role of plant uptake in P removal of CWs through bio-augmentation.

Exogenous IAA Alleviates Arsenic Toxicity to Rice and Reduces Arsenic Accumulation in Rice Grains

Arsenic (As) contamination in paddy soil reduces rice production and quality. It is important to increase the As tolerance of rice and reduce As accumulation in rice using exogenous methods. We examined the effects of exogenous plant hormones on the growth of and As accumulation in rice exposed to As. Under hydroponic conditions, 10 μmol L−1 As inhibited the growth of rice seedling. However, pretreatments with indole-3-acetic acid (IAA), salicylic acid (SA), and gibberellins (GA) rescued this inhibition, as evidenced by changes in plant morphology (root and shoot elongation, biomass, total root length, root surface area, root volume, and root tip number) and root activities, especially with the application of IAA. The As concentration in rice seedlings was significantly reduced. With soil culture, 20 mg L−1 IAA application significantly increased the grain biomass of both rice varieties, the 1000-grain weight and plant biomass of Mo Wang Gu Nei (MWGN), while decreased the As concentration in rice grains and total As accumulation in grains per plant. Furthermore, exogenous IAA reduced As translocation, as evidenced by lower As concentrations in upper leaves and internodes, but higher levels in lower leaves and internodes in Dong Ting Wan Xian (DTWX) after spraying with IAA compared to the control treatments. In conclusion, exogenous IAA can significantly promote rice growth and reduce As accumulation in rice grains.

Use of centrifugal pumps with canned asynchronous motors in irrigation systems

In most cases, taking into account the local geology and hydrology, water entering the system of humidified mobile irrigation from underground sources, such as from the depth of artesian wells, has an initial temperature below 12 degrees. Low temperature of irrigation water adversely affects the growth and absorption activity of plant roots, and the life of microorganisms, impairing the supply of plants with nutrients, mainly nitrogen. As a result, the use of water from aquifers in irrigation systems requires its preliminary settling in barrels or special storage ponds. Given that the water from the well rises to the surface using a pump (group of pumps), the choice of the type of pumping unit has a significant impact on the structure and composition of the equipment of the irrigation plant. The paper shows the features of using special-shaped centrifugal pumps in terms of increasing the water temperature at the outlet of the pumping unit due to its indirect heating in the design elements of the pump drive motor. Using the heat balance equation for the secondary conductive shells of the pump motor, the interval values of the water temperature at its outlet are calculated, proving the possibility of its further use for its intended purpose in the irrigation system without additional technical water treatment.

干旱胁迫对不同根型苜蓿根系生长及根际土壤细菌的影响

为明确干旱胁迫对根茎型清水紫花苜蓿、直根型陇东紫花苜蓿、根蘖型公农4号杂花苜蓿根系生长及根际土壤细菌群落的影响，采用盆栽试验，运用16S rRNA基因测序技术，研究了幼苗期干旱胁迫下各根型苜蓿根系生长及根际土壤细菌群落结构的变化。结果表明：干旱胁迫下各根型苜蓿的Chao1和ACE丰富度指数均在中度胁迫下最大，Simpson和Shannon-wiener多样性指数各处理间差异不显著；根际土壤细菌群落均以变形菌门、绿弯菌门、类杆菌门、放线菌门和厚壁菌门为主，干旱胁迫均显著增加了变形菌门和厚壁菌门的相对丰度，显著降低了绿弯菌门的相对丰度，但类杆菌门和放线菌门先提高后下降。统计学分析显示，幼苗期干旱胁迫显著影响各根型苜蓿生长发育，随胁迫程度增加，其株高、地上生物量、地下生物量、根系活力、根体积、根系总长均显著降低，根冠比先增加后下降且在中度胁迫时达到最大值。重度胁迫下，清水苜蓿的株高、根系活力显著大于其他品种，而根冠比、根系干重显著小于其他品种；陇东苜蓿的根长、根尖数均显著大于其他品种；根系平均直径、根系总表面积各根型苜蓿间差异不显著。研究结果为植物的抗干旱胁迫以及提高各根型苜蓿在干旱胁迫下的水分利用提供参考。;To study the effect of drought stress on morphological characteristics of alfalfa root and bacterial community structure and diversity in alfalfa rhizosphere soil, pot experiment using three root types of alfalfa (rhizomatous rooted Medicago sativa cv.Qingshui, tap rooted M. sativa cv.Longdong, creeping rooted M. varia Martin.cv.Gongnong No.4) as the experimental materials was conducted to set up the drought treatment experiments. The total DNA of the seedling rhizosphere soil was extracted and deep sequencing of V4 region of 16S rRNA gene was performed to characterize the bacterial community structure of drought-treated alfalfa. Compared to the normal condition (CK), the richness index of Chao1 and Ace was the highest under moderate stress, whereas the diversity index of Simpson and Shannon Wiener was not significant under different drought stress. Proteobacteria, Chloroflexi, Bacteroidota, Actinobacteria, and Firmicutes were the special bacteria. The relative abundance of Proteobacteria and Firmicutes dramatically increased, while that of Chloroflexi evidently decreased, whereas that of Bacteroidota and Actinobacteria significantly firstly increased then decreased. The plant height, aboveground and underground biomass, root activity, root volume, and total root length were significantly decreased with increasing of drought concentration, while root shoot ratio increased first and then decreased and reached the most under moderate stress. Under severe stress, the plant height and root activity of M. sativa cv.Qingshui were significantly higher than those of other varieties, while root shoot ratio and underground biomass were significantly lower than those of other varieties. The root length and root tip number of M. sativa cv.Longdong were significantly higher than those of other varieties. There was no significant difference between average root diameter and total root surface area among three root types of alfalfa. Results from this study would present reference to the resistance of plants to drought stress and the improvement of water use of three root types of alfalfa under drought stress.

Role of calcium as a possible regulator of growth and nitrate nitrogen metabolism in apple dwarf rootstock seedlings

As a crucial element for plants, calcium (Ca) is involved in both nitrogen (N) absorption and assimilation. Plants tend to exhibit lower nitrogen use efficiency (NUE) under Ca-deficient conditions. Improving NUE in apple production can reduce the negative effects of the excessive use of N fertilizer. However, the role of Ca in the regulation of nitrate uptake and reduction remains unclear. Herein, we investigated the growth response and nitrate (NO3−) metabolism of apple dwarf rootstock seedlings (M9T337) for Ca2+ concentrations of 0, 2, 4, 6, 8, 10, and 12 mM Ca2+ using 15N isotope labeling tracer, non-invasive micro-testing technology, and quantitative real-time polymerase chain reaction (qrt-PCR). Results showed that Ca accumulation rate in the plant tissue increased with increasing Ca supply levels; however, the plant biomass, photosynthesis, root activity, and 15NUE peaked for 6 mM of Ca2+ supply. Further investigation revealed that for 6 mM of Ca2+ supply, nitrate reductase (NR) activities were relatively high, the transcription of nitrate transporter (MdNRT1.1; MdNRT2.1) up-regulated and NO3− maximum influx rate in the roots occurred. Furthermore, seedlings treated with 6 mM Ca2+ had a significantly lower NO3- concentration in leaves and roots, a higher NH4+ concentration in leaves, and a higher amino acid compounds concentration. Moreover, both Ca deficiency and excessive Ca inhibit N absorption and utilization, and the adverse effects of Ca deficiency on seedling growth and N metabolism were greater than those associated with excessive Ca2+ supply. Conclusively, the results of this study indicate that appropriate Ca2+ supply (6 mM) was optimal as it increased NUE by enhanced photosynthesis, N metabolizing enzyme activities, NO3− uptake and transport.

Effects of a microbial restoration substrate on plant growth and rhizosphere bacterial community in a continuous tomato cropping greenhouse

Continuous cropping of tomato is increasingly practiced in greenhouse cultivation, leading to several soil-related obstacles. In this study, a type of microbial restoration substrate (MRS) was used to amend soils from the re-cropping of tomato for 8 years under greenhouse-cultivated conditions. Two treatments were established: using 1,500 kg hm−2 of MRS to amend soil as treatment (TR), and non-MRS as control (CK). The severity of bacterial wilt (BW), soil properties and rhizobacterial community composition under two different treatments were compared. The application of MRS led to an average 83.75% reduction in the severity of BW, and significantly increased the plant height, root activity and yield. Meanwhile, soil pH, soil organic contents (SOC), total nitrogen (TN) and exchangeable calcium were significantly increased (P < 0.05) by MRS treatment. Illumina-MiSeq sequencing analysis of the 16S rRNA genes revealed that MRS increased the diversity of the tomato rhizobacterial community. The relative abundances of Proteobacteria, Actinobacteria and Bacteroidetes were enhanced, whereas those of Acidobacteria, Chloroflexi, TM7 and Firmicutes were decreased by MRS. The redundancy analysis (RDA) revealed that the severity of tomato BW was negatively correlated with the relative abundances of Actinobacteria, Bacteroidetes and Proteobacteria, but positively correlated with those of Gemmatimonadetes, Firmicutes and Acidobacteria. In addition, the effects of MRS on rhizobacterial metabolic potentials were predicted using a Kyoto Encyclopedia of Genes and Genomes (KEGG) database, implying that MRS could significantly increase nitrogen metabolisms and reduce carbon metabolism. Together, our results indicated that the use of MRS could reestablish soil microbial communities, which was beneficial to plant health compared with the control.

Biological modification of bones in the Cretaceous of North Africa

Bones displaying evidence of modification by macro, meso and microorganisms occur frequently in the ?Albian - early Cenomanian Cretaceous Kem Kem Group of the Tafilalt in southeast Morocco. Excluding the traces made by vertebrates (bite marks, tooth punctures, scratch marks, trample fractures) the different types of modification identified include a variety of borings referable to the ichnogenera Cubiculum, Cuniculichnus, Osteichnus and Osteocallis. Although the identity of the borers cannot always be confirmed several are attributed to dermestid beetles, possibly mayflies of the family Polymitarcidae, and perhaps to the activity of plant roots or fungal hyphae. Microbial damage to Kem Kem Group bones appears to be minimal.

Effects of exogenous nitric oxide and ethylenediaminetetraacetic acid on cadmium toxicity and accumulation in ryegrass

The effects of exogenous nitric oxide (NO) and ethylenediaminetetraacetic acid (EDTA) on cadmium toxicity and accumulation in ryegrass (Lolium perenne L.) were studied in a hydroponic experiment. The results show that in plants without Cd application, addition of EDTA and sodium nitroprusside (SNP, an exogenous NO donor) significantly reduced the plant height, root length, and root activity of ryegrass, and significantly increased the O2*- generation rate and H2O2 and malondialdehyde (MDA) content in the aboveground and underground parts of ryegrass. Cadmium stress significantly inhibited ryegrass growth. Addition of SNP or EDTA alleviated Cd toxicity, and addition of both had a better effect. Compared with Cd alone, the shoot height and root length in the Cd+EDTA+SNP treatment increased by 68.8 and 59.6 %, and plant fresh and dry masses by 62.6 and 60.0 %, respectively. Also, the superoxide dismutase activity in the shoots and roots increased by 32.5 and 67.6 %, the peroxidase activity by 49.8 and 67.6 %, the ascorbate peroxidase activity by 134 and 102 %, the MDA content decreased by 30.4 and 21.8 %, and the O2*- generation rate by 29.0 and 26.1 %, respectively. At the same time, Cd content in the shoots and roots increased significantly by 89.7 and 30.2 %, respectively. Overall, the results suggest that exogenous NO could enhance Cd tolerance of ryegrass, but addition of EDTA could promote plant Cd uptake. Combined application of NO and EDTA increased Cd accumulation in the aboveground parts of ryegrass. In this experiment, the treatment of 100 &#181;M CdCl2 + 0.25 mM EDTA + 50 &#956;M SNP showed the best effects in promoting Cd accumulation in ryegrass and enhancing its Cd tolerance.

AMF inoculation and phosphorus supplementation alleviates drought induced growth and photosynthetic decline in Nicotiana tabacum by up-regulating antioxidant metabolism and osmolyte accumulation

Arbuscular mycorrhizal fungi (AMF) improves phosphorus (P) uptake in plants and regulates growth under environmental stresses. Present trials were undertaken to study the effect of phosphorus (P, 40 mg kg−1 soil) supplementation and AMF (Glomus versiforme) inoculation on the growth performance of tobacco (Nicotiana tabacum L. variety Yunyan 87) under drought stress. Supplementation of P and inoculation of AMF significantly enhanced growth, biomass accumulation and root activity of tobacco plants under normal conditions and mitigated the drought induced decline. Chlorophyll and carotenoid contents, photosynthesis and PSII efficiency increased due to AMF and P treatment attaining maximal values due to their combined treatment. Drought resulted in generation of reactive oxygen species (ROS) like superoxide (O2−) and hydrogen peroxide (H2O2) resulting in increased lipid peroxidation hence reducing membrane stability. Plants inoculated with AMF and/or supplemented with P exhibited reduced accumulation of ROS and lipid peroxidation. Content of osmolytes including proline, sugars and free amino acids were enhanced due to P and AMF treatment under normal as well as drought conditions that influenced the leaf relative water content. Reduction in oxidative damage in AMF and P treated plants was apparently linked with the stimulation of antioxidant system in them. Activities of SOD, CAT, APX, POD and GR, and the content of AsA and GSH improved significantly due to P and AMF treatment both under normal and drought conditions thereby ameliorating the oxidative effects. Further, accumulation of phenols increased more obviously due to P and/or AMF inoculation than in drought. Increased osmolyte and phenol content due to P and/or AMF helped tobacco plants to counteract the drought mediated damage by strengthening the non-enzymatic antioxidant system. P and/or AMF ameliorated the decline in contents of nitrogen, potassium and phosphorous, and activity of nitrate reductase more due to their combined treatments. Drought induced decline in nicotine content was mitigated because of P and/or AMF treatment. Additionally, mycorrhizal inoculation along with P supplementation increased indole-3-acetic acid (IAA) and abscisic acid (ABA) concentrations both in roots and leaves under drought stress. Hence P supplementation along with AMF inoculation mitigates the photosynthetic alteration and growth in tobacco plants by up-regulating antioxidant system and osmolyte accumulation.

Nitrogen and phosphorus co-addition stimulates soil respiration in a subtropical evergreen broad-leaved forest

Nutrient availability is a key regulator of soil respiration. Anthropogenic activities have dramatically accelerated the inputs of reactive nitrogen (N) and phosphorous (P) and increased the availability of N and P in soils. However, many previous studies of soil respiration have focused more on the effects of N, and less on the effects of P and its interaction with N. Therefore, the objective here was to examine the roles of N availability, P availability and their interaction in determining soil respiration. A manipulative N addition (100 kg N ha−1 year−1), P addition (50 kg P ha−1 year−1) and NP co-addition (100 kg N ha−1 year−1 + 50 kg P ha−1 year−1) experiment was conducted in a subtropical forest in Southwest China. N and P inputs were added monthly beginning in October 2017. The soil respiration rate was measured monthly from March 2018 to February 2019, and soil properties, microbial biomass carbon (MBC), and fine root biomass were measured in July 2018 and January 2019. The soil respiration rate in the control (without fertilizer added) treatment was 13.5% higher than that in the N treatment but 1.6% and 34.7% lower than those in the P treatment and NP treatment, respectively. Soil respiration was closely associated with soil temperature and soil moisture, and soil temperature played a more important role in regulating soil respiration than did soil moisture. The temperature sensitivity of respiration (Q10 values) in the CT, N, P and NP treatments did not differ significantly. Path analysis showed that nutrient additions changed soil respiration by regulating the MBC and fine root biomass. Our results highlight the divergent effects of N addition and NP co-addition on soil respiration. Ongoing N and P inputs may increase soil respiration by stimulating soil microbial and plant root activities in the subtropical evergreen broad-leaved forests of Southwest China.

A Gaseous Milieu: Extending the Boundaries of the Rhizosphere.

Plant root activities shape microbial community functioning in the soil, making the rhizosphere the epicenter of soil biogeochemical processes. With this opinion article, we argue to rethink the rhizosphere boundaries: as gases can diffuse several centimeters away from the roots into the soil, the portion of soil influenced by root activities is larger than the strictly root-adhering soil. Indeed, gases are key drivers of biogeochemical processes due to their roles as energy sources or communication molecules, which has the potential to modify microbial community structure and functioning. In order to get a more holistic perspective on this key environment, we advocate for interdisciplinarity in rhizosphere research by combining knowledge of soluble compounds with gas dynamics.

Rhizosphere processes in nitrate-rich barley soil tripled both N2O and N2 losses due to enhanced bacterial and fungal denitrification

Plants can directly affect nitrogen (N) transformation processes at the micro-ecological scale when soil comes into contact with roots. Due to the methodological limitations in measuring direct N2 losses in plant-soil systems, however, the effect of rhizosphere processes on N2O production and reduction to N2 has rarely been quantified. For the first time, we developed a robotic continuous flow plant-soil incubation system (using a He+O2 + CO2) combined with N2O 15N site preference approach to examine the effect of plant root activity (barley – Hordeum vulgare L.) on: i) soil-borne N2O and N2 emissions, ii) the specific contribution of different pathways to N2O fluxes in moist soils (85% water holding capacity) receiving different inorganic N forms. Our results showed that when a nitrate-based N fertiliser was applied, the presence of plants tripled both N2O and N2 losses during the growth period but did not alter the N2O/(N2O + N2) product ratio. The 15N site preference data indicated that bacterial denitrification was the dominant source contributing to the observed N2O fluxes in both nitrate and ammonium treated soils, whereas the presence of barley increased the contribution of fungal N2O in the nitrate treated soils. During the post-harvest period, N2O and N2 emissions significantly increased in the ammonium-fertilised treatment, being more pronounced in the soil with a senescing root system. Overall, our study showed a significant interaction between rhizosphere processes and N forms on the magnitude, patterns, and sources of soil borne N2O and N2 emissions in moist agricultural soils.