Rhizosphere acidification of faba bean, soybean and maize

Effects of Bandwidth on Ear Differentiation and Grain Yield Formation of Maize in Strip Intercropping

In strip intercropping, increasing bandwidth enhances light energy utilization and facilitates mechanized production, yet it constrains the realization of maize yield advantages. The impact of bandwidth on the ear differentiation and development and yield formation requires further investigation. In this study, different bandwidths (T1, 1.6 m, T2, 2.0 m, T3, 2.4 m, and T4, 2.8 m) were arranged, and monoculture maize with varying row spacings (K1, 0.8 m, K2, 1.0 m, K3, 1.2 m, and K4, 1.4 m) was used as the control. The results show that increasing bandwidth inhibited the ear differentiation. The proportion of dry matter partitioning to leaves increased and to ears decreased, resulting in shorter ear length and higher floret and grain abortion rates. Maize yield losses amounted to 26.9% and 31.6% in T4 compared to K4 and T1, respectively. Moreover, the bandwidth did not affect the fertilized florets due to the smaller anthesis-silking interval created by the simultaneous effect. We concluded that the appropriate bandwidth, 1.6 m and 2.0 m, can stabilize the dry matter partitioning to the ear; stabilize ear length, floret, and grain abortion rate; and stabilize the maize yield.

Enhancing photosynthetic phosphorus use efficiency through coordination of leaf phosphorus fractions, allocation, and anatomy during soybean domestication

Soybean domestication has significantly changed key agronomic traits, yet its impact on leaf photosynthetic phosphorus use efficiency (PPUE) and its underlying traits remains poorly known. Further information on this would be important to increase soybean P use efficiency. To address this gap, 48 soybean accessions (16 wild relatives, 16 landraces, and 16 cultivars) were used to compare leaf anatomical traits, foliar chemical P fractions, P allocation, and PPUE under two P levels. The results showed that the cultivars had higher area-based and mass-based photosynthesis rates, PPUE, metabolite P concentration, and its percentage of leaf total P, as well as a greater percentage of lipid P, nucleic acid P, and residual P. Conversely, wild relatives tended to have higher leaf P concentration, palisade:spongy thickness ratio, and concentrations of inorganic P, nucleic acid P, lipid P, and residual P. PPUE was negatively correlated with leaf inorganic P concentration and its percentage relative to leaf total P, while it was positively correlated with the concentration and percentage of metabolite P. We concluded that soybean domestication increased PPUE, as a result of both increased photosynthesis rate and decreased leaf P concentration; domestication reduced the palisade:spongy thickness ratio coupled with increased allocation of P to P-containing metabolites, thereby contributing to faster photosynthesis and higher PPUE. This study sheds light on the significance of leaf P allocation and anatomical traits affecting PPUE during soybean domestication, offering a mechanistic understanding to further enhance soybean P use efficiency.

Transcriptional and physiological analyses uncover the mineralization and uptake mechanisms of phytic acid in symbiotically grown Vicia faba plants

Legume-rhizobia symbiosis requires high phosphorus (P) in the form of ATP to convert atmospheric nitrogen (N) into ammonia. The fixed ammonia is converted to NH4+ by H+-ATPase via protonation. To the best of our knowledge, most of these research works resort to using only inorganic P (Pi) to the neglect of the organic P (Po) counterpart. As it stands, the potential regulating roles of plasma membrane (PM) H+-ATPases during legume-rhizobia symbiosis in response to phytic acid supply and how it alters and modulates the regulation of PM H+-ATPases remain obscure. To contribute to the above hypothesis, we investigate the mechanisms that coordinately facilitate the growth, uptake, and transcript expression of PM H+-ATPase gene isoforms in response to different P sources when hydroponically grown Vicia faba plants were exposed to three P treatments, viz., low- and high-Pi (2.0 and 200 μM KH2PO4; LPi and HPi), and phytic acid (200 μM; Po) and inoculated with Rhizobium leguminosarum bv. viciae 384 for 30 days. The results consistently reveal that the supply of Po improved not only the growth and biomass, but also enhanced photosynthetic parameters, P uptake and phosphatase activities in symbiotically grown Vicia faba relative to Pi. The supply of Po induced higher transcriptional expression of all PM H+-ATPase gene isoforms, with possible interactions between phosphatases and H+-ATPase genes in Vicia faba plants when exclusively reliant on N derived from nodule symbiosis. Overall, preliminary results suggest that Po could be used as an alternative nutrition in symbiotic crops to improve plant growth.

Effects of N and P addition on nutrient and stoichiometry of rhizosphere and non-rhizosphere soils of alfalfa in alkaline soil

Nitrogen (N) and phosphorus (P) are important nutrients for plant growth and development. Soil alkalization is one of the main obstacles limiting the sustainable development of agriculture. Northern Ningxia is located in the arid and semi-arid region, with serious soil alkalinization. Alfalfa has the advantages of strong saline-alkali tolerance, high yield, high quality, and wide adaptability. It is an important forage for the comprehensive improvement and rational utilization of saline-alkali land and has great significance for solving land resource shortages, improving the ecological environment, and ensuring food security. It is important to study soil organic carbon (SOC), total N (TN), total P (TP), and stoichiometry of the rhizosphere and non-rhizosphere of alfalfa in alkaline soils. Therefore, N and P were added to the alkaline alfalfa field in the Yinchuan Plain of Hetao Basin in our experiment. Six treatments were set up, i.e., N-free (WN), medium N (MN) for 90 kg/hm², high N (HN) for 180 kg/hm², P-free (WP), medium P (MP) for 135 kg/hm², and high P (HP) for 270 kg/hm². The results are as follows: The N addition promotes SOC and TN but inhibits TP, and P addition promotes SOC and TP but inhibits TN of three soil layers. The N addition decreases C/N but increases C/P and N/P, while the P addition increases C/N but decreases C/P and N/P of three soil layers. The SOC, TN, TP, C/N, C/P, and N/P under HN and HP treatment reach the significance level (P < 0.05). Appropriate additions of N and P can improve rhizosphere and non-rhizosphere nutrients and stoichiometric structure, facilitating absorption and utilization by alfalfa and improve the production potential of alfalfa in alkaline soil.

Stoichiometric homeostasis of N:P ratio drives species-specific symbiotic N fixation inhibition under N addition

Introduction

Symbiotic N fixation inhibition induced by N supply to legumes is potentially regulated by the relative N and P availability in soil. However, the specific responses of different legume species to changes in N:P availability remain unclear, and must be better understood to optimize symbiotic N fixation inputs under N enrichment. This study investigated mechanisms by which soil N and P supply influence the symbiotic N fixation of eight legume species, to quantify the inter-specific differences, and to demonstrate how these differences can be determined by the stoichiometric homeostasis in N:P ratios (HN:P).

Methods

Eight herbaceous legume species were grown separately in outdoor pots and treated with either no fertilizer (control), N fertilizer (14 g N m-2), P fertilizer (3.5 g P m-2) or both N and P fertilizer. Plant nutrients, stoichiometric characteristics, root biomass, non-structural carbohydrates (NSC), rhizosphere chemistry, P mobilization, root nodulation and symbiotic N fixation were measured.

Results

N addition enhanced rhizosphere P mobilization but drove a loss of root biomass and root NSC via exudation of P mobilization compound (organic acid), especially so in treatments without P addition. N addition also induced a 2-14% or 14-36% decline in symbiotic N fixation per plant biomass by legumes in treatments with or without P addition, as a result of decreasing root biomass and root NSC. The changes in symbiotic N fixation were positively correlated with stoichiometric homeostasis of N:P ratios in intact plants without root nodules, regardless of P additions.

Discussion

This study indicates that N addition can induce relative P limitations for growth, which can stimulate rhizosphere P mobilization at the expense of root biomass and carbohydrate concentrations, reducing symbiotic N fixation in legumes. Legume species that had less changes in plant N:P ratio, such as Lespedeza daurica and Medicago varia maintained symbiotic N fixation to a greater extent under N addition.

Salinity decreases cadmium accumulation in Vicia faba

The study investigates the effect of cadmium (Cd), salinity (NaCl), and combined stress on rhizosphere pH, growth parameters, membrane leakage, and genotoxicity in Vicia faba. Germinated seeds were exposed for 48 h to 0.01 mM Cd(NO₃)₂ (Cd), 50 mM NaCl (S50), 150 mM NaCl (S150), and Cd-NaCl (CdS50 and CdS150). An accumulation of Cd and Na was found essentially in Vicia roots under each single stress factor associated with variations in rhizosphere pH. Additional NaCl in metallic solution significantly dropped the rhizosphere pH and decreased Cd concentrations in roots by 2.3 and 3.8 times for CdS50 and CdS150, respectively. Growth parameters (root length and fresh and dry matters), mitotic activity, and micronucleus formation were not influenced by Cd and low concentration of NaCl when applied separately or together, while 150 mM of NaCl, alone or combined with Cd, affected negatively all the studied parameters, as well as chromosome and nucleus stability. V. faba seems to reduce the transport of Cd in saline conditions and therefore salinity (50 mM) may act as a protection against Cd accumulation.

Development of Fertilizer Coatings from Polyglyoxylate-Polyester Blends Responsive to Root-Driven pH Change

Many current controlled-release fertilizers (CRFs) are coated with nonbiodegradable polymers that can contribute to microplastic pollution. Here, coatings of self-immolative poly(ethyl glyoxylate) (PEtG) capped with a carbamate and blended with polycaprolactone (PCL) or poly(l-lactic acid) (PLA) were evaluated. They were designed to depolymerize and release fertilizers in the vicinity of plant roots, where the pH is lower than that in the surrounding environment. PEtG/PCL coatings exhibited significant temperature and pH effects, requiring 18 days at pH 5 and 30 °C, compared to 77 days at pH 7 and 22 °C, to reach 15% mass loss. Plant roots were also effective in triggering coating degradation. Spray-coating and melt-coating were explored, with the latter being more effective in providing pellets that retained urea prior to polymer degradation. Finally, PEtG/PCL-coated pellets promoted plant growth to a similar degree or better than currently available CRFs.

Impacts of arbuscular mycorrhizal fungi on nutrient uptake, N2 fixation, N transfer, and growth in a wheat/faba bean intercropping system

Arbuscular mycorrhizal fungi (AMF) can play a key role in natural and agricultural ecosystems affecting plant nutrition, soil biological activity and modifying the availability of nutrients by plants. This research aimed at expanding the knowledge of the role played by AMF in the uptake of macro- and micronutrients and N transfer (using a ¹⁵N stem-labelling method) in a faba bean/wheat intercropping system. It also investigates the role of AMF in biological N fixation (using the natural isotopic abundance method) in faba bean grown in pure stand and in mixture. Finally, it examines the role of AMF in driving competition and facilitation between faba bean and wheat. Durum wheat and faba bean were grown in pots (five pots per treatment) as sole crops or in mixture in the presence or absence of AMF. Root colonisation by AMF was greater in faba bean than in wheat and increased when species were mixed compared to pure stand (particularly for faba bean). Mycorrhizal symbiosis positively influenced root biomass, specific root length, and root density and increased the uptake of P, Fe, and Zn in wheat (both in pure stand and in mixture) but not in faba bean. Furthermore, AMF symbiosis increased the percentage of N derived from the atmosphere in the total N biomass of faba bean grown in mixture (+20%) but not in pure stand. Nitrogen transfer from faba bean to wheat was low (2.5–3.0 mg pot^-1); inoculation with AMF increased N transfer by 20%. Overall, in terms of above- and belowground growth and uptake of nutrients, mycorrhization favoured the stronger competitor in the mixture (wheat) without negatively affecting the companion species (faba bean). Results of this study confirm the role of AMF in driving biological interactions among neighbouring plants.

Uptake of nicotine from discarded cigarette butts - A so far unconsidered path of contamination of plant-derived commodities

This study aimed to elucidate the origin of the widespread nicotine contamination of plant-derived commodities, by conducting field experiments with various herbs and spice plants. By scattering tobacco and cigarette butts on the field and subsequent nicotine analyses of the acceptor plants, we verified that the alkaloid is leached out into the soil and is taken up by the crop plants. This path of contamination pertains even when there is only one cigarette butt per square meter. Even such minor pollution results - at least in the case of basil and peppermint - in considerable high nicotine contaminations, which exceed the maximum residue level by more than 20-fold. The data reported here clearly outline the large practical relevance of this soil-borne contamination path and imply that unthoughtful disposal of cigarette butts in the field by farm workers may be the reason for the widespread occurrence of nicotine contamination in plant-derived commodities. Therefore, such misbehavior needs to be prevented using education and sensitization, and by including this issue into the guidelines of good agricultural practice.

Major Crop Species Show Differential Balance between Root Morphological and Physiological Responses to Variable Phosphorus Supply

The relationship between root morphological and physiological responses to variable P supply in different plant species is poorly understood. We compared root morphological and physiological responses to P supply in seven crop species (Zea mays, Triticum aestivum, Brassica napus, Lupinus albus, Glycine max, Vicia faba, Cicer arietinum) treated with or without 100 mg P kg-1 in two soils (acidic and calcareous). Phosphorus deficiency decreased root length more in fibrous root species (Zea mays, Triticum aestivum, Brassica napus) than legumes. Zea mays and Triticum aestivum had higher root/shoot biomass ratio and Brassica napus had higher specific root length compared to legumes, whereas legumes (except soybean) had higher carboxylate exudation than fibrous root species. Lupinus albus exhibited the highest P-acquisition efficiency due to high exudation of carboxylates and acid phosphatases. Lupinus albus and Cicer arietinum depended mostly on root exudation (i.e., physiological response) to enhance P acquisition, whereas Zea mays, Triticum aestivum and Brassica napus had higher root morphology dependence, with Glycine max and Vicia faba in between. Principal component analysis using six morphological and six physiological responses identified root size and diameter as the most important morphological traits, whereas important physiological responses included carboxylate exudation, and P-acquisition and P-utilization efficiency followed by rhizosphere soil pH and acid phosphatase activity. In conclusion, plant species can be grouped on the basis of their response to soil P being primarily via root architectural or exudation plasticity, suggesting a potential benefit of crop-specific root-trait-based management to cope with variable soil P supply in sustainable grain production.

Impact of Wheat/Faba Bean Mixed Cropping or Rotation Systems on Soil Microbial Functionalities

Cropping systems based on carefully designed species mixtures reveal many potential advantages in terms of enhancing crop productivity, reducing pest and diseases, and enhancing ecological services. Associating cereals and legume production either through intercropping or rotations might be a relevant strategy of producing both type of culture, while benefiting from combined nitrogen fixed by the legume through its symbiotic association with nitrogen-fixing bacteria, and from a better use of P and water through mycorrhizal associations. These practices also participate to the diversification of agricultural productions, enabling to secure the regularity of income returns across the seasonal and climatic uncertainties. In this context, we designed a field experiment aiming to estimate the 2 years impact of these practices on wheat yield and on soil microbial activities as estimated through Substrate Induced Respiration method and mycorrhizal soil infectivity (MSI) measurement. It is expected that understanding soil microbial functionalities in response to these agricultural practices might allows to target the best type of combination, in regard to crop productivity. We found that the tested cropping systems largely impacted soil microbial functionalities and MSI. Intercropping gave better results in terms of crop productivity than the rotation practice after two cropping seasons. Benefits resulting from intercrop should be highly linked with changes recorded on soil microbial functionalities.

Shift from complementarity to facilitation on P uptake by intercropped wheat neighboring with faba bean when available soil P is depleted

Rhizosphere processes stimulate overyielding and facilitative phosphorus (P) uptake in cereal/legume intercropping systems. However, little is known about when and how rhizosphere alteration of legumes plays a role in improving P uptake by cereals. Wheat was grown isolated, monocropped or intercropped with faba bean in pots with low-P soil. The biomass, P content, carboxylates and phosphatases activity were measured in 15 destructive samplings. Intraspecific competition of the biomass and P uptake of monocropped wheat was not significant before 40 and 36 days after sowing (DAS), whereas there was interspecific competition of biomass of intercropped wheat before 66 DAS. However, afterwards, the increments of the biomass and P uptake of the intercropped wheat were 1.3-1.9 and 1.9-2.3 times of increment of monocropped wheat. Meanwhile, the concentrations of malate and citrate and the acid phosphatase activity in the rhizospheres of intercropped wheat were significantly increased, which suggested that wheat/faba bean intercropping is efficient in P utilization due to complementary P uptake in the early growth stage and the positive interactions of the rhizosphere processes when the soil P was depleted.

The role of maize root size in phosphorus uptake and productivity of maize/faba bean and maize/wheat intercropping systems

Interspecific root/rhizosphere interactions affect phosphorus (P) uptake and the productivity of maize/faba bean and maize/wheat intercropping systems. The aim of these experiments was to determine whether manipulation of maize root growth could improve the productivity of the two intercropping systems. Two near isogenic maize hybrids (the larger-rooted T149 and smaller-rooted T222) were intercropped with faba bean and wheat, under conditions of high- and low-P availability. The larger-rooted T149 showed greater competitive ability than the smaller-rooted T222 in both maize/faba bean and maize/wheat intercropping systems. The higher competitive ability of T149 improved the productivity of the maize/faba bean intercropping system in P-sufficient conditions. In maize/wheat intercropping systems, root growth, shoot biomass, and P uptake of maize were inhibited by wheat, regardless of the P-supply. Compared with T222, the larger-rooted T149 suffered less in the intercropping systems. The total biomass of the maize/wheat intercropping system was higher for wheat/T149 than for wheat/T222 under low-P conditions. These data suggested that genetic improvement of maize root size could enhance maize growth and its ability to compete for P resources in maize/faba bean and maize/wheat intercropping systems. In addition, depending on the P availability, larger maize roots could increase the productivity of intercropping systems.

Interaction between BSM-contaminated soils and Italian ryegrass

The interaction among the bensulfuron-methyl, growth of Italian ryegrass, and soil chemical/biochemical/microbiological parameters was investigated in a microcosm experiment. The bensulfuron-methyl added to the soil can be rapidly degraded by certain fungi and actinomycetes present in the original paddy rice soil. The growth of Italian ryegrass significantly accelerated the in-soil degradation of bensulfuron-methyl in its rhizosphere. The uptake of bensulfuron-methyl by ryegrass increased with increasing dosage level of bensulfuron-methyl. However, the phytoextraction of bensulfuron-methyl by ryegrass contributed insignificantly to the total removal of the soil bensulfuron-methyl. Within the dosage range set in this study, the root development of ryegrass was not adversely affected by the presence of the soil bensulfuron-methyl although the fresh biomass of shoot was slightly reduced in the higher dosage treatments. This can be attributed to the adsorption of the added bensulfuron-methyl by soil colloids and consequently the reduction of bensulfuron-methyl level in the soil pore water to a concentration sufficiently lower than the toxic level. The growth of ryegrass significantly increased soil pH and the activities of phosphatase and peroxidase but reduced the EC and the activities of urease in the rhizospheric soil.

The alkaline tolerance in Arabidopsis requires stabilizing microfilament partially through inactivation of PKS5 kinase

High soil pH is harmful to plant growth and development. The organization and dynamics of microfilament (MF) cytoskeleton play important roles in the plant anti-alkaline process. In the previous study, we determined that alkaline stress induces a signal that triggers MF dynamics-dependent root growth. In this study we identified that PKS5 kinase involves in this regulatory process to facilitate the signal to reach the downstream target MF. Under pH 8.3 treatment, the depolymerization of MF was faster in pks5-4 (PKS5 kinase constitutively activated) than that in wild-type plants. The inhibition of wild-type, pks5-1, and pks5-4 root growth by pH 8.3 was correlated to their MF depolymerization rate. When the plants were treated with phalloidin to stabilize MF, the high pH sensitive phenotype of pks5-4 can be partially rescued. When the plants were treated with a kinase inhibitor Staurosporine, the MF depolymerization rate in pks5-4 was similar as that in wild-type under pH 8.3 treatment and the sensitivity of root growth was also rescued. However, when the plants were treated with LaCl(3), a calcium channel blocker, the root growth sensitivity of pks5-4 under pH 8.3 was rescued but MF depolymerization was even faster than that of plants without LaCl(3) treatment. These results suggest that the PKS5 involves in external high pH signal mediated MF depolymerization, and that may be independent of calcium signal.