Impact of pyrochar and hydrochar on soybean (Glycine max L.) root nodulation and biological nitrogen fixation

The aim of this study was to identify effects of carbonized organic material (“biochar”) on soybean growth, root nodulation and biological nitrogen fixation, and to elucidate possible underlying mechanisms. Soybean (Glycine max L.) was grown in four arable soils amended with carbonized organic material produced from wood or maize as feedstocks, by pyrolysis (“pyrochar”) or hydrothermal carbonization (“hydrochar”). Nodulation by Bradyrhizobium , biological nitrogen fixation (BNF) assessed by ¹⁵N techniques, plant growth, nutrient uptake and changes in chemical soil properties after soil amendment were determined. Data were analyzed by means of a three way ANOVA on the factors soil, carbonization technique and feedstock. It turned out that soybean root nodulation and BNF was influenced by the carbonization technique used to prepare the soil amendment. Hydrochar, in average and across all soils, increased nodule dry matter and BNF by factors of 3.4 and 2.3, respectively, considerably more than pyrochar, which led to 1.8 and 1.2 fold increases, respectively. Nodule dry matter and BNF correlated positively with available soil sulfur and negatively with available soil nitrogen. Hydrochars provided more available sulfur than pyrochars, and hydrochars caused a decrease in nitrogen availability in the soil solution, thereby exerting a positive influence on nodulation and BNF. Pyrochar amendment increased soil pH but had no effect on nodulation and BNF. Plant growth was affected by the soil and by the feedstock used for the “biochar”, and increased slightly more in treatments with pyrochar and hydrochar made from maize, which was richer in nitrogen and potassium. The results show that carbonized organic materials, and specifically hydrochar, have the capacity to increase BNF in soils. We suggest that this enhancement in BNF in response to soil amendments with carbonized organic materials is due to an increase in available sulfur and a reduction of available soil nitrogen.     

大豆生物固氮模型研究进展

定量描述大豆生物固氮量对于施肥管理以及农业非点源污染控制具有十分重要的意义。生物固氮模型作为一种重要工具,在定量预测大豆生物固氮速率方面具有不可替代的作用。国内研究者对不同环境因子对固氮的影响开展了一些工作,但多未从定量角度出发。国外的生物固氮模型按构建方式大致可以分为经验模型和机理模型两类。其中机理模型研究较多,也是目前生物固氮模型的主要发展方向。本文简述了这两类模型的研究现状,并着重介绍了5种目前国外使用较为广泛的田间尺度下的大豆生物固氮机理模型,比较了不同模型中采用的环境因子响应函数的差异,并对进一步的研究作了展望,以期为国内大豆生物固氮定量研究工作的开展提供借鉴。     

新型生物炭基氮肥对土壤一冬小麦系统氮素累积及相关生物活性的影响

通过田间试验,研究了掺混型、吸附型和反应型3种新型生物炭基硝酸铵氮肥在冬小麦生长过程中对土壤氮素累积及冬小麦对氮素的利用状况和相关生物活性的影响。试验处理包括CK（不施氮肥,不施生物炭）、硝酸铵氮肥、生物炭、掺混型生物炭基氮肥、吸附型及反应型生物炭基氮肥。研究结果表明：不同工艺制备的生物炭基氮肥对土壤铵态氮的累积具有显著影响,吸附型和反应型处理在冬小麦生长季铵态氮平均值大于对照（CK）,对于总氮、硝态氮和亚硝态氮累积量的影响不显著。除了生物炭单施处理外,其他处理均比CK显著提高冬小麦地上部的总氮累积量,但对冬小麦的氮素利用状况无显著影响,且三种炭基氮肥处理问无显著差异;施用不同类型生物炭基氮肥对土壤微生物量氮含量和硝酸还原酶活性具有提高作用,而对微生物量碳含量、亚硝酸还原酶和脲酶活性无显著影响。     

Nitrogen fixation potential in global chickpea mini-core collection

Biological nitrogen fixation (BNF) is a sustainable alternative for nitrogen supply to agriculture worldwide. One approach to increasing BNF in agriculture is to breed and use legumes with greater BNF capacity. To assess the capacity for BNF in chickpea (Cicer arietinum) global germplasm, a genetically diverse subset from the USDA global chickpea core collection was assayed for BNF potential. The greenhouse experiment assayed 39 global accessions and commercial cultivar UC-5, inoculated with Mesorhizobium ciceri. Plant height, branch number, nodule number, shoot weight, root weight, nodule weight, proportion of nitrogen fixed, and total nitrogen fixation were determined. All characteristics varied significantly among the accessions. Proportion of plant nitrogen fixed ranged from 47% to 78% and was correlated with shoot weight (r = 0.21, P < 0.01) and total plant weight (r = 0.20, P < 0.01), but not with nodule number or weight. Accession 254549 from Iraq produced the greatest total fixed nitrogen, more than any other accession and 121% more than that fixed by UC-5. The variation among BNF capacities of the accessions supports the preservation and use of global germplasm resources and suggests that nitrogen fixation in commercial chickpea varieties may be improved by introgressing positive alleles from the global chickpea germplasm collections.     

Biological nitrogen fixation in maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) by <Superscript>15</Superscript>N isotope-dilution and identification of associated culturable diazotrophs

The nitrogen-fixing capacity of a range of commercial cultivars of maize (Zea mays L.) was evaluated by the ¹⁵N isotope-dilution method. Biological nitrogen fixation (BNF) expressed as percent nitrogen derived from air (Ndfa) ranged from 12 to 33 regardless of nitrogen fertilization. BNF was not affected by mineral nitrogen fertilization except on cultivar Topacio and PAU-871 cultivars. Subsequently, culturable bacterial diazotrophs were isolated from endophytic tissue of maize: seed, root, stem, and leaf. All isolates were able to grow on N-free semisolid medium. Eleven bacteria isolates showed nitrogen-fixing capacity by the reduction of acetylene to ethylene and confirmed by PCR the presence of nifH gene in their genome. Identification of the 11 isolates was performed by bacteriological methods, 16S rRNA gene sequences, and phylogenetic analysis, which indicated that the bacteria isolated were closely related to Pantoea, Pseudomonas, Rhanella, Herbaspirillum, Azospirillum, Rhizobium (Agrobacterium), and Brevundimonas. This study demonstrated that maize cultivars obtain significant nitrogen from BNF, varying by maize cultivar and nitrogen fertilization level. The endophytic diazotrophic bacteria isolated from root, stem, and leaf tissues of maize cultivars may contribute to BNF in these plants.     

我国大豆的生物固氮潜力研究

【目的】根瘤菌与大豆共生结瘤固氮是大豆的重要氮素来源之一,而我国在大豆生产中普遍过量使用化学氮肥,不仅增加了生产成本,而且严重抑制了大豆的生物固氮效率。因此在生产中充分发挥生物固氮作用、 合理施用化学氮肥、 降低大豆生产成本是我国发展大豆产业的重要措施,本文对我国大豆主产区生物固氮潜力及其分布特征进行了研究,旨在了解不施氮肥条件下不同大豆产区生物固氮的最大供氮能力,为大豆的合理施肥和充分发挥生物固氮作用提供理论依据。【方法】采用15N自然丰度法,在2011年和2012年测定了在不施用氮肥条件下我国4个大豆主产区包括黑河、 大庆、 长春、 铁岭、 济宁、 延安、 南宁等7个试验点在内的大豆生物固氮效率、 生物固氮量及其对产量的贡献。15N自然丰度法的原理是利用非固氮参照作物从土壤中吸收的15N丰度高于固氮植物,根据两者的15N自然丰度差异估算出固氮植物的生物固氮率。所选的非固氮参照作物必须同大豆生长季一致,并且各试验点选用同一种非固氮植物以保证各地数据的可比性。通过查阅文献,有研究使用玉米作为参照作物,并且符合上述要求,因此本研究选择玉米作为非固氮参照作物。【结果】在不施氮肥条件下,我国大豆在正常降水年份的生物固氮效率为47%～70%,其中铁岭最高为60%～70%,黑河最低为47%～54%;大豆的生物固氮量在N 92～150 kg/hm2之间变化,其中籽粒中的生物固氮量占总固氮量的65%～81%,生物固氮量最高的试验点为长春,最低的试验点为延安;生物固氮对产量的贡献在1039～1867 kg/hm2之间,其中最高的试验点为长春,最低的试验点为延安;在延安试验点苗期～开花期极度干旱的2011年,大豆缺水严重抑制了根瘤菌的数量和固氮酶的活性,其生物固氮效率、 固氮量及对产量的贡献均达极低水平,分别为15%和N 24 kg/hm2和245 kg/hm2。【结论】我国大豆不同主产区的生物固氮潜力存在较大差异,并且具有明显的分布规律。生物固氮效率以温带的铁岭为最高,向北至寒温带的黑河、 向南到亚热带的南宁均呈现逐渐降低的趋势。受种植密度等因素的影响,大豆生物固氮量及其对产量贡献的分布规律与生物固氮效率不完全一致,其中东北地区最高,其次是济宁和南宁,延安最低。     

Mineral nitrogen impairs the biological nitrogen fixation in soybean of determinate and indeterminate growth types

Soybean (Glycine max Merrill) crop production in Brazil relies mainly on biological nitrogen fixation (BNF) for nitrogen (N) supply. Recent adoption of indeterminate growth-type genotypes has raised doubts on the need for supplemental mineral N that might negatively affect the BNF. We assessed the effects of mineral N on BNF attributes of soybean genotypes grown in central and southern Brazil. Genotypes were inoculated with Bradyrhizobium sp. and/or received mineral N in three sets of experiments. In the first set, two genotypes received increasing rates of mineral N in nutrient solution, which consistently reduced the BNF. In the second set, mineral N applied at sowing and/or topdressing reduced nodulation and ureides-N in determinate and indeterminate growth-type genotypes. In the third set, mineral N applied at R5.3 stage, foliar or as topdressing, did not increase grain yield in four field experiments. Mineral N impaired BNF irrespective of the growth type and had no effect on grain yield.     

15N同位素稀释法研究固氮菌接种对甘蔗生物固氮的影响

利用15N同位素稀释法,研究接种固氮菌klebsiella L03对甘蔗品种B8和ROC22的生物固氮的影响。结果表明： B8的固氮百分率最高为3128%Ndfa,从苗期开始就显著高于ROC22,分蘖期和伸长初期的固氮量和固氮百分率与ROC22相比差异达到极显著水平。B8和ROC22的根、茎、叶都可发生固氮,以伸长初期（60d）叶片中的固氮能力最强。接种L03能显著提高B8和ROC22各器官的含氮量,其中对ROC22叶片和B8茎的含氮量提高作用最明显。不同甘蔗品种、相同品种的不同器官甚至相同器官的不同生长时期固氮作用有很大差异。     

The amount,but not the proportion,of N2 fixation and transfers to neighboring plants varies across grassland soils

ABSTRACT

Biological nitrogen fixation (BNF) is an important nitrogen source for both N₂-fixers and their neighboring plants in natural and managed ecosystems. Biological N fixation can vary considerably depending on soil conditions, yet there is a lack of knowledge on the impact of varying soils on the contribution of N from N₂-fixers in mixed swards. In this study, the amount and proportion of BNF from red clover were assessed using three grassland soils. Three soil samples, Hallsworth (HH), Crediton (CN), and Halstow (HW) series, were collected from three grassland sites in Devon, UK. A pot experiment with ¹⁵N natural abundance was conducted to estimate BNF from red clover, and the proportion of N transferred from red clover to the non-N₂ fixing grass in a grass-clover system. The results showed that BNF in red clover sourced from atmosphere in the HH soil was 2.92 mg N plant^?1, which was significantly lower than that of the CN (6.18 mg N plant^?1) and HW (8.01 mg N plant^?1) soils. Nitrogen in grass sourced from BNF via belowground was 0.46 mg N plant^?1 in the HH soil, which was significantly greater than that in CN and HW soils. However, proportionally there were no significant differences in the percentage N content of both red clover and grass sourced from BNF via belowground among soils, at 65%, 67%, 65% and 35%, 27%, 31% in HH, CN, and HW, respectively. Our observations indicate that the amount of BNF by red clover varies among grassland soils, as does the amount of N sourced from BNF that is transferred to neighboring plants, which is linked to biomass production. Proportionally there was no difference among soils in N sourced from BNF in both the red clover plants and transferred to neighboring plants.     

Utilization of BNF Technology Supplementing Urea N for Sustainable Rice Production

The critical nitrogen (N) requirement of rice crops for maximum yields is well known. To overcome acute N deficiency in rice soils as a result of an increasing yield per unit area in the past 50 years of almost three-fold, this element has been usually supplied to the rice crop as the chemical fertilizer ‘urea’. Unfortunately a substantial amount of the urea-N is lost through different mechanisms, causing environmental pollution problems. In principle, utilization of biological nitrogen fixation technology can supplement the use of urea-N, reducing the environmental problems to a considerable extent by improving nitrogen use efficiency. Different biological nitrogen fixation (BNF) systems have different potentials to provide an N supplement. It is necessary to design appropriate strategies to obtain more sustainable N supply to the rice crop. This paper reviews research to evaluate the potential of different BNF systems to supply N for the rice crop, assessing the current information.     

稻田养萍模式下不同施氮量对稻田氨挥发及红萍生物固氮作用的影响

红萍对水体铵态氮浓度较为敏感，稻田放养红萍模式下，红萍的生物固氮作用及其抑制氨挥发的作用对不同施氮量的响应未知。红萍为水生蕨藻共生体，具有很强的生物固氮能力。红萍可作为优质绿肥放养于稻田，以替代部分化学氮肥，起到节能减排的效应。为明确稻田养萍模式下不同施氮量对红萍生物固氮作用和田间氨挥发的影响，采用盆栽试验设置了0、75、150、225、300kg/hm²共5个施氮(以纯N量计)水平，监测了稻田放养红萍和水稻单种各处理的氨挥发量、生物固氮速率和水稻产量。结果表明：(1)同一施氮水平下，稻田放养红萍可显著降低氨挥发日通量峰值及氨挥发总量。在施氮量为225 kg/hm²时，稻田放养红萍对氨挥发总量的抑制作用最大，与水稻单种相比，抑制幅度可达83.2%。(2)红萍的生物固氮速率及固氮总量与施氮量呈线性负相关关系，随施氮量的增加，固氮速率和固氮量逐渐降低，施氮量300 kg/hm²并放养红萍处理得到的固氮速率及总量同不施氮肥不养萍处理之间无显著差异。(3)与不养萍处理相比，放养红萍组各处理的水稻产量都明显增加，其中施氮量为225...     

Asymbiotic biological nitrogen fixation in a temperate grassland as affected by management practices

Estimates of asymbiotic biological N fixation (BNF) in temperate grasslands are few with large variations. In the past six decades, European grasslands have been subjected to intensive management practices and presently it is not known how asymbiotic BNF is influenced by these practices. Our objective was to assess the impact of fertilizer application and mowing frequency on asymbiotic BNF in a Central European grassland. In 2008, we established a three-factorial experiment with two fertilizer treatments (no fertilizer application and combined nitrogen (N), phosphorus (P) and potassium (K) fertilization at 180–30–100 kg ha⁻¹ yr⁻¹), two mowing frequencies (cut once and thrice per year) and three sward compositions through the application of herbicides (control, monocot- and dicot-enhanced swards). Three years after the initial sward manipulation, there was no more difference in functional group composition. Between June 2011 and May 2012, we measured in-situ asymbiotic BNF using the acetylene reduction assay, calibrated with ¹⁵N₂-fixation method. Across treatments, asymbiotic BNF rates in the 0–5-cm soil depth ranged from 1.7 (±0.2 SE) kg ha⁻¹ yr⁻¹ for fertilized plots cut once a year to 5.7 (±2.3 SE) kg ha⁻¹ yr⁻¹ for unfertilized plots cut thrice a year. Fertilization decreased asymbiotic BNF, suggesting that the potential positive effect of increased soil P levels might have been overruled by the negative effect of increased soil mineral N levels. Intensive mowing stimulated asymbiotic BNF, which was probably due to an increase in rhizodeposition. Our calibration of the acetylene reduction assay with the ¹⁵N₂-fixation method resulted in a conversion factor of 0.61, which largely deviates from the theoretical conversion factor of 3. Furthermore, laboratory incubations under increased soil moisture and temperature conditions overestimated BNF rates compared to in-situ measurements. Thus, laboratory measurements with altered soil moisture, temperature or disturbed soil may lead to strong biases in estimates of asymbiotic BNF. Our results suggest that input of N through BNF may be considerable in temperate grasslands. We conclude that BNF studies should be conducted in-situ and that the acetylene reduction assay should be calibrated against ¹⁵N₂-fixation calibration for reliable estimates.     

Increased phosphorus availability from sewage sludge ashes to maize in a crop rotation with clover

A recycling of Phosphorus (P) from the human food chain is mandatory to secure the future P supply for food production. However, many available recycled P fertilizers from sewage sludge do not have an adequate P bioavailability and, thus, are not suitable for their application in soils with pH >5.5–6.0, unless being combined with efficient mobilization measures. The aim of the study was to test the P mobilization ability of red clover (Trifolium pratense L.) from two thermally recycled P fertilizers for a subsequently grown maize. Two sewage sludge ashes (SSA) were investigated in a pot experiment at soil pH 7.5 with red clover differing in its nitrogen (N) supply (added N fertilizer or biological N₂ fixation (BNF)), followed by maize (Zea maize L.). Shoot dry matter of maize was almost doubled when N supply of previous grown clover was covered by BNF, instead of receiving added N fertilizer. Similarly, shoot P removal of maize following clover with BNF was significantly increased. It is suggested that the P mobilization is related to the BNF, and a proton release of N₂ fixing clover roots led to the measured decrease in soil pH and thereby increased P availability of the tested fertilizers.     

Impact of variety and farming practices on growth,yield, weed flora and symbiotic nitrogen fixation in faba bean cultivated for fresh seed production

The main objective of this study was to investigate the performance of faba bean landraces originating from different regions of Greece under both organic and conventional farming systems focusing mainly on yield, biological nitrogen fixation (BNF), and competitiveness to weeds. Faba bean exhibited a high ability to fix nitrogen from the atmosphere, as indicated by the percentage of N₂ derived from the atmosphere which exceeded 75% in all evaluated varieties, and the total amount of biologically fixed N up to full anthesis, which fluctuated from 118.5 to 193.9?kg?ha^?1 in the various cropping systems and cultivars. The weed density was appreciably higher in the organic plots, without significant differences among the faba bean cultivars, while wild mustard and corn poppy were the most competitive weeds. The application of inorganic starter fertiliser in the conventionally-treated plots had no negative effect on biologically-fixed nitrogen by faba bean plants, while the herbicide pendimethalin had no negative impact on the nodulation process. Protein concentrations in faba bean cultivars fluctuated from 27.3% to 31.4%. The evaluated landraces could be utilised in breeding programmes due to their earliness, and their high performance in terms of protein content, BNF ability, and productivity.     

Cropping history affects nodulation and symbiotic efficiency of distinct hairy vetch (Vicia villosa Roth.) genotypes with resident soil rhizobia

Compatible rhizobia strains are essential for nodulation and biological nitrogen fixation (BNF) of hairy vetch (Vicia villosa Roth, HV). We evaluated how past HV cultivation affected nodulation and BNF across host genotypes. Five groups of similar HV genotypes were inoculated with soil dilutions from six paired fields, three with 10-year HV cultivation history (HV+) and three with no history (HV?), and used to determine efficiency of rhizobia nodulation and BNF. Nodulation was equated to nodule number and mass, BNF to plant N and Rhizobium leguminosarum biovar viceae (Rlv) soil cell counts using qPCR to generate an amplicon of targeted Rlv nodD genes. Both HV cultivation history and genotype affected BNF parameters. Plants inoculated with HV+ soil dilutions averaged 60 and 70 % greater nodule number and mass, respectively. Such plants also had greater biomass and tissue N than those inoculated with HV? soil. Plant biomass and tissue N were strongly correlated to nodule mass (r ²?=?0.80 and 0.50, respectively), while correlations to nodule number were low (r ²?=?0.50 and 0.31, respectively). Although hairy vetch rhizobia occur naturally in soils, past cultivation of HV was shown in this study to enhance nodulation gene-carrying Rlv population size and/or efficiency of rhizobia capable of nodulation and N fixation.     

Evaluation of the field performance,nitrogen fixation efficiency and competitive ability of pea landraces grown under organic and conventional farming systems

In the present study, three pea Greek landraces Schinousa (AUASCHIN001), Andros (AUAANDRO001), and Amorgos (AUAAMORG001), and the commercial variety Onward were grown following either conventional or organic farming practices. The main objective of the study was to assess the suitability of these three landraces for organic cultivation as compared with a standard commercial variety. The total fresh pod yield produced by AUASCHIN001 and AUAAMORG001 was significantly lower than that obtained from ‘Onward’ and AUAANDRO001. Furthermore, the three landraces exhibited a higher competition to weeds than the commercial variety. Under organic farming conditions, AUASCHIN001 and AUAAMORG001 produced appreciably less shoot biomass than ‘Onward’ and this resulted in commensurate decreases in the total amount of BNF (biological nitrogen fixation) in their plant tissues, although the percentage of nitrogen (N) fixed from the atmosphere was significantly lower in ‘Onward’. AUAANDRO001 rendered the highest amounts of BNF in the organic farming systems, which was similar to that produced by ‘Onward’ in the conventional system. These results indicate that the tested landraces and especially AUAANDRO001 are more adaptable to low soil N levels and high weed competition, and thus they are more suitable for organic cultivation than ‘Onward’ which performs best in conventional cropping systems.     

Isotopic evidence of significant assimilation of atmospheric-derived nitrogen fixed by Azospirillum brasilense co-inoculated with phosphate-solubilising Pantoea dispersa in pepper seedling

The contribution of plant growth-promoting bacteria (PGPB) of the genus Azospirillum to the plant N budget through biological nitrogen fixation (BNF) is still controversial. The aim of this study was to determine the contribution of BNF by Azospirillum brasilense on pepper grown at different N levels, attained using the ¹⁵N natural abundance method. To this end, pepper plants were grown in a growth chamber and treated with A. brasilense combined with Pantoea dispersa and then irrigated at four different N levels (0, 1, 3 and 7 mM NO₃⁻). The assimilation of fixed N was clear from the lower δ¹⁵N values observed in bacteria-treated plants compared with those of non-bacteria treated plants. The percentage of BNF-derived N decreased with decreasing NO₃⁻ levels in the growth medium. BNF contribution to the total nitrogen content of plants was found to be as high as 46%. The results suggest that the bacteria have a potential to supply a considerable amount of N to pepper seedlings, as well as to stimulate plant growth and N uptake when Azospirillum–Pantoea treatment is combined with low NO₃⁻ levels.     

Paddy System with a Hybrid Rice Enhances Cyanobacteria Nostoc and Increases N2 Fixation

Biological nitrogen(N) fixation(BNF) plays a significant role in maintaining soil fertility in paddy field ecosystems. Rice variety influences BNF, but how different rice varieties regulate BNF and associated diazotroph communities has not been quantified. Airtight,field-based ~(15)N_2-labelling growth chamber experiments were used to assess the BNF capacity of different rice varieties. In addition,both the 16 S rRNA and nifH genes were sequenced to assess the influence of different rice varieties on bacterial and diazotrophic communities in paddy soils. After subjecting a rice-soil system to 74 d of continuous airtight, field-based ~(15)N_2 labelling in pots in a growth chamber, the amounts of fixed N were 22.3 and 38.9 kg ha~(-1) in inbred japonica(W23) and hybrid indica(IIY) rice cultivars planted in the rice-soil systems, respectively, and only 1%–2.5% of the fixed N was allocated to the rice plants and weeds. A greater abundance of diazotrophs was found in the surface soil(0–1 cm) under IIY than under W23. Sequencing of the 16 S rRNA gene showed significantly greater abundances of the cyanobacterial genera Nostoc, Anabaena, and Cylindrospermum under IIY than under W23.Sequencing of the nifH gene also showed a significantly greater abundance of Nostoc under IIY than under W23. These results indicate that the hybrid rice cultivar(IIY) promoted BNF to a greater extent than the inbred rice cultivar(W23) and that the increase in BNF might have been due to the enhanced heterocystous cyanobacteria Nostoc.     

Developed microbial biofilms can restore deteriorated conventional agricultural soils

Nitrogen fixing bacteria play a key role in the growth and persistence of effective microbial communities in the soil by supplying N through biological nitrogen fixation (BNF). In the long run, chemical inputs, particularly N fertilisers are known to adversely affect N₂ fixers and hence maintenance of soil fertility and crop productivity. This study examined the effect of developed microbial biofilms with N₂ fixers on restoration of soils deteriorated by conventional agricultural practices in tea cultivation. Just reducing recommended chemical fertiliser use by 50% significantly increased soil microbial biomass and BNF, and decreased soil NO₃⁻ and pest infestation. The lower chemical fertiliser addition coupled with the biofilm-based biofertilisers known as biofilmed biofertilisers (BFBFs) further increased BNF significantly. The combined application significantly increased soil organic C by ca. 20%, and reduced leaf transpiration by ca. 40%. It also supported plant growth, rhizoremediation and soil moisture conservation in comparison to the 100% chemical fertilisation. Those improved performances were observed to be proportional to the increased density of soil bacteria, and have several agronomic and environmental implications. It is apparent from this study that replenishing the depleted soil microbial communities by applying such biofertilisers is likely to be beneficial in agroecosystems with chemical N fertiliser use, if they are to be sustained for crop production.     

Arbuscular mycorrhizae affect the N and C economy of nodulated Phaseolus vulgaris (L.) during NH4 nutrition

In the symbiosis between nodulated legume roots and arbuscular mycorrhizal (AM) fungi, the C and N economy can be influenced by the source of N-supply from either AM-derived NH₄⁺ uptake or nodule-derived biological nitrogen fixation (BNF). This relationship was investigated in terms of NH₄⁺ supply and BNF by the two symbionts. Nodulated Phaseolus vulgaris seedlings with and without AM, were hydroponically grown with either 0 N or 1 mM NH₄⁺ supply. Plants were harvested at 30 days after emergence and measurements were taken for biomass, N₂ fixation, photosynthesis, CO₂ and O₂ root respiration, calculated C and N economy. AM roots had higher NH₄⁺ uptake and this was associated with the suppression of BNF and nodule growth. The higher NH₄⁺ uptake in AM roots occurred with lower root maintenance respiration, compared to when N was derived from BNF. There was also an increase in the below-ground sink strength of NH₄⁺ fed AM roots compared to NH₄⁺ fed non-AM roots, as evidenced by the increases in root CO₂ and O₂ respiration and photosynthetic stimulation. These results indicate that although the AM root had higher total below-ground respiratory costs during NH₄⁺ nutrition, there were lower respiratory C costs associated with N derived from AM symbionts in comparison to N from BNF.