Easily Extractable GRSP Research Articles

Humic substances and aggregate stability in rhizospheric and non-rhizospheric soil

PurposeThe paper describes rhizospheric (Rs) and non-rhizospheric (nRs) soil to demonstrate the zone of the plant root impact on physical and chemical properties of the soil. The effects of the process accompanying the transformations of organic matter into humic substances in the rhizosphere of “common dandelion” Taraxacum officinale have been determined, and the properties of humic acids (HAs) were described. The importance of iron and clay minerals for the formation of a stable and water-resistant soil structure has been emphasized.Materials and methodsThe laboratory analysis involved determination of basic physical and chemical soil properties: texture, pH, cation exchange capacity (CEC), electrical conductivity, and content of total organic carbon (TOC) and dissolved organic carbon (DOC) and quality of humic substances: optical properties of HAs and its separation into hydrophilic (HIL) and hydrophobic (HOB) fractions, speciation of iron, glomalin operationally described as an easily extractable glomalin-related soil protein (EE-GRSP), and soil aggregate stability (SAS) of six size classes of soil aggregates.Results and discussionThe Rs was reported with a higher TOC and DOC content (measured in the CaCl2 extracts), however not significantly. The HAs isolated from Rs revealed a significantly higher content of humic substances at its initial decomposition stage, as compared with nRs. A significantly higher concentration of EE-GRSP was noted in the aggregates of the rhizospheric zone (mean 1.14 g kg−1) than in the aggregates collected from root-free soil (mean 0.94 g kg−1). There was noted the highest mean share of 1–3 mm soil aggregates in Rs as well as in nRs, respectively 44.4 and 38.3%. The soil material both in Rs and in nRs contained high amounts of exchangeable Ca2+, and smectite is the predominant clay mineral. It was favorable for the accumulation of organic carbon and for the formation of good soil physical condition (tilth). Higher but insignificant SAS values were observed for Rs (mean SAS = 95.6%) than for nRs (mean SAS = 93.9%).ConclusionsThe studies confirm the role of common dandelion roots in the process of organic carbon accumulation in rhizospheric zone and a favorable effect on the mechanism of the formation of water-resistant aggregates. Higher values of SAS for the Rs were affected by the content of TOC, DOC, exchangeable Ca2+ and the concentration of EE-GRSP, and, less considerably, the content of Fe and clay minerals.

Exogenous easily extractable glomalin-related soil protein improves drought tolerance of trifoliate orange

ABSTRACTMycorrhiza-released glomalin-related soil protein (GRSP) influences rhizosphere properties, but it is not clear whether exogenous GRSP enhances drought tolerance of plants. In this work, easily extracted GRSP (EE-GRSP) was isolated from Satsuma mandarin soil, and half-strength EE-GRSP (0.007 mg protein mL−1) was weekly applied into rhizosphere of potted trifoliate orange (Poncirus trifoliata) exposed to well watered (WW) and drought stress (DS). After four months, EE-GRSP-treated seedlings exhibited significantly higher plant growth (plant height, leaf number and fresh weight) and root growth-related parameters (lateral root numbers and root morphology) than non-EE-GRSP-treated seedlings under both WW and DS conditions. Exogenous EE-GRSP generally significantly increased leaf water potential, net photosynthesis rate, transpiration rate, stomatal conductance and intercellular CO2 concentration, while dramatically decreased leaf temperature, regardless of soil water status. The seedlings treated with exogenous EE-GRSP observed significantly higher activities of leaf Fe-SOD and root Mn-SOD, Cu/Zn-SOD, and Fe-SOD than untreated control under DS. Leaf abscisic acid, indole-acetic acid and methyl jasmonate concentrations were significantly higher in EE-GRSP-treated seedlings than untreated control under DS. This work firstly reported that exogenous application of EE-GRSP improved drought tolerance of trifoliate orange, thereby, offering a strong possibility in favour of EE-GRSP to be used as a plant growth regulator.

Distribution of soil organic carbon and glomalin related soil protein in reclaimed coal mine-land chronosequence under tropical condition

The revegetation on mine spoiled lands has potential to improve the status of reclaimed mine-soil quality. However, to date the temporal dynamics of labile and stable fractions of soil organic carbon (SOC) and glomalin related soil protein (GRSP) have not been satisfactorily demonstrated. We investigated SOC and GRSP fractions including labile particulate OC (POC) and easily extractable GRSP (EE-GRSP) and stable non-particulate OC (NPOC) and difficulty extractable GRSP (DE-GRSP) along with other important soil properties in six reclaimed mine lands chronosequence (1 to 26 years old) and a reference forest site in Raniganj Coalfield, India. Our results demonstrated that the accumulation of SOC and GRSP significantly increased with increasing age of the sites, with greater extent of increment after 26 years were seen in labile POC (6.6×) and EE-GRSP (11.5×) compared to stable NPOC (1.8×) and DE-GRSP (6.2×). The higher contribution of GRSP-C in NPOC compared to TOC across the sites, indicate the proximate role of GRSP in accumulation and stabilization of SOC during the pedogenesis. The multivariate analysis revealed strong association among arbuscular mycorrhizal fungi (AMF) spore density, microbial biomass carbon, SOCs and GRSPs, suggesting the factors involved in SOC accumulation likely contributed to AMF proliferation and GRSP enrichment during the reclamation process. Moreover, strong correlation of GRSP and SOC with soil's bulk density, pH, total N and C/N ratio, suggest increasing GRSP and SOC content resulted in multi-level improvement in soil properties. Our results highlight the importance of using GRSP and SOC as indicator during mine land reclamation.

Glomalin contributed more to carbon, nutrients in deeper soils, and differently associated with climates and soil properties in vertical profiles

Despite vital importance in soil conditioning and a proxy for arbuscular mycorrhizal (AMF), glomalin-related soil protein (GRSP) contribution to soil carbon and nutrients at vertical soil profiles and underlying mechanism were not well-defined yet. Thus, 360 soil samples were collected from 72 farmland 1-m soil profiles in northeastern China, and soil physiochemical properties, nutrients, glomalin characteristics, local climates were determined. Linear decreases of glomalin amounts were observed from the top to deep soils, and glomalin/SOC (glomalin ratio to total SOC) in the 80–100 cm soil (EEG, easily-extracted GRSP, 2.2%; TG, total GRSP, 19%) was 1.34–1.5-fold higher than did in the 0–20 cm soil. Different statistical analyses crosschecked that the lower pH and higher SOC usually accompanied with the higher EEG and TG, while EEG was more sensitive to climates; Moreover, glomalin was more physiochemical-regulated in the deep soils, but more nutrient-regulation was found in the surface soils. Structure Equation Model showed that soil depths and climates indirectly affected TG and EEG features through soil properties, except significant direct effects on EEG. In future, glomalin assessment should fully consider these for identifying the AMF importance in the whole 1-m profile, and our findings also favor degrade soil improvement from glomalin rehabilitation.

Spatial distribution of glomalin-related soil protein and its relationship with sediment carbon sequestration across a mangrove forest

Arbuscular mycorrhizal (AM) fungi produce a recalcitrant glycoprotein, (glomalin-related soil protein (GRSP)), which can contribute to soil carbon sequestration. Here we made a first study to characterize the spatial distribution of GRSP fractions in a mangrove forest at Zhangjiang Estuary, Southeastern China and to explore potential contributions of GRSP to sediment organic carbon (SOC) in this forest. We identified GRSP fractions in surface sediments, as well as those at a depth of 50 cm. The contents of easily extractable GRSP (EE-GRSP), total GRSP (T-GRSP), GRSP in particulate organic matter (POM-GRSP) and GRSP in pore water (PW-GRSP) ranged between 1.20–2.22mgg−1, 1.38–2.61mgg−1, 1.45–10.78mgg−1 and 10.35–39.65mgL−1 respectively, and these four GRSPs are significantly affected by sample sites and sediment layers. Carbon in GRSP accounted for 2.8–5.9% of SOC and its contributions can far exceed that of microbial biomass carbon (0.21–0.73%) in the 0–50cm sediment layers. Our data indicate that GRSP could be transported by pore water and accumulated in sediment profiles. The non-linear regression analysis revealed that as SOC and particulate organic carbon (POC) contents decrease, GRSP proportions increase, indicating the increase of the recalcitrant carbon offsetting the effects of mangrove carbon loss, especially labile C. Regression and ordination analyses indicated that GRSP fractions were mainly positively correlated with sediment carbon fractions and spore density but were negatively correlated with sand, pH. Strikingly, the unfavorable environmental factors for microbial organisms, especially AM fungi, prove to be able to promote the production or accumulation of GRSP. We propose that there are two different pathways for affecting the pool size of GRSP in mangrove ecosystems: (i) directly via indigenous AM fungi propagules; (ii) or via the GRSP transport and deposition by pore water and tides.

Bamboo forest expansion increases soil organic carbon through its effect on soil arbuscular mycorrhizal fungal community and abundance

Moso bamboo (Phyllostachys pubescens) is a fast-growing species that can invade neighboring forests through its vigorous rhizome system, leading to large shifts of plant diversity and soil properties. A primary concern is the response of arbuscular mycorrhizal fungal (AMF) communities and related soil C sequestration to bamboo forest expansion. We used a long-term soil chronosequence from primary broadleaved forest to moso bamboo forest to examine the changes in AMF abundance and communities, as well as their role in soil C storage. AMF communities showed strong niche differentiation, and were highly structured by forest type (r 2 = 0.648, P = 0.001), and marginally correlated to soil pH and organic C. Bamboo forest expansion increased soil AMF biomass as indicated by neutral lipid fatty acids (NLFA) 16:1ω5 abundance, easily extracted glomalin-related soil protein (EE-GRSP), and water-stable macroaggregates. We observed that soil AMF biomass contributed substantially to both soil macroaggregates and EE-GRSP, which were tightly correlated with soil organic C. The influence of bamboo forest expansion on soil C sequestration was mainly due to its indirect effect on AMF biomass. Bamboo forest expansion significantly changed soil AMF communities and increased AMF biomass, which in turn contributed to enhanced soil aggregation and C storage.

Effects of soil salinity on the content, composition, and ion binding capacity of glomalin-related soil protein (GRSP).

Soil aggregation, an ecosystem function correlated with the concentration of glomalin-related soil protein (GRSP), is highly disturbed in saline soil. However, few studies have focused on differences in amount, composition, and ion binding capacity of GRSP in typical sodic-saline soils. In this study, a field study was performed in Songnen Plain. Combined indicators of soil salinity (Q value) were significant negatively correlated with GRSP concentration by Principal Component Analysis. Multiple linear regression models showed that soil salinity might account for 46%, 25% and 44% variation in total GRSP (T-GRSP), easily-extractable GRSP (EE-GRSP) and difficultly-extractable GRSP (DE-GRSP), respectively. Soil bulk density had most important impact on GRSP concentration, followed by the pH, soil EC had the weak influence. Comparative analysis was carried out between low-salinity and high-salinity soil. Purified T-GRSP of high-saline soil contained higher N content (13.13%), lower C content (43.41%) and lower functional groups relative content (e.g. CO and SiOSi). Purified T-GRSP of high-salinity soil had a greater binding capacity with calcium and phosphorus, the binding capacity could compensate the GRSP loss about 29.8% and 14.1%, respectively. Our findings suggested that sodic salinization of the soil led to a decrease in GRSP concentration and a change in the component percentages. This change in composition might be related to adaptation of fungi-plant systems to varied environments. The calcium and phosphorus binding capacity had a positive dependent of soil salinization, which was possible to develop ecological management or recovery technology in the future.

落叶松、水曲柳、樟子松和农田土壤指标差异及其综合比较

PDF HTML阅读 XML下载 导出引用 引用提醒 落叶松、水曲柳、樟子松和农田土壤指标差异及其综合比较 DOI: 10.5846/stxb201603080412 作者: 作者单位: 东北林业大学，森林植物生态学教育部重点实验室,东北林业大学，森林植物生态学教育部重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家"十三五"重点研发项目（2016YFA0600802）；黑龙江省杰出青年基金（JC201401）；中央高校创新团队与重大项目培育资金项目（2572014EA01）；国家自然基金资助项目（41373075） Larch, ash, Scots pine, and farmland-induced differences on 17 soil parameters and their comprehensive analyses Author: Affiliation: Key Laboratory of Forest Plant Ecology Ministry of Education, Northeast Forestry University,Key Laboratory of Forest Plant Ecology Ministry of Education, Northeast Forestry University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:东北地区以大森林和大农业为主要特色，主要造林树种落叶松、水曲柳、樟子松及农田对土壤肥力、物理指标、盐碱度、碳截获等的影响差异是本文研究目的。选择秀水林场和帽儿山林场的4种植被类型进行0-60cm分层土壤采样，对根系密度、土壤pH、电导率、全氮、全磷、全钾、碱解氮、速效磷、速效钾、土壤真菌代谢产物（球囊霉素相关蛋白易提取球囊霉素EEG、总提取球囊霉素TG）、容重、比重、孔隙度、比表面积、SOC、有机碳矿化速率等17个指标进行研究。主要结论如下：植被类型间的差异在不同土层之间表现一致的指标所占比例很大，其中秀水林场13个指标，帽儿山林场全部17个指标。尽管不同地点间土壤差异较大，但也存在树种差异一致性。土壤物理性质（容重、比重、孔隙度、比表面积）维持方面，两个林场均显示水曲柳综合得分最高，说明其具有更好的土壤物理性质维持能力，且多通过土壤容重下降来实现。土壤固碳能力得分最高的也是水曲柳，并且两个研究地点结果类似，主要与其高根系密度有关。综合土壤肥力维持能力（N、P、K及其有效态及真菌代谢产物球囊霉素相关蛋白），不同地点间植被类型差异排序不同。降低土壤盐碱能力（pH和电导率）方面，樟子松得分最高，尽管不同地点不尽一致。不同植被类型对土壤影响尽管不同地点、不同土壤深度多不相同，但总体上存在规律性，特别是土壤物理性质维持和土壤固碳能力方面。进行造林绿化时应该根据造林目的进行树种选择，提升土壤物理性质应该考虑种植更能够维持良好土壤物理性质的树种（如水曲柳、樟子松等），而提升土壤碳截获则要考虑根系密度大的树种（如水曲柳）。相关研究结果对国家重大生态工程（三北防护林、退耕还林）工程生态功能评价以及后续管理、树种选择具有支撑作用。 Abstract:The main characteristics of Northeast China are large forests and agriculture. The effect of the primary afforestation species (larch: Larix gmelinii, ash: Fraxinus mandschurica, Scots pine: Pinus sylvestris var. mongolica) and farmland on soil fertility, physical properties, salinity, and carbon sequestration were analyzed. In the present study, four vegetation types were selected from Xiushui Forest and Maoershan Forest Farms, and samples from 0–60 cm soils were collected for measuring 17 parameters, including root density, soil pH, electrical conductance(EC), alkali-hydrolyzed nitrogen(AN), total nitrogen(TN), available phosphorus(AP), total phosphorus(TP), available potassium(AK), total potassium(TK), glomalin related soil protein (GRSP) (including easily extracted GRSP (EEG) and total GRSP (TG)), soil bulk density, soil specific gravity, soil porosity, soil specific surface area, soil organic carbon(SOC), and organic carbon mineralization rate. The main conclusions were as follows: inter-species differences between most of the measured indicators were consistent in different soil layers, including 13 indicators in the Xiushui Forest Farm and all 17 indicators in the Maoershan Forest Farm samples. Although there were considerable differences in soil between different locations, the inter-species differences were consistent. Through comprehensive analyses, standardized comprehensive scores of two forest farm-related indicators showed that ash had the highest scores regarding its ability to maintain the physical properties of soil. Therefore, ash had the greatest ability of all the trees and farmland to maintain the physical properties of soil, and depended primarily on decreased soil bulk density. Ash also showed the highest scores for soil carbon sequestration, with similar results at both locations, mainly related to its higher root density. The comprehensive soil fertility (N, P, K, and its effective state, and fungal metabolic product GRSP) indicated inter-species differences between the different locations. Scots pine had the highest scores for reducing the soil salinity (pH and EC). The effects of different vegetation types on the soil were not the same in different locations and soil depths, but there was a general regularity, especially regarding the soil physical properties and carbon sequestration. Therefore, the selection of tree species for afforestation should be planned depending on the particular purpose of afforestation. To improve the physical properties of soil, plant species with the ability to maintain the physical properties effectively (e.g.,ash, Scots pine) should be considered; and to enhance soil carbon sequestration, plant species with large root densities (e.g., ash) should be considered. The findings in this paper will enhance the evaluation of the national ecological projects of the Three-North Shelterbelt Project and Returning Farmland to Forest Project, and forest management including tree species selections. 参考文献 相似文献 引证文献

EDAPHIC ATTRIBUTES OF A CROP-LIVESTOCK INTEGRATION SYSTEM IN THE CERRADO BIOME

ABSTRACT A significant increase in the use of integrated farming systems have been observed in the Brazilian Cerrado, such as crop-livestock integration (CLI), which combined with the no-tillage system (NTS) have shown significant influence on soil properties. Therefore, the objective of this work was to evaluate the influence of a CLI system on the chemical, physical and microbiological soil characteristics, in an area in the Cerrado biome, Montividiu, State of Goias, Brazil. The soil fertility, remaining phosphorus (Prem), total organic carbon (TOC), total nitrogen (Nt), aggregate stability (geometric mean diameter - GMD), microbial respiration (C-CO2) and easily-extractable glomalin-related soil protein (EE-GRSP) were evaluated. Soil samples were collected at depth of 0-5 and 5-10 cm in three areas with: CLI (13 years of annual rotation with Urochloa ruziziensis); Urochloa decumbens pasture (15 years of implementation); and native Cerrado vegetation. The CLI area had higher pH, Mg, P available (0-10 cm) and Prem (5-10 cm) values compared to the other areas, and equal values of TOC, Nt, EE-GRSP (0-10 cm) and aggregate stability (5-10 cm) compared to the pasture area. The CLI had no differences in C-CO2 emissions compared to the Cerrado, but had lower rates compared to the pasture. The P available and Prem were sensitive indicators to show the differences between the CLI and pasture systems, with higher contents in the CLI area. The TOC and Nt indicators had no differences between these two systems. The GMD results indicated a better aggregation in the pasture (0-5 cm) compared to the CLI area, while the EE-GRSP were similar in these areas. The total values of C-CO2 emission from the soil aggregates showed the stability of respirometry rates in the CLI and Cerrado areas.

Arbuscular mycorrhizas improve plant growth and soil structure in trifoliate orange under salt stress

ABSTRACTArbuscular mycorrhizal fungi (AMF) as a biostimulant enhance salt tolerance in plants, while the informations regarding AMF-induced changes in soil structure are only available to a limited degree. In this study, trifoliate orange (Poncirus trifoliata) seedlings were inoculated with Diversispora versiformis under 100 mM NaCl for 85 days. The salt stress considerably inhibited mycorrhizal colonization by 26%, compared with non-salt stress. Mycorrhizal inoculation significantly increased plant height, stem diameter, leaf number, shoot biomass, and root biomass, length, surface area, and volume in comparison to non-mycorrhizal inoculation under salt stress or non-salt stress. Mycorrhization induced significantly higher production of easily extractable glomalin-related soil protein (EE-GRSP), and total glomalin-related soil protein (T-GRSP), higher percentage of water-stable aggregates (WSAs) in 0.25–0.50, 0.50–1.00, and 1.00–2.00 mm size, and lower in 2.00–4.00 mm size, regardless of non-salt stress or salt stress. Mycorrhizal soils represented higher aggregate stability (in terms of mean weight diameter) under salt and non-salt stress, which was related with root colonization, root surface area, root volume, EE-GRSP, and T-GRSP. The better soil structure by mycorrhization provided higher leaf water potential under salt stress. It suggests that mycorrhizas had a positive contribution to improve plant growth and soil structure, thereby enhancing salt tolerance.

Elevated CO2 increases glomalin-related soil protein (GRSP) in the rhizosphere of Robinia pseudoacacia L. seedlings in Pb- and Cd-contaminated soils

Glomalin-related soil protein (GRSP), which contains glycoproteins produced by arbuscular mycorrhizal fungi (AMF), as well as non-mycorrhizal-related heat-stable proteins, lipids, and humic materials, is generally categorized into two fractions: easily extractable GRSP (EE-GRSP) and total GRSP (T-GRSP). GRSP plays an important role in soil carbon (C) sequestration and can stabilize heavy metals such as lead (Pb), cadmium (Cd), and manganese (Mn). Soil contamination by heavy metals is occurring in conjunction with rising atmospheric CO2 in natural ecosystems due to human activities. However, the response of GRSP to elevated CO2 combined with heavy metal contamination has not been widely reported. Here, we investigated the response of GRSP to elevated CO2 in the rhizosphere of Robinia pseudoacacia L. seedlings in Pb- and Cd-contaminated soils. Elevated CO2 (700 μmol mol−1) significantly increased T- and EE- GRSP concentrations in soils contaminated with Cd, Pb or Cd + Pb. GRSP contributed more carbon to the rhizosphere soil organic carbon pool under elevated CO2 + heavy metals than under ambient CO2. The amount of Cd and Pb bound to GRSP was significantly higher under elevated (compared to ambient) CO2; and elevated CO2 increased the ratio of GRSP-bound Cd and Pb to total Cd and Pb. However, available Cd and Pb in rhizosphere soil under increased elevated CO2 compared to ambient CO2. The combination of both metals and elevated CO2 led to a significant increase in available Pb in rhizosphere soil compared to the Pb treatment alone. In conclusion, increased GRSP produced under elevated CO2 could contribute to sequestration of soil pollutants by adsorption of Cd and Pb.

Effect of long term land use systems on fractions of glomalin and soil organic carbon in the Indo-Gangetic plain

Long-term history of tillage and cropping mediated disturbed and undisturbed use soils effect on glomalin related soil protein (GRSP) and soil organic carbon (SOC) and on their sub fractions were investigated in Indo-Gangetic plain region. In this study, shallow soils were collected from 50-year-old monoculture treatments of undisturbed (Dendrocalamus calostachyus, Mangifera indica and Saccharum munja Roxb.) and disturbed (Oryza sativa cultivated field) land use. Our results showed that compared with undisturbed soils, soils under the disturbed use dramatically depleted in SOC, particulate OC (POC), non-particulate OC (NPOC), GRSP, easily extractable GRSP (EE-GRSP) and difficulty extractable GRSP (DE-GRSP). The depletion in labile POC was found to be little higher than physically protected NPOC, and were almost similar among the fractions of GRSP (each decreased by 50%). Further, a linear correlation was found among the fractions of GRSP and SOC, and in turn resulted in the similar relationship with soils bulk density, porosity, pH, available phosphorus, total phosphorus, organic nitrogen's, cations (calcium and potassium), arbuscular mycorrhizal (AM) abundance, and with microbial activity. These results indicate that the factors involve in SOC accumulation simultaneously encourage AM proliferation and in turn GRSP enrichment. Apart from this, the higher contribution of GRSP-C in NPOC (13 to 17%), tended to increase with decreasing soil disturbance, suggesting the role of GRSP in accumulation and stabilization of SOC in this zone. A two component factor structure showed component 1 considerably occupied by fractions of GRSP, SOC and those other variables favouring GRSP and SOC, primarily scored by undisturbed (M. indica and D. calostachyus treatments) soils. The second component which has fewer influence over soil variables, considerably occupied by microbial activity, electrical conductivity, cations and nutrients (available nitrogen, phosphorus) was also exemplified by undisturbed soils (except D. calostachyus treatment). Thus, improving GRSP and SOC stock in disturbed agricultural soil in studied area is of urgent requirement for the long-term goal of C sequestration and sustainable soil health. Our finding should stimulate management plans for degraded lands aimed at recovering the landscape heterogeneity.

Restoration techniques affect soil organic carbon, glomalin and aggregate stability in degraded soils of a semiarid Mediterranean region

The first step to restoring degraded mine soils from calcareous quarries in semiarid environments, usually without soil structure, mainly consists in creating a structured topsoil with suitable physical, chemical and biological properties. The aim of this study is to determine the effects of organic amendments and mulches on soil aggregate stability and aggregation-associated soil characteristics, six years after beginning experimental restoration in the Gádor Mountains (Almería, SE Spain). Experimental plots were set up to test two organic amendments (sludge and compost) and two mulches (gravel and woodchip) and their respective control plots. Soil samples from neighboring undisturbed soils were used as the quality reference threshold. The tested variables were total organic C (TOC), glomalin-related soil protein (GRSP), easily extractable glomalin-related soil protein (EE-GRSP) and water aggregate stability evaluated by both wet sieving (WS) and water-drop test (WDT). Relationships among the measured soil properties were checked in order to assess the best indicators for the most suited restoration practices. After 6years, the results showed that the combination of organic amendments and mulches enhanced soil aggregate stability and the content of aggregate binding agents such as TOC and glomalin. Nevertheless, the role of organic amendments, especially compost, was more important than mulch treatments in increasing TOC and glomalin, showing the closest values to the undisturbed reference soils (over 30gkg−1 for TOC and 3.5gkg−1 for GRSP). Despite the considerable improvement in water stable aggregates found in sludge-amended plots (average mean weight diameter of 2.13mm in WS, and 25-drop impacts in WDT), the reference soils provided the highest values (average mean weight diameter of 3.32mm in WS, and 99-drop impacts in WDT). The lack of a good correlation between soil structure-related variables restricted the evaluation of the real effects of restoration treatments, and suggested considering other soil properties (e.g., hydrophobicity, hardening) associated to aggregate stability.

Mycorrhizal hyphal disruption induces changes in plant growth, glomalin-related soil protein and soil aggregation of trifoliate orange in a core system

By breaking up soil, tillage often disrupts mycorrhizal extraradical mycelium (ERM). In a core having four windows covered with 37-μm mesh in a perspex box, trifoliate orange (Poncirus trifoliata) seedlings were colonized with an arbuscular mycorrhizal (AM) fungus, Funneliformis mosseae. The core was rotated weekly at 180° around vertical axes, in order to simulate ERM disruption. After 13 such rotations, root mycorrhizal colonization, soil hyphal length inside and outside the core, and plant biomass were substantially reduced. On the other hand, mycorrhizal inoculation without disruption of ERM (static core) was associated with significant increase in biomass production, compared with disruption of ERM (rotating core). Disruption of ERM (rotating core) inhibited the production of easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP) inside the core under mycorrhization, due to breakdown of ERM. Mycorrhization markedly increased soil organic carbon content, distribution of water-stable aggregate (WSA) at 0.5–4mm size and mean weight diameter (MWD), whereas core rotation showed a negative effect on MWD and the percentage of WSA within 1–4mm size under mycorrhization and within 0.25–2mm size under non-mycorrhization. It was proposed that soil tillage, in terms of the core rotation, strongly disrupted ERM network, which adversely influenced EE-GRSP and T-GRSP production and plant growth under mycorrhization, subsequently weakening the GRSP functioning on WSA stability.

Arbuscular mycorrhizal fungal activity responses to winter cover crops in a sunflower and maize cropping system

The symbiosis between plants and arbuscular mycorrhizal fungi (AMF) benefits the health, nutrition and abiotic stress tolerance of the host plant. The maintenance of potential AMF inoculum in the winter is important because it will affect the colonization process in the subsequent crop. The objective of this study was to evaluate the effect of winter cover crops (CC) on AMF parameters (root colonization, length of hyphae and number of AMF spores), other variables indirectly related to AMF (the easily extractable glomalin-related soil protein (EE-GRSP) and the enzymatic activity of β-glucosaminidase), along with water-stable aggregates (WSA) as a soil quality indicator. In addition, the effect of two sampling dates on the variables in maize and the relationships among all of the variables were studied. The samples were obtained from a field experiment established in 2006 located in Aranjuez (Central Spain) under a Mediterranean semiarid climate. The treatments were winter cover crops of barley (Hordeum vulgare L.) or vetch (Vicia villosa L.) and fallow as a control. The study covered two seasons in 2011–12 and 2012–13 with sunflower (Helianthus annuus L.) and maize (Zea mays L.) as the main crop, respectively, with both sown in the spring. The main crops were irrigated according to the crop demand. Compared with the bare fallow conditions, cover crops improved most of the variables, maintaining the benefits of CC on AMF under the semiarid conditions of the Mediterranean climate. Barley as a cover crop gave the best results, whereas the performance of vetch was poorer. In sunflower, barley increased by 80% the hyphae length and β-glucosaminidase activity and by 30% other variables compared with the fallow; whereas in maize, 60–70% increments were found in AMF spores and the hyphae length and 2-fold in the enzyme activity. The sampling date affected all of the variables analyzed in the maize crop, except for the EE-GRSP and the WSA. Positive relationships were found between the variables directly related to AMF, EE-GRSP content and β-glucosaminidase activity. This suggests that the variables indirectly related to AMF, mainly the EE-GRSP, could be used as indicators of AMF. Finally, the enhancement of soil aggregate stability by the CC via AMF promotion was corroborated.

Effects of Common Mycorrhizal Network on Plant Carbohydrates and Soil Properties in Trifoliate Orange-White Clover Association.

Common mycorrhizal network (CMN) allows nutrients and signals to pass between two or more plants. In this study, trifoliate orange (Poncirus trifoliata) and white clover (Trifolium repens) were planted in a two-compartmented rootbox, separated by a 37–μm nylon mesh and then inoculated with an arbuscular mycorrhizal fungus (AMF), Diversispora spurca. Inoculation with D. spurca resulted in formation of a CMN between trifoliate orange and white clover, whilst the best AM colonization occurred in the donor trifoliate orange–receptor white clover association. In the trifoliate orange–white clover association, the mycorrhizal colonization of receptor plant by extraradical hyphae originated from the donor plant significantly increased shoot and root fresh weight and chlorophyll concentration of the receptor plant. Enzymatic activity of soil β-glucoside hydrolase, protease, acid and neutral phosphatase, water-stable aggregate percentage at 2–4 and 0.5–1 mm size, and mean weight diameter in the rhizosphere of the receptor plant also increased. The hyphae of CMN released more easily-extractable glomalin-related soil protein and total glomalin-related soil protein into the receptor rhizosphere, which represented a significantly positive correlation with aggregate stability. AMF inoculation exhibited diverse changes in leaf and root sucrose concentration in the donor plant, and AM colonization by CMN conferred a significant increase of root glucose in the receptor plant. These results suggested that CMN formed in the trifoliate orange–white clover association, and root AM colonization by CMN promoted plant growth, root glucose accumulation, and rhizospheric soil properties in the receptor plant.

Exogenous application of EE-GRSP and changes in citrus rhizosphere properties

Mycorrhization-induced secretion of glomalin-related soil protein (GRSP) is known to contribute in improving soil fertility and aggregate stability. But, there is hardly any evidence that exogenous GRSP could produce the similar type of response. The present study was, therefore, carried out to extract easily extractable GRSP (EE-GRSP) from citrus rhizosphere soils and evaluate the response at 1/4, 1/2 and full strength EE-GRSP solutions watered into the rhizosphere of 27-year-old Satsuma mandarin (Citrus unshiu) grafted on the rootstock of Poncirus trifoliata. After ~5 months, exogenous EE-GRSP treatments produced significantly positive responses on endogenous EE-GRSP, difficultly-extractable GRSP (DE-GRSP), total GRSP production and soil organic carbon (SOC) content. A significantly positive correlation of these endogenous GRSP fractions with SOC indicated an active participation of GRSP on soil C pool. Exogenous GRSP showed a key role in binding water-stable aggregate (WSA) at 2–4, 1–2, 0.5–1, and 0.25– 0.5 mm size and enhancing WSA stability through changes in mean weight diameter (MWD). A stronger correlation of EE-GRSP and total GRSP with MWD was observed than DE-GRSP fraction. On the other hand, exogenous EEGRSP showed a positive effect on soil phosphatase activity, and soil endogenous EE-GRSP was significantly and positively correlated only with neutral phosphatase. Our studies suggest that exogenous EE-GRSP could be used as an effective regulator to affect soil fertility and soil structure within citrus rhizosphere.

Disruption of mycorrhizal extraradical mycelium and changes in leaf water status and soil aggregate stability in rootbox-grown trifoliate orange.

Arbuscular mycorrhizas possess well developed extraradical mycelium (ERM) network that enlarge the surrounding soil for better acquisition of water and nutrients, besides soil aggregation. Distinction in ERM functioning was studied under a rootbox system, which consisted of root+hyphae and root-free hyphae compartments separated by 37-μm nylon mesh with an air gap. Trifoliate orange (Poncirus trifoliata) seedlings were inoculated with Funneliformis mosseae in root+hyphae compartment, and the ERM network was established between the two compartments. The ERM network of air gap was disrupted before 8 h of the harvest (one time disruption) or multiple disruptions during seedlings acclimation. Our results showed that mycorrhizal inoculation induced a significant increase in growth (plant height, stem diameter, and leaf, stem, and root biomass) and physiological characters (leaf relative water content, leaf water potential, and transpiration rate), irrespective of ERM status. Easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP) concentration and mean weight diameter (MWD, an indicator of soil aggregate stability) were significantly higher in mycorrhizosphere of root+hyphae and root-free hyphae compartments than non-mycorrhizosphere. One time disruption of ERM network did not influence plant growth and soil properties but only notably decreased leaf water. Periodical disruption of ERM network at weekly interval markedly inhibited the mycorrhizal roles on plant growth, leaf water, GRSP production, and MWD in root+hyphae and hyphae chambers. EE-GRSP was the most responsive GRSP fraction to changes in leaf water and MWD under root+hyphae and hyphae conditions. It suggests that effect of peridical disruption of ERM network was more impactful than one-time disruption of ERM network with regard to leaf water, plant growth, and aggregate stability responses, thereby, implying ERM network aided in developing the host plant metabolically more active.

Glomalin-related soil protein responses to elevated CO2 and nitrogen addition in a subtropical forest: Potential consequences for soil carbon accumulation

According to the economy theory, plants should preferentially allocate photosynthate to acquire below-ground resources under elevated atmospheric carbon dioxide (eCO2) but decrease below-ground C allocation when nitrogen (N) is sufficient for plant growth. Arbuscular mycorrhizae (AM) represent a critical mechanism of below-ground nutrient acquisition for plants. The dynamics of arbuscular mycorrhizal fungi (AMF) could therefore reflect the response of plant C allocation under eCO2 and N addition. We examined the responses of glomalin-related soil protein (GRSP) to eCO2 (approximately 700 μmol mol−1 CO2) and/or N addition (100 kg Nha−1 yr−1 as NH4NO3) in a modeled subtropical forest to better understand its potential influence on soil C storage. We hypothesized that GRSP would increase under eCO2 and decrease under N addition. Furthermore, the positive effects of eCO2 on GRSP would be offset by extra N addition, and GRSP would remain unchanged under combined eCO2 and N addition. Our results showed that the mean concentrations of easily extractable GRSP (EE-GRSP) and total GRSP (T-GRSP) were 0.35 ± 0.05 and 0.72 ± 0.13 mg C cm−3, respectively, which accounted for 2.76 ± 0.53% and 5.67 ± 0.92% of soil organic carbon (SOC) in the 0–10 cm soil layer. Elevated CO2 significantly increased T-GRSP by 35.02% but decreased EE-GRSP by 5.09% in the top 10 cm soil layer. The opposite responses of T-GRSP and EE-GRSP to eCO2 might result from an unchanged photosynthate investment to AMF with possible changes in their decomposition rates. The effect of N on GRSP was contrary to our hypothesis, i.e., there was a 1.72%–48.49% increase in T-GRSP and a slightly increase in EE-GRSP. Both EE-GRSP and T-GRSP concentrations increased under the combination of eCO2 and N addition, which was inconsistent with our hypothesis. The significant increase of EE-GRSP under the combination of eCO2 and N addition was partly caused by more rapid plant growth and reduced microbial diversity, and the marginal increase of T-GRSP indicated that the interaction between eCO2 and N addition offset their independent effects. In addition, the relatively higher accumulation ratios of GRSP (22.6 ± 13.6%) compared with SOC (15.9 ± 9.4%) indicated that more rapid GRSP deposition in the soil might accelerate SOC accumulation under eCO2 and N addition. Our results will improve the understanding of the functioning of GRSP in soil C sequestration under global environmental change scenarios.

Calcium and Calmodulin Involve in Mycorrhizal and Root Development in Trifoliate Orange Colonized by <i>Rhizophagus intraradices</i>

A pot experiment was made to study effects of ethylene glycol tetraacetic acid (EGTA, an inhibitor of Ca2+) and trifluoperazine (TFP, an inhibitor of calmodulin (CaM) on mycorrhizal colonization, growth performance, and chlorophyll, sucrose and glucose concentrations of four-month-old trifoliate orange (Poncirus trifoliata) seedlings under mycorrhization with Rhizophagus intraradices. Exogenous EGTA and TFP notably inhibited root mycorrhizal colonization, and the addition of EGTA also decreased soil hyphal length. In general, EGTA treatment decreased but TFP increased easily extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP) concentrations. In addition, EGTA and TFP applications generally significantly inhibited growth performance (height, stem diameter, leaf number, and shoot and root biomass), root traits (total length, surface area, volume, and number of 1st, 2nd and 3rd order lateral root), and chlorophyll a,b and a+b concentrations, the mycorrhizal inoculation generally reversed the negative effects and markedly increased these variables, irrespective of whether the seedlings were applied by inhibitors or not. EGTA and TFP treatments generally inhibited sucrose and glucose levels of leaf and root, except that TFP application notably increased root glucose in AM and non-AM seedlings. AMF inoculation resulted in carbohydrate modification: decrease in leaf sucrose, increase in root sucrose and leaf glucose, as well increase in root glucose under no-inhibitor and EGTA conditions and decrease in root glucose under TFP. It suggests that Ca2+ and CaM were involved in mycorrhizal and root development in trifoliate orange.