Bradford-reactive Soil Protein Research Articles

AM fungal diversity and its impact across three types of mid-temperate steppe in Inner Mongolia, China.

Arbuscular mycorrhizal (AM) fungal diversity was measured in three different natural mid-temperate steppe types: the meadow steppe, typical steppe, and desert steppe. In these steppe soils, 24 AM fungal species from eight genera were identified, in which Glomus had the highest relative abundance. Funneliformis geosporus, Glomus microaggregatum, and Septoglomus constrictum had high relative abundance and were found widely across varying soil depth and steppe type. Meadow steppes had significantly higher AM fungal species richness compared to typical steppes and desert steppes, but there was no significant difference between typical steppes and desert steppes. AM fungal spore density, two Bradford-reactive soil protein (BRSP) fractions, and extraradical hyphal length densities (HLDs) were significantly different among the three steppe types. Alkaline phosphatase and acid phosphatase activity, urease activity, and soil bacterial and actinomycotic quantity were significantly related to the AM fungal spore density and species richness in these arid and semi-arid steppes. Therefore, steppe types could influence the distribution pattern of AM fungal diversity and the content of glomalin-related soil protein (GRSP).

Temporal and spatial variation of arbuscular mycorrhizal fungi under the canopy of Hedysarum scoparium in the northern desert, China

Despite the evident importance of arbuscular mycorrhizal fungi (AMF) associated with the root system of plants inhabiting desert regions, limit is known about the distribution and activity of AMF in desert ecosystems. Accordingly, AMF diversity, community composition and glomalin were investigated in the northern desert of China. Soil samples from 0 to 30 cm in depth over seven plots were collected under the canopy of Hedysarum scoparium in July of 2015 and 2016. A total of 51 molecular operational taxonomic units (OTUs) were identified by MiSeq sequencing based on small subunit (SSU) ribosomal RNA genes, and Diversispora celata and Diversispora trimurales were discovered for the first time in a desert ecosystem in China. The abundant genera included Glomus (56.4%), Diversispora (25.1%), Claroideoglomus (6.0%), Funneliformis (6.1%) and Paraglomus (5.5%). Archaeospora and Scutellospora sequences represented <1.0% of total sequences. AMF community composition and diversity and two Bradford-reactive soil protein (BRSP) assays were significantly different among the seven studied plots and sampling times. Moreover, AMF diversity and richness tended to increase first and then decrease as the precipitation decreased in the barren sandy grey desert and aeolian sandy soil. Correlation coefficient analysis demonstrated that the Shannon-Wiener index was significantly and positively correlated with acid phosphatase (P < 0.05) and precipitation (P < 0.01) and was significantly and negatively correlated with soil pH (P < 0.01). The richness of AMF was significantly and positively correlated with precipitation (P < 0.01) and negatively correlated with soil organic carbon (SOC) (P < 0.05) and soil pH (P < 0.01). The BRSP fractions were also significantly and positively correlated with edaphic factors (e.g., soil moisture, soil organic carbon) and soil enzymes (e.g., soil acid and alkaline phosphatase). The means of total BRSP and easily extractable BRSP were 5.86 mg·g−1 and 1.90 mg·g−1, respectively. The levels of BRSP in the desert soil were slightly lower than those in native and arable soils, but the ratios of BRSP to SOC were much higher than in farmland soils. Our findings provide insights into important factors affecting the native AMF community and glomalin in the northern desert of China and suggest that AMF diversity and glomalin might be useful for monitoring desertification and soil degradation.

Contribution of inoculation with arbuscular mycorrhizal fungi to the bioremediation of a copper polluted soil using Oenothera picensis

The Bradford-reactive soil protein (BRSP) fraction includes glomalin, a glycoprotein produced by arbuscular mycorrhizal (AM) fungi that is able to bind some metals, such as copper (Cu), which could promote the bioremediation of Cu-polluted soils. This study aimed to analyze the Cu-binding capacity of BRSP in Oenothera picensis that was inoculated or not inoculated with AM fungi. O. picensis plants were established in a Cu contaminated sterilized soil and treated with the following: i) uninoculated (-M); ii) inoculated with native AM fungal propagules (+M); or iii) inoculated with a Claroideoglomus claroideum (CC) strain isolated from non-contaminated soil. In each case, five Cu levels were applied to the soil (basal level 497.3 mg Cu kg-1): 0 (T1); 75 (T2); 150 (T3); 225 (T4); and 300 mg Cu kg-1 (T5). A high BRSP accumulation in AM inoculated treatments, especially with CC, was observed. A higher Cu-bound-to-BRSP content was found with increasing Cu concentrations, representing up to 20-22% of the total Cu in the soil. Moreover, a higher root Cu concentration in +M was observed. These results suggest a high Cu binding capacity by BRSP, which is a relevant aspect to consider in the design of bioremediation programs together with the selection of endemic metallophytes and AM fungal strains, which are able to produce glomalin at high quantities.

Spatio-temporal dynamics of arbuscular mycorrhizal fungi associated with glomalin-related soil protein and soil enzymes in different managed semiarid steppes

Temporal and spatial patterns of arbuscular mycorrhizal fungi (AMF) and glomalin and soil enzyme activities were investigated in different managed semiarid steppes located in Inner Mongolia, North China. Soils were sampled in a depth up to 30cm from non-grazed, overgrazed, and naturally restored steppes from June to September. Roots of Leymus chinense (Trin.) Tzvel. and Stipagrandis P. Smirn. were also collected over the same period. Results showed that overgrazing significantly decreased the total mycorrhizal colonization of S. grandis; total colonization of L. chinensis roots was not significantly different in the three managed steppes. Nineteen AMF species belonging to six genera were isolated. Funneliformis and Glomus were dominant genera in all three steppes. Spore density and species richness were mainly influenced by an interaction between plant growth stage and management system (P < 0.001). Spore densities were higher in 0-10-cm soil depth. AMF species richness was significantly positively correlated with soil acid phosphatase activity, alkaline phosphatase activity, and two Bradford-reactive soil protein (BRSP) fractions (P < 0.01). It is concluded that the dynamics of AMF have highly temporal and spatial patterns that are related to soil glomalin and phosphatase activity in different managed semiarid steppes. Based on these observations, AMF communities could be useful indicators for evaluating soil quality and function of semiarid grassland ecosystems.

The effect of mycorrhizal inoculation on the rhizosphere properties of trifoliate orange (Poncirus trifoliata L. Raf.)

Key rhizosphere properties influenced by microorganism-mediated processes need to be identified for better understanding of their possible role in improving crop performance. This study monitored the changes in concentration of Bradford-reactive soil protein (BRSP), soil organic carbon (SOC) content, hyphal length, aggregate stability [fractal dimension (D), geometric mean diameter (GMD), and mean weight diameter (MWD)] and distribution of water-stable aggregate (WSA) in rhizosphere of trifoliate orange (Poncirus trifoliata L. Raf.) infected by five arbuscular mycorrhizal fungal species (Diversispora spurca, Glomus intraradices, Glomus mosseae, Glomus versiforme, and Paraglomus occultum). After four months of mycorrhizal inoculation, all the mycorrhizal plants showed higher shoot and root biomass but the increase was a function of the tested fungal species. The induced changes in rhizosphere properties were of much higher magnitude in mycorrhizal treatment than in non-mycorrhizal treatment. Mycorrhizal inoculation induced significant increases in the percentage of WSA at 1.00–2.00mm size, fraction 1 of BRSP, SOC, and hyphal density, collectively aiding in improving the indices of soil aggregate stability, like GMD and MWD. Higher MWD and GMD conferred better soil structure in mycorrhizosphere of trifoliate orange. Correlation analysis further revealed that fraction 1 of BRSP as a new and more active glomalin may take part in stabilizing WSA but fraction 2 of BRSP as an older and more stable glomalin may contribute SOC pools. Our results suggest that mycorrhizal-mediated better soil aggregate stability might mainly be due to soil hyphal length, integrated with SOC and fraction 1 of BRSP.

Glomalin and Soil Aggregation under Six Management Systems in the Northern Great Plains, USA

The soil environment is linked to aboveground management including plant species composition, grazing intensity, levels of soil disturbance, residue management, and the length of time of a living plant is growing. Soil samples were collected under rangeland [native grass, rotational grazing (NGRG); tame grass, heavy grazing (TGRG); and tame grass, rotational grazing (TGHG)] and cropland [conventional till (CT); CT plus manure (CTM); and long term no till (NT)] systems. The rangeland systems were hypothesized to have higher glomalin content [measured as Bradford-reactive soil protein (BRSP)] and water stable aggregation (WSA) than the cropland systems. In addition, within both rangeland and cropland systems, BRSP and WSA were expected to decline with increased disturbance due to grazing or tillage and going from native to introduced plant species. Differences were detected for BRSP with NGRG and CTM having the highest values in range and cropland systems, respectively. However, the CTM system had higher BRSP values than one or both of the tame grass systems while the CT and NT systems had similar values. Correlation analysis showed strong relationships between all of the BRSP values and WSA.

Patterns of soil organic carbon, glomalin and structural stability in abandoned Mediterranean terraced lands

Soil carbon (C) storage potential has received considerable attention for its role in climate change mitigation, and much research work has been devoted to studying the effect of land‐use change, including land abandonment, on carbon dynamics. A comparative analysis of soil organic carbon (SOC), easily extractable Bradford‐reactive soil protein (EE‐BRSP) and Bradford‐reactive soil protein (BRSP) was carried out at monthly intervals in a land‐use sequence including cultivated soils, forest soils, shrubs and pasture in northeast Spain. In general, greater seasonal variations of both EE‐BRSP and BRSP were found in soils with less carbon storage capacity. Turnover of glomalin into more stable C forms was associated with a small EE‐BRSP:BRSP ratio in better structured soils and BRSP was related to organic carbon, suggesting positive contributions to both the recalcitrant carbon pool and soil structure. This effect seemed to be more pronounced in August when more BRSP was found, probably because of high temperature and dry soils in which glomalin may react to preserve residual adsorbed water and provide better protection in soil microsites. The role of glomalin was further enhanced by the structural stability of aggregates (WSA) investigated in two aggregate fractions (0.25–2.00 and 2.00–5.60 mm), indicating its beneficial effect in aggregation and carbon storage potential. BRSP, SOC and WSA increased significantly (P &lt; 0.001) along the transect and abandonment sequence; the largest WSA values were generally greater in summer in both aggregate fractions. However, values in cultivated soils were always smaller than in soils under shrubs and pasture. Similarly, soils with a smaller carbon pool had the largest proportion of carbon loss as CO2‐C when land use changes from vines to pasture. The role of aggregates in protecting organic carbon against mineralization was therefore postulated and highlighted the importance of soil monitoring after land abandonment.

Spatial distribution of arbuscular mycorrhiza and glomalin in the rhizosphere of Caragana korshinskii Kom. in the Otindag sandy land, China

To understand the ecological significance of arbuscular mycorrhizal (AM) associations in arid ecosystem, the spatial patterns of AM fungi, glomalin and soil enzymes were surveyed at four sites located in the Otindag sandy land, northern China. Soil samples in the rhizosphere of Caragana korshinskii Kom. were collected at 0-10, 10-20, 20-30, 30-40 and 40-50 cm depth in July 2009. The study showed that C. korshinskii Kom. could form strong symbiotic relationship with AM fungi. AM fungal colonization, spore density, total Bradford-reactive soil protein (T-BRSP) and easily extractable Bradford-reactive soil protein (EE-BRSP) significantly differed among four sites and soil depths. Correlation analysis showed hyphal colonization had positive correlation with soil urease (P < 0.01). Spore density, T-BRSP and EE-BRSP were positively correlated with soil organic carbon, available N and P, and soil urease, acid phosphatase and alkaline phosphatase (P < 0.01). Based on stepwise regression, soil urease, available N and organic carbon were principal soil factors affecting the spatial distribution of AM fungi and glomalin. The results support the conclusion that glomalin may be an appropriate index for evaluating soil fertility. Moreover, the spatial distribution pattern of AM fungi and glomalin are useful to monitor desertification and soil degradation. Key words: Spatial dynamics, arbuscular mycorrhiza, glomalin-related soil protein,Caragana korshinskii Kom., Otindag sandy land.

Spatial distribution of glomalin-related soil protein and its relationships with root mycorrhization, soil aggregates, carbohydrates, activity of protease and β-glucosidase in the rhizosphere of Citrus unshiu

Relationships between the spatial distributions of glomalin-related soil protein (GRSP) and soil aggregates, carbohydrates or relevant enzymes are poorly studied. We found that two categories of GRSP, the easily extractable Bradford-reactive soil protein (EE-BRSP) and total BRSP (T-BRSP), respectively ranged between 0.3–0.6 and 0.5–0.8mg/g DW soil, and these two BRSPs decreased with the increase of soil depth (0–40cm) in the rhizosphere of a 22-year-old Citrus unshiu orchard. Both EE-BRSP and T-BRSP were significantly positively correlated with mycorrhization, 0.25–0.50mm soil water-stable aggregates, water-extractable or hydrolyzable carbohydrates, and β-glucosidase, but significantly negatively correlated with protease. Our results demonstrate that the spatial distribution of GRSP is significantly affected by mycorrhization, soil carbohydrate, β-glucosidase and protease.

Influence of Arbuscular Mycorrhizal (AM) Fungi and Salinity on Seedling Growth, Solute Accumulation, and Mycorrhizal Dependency of Jatropha curcas L.

Production of Jatropha curcas as a biodiesel feedstock on marginal lands is growing rapidly. Biomass production on these lands is limited. Hence, the objective of this study was to evaluate the effect of arbuscular mycorrhiza (AM) fungi and salinity (0.1, 0.2, 0.3, 0.4, and 0.5% NaCl) on (1) seedling growth, leaf relative water content (RWC), lipid peroxidation, solute accumulation (proline and sugars), and photosynthetic pigments (Chl a and b) of Jatropha; (2) mycorrhizal colonization (%) and mycorrhizal dependency (MD) of Jatropha; and (3) glomalin content (Bradford reactive soil protein) in soil. Increased soil salinity significantly (P < 0.05) decreased AM root colonization (r 2 = 0.98) of AM-inoculated plants and decreased survival (r 2 = 0.93) and growth (shoot length, r 2 = 0.89; tap root length, r 2 = 0.93; shoot diameter, r 2 = 0.99; shoot dry weight, r 2 = 0.92; and root dry weight, r 2 = 0.92) of non-AM-inoculated Jatropha. Under salt stress, AM-inoculated Jatropha plants had greater dry weight of shoots and roots, better leaf water status, less leaf membrane damage (low lipid peroxidation activity), higher solute (proline and sugars), and higher leaf chlorophyll concentrations than non-AM-inoculated plants. The mycorrhizal dependency (MD) of Jatropha increased from 12.13 to 20.84% with salinity (0–0.4% NaCl). Root AM colonization (%) and glomalin content in soil were negatively correlated with salinity (P < 0.05, r = −0.95). We conclude that inoculation with AM fungi lessens the deleterious effect of salt stress on seedling growth parameters under salt levels up to 0.5% NaCl (electrical conductivity of 7.2 dS m−1). Inoculation of Jatropha seedlings with AM fungi can promote the establishment of Jatropha under NaCl-induced stress.

Bradford-reactive soil proteins and aggregate stability under abandoned versus tilled olive groves in a semi-arid calcisol

Glomalin, a substance produced by arbuscular mycorrhizal fungi, is reported to play a role in soil aggregation, but this role has been questioned in soils rich in calcium carbonate. We studied the relationship between aggregation stability and glomalin in a Haplic Calcisol comparing abandoned and active cultivation of olive groves. Abandonment was associated with increases in soil organic carbon, the percentage of water stable aggregates (WSA 1–2mm), and easily extractable and total Bradford-reactive soil protein. WSA 1–2mm was strongly positively correlated with both easily extractable and total Bradford-reactive soil protein. While easily extractable Bradford-reactive soil protein measured in both stable and unstable aggregates did not show any significant differences, Bradford-reactive soil protein was twice as high in stable than in unstable aggregates under both tillage and abandonment. Our results suggest that Bradford-reactive soil protein influences aggregate stability, even in soils with low organic matter and high calcium carbonate contents. However, more research is needed to elucidate the role of easily extractable Bradford-reactive soil protein in soil aggregation.

Spatial distribution of arbuscular mycorrhizal fungi, glomalin and soil enzymes under the canopy of Astragalus adsurgens Pall. in the Mu Us sandland, China

To measure and manage plant growth in arid and semi-arid sandlands, improved understanding of the spatial patterns of desert soil resources and the role of arbuscular mycorrhizal (AM) fungi is needed. Spatial patterns of AM fungi, glomalin and soil enzyme activities were investigated in five plots located in the Mu Us sandland, northwestern China. Soils to 50 cm depth in the rhizosphere of Astragalus adsurgens Pall. were sampled. The study demonstrated that A. adsurgens Pall. could form strong symbiotic relationships with AM fungi. Arbuscular mycorrhizal fungal status and distributions were significantly different among the five studied plots. Correlation coefficient analysis demonstrated that spore density was significantly and positively correlated with soil organic carbon (SOC), soil acid phosphatase and to two Bradford-reactive soil protein (BRSP) fractions ( P < 0.01). Colonization of arbuscules and vesicles were positively correlated with protease activity. The BRSP fractions were also significantly and positively correlated to edaphic factors (e.g. SOC, available nitrogen, and Olsen phosphorus) and soil enzymes (e.g. soil urease and acid phosphatase). The means of total BRSP and easily extractable BRSP were 0.95 mg g −1 and 0.5 mg g −1 in all data, respectively. The levels of BRSP in the desert soil were little lower than those in native and arable soils, but the ratios of BRSP to SOC were much higher than farmland soils. The results of this study support the conclusion that glomalin could be an appropriate index related to the level of soil fertility, especially in desert soil. Moreover, AM fungal colonizations and glomalin might be useful to monitor desertification and soil degradation.

Carbon and nitrogen accumulation and microbial activity in Mount St. Helens pyroclastic substrates after 25 years

Lupines (Lupinus lepidus var. lobbii) are important integrators of above and belowground development of Mount St. Helens (1980) pyroclastic substrates because they increase soil organic matter formation and microbial activity and influence other biotic processes. However, basic information is required to understand the unfolding pattern of soil development and to corroborate evidence for increasing rates of organic matter accumulation suggested by earlier work. Soil properties were measured in bare pyroclastic sites without lupines or other plants, under live and under dead L. lepidus. In 2005, pyroclastic substrates had low cation exchange capacity but appeared able to supply sufficient P for plant growth. Soil under live and dead lupines contained higher concentrations of soluble and total C and N, larger, more active microbial communities, more Bradford reactive soil protein and enzymes, and had higher mineralization potentials than bare soil. Comparatively, lupine soil was less dense and had lower C to N ratios and relative respiration rates. Soil microbial biomass-C, determined by substrate-induced respiration, had not increased under lupines since 1990, and was indistinguishable from hot water soluble-C, suggesting microorganisms were a predominant pool of labile-C in these developing soils. Evidence for an important soil glycoprotein, glomalin, in these pyroclastic substrates suggests it can form early during soil development. Concentrations of total C and N under lupines have risen to nearly 4 and 0.4 g kg−1 respectively since the 1980 eruption, but 2005 data indicate little change since 1997 and imply inputs from lupines into soil are in equilibrium with losses.

Fractionation and Long‐Term Laboratory Incubation to Measure Soil Organic Matter Dynamics

Soil organic matter (SOM) in agricultural soils comprises a significant part of the global terrestrial C pool. It has often been characterized by utilizing a combination of chemical dispersion of the soil followed by physical separation. We fractionated soil samples under continuous corn (Zea mays L.) rotations at four long‐term sites in the Corn Belt to determine the concentration of C and N associated with soil fractions (light fraction [LF], particulate organic matter [POM], silt size, clay size, and Bradford reactive soil protein [BRSP]) and to identify the change in C concentration and δ13C signal of each fraction using laboratory incubations. Light fractions comprised 3 to 5% of the soil organic carbon (SOC), with no significant difference between conventional tillage (CT) and no‐till (NT) treatments. The POM fraction accounted for 5 to 11% of the SOC in the soils with &gt;30% clay and 17 to 23% for the soils with &lt;20% clay. The clay‐size fraction contained the highest proportion of SOC. Measurement of 13C during long‐term incubation showed that the average mean residence time (MRT) of corn‐derived C in the LF was 3.5 yr, whereas the POM fractions ranged from 6 to 12 yr. The 13C changes during incubation show that both fractions consist of a mixture of active and resistant materials, with movement between fractions. The BRSP has long MRTs except in the NT Hoytville soil. Measurement of the dyna mics of these fractions provides a basis for C models to test the impacts of land use and management on C sequestration.

Improved soil structure and citrus growth after inoculation with three arbuscular mycorrhizal fungi under drought stress

In a controlled potted experiment, citrus ( Poncirus trifoliata) seedlings were inoculated with three species of arbuscular mycorrhizal (AM) fungi, Glomus mosseae, G. versiforme or G. diaphanum. Two soil-water levels (ample water, −0.10 MPa; drought stress, −0.44 MPa) were applied to the pots 4 months after transplantation. Eighty days after water treatments, the soils and the citrus seedlings were well colonized by the three AM fungi. Mycorrhizal fungus inoculation improved plant biomass regardless of soil-water status but decreased the concentrations of hot water-extractable and hydrolyzable carbohydrates of soils. Mycorrhizal soils exhibited higher Bradford-reactive soil protein concentrations than non-mycorrhizal soils. Mycorrhizas enhanced >2 mm, 1–2 mm and >0.25 mm water-stable aggregate fractions but reduced 0.25–0.5 mm water-stable aggregates. Peroxidase activity was higher in AM than in non-AM soils whether drought stressed or not, whereas catalase activity was lower in AM than non-AM soils. Drought stress and AM fungus inoculation did not affect polyphenol oxidase activity of soils. A positive correlation between the Bradford-reactive soil protein concentrations, soil hyphal length densities, and water-stable aggregates (only >2 mm, 1–2 mm and >0.25 mm) suggests beneficial effects of the AM symbiosis on soil structure. It concluded that AM fungus colonization enhanced plant growth under drought stress indirectly through affecting the soil moisture retention via glomalin's effect on soil water-stable aggregates, although direct mineral nutritional effects could not be excluded.

Tannic acid reduces recovery of water-soluble carbon and nitrogen from soil and affects the composition of Bradford-reactive soil protein

Tannins are plant-derived polyphenolic compounds that precipitate proteins, bind to metals and complex with other compounds. Solutions of tannic acid, or other phenolic compounds, were added to soil samples to determine if they would affect recovery of soluble soil carbon (WSC) or –nitrogen (WSN) or influence the extraction and composition of Bradford-reactive soil protein (BRSP), associated with glomalin. Tannic acid-C added with water was not completely recovered from samples and the amount of total net WSC and WSN recovered was reduced, suggesting formation of insoluble complexes. By comparison, non-tannin phenolics like gallic acid, or methyl gallate, had little effect on extraction of WSC or WSN while a simple gallotannin derived from tannic acid, 1,2,3,4,6-penta- O-galloyl- d-glucose (PGG), inhibited extraction most. The C and N concentrations in BRSP increased when soil samples were treated with tannic acid or PGG before extraction, a procedure that includes autoclaving. Increases were greatest in the 10–20 cm compared to 0–5 cm depth. Accompanying these were declines in the ratio of absorbance at 465 and 665 nm ( E4/ E6 ratio) of BRSP extracts suggesting formation of larger or heavier molecules. In contrast, C and N composition in lyophilized BRSP was unaffected or even slightly reduced when tannic acid or PGG were added to the BRSP extract solution after the extraction process. We conclude that some tannins can reduce the solubility of labile soil C and N, at least temporarily and given unpredictability of response associated with phenolic substances, the Bradford assay should not be relied on to quantify pools or composition of soil proteins like glomalin.

Responses of Bradford-reactive soil protein to experimental nitrogen addition in three forest communities in northern lower Michigan

Increased use of anthropogenically fixed N and the release of N in combustion products have led to concerns about possible long-term impacts on terrestrial ecosystems. Previous studies demonstrating the potential of atmospheric N deposition to influence forest soil carbon have focused on decomposition processes with much less known about potential impacts on mycorrhiza-derived carbon. Glomalin is a unique glycoprotein produced by arbuscular mycorrhizal (AM) fungi that has been implicated in the formation of soil aggregates and potentially a significant store of soil carbon. To determine the possible impact of experimental N deposition of such stores we examined the operationally defined glomalin-related soil protein (GRSP) levels over two growing seasons in three forest types receiving background N deposition (control) or treated with 80 kg N ha−1 year−1 as NaNO3. Three sites of each of three forest types, sugar maple-basswood (SMBW), sugar maple-red oak (SMRO), and black oak-white oak (BOWO), in northern Lower Michigan were studied during the 2001 and 2002 growing seasons. GRSP were extracted from air-dried soils with citric acid and measured by the Bradford method. Analysis of variance revealed significant differences related to forest type and sample date in easily extractable Bradford reactive (EE-BRSP) and Bradford-reactive soil protein (BRSP), but failed to detect significant effects of experimental N amendment. EE-BRSP and BRSP varied in a pattern that was consistent with an AM fungal origin; a pattern that reflected the mycorrhizal types of the dominant over and understory plants of each forest ecosystem. SMBW forests dominated by AM plants had the highest levels of protein. BOWO forests with low AM plant cover had the lowest protein levels and SMRO forests were intermediate. Both Bradford-reactive fractions and their ratio varied seasonally, generally being highest in fall samples. Significant correlations observed between BRSP fractions, phosphorous, and soil organic matter were likely related to covariation of soil properties across forest types. While not statistically significant, response patterns of BRSP to N deposition were ecosystem-specific and reflected mycorrhizal types of dominant species. Abundance of these proteins reflected previously observed changes in SOC in the two forest types examined with abundant AM hosts. Specifically, nitrate addition led to BRSP decreases in SMBW and increases in SMRO forests. Changes in BRSP accounted for a small fraction of the changes in SOC; appearing to increase as a fraction of residual SOC consistent with the idea that GRSP are recalcitrant. BRSP remained unchanged at BOWO sites despite a significant increase in SOC at these sites. Our results point to the potential of proteins as contributors to differential, mycorrhizal type-specific responses to changes in soil carbon following N amendment.

Losses of glomalin-related soil protein under prolonged arable cropping: A chronosequence study in sandy soils of the South African Highveld

Residues of arbuscular mycorrhizal fungi (AMF) may be important for agroecosystem functioning due to their ability to promote soil aggregation, especially in coarse textured soils with little biomass input and low capacity to conserve soil organic matter (SOM). Our aim was to assess the fate of AMF residues with prolonged arable cropping in coarse textured soils in a subtropical savannah assuming that glomalin-related soil protein (GRSP), especially the MAb32B11-immunoreactive fraction, mainly constitutes material of AMF origin. In three agroecosystems on the South African Highveld, surface soils were sampled. The former grassland soils had a history of up to 98 yr of cropping. We measured four GRSP fractions: Bradford-reactive soil protein (BRSP) and immunoreactive soil protein (IRSP), and easily extractable fractions of both. The primary grassland sites exhibited generally low contents of SOM and low GRSP contents. Prolonged arable land use of former grassland soils reduced the content of GRSP further. The decline could be described with a mono-exponential function with rate constants ranging from 0.04 to 0.41 yr −1. Depending on the GRSP fraction, steady-state conditions were reached after 11–92 yr on a level of 39–69% of the initial contents. We conclude that even though GRSP fractions had the same hypothesized origin, they comprised pools with different stability or replacement rate. Easily extractable IRSP was lost most rapidly. In contrast to carbon, nitrogen and microbial residue dynamics, GRSP contents were not reduced below a certain steady-state level, despite potentially negative management effects on AMF, such as tillage, inclusion of fallows into crop rotation and fertilization with inorganic phosphorus. The steady-state GRSP contents coincided with low, but steady agroecosystem yields under the given cropping management.

Bradford reactive soil protein in Appalachian soils: distribution and response to incubation, extraction reagent and tannins

Bradford reactive soil protein (BRSP) is thought to correlate to glomalin, an important soil glycoprotein that promotes soil aggregate formation and may represent a significant pool of stable soil organic matter (SOM). However, more information is needed about its importance in Appalachian soils and its relationships with other soil properties. We measured BRSP in 0-20 cm soil from pastures, hayfields, cultivated fields or forest areas in southern West Virginia. Highest amounts of BRSP were found near the soil sur- face and decreased significantly with depth for all land uses except cultivated sites. Forest and pas- ture sites contained more BRSP than hayfields or cultivated fields but these differences occurred only in the 0-5 cm depth. Overall averages of C and N in BRSP represented about 4.0 and 6.5% of the total soil C and N respectively. During a 395 day soil incubation, we found CO2-C evolu- tion rates comparable to other studies but only small changes in BRSP ( < 10%) including some evidence for increases during incubation. Sodium citrate, sodium pyrophosphate, and sodium oxa- late recovered significantly more BRSP from soil than the other extractants we tested with highest extraction efficiencies observed for sodium citrate and pyrophosphate. Recovery of BRSP appears related to negative charge and buffering capacity of both the soil and extractant. Extractants with low negative charge had little buffering capacity and yielded little BRSP. Tannic acid appeared to increase extraction of BRSP but less soluble-N was recovered from tannin-treated samples than from untreated controls and E4/E6, the ratio of absorbance at 465 and 665 nm, decreased, evi- dence for the formation of larger or heavier molecules. Formation of dark-colored substances during extraction suggests the colorimetric Brad- ford assay may overestimate soil protein when tannins are present. Recovery of less soluble-N from soil extracts and lower E4/E6 ratios suggests tannins may bind with soil constituents them- selves or form non-extractable N-containing complexes.

Mycorrhizae activity and diversity in conventional and organic apple orchards from Brazil

The aim of this study was to characterize the impacts of a conventional, an organic apple orchard and a native grassland on the activity and diversity of arbuscular mycorrhizal fungi (AMF) located at the south of Brazil during winter and summer. AMF activity was measured by the mycorrhizal inoculum potential (MIP), mycorrhizal fungal hyphal length (HL), easily extractable and total Bradford-reactive soil protein (BRSP). AMF diversity was represented by richness, Shannon diversity index and number of spores. Orchards reduced the MIP of the soil and increased the HL when compared to the grassland site. The amount of easily extractable BRSP was not different among orchards and between seasons evaluated, with overall mean value of 1.23 mg g −1. However, the amount of total-BRSP was smaller in the conventional orchard (4.55 mg g −1) than in the organic orchard (4.91 mg g −1) and in the native grassland (5.12 mg g −1). T-BRSP and total organic carbon were strongly correlated in the grassland during the winter, suggesting the contribution of this protein for carbon stocks in the native soil of this region. The organic orchard presented the highest AMF richness, but sporulation and Shannon diversity index were larger in the conventional orchard. Our data suggest that the conventional orchard promoted higher impacts on the natural condition of AMF activity, being considered an unadvisable practice to soil conservation.