Interactions between N fertilization, grass clipping addition and pH in turf ecosystems: Implications for soil enzyme activities and organic matter decomposition

Turf has been acknowledged as an important ecosystem with potential for soil C sequestration. As a major process dictating soil C storage, organic matter decomposition has received little attention in turf systems. Given that soil enzyme-catalyzed biochemical reactions are the rate limiting steps of organic matter decomposition, we examined the activities of oxidative and hydrolytic soil enzymes and their relations with soluble organic compounds and soil C and N mineralization in two turf chronosequences with contrasting soil pH and in response to N fertilization and grass clipping addition. In comparison with turf ecosystems under acidic soil, phenol oxidase activity was about two-fold greater in turf ecosystems under alkaline soil and positively correlated to about two-fold differences in soluble phenolics and dissolved organic C between alkaline and acidic soils. However, the activities of hydrolytic enzymes including cellulase, chitinase, and glucosidase were lower in alkaline soil. It appears that the high concentration of soluble phenolics inhibited the activities of hydrolytic enzymes that in turn limited the decomposition of dissolved organic C and resulted in its accumulation in alkaline soil. Nitrogen mineralization was comparable between alkaline and acidic soils, but CO₂ evolution was about two-fold greater in alkaline soil, possibly due to considerable abiotic carbonate dissolution. We observed that mineral N input at 60 mg N kg⁻¹ soil had very minor negative effects on the activities of both phenol oxidase and hydrolytic enzymes. Grass clipping addition did not affect the activity of phenol oxidase, but increased the activities of soil chitinase, cellulase, glucosidase, and glucosaminidase by up to 20% and also soluble phenolics in soil by about 10%. Our results suggest that soil phenol oxidase might regulate the activities of hydrolytic soil enzymes via its control on soluble phenolics and function as an ‘enzymatic latch’ to hold soil organic C in highly managed turf ecosystems. While soil pH is important to affect phenol oxidase activity and therefore decomposition, management practices, i.e., N fertilization and grass clipping addition may indirectly affect the decomposition through enhancing turfgrass productivity and thus soil C input.     

Bacterial and enchytraeid abundance accelerate soil carbon turnover along a lowland vegetation gradient in interior Alaska

Boreal wetlands are characterized by a mosaic of plant communities, including forests, shrublands, grasslands, and fens, which are structured largely by changes in topography and water table position. The soil associated with these plant communities contain quantitatively and qualitatively different forms of soil organic matter (SOM) and nutrient availability that drive changes in biogeochemical cycling rates. Therefore different boreal plant communities likely contain different soil biotic communities which in turn affect rates of organic matter decomposition. We examined relationships between plant communities, microbial communities, enchytraeids, and soil C turnover in near-surface soils along a shallow topographic soil moisture and vegetation gradient in interior Alaska. We tested the hypothesis that as soil moisture increases along the gradient, surface soils would become increasingly dominated by bacteria and mesofauna and have more rapid rates of C turnover. We utilized bomb radiocarbon techniques to infer rates of C turnover and the ¹³C isotopic composition of SOM and respired CO₂ to infer the degree of soil humification. Soil phenol oxidase and peroxidase enzyme activities were generally higher in the rich fen compared with the forest and bog birch sites. Results indicated greater C fluxes and more rapid C turnover in the surface soils of the fen sites compared to the wetland forest and shrub sites. Quantitative PCR analyses of soil bacteria and archaea, combined with enchytraeid counts, indicated that surface soils from the lowland fen ecosystems had higher abundances of these microbial and mesofaunal groups. Fungal abundance was highly variable and not significantly different among sites. Microbial data was utilized in a food web model that confirmed that rapidly cycling systems are dominated by bacterial activity and enchytraeid grazing. However, our results also suggest that oxidative enzymes play an important role in the C mineralization process in saturated systems, which has been often ignored.     

Long-Term Effects of Different Cropping Systems on Selected Enzyme Activities

The historic Sanborn Field located on University of Missouri campus at Columbia, Missouri, was designed to demonstrate the importance of agricultural practices, such as fertilization, tillage, and crop rotation. Knowledge of the effect of long-term agricultural practices on the soil quality is critical for farmers to make better management decisions to efficiently and sustainably produce crops. This study examined long-term fertilization, tillage, and crop rotation effects on the activities of soil enzymes including phenol oxidase, peroxidase, dehydrogenase, cellulose, and β-glucosaminidase in the top soil layer (0–10 cm). The results showed that pH, organic matter, and cation exchange capacity are important factors that are associated with enzyme activities. Compared to conventional tillage, no-tillage treatment significantly increased activities of phenol oxidase, peroxidase, dehydrogenase, and d β-glucosaminidase. Fertilization increased cellulase and β-glucosaminidase activity, but had mixed effects for phenol oxidase, peroxidase, and dehydrogenase depending on the type of fertilizer applied. The amount of nitrogen applied significantly affected soil enzyme activities. The influences of the crop type and rotation are significant but differ for each enzyme. Due to the sensitivity of soil enzymes to environmental factors, soil enzymes such as phenol oxidase, dehydrogenase, cellulose, and β-glucosaminidase are suitable as indicators of soil quality.     

Biochar is an effective amendment to remediate Cd-contaminated soils—a meta-analysis

Journal of Soils and Sediments - Cd immobilization can be affected by many factors, among which the soil pH, soil organic matter (SOM), and amendment types are the most critical factors that have...     

Stabilization of oxidative enzymes in desert soil may limit organic matter accumulation

Phenol oxidase and peroxidase activities in desert grassland soils at the Sevilleta Long Term Ecological Research site in central New Mexico (USA) are far greater than those of temperate soils. Activity is uniformly distributed across particles ranging from >1 mm to <38 μm and is unaffected by autoclaving, in contrast to hydrolase activities. The sorbed enzymes are readily extractable and inactivated by boiling. High soil pH, high stabilized oxidative enzyme activity, and carbonates create optimal conditions for degradation of phenols which increase decomposition potentials and limit soil organic matter accumulation.     

Long-term management effects on organic C and N pools and activities of C-transforming enzymes in prairie soils

Changes in soil microbial and biochemical properties in response to management practices reflect changes in the functional capacity of soil ecosystems. The objectives were to evaluate effects of long-term management practices on different soil organic C and N pools and activities of glycoside hydrolases, including α- and β-glucosidases, α- and β-galactosidases, cellulase, and invertase, in semiarid prairie soils. Soils were sampled from five long-term management systems including: undisturbed, abandoned from cultivation, moderately grazed, heavily grazed, and cultivated with winter wheat (Triticum aestivum L.). Activities of C-transforming enzymes were sensitive in discriminating soil ecosystems under various land uses and can be used as indicators for detecting impact of soil management practices on the soil capacity to cycle C. Long-term cultivation (more than 30 yr) decreased total organic C and N, microbial biomass, and activities of C-transforming enzymes, and led to development of a microbial community with enhanced metabolic activity. Grazing, especially at moderate intensity, did not lessen soil capacity to support microbial life and cycle C. The intermediate status of the chemical, microbial, and biochemical properties in the abandoned from cultivation soils suggested that through secondary succession the soil ecosystem is restoring its capacity to sequester C and support microbial life.     

Microbial community composition shapes enzyme patterns in topsoil and subsoil horizons along a latitudinal transect in Western Siberia

Soil horizons below 30 cm depth contain about 60% of the organic carbon stored in soils. Although insight into the physical and chemical stabilization of soil organic matter (SOM) and into microbial community composition in these horizons is being gained, information on microbial functions of subsoil microbial communities and on associated microbially-mediated processes remains sparse. To identify possible controls on enzyme patterns, we correlated enzyme patterns with biotic and abiotic soil parameters, as well as with microbial community composition, estimated using phospholipid fatty acid profiles. Enzyme patterns (i.e. distance-matrixes calculated from these enzyme activities) were calculated from the activities of six extracellular enzymes (cellobiohydrolase, leucine-amino-peptidase, N-acetylglucosaminidase, chitotriosidase, phosphatase and phenoloxidase), which had been measured in soil samples from organic topsoil horizons, mineral topsoil horizons, and mineral subsoil horizons from seven ecosystems along a 1500 km latitudinal transect in Western Siberia. We found that hydrolytic enzyme activities decreased rapidly with depth, whereas oxidative enzyme activities in mineral horizons were as high as, or higher than in organic topsoil horizons. Enzyme patterns varied more strongly between ecosystems in mineral subsoil horizons than in organic topsoils. The enzyme patterns in topsoil horizons were correlated with SOM content (i.e., C and N content) and microbial community composition. In contrast, the enzyme patterns in mineral subsoil horizons were related to water content, soil pH and microbial community composition. The lack of correlation between enzyme patterns and SOM quantity in the mineral subsoils suggests that SOM chemistry, spatial separation or physical stabilization of SOM rather than SOM content might determine substrate availability for enzymatic breakdown. The correlation of microbial community composition and enzyme patterns in all horizons, suggests that microbial community composition shapes enzyme patterns and might act as a modifier for the usual dependency of decomposition rates on SOM content or C/N ratios.     

TRENDS IN RECOVERY OF MEDITERRANEAN SOIL CHEMICAL PROPERTIES AND MICROBIAL ACTIVITIES AFTER INFREQUENT AND FREQUENT WILDFIRES

Since the 1970s, increase in fire frequency has been observed in all European Mediterranean regions. The objectives of this study were (1) to determine the effects of wildfire frequency on the recovery at short‐ and long‐term of soil chemical and microbial properties and (2) to identify the mechanisms underlying the recovery of these sites properties. Soils from 17 plots (Maures mountains range, Var, France) were classified into 5 wildfire regimes (i.e. not burned since at least 57 years ago, infrequently and frequently burned‐with time since fire between 4 and 17 years). Soil samples from these plots were analysed for their nutrient content, chemical functions of soil organic matter (SOM) using FT‐MIR spectroscopy and microbial mineralising activities. Our results showed that the frequent wildfire regime slowed down the recovery in the short term of SOM spectroscopic properties and nutrient availability. Both low quantity and low quality (i.e. high percentage of aromatic and phenolic organic forms) of soil organic matter were found to be related to soil microbial recovery at 4 years after frequent wildfires. The frequent wildfires improved the recovery in net nitrification and nitrate content, leading to an increase in catabolic evenness and a recovery in microbial C‐substrate utilisation profiles between 4 and 17 years. However, frequent wildfires slowed down the recovery of hydrolytic enzyme pool (i.e. FDA hydrolases) and phenol oxidase activity, both involved in soil C cycling. Overall, our observations suggest that 4 fires in 50 years is a threshold beyond which soil quality may be endangered. Copyright © 2011 John Wiley & Sons, Ltd.     

Vertical gradients of potential enzyme activities in soil profiles of European beech,Norway spruce and Scots pine dominated forest sites

Management of forest sites has the potential to modulate soil organic matter decomposition by changing the catalytic properties of soil microorganisms within a soil profile. In this study we examined the impact of forest management intensity and soil physico-chemical properties on the variation of enzyme activities (β-glucosidase, β-xylosidase, α-glucosidase, phenol oxidase, N-acetyl-glucosaminidase, l-leucine aminopeptidase, phosphatase) in the topsoil and two subsoil horizons in three German regions (Schorfheide-Chorin, Hainich-Dün, Schwäbische Alb). The sandy soils in the Schorfheide-Chorin (SCH) showed lower ratios of the activity of carbon (C) acquiring enzymes (β-glucosidase) relative to nitrogen (N) acquiring enzymes (N-acetyl-glucosaminidase + l-leucine aminopeptidase), and activity of C acquiring enzymes relative to phosphorous (P) acquiring enzymes (phosphatase) than the finer textured soils in the Hainich-Dün (HAI) and Schwäbische Alb (ALB), indicating a shift in investment to N and P acquisition in the SCH. All enzyme activities, except phenol oxidase activity, decreased in deeper soil horizons as concentrations of organic C and total N did, while the decrease was much stronger from the topsoil to the first subsoil horizon than from the first subsoil to the second subsoil horizon. In contrast, phenol oxidase activity showed no significant decrease towards deeper soil horizons. Additionally, enzyme activities responsible for the degradation of more recalcitrant C relative to labile C compounds increased in the two subsoil horizons. Subsoil horizons in all regions also indicate a shift to higher N acquisition, while the strength of the shift depended on the soil type. Further, our results clearly showed that soil properties explained most of the total variance of enzyme activities in all soil horizons followed by study region, while forest management intensity had no significant impact on enzyme activities. Among all included soil properties, the clay content was the variable that explained the highest proportion of variance in enzyme activities with higher enzyme activities in clay rich soils. Our results highlight the need for large scale studies including different regions and their environmental conditions in order to derive general conclusions on which factors (anthropogenic or environmental) are most influential on enzyme activities in the whole soil profile in the long term at the regional scale.     

Labile carbon limits in-stream mineralization in a subtropical headwater catchment affected by gully and channel erosion

Journal of Soils and Sediments - Gully and channel erosion are known to export large quantities of soil organic matter (SOM) to stream ecosystems. However, the implications for in-stream processing...