Temperate Forest Soils Research Articles

Soil Organic Carbon Content Decreases in Both Surface and Subsoil Mineral Horizons by Simulated Future Increases in Labile Carbon Inputs in a Temperate Coniferous Forest

Soils represent important pools of soil organic carbon (SOC) that can be greatly influenced by labile C inputs, which are expected to increase in future due to CO2 enrichment of atmosphere and a concomitant rise in plant primary productivity. Studying effects of variable labile C inputs on SOC pool helps to understand how soils respond to global change. However, this knowledge is missing for coniferous forest soils despite being widespread throughout the northern temperate zone. We conducted a 7-month field manipulation experiment to study the effects of variable labile C inputs (simulated by additions of C4 sucrose) on the C content in soil fractions and on microbial abundance in the organic (O), surface mineral (A), and subsoil mineral (B) horizons of a temperate coniferous forest soil. SOC in less-protected soil fractions and total organic C were substantially decreased by labile C additions that simulated future increases in C inputs. The SOC losses were comparable between the A and B horizon (40% vs. 30%). However, because sucrose availability estimated from its incorporation into soil fractions and microbial biomass sharply decreased with soil depth, the loss of C was higher in the B than in the A horizon when related to the amount of sucrose added. Utilization of sucrose was highest by fungi in the O horizon and by bacteria in the mineral soil horizons. The results indicate that future increases in labile C inputs to coniferous forest soils will cause rapid and substantial losses of SOC in both the surface and subsoil mineral horizons.

The function of root mat fungal communities: Changes in response to pH and phosphorus addition

Societal Impact StatementAcid deposition affects forests in eastern North America, Europe, and eastern Asia, and reduces nutrient availability for forest trees. Reduced nutrient availability can reduce tree growth and forest productivity. Our research suggests that trees may rely on fungi, including mycorrhizal fungi, that colonize root mats near the soil surface for nutrient acquisition in forests subjected to acid‐induced nutrient limitation. These fungi may increase acquisition of nutrients from organic matter. Forest management practices that limit surface soil disturbance and damage to root mats, especially during timber harvesting activities, may be important for conserving forest productivity in regions subjected to acid deposition.Summary Many temperate forest soils are affected by a legacy of acid deposition, which can mobilize soil aluminum and reduce phosphorus (P) availability. These chemical changes are mostly manifest in mineral soil. However, many temperate trees have extensive shallow roots, or root mats, which are found on the surface of mineral soil. These root mats are in contact with the O horizon where substantial organic nutrients exist. But the role of root mats in accessing nutrients in nutrient limited, acidic soil is not well understood. We examined root mat fungal communities and their function using an existing 6‐year ecosystem‐level pH and P manipulation experiment, which artificially increased pH by more than 1.5 units and increased available P threefold. Dominant fungal taxa on roots were identified using Sanger sequencing and broad community changes were assessed using DNA fragment analysis. Nutrient acquisition within root mats was assessed by measuring the extracellular enzyme activity in rhizosphere soil. Fungal community structure changed with soil pH, while P availability altered extracellular enzyme production of phosphomonoesterase, β‐1,4‐glucosidase, and leucine aminopeptidase. Quercus–Fagus root mats contained ectomycorrhizal fungi and Acer roots contained both ectomycorrhizal and arbuscular mycorrhizal fungi. Interestingly, both Acer and Quercus–Fagus root mats contained ericoid mycorrhizal fungi, which were less abundant at higher pH. Our results suggest an important role of root mats in nutrient acquisition from organic sources in temperate forests. These root mats could assist plants in overcoming the legacy of acid deposition in temperate forests.

Stoichiometric imbalance and microbial community regulate microbial elements use efficiencies under nitrogen addition

Microbial elements use efficiencies are the important parameters in regulating soil carbon (C) and nitrogen (N) mineralization processes. Microbial C use efficiency (CUE) describes the proportion of C used for growth relative to the total organic C uptake. As such, high CUE values mean relatively less CO2 emission and more C retention in microbial biomass. Similarly, a higher microbial N use efficiency (NUE) indicates efficient biomass N sequestration and less N mineralization. However, very little is known how the microbial CUE and NUE are affected by N enrichment in forest soils. Here, we studied soil microbial CUE and NUE simultaneously using 18O-water tracer approach in a long-term N addition experiment comprising control (atmospheric N deposition, 2.7 g N m−2 yr−1), low N addition (atmospheric N deposition + 2.5 g N m−2 yr−1) and high N addition (atmospheric N deposition + 7.5 g N m−2 yr−1) in a temperate forest. We found microbial CUE responses to N addition were dependent on N addition rates and soil horizons. Specifically, low N addition significantly increased the microbial CUE by 45.12% while high N addition significantly reduced it by 27.84% in organic soil. Further, mineral soil microbial CUE did not change under low N addition but significantly increased by 133.18% under high N addition. We also found microbial NUE decreased with increasing N addition rate in organic soil but showed an opposite pattern in mineral soil. The stoichiometric imbalances associated with phosphorus between microbial biomass and resources and the microbial community changes under N addition were correlated with microbial CUE and NUE. Further, N addition decreased microbial biomass turnover in organic soil but accelerated it in mineral soil. Altogether, our results indicated that N addition could control soil C and N cycling processes by affecting microbial elements use efficiencies (i.e. CUE and NUE), which may consequently impact C and N sequestration in this temperate forest soil.

Skid Trail Effects on Soil Methane and Carbon Dioxide Flux in a Selection-Managed Northern Hardwood Forest

Temperate forest soils are an important sink for methane (CH4); however, disturbance through forest management and the creation of skid trails may significantly decrease soil’s ability to uptake CH4 or in some cases cause CH4 emissions. Skid trails might also be expected to show reductions in carbon dioxide (CO2) flux due to anaerobic conditions and reduced root activity. Studies to date have investigated skid trail greenhouse gas flux dynamics on experimentally created skid trails, which may not experience the full extent of traffic intensity or contain the various microsites found in actual harvested areas. We investigated variation of CH4 and CO2 fluxes based on traffic intensity, trail topography, and trail microsites in selection-managed hardwood forests in the Haliburton Highlands of Ontario, Canada. Skid trail soils showed reduced CH4 uptake, and primary and secondary trails were found to commonly be a CH4 source, especially on lower slope locations and on wheel track and trail middle ridge microsites. Skid trails also showed high CO2 emissions in the same areas. CH4 emissions on skid trails were correlated with low surface soil porosities and high soil moisture contents, which were found to occur most frequently on highly impacted trails, in low-lying areas, and in the wheel tracks and trail middle ridges. Scaling up, skid trails offset ~ 45% of CH4 uptake in untrafficked soils, an effect that should be accounted for in future greenhouse gas budgets of managed forests.

Long-term effects of biochar application on greenhouse gas production and microbial community in temperate forest soils under increasing temperature

Biochar management has been proposed as a promising strategy to mitigate climate change. However, the long-term effects of biochar amendment on soil greenhouse gas (GHG) production and microbial community in forest ecosystems under projected warming remain highly uncertain. In this study, we conducted a 49-day incubation experiment to investigate the impact of biochar application on soil physico-chemical properties, GHG production rates, and microbial community at three temperature levels using a temperate forest soil amended with spruce biochar four years ago. Our results showed that temperature exerted a positive effect on soil CO2, CH4 and N2O production, leading to an increase in total global warming potential by 169% and 87% as temperature rose from 5 to 15 °C and from 15 to 25 °C, respectively, and thus a positive feedback to warming. Moreover, warming was found to reduce soil microbial biomass significantly, but at the same time promote the selection of an activated microbial community towards some phyla, e.g. Acidobacteria and Actinobacteria. We observed that biochar amendment reduced soil CH4 consumption and N2O production in the absence of litter by 106% and 94%, respectively, but did not affect soil CO2 production. While biochar had no significant influence of total global warming potential of forest soil, it could promote climate change mitigation by increasing the total soil carbon content by 26% in the presence of litter. In addition, biochar application was shown to enhance soil available phosphorus and dissolved organic carbon concentrations, as well as soil microbial biomass under a warmer environment. Our findings highlighted the potential of spruce biochar as a soil amendment in improving soil fertility and carbon sequestration in temperate forest over the long term, without creating any adverse climatic impacts associated with soil GHG production.

Effects of warming, wetting and nitrogen addition on substrate-induced respiration and temperature sensitivity of heterotrophic respiration in a temperate forest soil

Soil heterotrophic respiration and its temperature sensitivity are affected by various climatic and environmental factors. However, little is known about the combined effects of concurrent climatic and environmental changes, such as climatic warming, changing precipitation regimes, and increasing nitrogen (N) deposition. Therefore, in this study, we investigated the individual and combined effects of warming, wetting, and N addition on soil heterotrophic respiration and temperature sensitivity. We incubated soils collected from a temperate forest in South Korea for 60 d at two temperature levels (15 and 20 °C, representing the annual mean temperature of the study site and 5 °C warming, respectively), three moisture levels (10%, 28%, and 50% water-filled pore space (WFPS), representing dry, moist, and wet conditions, respectively), and two N levels (without N and with N addition equivalent to 50 kg N ha–1 year–1). On day 30, soils were distributed across five different temperatures (10, 15, 20, 25, and 30 °C) for 24 h to determine short-term changes in temperature sensitivity (Q10, change in respiration with 10 °C increase in temperature) of soil heterotrophic respiration. After completing the incubation on day 60, we measured substrate-induced respiration (SIR) by adding six labile substrates to the three types of treatments. Wetting treatment (increase from 28% to 50% WFPS) reduced SIR by 40.8% (3.77 to 2.23 µg CO2-C g–1 h–1), but warming (increase from 15 to 20 °C) and N addition increased SIR by 47.7% (3.77 to 5.57 µg CO2-C g–1 h–1) and 42.0% (3.77 to 5.35 µg CO2-C g–1 h–1), respectively. A combination of any two treatments did not affect SIR, but the combination of three treatments reduced SIR by 42.4% (3.70 to 2.20 µg CO2-C g–1 h–1). Wetting treatment increased Q10 by 25.0% (2.4 to 3.0). However, warming and N addition reduced Q10 by 37.5% (2.4 to 1.5) and 16.7% (2.4 to 2.0), respectively. Warming coupled with wetting did not significantly change Q10, while warming coupled with N addition reduced Q10 by 33.3% (2.4 to 1.6). The combination of three treatments increased Q10 by 12.5% (2.4 to 2.7). Our results demonstrated that among the three factors, soil moisture is the most important one controlling SIR and Q10. The results suggest that the effect of warming on SIR and Q10 can be modified significantly by rainfall variability and elevated N availability. Therefore, this study emphasizes that concurrent climatic and environmental changes, such as increasing rainfall variability and N deposition, should be considered when predicting changes induced by warming in soil respiration and its temperature sensitivity.

Natural recovery of skid trails: a review

In recent years, the study of skid trail recovery processes has gained momentum. In this review, 121 studies on various aspects of skid trail recovery were evaluated to determine when, where, and how the dominant factors that influence the process of recuperation occur. These studies were located proportionally in the following forest biomes: temperate (60%), tropical (31%), and boreal (9%). Research focused mainly on soil physical properties to ascertain if there had been evidence of recovery. The majority of studies of a decade or less after abandonment demonstrated that heavily used skid trails had not recovered. On the contrary, lightly used skid trails did present full recoveries over the same time span. Soil recovery tended to occur in medium- to coarse-textured soils in temperate and boreal forests. Considering all forest biomes, the impacts of compaction persisted at least two to five decades after logging operations. The impacts were evident in diminished tree heights and volumes from trees growing on skid trails. The last 50 years of research indicates that skid trails, globally, do recover from compaction, albeit slowly.

秦岭太白山不同林带土壤微生物呼吸速率及其影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 秦岭太白山不同林带土壤微生物呼吸速率及其影响因素 DOI: 10.5846/stxb201905171016 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金青年基金（41601578）；中国博士后特别资助（2018T111089）；森林生态系统可持续经营教育部重点实验室（东北林业大学）开发基金（KFJJ2019ZD01） The soil microbial respiration rate and its influencing factors in different forest belts of Taibai Mountain, Qinling Mountains Author: Affiliation: 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:为探究森林土壤微生物呼吸对温度的敏感性及其影响因素，在太白山选取典型的4个不同海拔的林带（锐齿栎林、辽东栎林、红桦林、牛皮桦林）的0-10 cm表层土壤为对象，分别在15、25、35℃下进行控温培养实验并测量其土壤呼吸速率、微生物量和胞外酶活性等指标。结果表明：1）在1-20 d与20-72 d时的微生物呼吸速率分别呈现波动下降趋势与缓慢下降趋势，相比于其初始速率平均下降了68%与90%；表明高温在短期内促进土壤呼吸；2）太白山地区土壤温度敏感系数（Q10）随温度的升高而降低；3）在培养过程中，出现15℃和25℃下微生物量先增多后减少，35℃下微生物量一直减少的现象，并且胞外酶是影响土壤微生物呼吸的重要因素，其中BG（β-葡萄糖苷酶）是胞外酶中最重要的影响因子；4）培养72 d以后，BG已无法为微生物生长繁殖提供充足的碳，在25℃和35℃下，由BX（β-木糖苷酶）提供的碳已成为微生物生长繁殖的重要碳源之一。在15℃和25℃下，N是培养前期限制土壤呼吸的因素，C是后期限制因素；在35℃下，N一直是限制土壤呼吸的因素。在15℃和35℃下，土壤呼吸不存在P限制；在25℃的培养前期，P是限制土壤呼吸的因子，而在培养后期不存在P限制。本研究结果阐明抑制土壤碳排放的关键在于抑制土壤微生物呼吸，揭示了在胞外酶驱动下的土壤碳循环特征，为准确预测全球未来气候变化的趋势提供理论基础。 Abstract:Soil microbial respiration is a major source of CO2 efflux to the atmosphere from forest ecosystems and plays a decisive role in predicting future global climate change. A typical temperate forest ecosystem, the Taibai Mountain contains a mosaic of stands with various attitudes. The objective of the present study was to investigate the trends and influencing factors of microbial respiration in temperate forest soils without external carbon input. In the Taibai Mountain, 0-10 cm topsoil of typical forest belts of different altitudes (Quercus aliena var. acuteserrata, Q. liaotungensis, Betula albosinensis, and B. albosinensis var. septentrionalis) were sampled and incubated at 15 ℃, 25 ℃, and 35 ℃. The microbial respiration rate showed a fluctuating downward trend and a slowly decreasing trend at Days 1-20 and Days 20-72, with a 68% and 90% decrease compared to the initial rate, respectively. Thus, high temperature promoted soil respiration in the short term whereas it retarded soil respiration in the long term. The temperature sensitivity index (Q10) of the soil in the Taibai Mountain decreased with warming. Microbial biomass increased initially and then decreased during the incubation at 15 ℃ and 25 ℃, whereas it decreased throughout the incubation at 35 ℃. Furthermore, BG (β-1,4-glucosidase) was the most important extracellular enzyme affecting microbial respiration. After 72 days of incubation, BG failed to provide adequate carbon for microbial growth and reproduction. At 25 ℃ and 35 ℃, the carbon provided by BX (β-1,4-xylosidase) became one of the most important carbon sources for microbial growth and reproduction. At 15 ℃ and 25 ℃, N was the limiting factor for soil respiration during the early incubation stage and C was the limiting factor for the later stage; at 35 ℃, N was the limiting factor of soil respiration throughout the incubation. At 15 ℃ and 35 ℃, there was no P limitation for soil respiration; however, P was a limiting factor for soil respiration during the early incubation stage at 25 ℃. The results of this study demonstrated that the key to limiting soil carbon emissions is to retard soil microbial respiration, with extracellular enzymes significantly influencing soil microbial respiration. 参考文献 相似文献 引证文献

The fate of calcium in temperate forest soils: a Ca K-edge XANES study

Calcium (Ca) plays a crucial role for plant nutrition, soil aggregation, and soil organic matter (SOM) stabilization. Turnover and ecological functions of Ca in soils depend on soil Ca speciation. For the first time, we used synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy at the Ca K-edge (4038 eV) to investigate Ca speciation in soils. We present Ca K-edge XANES spectra of standard compounds with relevance in soils (e.g. calcite, dolomite, hydroxyapatite, anorthite, clay mineral-adsorbed Ca; Ca oxalate, formate, acetate, citrate, pectate, phytate). Calcium XANES spectra with good signal-to-noise ratios were acquired in fluorescence mode for Ca concentrations between 1 and 10 mg g−1. Most standard spectra differed markedly among each other, allowing the identification of different Ca species in soils and other environmental samples as well as Ca speciation by linear combination fitting. Calcium XANES spectra obtained for samples from different horizons of twelve temperate forest soils revealed a change from dominating lithogenic Ca to clay mineral-bound and/or organically bound Ca with advancing pedogenesis. O layer Ca was almost exclusively organically bound. With increasing SOM decomposition, shares of oxalate-bound Ca decreased. Oxalate-bound Ca was absent in calcareous, but not in silicate subsoil horizons, which can be explained by microbial decomposition in the former vs. stabilization by association to pedogenic minerals in the latter soils. Synchrotron-based Ca XANES spectroscopy is a promising novel tool to investigate the fate of Ca during pedogenesis and—when performed with high spatial resolution (µ-XANES), to study aggregation and SOM stabilization mechanisms produced by Ca.

Organic nitrogen addition causes decoupling of microbial nitrogen cycles by stimulating gross nitrogen transformation in a temperate forest soil

External inorganic and organic nitrogen (N) inputs can contrastingly affect the transformation and availability of N in forest soils. Studies have mainly focused on the effects of inorganic N enrichment, whereas little is known about the effects of organic N input on soil gross N transformation and the underlying microbial mechanisms. Here we conducted a laboratory 15N tracing study in a temperate needle-broadleaved mixed forest with a fertilization rate of 0, 20, 60, and 120 kg urea-N ha−1 yr−1 over three years. We investigated the key drivers of soil N transformation processes using a 15N tracing model in the context of selected soil chemical properties and microbial characteristics. Urea addition did not change soil gross N mineralization rates, while stimulating mineralization of labile organic N (MNlab). Urea addition at a rate of 120 kg N ha−1 yr−1 significantly increased autotrophic nitrification and gross nitrification rates by 88% and 96%, respectively. In contrast, all the three levels of urea addition significantly reduced gross microbial N immobilization by 28% to 52%, leading to an increase in the accumulation of soil NO3−-N in the top 10 cm soil layer by 38% to 88%. The changes in autotrophic nitrification were primarily driven by acid-tolerant ammonia-oxidizing archaea (AOA). Fungi were responsible for the change in heterotrophic nitrification under organic N enrichment. Gross N transformation rates were predominately regulated by AOA and fungal abundances as well as soil NO3−-N content under high level of organic N addition. The response of soil N transformation to exogenous organic N input depended on N addition level with the threshold rate being estimated to be 60–120 kg N ha−1 yr−1. All lines of evidence showed that the temperate needle-broadleaved mixed forest is moving towards an opener microbial N cycle under elevated organic N deposition. Our finding suggests that the effect of organic N input on soil gross N transformation is different from that of inorganic N input, which should be considered in ecosystem process models.

Carbon Isotope Measurements to Determine the Turnover of Soil Organic Matter Fractions in a Temperate Forest Soil

Soil organic matter (SOM) is a combination of materials having different origin and with different stabilization and decomposition processes. To determine the different SOM pools and their turnover rates, a silt loam-textured Luvisol from West Hungary was taken from the 0–20 cm soil depth and incubated for 163 days. Maize residues were added to the soil in order to obtain natural 13C enrichment. Four different SOM fractions—particulate organic matter (POM), sand and stable aggregate (S + A), silt- plus clay-sized (s + c) and chemically resistant soil organic carbon (rSOC) fractions—were separated and analyzed using FT-IR, δ13C, and 14C measurements. The mean residence time (MRT) of the new C and the proportion of maize-derived C in the fractions were calculated. The POM fraction was found to be the most labile C pool, as shown by the easily decomposable chemical structures (e.g., aliphatic, O-alkyl, and polysaccharides), the highest proportion (11.7 ± 2.5%) of maize-derived C, and an MRT of 3.6 years. The results revealed that the most stable fraction was the rSOC fraction which had the smallest proportion of maize-derived C (0.18 ± 2.5%) and the highest MRT (250 years), while it was the only fraction with a negative value of Δ14C (−75.0 ± 2.4‰). Overall, the study confirmed the hypothesis that the SOM associated with finer-sized soil particles decomposes the least, highlighting the significance of the fractionation process for more accurate determination of the decomposition processes of SOM pools.

Divergent drivers of the microbial methane sink in temperate forest and grassland soils.

Aerated topsoils are important sinks for atmospheric methane (CH4 ) via oxidation by CH4 -oxidizing bacteria (MOB). However, intensified management of grasslands and forests may reduce the CH4 sink capacity of soils. We investigated the influence of grassland land-use intensity (150 sites) and forest management type (149 sites) on potential atmospheric CH4 oxidation rates (PMORs) and the abundance and diversity of MOB (with qPCR) in topsoils of three temperate regions in Germany. PMORs measurements in microcosms under defined conditions yielded approximately twice as much CH4 oxidation in forest than in grassland soils. High land-use intensity of grasslands had a negative effect on PMORs (-40%) in almost all regions and fertilization was the predominant factor of grassland land-use intensity leading to PMOR reduction by 20%. In contrast, forest management did not affect PMORs in forest soils. Upland soil cluster (USC)-α was the dominant group of MOBs in the forests. In contrast, USC-γ was absent in more than half of the forest soils but present in almost all grassland soils. USC-α abundance had a direct positive effect on PMOR in forest, while in grasslands USC-α and USC-γ abundance affected PMOR positively with a more pronounced contribution of USC-γ than USC-α. Soil bulk density negatively influenced PMOR in both forests and grasslands. We further found that the response of the PMORs to pH, soil texture, soil water holding capacity and organic carbon and nitrogen content differ between temperate forest and grassland soils. pH had no direct effects on PMOR, but indirect ones via the MOB abundances, showing a negative effect on USC-α, and a positive on USC-γ abundance. We conclude that reduction in grassland land-use intensity and afforestation has the potential to increase the CH4 sink function of soils and that different parameters determine the microbial methane sink in forest and grassland soils.

Effects of soil organism interactions and temperature on carbon use efficiency in three different forest soils

Microbial carbon use efficiency (CUE) affects the soil C cycle to a great extent, but how soil organisms and the abiotic environment combine to influence CUE at a regional scale remains poorly understood. In the current study, microcosms were used to investigate how microbial respiration, biomass, and CUE responded to biotic and abiotic factors in natural tropical, subtropical, and temperate forests. Soil samples from the forests were collected, sterilized, and populated with one or a combination of three types of soil organisms (the fungus Botrytis cinerea, the bacterium Escherichia coli, and the nematode Caenorhabditis elegans). The microcosms were then kept at the mean soil temperatures of the corresponding forests. Microbial respiration, biomass, and CUE were measured over one-month incubation period. The results showed that microbial biomass and CUE were significantly higher, but microbial respiration lower in the subtropical and temperate forest soils than in tropical forest soil. Biotic factors mainly affected CUE by their effect on microbial biomass, while temperature affected CUE by altering respiration. Our results indicate that temperature regulates the interactive effects of soil organisms on microbial biomass, respiration, and CUE, which would provide a basis for understanding the soil C cycle in forest ecosystems.

Enzymes, Manganese, or Iron? Drivers of Oxidative Organic Matter Decomposition in Soils.

Oxidative decomposition of soil organic matter determines the proportion of carbon that is either stored or emitted to the atmosphere as CO2. Full conversion of organic matter to CO2 requires oxidative mechanisms that depolymerize complex molecules into smaller, soluble monomers that can be respired by microbes. Current models attribute oxidative depolymerization largely to the activity of extracellular enzymes. Here we show that reactive manganese (Mn) and iron (Fe) intermediates, rather than other measured soil characteristics, best predict oxidative activity in temperate forest soils. Combining bioassays, spectroscopy, and wet-chemical analysis, we found that oxidative activity in surface litters was most significantly correlated to the abundance of reactive Mn(III) species. In contrast, oxidative activity in underlying mineral soils was most significantly correlated to the abundance of reactive Fe(II/III) species. Positive controls showed that both Mn(III) and Fe(II/III) species are equally potent in generating oxidative activity, but imply conventional bioassays have a systematic bias toward Fe. Combined, our results highlight the coupled biotic-abiotic nature of oxidative mechanisms, with Mn-mediated oxidation dominating within Mn-rich organic soils and Fe-mediated oxidation dominating Fe-rich mineral soils. These findings suggest microbes rely on different oxidative strategies depending on the relative availability of Fe and Mn in a given soil environment.

Fungal Community, Not Substrate Quality, Drives Soil Microbial Function in Northeastern U.S. Temperate Forests

Mycorrhizal fungi can affect soil organic matter cycling through several mechanisms including priming, nutrient competition, and direct enzyme production. Differences in nutrient foraging strategies between ectomycorrhizal (EcM) and arbuscular mycorrhizal (AM) fungi produce divergent belowground dynamics: where EcM can take up organic nitrogen and directly break down soil organic matter (SOM) by producing enzymes, AM fungi are limited to scavenging mineral N. EcM-associated tree species also have leaf litter with relatively higher ratios of carbon to nitrogen (C:N), and belowground saprotrophic communities more dominated by fungi. Consequently, free-living microbes in EcM-dominated soils should experience nitrogen limitation, with subsequent increases in enzyme production and decreased carbon use efficiency (CUE). However, the relative importance of the effects of substrate quality and fungal community composition on enzyme production and CUE are unclear. To assess this distinction, we sampled the organic horizon and 10 cm of the mineral horizon in northern temperate forest soils along a gradient of EcM dominance. We characterized fungal community composition by measuring EcM relative abundances from extracted fungal DNA and the fungal to bacterial (F:B) ratios from phospholipid fatty acid (PLFA) analysis. We assessed soil substrate quality as the soil C:N ratio. Soil microbial functions were measured as potential activities of five hydrolytic and two oxidative enzymes, and microbial CUE. We found that the fungal community, represented by either the F:B ratio, EcM relative abundance, or both, affected CUE and six measured enzyme activities, while the C:N ratio affected only oxidative and chitin-targeting extracellular enzyme activities. Our results highlight the use of EcM relative dominance as a predictor of soil microbial community composition and function independent of substrate quality.

Microbial solubilization of silicon and phosphorus from bedrock in relation to abundance of phosphorus-solubilizing bacteria in temperate forest soils

Biogeochemical weathering of bedrock is the most important input of silicon (Si) and phosphorus (P) to forest ecosystems. While soil microbes, and in particular P-solubilizing bacteria (PSB), are known to accelerate the solubilization of Si and P from silicate rocks, our understanding of the mechanisms driving biogenic weathering are still limited. To fill this gap, incubation experiments with weathered parent materials (i.e. basalt, andesite and paragneiss) of four soils and water extracts of the four soils, differing in P stocks, were conducted. We found that the net Si solubilization rate ranged from 5.0 (±1.8) to 91.0 (±2.4) nmol m−2 d−1 across all examined soils. The silicate dissolution rates were negatively related to the decrease in pH (ΔpH) and positively related to the amounts of organic acids released by microbes. We found that the gross P solubilization rates from the parent materials were ~11 times higher at the P-rich site (BBR) compared to the P-poor site (CON). In addition, we determined the abundance and the taxonomic composition of PSB communities in the four soils. The abundance of PSB ranged from 2% at the P-rich site to 22.1% at the P-poor site, indicating that a selective pressure exists in P-poor soils towards a higher abundance of P-solubilizers. Yet, despite the relative high abundance of PSB, the gross P solubilization rates were low in the soils derived from P-poor parent material. The genus Pseudomonas was found only in the PSB community at the P-poor site. Burkholderiales and Bacillales together were by far the two most abundant orders among the PSB communities in all soils and depths. In conclusion, this study shows that PSB are more abundant in P-poor soil than in P-rich soil, while the weathering rate seems to be mostly dependent on the bedrock.

Genome Sequences of Frankineae sp. Strain MT45 and Jatrophihabitans sp. Strain GAS493, Two Actinobacteria Isolated from Forest Soil.

Frankiaceae are bacterial endosymbionts that are also found free-living in soil. Here, we present the genome sequences of two novel bacterial members of the order Frankiales, class Actinobacteria, isolated from temperate terrestrial forest soils. The genomes for MT45 and GAS493 indicate a genetic capacity for carbohydrate degradation but not nitrogen fixation.

Impactos del manejo forestal sobre las propiedades de los suelos: un tema de investigación fundamental para México

Introducción: El incremento en la intensidad de cosecha de madera influye negativamente en las funciones ecosistémicas de los suelos en los bosques templados y boreales.Objetivo: Conocer los impactos de los métodos de manejo forestal intensivos y extensivos sobre las propiedades físicas, químicas y biológicas de los suelos, y sus consecuencias en los procesos de disponibilidad y estabilización de nutrientes en los bosques templados y boreales.Resultados y discusión: Los métodos de manejo forestal intensivo pueden generar mayor desequilibrio en los procesos de disponibilidad y estabilización de nutrientes, comparados con los métodos selectivos. El impacto se refleja en el deterioro de la estructura del suelo y en la disminución de reservas de nutrientes y comunidades microbianas. Estos daños afectan la fertilidad y el funcionamiento del suelo, disminuyendo la productividad a largo plazo. Las afectaciones dependen de la intensidad de biomasa extraída, condiciones ambientales y preparación del sitio. Lo anterior hace evidente la necesidad del monitoreo del manejo forestal y su impacto en la ecología del suelo en los bosques templados, que mantenga la productividad a largo plazo y garantice la disponibilidad de los volúmenes de madera.Conclusión: En México, el impacto del manejo forestal ha sido escasamente analizado y es indispensable comprender los cambios funcionales de los procesos que determinan la fertilidad del suelo y la productividad de los bosques.

Effects of Nitrogen Deposition on Nitrogen-Mineralizing Enzyme Activity and Soil Microbial Community Structure in a Korean Pine Plantation.

To predict the effects of nitrogen deposition on nitrogen-mineralizing enzyme activity and soil microbial community structure in artificial temperate forests in northern China, we studied the soil properties, nitrogen-mineralizing enzyme activity, and microbial community structure in the soil of a Korean pine plantation in which different concentrations (0, 20, 40, 80 kg N ha-1 year-1) of ammonium nitrate were applied for 5 consecutive years. The results showed that nitrogen addition at different concentrations did not significantly affect the soil pH. High nitrogen addition (80 kg N ha-1 year-1) significantly increased the soil organic matter, ammonium nitrogen, and nitrate nitrogen content in the Korean pine plantation, and ammonium nitrogen was the key factor that influenced the soil fungal community structure. The urease activity under the moderate nitrogen addition treatment (40 kg N ha-1 year-1) was significantly lower than that under the control (0 kg N ha-1 year-1), and the protease activity in the three treatments was also significantly lower than that in the control. There was no significant correlation between microbial community structure and the four mineralizing enzymes. After nitrogen addition at different concentrations, the Simpson and Shannon indexes of soil bacteria decreased significantly under low nitrogen addition (20 kg N ha-1 year-1), but the α-diversity index of soil fungi did not show significant differences under nitrogen addition. The microbial community composition was significantly changed by the different treatments. PLS-DA analysis showed that Tardiphaga was an important genus that made the greatest contribution to the differences in bacterial community composition among treatments, as was Taeniolella for fungal community composition. The low level of nitrogen addition inhibited nitrogen mineralization in the Korean pine plantation by reducing the relative abundances of Nitrosomonadaceae and Betaproteobacteriales and by reducing the abundances of symbiotrophic fungi. Berkelbacteria and Polyporales were bacteria and fungi, respectively, that changed significantly under the high nitrogen addition treatment (80 kg N ha-1 year-1). This study provides more data to support predictions of the changes in nitrogen-mineralizing enzyme activity and microbial community structure in artificial temperate forest soils in response to increased nitrogen deposition.

Seasonality is more important than forest type in regulating the pool size and composition of soil soluble N in temperate forests

Soil soluble nitrogen (N) is crucial to the N nutrition and productivity of plants. Consequently, understanding the factors that affect its pool size and composition is of considerable importance. Here, six typical forest types in northeast China were investigated to determine the dynamics of soil soluble N across seasons and plant communities, and the potential drivers. Soil free amino acids, NH4+, NO3−, dissolved organic N (DON) and a variety of soil characteristics were measured over the growing season (from May to September). Seasonality showed a stronger effect on the availability of soil inorganic N and free amino acids than vegetation. The coefficients of variation of soil inorganic N, amino acid-N and the potential drivers (moisture and DON) appeared to be greater for season, and the concentrations of these available N sources tended to be higher at the beginning than at the height of growing season. Potential soil drivers (e.g. moisture, microbial biomass-N and DON) and plant phenology together drove the seasonal dynamics of inorganic N and amino acid-N. Arginine, histidine, serine, leucine, aspartic acid, glycine, glutamic acid and proline composed the dominant soil amino acid pool in the temperate forest soils. The basic amino acids (arginine and histidine) were consistently dominant irrespective of vegetation and season, suggesting that selective sorption by the soil solid phase could play an important role in regulating the cycling of amino acid-N in these temperate forest ecosystems. This research indicates that changes in local soil properties, and plant phenology caused by seasonality, exert a powerful influence on the characteristics of plant-soil N cycling.