Coniferous Forest Soils Research Articles

Dark CO2 fixation in temperate beech and pine forest soils

Soils are the largest terrestrial organic carbon pool and the largest terrestrial source of atmospheric CO2. Non-phototrophic CO2 fixation by microbes re-fixes and recycles CO2 respired in soils. Our previous study showed that in temperate deciduous forest soil profiles, rates of dark CO2 fixation were proportional to microbial biomass, irrespective of soil depth. However, the amount and quality of organic matter entering different soil depths vary for different temperate forest types and these influence microbial communities with unknown consequences for CO2 fixation rates. To test whether differences in the amount and quality of SOC caused by tree species affect dark CO2 fixation rates with depth, we conducted a study using acidic soils from two forest plots from the Schorfheide-Chorin Exploratory, Germany. These soils, dominated by either beech (deciduous) or pine (coniferous) tree stands differ in their SOC content and quality. We traced the incorporation of 2% (v:v) 13C–CO2 label into microbial biomass and estimated the CO2 fixation rates relative to microbial biomass carbon content (in μg C g MBC−1 d−1) across the soil profiles. The rates of dark CO2 fixation per g MBC were similar across the beech soil profiles, but significantly lower in the pine soils at the B2 and BC horizons, suggesting that while dark CO2 fixation rates are linked to MBC in deciduous forest soils, other factors influence dark CO2 fixation rates in coniferous forest soils. The pine subsoils had low SOC content and quality, with a microbial community enriched with heterotrophic fermenters like Chloroflexi that are predicted to have a lower potential for heterotrophic CO2 fixation compared to the other dominant bacteria phyla. In contrast, the beech soil profiles, characterized by higher SOC inputs, featured higher fractions of copiotrophs like Proteobacteria, Acidobacteria, and Actinobacteria predicted to have high heterotrophic CO2 fixation potential. We thus speculate that in contrast to the beech soils, lower SOC inputs in the pine subsoils affected the community composition, leading to lower CO2 fixation rates. We further made comparisons to soils dominated by mixed deciduous trees and featuring a higher MBC and SOC content. Over this range of temperate forest soils, CO2 fixation rates were highest in the mixed deciduous forest soils, with MBC and Shannon index (used as a proxy parameter for community composition) showing the strongest correlations with the varying CO2 fixation rates. Our study suggests that predictions of dark CO2 fixation rates need to consider tree-species specific or site-specific conditions, as these may alter root carbon inputs and affect microbial community composition and their metabolic CO2 fixation potentials in soil.

Terpenes and fungal biomass in the nest mounds of Formica aquilonia wood ants

Nest mounds of wood ants of the Formica rufa group are built using conifer needles, small branches, other plant materials and soil. Conifer needles contain several mono and sesquiterpenes. Thus, wood ant nests may act as terpene hotspots in conifer forest soils. Some of the terpenes show antifungal activity and may thus cause small-scale heterogeneity in fungal biomass. We compared terpene concentrations and fungal biomass (ergosterol concentration) of nest material of the wood ant Formica aquilonia from the top, core and basement of 14 nest mounds in eastern Finland. Overall, α-pinene, camphene, sabinene, β-pinene, myrcene, limonene, camphor and longifolene were detected the most and were commonly present in all the studied layers. We found that terpene concentrations differed between the sampled nest material layers, being generally highest in the core of the nest and lowest at the basement of the nest. There was no association between the terpene concentration and material moisture. Fungal biomass was highest in the top layer, intermediate in core and lowest in basement; however, it was not negatively associated with terpene concentrations. Fungal biomass in nest mounds was positively associated with moisture and alkalinity. Nest mounds of Formica rufa group wood ants are complex structures with different chemical and microbial properties among its layers.

Low-intensity frequent fires in coniferous forests transform soil organic matter in ways that may offset ecosystem carbon losses.

The impact of shifting disturbance regimes on soil carbon (C) storage is a key uncertainty in global change research. Wildfires in coniferous forests are becoming more frequent in many regions, potentially causing large C emissions. Repeated low-intensity prescribed fires can mitigate wildfire severity, but repeated combustion may decrease soil C unless compensatory responses stabilize soil organic matter. Here, we tested how 30years of decadal prescribed burning affected C and nitrogen (N) in plants, detritus, and soils in coniferous forests in the Sierra Nevada mountains, USA. Tree basal area and litter stocks were resilient to fire, but fire reduced forest floor C by 77% (-36.4 Mg C/ha). In mineral soils, fire reduced C that was free from minerals by 41% (-4.4 Mg C/ha) but not C associated with minerals, and only in depths ≤ 5cm. Fire also transformed the properties of remaining mineral soil organic matter by increasing the proportion of C in a pyrogenic form (from 3.2% to 7.5%) and associated with minerals (from 46% to 58%), suggesting the remaining soil C is more resistant to decomposition. Laboratory assays illustrated that fire reduced microbial CO2 respiration rates by 55% and the activity of eight extracellular enzymes that degrade cellulosic and aromatic compounds by 40-66%. Lower decomposition was correlated with lower inorganic N (-49%), especially ammonium, suggesting N availability is coupled with decomposition. The relative increase in forms of soil organic matter that are resistant to decay or stabilized onto mineral surfaces, and the associated decline in decomposition suggest that low-intensity fires may promote mineral soil C storage in pools with long mean residence times in coniferous forests.

Different climate sensitivity of particulate and mineral-associated soil organic matter

Soil carbon sequestration is seen as an effective means to draw down atmospheric CO2, but at the same time warming may accelerate the loss of extant soil carbon, so an accurate estimation of soil carbon stocks and their vulnerability to climate change is required. Here we demonstrate how separating soil carbon into particulate and mineral-associated organic matter (POM and MAOM, respectively) aids in the understanding of its vulnerability to climate change and identification of carbon sequestration strategies. By coupling European-wide databases with soil organic matter physical fractionation, we assessed the current geographical distribution of mineral topsoil carbon in POM and MAOM by land cover using a machine-learning approach. Further, using observed climate relationships, we projected the vulnerability of carbon in POM and MAOM to future climate change. Arable and coniferous forest soils contain the largest and most vulnerable carbon stocks when cumulated at the European scale. Although we show a lower carbon loss from mineral topsoils with climate change (2.5 ± 1.2 PgC by 2080) than those in some previous predictions, we urge the implementation of coniferous forest management practices that increase plant inputs to soils to offset POM losses, and the adoption of best management practices to avert the loss of and to build up both POM and MAOM in arable soils. Particulate and mineral-associated soil organic carbon have different climate sensitivity and distributions in Europe, according to analyses of measurements of soil carbon fractions from 352 topsoils.

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.

Soil bacterial communities at the treeline in subtropical alpine areas

As a temperature-sensitive transition zone, the subtropical alpine region responds quickly to global warming. However, little is known about soil microbial communities at the treeline, where changes in vegetation in response to global warming are anticipated. Barcoded pyrosequencing of the 16S rRNA gene was used to investigate the bacterial communities of coniferous forest and grassland soils at the treeline of four different peaks above 3,000 m a.s.l. Although the forest soils were more acidic than the grassland soils, the other soil properties were highly variable with no consistent pattern in C and N contents and microbial biomass between two vegetation types. The Acidobacteria and α-Proteobacteria were the most abundant phylogenetic groups, although their relative abundances differed among the forest and grassland soil communities and between sites. The composition of bacterial communities or β-diversity, varied significantly between the sites and vegetation types. In contrast, α-diversity only differed significantly between sites. Two of the grassland sites and one forest had converted from forests and grassland, respectively within the last 60 years. The abundances of some genera, such as Acidobacteria Gp2 in the grasslands converted from forests, more closely resembled those of the other forest sites than the historically grassland sites, while the abundance of Acidobacteria Gp1 in the forest converted from grassland was more similar to the historically grassland sites. These results suggest a legacy effect for the transition of forest to grassland. Bacterial community structure also correlated significantly with soil pH, organic C and C/N. These results suggest that the present vegetation at the treeline influences soil bacterial community structure, although there is also a significant legacy effect on the abundance of certain bacterial groups.

Effect of Rock Fragments on Tracer Transport in Broadleaved and Coniferous Forest Soils: Column Study

This study investigated the effect of rock fragments on tracer transport in broadleaved and coniferous forest soils from the 0 - 100 cm depth of Gongga Mountain in eastern margin of Qinghai Tibetan Plateau. Using repacked soil columns (20 cm in height and 10 cm in diameter) with different rock fragments contents (0%, 5%, and 15% in v/v), breakthrough curves of bromide (as non-reactive tracer) were obtained under saturated condition. A two-region model was applied and the parameters were estimated by inverse modeling. Results show that with increasing rock fragment content the dispersivity (λ) generally increased while the mobile-immobile partition coefficient (β) and the mass transfer coefficient (ω) decreased. The presence of rock fragments led to an increase in the fraction of immobile domain as well as soil tortuosity. A plausible explanation is that the soil beneath the rock fragments behaved as immobile domain and soil-rock interfaces could serve as preferential flow paths.

Chemical speciation of mercury, sulfur and iron in a dystrophic boreal lake sediment, as controlled by the formation of mackinawite and framboidal pyrite

The chemical speciation of mercury (Hg), methyl mercury (MeHg), sulfur and iron was investigated in the sediment and porewater of Lake Ängessjön, a boreal, shallow (maximum depth 2.5 m), oligo-/dystrophic lake in northern Sweden. The lake receives terrestrial stream runoff from surrounding coniferous forest soils and peatlands having a low pH (4.6) and high concentrations of dissolved organic matter (DOM, annual average: 45 mg L−1), Fe (60 µM), sulfate (105 µM), inorganic Hg (1200 pM) and MeHg (250 pM). Sulfur K-edge XANES and Hg LIII-edge EXAFS spectroscopic measurements were used to characterize and quantify the sulfur speciation in the lake sediment at nine occasions, covering different seasons in the years of 2007 and 2009. In the surface sediment (0–3 cm) sulfate is reduced to zero-valent S and inorganic sulfide, that in turn reacts with Fe to form FeSm (mackinawite) and FeS2 (framboidal pyrite). The latter mineral becomes increasingly dominant by depth in the sediment. Thermodynamic modeling successfully predicted measured porewater concentrations of Hg in the sediment. Metacinnabar (β-HgS) and Hg(NOM-RS)2 complexes (the latter formed as a reaction between Hg(II) and thiol groups associated with natural organic matter, NOM-RSH) were the dominant forms of Hg(II) in the solid phase of sediments and Hg(II)-polysulfides (aq) dominated in the porewater. We argue that FeSm is a key component that indirectly controlled the Hg(II) speciation in the sediment by keeping the aqueous phase concentration of inorganic sulfide in the 0.5–2 µM range throughout the year. Besides providing a pool of readily soluble inorganic sulfide for formation of β-HgS(s), as demonstrated by previously reported EXAFS experiments, we further suggest FeSm may serve as a precursor for the formation of a more crystalline (less soluble) β-HgS(s) phase than present in environments devoid of FeSm. Support for this was provided by comparing our results with previously reported thermodynamic modelling results of Hg(II) and MeHg solubility in organic soils devoid of FeSm. In more general terms, we suggest the presence or absence of FeSm, through its influence on the chemical speciation of Hg and MeHg, may be a key factor behind the variability in rates of Hg(II) and MeHg transformation processes, such as methylation, reduction and demethylation, reported for different environmental settings.

Radiocesium concentrations in invertebrates and their environmental media at two distances from the Fukushima Dai-ichi Nuclear Power Plant during 3–6 years after the 2011 accident

Activity concentrations of the radioactive cesium (134Cs and 137Cs) were investigated in invertebrates at two sites of moderately high and higher air radiation dose rates, 14 km and 11 km distances, respectively, from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) from 2013 to 2016. At a14-km point, the 134+137Cs concentrations of soils in coniferous and broadleaf forests increased from 2013 to 2014, and thereafter declined until 2016. The 134+137Cs concentrations of the phytophagous beetle Anomala cuprea (Hope) rapidly decreased by 76.1% from 2013 to 2014, reflecting reduction in those of broadleaves. The 134+137Cs concentration levels of the carnivorous beetle Dolichus halensis (Schaller) showed a relatively low levels. The 137Cs concentrations of the necrophagous beetle Eusilpha japonica (Motshulsky) and coprophagous beetle Onthophagus lenzii (Harold) remained constant without reduction from 2013 to 2016. Average 134+137Cs concentrations throughout four years were the highest in the geophagous crustacean (Armadillidium vulgare Latreille), followed by necrophagous beetle and coprophagus beetle. The 134+137Cs concentrations in earthworms with gut contents were significantly correlated with those in soils at each habitat from 2014 to 2015 at a14-km point, and the concentration levels at an 11-km point in 2015 were remarkably high (898 kBq kg−1). Transfer factors (TFs) in earthworms ranged from 1.02 to 2.66 at a 14-km point and 0.66 to 5.0 at an11-km point. The transfer and chronological changes of radiocesium in invertebrates were discussed in relation to food habits through trophic levels in woodlands and pasturelands.

Effects of Different Forest Vegetation Types on Soil Nitrogen-Related Microbial Communities and Functions in Jinyun Mountain

To clarify the response of a nitrogen-related microbial community and function to different vegetation types in subtropical forest, soil samples were collected for analysis from the topsoil of five vegetation types in the Jinyun Mountain National Nature Reserve, i.e., coniferous forest, broadleaf forest, mixed broadleaf-coniferous forest, P. pubescen forest, and grassland. To analyze the microbial abundance, community, and function discrepancy between different vegetation soils, multiple molecular techniques, such as terminal restriction fragment length polymorphism (T-RFLP) and quantitative polymerase chain reaction (qPCR) analysis, and nitrogen-related microbial enzyme activity procedures were used. The results showed:① The denitrifying enzyme activity was much higher than nitrifying potential in Jinyun Mountain National Nature Reserve, and the two enzyme activities were much lower in coniferous forest soil than in the other vegetation soils (P<0.05). In addition, dissolved organic carbon, soil water content, and total nitrogen were the key environmental factors controlling enzyme activity. ② The qPCR data showed that the abundance of nitrogen-related microbes was highest in P. pubescen forest, whereas it was lowest in coniferous forest. The abundances of the three nitrogen-related microbes were all significantly correlated with dissolved organic carbon, total nitrogen, available nitrogen, total potassium, and available potassium (P<0.01). ③ Based on T-RFLP data, the α-diversity of nitrogen-related microbes was highest in broadleaf forest, whereas it was lowest in P. pubescen forest. Principal co-ordinates analysis (PCoA) showed that the community structure of ammonia-oxidizing archaea responded significantly to different vegetations, and the community structure of nitrogen-related microbes showed the most difference in coniferous forest. In addition, distance-based redundancy analysis (db-RDA) showed that the community structure of nitrogen-related microbes was mainly shaped by dissolved organic carbon (P<0.001), available nitrogen (P<0.002), and soil water content (P<0.001). ④ Soil-denitrifying enzyme activity was mainly affected by the abundance of nirS-denitrifiers, ammonia-oxidizing archaea, and the community structure of nitrogen-related microbes, whereas nitrifying potential was only controlled by the abundance of ammonia-oxidizing archaea. Above all, subtropical forest vegetation significantly affects the abundance and community structure of soil nitrogen-related microbes, thereby changing their function of controlling the soil nitrogen cycle. This study can provide basic data for the coupling mechanism between soil microbes and N2O release in subtropical forests in China.

Decoupling of protein depolymerization and ammonification in nitrogen mineralization of acidic forest soils

Soil nitrogen (N) mineralization is generally limited by amino acid production by proteases (depolymerization). Protease activities can be stimulated under N limitation, but it cannot directly increase microbial N release (ammonification) in temperate forest soils. To analyze factors determining rate-limiting steps of soil N mineralization, we compared microbial potentials of depolymerization and ammonification by measuring casein degradation and arginine ammonification rates in casein- or arginine-amended and control soils, respectively. The microbial potentials of casein depolymerization were positively correlated with soil carbon (C)/N ratios, whereas arginine ammonification exhibited the opposite pattern. The soil N mineralization was limited by depolymerization in N-rich broad-leaved forest and cropland soils, while N mineralization could be limited by the low microbial potentials of ammonification for microbial N conservation in coniferous forest soils with C/N ratios > 20. Due to the increased depolymerization and microbial N conservation under N limitation, ammonification as well as depolymerization can be a rate-limiting step of N mineralization in fungi-dominated acidic forest soils. Contrasting responses of depolymerization and ammonification to N limitation and low pH can induce a shift in rate-limiting steps in soil N mineralization.

Iron(III) fate after complexation with soil organic matter in fine silt and clay fractions: An EXAFS spectroscopic approach

Iron (Fe) speciation in soils is highly dependent on environmental conditions, mineralogy, and chemical interactions with soil organic matter (SOM). The fine silt and clay (FSi + Cl) particle size fraction of soils constitutes a primary organo-mineral fraction and contains SOM with long turnover time. In this study, the FSi + Cl particle size fractions isolated from a coniferous forest, a grassland, a technosol, and an agricultural soil were reacted with Fe(III) at pH 7. Unreacted and reacted samples were then investigated by means of extended X-ray absorption fine structure (EXAFS) spectroscopy. Statistical methods were used to determine goodness-of-fit parameters for linear combination fitting (LCF) and wavelet transformation (WT) of the Fe K-edge EXAFS data. WT separated spectral contributions from different backscattering atoms in higher coordination shells located at similar interatomic distances from the central absorbing Fe atom. LCF results paired with WT showed that the FSi + Cl particle size fractions consisted of a mixture of Fe phyllosilicates, Fe (hydr)oxides, and organically complexed Fe in different proportions. Our research revealed that after sorption experiments, in which Fe(III) was added to the system, increasing amounts of Fe(III)-SOM complexes were found in the solid phase of grassland and agricultural soils, whereas the precipitation of Fe(III) led to the preferential formation of ferrihydrite in the coniferous forest soil and in the technosol. Although the quantitative Fe-mediated organic carbon stabilization effect after Fe(III) addition is shown in this work, Fe speciation is not clearly related to SOM amount or quality (i.e., carbon-to-nitrogen ratio). The variation of Fe chemical speciation among the soil fractions likely translates into differences in their environmental fate.

Influence of Soil Characteristics and Land Use Type on Existing Fractions of Radioactive 137Cs in Fukushima Soils

Radioactive cesium (137Cs) in distinct soil fractions provides key information to its bioavailability, and therefore determining the effect of soil characteristics and land use types on existing fractions of 137Cs in soils is important for predicting future 137Cs mobility in Fukushima. Thus, the objective of this study was to investigate the influence of soil characteristics and land use types on sequentially extracted fractions of 137Cs in Fukushima. In this study, five coniferous forest soils, eight arable soils, and eight paddy rice soils were sampled in 2012 and 2013. The 137Cs in the soils were separated into four fractions; water-soluble, exchangeable, organic matter-bound and residual fractions. More than 90% of the soil 137Cs fraction for arable and paddy rice soils was found in the residual fraction, implying significantly reduced bioavailable 137Cs with higher fixation. In contrast, forest soils measured higher exchangeable and organic matter-bound fractions of 5%–33% and 9%–44%, respectively, implying future 137Cs mobility in the forest ecosystem. Correlation analysis showed a significant negative correlation (p &lt; 0.05) between the organic matter fraction and residual fraction in both arable and paddy rice soils. There was a significant positive correlation (p &lt; 0.05) for both exchangeable and residual fractions with cation exchange capacity (CEC), total carbon (TC) and total nitrogen (TN) values in arable soils. Organic matter content influenced both exchangeable and residual fractions. It was not clear whether organic matter played a direct role in 137Cs fixation or mobility in the agricultural soils. In paddy rice soils, the organic matter fraction showed a significant negative correlation with TC and TN values. Soil pH was significantly negatively correlated (p &lt; 0.05) with both water-soluble and residual fractions in forest soils but positively (p &lt; 0.1) with the organically bound 137Cs fraction.

Organic matter decomposition and carbon content in soil fractions as affected by a gradient of labile carbon input to a temperate forest soil

Labile carbon (C) input to soils is expected to affect soil organic matter (SOM) decomposition and soil organic C (SOC) stocks in temperate coniferous forests. We hypothesized that the SOM decomposition rate, C content in soil fractions, and microbial and faunal abundance and activity were increased along the gradient in labile C input around wood ant nests. Three distances from the nest that differed in annual labile C input to soil were selected: 4 m with 6379 mg C m−2, 30 m with 9060 mg C m−2, and 70 m with 9215 mg C m−2. Soil from the organic horizon (Oe+Oa), surface mineral horizon (A), and subsoil mineral horizon (B) was analyzed for C content in soil fractions and for activity and abundance of soil microorganisms and fauna. In addition, a 1-year litter-bag and soil-bag decomposition experiment was conducted. Although the rate of soil decomposition did not differ along the labile C input gradient, the rate of litter decomposition in the B horizon increased as labile C input increased with distance from the nest. Correspondingly, the C content in bulk soil and in the labile and less-protected soil fractions in the B horizon decreased as labile C input increased. We infer that, because the O and A horizons are less C-limited than the B horizon, the changes in the labile C input along the gradient affected the B horizon more than the surface O and A horizons. However, soil microbial and faunal activity and abundances were not consistently affected by the gradient. Apparently, C stocks in soil fractions are more important for microbial and faunal communities than labile C inputs. Although the results indicate that SOC content changes very slowly in the coniferous forest soil of the current study, increases in the input of natural labile C leads to decreases in the SOC stock in the B horizon. By increasing the labile C input to temperate forest soils, future increases in atmospheric CO2 concentration may therefore lead to a significant loss of SOC in deep soil layers.

冻融循环对川西亚高山森林土壤酶活性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 冻融循环对川西亚高山森林土壤酶活性的影响 DOI: 10.5846/stxb201902250355 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项目（31700542）；重点实验室开放基金（四川省科技厅）（ESP1704） Effects of the freeze-thaw cycle on soil enzyme activities in a sub-alpine forest in western Sichuan 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:土壤酶活性的研究有助于认识植物-微生物-土壤有机质之间的相互关系，土壤酶的生产遵循"经济法则"，冻融循环将会改变生产土壤酶的资源分配，最终影响土壤的有机质分解过程。亚高山森林土壤具有明显的季节性冻融循环，为深入研究亚高山森林冬季土壤生态过程，以川西亚高山针阔混交林、针叶林以及阔叶林土壤为研究对象，通过室内培养研究冻融循环对6种与碳（C）、氮（N）、磷（P）相关土壤酶活性的影响。结果表明，与N和P相关的土壤β-N-乙酰葡萄糖苷酶、磷酸酶活性受冻融循环影响显著，其中，β-N-乙酰葡萄糖苷酶活性在整个冻融处理过程中表现出先升高后降低并趋于平稳的趋势，磷酸酶活性在后期明显增加。与C相关的土壤纤维素酶、β-葡萄糖苷酶、过氧化物酶、多酚氧化酶在冻融循环过程中没有显著变化。林型对土壤酶活性产生了显著影响。其中，阔叶林的土壤纤维素酶活性显著低于针叶林；阔叶林的土壤过氧化物酶活性显著低于针阔混交林和针叶林；针叶林的土壤磷酸酶活性显著高于针阔混交林和阔叶林。冻融循环和林型的交互作用对土壤酶活性没有显著影响。结果表明，该地区土壤酶活性对冻融循环响应存在差异，气候变化引起的冻融循环将进一步影响川西亚高山森林土壤生态系统的有机质分解过程。 Abstract:Research on soil enzyme activities is beneficial to identify relationships between plants, microbes, and soil organic matter. Freeze-thaw cycles will change resource allocations for the production of soil extracellular enzymes, which affects organic matter decomposition processes in the soil. Based on the pre-recognition of sub-alpine seasonal freeze-thaw cycles and considering typical coniferous-broadleaf mixed forest, coniferous forest, and broadleaf forest soil in the sub-alpine region of western Sichuan, we controlled the freeze-thaw environment and analyzed the effects of freeze-thaw cycles on enzyme activities in the soil, including carbon, nitrogen, and phosphorus. According to the results, the freeze-thaw cycles had a significant impact on β-N-acetylglucosidase and phosphatase activities associated with soil N and P. The activity of β-N-acetylglucosidase was elevated at the beginning of freeze-thaw period and then decreased with an increase in freeze-thaw frequency. The phosphatase activity increased significantly in the later portion of the freeze-thaw cycle. However, the freeze-thaw cycle had no significant effect on C-related soil enzyme activities. The changes in C-related soil enzyme activities in this study were more determined by litter decomposition processes and forest types. Among them, cellulase and β-glucosidase activities were significantly correlated with the decomposition process of organic matter. The limiting factors of peroxidase and polyphenol oxidase and low temperature and low oxygen were still present in this test, so the activities of these two enzymes did not change significantly. On the other hand, the effect of forest types on cellulase, peroxidase and phosphatase activities was significant. The soil cellulase activity of broadleaf forest was significantly lower than that of coniferous forest. The peroxidase activity of broadleaf forest soil was significantly lower than that of coniferous-broadleaf mixed forest and coniferous forest. The soil phosphatase activity of coniferous forest soil was significantly higher than that of coniferous-broadleaf mixed forest and broadleaf forest. Our results indicate that the effects of the freeze-thaw cycles on extracellular enzyme activities in the soil vary in this area. Freeze-thaw cycles that result from climate change will further influence the organic matter decomposition processes of the soil ecology system in the sub-alpine forest in western Sichuan. 参考文献 相似文献 引证文献

Temporal distribution of Fukushima-derived 137Cs in coniferous forest soil evaluated based on compartment-exponential model

Based on the compartment and exponential models, the distribution of Fukushima-derived 137Cs was evaluated at four sampling dates in undisturbed coniferous forest soil. The compartment model was employed to evaluate the dynamic of 137Cs in the three sub-sections of the forest floor (FF), namely undergrowth (UG), litter layer (OL), and fragmented litter layer (OF), while the exponential model was administrated to describe its distribution below the FF. According to the compartment model, the derived ecological half-life of 137Cs in the UG, OL, and OF layers was 0.97, 1.1, and 4.9 years, respectively, indicating 137Cs resides much longer in the OF layer. Hence, this soil section remains a potential source of radiation dose mainly due to its high 137Cs content associated with low attenuation effect. Below the OF layer, the 137Cs distribution was well described by exponential model and its derived relaxation lengths were in the range of 0.8-1.4 cm, implying the migration of 137Cs in mineral soil is very slow and almost intact during the observation time. Collectively, our results highlighted that the compartment model for the FF and the exponential model for the soil below the FF are adequate enough to generate essential information. Thus, the potential decontamination measures should have to be chosen on their effect on the FF's 137Cs. Graphical abstract.

Influence of Root Distribution on Preferential Flow in Deciduous and Coniferous Forest Soils

Root-induced channels are the primary controlling factors for rapid movement of water and solute in forest soils. To explore the effects of root distribution on preferential flow during rainfall events, deciduous (Quercus variabilis BI.) and coniferous forest (Platycladus orientalis (L.) Franco) sites were selected to conduct dual-tracer experiments (Brilliant Blue FCF and Bromide [Br−]). Each plot (1.30 × 1.30 m) was divided into two subplots (0.65 × 1.30 m), and two rainfall simulations (40 mm, large rainfall and 70 mm, extreme rainfall) were conducted in these. Vertical soil profiles (1.00 m × 0.40 m) were excavated, and preferential flow path features were quantified based on digital image analysis. Root (fine and coarse) abundance and Br− concentration were investigated for each soil profile. In deciduous forest, accumulated roots in the upper soil layer induce larger lateral preferential flow as compared to the coniferous forest soil during large rainfall events. Compared with deciduous forest, coniferous forest soil, with higher (horizontal and vertical) spatial variability of preferential flow paths, promotes higher percolation and solute leaching to deeper soil layers during extreme rainfall events. Fine roots, accounting for a larger proportion of total roots (compared to coarse roots), facilitate preferential flow in the 0–40 cm forest soil layer. Overall, our results indicate that the root distribution pattern of different tree species can exert diverse effects on preferential flow in forest soils.

Dosimetric depth distribution of Fukushima-derived 137Cs in coniferous forest soil

The ambient dose rate (ADR) in a coniferous forest floor contaminated by Fukushima-derived 137Cs was calculated for small temporal scale as a function of depth. The calculated total ADR was statistically evaluated along the soil vertical strata and among the sampling time series. Moreover, the contribution of the forest floor components to the total radiation dose were examined. Accordingly, the litter and fragmented organic layers accounted for about 58 to 96% (mean 77 ± 14%) of the ambient dose, indicating the organic layer is a chief sources of external radiation exposure, and an important radiological soil section.

Effects of Changing Temperature on Gross N Transformation Rates in Acidic Subtropical Forest Soils

Soil temperature change caused by global warming could affect microbial-mediated soil nitrogen (N) transformations. Gross N transformation rates can provide process-based information about abiotic–biotic relationships, but most previous studies have focused on net rates. This study aimed to investigate the responses of gross rates of soil N transformation to temperature change in a subtropical acidic coniferous forest soil. A 15N tracing experiment with a temperature gradient was carried out. The results showed that gross mineralization rate of the labile organic N pool significantly increased with increasing temperature from 5 °C to 45 °C, yet the mineralization rate of the recalcitrant organic N pool showed a smaller response. An exponential response function described well the relationship between the gross rates of total N mineralization and temperature. Compared with N mineralization, the functional relationship between gross NH4+ immobilization and temperature was not so distinct, resulting in an overall significant increase in net N mineralization at higher temperatures. Heterotrophic nitrification rates increased from 5 °C to 25 °C but declined at higher temperatures. By contrast, the rate of autotrophic nitrification was very low, responding only slightly to the range of temperature change in the most temperature treatments, except for that at 35 °C to 45 °C, when autotrophic nitrification rates were found to be significantly increased. Higher rates of NO3− immobilization than gross nitrification rates resulted in negative net nitrification rates that decreased with increasing temperature. Our results suggested that, with higher temperature, the availability of soil N produced from N mineralization would significantly increase, potentially promoting plant growth and stimulating microbial activity, and that the increased NO3− retention capacity may reduce the risk of leaching and denitrification losses in this studied subtropical acidic forest.

Fungal diversity in the brown coniferous forest soils of Daxing'anling Mountains, Northeast China

To explore the distribution of fungal community in soil of brown coniferous forest in Daxing'anling and its relationship with soil characteristics, soil fungal community structure and diversity in three forest types, light brown coniferous forest, grass brown coniferous forest, and typical brown coniferous forest, were analyzed by high-throughput sequencing technology. The relationship between soil fungal community and soil characteristics was analyzed by R and SPSS 17.0 software. The results showed that soil physical and chemical characteristics differed significantly across the three brown coniferous forests. A total of 111 species belonged to six phyla, 23 class, 46 orders, 74 families and 88 genera were recorded in this study. Ascomycetes and basidiomycetes were dominant phyla. There were significant differences in relative abundance of phyla among three forest types. There was no significant difference in the Ace and Chao1 diversity indices among three brown coniferous forests, whereas there were significant differences in the Shannon and Simpson indices. Results from canonical correlation analysis and correlation analysis showed that both α and β diversity were significantly correlated with soil moisture, soil pH, soil organic matter, soil total nitrogen, and soil total potassium. The results indicated that soil characteristics were important factors affecting soil fungal diversity of brown coniferous forest in Xing'an larch forest in Daxing'anling.