Total, hot water extractable, and oxidation-resistant carbon in sandy hydromorphic soils-analysis of a 220-year chronosequence

Soil organic carbon stocks decrease after conversion of soils from pasture to cropland. It has been assumed that this applies especially to mineral hydromorphic soils. In this paper we evaluate hot-water extractable carbon (C_hwe) as a measure for detecting long-term changes in the SOM following land use change. Furthermore, we assess whether a treatment of the soils with NaOCl leads to the isolation of long-term stable C fractions. For these purposes, we established a chronosequence of sandy hydromorphic soils that have been converted from pasture to cropland at different periods of history. To gain further insight into the impacts of different types of land use on carbon sequestration, soils under forest, either afforested or permanent, were studied. Bulk density, total organic carbon (TOC), C_hwe, and NaOCl-resistant C were quantified in the surface soils of 72 Gleyic Podzols and Haplic Gleysols. The bulk density increased from 0.9 (±0.2) g cm^?3 to 1.4 (±0.1) g cm^?3 during the first 25 years after the conversion of the soils from permanent pasture to cropland. In the permanent pasture sites, the TOC concentration amounted to 35.4 (±12.1) g kg^?1. It decreased to 12.88 (±5.9) g kg^?1 during the first 46 years of cultivation (R²?=?0.71). In the permanent forest soils the TOC concentrations were significantly higher than in the soils that have been afforested. C_hwe concentrations of the chronosequence sites were linearly correlated to the TOC concentrations (R²?=?0.84), while permanent forest sites exhibited significantly higher C_hwe/TOC ratios. This shows that the determination of the C_hwe is a very promising measure for detecting changes in SOM dynamics following afforestation. In the permanent pasture sites, 14.3 (±5.38) g kg^?1 NaOCl-resistant C was measured, while 46 years after conversion, only 2.8 (±1.2) g kg^?1remained. No enrichment of NaOCl-resistant C was observed in the chronosequence, as NaOCl-resistant C decreased faster in the course of cultivation than the TOC. Therefore, we conclude that that the C fraction that resists the oxidation with NaOCl is not long-term stable in soils, and most probably, there is no such long-term stable C fraction in the soils under study.     

Prediction of soil carbon levels in calcareous soils of Iran by mid-infrared reflectance spectroscopy

The objective of this study was to assess the predictive performance of midDRIFTS-PLSR models in quantifying total carbon (TC), total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), hot water extractable carbon and nitrogen (C_HWE, N_HWE), pH, and the clay, silt, and sand content of soils. A total of 68 soil samples were taken across an agroecological region in southwest Iran, and analyzed in the laboratory using mid-DRIFTS-PLSR. midDRIFTS-PLSR calibration models were developed, and external validation was performed for each of the soil properties via an independent algorithm. The calibration and validation models allowed for a sufficient prediction of TC, TIC, and TOC with residual prediction deviations ≥3 and R² values >0.9. The precise prediction ofcarbon fractions, such as TC, TIC, and TOC, in a rapid and inexpensive manner confirmed that midDRIFTS analysis was a rapid-throughput and cost-effective technique for monitoring soil carbon at the regional scale.     

Microbial diversity of topographical gradient profiles in Fushan forest soils of Taiwan

To evaluate the microbial diversity of Fushan forest soils, the variation of soil properties, microbial populations, and soil DNA with soil depth in three sites of different altitude were analyzed. Microbial population, moisture content, total organic carbon (C_org), and total nitrogen (N_tot) decreased with increasing soil depth. The valley site had the lowest microbial populations among the three tested sites due to the low organic matter content. Bacterial population was the highest among the microbial populations. The ratios of cellulolytic microbes to the total bacteria in organic layers were high, implying their roles in the carbon cycle. The microbial biomass carbon (C_mic) and nitrogen (N_mic) contents ranged from 130.5 to 564.1 μg g⁻¹ and from 16.7 to 95.4 μg g⁻¹, respectively. The valley had the lowest C_mic and N_mic. The organic layer had the highest C_mic and N_mic and decreased with soil depth. Analysis using denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR) amplicons of 16S rDNA showed that the bacterial diversity of the three sites were very similar to each other in the major bands, and the variation was in the minor bands. However, the patterns in PCR-DGGE profile through gradient horizons were different, indicating the prevalence of specific microbes at different horizons. These results suggest that the microbial diversity in the deeper horizons is not simply the diluted analogs of the surface soils and that some microbes dominate only in the deeper horizons. Topography influenced the quantity and diversity of microbial populations.     

林冠氮添加和林下植被去除对杉木林土壤有机碳组分的影响

为探讨氮添加和林下植被管理对杉木人工林土壤有机碳组分的影响,以福建沙县官庄国有林场杉木人工林为对象,设置对照（CK）、林冠氮添加（CN）、林下植被去除（UR）、林冠氮添加和林下植被去除（CNUR）4个处理的野外控制实验,研究林冠氮添加和林下植被去除对土壤总有机碳、惰性有机碳、易氧化有机碳、颗粒有机碳、微生物生物量碳和水溶性有机碳的影响。结果表明：5年CN添加处理显著降低易氧化有机碳（10—20 cm）和微生物生物量碳（20—40 cm）含量,增加表层土壤颗粒有机碳占总有机碳的比例。UR处理对土壤有机碳组分的作用不显著,而CNUR处理显著降低表层土壤水溶性有机碳含量及其比例。土壤各有机碳组分均与土壤含水量、可溶性有机氮、微生物生物量氮和铵态氮呈显著正相关。研究表明,土壤活性有机碳比惰性有机碳对林冠氮添加（5年）的响应更敏感,且表现为中下层土壤响应大于表层土壤,短期氮添加能促进土壤活性有机碳的分解,而林下植被去除在短时间内可能通过改变土壤含水量和可利用氮减缓有机碳的分解与转化,从而补偿由于氮添加引起的土壤活性有机碳下降,未来需要通过长期氮添加实验进一步研究土壤有机碳动态变化的响应机制。     

Effects of repeated (NH4)2SO4 application on sulfur pools in soil,soil microbial biomass,and ground vegetation of two watersheds in the Black Forest/Germany

The effect of repeated (NH₄)₂SO₄ applications (3 × 700 kg ha^–1 in 1988, 1991, and 1994, respectively) on S pools in soil, soil microbial biomass, and ground vegetation was studied at two Norway spruce (Picea abies L. [Karst.]) sites in the Black Forest/Germany. In both eco-systems, most of the total S pool was located in the soil. The soil also was the predominant compartment for retention of applied SO₄ ^2--S. The fractions of organic and inorganic S forms in the initial soil S content, and the retention of experimentally applied S was different for both sites. In the podzol Schluchsee, organic S accounted for 92% of total S. In the cambisol Villingen, the S pool consisted of 33% organic S and 67% inorganic S. The retention of applied S in various compartments of both ecosystems reflected these proportions. Only minor amounts of fertilized S (<1%) was retained in the spruce trees, ground vegetation, and soil microbial biomass. However, between 51% (Villingen) and 72% (Schluchsee) of the applied S was retained in the soil. In the Schluchsee podzol, 75% of retained fertilizer S was accumulated as ester sulfate, whereas SO₄ ^2-adsorption and precipitation of Al hydroxy sulfates were restricted by dissolved organic matter in the soil solution. In the Villingen cambisol, SO₄ ^2- adsorption was the dominant process of S retention, although 20% of the fertilized S again was retained as ester sulfate. The significant relevance of organic S forms in the retention of fertilizer S in both soils emphasizes the need for models which include the formation and re-mineralization of organic S compounds, especially of ester sulfates, for correctly simulating and predicting the retention and remobilization of S in acid forest soils subject to changing atmospheric N and S deposition.     

The variation of soil microbial respiration with depth in relation to soil carbon composition

The vertical variation in soil microbial respiratory activity and its relationship to organic carbon pools is critical for modeling soil C stock and predicting impacts of climate change, but is not well understood. Mineral soil samples, taken from four Scottish soils at different depths (0–8, 8–16, 16–24, 24–32 cm), were analyzed and incubated in the laboratory under constant temperature and environmental conditions. The vegetation type/plant species showed significant effects on the absolute concentration of C components and microbial activity, but the relative distribution of C and respiration rate with soil depth are similar across sites. Soil C pools and microbial respiratory activity declined rapidly with soil depth, with about 30% of total organic carbon (TOC) and dissolved organic carbon (DOC), and about half microbial carbon (C_mic) and respired CO₂ observed in the top 8 cm. The ratio of CO₂:TOC generally decreased with soil depth, but CO₂:DOC was significantly higher in the top 8 cm of soil than in the subsoil (8–32 cm). No general pattern between qCO₂ (CO₂:C_mic) and soil depth was found. The vertical distributions of soil C pools and microbial respiratory activity were best fitted with a single exponential equation. Compared with TOC and DOC, C_mic appears to be an adequate predictor for the variation in microbial respiration rate with soil depth, with 95% of variation in normalized respiration rate accounted for by a linear relationship.     

帽儿山地区不同土地利用方式下土壤-微生物-矿化碳氮化学计量特征

土地利用方式的变化导致土壤碳氮含量及其化学计量关系的变化,然而土壤微生物化学计量及其驱动的碳氮矿化过程如何响应这种变化仍不明确。以帽儿山地区天然落叶阔叶林、人工红松林、草地和农田4种不同土地利用类型为对象,测定其土壤有机碳(C_(soil))、全氮(N_(soil))、微生物生物量碳和氮(C_(mic)和N_(mic))、土壤碳和氮矿化速率(C_(min)和N_(min)),旨在比较不同土地利用方式对土壤、微生物碳氮化学计量特征及矿化速率的影响,探索土壤-微生物-矿化之间碳氮化学计量特征的相关性,揭示微生物对土壤碳氮化学计量变化的响应和调控机制。结果显示:C_(soil)、N_(soil)、C_(mic)、N_(mic)和C_(min)均呈现天然落叶阔叶林人工红松林草地农田,而天然落叶阔叶林和草地的N_(min)显著高于人工红松林和农田。土地利用方式显著影响土壤和微生物碳氮比(C∶N_(soil)和C∶N_(mic)),均呈现农田最高。不同土地利用方式的数据综合分析发现:碳氮矿化速率比与C∶N_(mic)呈负相关,而和微生物与土壤碳氮化学计量不平衡性(C∶N_(imb))显著正相关。单位微生物生物量的碳矿化速率(qCO_2)随着C∶N_(mic)的增加而降低,而单位微生物生物量的氮矿化速率(qAN)随着C∶N_(mic)的增加而增加。C∶N_(imb)与qCO_2正相关,与qAN负相关。以上结果表明,微生物会通过改变自身碳氮化学计量、调整碳氮之间相对矿化速率,以适应土地利用变化导致的土壤碳氮及其化学计量的变异性,以满足自身生长和代谢的碳氮需求平衡。     

Differences of Soil Microbial Biomass and Nitrogen Transformation under Two Forest Types in Central Germany

In order to observe the tree species effect on soil N status, soil microbial biomass C and N (C_mic, N_mic), potential N mineralization and potential nitrification (under laboratory incubation conditions, 22 °C) in different subhorizons (LOf₁, Of₂, Oh and mineral soil at 0–10 cm depth) were determined at three forest sites in central Germany. At each site, two contrasting stands (Beech, Norway spruce or Scots pine) were selected, where the initial soil conditions were similar. Three sampling dates that represented different stages of tree growth were selected: growing season - August, dormant season - November, after budbreak – April. In organic layers, C_mic-to-total C (C_t) ratios under beech and under conifer were 0.72–4.74% and 0.34–2.11%, respectively. N_mic-to-total N (N_t) ratios were 2.47–11.61% and 0.71–5.77%, respectively. Both concentrations of C_mic and N_mic were significantly affected by the stand type and sampling time. Potential N mineralization rates, ranging from 3.7 to 19.7 mg N kg⁻¹ d⁻¹, showed no clear pattern in relation to stand type. However, potential nitrification rates were mostly significantly higher under beech than under contrasting conifer. In mineral soils, concentrations of C_mic and N_mic showed a clear temporal pattern in the order: August>November>April. The average N_mic and N_mic-to-N_t were higher in soils from beech than conifer, while C_mic and C_mic-to-C_t ratios were similar between the two forest types. In organic layers, the highest values of C_mic-to-N_mic ratio and C_mic were found in November samples, especially under beech. By contrast, in mineral soils the highest value of C_mic-to-N_mic ratios were found in April samples, and at that time the C_mic concentrations were the lowest, especially under conifer. These results revealed the differences in microbial growth form and survival strategy associated with different tree species and soil layers.     

模拟氮沉降和降雨量改变对华西雨屏区常绿阔叶林土壤有机碳的影响

从2013年11月至2015年12月,通过原位试验,在华西雨屏区常绿阔叶林内设置了对照(CK)、氮沉降(N)、减雨(R)、增雨(A)、氮沉降+减雨(NR)、氮沉降+增雨(NA)6个处理水平,研究了模拟氮沉降和降雨量改变对常绿阔叶林土壤有机碳的影响。结果表明:华西雨屏区常绿阔叶林土壤各土层有机碳含量表现为夏季较高,春冬季较低,0—10 cm土层有机碳含量高于10—20 cm土层。从各处理土壤有机碳含量的平均值来看,0—10 cm土层土壤有机碳含量高低顺序表现为:RNRCKANNA;10—20 cm土层表现为:RNRACKNAN。模拟氮沉降和增雨处理促进了华西雨屏区常绿阔叶林土壤有机碳的累积,模拟减雨抑制了土壤有机碳的累积。常绿阔叶林0—10cm土层土壤C/N值显著高于10—20 cm,土壤C/N值随土层加深而呈现出增加的趋势,降雨使土壤C/N降低,增雨使土壤C/N增高。同一氮沉降条件下,增雨处理增加了土壤有机碳的含量,减雨处理减少了土壤有机碳的含量;同一降雨条件下,氮沉降增加土壤有机碳的含量。氮沉降和降雨对土壤可溶解性有机碳和微生物生物量碳含量产生显著影响(P0.05),对土壤活性碳含量影响不显著(P0.05);其交互作用对土壤有机碳、可溶解性有机碳、微生物生物量碳和活性碳含量影响不显著(P0.05)。     

Interactions of tropospheric CO2 and O3 enrichments and moisture variations on microbial biomass and respiration in soil

Soil microbial biomass C (C_mic) is a sensitive indicator of trends in organic matter dynamics in terrestrial ecosystems. This study was conducted to determine the effects of tropospheric CO₂ or O₃ enrichments and moisture variations on total soil organic C (C_org), mineralizable C fraction (C_Min), C_mic, maintenance respiratory (qCO₂) or C_mic death (qD) quotients, and their relationship with basal respiration (BR) rates and field respiration (FR) fluxes in wheat‐soybean agroecosystems. Wheat (Triticum aestivum L.) and soybean (Glycine max. L. Merr) plants were grown to maturity in 3‐m dia open‐top field chambers and exposed to charcoal‐filtered (CF) air at 350 μL CO₂ L^?1; CF air + 150 μL CO₂ L^?1; nonfiltered (NF) air + 35 nL O₃ L^?1; and NF air + 35 nL O₃ L^?1 + 150 μL CO₂ L^?1 at optimum (? 0.05 MPa) and restricted soil moisture (? 1.0 ± 0.05 MPa) regimes. The + 150 μL CO₂ L^?1 additions were 18 h d^?1 and the + 35 nL O₃ L^?1 treatments were 7 h d^?1 from April until late October. While C_org did not vary consistently, C_Min, C_mic and C_mic fractions increased in soils under tropospheric CO₂ enrichment (500 μL CO₂ L^?1) and decreased under high O₃ exposures (55 ± 6 nL O₃ L^?1 for wheat; 60 ± 5 nL O₃ L^?1 for soybean) compared to the CF treatments (25 ± 5 nL O₃ L^?1). The qCO₂ or qD quotients of C_mic were also significantly decreased in soils under high CO₂ but increased under high O₃ exposures compared to the CF control. The BR rates did not vary consistently but they were higher in well‐watered soils. The FR fluxes were lower under high O₃ exposures compared to soils under the CF control. An increase in C_mic or C_mic fractions and decrease in qCO₂ or qD observed under high CO₂ treatment suggest that these soils were acting as C sinks whereas, reductions in C_mic or C_mic fractions and increase in qCO₂ or qD in soils under elevated tropospheric O₃ exposures suggest the soils were serving as a source of CO₂.     

模拟氮沉降对华西雨屏区苦竹林土壤有机碳和养分的影响

从2007年11月至2009年10月, 对华西雨屏区苦竹(Pleioblastus amarus)人工林进行了模拟氮(N)沉降试验, N沉降水平分别为对照(CK, 0 g N·m^-2·a^-1)、低N (5 g N·m^-2·a^-1)、中N (15 g N·m^-2·a^-1)和高N (30 g N·m^-2·a^-1)。在N沉降进行1年后, 每月采集各样方0-20 cm的土壤样品, 连续采集12个月, 测定其土壤总有机C、微生物生物量C、浸提性溶解有机C、活性C、全N、微生物生物量N、NH₄⁺-N、NO₃^--N、有效P和速效K。结果表明: N沉降显著增加了土壤总有机C、微生物生物量C、全N、微生物生物量N、NH₄⁺-N和有效P含量, 对其余几个指标无显著影响。土壤微生物生物量C和微生物生物量N的季节变化明显, 并与气温极显著正相关。土壤有效P、速效K与微生物生物量C、微生物生物量N呈极显著负相关关系。N沉降提高了土壤中C、N、P元素的活性, 并通过微生物的转化固定作用使得C、N、P元素在土壤中的含量增加。苦竹林生态系统处于N限制状态, 土壤有机C和养分对N沉降呈正响应, N沉降的增加可能会提高土壤肥力并促进植被的生长, 进而促进生态系统对C的固定。     

放牧和刈割对内蒙古典型草原土壤可提取碳和氮的影响

依托内蒙古典型草原的长期野外放牧控制试验,探讨了放牧和刈割对土壤有机碳、全氮、可提取碳和氮、微生物生物量碳和氮的影响.结果表明: 放牧使可提取有机碳降低11.4%～37.1%,而刈割使可提取有机碳升高5.8%.放牧和刈割分别使可提取氮升高10%～340%和10%～240%.放牧强度不高于6.0 sheep·hm^-2的条件下有利于维持甚至增加微生物生物量碳,而重度放牧(7.5和9.0 sheep·hm^-2)则减少微生物生物量碳.刈割处理下微生物生物量碳和氮分别升高31.0%和9.8%.通径分析表明,放牧处理下微生物生物量碳的主要影响因素是有机碳、可提取全氮和全氮,其中直接影响因素是有机碳和可提取全氮;微生物生物量氮的主要影响因素是土壤pH、可提取有机碳、有机碳和可提取全氮,其中直接影响因素是有机碳和可提取全氮.刈割及轻度和中度放牧有利于维持或改善土壤功能,重度放牧将引起土壤退化.     

Land cover change effects on soil chemical and biological properties after planting Mongolian pine (Pinus sylvestris var. mongolica) in sandy lands in Keerqin, northeastern China

We compared soil moisture content, pH, total organic carbon (C _org), total nitrogen (TN), total phosphorus (TP) and inorganic N (NH₄ ⁺–N, NO₃ ^?–N) concentrations, soil potential C and N mineralization rates, soil microbial biomass C (C _mic), soil metabolic quotient (qCO₂), soil microbial quotient (C _mic/C _org) and soil enzyme (urease and invertase) activities in semiarid sandy soils under three types of land cover: grassland, Mongolian pine (Pinus sylvestris var. mongolica) plantation, and elm (Ulmus punila)–grass savanna in southeastern Keerqin, in northeast China. Soil C _org, TN and TP concentrations (0–10, 10–20, 20–40 and 40–60 cm) were lower while soil C/N and C/P ratios were higher in the plantation than in grassland and savanna. The effects of land cover change on NH₄ ⁺–N and NO₃ ^?–N concentrations, soil potential nitrification and C mineralization rates in the surface soil (0–10 cm) were dependent on sampling season; but soil potential N mineralization rates were not affected by land cover type and sampling season. The effects of land cover change on C _mic and qCO₂ of surface soil were not significant; but C _mic/C _org were significantly affected by land cover change and sampling season. We also found that land cover change, sampling season and land cover type?×?sampling season interaction significantly influenced soil enzyme (urease and invertase) activities. Usually soil enzyme activities were lower in the pine plantations than in grassland and savanna. Our results suggest that land cover change markedly influenced soil chemical and biological properties in sandy soils in the semiarid region, and these effects vary with sampling season.     

Plant functional traits and soil microbial biomass in different vegetation zones on the Loess Plateau

Plant functional traits built the relationships between plant diversity, species composition, and physiology along with the environmental changes, thus influencing soil microbial community. As the sensitivity indicators, soil microbial biomass and plant functional traits responses soil micro-organism and plant characteristics in direct way. Ten plant functional traits of 149 species and soil microbial biomass (carbon, nitrogen, and phosphorus) were analyzed across the different vegetation types (forest, forest-steppe, and steppe) that are divided by environmental gradient (temperature and precipitation), aimed to find the correlations among them. Our results confirmed the greatest values of plant functional traits (except the leaf density and the fine root density) that were distributed in the steppe zone, mainly due to the different mean annual temperature and mean annual precipitation conditions. For different plant growth forms, the plant functional traits were significant differences among the vegetation zones. The advantages of higher rate nutrient cycling, plentiful biomass supplements, and favorite habit conditions lead to the forest-steppe zone with the highest C_mic and N_mic concentrations. The canonical correlation analysis indicated that leaf nitrogen, root nitrogen, and fine root densities were correlated with root exudate and tissue which affected the concentrations of soil organic carbon (SOC) and total nitrogen (N), consequently impacting soil microbial biomass carbon (C_mic) and soil microbial biomass nitrogen (N_mic). Soil is the medium that connects micro-organism and plant root system that influenced leaf nitrogen, root nitrogen, and fine root density of plant functional traits, the concentrations of SOC and total N that plant feedback are consequently influencing C_mic and N_mic.     

Responses of soil microbiota of a late successional alpine grassland to long term CO2 enrichment

We investigated microbial responses in a late successional sedge-dominated alpine grassland to four seasons of CO₂ enrichment. Part of the plots received fertilizer equivalent to 4.5g N m⁻² a⁻¹. Soil basal respiration (R _mic ), the metabolic quotient for CO₂ (qCO₂=R _mic /C _mic ), microbial C and N (C _mic and N _mic ) as well as total soil organic C and N showed no response to CO₂ enrichment alone. However, when the CO₂ treatment was combined with fertilizer addition R _mic and qCO₂ were statistically significantly higher under elevated CO₂ than under ambient conditions (+57% and +71%, respectively). Fertilizer addition increased microbial N pools by 17%, but this was not influenced by elevated CO₂. Microbial C was neither affected by elevated CO₂ nor fertilizer. The lack of a CO₂-effect in unfertilized plots was suprising in the light of our evidence (based on C balance) that enhanced soil C inputs must have occurred under elevated CO₂ regardless of fertilizer treatment. Based on these data and other published work we suggest that microbial responses to elevated CO₂ in such stable, late-successional ecosystems are limited by the availability of mineral nutrients and that results obtained with fertile or heavily disturbed substrates are unsuitable to predict future microbial responses to elevated CO₂ in natural systems. However, when nutrient limitation is removed (e.g. by wet nitrogen deposition) microbes make use of the additional carbon introduced into the soil system. We believe that the response of natural ecosystems to elevated CO₂ must be studied in situ in natural, undisturbed systems.     

Fungal to bacterial biomass ratio in the forests soil profile

The carbon content in microbial biomass (C_mic-MB) was determined in various horizons of the soil profile (sod-podzo, gray, podzol, and rzhavozem) of various forests (oak, spruce archangel, spruce moss, aspen, spruce broadleaf) in the southern taiga of European Russia (Moscow and Kaluga regions) by the substrate-induced respiration (SIR) and direct microscopy (DM) methods. The fungi-to-bacteria ratio was measured by the selective inhibition technique and DM. A quantitative differentiation of the fungal mycelium was suggested. The C_mic-DM / C_mic-SIR in various horizons of the soil profile was about 98%. The fungal contribution to MB was 52–74% and 92–99% according to the SIR and DM methods, respectively. The microbial parameters were associated with the CO₂ and N₂O production by the soils. The contradictory data about the fungal portion in the MB of soils of various ecosystems were discussed.     

江西官山常绿阔叶林土壤有机碳组分沿海拔的变化

对江西官山国家级自然保护区不同海拔(400、600、800、1000、1200 m)常绿阔叶林土壤总有机碳、惰性有机碳和活性有机碳进行分析,研究土壤有机碳的海拔分布特征。结果表明: 土壤总有机碳、惰性有机碳及活性有机碳含量在土壤表层最高,随土层加深而逐渐下降。随海拔升高,土壤总有机碳、惰性有机碳、易氧化有机碳、微生物生物量碳及0～20 cm土层土壤颗粒有机碳含量均出现先增后降的趋势, 且在海拔1000 m达到峰值,而土壤水溶性有机碳及20～40 cm土层土壤颗粒有机碳含量无明显变化。在0～10 cm土层,土壤惰性有机碳占总有机碳的比例在海拔800和1200 m显著高于海拔400和1000 m,而土壤活性有机碳占总有机碳的比例在海拔400 m最高;土壤惰性有机碳和活性有机碳占总有机碳的比例在10～40 cm土层随海拔的增加均呈先增加后降低的趋势,峰值分别在1000和600 m处。各组分有机碳与土壤湿度、微生物生物量氮、可溶性有机氮均呈显著正相关,而且活性有机碳与铵态氮呈显著正相关。海拔显著影响常绿阔叶林土壤有机碳组分的分布,惰性有机碳、易氧化有机碳和微生物生物量碳对海拔变化的响应更敏感。高海拔土壤惰性有机碳和活性有机碳在水分和氮素充足条件下易发生分解与转化,降低土壤碳库的稳定性。在全球气温持续升高背景下,要加强高海拔地区森林土壤有机碳的动态变化研究。     

Effects of elevated CO2 and nitrogen addition on soil organic carbon fractions in a subtropical forest

Aims

The aim of this study was to investigate the effects of elevated CO₂ concentration and nitrogen addition on soil organic carbon fractions in subtropical forests where the ambient N deposition was high.

Methods

Seedlings of typical subtropical forest ecosystems were transplanted in ten open-top chambers and grown under CO₂ and nitrogen treatments. The treatments included: 1) elevated CO₂ (700?μmol?mol^-1); 2) N addition of 100?kg NH₄NO₃ ha^-1?yr^-1; 3) combined elevated CO₂ and N addition; and 4) control. We measured soil total organic carbon (TOC), particulate organic carbon (POC), readily oxidizable organic carbon (ROC), and microbial biomass carbon (MBC).

Results

Results showed that elevated CO₂ alone did not significantly affect soil TOC, POC and ROC after 4?years of treatment, but increased soil MBC and soil respiration compared to the control. N addition alone had no significant effect neither on soil TOC, POC and ROC, but decreased MBC and soil respiration over time. However, the elevated CO₂ and N addition together significantly increased soil POC and ROC, and had no significant effect on soil MBC.

Conclusions

This study indicated that even in N-rich subtropical forest ecosystems, inputs of N are still needed in order to sustain soil C accumulation under elevated CO₂.     

天山中段北坡森林土壤有机碳库稳定性组分沿海拔的分异规律

在高纬度高海拔区域气温增幅更大的背景下,高山亚高山森林土壤有机碳稳定性组分分配比关系以及由于此差异导致对增温的反馈效应均有待深入阐释。天山森林是以雪岭云杉(Picea Schrenkiana)为单优树种的温带针叶林,在天山北坡中山带(海拔约1760—2800 m)呈垂直落差超过1000 m的带状斑块分布,便于排除混交树种的影响,而量化土壤有机碳库稳定性组分分配比关系沿海拔的分异规律,及其对气候变化的响应情况。沿海拔梯度设置森林样地并分层采集土样,研究各土层土壤总有机碳库(C_SOC)、活性碳库(C_a)、缓效性碳库(C_s)、惰性碳库(C_p)、微生物量碳(MBC)在海拔梯度上的变化特征,通过碳库活度(A)、碳库活度指数(AI)、碳库指数(CPI)、土壤碳密度(SOCD),探讨天山森林土壤有机碳稳定性组分沿海拔的分异特征。结果表明：(1)随着海拔的升高,天山中段北坡云杉森林土壤C_a占比逐步升高,C_s和C_p占比逐步降低,这意味着天山中段北坡云杉...     

降水变率对森林土壤有机碳组分与分布格局的影响

2006年12月-2008年6月,通过加倍降水、自然降水和去除降水3种处理的人工控制试验,研究了降水变率改变对南亚热带不同演替阶段的季风常绿阔叶林、针阔叶混交林和马尾松针叶林土壤有机碳组分与空间分布格局的影响.结果表明：在3种降水强度条件下,相同森林类型的同一层次土壤总有机碳（TOC）含量差异不显著（P>0.05）;去除降水处理下土壤表层（0～10 cm）颗粒有机碳（POC）和轻组有机碳(LFOC)含量有明显的积累趋势,加倍降水和自然降水处理下增加了POC、LFOC向下层土壤（10～20 cm、20～30 cm、30～50 cm）的运输;去除降水处理下,马尾松林土壤易氧化有机碳（ROC）含量显著高于降水处理（P<0.05）;演替早期森林土壤的POC、ROC、LFOC占总有机碳的比例大于演替后期土壤,不利于土壤有机碳的存埋.森林土壤总有机碳含量变化缓慢,而其活性有机碳组分（POC、LFOC、ROC）对降水变率改变的响应更敏感.