不同森林植被下土壤活性有机碳的含量及动态变化

Soil organic matter （SOM） in forest ecosystems is not only important to global carbon （C） storage but also to sustainable management of forestland with vegetation types, being a critical factor in controlling the quantity and dynamics of SOM. In this field experiment soil plots with three replicates were selected from three forest vegetation types： broadleaf, Masson pine （Pinus massoniana Lamb.）, and Chinese fir （Cunninghamia lanceolata Hook.）. Soil total organic C （TOC）, two easily oxidizable C levels （EOC1 and EOC2, which were oxidized by 66.7 mmol L^-1 K2Cr2O7 at 130-140℃ and 333 mmol L^-1 KMnO4 at 25 ℃, respectively）, microbial biomass C （MBC）, and water-soluble organic C （WSOC） were analyzed for soil samples. Soil under the broadleaf forest stored significantly higher TOC （P ≤ 0.05）. Because of its significantly larger total soil C storage, the soil under the broadleaf forest usually had significantly higher levels （P ≤ 0.05） of the different labile organic carbons, EOC1, EOC2, MBC, and WSOC; but when calculated as a percentage of TOC each labile C fraction of the broadleaf forest was significantly lower （P ≤ 0.05） than one of the other two forests. Under all the three vegetation types temperature as well as quality and season of litter input generally affected the dynamics of different organic C fractions in soils, with EOC1, EOC2, and MBC increasing closely following increase in temperature, whereas WSOC showed an opposite trend.     

Organic‐carbon and nitrogen stocks and organic‐carbon fractions in soil under mixed pine and oak forest stands of different ages in NE Germany

The objective of this work was to evaluate the C and N stocks and organic‐C fractions in soil under mixed forest stands of Scots pine (Pinus sylvestris L.) and Sessile oak (Quercus petraea [Matt.] Liebl.) of different ages in NE Germany. Treatments consisted of pure pine (age 102 y), and pine (age 90–102 y) mixed with 10‐, 35‐, 106‐, and 124‐y‐old oak trees. After sampling O layers, soils in the mineral layer were taken at two different depths (0–10 and 10–20 cm). Oak admixture did not affect total organic‐C (TOC) and N stocks considering the different layers separately. However, when the sum of TOC stocks in the organic and mineral layers was considered, TOC stocks decreased with increasing in oak age (r² = 0.58, p < 0.10). The microbial C (C_MB) was not directly correlated with increase of oak age, however, it was positively related with presence of oak species. There was an increase in the percentage of the C_MB‐to‐TOC ratio with increase of oak‐tree ages. On average, light‐fraction C (C_LF) comprised 68% of the soil TOC in upper layer corresponding to the highest C pool in the upper layer. C_LF and heavy‐fraction C (C_HF) were not directly affected by the admixture of oak trees in both layers. The C_HF accounted on average for 30% and 59% of the TOC at 0–10 and 10–20 cm depths, respectively. Despite low clay contents in the studied soils, the differences in the DCB‐extractable Fe and Al affected the concentrations of the C_HF and TOC in the 10–20 cm layers (p < 0.05). Admixture of oak in pine stands contributed to reduce topsoil C stocks, probably due to higher soil organic matter turnover promoted by higher quality of oak litter.     

Coniferous afforestation increases soil carbon in maritime sand dunes

Afforestation of grasslands can increase C sequestration and provide additional economic and environmental benefits. Pine plantations, however, have often been found to deplete soil organic C and trigger detrimental effects on soils. We examined soil characteristics under a 45-year-old Pinus radiata stand and under adjacent grassland on maritime dunes in temperate Argentina. Soil under the pine plantation had greater soil organic C (+93%), total N (+55%) and available P (+100%) concentrations than under grassland. Carbon was stored under the pinestand at an estimated mean accretion rate of 0.64 Mg ha^?1 y^?1. At 0- to 25-cm depth, soil C amounted to 61 Mg ha^?1 under pine and 27 Mg ha^?1 under grassland. Soil C accumulated more on dune slopes (35 Mg ha^?1 y^?1) than on ridges(29 Mg ha^?1 y^?1) and bottoms (12 Mg ha^?1 y^?1). Compared with the grassland, soil acidity, cation-exchange capacity, base losses (K > Ca = Mg) and C/N ratio increased under pine. Spatial heterogeneity in soil characteristics was greater under pine than under grassland. Such variability was non-systematic and did not support the ‘single-tree influence circle’ concept. Afforestation increased C in soil, forest floor and tree biomass in dunes with ustic climate regime.     

Responses of Soil Acid Phosphomonoesterase Activity to Simulated Nitrogen Deposition in Three Forests of Subtropical China

Soil acid phosphomonoesterase activity(APA)plays a vital role in controlling phosphorus(P)cycling and reflecting the current degree of P limitation.Responses of soil APA to elevating nitrogen(N)deposition are important because of their potential applications in addressing the relationship between N and P in forest ecosystems.A study of responses of soil APA to simulated N deposition was conducted in three succession forests of subtropical China.The three forests include a Masson pine(Pinus massoniana)forest (MPF)-pioneer community,a coniferous and broad-leaved mixed forest(MF)-transition community and a monsoon evergreen broad-leaved forest(MEBF)-climax community.Four N treatments were designed for MEBF:control(without N added),low-N(50 kg N ha^-1 year^-1),and medium-N(100 kg N ha^-1 year^-1)and high-N(150 kg N ha^-1 year^-1),and only three N treatments(i.e.,control, low-N,medium-N)were established for MPF and MF.Results showed that soil APA was highest in MEBF,followed by MPF and MF.Soil APAs in both MPF and MF were not influenced by low-N treatments but depressed in medium-N treatments.However,soil APA in MEBF exhibited negative responses to high N additions,indicating that the environment of enhanced N depositions would reduce P supply for the mature forest ecosystem.Soil APA and its responses to N additions in subtropical forests were closely related to the succession stages in the forests.     

Nitrate leaching in forest soils: an analysis of long‐term monitoring sites in Germany

Elevated atmospheric inputs of NH₄⁺ and NO₃^– have caused N saturation of many forest ecosystems in Central Europe, but the fate of deposited N that is not bounded by trees remains largely unknown. It is expected that an increase of NO₃^– leaching from forest soils may harm the quality of groundwater in many regions. The objective of this study was to analyze the input and output of NH₄⁺ and NO₃^– at 57 sites with mature forest stands in Germany. These long‐term study sites are part of the European Level II program and comprise 17 beech, 14 spruce, 17 pine, and 9 oak stands. The chloride balance method was used to calculate seepage fluxes and inorganic N leaching below the rooting zone for the period from 1996 to 2001. Nitrogen input by throughfall was significantly different among most forest types, and was in the order: spruce > beech/oak > pine. These differences can be largely explained by the amount of precipitation and, thus, it mirrors the regional and climatic distribution of these forest types in Germany. Mean long‐term N output with seepage was log‐normal distributed, and ranged between 0 and 26.5 kg N ha^–1 yr^–1, whereby 29 % of the sites released more than 5 kg N ha^–1 yr ^–1. Leaching of inorganic N was only significantly lower in the pine stands (P < 0.05) compared with leaching rates of the spruce stands. Median N output : input ratio ranged between 0.04 and 0.11 for the beech, oak, and pine stands, while the input : output ratio of the spruce stands was 0.24, suggesting a higher risk of NO₃^– leaching in spruce forests. Following log‐transformation of the data, N input explained 38 % of the variance in N output. The stratification of the data by the C : N ratio of the O horizon or the top mineral soil revealed that forests soils with a C : N ratio < 25 released significantly more NO₃^– (median of 4.6 kg N ha^–1 yr^–1) than forests with a C : N ratio > 25 (median of 0.8 kg N ha^–1 yr^–1). The stratification improved the correlation between N input and N output for sites with C : N ratios < 25 (r² = 0.47) while the correlation for sites with C : N ratios > 25 was weaker (r = 0.21) compared with the complete data set. Our results suggest that NO₃^– leaching may increase in soils with wide C : N ratios when N deposition remains on a high level and that the potential to store inorganic N decreases with C : N ratios in the O horizons becoming more narrow.     

Impacts of 22-year organic and inorganic N managements on soil organic C fractions in a maize field,northeast China

Impacts of 22-year organic and inorganic N managements on total organic carbon (TOC), water-soluble organic C (WSOC), microbial biomass C (MBC), particulate organic C (POC) and KMnO₄ oxidized organic C (KMnO₄-C) concentrations, C management index (CMI), and C storage in surface soil (0–20 cm) were investigated in a maize (Zea may L.) field experiment, Northeast China. The treatments included, CK: unfertilized control, M: organic manure (135 kg N ha^− 1 year^− 1), N: inorganic N fertilizer (135 kg N ha^− 1 year^− 1) and MN: combination of organic manure (67.5 kg N ha^− 1 year^− 1) and inorganic N fertilizer (67.5 kg N ha^− 1 year^− 1). TOC concentration and C storage were significantly increased under the M and MN treatments, but not under the inorganic N treatment. The organic treatments of M and MN were more effective in increasing WSOC, MBC, POC and KMnO₄-C concentrations and CMI than the N treatment. The M treatment was most effective for sequestrating SOC (10.6 Mg ha^− 1) and showed similar increase in degree of grain yield to the N and MN treatments, therefore it could be the best option for improving soil productivity and C storage in the maize cropping system.     

Humusveränderungen nach Einbringung von Buche und Eiche in Kiefernreinbestände

Humus changes after introduction of beech and oak into Scots‐pine monocultures Medium‐ and long‐term (16 to 83 years) effects of an introduction of broadleaf‐tree species (Common beech [Fagus sylvatica] and European‐Sessile Oak [Quercus robur/petraea]) into mature Scots‐pine (Pinus sylvestris) stands on humus type and chemical properties of the Oh layer (pH value, base saturation, C : N ratio) were studied on 16 sites in Bavaria/Germany. The sites investigated covered a large range with respect to elevation, climate, parent material, and soil type. At most sites, the introduction of beech resulted in a significant change of the soil humus type from biologically inactive humus types to more active ones. The strongest changes occurred on the poorest sites, where forest floors under pure pine were particularly biologically inactive. In most cases, the changes in humus type were accompanied by significant increases in the pH value and the base saturation and significant decreases in the C : N ratio of the Oh layer. However, the latter effect was not noticed at most sites with initial C : N ratios higher than 30. In contrast to beech, the introduction of oak did not result in a systematic change of the humus type, the pH value, or the base saturation of the Oh layer. In spite of the considerable change of humus type under beech to biologically more active types, the introduction of broadleaf trees did not result in a systematic change of the thickness or the mass of the forest floor. A decrease in the mass of the Of layer was compensated by an increase of the Oh‐layer mass. All studied sites considered, the introduction of broadleaf trees into Scots‐pine monocultures resulted on average in an 8% decrease of the total amount of organic carbon (C_org) in the forest floor; the C_org amount in the uppermost 10 cm mineral soil increased by 9%. At 35% of all investigated sites, broadleaf tree introduction resulted in increased (+5% to +18%) topsoil (forest floor and uppermost 10 cm mineral soil) C_org stocks. At 30% of the sites, the stock changes were less than ±5%, and on 35% of all sites, soil C_org stocks decreased by –5% to –36%. The average change in the topsoil C_org stock for all studied sites was –5%. The introduction of beech into Scots‐pine monocultures resulted in an ecologically desired translocation of soil organic matter from the forest floor into the mineral topsoil. It is an effective and sustainable silvicultural measure to restore and revitalize acidified, nutrient‐depleted topsoils with biologically inactive humus types.     

南亚热带森林干季期间土壤变湿后一氧化氮排放

Information about soil nitric oxide (NO) emissions from subtropical forests is quite limited, and even less is known about the pulse emission of NO when wetting soils after a long period of dryness. In this study, we measured NO fluxes following wetting of dry soil in a broadleaf forest and a pine forest in subtropical China. Large pulses of NO fluxes were observed after soil wetting in both forests. NO fluxes increased significantly within 0.5 h following wetting in both forests and reached peak 1 h and 4 h after soil wetting in the pine forest and the broadleaf forest, respectively. In the broadleaf forest, averaged peak flux of NO pulses was 157 ng N m–2 s–1, which was 8 times the flux value before wetting, and in the pine forest, the averaged peak flux was 135 ng N m–2 s–1, which was 15.5 times the flux value before wetting. The total pulses-induced NO emissions during the dry season were roughly estimated to be 29.4 mg N m–2 in the broadleaf forest and 22.2 mg N m–2 in the pine forest or made up a proportion of 4.6% of the annual NO emission in the broadleaf forest and 5.3% in the pine forest.     

Accumulation and composition of total organic carbon in reclaimed coal mine lands

Reclaimed coal mine lands have the potential to sequester atmospheric carbon (C); however, limited information exists for the western USA coalfields. This study was carried out on two chronosequences (BA‐C₃ grasses and DJ‐shrubs) of reclaimed sites at two surface coal mines to determine the effects of vegetation, soil texture, and lignin content on soil total organic carbon (TOC) accumulations. In the BA chronosequence, TOC increased over 26 years at an average rate of 0·52 Mg C ha⁻¹ yr⁻¹ in the 0–30 cm depth and was significantly correlated with clay content. Comparison between < 1 and 16‐year‐old stockpile soils indicated TOC content did not differ significantly. In the DJ chronosequence, TOC content in the 0–30 cm depth declined from 31·3 Mg ha⁻¹ in 5‐year‐old soils to 23·4 Mg ha⁻¹ in 16‐year‐old soils. The C:N ratios suggested that some (up to 2·0 per cent) of the TOC was potentially derived from coal particles in these reclaimed soils. Soil total N (TN) contents followed a similar trend as TOC with TOC and TN concentrations strongly correlated. Lignin contents in TOC of all reclaimed soils and topsoil stockpiles (TSs) were higher than that of nearby undisturbed soils, indicating the recalcitrant nature of TOC in reclaimed soils and/or possibly the slow recovery of lignin degrading organism. Results indicated that TOC accumulations in DJ were largely controlled by its composition, particular lignin content. In BA sites TOC accumulation was strongly influenced by both clay and lignin contents. Copyright © 2008 John Wiley & Sons, Ltd.     

果园土壤有机碳及呼吸速率对豆科和禾本科草类的差异反应

在行间长期(连续6年)种植豆科植物毛苕子和禾本科植物黑麦草的苹果园,调查土壤不同深度的有机碳组分和表层土壤呼吸速率日变化。结果表明:间作2种植物后,行间土壤0—20,20—40cm土层总有机碳(TOC)、轻质有机碳(LFOC)、可溶性有机碳(DOC)、颗粒有机碳(POC)、易氧化有机碳(ROC)和微生物生物量碳(MBC)含量均显著提高;在40—60cm土层,仅DOC含量明显提高;0—20cm土层的TOC和全部有机碳组分及20—40cm土层的TOC、DOC、POC和ROC的含量在种植毛苕子后均明显高于种植黑麦草。TOC与LFOC、TOC与POC、DOC与LFOC、DOC与MBC、DOC与ROC、MBC与ROC、ROC与POC、LFOC与ROC之间均呈显著正相关,土壤呼吸速率与LFOC、DOC、MBC和ROC之间也呈显著正相关。种植2种草类均显著提高土壤呼吸速率,并使呼吸速率日变化峰型更突出,其中毛苕子的作用效果比黑麦草更显著。