Long-term effects of continuous direct seeding mulch-based cropping systems on soil nitrogen supply in the Cerrado region of Brazil

In the Cerrado region of Brazil conventional soybean monoculture is since the 1980s being replaced by direct seeding mulch-based cropping (DMC) with two crops per year and absence of tillage practices. The objective of this study was to assess the long-term impact of DMC on soil organic matter accumulation and nitrogen (N) mineralization. Measurements of soil organic carbon (C) content, soil total N content and soil N mineralization, both under laboratory conditions using disturbed soil samples and under field conditions using intact soil cores were conducted on a chronosequence of 2-, 6-, 9- and 14-year-old DMC fields (DMC-2, DMC-6, DMC-9 and DMC-14, respectively). The average increase of organic C in the 0–30 cm topsoil layer under DMC was 1.91 Mg C ha⁻¹ year⁻¹. Soil total N increased with 103 kg N ha⁻¹ year⁻¹ (0–30 cm). The potential N mineralization rate under laboratory conditions (28°C, 75% of soil moisture at field capacity) was 0.27, 0.28, 0.39 and 0.36 mg N kg soil⁻¹ day⁻¹ for, respectively, the DMC-2, DMC-6, DMC-9 and DMC-14 soils. The corresponding specific N mineralization rates were 0.16, 0.15, 0.22 and 0.17 mg N g N⁻¹ day⁻¹. There was no obvious explanation for the higher specific N mineralization rate of soils under DMC-9, given the similar soil conditions and land-use history before DMC was introduced. Results from the in situ N incubation experiments were in good agreement with those from the laboratory incubations. We estimated that soil N mineralization increases with about 2.0 kg N ha⁻¹ year⁻¹ under DMC. The increase was mainly attributed to the larger soil total N content. These results indicate that even in the medium term (10 years), continuous DMC cropping has limited implications for N fertilization recommendations, since the extra soil N supply represents less than 20% of the common N fertilization dose for maize in the region.     

秦岭典型林分土壤有机碳储量及碳氮垂直分布

以秦岭典型林分锐齿栎(马头滩林区)、油松、华山松、松栎混交林、云杉、锐齿栎(辛家山林区)为对象,研究了不同林分土壤剖面上有机碳、全氮、有机碳储量的分布规律。结果表明:在秦岭地区,随着土壤剖面深度增加,不同林分的土壤有机碳、全氮含量均逐渐降低;不同林分的土壤有机碳、氮素的积累和分解存在一定差异。其中,云杉和松栎混交林的土壤有机碳、全氮含量较高,锐齿栎(辛家山林区)含量较低,不同林分土壤剖面有机碳、全氮含量平均值分别为13.46—26.41 g/kg、4.47—9.51 g/kg,大小顺序均为云杉松栎混交林锐齿栎(马头滩林区)油松华山松锐齿栎(辛家山林区);各个林分的土壤C/N在5.93—15.47之间,C/N平均值大小为松栎混交林﹥华山松﹥油松﹥云杉﹥锐齿栎(辛家山林区)﹥锐齿栎(马头滩林区);各个林分0—60 cm土层的土壤有机碳储量大小为云杉锐齿栎(马头滩林区)松栎混交林华山松锐齿栎(辛家山林区)油松,分别为150.94、135.28、124.93、109.24、102.15、96.62 t/hm2;各个林分土壤有机碳含量与土壤全氮含量存在极显著正相关,土壤有机碳、全氮与C/N则没有明显相关性。     

不同水旱复种轮作方式对稻田土壤有机碳及其组分的影响

通过连续2年的田间试验,研究不同水旱复种轮作方式对土壤有机碳及其组分的影响.结果表明: 稻田2年水旱复种轮作后的土壤总有机碳(TOC)呈现先升高后下降的趋势,易氧化有机碳(ROC)分蘖期最高、成熟期最低,土壤微生物生物量碳(SMBC)在分蘖期最高,可溶性有机碳(DOC)则在成熟期达到最高.土壤TOC的差异变化最大值和最小值分别出现在孕穗期和成熟期,ROC出现在返青期和孕穗期,DOC出现在成熟期和返青期,SMBC出现在分蘖期和返青期.“冬闲-早稻-晚稻→冬闲-早稻-晚稻”的土壤TOC、DOC变化幅度最大,“紫云英-早稻-晚稻→油菜-花生-晚稻”的土壤ROC变化幅度最大,“蔬菜-花生/玉米-晚稻→紫云英-早稻-晚稻”模式的SMBC变化幅度最大.“马铃薯-玉米/大豆-晚稻→蔬菜-花生/玉米-晚稻”在孕穗期的TOC含量较高;“紫云英-早稻-晚稻→油菜-花生-晚稻”能在晚稻生长的前期和中期积累较多的土壤ROC;“油菜-花生-晚稻→马铃薯-玉米/大豆-晚稻”在返青期和成熟期的土壤DOC含量较高,在孕穗期和抽穗期的SMBC较高.土壤各有机碳及其组分的大小关系为:TOC>ROC>SMBC>DOC.可见在当地土壤肥力条件下,水旱复种轮作方式能提高土壤有机碳及其组分的含量,有利于改善土壤质量,提高土壤肥力.     

晋西北黄土高原丘陵区不同土地利用方式下土壤碳氮储量

对晋西北黄土高原丘陵区杨树-小叶锦鸡儿人工林、小叶锦鸡儿人工灌丛、杨树人工林、撂荒地和农田5种土地利用方式下土壤碳氮储量进行研究.结果表明: 不同土地利用方式下土壤碳氮含量、碳氮密度和碳氮储量存在显著差异.5种土地利用方式0～20 cm表层土壤碳氮含量和碳氮密度均显著大于20～40 cm和40～60 cm土层.5种土地利用方式同一土层碳氮含量和碳氮密度大小为: 杨树-小叶锦鸡儿人工林>小叶锦鸡儿人工灌丛>杨树人工林>撂荒地>农田;0～60 cm土层土壤有机碳储量大小为:杨树-小-叶锦鸡儿人工林(30.09 t·hm^-2)>小叶锦鸡儿人工灌丛(24.78 t·hm^-2)>杨树人工林(24.14 t·hm^-2)>撂荒地(22.06 t·hm^-2)>农田(17.59 t·hm^-2);土壤氮储量与有机碳储量变化规律相似,杨树-小叶锦鸡儿人工林0～60 cm土层土壤氮储量(4.94 t·hm^-2)最高,其次是小叶锦鸡儿人工灌丛(3.53 t·hm^-2)、杨树人工林(3.51 t·hm^-2)和撂荒地(3.40 t·hm^-2),农田土壤氮储量(2.71 t·hm^-2)最低.杨树-小叶锦鸡儿人工林和小叶锦鸡儿人工灌丛是晋西北黄土高原丘陵区植被建设和生态恢复过程中较好的两种土地利用方式.     

Soil inorganic carbon storage pattern in China

Soils with pedogenic carbonate cover about 30% (3.44 × 10⁶ km²) of China, mainly across its arid and semiarid regions in the Northwest. Based on the second national soil survey (1979–1992), total soil inorganic carbon (SIC) storage in China was estimated to be 53.3±6.3 PgC (1 Pg=10¹⁵ g) to the depth investigated to 2 m. Soil inorganic carbon storages were 4.6, 10.6, 11.1, and 20.8 Pg for the depth ranges of 0–0.1, 0.1–0.3, 0.3–0.5, and 0.5–1 m, respectively. Stocks for 0.1, 0.3, 0.5, and 1 m of depth accounted for 8.7%, 28.7%, 49.6%, and 88.9% of total SIC, respectively. In contrast with soil organic carbon (SOC) storage, which is highest under 500–800 mm yr⁻¹ of mean precipitation, SIC storage peaks where mean precipitation is <400 mm yr⁻¹. The amount and vertical distribution of SIC was related to climate and land cover type. Content of SIC in each incremental horizon was positively related with mean annual temperature and negatively related with mean annual precipitation, with the magnitude of SIC content across land cover types showing the following order: desert, grassland >shrubland, cropland >marsh, forest, meadow. Densities of SIC increased generally with depth in all ecosystem types with the exception of deserts and marshes where it peaked in intermediate layers (0.1–0.3 m for first and 0.3–0.5 m for latter). Being an abundant component of soil carbon stocks in China, SIC dynamics and the process involved in its accumulation or loss from soils require a better understanding.     

The potential of cropping systems and soil amendments for carbon sequestration in soils under long-term experiments in subtropical India

An understanding of the dynamics of carbon (C) stock in soils, as impacted by management strategies, is necessary to identify the pathways of C sequestration in soils and for maintaining soil organic C (SOC) at a level critical for upkeeping soil health and also for restraining global warming. This is more important in tropical and subtropical region where soils are inherently low in organic C content and the production system is fragile. We evaluated the long‐term role of crop residue C inputs to soil in SOC sequestration and also the critical value of C inputs for maintenance of SOC across five different rice‐based cropping systems and four soil management practices including a fallow (no cultivation since initiation of the experiments) using five long‐term (7–36 years) fertility experiments in subtropical India. Cropping per se always caused a net depletion of SOC. Such depletion was inversely proportional to the amount of crop residue C incorporated into the soils (r=−0.92, P=0.001). Balanced fertilization with NPK, however, caused an enrichment (9.3–51.8% over the control) of SOC, its extent being influenced by the cropping systems. Long‐term application of organic amendments (5–10 Mg ha⁻¹ yr⁻¹) through farmyard manure (FYM) or compost could increase SOC hardly by 10.7% constituting only 18% of the applied C, the rest getting lost through oxidation. The total quantity of soil C sequestered varied from −11.5 to 14.5 Mg C ha⁻¹ and was linearly related (r²=0.40, P=0.005) with cumulative crop residue C inputs to the soils. On an average, the rate of its conversion to SOC came out to be 6.4%. This was more in presence of added organics (6.9%) than in its absence (4.2%). For sustenance of SOC level (zero change due to cropping) we found that a minimum quantity of 2.9 Mg C is required to be added per hectare per annum as inputs. The cropping systems and the management practices that could provide C input higher than the above critical level are likely to sustain the SOC level and maintain good soil health in the subtropical regions of the Indian subcontinent.     

Mechanisms for changes in soil carbon storage with pasture to Pinus radiata land-use change

In this study, we simulated pasture to Pinus radiata land‐use change with the Generic Decomposition And Yield (G'DAY) ecosystem model to examine mechanisms responsible for the change in soil carbon (C) under pine. We parameterized the model for paired sites in New Zealand. Our simulations successfully reproduced empirical trends in ecosystem productivity and soil inorganic nitrogen (N), and modeled an increase in soil C and a small decline in soil N after 30 years under pine. We determined the mechanisms contributing to soil C change based on an established hypothesis that attributes increases in soil C storage to three main factors: increased ecosystem N inputs relative to outputs, increased C/N ratios in plant and soil, or a shift of N from plant to soil. The mechanisms we attributed to the simulated increase in soil C under pine were increased soil C inputs through tree litterfall, and an increase in the soil C/N ratio. In the first 7 years following pine establishment, a decline in soil C was simulated; this was matched by a decline in soil N. The simulated longer‐term increase in soil C with afforestation by pine contrasts with results from published field studies, which show either a decline or no change in soil C under pine. The discrepancy between measured and simulated changes in soil C was attributed to the G'DAY model overestimating the transfer of litter C into the mineral soil.     

Soil carbon storage and its determinants in the forests of Shaanxi Province,China

Aims The bank of soil carbon of forests plays an important role in the global carbon cycle. Our aim is to understand the characteristics of soil carbon storage and its determinants in the forests in Shaanxi Province.Methods The data of forest inventory in 2009 and resampling in 2011 were used to analyze the characteristics of soil carbon storage and its determinants in the forest soil in Shaanxi Province.Important findings The soil carbon storage in the forests in Shaanxi Province was 579.68 Tg. Soil carbon storage of Softwood and Hardwood forests were the highest among all forest types, accounting for 36.35% of the whole province forest soil carbon storage. The forest soil carbon storage was 4.15 times greater in the natural forest (467.17 Tg) than that in the plantations. The young and middle-aged forests were the main contributors to the total carbon storage across all age groups, accounting for about 57.30% of the total forest soil carbon storage. The average soil carbon density of forests in Shaanxi Province was 90.68 t∙hm^-2, in which the soil carbon density of Betula forests was the highest (141.74 t∙hm^-2). Soil carbon density of different forest types were gradually decreased with soil depth. In addition, it was highest in middle-aged forest. Soil carbon density was higher in the natural forest ecosystems than that in the plantations within the each age group, indicating natural forest ecosystems have higher capacity of carbon sequestration. Differences in the spatial patterns between carbon storage and density indicated that carbon storage was related to forest coverage. The soil carbon density and storage of forests in Yulin were the lowest across the province. This suggests that, in order to enhance the regional carbon sequestration capacity in this region, we need to appropriately strengthen artificial afforestation activities and manage them scientifically and rationally. The soil carbon density of forests in Shaanxi Province decreased with the increase of longitude, latitude, and annual temperature, but increased with the increase of altitude and annual rainfall. This study provides data basis for provincial estimation of forest soil carbon bank in China.     

芦芽山典型植被土壤有机碳剖面分布特征及碳储量

摘要: 基于芦芽山沿海拔梯度分布的灌丛草地、针阔混交林、寒温性针叶林和亚高山草甸四类典型植被下土壤剖面实测数据,分析了土壤有机碳的垂直分布特征及其与土壤理化因子的关系。结果表明,各植被类型下土壤剖面上层SOC含量最高,最大值往往出现在10—20 cm层,然后向下逐渐减小。土壤有机质含量由剖面上层最大值向下降低过程中,某深度土壤剖面层段有机质含量急剧减小。亚高山草甸剖面这一深度为20 cm,寒温性针叶林剖面为50 cm,针阔混交林剖面为20 cm,灌丛草地剖面为40 cm。0—10 cm层各植被类型间SOC含量差异不显著;10—20 cm层,亚高山草甸和寒温性针叶林SOC含量显著高于其他类型;20—50 cm层,亚高山草甸SOC含量与灌丛草地接近,显著高于针阔混交林,低于寒温性针叶林。植被类型对有机碳剖面分布影响较大。土壤剖面各层有机碳含量与容重呈显著负相关,与土壤含水量和全氮含量呈显著正相关,与土壤pH值呈弱的负相关,与深层黏粒和粉粒含量正相关,在30—50 cm正相关性显著。逐步回归分析结果表明,亚高山草甸SOC含量与土壤总氮含量、含水量和容重的显著相关,寒温性针叶林SOC含量与全氮含量显著相关,针阔混交林SOC含量则与总氮含量和土壤容重显著相关,而灌丛草地SOC含量与容重显著相关。在20 cm深度,四种植被土壤有机碳密度差异不显著;50 cm深度亚高山草甸、寒温性针叶林土壤有机碳储量显著高于针阔叶混交林和灌丛草地,50 cm深度土壤有机碳储量与海拔高度呈显著线性正相关（R2=0.299,P=0.01）。     

青海省森林土壤有机碳氮储量及其垂直分布特征

森林土壤在调节森林生态系统碳、氮循环和减缓全球气候变化中起着关键的作用。但是,由于林型、林龄以及环境因子(海拔)的差异,至今对于森林土壤碳、氮储量的估算依然存在极大的不确定性。因此,利用森林土壤实测数据估算了青海森林土壤有机碳、氮密度和碳、氮储量,分析了土壤有机碳、氮密度的垂直分布格局。结果表明:1)土壤有机碳密度随海拔的增加呈单峰曲线变化,在海拔3100—3400 m达到最大34.33 kg/m~2;氮密度随海拔的增加而增加,范围为1.39—2.93 kg/m~2。2)在0—30 cm土层,土壤有机碳、氮密度均随土层的增加而降低,范围分别为3.84—4.63 kg/m~2、0.22—0.27 kg/m~2。3)青海省森林土壤碳储量为1098.70 Tg,氮储量为61.78 Tg。4)海拔与氮含量和密度之间存在极显著正相关关系(P0.01,P0.01)。土层深度与有机碳含量存在极显著负相关关系(P0.01);与有机碳密度、氮密度存在极显著正相关关系(P0.01,P0.01)。说明海拔和土层是影响青海省森林土壤有机碳、氮分布的关键因子。     

Effect of cropping systems on soil chemical characteristics,with emphasis on soil acidification*

The soil under intensive cultivation and low addition of crop residues is exposed to erosion and reduction of organic matter. Increases in soil organic matter, cation exchange capacity (CEC) and nutrient availability may occur in no-till systems with legumes and with large additions of organic residues. Nevertheless, some legumes may increase soil acidification through the carbon and nitrogen cycles. An experiment was carried out over 10 years, with 10 cropping systems on a Dark Red Podzolic soil (Paleudult) to evaluate the effect of no-till cropping systems on soil chemical characteristics. Legume cropping systems resulted in the greatest soil organic C gain and the highest ECEC to a depth of 17.5 cm. The increase was greatest at 0 - 2.5 cm layer. Clover systems resulted in the highest soil acidification at 2.5 - 7.5 and 7.5 - 17.5 cm depths. The rate of soil pH decrease at 2.5 - 7.5 cm depth under clover+ t Spergula/maize system was 0.1 unit year^-1. Differences in soil acidification affected soil ECEC. Soil exchangeable cation data indicate that nitrate leaching increased soil acidification. Maize yields were greatest in legume systems due to increased N supply.     

Soil carbon sequestration potential of permanent pasture and continuous cropping soils in New Zealand

Understanding soil organic carbon (SOC) sequestration is important to develop strategies to increase the SOC stock and, thereby, offset some of the increases in atmospheric carbon dioxide. Although the capacity of soils to store SOC in a stable form is commonly attributed to the fine (clay + fine silt) fraction, the properties of the fine fraction that determine the SOC stabilization capacity are poorly known. The aim of this study was to develop an improved model to estimate the SOC stabilization capacity of Allophanic (Andisols) and non‐Allophanic topsoils (0–15 cm) and, as a case study, to apply the model to predict the sequestration potential of pastoral soils across New Zealand. A quantile (90th) regression model, based on the specific surface area and extractable aluminium (pyrophosphate) content of soils, provided the best prediction of the upper limit of fine fraction carbon (FFC) (i.e. the stabilization capacity), but with different coefficients for Allophanic and non‐Allophanic soils. The carbon (C) saturation deficit was estimated as the difference between the stabilization capacity of individual soils and their current C concentration. For long‐term pastures, the mean saturation deficit of Allophanic soils (20.3 mg C g^?1) was greater than that of non‐Allophanic soils (16.3 mg C g^?1). The saturation deficit of cropped soils was 1.14–1.89 times that of pasture soils. The sequestration potential of pasture soils ranged from 10 t C ha^?1 (Ultic soils) to 42 t C ha^?1 (Melanic soils). Although meeting the estimated national soil C sequestration potential (124 Mt C) is unrealistic, improved management practices targeted to those soils with the greatest sequestration potential could contribute significantly to off‐setting New Zealand's greenhouse gas emissions. As the first national‐scale estimate of SOC sequestration potential that encompasses both Allophanic and non‐Allophanic soils, this serves as an informative case study for the international community.     

Changes in carbon storage in temperate humic loamy soils after forest clearing and continuous corn cropping in France

Soil samples from forest and agricultural sites in three areas of southwest France were collected to determine the effect of forest conversion to continuous intensive corn cropping with no organic matter management on soil organic carbon (C) content. Soils were humic loamy soils and site characteristics that may affect soil C were as uniform as possible (slope, elevation, texture, soil type, vegetation). Three areas were selected, with adjacent sites of various ages of cultivation (3 to 35 yr), and paired control forest sites. The ploughed horizon (0-Dt cm) and the Dt-50 cm layer were collected at each agricultural site. In forest sites, each 10 cm layer was collected systematically down to 1 meter depth. Carbon concentrations were converted to total content to a given depth as the product of concentration, depth of sample and bulk density, and expressed in units of kg m^-2. For each site and each sampled layer, the mineral mass of soil was calculated, in order to base comparisons on the same soil mass rather than the same depth. The pattern of C accumulation in forest soils showed an exponential decrease with depth. Results suggested that soil organic carbon declined rapidly during the first years of cultivation, and at a slower rate thereafter. This pattern of decrease can be fitted by a bi-exponential model assuming that initial soil organic carbon can be separated into two parts, a very labile pool reduced during the first rapid decline and more refractory fractions oxidizing at a slower rate. Sampling to shallow depths (0-Dt cm) resulted in over-estimation of the rate of carbon release in proportion to the initial amount of C, and in under-estimation of the total loss of C with age. The results for the 0–50 cm horizon indicated that losses of total carbon average about 50% in these soils, ranging in initial carbon content from 19 to 32.5 kg m^-2. Carbon release to the atmosphere averaged 0.8 kg m^-2 yr^-1 to 50 cm depth during the first 10 years of cultivation. The results demonstrate that temperate soils may also be an important source of atmospheric carbon, when they are initially high in carbon content and then cultivated intensively with no organic matter management.     

Soil carbon stocks in stable tropical landforms are dominated by geochemical controls and not by land use

Soil organic carbon (SOC) dynamics depend on soil properties derived from the geoclimatic conditions under which soils develop and are in many cases modified by land conversion. However, SOC stabilization and the responses of SOC to land use change are not well constrained in deeply weathered tropical soils, which are dominated by less reactive minerals than those in temperate regions. Along a gradient of geochemically distinct soil parent materials, we investigated differences in SOC stocks and SOC (Δ¹⁴C) turnover time across soil profile depth between montane tropical forest and cropland situated on flat, non-erosive plateau landforms. We show that SOC stocks and soil Δ¹⁴C patterns do not differ significantly with land use, but that differences in SOC can be explained by the physicochemical properties of soils. More specifically, labile organo-mineral associations in combination with exchangeable base cations were identified as the dominating controls over soil C stocks and turnover. We argue that due to their long weathering history, the investigated tropical soils do not provide enough reactive minerals for the stabilization of C input in either high input (tropical forest) or low-input (cropland) systems. Since these soils exceeded their maximum potential for the mineral related stabilization of SOC, potential positive effects of reforestation on tropical SOC storage are most likely limited to minor differences in topsoil without major impacts on subsoil C stocks. Hence, in deeply weathered soils, increasing C inputs may lead to the accumulation of a larger readily available SOC pool, but does not contribute to long-term SOC stabilization.     

保护性耕作对紫色水稻土团聚体组成和有机碳储量的影响

通过长期定位试验,研究了保护性耕作对四川盆地紫色水稻土耕层团聚体组成和有机碳储量的影响.结果表明,保护性耕作显著影响耕层团聚体组成及其有机碳含量.油菜免耕、厢作免耕、绿肥免耕、垄作翻耕和厢作翻耕0～10 cm土壤大团聚体分别比对照(12%)增加23%、69%、9%、36%和28%,而10～20 cm土壤大团聚体比对照低9%～38%.冬水免耕、油菜免耕和绿肥免耕0～10 cm土壤大团聚体中有机碳含量分别比对照增加13%、31%和32%,而10～20 cm土壤各处理有机碳含量低于对照28%～54%,其土壤大团聚体和微团聚体中碳浓度差异低于0～10cm土壤.各处理0～10 cm土壤总有机碳储量比对照增加8%～28%,而10～20 cm土壤总有机碳储量低于对照4%～22%.传统耕作转变为保护性耕作13年后0～10和10～20 cm土壤有机碳固定率分别为53和25 g·m^-2·a^-1,传统耕作有机碳固定率分别为26和33 g·m^-2·a^-1.保护性耕作有利于紫色水稻土表层大团聚体的形成和土壤总有机碳储量的提高.     

氮输入对中国东北地区土壤碳蓄积的影响

由于人类活动的干扰,通过沉降和施肥形式进入陆地生态系统的氮素持续增加,中国已经成为继欧洲和北美之后的第三大氮沉降区,同时也是最大的化肥消费国。氮输入与陆地生态系统生物地球化学循环的一系列过程都相互联系,碳循环及其格局也受到氮输入的影响。土壤有机碳库在全球碳循环中具有重要作用,氮输入能否或在多大程度上对土壤碳库产生影响已经成为全球变化和氮沉降研究中不可回避的问题。东北地区是世界三大黑土带之一,土壤碳的变化不仅对于土壤肥力维持具有重要意义,而且对区域碳收支具有重要影响。利用生态系统过程模型——CEVSA2模型,基于我国能源消费、施氮数据和降水数据生成了一套中国大气氮沉降的时空网格数据,结合大气CO_2浓度、气候、土地覆被、土壤类型和质地的时空数据,模拟评估了1961-2010年氮输入对中国东北地区土壤碳蓄积的影响。结果表明:(1)1961-2010年东北地区的平均氮沉降速率为1.00gNm~(-2)a~(-1),年增长率为0.047 gN m~(-2)a~(-1)。东北农田总氮输入速率达到5.78 gN m~(-2)a~(-1),从20世纪80年代开始显著增加。(2)氮输入促进了东北地区土壤碳的蓄积,东北陆地生态系统的土壤碳密度平均增加了135 gC/m~2,50a氮输入共增加土壤碳蓄积0.16 PgC。(3)氮输入引起的东北地区土壤碳蓄积量的变化呈现出东高西低、南高北低的空间格局,辽河平原、松嫩平原和三江平原的土壤碳密度增加量超过了300 gC/m~2。(4)不同植被类型下的土壤碳密度对氮输入的响应存在较大差异,农田土壤碳密度平均增加了230 gC/m~2,森林、灌丛和草地则分别增加了76、169 gC/m~2和89 gC/m~2。氮输入的空间差异和不同植被类型对氮输入响应的差异共同决定了东北地区土壤碳增加量的空间格局。通过本研究阐明了氮输入对东北农田土壤碳蓄积的影响,从而为农田生态系统的固碳减排和农田土壤碳氮管理提供了决策依据。     

Elevated atmospheric CO2 effects on biomass production and soil carbon in conventional and conservation cropping systems

Increasing atmospheric CO₂ concentration has led to concerns about potential effects on production agriculture as well as agriculture's role in sequestering C. In the fall of 1997, a study was initiated to compare the response of two crop management systems (conventional and conservation) to elevated CO₂. The study used a split‐plot design replicated three times with two management systems as main plots and two CO₂ levels (ambient=375 μL L^?1 and elevated CO₂=683 μL L^?1) as split‐plots using open‐top chambers on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudults). The conventional system was a grain sorghum (Sorghum bicolor (L.) Moench.) and soybean (Glycine max (L.) Merr.) rotation with winter fallow and spring tillage practices. In the conservation system, sorghum and soybean were rotated and three cover crops were used (crimson clover (Trifolium incarnatum L.), sunn hemp (Crotalaria juncea L.), and wheat (Triticum aestivum L.)) under no‐tillage practices. The effect of management on soil C and biomass responses over two cropping cycles (4 years) were evaluated. In the conservation system, cover crop residue (clover, sunn hemp, and wheat) was increased by elevated CO₂, but CO₂ effects on weed residue were variable in the conventional system. Elevated CO₂ had a greater effect on increasing soybean residue as compared with sorghum, and grain yield increases were greater for soybean followed by wheat and sorghum. Differences in sorghum and soybean residue production within the different management systems were small and variable. Cumulative residue inputs were increased by elevated CO₂ and conservation management. Greater inputs resulted in a substantial increase in soil C concentration at the 0–5 cm depth increment in the conservation system under CO₂‐enriched conditions. Smaller shifts in soil C were noted at greater depths (5–10 and 15–30 cm) because of management or CO₂ level. Results suggest that with conservation management in an elevated CO₂ environment, greater residue amounts could increase soil C storage as well as increase ground cover.     

尕海湿地植被退化过程中植被——土壤系统有机碳储量变化特征

青藏高原湿地作为陆地生态系统的重要组成部分,在全球碳循环中发挥着重要作用.以青藏高原东缘尕海湿地植被不同退化程度样地(未退化CK、轻度退化SD、中度退化MD及重度退化HD)为研究对象,通过分析地上植物、凋落物、根系和土壤有机碳,研究湿地植被退化过程中植被-土壤系统有机碳储量变化特征.结果表明:除HD外,不同退化程度湿地地上植被碳储量为99.58～205.64 g·m^-2,根系(0～40 cm)碳储量为56.96～754.37 g·m^-2,地上、根系碳储量随退化程度的加剧显著下降,土壤容重随退化程度加剧呈先增加后减少趋势,植被退化湿地各层土壤容重均大于对照样地,而凋落物碳储量为17.29～35.69 g·m^-2,CK和MD均显著高于SD;不同退化程度湿地土壤0～40 cm碳储量为7265.06～9604.30 g·m^-2,且MD>CK>SD>HD,土壤有机碳储量CK和MD显著高于SD、HD;植被-土壤系统的碳储量为7265.06～10389.94 g·m^-2,各样地大小顺序为CK>MD>SD>HD,有机碳主要储存于土壤中,占湿地总碳贮量的90%以上,说明适度干扰有利于发挥高寒湿地生态系统的碳汇功能.     

尕海湿地植被退化过程中植被-土壤系统有机碳储量变化特征

青藏高原湿地作为陆地生态系统的重要组成部分,在全球碳循环中发挥着重要作用.以青藏高原东缘尕海湿地植被不同退化程度样地(未退化CK、轻度退化SD、中度退化MD及重度退化HD)为研究对象,通过分析地上植物、凋落物、根系和土壤有机碳,研究湿地植被退化过程中植被-土壤系统有机碳储量变化特征.结果表明: 除HD外,不同退化程度湿地地上植被碳储量为99.58～205.64 g·m^-2,根系(0～40 cm)碳储量为56.96～754.37 g·m^-2,地上、根系碳储量随退化程度的加剧显著下降,土壤容重随退化程度加剧呈先增加后减少趋势,植被退化湿地各层土壤容重均大于对照样地,而凋落物碳储量为17.29～35.69 g·m^-2,CK和MD均显著高于SD;不同退化程度湿地土壤0～40 cm碳储量为7265.06～9604.30 g·m^-2,且MD＞CK＞SD＞HD,土壤有机碳储量CK和MD显著高于SD、 HD;植被-土壤系统的碳储量为7265.06～10389.94 g·m^-2,各样地大小顺序为CK＞MD＞SD＞HD,有机碳主要储存于土壤中,占湿地总碳贮量的90%以上,说明适度干扰有利于发挥高寒湿地生态系统的碳汇功能.