Bio-char Sequestration in Terrestrial Ecosystems – A Review

The application of bio-char (charcoal or biomass-derived black carbon (C)) to soil is proposed as a novel approach to establish a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems. Apart from positive effects in both reducing emissions and increasing the sequestration of greenhouse gases, the production of bio-char and its application to soil will deliver immediate benefits through improved soil fertility and increased crop production. Conversion of biomass C to bio-char C leads to sequestration of about 50% of the initial C compared to the low amounts retained after burning (3%) and biological decomposition (< 10–20% after 5–10 years), therefore yielding more stable soil C than burning or direct land application of biomass. This efficiency of C conversion of biomass to bio-char is highly dependent on the type of feedstock, but is not significantly affected by the pyrolysis temperature (within 350–500 ^∘C common for pyrolysis). Existing slash-and-burn systems cause significant degradation of soil and release of greenhouse gases and opportunies may exist to enhance this system by conversion to slash-and-char systems. Our global analysis revealed that up to 12% of the total anthropogenic C emissions by land use change (0.21 Pg C) can be off-set annually in soil, if slash-and-burn is replaced by slash-and-char. Agricultural and forestry wastes such as forest residues, mill residues, field crop residues, or urban wastes add a conservatively estimated 0.16 Pg C yr⁻¹. Biofuel production using modern biomass can produce a bio-char by-product through pyrolysis which results in 30.6 kg C sequestration for each GJ of energy produced. Using published projections of the use of renewable fuels in the year 2100, bio-char sequestration could amount to 5.5–9.5 Pg C yr⁻¹ if this demand for energy was met through pyrolysis, which would exceed current emissions from fossil fuels (5.4 Pg C yr⁻¹). Bio-char soil management systems can deliver tradable C emissions reduction, and C sequestered is easily accountable, and verifiable.     

Transformation of Organic Matter of the Larch Forest Soils in the Northern Taiga of Nizhne-Tungusskoe Plateau, Central Siberia

The evaluation of biospheric role of the boreal forests in the accumulation of carbon is connected with the evaluation of organic matter (OM) pool in soils. The research sites were larch forests, they are situated on Nizhne-Tungusskoe Plateau. Larch forests of feather-moss and lichen types (110 and 380 years old) were formed on 'ochric podbur' soils. Litter stocks are 3.5–4.5 kg m^{− 2} with thickness 10–25 cm. Cryomezomorphic northern taiga soils contains 38–73 t (carbon) ha^{− 1}. Pool of fast mineralized OM has average value 38.1 t (carbon) ha^{− 1}, including 20.5 and 6.4 t (Carbon) ha^{− 1} of labile compounds on surface and in the soil, and 11.2 t (carbon) ha^{− 1} of mobile OM. Microbial mass reaches 1.78–3.47 t (carbon) ha^{− 1}, its proportion is 3.6–4.9% of the total OM carbon. Zoomass of feather-moss larch forest is 0.20–0.61 * 10^{− 2}, in lichen larch forest −0.01–0.07 * 10^{− 2} t (carbon) ha^{− 1}. A pool of resistant to biological decomposition and bonded to mineral soil matrix OM is 17.7 t (carbon) ha^{− 1} and it varies from 18.6 to 29.0 in feather-moss larch forest, and from 6.4 to 17.0 t (carbon) ha^{− 1} in lichen larch forest. Two-years field experiment has been performed to determine transformation rates of various plant litter fractions and to clarify the role of soil biota in these processes. The results showed participation of all biota groups in the decomposition of plant residues caused weight loss of larch-needles and root mortmass. Isolation of organic matter from all-size invertebrate groups leads to some decrease of decomposition activity.     

中亚热带针阔混交林土壤-大气界面释汞通量研究

为了揭示不同气候条件下森林与大气间汞交换的规律,应用动力学通量箱与Lumex RA 915+测汞仪联用技术,选择重庆缙云山国家级自然保护区为研究地点,于2011年4月~2012年3月对针阔混交林土/气界面释汞通量进行了为期1 a的连续监测,并考察了各环境因子对土壤释汞通量的影响.结果表明,缙云山针阔混交林林地土壤年平均释汞通量值为(16.82±6.70)ng·(m2·h)-1,明显高于欧美国家自然背景区;受光照、温度、相对湿度等气象因素以及亚热带地区森林植被生长变化规律影响,缙云山地区林地土壤释汞通量存在显著的季节性差异,暖季林地土壤释汞通量[(22.23±13.19)ng·(m2·h)-1]明显高于冷季[(6.01±4.05)ng·(m2·h)-1];通径分析结果表明林地土壤释汞通量的日变化特征和1 d中光照强度变化有密切关系,土温、气温和相对湿度与土壤释汞通量之间的显著相关关系可能是光照强度与土壤释汞通量相关关系的表象.     

Decay of cacti and carbon cycling

Cacti contain large quantities of Ca-oxalate biominerals, with C derived from atmospheric CO₂. Their death releases these biominerals into the environment, which subsequently transform to calcite via a monohydrocalcite intermediate. Here, the fate of Ca-oxalates released by plants in arid environments is investigated. This novel and widespread form of biomineralization has unexpected consequences on C cycling and calcite accumulation in areas with large numbers of cacti. The magnitude of this mineralization is revealed by studying the large columnar cactus Carnegiea gigantea (Engelm.) Britton and Rose in southwestern Arizona (locally called the saguaro). A large C. gigantea contains on the order of 1×10⁵ g of the Ca-oxalate weddellite—CaC₂O₄·2H₂O. In areas with high C. gigantea density, there is an estimated 40 g C_atm m⁻² sequestered in Ca-oxalates. Following the death of the plant, the weddellite transforms to calcite on the order to 10–20 years. In areas with high saguaro density, there is an estimated release of up to 2.4 g calcite m⁻² year⁻¹ onto the desert soil. Similar transformation mechanisms occur with the Ca-oxalates that are abundant in the majority of cacti. Thus, the total atmospheric C returned to the soil of areas with a high number density of cacti is large, suggesting that there may be a significant long-term accumulation of atmospheric C in these soils derived from Ca-oxalate biominerals. These findings demonstrate that plant decay in arid environments may have locally significant impacts on the Ca and inorganic C cycles.     

Assessing soil chemical and physical property responses to deforestation and subsequent cultivation in smallholders farming system in Ethiopia

In Ethiopia land degradation in the forms of soil erosion and declining soil fertility are serious challenges to agricultural productivity and economic growth. Despite the general recognition of the threat from land degradation on agricultural productivity, few studies have been made to quantify the extent, rate and process of soil fertility depletion under various land use systems and management practices in the country. In this study we assessed soil chemical and physical property responses to deforestation and subsequent cultivation along a chronosequence of closely located farmlands of different ages (7, 10, 26, 34 and 53 years) since conversion from a tropical dry Afromontane natural forest in Ethiopia. These properties were compared with soil properties under an adjacent natural forest. The changes were used as indicators to evaluate the sustainability of the farm management. All the soils in the study were Mollic Andosols/Humic Haplustands. Soil bulk density (g cm⁻³) in the 0–10 and 10–20 cm soil layers increased significantly while percent pore space decreased significantly in a continuum with increasing cultivation period. Soil C and total N contents (g kg⁻¹) in the 0–10 cm soil layer declined significantly and exponentially with increasing years under cultivation. However, in the 10–20 cm soil layer both soil C and total N on the farmlands were significantly higher until after 34 years of continuous cultivation compared to the same soil layer under the natural forest. Consequently, the soil C stock (g m⁻²) of the upper 0.20 m mineral soil was not significantly lower on the farmlands until after 26 years of continuous cultivation compared to the natural forest soil. Available P and K (mg kg⁻¹) in the 0–10 cm layer were higher in the soils of the farmlands throughout the 53 years of continuous cultivation compared to the soil under the natural forest. Exchangeable Ca, CEC and base saturation in the 0–10 cm soil layer declined more or less throughout the cultivation period while in the 10–20 cm soil layer they followed the patterns of soil C of that depth. Generally, the magnitudes and rates of degradation of the soil properties following conversion and subsequent cultivation were lower than expected for a low input tropical farming system as the one investigated. Nevertheless, almost all soil quality attributes showed overall declining trends in the long perspective. This continuous decline, albeit slowly, in soil quality with increasing cultivation period indicated that the present land management is not sustainable. Therefore, improved management is imperative to sustain the soil quality and maintain long-term productivity of the farmlands.     

缙云山不同林分下土壤有机碳及矿化特征

土壤有机碳库是陆地最大的有机碳储存库,其微弱的变化就能影响大气CO2浓度的显著变化,其中森林土壤碳库约占全球土壤碳库的70%,因此如何实现森林生态系统土壤有机碳库的高效管理成为目前的研究热点.本研究以缙云山5种典型林分:阔叶林、针叶林、针阔叶混交林、竹林及研究区内弃耕15 a的荒草地(对照土壤)为对象,采用矿化培养实验,分析了不同林分的土壤在不同土层(0～20、20～40、40～60、60～100 cm)中的有机碳矿化特征.结果表明,林分类型、培养时长和土层深度均对土壤有机碳矿化速率有显著影响.不同林分土壤有机碳矿化速率均随着土层加深而降低,其中0～20 cm土层的矿化速率[11. 97～25. 12 mg·(kg·d)-1]均显著高于其他土层(P 0. 05),其他土层间矿化速率[4. 79～6. 51mg·(kg·d)-1]无显著性差异. 5种林分的土壤有机碳累积矿化量均随着土层加深而降低,0～20 cm土层中竹林和阔叶林土壤有机碳累积矿化量最高,分别为177. 66 mg·kg~(-1)和120. 38 mg·kg~(-1),随着土层加深在60～100 cm土层中,针叶林累计矿化量最高达到了46. 96 mg·kg~(-1).双库一级动力学方程可以较好地拟合缙云山不同林分下土壤有机碳矿化过程,不同林分下土壤易分解有机碳含量均随土层加深而降低,针叶林土壤矿化能力较强,对难分解有机碳库的利用程度较高,而竹林和阔叶林土壤微生物活性较高,可以有效促进碳循环,提高土壤固碳能力.     

济宁南部区域耕作层土壤有机碳密度及储量研究

济宁市南部区域是著名的国家商品粮、优质大蒜、优质稻米和有机蔬菜生产基地,由于土壤有机碳作为农田生态系统中土壤肥力的重要组成成分之一,在土壤改良、作物质量和产量提高等方面都有十分重要的作用,因此,对济宁南部区域耕作层土壤有机碳密度及储量的研究具有十分重要的意义。本文以济宁南部煤田地区作为典型区域,以耕作层土壤(0~20cm)为研究对象,采集了79件耕作层土壤样品,利用元素分析仪测定了土壤样品中有机碳含量。经统计分析发现,各类型土壤有机碳密度介于1.92~4.83kg/m2之间,有机碳密度的加权平均值为4.03kg/m2,高于中国表层土壤有机碳密度的平均值2.97kg/m2;通过壤质类型分类而估算的有机碳总储量为4.57×109 kg,通过土壤利用方式分类而估算的有机碳总储量为4.53×109 kg,二者基本吻合;济宁南部区域耕作层土壤有机碳富集程度受人类活动影响较大,耕作层土壤中氮含量与有机碳的线性相关系数为0.924 9;另外,有机碳富集程度与秸秆返田规模也有着一定的关联。研究结果不仅为研究区今后开展耕作层土壤环境质量评价提供依据,也为区域生态平衡研究奠定了基础。     

Optimizing carbon sequestration in commercial forests by integrating carbon management objectives in wood supply modeling

This paper provides a methodology for generating forest management plans, which explicitly maximize carbon (C) sequestration at the forest-landscape level. This paper takes advantage of concepts first presented in a paper by Meng et al. (2003; Mitigation Adaptation Strategies Global Change 8:371–403) by integrating C-sequestration objective functions in existing wood supply models. Carbon-stock calculations performed in Woodstock^TM (RemSoft Inc.) are based on C yields generated from volume table data obtained from local Forest Development Survey plots and a series of wood volume-to-C content conversion factors specified in von Mirbach (2000). The approach is used to investigate the impact of three demonstration forest-management scenarios on the C budget in a 110,000 ha forest in south-central New Brunswick, Canada. Explicit demonstration scenarios addressed include (1) maximizing timber extraction either by clearcut or selection harvesting for greatest revenue generation, (2) maximizing total C storage in the forest landscape and in wood products generated from harvesting, and (3) maximizing C storage together with revenue generation. The level of clearcut harvesting was greatest for scenario 1 (≥15 × 10⁴ m³ of wood and ≥943 ha of land per harvesting period), and least for scenario 2 (=0 m³ per harvesting period) where selection harvesting dominated. Because softwood saw logs were worth more than pulpwood ($60 m⁻³ vs. $40 m⁻³) and were strategic to the long-term storage of C, the production of softwood saw logs exceeded the production of pulpwood in all scenarios. Selection harvesting was generally the preferred harvesting method across scenarios. Only in scenario 1 did levels of clearcut harvesting occasionally exceed those of selection harvesting, mainly in the removal of old, dilapidated stands early in the simulation (i.e., during periods 1 through 3). Scenario 2 provided the greatest total C-storage increase over 80 years (i.e., 14 × 10⁶ Mg C, or roughly 264 Mg ha⁻¹) at a cost of $111 per Mg C due to lost revenues. Scenarios 3 and 1 produced reduced storage rates of roughly 9 × 10⁶ Mg C and 3 × 10⁶ Mg C, respectively; about 64% and 22% of the total, 80-year C storage calculated in scenario 2. The bulk of the C in scenario 2 was stored in the forest, amounting to about 76% of the total C sequestered.     

许昌市典型区域土壤磁化率与有机质含量的相关性研究

为探讨土壤磁化率对有机质含量的指示作用,对许昌市典型区域土壤磁化率与有机质含量的相关性进行研究,结果显示:研究区域土壤样品Xlf变化范围在15×10~(-8)~125×10~(-8)m~3/kg,平均值为64×10~(-8)m~3/kg,说明研究区土壤样品中磁性矿物含量较低。Xfd值在4.67%~26.67%之间,平均值为10.02%,反映了样品中超顺磁颗粒含量很高,说明研究区域土壤磁性矿物主要由自然成土作用形成,现代工业生产活动和人类的生活活动贡献较小。土壤有机质含量范围为3.74~31.93 g/kg,均值为17.09 g/kg。研究区域土壤磁化率与有机质含量呈不显著正相关性,反映了在长期人工施肥活动和城市化进程中人类活动导致土壤各理化因子之间发生学联系的弱化。     

秦岭太白红杉林土壤有机碳密度研究

土壤有机碳(Soil Organic Carbon,SOC)库是陆地生态系统中最大的碳库,确定土壤有机碳储量及影响因子对碳循环和气候变化的研究具有重要意义.在秦岭太白山南、北坡分别沿不同海拔梯度共调查了太白红杉(Larix chinensis Beissn)林的18个样点,共计54个土壤剖面,分南、北坡对太白红杉林土壤有机碳密度进行了估算,并分析了土壤有机碳的主要影响因子.结果表明:太白红杉林北坡土壤有机碳平均密度在枯落物层为(0.31±0.18)kg/m2,在0～100 cm土层为(15.84±9.08)kg/m2;南坡土壤有机碳平均密度在枯落物层为(0.27±0.07)kg/m2,在0～100 cm土层为(14.51±7.85)kg/m2;太白红杉林南、北坡0～100 cm土层土壤有机碳平均密度为(15.18±8.51)kg/m2.秦岭太白红杉林北坡0～100 cm土层土壤有机碳密度随海拔的增加呈显著减小趋势(P0.05),此外,该层土壤有机碳密度随年降水量的增加呈下降趋势.土壤容重与w(有机碳)呈显著负相关(P0.05).     

重庆铁山坪森林土壤汞释放通量的影响因子研究

对位于重庆铁山坪的马尾松林下的山地黄壤进行表层土壤(0~5 cm)的原状采集,并在实验室中进行控制实验,利用通量箱法测量原状土块表面的汞释放通量,以研究环境因子对土壤汞释放量的影响.结果表明,土壤汞释放量与辐射强度呈显著的正相关,在相同的空气温度和土壤含水量等条件下,土壤汞释放量在光下是遮阳条件下的3~9倍.不过,由于林下土壤常处于背阴状态,可能遮阳条件更能代表白天林下土壤汞的排放情况.土壤汞释放量存在明显的季节变化,夏季>春秋季>冬季,空气温度与土壤汞释放呈正相关.在低温下土壤汞释放量很低,土壤含水量影响较弱,而在高温时土壤含水量增加能明显促进土壤汞释放.枯落物的移除会显著降低土壤汞释放通量,主要原因可能是枯落物的汞含量较高并易于还原.土壤汞释放量在一天内也存在明显的衰减趋势,表明土壤表层的汞含量可能是森林土壤汞释放的重要限制因素.本研究测得森林土壤汞释放通量(白天)为:夏季(14.3±19.6)ng·(m2·h)-1、春秋季(3.50±5.36)ng·(m2·h)-1、冬季(1.48±3.27)ng·(m2·h)-1,以上稳态测试结果可能高估了实际的汞排放量.     

Management Options to Conserve and Sequester Carbon in the Agricultural Sector of the Former Soviet Union

Several management practices are available to conserve and sequester C in the agricultural sector of the former Soviet Union (FSU). The highest rate of C accumulation would result from the implementation of a no-till management option which will only continue during the first ten years until new C equilibrium is reached. Agroforestry management options provide a longer period for C accumulation, but at a lower rate. It is possible that the longest period of C conservation may be achieved by increasing the area under perennial grasses in the crop rotation. During the first decade of implementation of the management practices, the amount of C conserved or sequestered would be approximately equal to the current rate of net C sequestration in FSU forest sector. At present, agricultural soils and vegetation of the FSU store approximately 120 Pg C; the accumulation of soil organic matter is 0.032 Pg C yr^-1. The annual C loss in the FSU agricultural sector was estimated at 0.21 Pg C yr^-1.     

重庆缙云山4种典型植被覆盖下汞的释放通量及影响因素

为了揭示不同植被覆盖下土壤/大气界面释汞通量及其交换特征,在缙云山国家级自然保护区内选择4种典型植被覆盖类型(常绿阔叶林、楠竹林、灌木林以及草地)为研究对象,连续同步监测不同植被覆盖下土/气界面汞释放通量,同时考察各环境因子对土壤释汞的影响.结果表明,缙云山在4种不同植被覆盖下土壤汞释放通量具有明显的差异,总体表现为楠竹林[17.77 ng·(m~2·h)~(-1)]草地[17.58 ng·(m~2·h)~(-1)]灌木林[16.87 ng·(m~2·h)~(-1)]常绿阔叶林[14.32 ng·(m~2·h)~(-1)];不同植被覆盖下土壤释汞通量在季节变化上呈现相似的规律性,但不同植被覆盖类型之间也存在明显差异,主要体现在暖季汞释放通量高于冷季;缙云山地区不同林植被覆盖下土壤释汞通量存在明显的日变化;气象因素光照强度、气温、土温和相对湿度,对土/气界面汞释放通量影响也不相同,气温为常绿阔叶林,灌木林与楠竹林的主要影响因子,光照强度为草地的主要影响因子.     

Dissolved Organic Carbon in Upland Forested Watersheds Underlain by Continuous Permafrost in Central Siberia

Hydroclimatic variability and plant species ecology cause mosaics in forested watersheds in permafrost zones. Measurements of organic matter accumulation, stock of dissolved organic carbon (DOC), DOC concentrations in litter leachates, subsurface flow, stream and seasonal and annual export were made in two contrasting slopes and valleys in the northern taiga of Central Siberia. Increased organic carbon accumulation in litter was found in poor hydroclimatic conditions of the north-facing slope and bottom valleys. In contrast, DOC contents and its export to soil were almost two-fold higher in warmer well-drained sites of the south-facing slope. The overall DOC flux to mineral soil from the beginning of June to mid-September was 17 g C m⁻² in the south-facing slope sites and only 9 g C m⁻² in the north-facing slope sites. DOC export was positively correlated with precipitation stimulating leaching of mobilizable organic matter. Accordingly intra-seasonal and inter-annual variability of the DOC fluxes was tightly coupled with water input. Meanwhile DOC export in Sphagnum and feathermoss sites showed different behavior in dry and wet years. The presence of permafrost preventing deep seepage of organic solutes results in higher stream DOC fluxes compared to permafrost-free or island permafrost regions. However, thawing of seasonally frozen soil layer during the growing season led to the decreasing concentrations of DOC in the stream from June to September. For two seasons of continuous stream water sampling (June and August–September), the riverine DOC flux constituted about 14% of DOC entering mineral soil on both slopes. The ratio of hydrologic DOC loss to NPP of larch forests of the region was estimated to be 1.1%.     

Net Ecosystem Production of Boreal Larch Ecosystems on the Yenisei Transect

The study was carried out in the Turukhansk Research Station of Yenisei Transect (65^°46^′N, 89^°25^′E). Larch (Larix gmelinii (Rupr.) Rupr.) is the dominant overstory tree species. The research has been conducted on four permanent test plots in same-age mature (110-year old) and overmature (380-year old) post-fire larch stands of green moss and lichen groups of forest type. Carbon cycle parameters were assessed based on a biometric method. Quantitative analysis of carbon pools and fluxes shows that net ecosystem production of north taiga larch stands averages 32% of net primary production. Sink of atmospheric CO₂ makes 1.22 and 0.74 t C ha^{− 1} year^{− 1} for mature and overmature green moss larch stands, and 0.65 and 0.35 t C ha^{− 1} year^{− 1} for lichen type. Net carbon sink in the tree layer make up 9% of net primary production carbon, ground vegetation – 15%, and dead plant residues accumulation – 8% of atmospheric carbon uptake via photosynthesis.     

Quantification of net primary production of Chinese forest ecosystems with spatial statistical approaches

Net primary production (NPP) of terrestrial ecosystems provides food, fiber, construction materials, and energy to humans. Its demand is likely to increase substantially in this century due to rising population and biofuel uses. Assessing national forest NPP is of importance to best use forest resources in China. To date, most estimates of NPP are based on process-based ecosystem modeling, forestry inventory, and satellite observations. There are little efforts in using spatial statistical approaches while large datasets of in-situ observed NPP are available for Chinese forest ecosystems. Here we use the surveyed forest NPP and ecological data at 1,266 sites, the data of satellite forest coverage, and the information of climate and topography to estimate Chinese forest NPP and their associated uncertainties with two geospatial statistical approaches. We estimate that the Chinese forest and woodland ecosystems have total NPP of 1,325 ± 102 and 1,258 ± 186 Tg C year⁻¹ in 1.57 million km² forests with a regression method and a kriging method, respectively. These estimates are higher than the satellite-based estimate of 1,034 Tg C year⁻¹ and almost double the estimate of 778 Tg C year⁻¹ using a process-based terrestrial ecosystem model. Cross-validation suggests that the estimates with the kriging method are more accurate. Our developed geospatial statistical models could be alternative tools to provide national-level NPP estimates to better use Chinese forest resources.     

长江上游高山森林小溪流磷输出及其汇流特征

长江上游水源涵养地高山森林溪流磷输出不仅是森林生态系统磷输出的主要形式,而且与下游水域环境密切相关,但对此人们一直缺乏必要的关注.因此,为了解森林溪流磷的最大输出潜力,于2013年8月中旬溪流流量较大的季节,调查了海拔3600~3700 m的高山森林18条溪流的磷输出及其从源头到尽头的变化特征.结果表明:在所选样地内,溪流中总磷储量为8120.1 mg,单位水体面积储量为5.4 mg·m-2,单位水体面积总输出量为150.3 kg·km-2·d-1,单位集水区面积总输出量为0.2 kg·km-2·d-1,集水区潜在年输出总量约为67.7 kg·km-2.溪流中总磷含量维持在检出限0.01~0.6 mg·L-1之间,所有溪流上游总磷含量和储量均明显高于下游;溪流尽头总磷储量仅为源头总储量的29.2%,尽头平均浓度为源头平均浓度的30.9%.这些结果表明,高山森林溪流具有明显的磷输出特征,但从源头到尽头的汇流过程中,溪流水体能显著降低总磷含量及储量,表现出明显的自净能力,这也是高山森林生态系统养分传输纽带的重要体现.     

季节性冻融格局变化对高山森林土壤氮素淋溶损失的影响

气候变化情景下冻融格局的改变可能导致寒冷生物区土壤氮的淋溶损失,从而改变土壤养分循环和森林溪流的水体环境.因此,为了解季节性冻融循环及其变化对高山森林土壤氮淋溶损失的影响,于2010年5月到2012年4月期间,采用土柱培养实验,利用海拔形成的温度差异模拟气候变暖过程,将高山森林(海拔3600 m)土壤分别培养在海拔3600 m(A1)、3300 m(A2)和3000 m(A3)的森林地表,研究了生长季节与冻融季节不同关键时期的土壤氮淋溶特征.结果表明:川西高山森林土壤氮素淋溶损失随着海拔增加而增加,其损失量为(1.85±0.39)kg·hm-2·a-1(A3)(1.87±0.34)kg·hm-2·a-1(A2)(2.94±0.73)kg·hm-2·a-1(A1),其中,62%以上的氮损失发生在季节性冻融期间.冻融季节高山森林土壤氮素淋溶流失的主要形式为铵态氮和硝态氮,且铵态氮的淋溶损失量高于硝态氮,而生长季节土壤氮素淋溶损失的主要形式是可溶性有机氮.这意味着冻融循环格局在很大程度上控制着高山森林土壤氮素淋溶损失特征,未来气候变暖可能降低高寒森林土壤氮素肥力,增加森林溪流中的氮含量.     

The potential of world cropland soils to sequester C and mitigate the greenhouse effect

Soil emission of CO₂ is closely linked to soil degradation, decrease in soil organic carbon (SOC) content and decline in soil quality. Enhancing soil quality through adoption of best management practices (BMPs) and soil restoration can increase SOC content and soil productivity, and partially mitigate the greenhouse effect. The C sequestration potential through judicious management of world cropland includes 0.08–0.12 Pg/yr by erosion control, 0.02–0.03 Pg/yr by restoration of severely degraded soils, 0.02–0.04 Pg/yr by reclamation of salt-affected soils, 0.15–0.175 Pg/yr by adoption of conservation tillage and crop residue management, 0.18–0.24 Pg/yr by adoption of improved cropping system and 0.30–0.40 Pg/yr as C offset through biofuel production. The total C sequestration potential of the world cropland is about 0.75–1.0 Pg/yr or about 50% of annual emission of 1.6–1.8 Pg by deforestation and other agricultural activities. This finite soil-C sink could be filled over a 20 to 50-year period, during which energy related emission reductions gradually take effect at global scale. Improving soil quality is a win–win strategy, while increasing productivity it also improves environment and partially mitigates the greenhouse effect. Intensification of farming and increasing biomass production can lead to increased sequestration of C in soils, and to partly meet commitments under the Kyoto Protocol at national and global scales. Global reduction in C emission may have to be substantial if the atmospheric concentration of CO₂ is to be stabilized at 550 ppmv. However, realization of this potential would require developing channels of communication between scientists and land managers and policy makers, and providing economic incentives.     

Ancient paddy soils from the Neolithic age in China’s Yangtze River Delta

Identifying prehistoric irrigated rice fields and characterizing the beginning of paddy soil development are important for a better understanding of human development and agricultural history. In 2003, paddy soils and irrigated rice fields buried at a depth of 100–130 cm were excavated at Chuo-dun-shan in the Yangtze River Delta, close to Suzhou, China. The fields of sizes between 1.4 and 16 m² were surrounded with ridges that were connected to ditches/ponds via outlets to control the water level within the fields. Many carbonized and partly carbonized rice grains with an age of 3,903 B.C.(measured ¹⁴C age 5,129±45 a BP) were recovered. The surface layers of these buried paddy fields showed a high content of soil organic matter and a considerable high density of rice opals. The latter were identified to derive from Oryza spp. Solid-state ¹³C nuclear magnetic resonance spectroscopy revealed aromatic carbon (C) as the predominant organic C form in the fossil surface layer. This is expected, if the major source represents burnt rice and straw. In summary, our data are in agreement with new evidences indicating that in China, paddy soils and irrigated rice cultivation were initiated and developed more than 6,000 years ago.