Scenario analysis of alternative vegetation management options on the greenhouse gas budget of two grazing businesses in north-eastern Australia

The emerging carbon economy will have a major impact on grazing businesses because of significant livestock methane and land-use change emissions. Livestock methane emissions alone account for similar to 11% of Australia's reported greenhouse gas emissions. Grazing businesses need to develop an understanding of their greenhouse gas impact and be able to assess the impact of alternative management options. This paper attempts to generate a greenhouse gas budget for two scenarios using a spread sheet model. The first scenario was based on one land-type '20-year-old brigalow regrowth' in the brigalow bioregion of southern-central Queensland. The 50 year analysis demonstrated the substantially different greenhouse gas outcomes and livestock carrying capacity for three alternative regrowth management options: retain regrowth (sequester 71.5 t carbon dioxide equivalents per hectare, CO2-e/ha), clear all regrowth (emit 42.8 t CO2-e/ha) and clear regrowth strips (emit 5.8 t CO2-e/ha). The second scenario was based on a 'remnant eucalypt savanna-woodland' land type in the Einasleigh Uplands bioregion of north Queensland. The four alternative vegetation management options were: retain current woodland structure (emit 7.4 t CO2-e/ha), allow woodland to thicken increasing tree basal area (sequester 20.7 t CO2-e/ha), thin trees less than 10 cm diameter (emit 8.9 t CO2-e/ha), and thin trees <20 cm diameter (emit 12.4 t CO2-e/ha). Significant assumptions were required to complete the budgets due to gaps in current knowledge on the response of woody vegetation, soil carbon and non-CO2 soil emissions to management options and land-type at the property scale. The analyses indicate that there is scope for grazing businesses to choose alternative management options to influence their greenhouse gas budget. However, a key assumption is that accumulation of carbon or avoidance of emissions somewhere on a grazing business (e.g. in woody vegetation or soil) will be recognised as an offset for emissions elsewhere in the business (e.g. livestock methane). This issue will be a challenge for livestock industries and policy makers to work through in the coming years.

Participatory adaptation and mitigation strategies for climate change on mixed farms

The project uses participatory methods to engage primary producers and advisers in central Queensland, southern Queensland, and north east New South Wales on-farm trials and demonstrations to adapt mixed farming systems to changed climate conditions. The focus is adaptation to climate change but will support abatement of greenhouse gas emissions by building soil carbon, better managing soil nitrogen and soil organic carbon. Data will be collected and integrated with data from Round 1 of the Climate Change Research Program to extend industry understanding beyond a general awareness of ‘climate change’. Nitrous oxide and soil carbon data will help farmers/advisers understand the implications of climate change and develop adaptation strategies for a more sustainable, climate sensitive future.

Strategic tillage in no-till farming systems in Australia’s northern grains-growing regions: I. Drivers and implementation

Development of no-tillage (NT) farming has revolutionized agricultural systems by allowing growers to manage greater areas of land with reduced energy, labour and machinery inputs to control erosion, improve soil health and reduce greenhouse gas emission. However, NT farming systems have resulted in a build-up of herbicide-resistant weeds, an increased incidence of soil- and stubble-borne diseases and enrichment of nutrients and carbon near the soil surface. Consequently, there is an increased interest in the use of an occasional tillage (termed strategic tillage, ST) to address such emerging constraints in otherwise-NT farming systems. Decisions around ST uses will depend upon the specific issues present on the individual field or farm, and profitability and effectiveness of available options for management. This paper explores some of the issues with the implementation of ST in NT farming systems. The impact of contrasting soil properties, the timing of the tillage and the prevailing climate exert a strong influence on the success of ST. Decisions around timing of tillage are very complex and depend on the interactions between soil water content and the purpose for which the ST is intended. The soil needs to be at the right water content before executing any tillage, while the objective of the ST will influence the frequency and type of tillage implement used. The use of ST in long-term NT systems will depend on factors associated with system costs and profitability, soil health and environmental impacts. For many farmers maintaining farm profitability is a priority, so economic considerations are likely to be a primary factor dictating adoption. However, impacts on soil health and environment, especially the risk of erosion and the loss of soil carbon, will also influence a grower’s choice to adopt ST, as will the impact on soil moisture reserves in rainfed cropping systems.

Mykorritsa fosforin kierrättäjänä

Suomen maatalousmaihin kertynyttä fosforia hyödynnetään tehottomasti, ja samalla muokkauskerroksen suuri fosforimäärä on alttiina huuhtoutumiselle. Arbuskelimykorritsaa (AM) hyödyntämällä on mahdollista tehostaa viljelykasvin fosforinottoa ja kasvua, ja siten vähentää fosforin huuhtoutumista. Tämän tutkielman tavoitteena oli selvittää mykorritsan vaikutus kasvin kasvuun ja fosforinottoon karjanlantalannoituksella mineraalilannoitukseen verrattuna sekä näiden lannoitusten pitkäaikaisvaikutusta AM-sieniyhteisöihin. Jotta lannoituskäytäntöjen vaikutus mykorritsaan voitiin suhteuttaa muihin maan laatutekijöihin, näiden käytäntöjen vaikutus myös satomääriin sekä muihin maan laatumittareihin arvioitiin. Pitkäaikainen kenttäkoe perustettiin kolmelle paikkakunnalle Pohjois-Ruotsissa vuosina 1965–66. Kuusivuotinen viljelykierto koostui joko viisivuotisesta nurmesta ja ohrasta tai ohramonokulttuurista. Lannoituskäsittelyt 32-vuoden ajan olivat suositusten mukainen (NPK) ja edelliseen nähden kaksinkertainen (2NPK) mineraalilannoitus sekä karjanlantalannoitus (KL), jonka ravinnemäärä vastasi NPK -käsittelyä. Kolmen lannoituskäsittelyn vaikutusta mykorritsan tehokkuuteen kasvin kasvun ja fosforiravitsemuksen näkökulmasta tutkittiin astiakokeissa. Mykorritsasieniyhteisöjen toiminnallisten erojen selvittämiseksi tehtiin takaisin- ja ristiinsiirrostuskoe. (5 v-%) steriloitua maanäytettä NPK- ja KL -käsittelyistä siirrostettiin käsittelemättömiin maanäytteisiin, jotka olivat samoista lannoituskäsittelyistä. Mykorritsan positiivinen vaikutus kasvin kasvuun ja fosforiravitsemukseen oli suurin kun käytettiin karjanlantaa. NPK ja 2NPK -käsittelyiden välillä ei havaittu eroja. Takaisin- ja ristiinsiirrostuskokeessa ei ollut tilastollisesti merkitseviä eroja. Nurmi- ja ohrasadot olivat suurimmat kun mineraalilannoitetta annettiin suosituksiin nähden kaksinkertainen määrä. Satomäärät olivat yhtä suuret tai suuremmat kun käytettiin karjanlantaa NPK –lannoituksen sijaan. Karjanlantakäsittely lisäsi maaperän kokonaishiili- ja kokonaistyppipitoisuutta verrattuna NPK -käsittelyyn, joka sisälsi saman määrän ravinteita. Samalla huuhtoutumiselle altis liukoisen fosforin pitoisuus säilyi alhaisella tasolla. Karjanlanta edisti mykorritsan toimintaedellytyksiä, ja siksi mykorritsasta saatua hyötyä fosforinotossa ja kasvuvaikutuksena mineraalilannoitteisiin verrattuna, mutta se ei vaikuttanut mykorritsasieniyhteisön toiminnallisiin ominaisuuksiin. Karjanlantalannoitus paransi mitattuja maan ominaisuuksia kokonaisuudessaan, eikä se vähentänyt satoja.

Sensitivity of wetland methane emissions to model assumptions: application and model testing against site observations

Abstract. Methane emissions from natural wetlands and rice paddies constitute a large proportion of atmospheric methane, but the magnitude and year-to-year variation of these methane sources is still unpredictable. Here we describe and evaluate the integration of a methane biogeochemical model (CLM4Me; Riley et al., 2011) into the Community Land Model 4.0 (CLM4CN) in order to better explain spatial and temporal variations in methane emissions. We test new functions for soil pH and redox potential that impact microbial methane production in soils. We also constrain aerenchyma in plants in always-inundated areas in order to better represent wetland vegetation. Satellite inundated fraction is explicitly prescribed in the model because there are large differences between simulated fractional inundation and satellite observations. A rice paddy module is also incorporated into the model, where the fraction of land used for rice production is explicitly prescribed. The model is evaluated at the site level with vegetation cover and water table prescribed from measurements. Explicit site level evaluations of simulated methane emissions are quite different than evaluating the grid cell averaged emissions against available measurements. Using a baseline set of parameter values, our model-estimated average global wetland emissions for the period 1993–2004 were 256 Tg CH4 yr−1, and rice paddy emissions in the year 2000 were 42 Tg CH4 yr−1. Tropical wetlands contributed 201 Tg CH4 yr−1, or 78 % of the global wetland flux. Northern latitude (>50 N) systems contributed 12 Tg CH4 yr−1. We expect this latter number may be an underestimate due to the low high-latitude inundated area captured by satellites and unrealistically low high-latitude productivity and soil carbon predicted by CLM4. Sensitivity analysis showed a large range (150–346 Tg CH4 yr−1) in predicted global methane emissions. The large range was sensitive to: (1) the amount of methane transported through aerenchyma, (2) soil pH (± 100 Tg CH4 yr−1), and (3) redox inhibition (± 45 Tg CH4 yr−1).

Tamarind orchards: Agroforestry for dry lands

Agroforestry has a potential for sequestering as much carbon if not more than forests. Massive benefits can be channeled to small farmers and landless labourers through cultivation of Tamarind and other fast growing and fruit yielding trees. This paper describes a project started by small farmers and landless labourers in a semiarid areas of south India. The aim is to upgrade dryland holdings of the member families through economically sound dry land horticulture, community woodlots, and planting of fast growing species along orchard and field boundaries. The small farmers invest massive labour inputs and project gives economic benefits to change their land use practices and improve environmental quality. This paper describes the planning. processes of the project, hurdles in finding AIJ partners, current monitoring procedures and costs of C sequestration. This shows this project is economically viable on its own, but initially needed, and continues to need Carbon credit investment in order to spread rapidly across the geopolitical region covered by the organization. It argues that economic gains to small farmers and landless labourers are the most certain way of achieving massive biomass increase and soil carbon replenishment, and that multiple holistic benefits are achieved through this kind of project.

土壤有机碳和氮的分布及其对气候变化的响应

碳、氮不仅是生物体必需的营养元素，也是重要的生态元素。大气中温室气体C02、N2O等浓度的增加使得碳、氮的生物地球化学循环及其温室气体的减缓排放措施研究成为全球变化研究中的热点问题。 土壤是陆地生态系统的核心，是连接大气圈、水圈、生物圈、岩石圈的纽带;它是陆生生物赖以生存的物质基础，是陆地生态系统中物质与能量交换的重要场所，其在全球碳、氮循环中起着十分重要的作用。一方面，土壤有机碳和氮的含量与分布直接关系到生态系统的生产力和生态系统的规模，同时土壤有机碳和氮的转化与迁移又直接影响到温室气体的组成与含量。而土壤本身又是生态系统中生物与环境相互作用的产物。因此，研究土壤有机碳和氮的分布、转化及其对全球变化的响应对于正确理解碳、氮的生物地球化学循环及其对全球变化的响应制定应对策略具有重要意义。 全球变化的陆地样带是从机理上理解陆地生态系统对全球变化的响应，预测全球变化对陆地生态系统的可能影响，实现预警、调节和减少全球变化不良影响，科学地规划和管理陆地生态系统的有效平台。目前，国际地圈一生物圈计划(IGBP)基于不同地区全球变化驱动因素的不同以及全球变化的潜在反馈作用强度的不同，在全球4个关键地区共启动了15条IG8P陆地样带。以水分为主要驱动力的中国东北样带(NECT：Northeast China Transect)即为IGBP的陆地样带之一。 本文以中国东北样带为平台，基于2001年对中国东北样带科学考察所采土壤样品的实测结果和气候资料分析了土壤有机碳和氮的梯度分布及其与土壤、气候等因子之间的关系;借助C02浓度升高和不同土壤湿度的模拟试验探讨了土壤有机碳和氮对气候变化的响应;根据作物残体还田的长期定位试验和盆栽试验研究了作物残体还田对土壤有机碳和氮转化的影响，讨论了农田生态系统通过作物残体还田对减缓温室气体排放的效应。主要结果和结论如下： (1).样带表层土壤有机碳平均为22.3土4.93 g．kg-1，下层土壤有机碳平均为8.9±1.20 g．kg-1。样带表层土壤活性有机碳平均为3.52±0.881 g.kg-1，占表层土壤有机碳的13.1±0.78%;下层土壤活性有机碳平均为1.14±0.250g.kg-l，占下层土壤有机碳的10.9±0.79%。样带土壤活性有机碳与土壤有机碳之间呈极显著正相关关系(相关系数r=0.993，P<0.001)。 (2).不同生态类型土壤有机碳和活性有机碳含量不同。中国东北样带东部(经度126°～131°)为温带针阔混交林山地，植被种类极其丰富，地带性土壤为暗棕壤，并且多为自然土壤，土壤有机碳和活性有机碳含量较高。但由于采样区局部地理环境、植被结构及人类干扰程度的不同，土壤有机碳和活性有机碳含量变异较大，平均为61.9±13.84 g．kg-1和10. 88±2.236g. kg-1。样带中部（经度119°～126°）为松辽平原栎林草原、农田区和大兴安岭山地草甸草原区，属半湿润向半干旱过渡的气候。该区域主要土壤类型为黑土、黑钙土、盐化或碱化草甸土及风沙土，土壤沙化、碱化严重，土壤有机碳和活性有机碳含量明显降低，平均为10.5±1.97 g．kg-l和1. 35±0.327 g．kg-1。样带中西部（经度113°～119°）为内蒙古高原草甸草原和典型草原区域，具有典型的半干旱气候特征。该区地带性土壤为栗钙土，局部丘陵区分布黑钙土，土壤有机碳和活性有机碳含量为14.6±1.65 g．kg-1和2.07±0.342g.kg-1。样带西部（经度111°～113°）为内蒙古高原荒漠草原区域，地带性土壤为棕钙土，土壤较为贫瘠，其有机碳和活性有机碳含量最低，平均为7.99±1.51 g．kg-1和0.51±0.216 g．kg-1。从总的趋势看，样带表层土壤有机碳和活性有机碳的梯度分布趋势一致，都呈现出随经度降低而下降的趋势，局部因土壤退化而出现波动。 (3).样带土壤有机碳和活性有机碳与土壤全量氮、磷、硫、锌及有效氮、磷、钾、锰、锌等均呈显著或极显著相关关系，与土壤PH、容重、持水量及孔隙度也呈显著或极显著相关关系。土壤表层有机碳和活性有机碳与降水量之间具有正的相关关系，其相关系数为r=0.677（P<0.001）和r=0.712（P<0.001）。但下层土壤有机碳和活性有机碳与降水量之间没有显著的相关关系。 (4).样带下层土壤有机碳和活性有机碳与经度之间仍具有显著的相关关系（r=0.454，P=0.026; r=0.473，P=0.020）。样带下层土壤有机碳和活性有机碳的变异小于表层。不同的生态系统，下层土壤有机碳和活性有机碳与表层土壤有机碳和活性有机碳的比率不同。总的来看，土壤活性有机碳含量随深度的增加而下降的幅度大于土壤有机碳。 (5).短期培养条件下，CO2浓度升高及干旱胁迫下，土壤有机碳的变化不大，其变异系数为1.28%;相比较之下，土壤活性有机碳对气候变化比较敏感，其变异系数为29.67%。不同土壤湿度，土壤活性有机碳含量发生变异的幅度因CO2浓度升高而降低。 (6).样带土壤全氮和有效氮与经度呈极显著正相关，其相关系数分别是r=0.695 (P<0.001)和0.636(P<0.001)。土壤表层全氮和有效氮的梯度分布与土壤有机碳的分布基本一致：沿经度呈现东高西低的趋势，局部由于土壤退化而出现低谷。样带除东部山区外，其它各部分土壤有效氮都很低，成为其植被生长的限制因子之一。样带下层土壤全氮和有效氮的含量低于表层，但样带不同部位下层土壤全氮和有效氮下降的幅度不同。总的来看，土壤全氮的剖面分布和土壤有机碳相似，而土壤有效氮则有所不同。 (7).土壤全氮和有效氮是土壤生化环境中两个重要的因子。样带土壤全氮和有效氮和土壤有机碳、全磷、全硫、全锌、土壤活性碳、有效磷、有效钾、有效锰、有效锌、土壤容重、田间持水量土壤总孔度等因子均呈显著或极显著的相关关系。 (8).样带表层土壤全氮和有效氮与降雨量之间呈极显著的正相关关系，相关系数分别是0.682(P<0.001)和0.688(P<0.001)。而下层土壤全氮和有效氮与降雨量之间的没有显著的相关关系（r=0.241，P=0.256; r=0.366，P=0.079）。土壤有效氮占全氮的比例与年均温呈显著正相关关系（相关系数r=0.390，p=0.044）。 (9).短期培养试验中，CO2浓度加倍和不同土壤湿度对土壤全氮和有效氮的影响没有达到显著水平。整个试验中土壤全氮和有效氮的变异较小（变异系数分别是5.55%和3.84%），但仍能反映一定的变化趋势。 (10)．玉米残体还田能够增加土壤氮素含量，减轻因其作为燃烧材料而造成的氮素损失和对大气的污染;玉米残体施入土壤，增加了土壤微生物氮含量，提高土壤氮活性，有利于土壤氮素养分的协调供应;玉米残体还田能够促进氮素从营养器官向籽粒中转移，提高氮素养分的利用效率。同时，玉米残体还田可以降低土壤NO3--N的累 积，减少肥料氮的损失4.7～5.6%。 (ll)．根据国内外文献和我们连续10年作物残体还田的肥料长期定位试验及盆栽试验结果，从减缓CO2排放、增加土壤碳固存、提高土壤生产力入手，分析了农业生态系统作物残体还田的必要性与可行性，讨论了农田作物残体还田，增加土壤碳固存对于减缓CO2排放、提高土壤生产力的作用与意义。提倡作物残体因地制宜地归还土壤，但作物残体还田后土壤固存与减缓温室气体排放的潜力还需要进一步进行研究。

开垦和放牧对内蒙古草原土壤碳库和温室气体通量的影响

本文采用野外观测和室内测定相结合的方法，研究了内蒙古草原两种主要的土地利用方式（开垦和放牧）对土壤碳库和温室气体通量的影响，结果如下： 1．内蒙古草甸草原开垦后30年后，与天然草原相比，在休闲年份0～20 cm土壤有机碳和土壤微生物量碳含量均没有显著下降，但开垦导致土壤易分解碳下降了24%。土壤易氧化碳受季节性水热因子的驱动，表现出明显的季节变化动态。因此，土壤易分解碳的较土壤碳库的其他组分对开垦更敏感，是表征土壤管理措施引起有机质变化的一个重要指标。 草原开垦后，土壤-植物系统氧化大气甲烷的能力明显提高，农田和天然草原CH4平均吸收通量分别是48.9 和 29.0 μg C m-2 h-1，开垦后增加了1.7倍。开垦没有改变CH4吸收通量 “夏季高秋季低” 的季节变化规律（由降水决定）;开垦使N2O的平均释放通量增加了47%，农田和天然草原N2O平均吸收通量分别是56.6 和 38.6 ugN m-2 h-1;开垦同时也增大了通量的变异幅度;但没有改变N2O季节变化规律，只是出现高峰的时间较天然草原推后约10天左右。 2．开垦后的农田土壤在模拟添加厩肥后，刺激了土壤微生物的呼吸代谢，使CO2的释放量增加了5-7倍。试验期间总体排放的CO2中，约60%来源于羊粪，40% 来源于土壤。两种土壤即羊草顶级草原土壤（高碳高氮）和冷蒿－小禾草退化草原土壤（低碳低氮），在CO2的释放总量和释放比例上都没有显著性差异。添加厩肥均造成两种土壤碳库的净碳损失，并且退化草原土壤（7.0%）的土壤净碳损失要大于羊草草原（2.6%）。说明与开垦后的高C土壤相比，在已经退化草原的低C土壤上施厩肥将趋向于土壤更大的净碳损失。 3．自由放牧22年后，羊草草原0～10 cm土壤有机碳、微生物量碳和易分解碳分别下降了14.1%、27.9%和22.0%;大针茅草原0～5 cm土壤有机碳和微生物量碳分别下降了27.6%和38.2%。两类草原土壤碳组分的季节变化受水热因子的驱动，大针茅草原季节波动出现高峰的时间较羊草草原迟。土壤微生物量碳在表征羊草草原和大针茅草原土壤碳素的动态变化时，要敏感于土壤总有机碳。放牧对冷蒿-小禾草草原土壤各碳素组分影响不明显。在表征放牧对冷蒿-小禾草草原土壤的影响指示上，MB-C/ Org-C和Lab-C/ Org-C要比MB-C和Lab-C更加敏感。这说明在研究放牧对草原土壤碳库影响时，不同的草原类型应使用不同的指标来表征其变化。 内蒙古羊草草原是大气CH4的汇，自由放牧增加土壤对CH4的吸收。CH4平均吸收通量增加了27%，但CH4吸收的季节变化形式没有改变;放牧使。自由放牧还增大了N2O的排放通量，将原来N2O源、汇的双重功能改变为单一的源功能;放牧使N2O平均释放通量增加了1倍;放牧显著增加了羊草草原向大气排放CO2的量（p<0.05），并且年度排放量范围也有所增大。 4．草原羊尿斑土壤的pH和NH4+浓度在施后显著升高，但土壤微生物C和N没有明显变化，尿斑N素会发生大量的流失。粪斑和厩肥斑中各有46%和27%的N素分解后转移到植物中。羊草种群斑块上粪尿斑引起CO2和N2O通量的变化，要大于星毛委陵菜种群斑块。与植被类型的影响相比，羊粪尿斑尤其是尿斑对温室气体通量的影响更大。尿斑既降低了土壤对CH4的吸收，又增加了CO2和N2O的释放，使粪尿斑上相当于CO2的净排放量比对照土壤增加了15%。 在内蒙古草原中等放牧条件下，家畜粪尿斑在放牧草地上的覆盖面积约只有2%，与未被家畜排泄物覆盖的草原土壤 相比，粪尿斑对内蒙古草原温室气体总体收支产生的影响可以忽略不计。因此内蒙古草原地区温室气体减排措施的重点，应放在家畜的食性食量对温室气体的影响以及厩肥的科学利用上。但随放牧强度的加大，家畜排泄物覆盖草地的面积将大大增加，加之放牧生态系统中家畜瘤胃代谢产生的的大量温室气体，其对草原温室气体的核算将会产生的影响也是不容忽视的。

内蒙古典型温带草原植物功能群去除对土壤氮矿化的影响

由于人为因素导致的全球范围内的第六次物种大灭绝已经成为不争的事实，但人类还不清楚这种现象对生态系统功能的影响。在回答生物多样性与生态系统功能关系的问题上，补偿作用是一个争论的热点。为了阐明生物多样性对生态系统功能的影响，于2005年夏开始，在内蒙古温带典型草原开展了一个研究生物多样性与生态系统功能的物种去除试验。本研究是该项目的一部分。 元素循环是生态系统的重要功能之一，而氮素是限制草地生态系统生产力的主要因素，氮矿化是氮循环的关键步骤，因此，本研究重点讨论植物功能群对土壤氮矿化作用的影响，提出3点假设：1. 不同植物功能群对土壤氮矿化速率影响不同；2. 植物功能群去除前后氮矿化速率不同；3.植物功能群之间存在补偿效应。为了证明这些假设，于2006年9月、2007年6月和2007年8月份分别进行了室内培养（温度25℃，湿度60％田间最大持水量）用于测量氮矿化速率，同时于2007年6月和2007年8月份进行野外培养用于测量野外条件下的氮矿化速率，并在去除处理2年后得到以下主要结果： 1.　植物功能群去除数与土壤氮矿化速率呈单峰曲线关系（P<0.05），去除少量植物功能群氮矿化速率上升，去除更多的植物功能群后氮矿化速率下降； 2.　植物功能群去除数与土壤硝态氮含量呈线性正相关关系（P<0.0001），植物功能群的丧失加剧了土壤NO3--N的流失； 3.　多年生非禾草（PF）比其他植物功能群显著降低了氮矿化速率（P<0.05）； 4.　短期内（去除处理1年内）在凋落物回填的情况下，去除0个植物功能群与去除全部植物功能群的氮矿化速率无显著差异（P>0.05）； 5.　内蒙古温带典型草原在近3年内（2005、2006、2007）土壤碳库、氮库变化较小。

子午岭林区人工与天然油松林(Pinus tabulaeformis)养分库和碳库特征

为了揭示黄土高原地区人工油松林自然化发育过程中的植物叶片与土壤养分库和碳库的变化规律,采用典型样地法,以子午岭林区天然油松群落为参照,选择了不同立地条件的人工油松林,分别对其土壤的氮库、碳库及植物叶片养分库和碳库进行了分析。结果表明,该区油松针叶C、N、P的含量平均值分别为(499.5±63.75)mg/g、(8.53±0.50)mg/g和(0.94±0.64)mg/g,叶片C含量大小依次为阳坡天然林>阴坡天然林>阴坡人工林>阳坡人工林,阳坡人工林叶片N、P含量显著高于阳坡天然林。不同立地条件下油松林叶片C/N、C/P差异显著,叶片N、P和N/P均达到极显著水平,但是叶片C含量差异不显著。油松叶片C含量与N、P含量均呈极显著负相关,N和P之间的呈显著正相关。不同立地的油松林除40～60cm土层土壤C、N含量无显著差异外,0～20cm和20～40cm两个土层的人工林土壤C、N含量显著高于天然林,同时阳坡人工林土壤C、N含量显著高于阴坡人工林。0～20cm、20～40cm两个土层土壤C含量与N含量均呈极显著正相关,与植物N、P均呈显著正相关。子午岭林区阳坡的人工油松林不仅叶片养分含量较高,而且林地土壤是该区土壤的...

土地利用方式对土壤有机质及其碳库管理指数的影响

采用野外调查和室内分析的方式对子午岭不同土地利用方式下,土壤有机质、3种活性有机质及其碳库管理指数(CMI)进行了研究,结果表明,土壤有机质、3种活性土壤有机质含量均随土层的加深逐渐降低,在土壤剖面基本表现为林地、撂荒未翻耕地>撂荒翻耕地>农用地.同一土层,3种土壤活性有机质含量及其有效率表现为低活性有机质>中活性有机质>高活性有机质.不同利用方式下,活性有机质有效率随有机质活性增强,呈现撂荒未翻耕地>林地>撂荒翻耕地>农用地的趋势.不同利用方式之间的CMI的差异随有机质活性的增强而增大,且影响深度也逐渐加深.在0~30cm土层内,林地3种活性有机质的CMI高于撂荒翻耕地和农用地;而在30cm之下土层,3种利用方式低活性有机质的CMI相差不大,但中活性有机质和高活性有机质的CMI表现为林地>撂荒翻耕地>农用地.3种活性土壤有机质与其他生物化学性质之间均表现为显著或极显著相关关系,表明活性有机质可以指示土地利用方式对土壤有机质和CMI的影响.

侵蚀环境人工灌木林土壤活性有机碳与碳库管理指数演变

采用时空互代法,以黄土丘陵区纸坊沟流域生态恢复过程中不同年限的人工柠条和沙棘林为研究对象,选取坡耕地和天然侧柏林为对照,分析了植被恢复过程中土壤有机碳(TOC)、活性有机碳(LOC)、非活性有机碳(NLOC)及碳库管理指数的演变特征。结果表明,侵蚀环境下的坡耕地由于人为干扰,土壤碳库含量偏低,退耕营造柠条林可以显著增加土壤碳库各组分含量,并随恢复年限呈显著线性关系,25 a时TOC、LOC和NLOC分别较坡耕地增加271%、144%和204%,仅为侧柏林的32%、30%和29%,碳库指数和碳库管理指数较坡耕地明显增加,增幅分别达到144%和108%,仅为侧柏林的28%和43%;不同灌木林对土壤碳库管理的改善作用不同,恢复年限相同的沙棘林土壤碳库组分含量和管理指数明显高于柠条林,坡耕地营造灌木林后土壤经营和管理水平得到了显著改善,土壤系统向着良性方向转变。相关性分析表明有机碳、活性有机碳、非活性有机碳、碳库指数、碳库管理指数与土壤主要肥力因子相关性极其密切,可以作为反映生态恢复过程土壤质量演变的指标。

黄土高原沟壑区不同年限苹果园土壤碳、氮、磷变化特征

管理措施是影响土壤质量演变的重要因素。分析和讨论了5、101、5年苹果园耕层(0—20 cm)和0—200 cm土壤有机碳、全氮、全磷、有效磷和硝态氮含量及其影响因素。结果表明,5年、10年和15年的塬面苹果园表层土壤有机碳依次为7.5、6.7和6.7 g/kg;全氮依次为0.940、.85和0.83 g/kg;但土壤全磷和速效磷含量随着种植年限而增加,与5年苹果园相比,塬面10年苹果园土壤全磷、速效磷含量分别提高了11%、60%,并且磷素的变异性随年限而增加。坡地10年、15年和20年苹果园土壤有机碳依次为6.36、.2和6.5 g/kg,全氮依次为0.76、0.76和0.81 g/kg;与10年苹果园相比,15年苹果园土壤全磷、速效磷含量分别提高了20%、28%。土壤剖面0—80 cm内不同土地利用方式土壤碳、氮、磷含量随土层加深而降低,80 cm以下不同利用条件苹果园土壤碳、磷含量差异不大,氮素含量在100 cm土层下随苹果园种植年限增加而增加。

长白山典型森林生态系统土壤碳通量研究

森林生态系统是陆地最大的碳储存库，森林土壤呼吸是陆地生态系统土壤呼吸的重要组成部分，其动态变化将刘全球碳平衡产生深远的影响。精确测定土壤呼吸及其各组分的贡献，是目前全球变化研究中最基础和最迫切需要解决的问题。本文对长白山典型森林生态系统土壤碳通量及其过程机理进行了研究，结果表明：（1）阔叶红松林、红松云冷衫林、岳桦云冷杉林和岳桦林有不同的凋落节律；随海拔高度的上升，年凋落物量逐渐减少，分别为4.90、4.51、3.08和2.65thm-2；凋落物分解残留率与时间均呈指数关系，不同类型森林凋落物年分解常数的变化范围是25-47％之间。（2）阔叶红松林土壤总呼吸和断根土壤呼吸速率都存在明显的昼夜变化，为单峰型曲线，与土壤温度的昼夜变化趋势一致；不同森林类型土壤总呼吸和断根土壤呼吸的季节变化都比较明显，阔叶红松林、红松云冷杉林和岳桦云冷杉林变化趋势基本相似，都呈双峰型，岳桦林呈单峰型；土壤呼吸与土壤温度、大气温度之间都呈极显著（P＜0.01）指数相关关系，且与土壤温度的相关性要好于与大气温度的相关性；长白山四种类型森林土壤和根系呼吸的Q10值变化范围是1.8-2.9，根系呼吸的Q10值均大于土壤总呼吸和断根土壤呼吸的Q10值；土壤含水量对呼吸速率影响较为复杂，与土壤呼吸之间没有明显的相关关系；根系对土壤总呼吸贡献的季节变化与根系呼吸的季节变化相似，生长季内测定的阔叶红松林、红松云冷杉林、岳桦云冷杉林和岳桦杉林根系呼吸对土壤总呼吸贡献平均值分别为43.6％、44.1％、45.5％和44.4％。（3）长白山典型森林生态系统土壤碳的年释放量有随海拔高度上升而减小的趋势，且阔价卜林大于针叶林。阔叶红松林、红松云冷杉林、岳桦云冷杉林和岳桦林土壤碳的年释放量分别为7392.43、7181.83、6507.29和6841.09kghm-2a-1；根系的年碳释放量分别为3332.93、2965.68、2708.84和3015.48kghm-2a-1。

次生植被土壤碳、氮养分季节动态及凋落物输入与温度的影响

土壤微生物量、可溶性有机碳与氮虽然只占土壤有机碳、氮总量的较小部分，但可以在土壤全碳、氮变化之前反映土壤微小的变化，又直接参与土壤生物化学转化过程，因而在植被恢复过程中，较其它土壤理化性质等能够更好地指示土壤恢复情况。在青藏高原东缘存在大面积的次生人工林替代灌丛或采伐迹地，而关于这些人工林替代后的生态效果和生态过程的评估却十分缺乏，本研究通过评估岷江上游植被恢复重建过程中典型人工替代次生植被凋落物层与土壤碳、氮等养分大小，动态监测土壤微生物生物量、水溶性碳、氮等指标，结合温度与凋落物输入等影响土壤活性有机碳、氮因子的控制试验，系统分析不同人工替代次生植被土壤碳、氮等养分的差异原因，试图寻找低效人工林优化调控与持续管理技术，为区域生态公益林持续管理提供理论和技术依据。主要结论如下： 1. 通过对不同人工替代次生植被凋落物层和土壤碳、氮分析发现，油松和华山松人工林替代次生灌丛后土壤碳、氮含量较灌丛和阔叶人工林低，主要原因可能为凋落物质量(C/N)较差，而引起碳、氮等元素难以归还土壤。进而通过对不同人工替代次生植被凋落物层和土壤微生物生物量、水溶性有机碳、氮等指标的季节性动态模式的分析，发现各次生植被土壤微生物生物量C、N，P以及土壤水溶性碳、氮含量均呈明显季节性动态，呈现秋季明显大于其它季节，冬季最低，在表层土壤最为明显。 2. 油松、华山松人工林凋落物层和土壤水溶性有机碳(WDOC)、土壤水溶性有机氮(WDON)明显低于灌丛和连香树，土壤微生物生物量C、N也以油松和华山松人工林最低，而落叶类植被，如灌丛、连香树和落叶松之间没有明显差异，说明可利用底物的数量和质量差异是影响各次生植被凋落物分解和土壤微生物活性的主要原因。MBC/OC和MBN/ON能较好地指示土壤微生物活性的变化，MBC/OC凋落层总体以灌丛和连香树人工林最高，油松和华山松人工林最低；而土壤中MBC/OC连香树人工最高，华山松人工林最低。说明以油松和华山松为主的人工造林替代乡土阔叶灌丛造成土壤C、N等养分严重匮乏，微生物活性低下是影响其养分周转的主要原因。 3. 从各次生植被凋落物产生看，凋落物年归还量最大的为华山松人工林(5.1×103 kg ha-1)，其次为落叶松人工林(4.8×103 kg ha-1)，阔叶灌丛林地凋落物产生总量(4.4×103 kg ha-1)略大于油松人工林(4.2×103 kg ha-1)，最小的为连香树人工林(3.6×103 kg ha-1)；叶是凋落物的主体，落叶类树种月动态表现为单峰型，高峰主要在10-11月，如落叶松、连香树和灌丛林；常绿的松类月动态不明显，各月基本相同，最为明显地为油松林，华山松人工林略有二个小峰，分别出现在11月和5月。落叶阔叶灌丛的凋落物分解速率大于常绿针叶林，如油松和华山松。结合凋落物的产生量和分解速率，不同树种人工林替代次生阔叶灌丛后，人工油松和华山松林枯落物总贮量和厚度明显大于落叶松人工林、灌丛林和连香树人工林，说明以油松和华山松为主的人工造林替代乡土阔叶灌丛延缓了有机物向土壤的顺利归还，不利于土壤C、N等养分循环。 4. 通过控制地面凋落物和地下根系输入有机物对土壤碳、氮的影响研究发现，(1) 单独去除根系以及根系与地面凋落物同时去除处理1年后对表层(0-10cm)土壤WDOC均没有显著影响，而土壤WDON显著增加，油松人工林土壤微生物生物量C、N显著降低，人工落叶松林没有显著差异，说明油松人工林土壤微生物活性对地下碳输入的依赖大于其它次生植被，而落叶松土壤微生物活性对地下碳输入依赖性较小；去除地面凋落物，明显降低了落叶松人工林土壤WDOC，华山松和连香树土壤WDON均较对照显著减少，油松人工林土壤微生物量C较对照显著减少；双倍增加地面凋落物处理对土壤微生物生物量、WDOC和WDON没有明显地增加，相反，连香树、华山松和油松人工林土壤WDON较对照减少。说明油松人工林微生物活性不仅依赖于地下碳输入，而且对地上有机物输入的依赖性也较大；连香树、落叶松和华山松人工林土壤微生物生物量并没有因地面凋落物的去除减少可能与土壤总有机碳含量及活性均较高有关，而双倍增加地面凋落物反而降低了土壤微生物生物量，说明凋落物覆盖后改变了土壤微气候。 5. 碳矿化累积量与有机碳含量和活性有机碳含量之间存在显著地正相关关系。凋落物碳累积矿化量、矿化速率以连香树最高，油松和华山松人工林次之，落叶阔叶灌丛低于常绿针叶纯林，导致其差异的主要原因可能为凋落物产生的时间动态模式不一样，致使凋落物起始分解时间不一致。而土壤层有机碳矿化速率和矿化量以阔叶落叶灌丛和连香树最高，油松和华山松人工土壤最低，再次证实利用针叶纯林恢复植被阻碍了有机质周转与循环。 6. 凋落物累积矿化量与C/N值呈显著地相关关系，并随着温度的升高而明显增加，而土壤累积矿化量与C/N值没有显著相关关系，说明土壤有机碳质量(C/N)对温度的响应不十分明显。通过双指数模型对不同温度下碳矿化过程进行模拟和计算出活性有机碳与惰性有机碳比例，发现温度升高促进了惰性有机碳向活性有机碳的转化，增加了活性有机碳含量，说明温度升高可促进次生植被凋落物与土壤有机质的分解，进而可影响到林地碳源/汇关系的变化。 综上，通过对不同人工替代次生植被凋落物与土壤C、N大小、以及土壤微生物生物量、水溶性C、N等指标动态变化模式研究，结合温度与凋落物数量输入等影响土壤活性C、N因子的综合分析，以油松和华山松人工纯林对山地植被恢复，延缓或阻碍了有机质周转与循环，造成了土壤肥力退化。对现有低效人工纯林改造，应为地面大量有机物分解创造条件。 Although soil microbial biomass, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) are a small part of total soil organic carbon and nitrogen, they can directly participate in the process of soil biochemical translation and indicate the fine changes before changes of soil total organic carbon and nitrogen occur. So, they are good indexes to indicate soil restoration condition during the process of vegetation rehabilitation. There are large areas of secondary vegetations which substitute for indigenous shrubs in the eastern fringe of Qinghai-Tibet Plateau. However, it is not well known that the ecological effect and process after substitution by different secondary plantations. Based on comparison of soil organic and nitrogen contents in litter layer and soil under different secondary vegetations in upper reaches of Minjiang River, soil microbial biomass, DOC and DON in litter layer and soil were investigated in order to analyze the seasonal dynamic. Combining the effects of temperature, litter input and root exclusion on soil microbial biomass, DOC and DON, we also aim to understand the reason and mechanism of difference in soil carbon and nitrogen contents among different secondary vegetations. The study would contribute to comprehensively understanding C and N cycling processes and provide optimal control and sustainable technology of low-effect plantations in these regions. The results are as follows: (1) Organic carbon and nitrogen in litter layers and soil under different substitution plantations were investigated. The results showed that contents of soil organic carbon and nitrogen were lower in P. tabulaeformis (PT) and P. armandi Franch(PA) than those in native broad-leaf shrub and broad-leaf plantation. The low quality (C/N) of litter in PT and PA plantations caused carbon and nitrogen returning to soil difficultly. Seasonal dynamic of soil microbial carbon (MBC),-nitrogen (MBN),-phosphor (MBP), and WDOC and WDON showed similar pattern, which had the highest values in autumn and the lowest values in winter. (2) WDOC and WDON in litter layers and soil under PT and PA plantations were significantly lower than those in native broad-leaf shrub and Cercidiphyllum japonicum Sieb. et Zucc.(CJ). Soil MBC and MBN were also the lowest, while there were no significant differences among deciduous vegetations, i.e. native broad-leaf shrub, CJ and Larix kaempferi Lamb.(LK) plantation. The results suggested that difference in quantity and quality of available substance was main reason that affected the activity of microbe in soil and litter layer. MBC/OC and MBN/ON were good indexes to indicate the change of soil microbial activity. MBC/OC of litter had the highest value under native broad-leaf shrub and CJ plantation, and had the lowest value in PT and PA plantations, while MBC/OC of soil was the highest under CJ plantation, and was the lowest in PT and PA plantations. These results indicated that PT and PA plantations substituting for native broad-leaf shrub caused deficit of carbon and nitrogen in soil, low microbial activity was a main reason influencing the cycling and turnover of carbon and nitrogen in soil. (3) The annual litter fall production, composition, seasonal dynamic and decomposition of five typical secondary stands in upper reaches of Minjiang River were studied in this paper. The annual litter productions were: PA (5.1×103 kg ha-1), LK(4.8×103 kg ha-1), native broad-leaf shrub (4.4×103 kg ha-1), PT(4.2×103 kg ha-1)，CJ(3.6×103 kg ha-1). The litter production of leaves in five secondary vegetations occupied a higher percentage in the annual total litter production than those of other components. The litterfall was mostly producted in the cool and dry period (October-November) for deciduous vegetations and relatively equably producted in every season for evergreen coniferous vegetations. The decomposition rate of leaf litter in the broad-leaf stand was higher than those in evergreen coniferous stand. Combined with annual litter fall production and decomposition rate of leaf litter, we found that stock and depth of litter layer were significantly larger in PT and PA plantations than those in native broad-leaf shrub, LK and CJ plantations. The results confirmed that PT and PA plantations substituting for native broad-leaf shrub delayed organic matter returning to soil and hindered cycling of carbon and nitrogen again. (4) We explored plant litter removal, double litter addition, root trenching, and combining root trenching and litter removal treatments to examine the effects of above- and belowground carbon inputs on soil microbial biomass, WDOC and WDON in four secondary plantations. During the experimental period from June 2007 to July 2008, 1 year after initiation of the treatments, WDOC in soil did not vary in root trenching, and combining root trenching and litter removal treatments, while WDON in soil significantly increased compared with CK treatment. Root trenching reduced soil MBC and MBN in PT plantation, while MBC and MBN in soil did not vary in LK plantation. The rasults implied that soil microbial activity was more dependent on belowground carbon input in PT plantation than those in other secondary plantations, on the contrary, soil microbial activity in LK plantation was not dependent on belowground carbon input. Plant litter removal significantly decreased soil WDOC in LK plantation, decreased WDON in PA and CJ plantations, and also significantly reduced soil MBC in PT plantation. However, double litter addition did not increase soil microbial biomass, WDOC and WDON, on the contrary, soil WDON in CJ, PA and PT plantations were decreased. These suggested that soil microbial activity was not only dependent on belowground carbon input, but also on aboveground organic material input. Double litter addition could change the microclimate and result in the decrease of soil microbial activity in CJ, PA and PT plantations. (5) We measured carbon mineralization in a 107 days incubation experiment in 5℃,15℃ and 25℃. Carbon cumulative mineralization was positively correlated with organic matter and labile organic carbon in litter layer and soil. Cumulative carbon mineralization and mineralization rate of litter layers in PT and PA plantations were higher than that in native broad-leaf shrub. This difference between native broad-leaf shrub and coniferous plantations in cumulative carbon mineralization and mineralization rate of litter layers could be attributed to the initiating time of decomposition due to the difference in seasonal dynamic of litter fall production between two types of secondary plantations. However, cumulative carbon mineralization and mineralization rate in soil were the highest in native broad-leaf shrub and CJ plantation, and were the lowest in PT and PA plantations. This also confirmed that PT and PA plantations substituting for native broad-leaf shrub hindered the cycling and turnover of organic matter again. (6) Carbon cumulative mineralization was positively correlated with C/N in litter layer and increased with temperature increasing, while carbon cumulative mineralization was not correlated with C/N in soil. This indicated that soil organic matter quality (C/N) was insensitive to temperature. Applying bi-exponential model, we computed the percent of labile and stable carbon in different temperature incubation and found that temperature increasing would accelerate the transform from stable carbon to labile carbon and increase the percentage of labile organic carbon. This illuminated that temperature incraesing could facilitate the decomposition of litter and soil organic matter in secondary vegetations and hence affect the relationship between carbon source and sink.