黄土高原不同人工林叶片-凋落叶-土壤生态化学计量特征

为探究“退耕还林(牧)”工程对陕西省子午岭林区的影响,分析3种典型的人工林(刺槐林、油松林和侧柏林)叶片-凋落叶-土壤的C、N、P含量及其生态化学计量特征.结果表明: 3种人工林不同组分中C、N、P含量大小均为叶片>凋落叶>土壤,刺槐林叶片N、P含量显著高于油松林和侧柏林.刺槐林、油松林和侧柏林叶片N∶P分别为12.2、5.4和6.1,油松和侧柏较刺槐林存在N亏损,C∶N和C∶P大小均为凋落叶>叶片>土壤,N∶P为叶片>凋落叶>土壤.油松林叶片C∶N与凋落叶C∶N间存在显著正相关关系.刺槐叶片在生长周期内吸收利用的N和P存在比例关系,且其凋落叶在元素再吸收后N和P的残留量也存在比例关系.与油松和侧柏相比,刺槐是黄土高原南部森林带最适宜的造林树种.     

黄土高原生态分区及概况

黄土高原地域广阔,水土流失区域差异显著。为了有效治理水土流失,评估水土流失治理技术和模式及生态恢复建设工程的成效性,需要对黄土高原进行区域划分。依据自然条件、水土流失治理技术和模式的区域性特征及差异,基于国家基础地理信息系统数据的县级行政界,对其进行合并,进行生态分区的划分,并分别统计其气候、地形地貌、植被特征及水土流失现状,以期为黄土高原水土流失治理技术和模式的改良优化提供依据。主要结论如下:(1)黄土高原分为黄土高塬沟壑区,黄土丘陵沟壑区,沙地和农灌区,土石山区及河谷平原区。其中黄土高塬沟壑区和黄土丘陵沟壑区分别划分为两个副区。(2)黄土高原的气候、植被、水土流失具有明显的分区差异。降水和植被覆盖度自东南向西北递减,二者在空间分布上具有很好的一致性,降水量大的分区,植被覆盖度也高。在年际变化方面,丘陵沟壑区B2副区降水量呈增加趋势,其他分区呈减小趋势,变化均不显著。80年代以来,黄土高原和各生态分区的植被覆盖度均逐渐增加,黄土丘陵沟壑区的增加量最大。各分区的面平均气温均呈非显著增加趋势,90年代以来增温明显。(3)1970年以来,黄土高原侵蚀产沙强度减弱趋势显著,至2002—2015年,多年平均输沙模数在0.13—3924 t km~(-2) a~(-1)之间,侵蚀强度最大为中度侵蚀(2500—5000 t km~(-2) a~(-1)),但面积较小,主要分布于第二高塬沟壑区的泾河流域。     

黄土高原丘陵沟壑区抗侵蚀植物叶表皮的生态适应性

采用叶表皮临时装片法研究了黄土高原丘陵沟壑区不同土壤侵蚀环境沟间地、沟谷地和沟间人工刺槐林地6种抗侵蚀植物叶表皮组成细胞的形态特征.结果表明:沟间地抗侵蚀植物叶的上表皮气孔开度、气孔密度、气孔指数、气孔器长宽比可塑性、气孔器面积可塑性、表皮毛密度和表皮细胞密度分别比沟谷地提高93.8％、66.8％、17.9％、36.4％、42.3％、199.4％和46.5％,下表皮分别提高90.4％、76.6％、9.8％、47.1％、43.9％、98.2％和50.1％;沟间人工刺槐林地叶上表皮各形态指标分别比沟谷地提高66.7％、20.5％、11.9％、37.9％、19.8％、113.1％和10.8％,叶下表皮分别提高106.7％、45.8％、11.9％、41.3％、21.2％、52.2％和28.1％.沟间地植物叶上、下叶表皮毛长度分别比沟谷地缩短58.8％和29.7％,表皮细胞面积分别比沟谷地减少40.3％和37.0％.沟间人工刺槐林地叶上、下表皮毛长度分别比沟谷地缩短25.0％和23.6％,表皮细胞面积分别比沟谷地减少22.2％和19.2％.抗侵蚀植物通过增加叶表皮气孔开度、气孔密度、气孔指数、气孔器长宽比可塑性、气孔器面积可塑性、表皮毛密度、表皮细胞密度和减少表皮毛长度、表皮细胞面积来适应较强的土壤侵蚀环境.     

Soil Carbon and Nitrogen Changes following Afforestation of Marginal Cropland across a Precipitation Gradient in Loess Plateau of China

Cropland afforestation has been widely found to increase soil organic carbon (SOC) and soil total nitrogen (STN); however, the magnitudes of SOC and STN accumulation and regulating factors are less studied in dry, marginal lands, and therein the interaction between soil carbon and nitrogen is not well understood. We examined the changes in SOC and STN in younger (5–9-year-old) and older (25–30-year-old) black locust (Robinia pseudoacacia L., an N-fixing species) plantations that were established on former cropland along a precipitation gradient (380 to 650 mm) in the semi-arid Loess Plateau of China. The SOC and STN stocks of cropland and plantations increased linearly with precipitation increase, respectively, accompanying an increase in the plantation net primary productivity and the soil clay content along the increasing precipitation gradient. The SOC stock of cropland decreased in younger plantations and increased in older plantations after afforestation, and the amount of the initial loss of SOC during the younger plantations’ establishment increased with precipitation increasing. By contrast, the STN stock of cropland showed no decrease in the initial afforestation while tending to increase with plantation age, and the changes in STN were not related to precipitation. The changes in STN and SOC showed correlated and were precipitation-dependent following afforestation, displaying a higher relative gain of SOC to STN as precipitation decreased. Our results suggest that the afforestation of marginal cropland in Loess Plateau can have a significant effect on the accumulation of SOC and STN, and that precipitation has a significant effect on SOC accumulation but little effect on STN retention. The limitation effect of soil nitrogen on soil carbon accumulation is more limited in the drier area rather than in the wetter sites.     

黄土高原土壤水分-有机碳-微生物耦合作用研究进展

黄土高原植被恢复后土壤水分、有机碳和微生物群落发生了非同步性演变。土壤微生物是各种生命活动的载体,在土壤水-碳耦合过程中参与了一系列的氧化与还原反应,因此,土壤微生物在水-碳耦合关键过程中起着重要的调节作用,三者存在着密切的耦合关系。尽管关于植被恢复后土壤水分和有机碳变化的研究已开展较多,但是由于土壤微生物活动和群落结构复杂性和易变性,这给土壤微生物介导的水-碳耦合研究带来了相当大的困难。迄今为止,黄土高原植被恢复后土壤水、碳、微生物三者之间的耦合关系缺乏总体性的融合,大多数研究只能假设各个生物化学过程是相对独立的,对土壤水、碳、微生物耦合的认知仍存在局限性。由此,首先对黄土高原植被恢复进程、土壤水分过程和有机碳变化分别进行了综述,结合已有的理论和证据进一步概括了黄土高原土壤有机碳、微生物群落对降水格局的响应。最后整合植被、土壤和微生物界面等关键生态过程,总结了黄土高原土壤水-碳-微生物耦合界面过程,采用HYDRUS-2D模型(水文过程模型)和ORCHIDEE模型(生态系统碳模型),并融入土壤微生物种群生长动态,基于稳定碳、水同位素技术和DNA探针技术,初步构建了黄土高原土壤水-碳-微...     

Political ecology and environmental management in the Loess Plateau,China

This paper explores the changing political ecology of soil and water management—the articulation of physical and political-economic processes—in the Loess Plateau of north-central China. Market-oriented reforms and the shift from collective to household farming have created a diverse array of tenure, management, and financing arrangements. In the process relationships between farm households, the collective, and the state have been altered, with profound implications for land use and sustainability. The paper reviews the political ecology approach and its relevance to environmental management in China. An outline of the physical and economic context of soil erosion in the Loess Plateau is followed by examination of the impact of reform on rural environmental management. Local innovations in the organization of environmental management are highlighted. The conclusion comments on the utility of the regional political ecology approach and suggests some critical issues for further research.     

The Late Neogene mammal biochronology in the Loess Plateau,China

For lacking of absolute dating, and because of the strong mammalian faunal endemism, the Chinese late Neogene has long been subdivided into mammalian ages mostly based on isolated local faunas by evolutionary stages of fossil taxa. The correlation with European stages and or mammalian units remains unsatisfied. We report the recent advances of the land mammal biochronology of late Neogene based on fossils found from continuous sections located at Lantian, Shaanxi Province and Lingtai, Gansu Province. There recognized three biozones for the late Miocene by fossils from the Bahe and Lantian formations, and three biozones for Pliocene on the data from Lingtai. The detailed biochronology work in combination with paleomagnetic data may improve the precision of correlation in the continental scale.     

Exploring the Use of Ecological Footprint in Life Cycle Impact Assessment

Ecological footprint (EF) is a metric that estimates human consumption of biological resources and products, along with generation of waste greenhouse gas (GHG) emissions in terms of appropriated productive land. There is an opportunity to better characterize land occupation and effects on the carbon cycle in life cycle assessment (LCA) models using EF concepts. Both LCA and EF may benefit from the merging of approaches commonly used separately by practitioners of these two methods. However, few studies have compared or integrated EF with LCA. The focus of this research was to explore methods for improving the characterization of land occupation within LCA by considering the EF method, either as a complementary tool or impact assessment method. Biofuels provide an interesting subject for application of EF in the LCA context because two of the most important issues surrounding biofuels are land occupation (changes, availability, and so on) and GHG balances, two of the impacts that EF is able to capture. We apply EF to existing fuel LCA land occupation and emissions data and project EF for future scenarios for U.S. transportation fuels. We find that LCA studies can benefit from lessons learned in EF about appropriately modeling productive land occupation and facilitating clear communication of meaningful results, but find limitations to the EF in the LCA context that demand refinement and recommend that EF always be used along with other indicators and metrics in product‐level assessments.     

Climate and Land Use Controls on Soil Organic Carbon in the Loess Plateau Region of China

The Loess Plateau of China has the highest soil erosion rate in the world where billion tons of soil is annually washed into Yellow River. In recent decades this region has experienced significant climate change and policy-driven land conversion. However, it has not yet been well investigated how these changes in climate and land use have affected soil organic carbon (SOC) storage on the Loess Plateau. By using the Dynamic Land Ecosystem Model (DLEM), we quantified the effects of climate and land use on SOC storage on the Loess Plateau in the context of multiple environmental factors during the period of 1961–2005. Our results show that SOC storage increased by 0.27 Pg C on the Loess Plateau as a result of multiple environmental factors during the study period. About 55% (0.14 Pg C) of the SOC increase was caused by land conversion from cropland to grassland/forest owing to the government efforts to reduce soil erosion and improve the ecological conditions in the region. Historical climate change reduced SOC by 0.05 Pg C (approximately 19% of the total change) primarily due to a significant climate warming and a slight reduction in precipitation. Our results imply that the implementation of “Grain for Green” policy may effectively enhance regional soil carbon storage and hence starve off further soil erosion on the Loess Plateau.     

A Quantitative Health Evaluation of an Eco-Economy in the Semi-Arid Loess Plateau of China

Understanding the factors that affect the health of a semi-arid region's eco-economy is necessary for its sustainable development. The health evaluation, or diagnoses, of an eco-economy at the small watershed scale requires the integrated analysis of ecological, economic, and social factors, yet few studies have achieved this. The health of an eco-economy comprises three components: vigor, organization, and resilience. We use an analytic hierarchy process to develop a health evaluation index system that evaluates the health of an eco-economy system. We then use this diagnostic method to explore the factors affecting the health status of a semi-arid loess watershed in China in 2007 and 2009. The results show that between 2007 and 2009 the health status of the eco-economy improved from the “better” stage to the “benign circle” stage. The primary productivity of grassland, land productivity, rural per capita net income, number of livestock per household, input–output ratio, commodity rate of farm produce, and labor productivity were the main factors influencing the health of this eco-economy. Furthermore, this study shows that the eco-economy depends on material input from regions outside the watershed.     

黄土高原沟壑区粮食生产中的生态成本

以黄土高原沟壑区的陕西省长武县为研究对象,应用生态学和经济学方法,对粮食生产生态成本进行了初步研究.结果表明： 2008年该区粮食生产生态损失总价值相当于当年种植业总产值的7.2%;小麦和玉米生态成本已分别达到2.42和2.12元·kg^-1,而出售单价分别为1.70和1.28元·kg^-1,高成本低收益的情况对该区域生态经济可持续发展产生不利影响;利用灰色关联对粮食生产生态成本中各因素进行分析,单位产量、播种面积和农业机械费用是影响生态成本的重要因素,化肥费用和有机肥费用对其影响不大;在当前生产力水平下,适当加大科学技术投入水平,提高粮食产量,扩大家庭种植规模,可以降低生产单位粮食的生态成本.     

黄土高原典型草原地上生物量估测模型

为了寻求有效的草地地上生物量估测方法和精确估测黄土高原典型草原草原地上生物量。于2014年8月中旬,在黄土高原典型草原草原地上生物量达到最大值,分别从单株水平和种群水平进行野外调查。以株高(H)和盖度(C)的复合因子(C×H)为自变量,通过回归分析,建立地上生物量估测模型,采用留一法对其精确性进行评估;并通过校正系数以及群落总生物量估测值和实测值比较单株水平和种群水平所建模型的精确性。结果表明:黄土高原典型草原草地,无论在单株水平还是种群水平,线性和幂函数对该区域生物量的拟合效果更好。估测模型检验结果表明,在单株水平各个物种的生物量估测值与实测值相关性较好,均达到了显著水平(P0.05),其r值均大于0.6,总相对误差RS均小于10%,平均相对误差绝对值RMA(average absolute value of relative error)均小于30%,总生物量的实测值与估测值比较接近,校正系数均接近1;而在种群水平上,虽然各物种的生物量估测值与实测值相关性均达到了显著水平(P0.05),但多数物种平均相对误差绝对值RMA大于30%,总相对误差RS(total relative error)均大于10%,总生物量的估测值均大于实测值,校正系数均偏离了1,说明在黄土高原典型草原通过单株水平建立的物种生物量估测模型的精度优于种群水平建立的物种生物量估测模型的精度。     

黄土丘陵沟壑区森林生态系统生态化学计量特征

为了阐明黄土丘陵沟壑区森林生态系统植物与土壤之间的养分循环关系,明确叶片与乔木层整体生态化学计量特征差异性,采用野外调查与室内分析相结合的方法对研究区内主要森林生态系统不同乔木器官和土壤C、N、P含量进行了测定,分析了叶片、乔木层和土壤化学计量特征及之间的关系。结果表明:研究区内森林生态系统乔木层平均C、N、P含量均显著低于叶片水平,表层土壤(0—10 cm)C、N含量以及C∶P、N∶P值均显著高于土壤(0—100 cm)平均值;叶片与乔木层及二者与土壤间的生态化学计量特征关系不同;乔木层平均C含量与降水呈显著正相关,乔木层平均P含量仅与海拔呈显著正相关,影响本地区植物生长状态的主要因素是降水。土壤平均C、N含量仅受土壤容重的影响,土壤平均P含量主要受土壤容重、温度和降水的影响。研究结果可以为黄土丘陵沟壑区人工林的建设和管理提供理论依据。     

黄土高原多年生草本根部年轮特征

多年生草本年轮资料是反映草本物种生长状态的重要指标,已被应用于草本物种年际生长动态特征、生活史策略及气候响应敏感性研究当中,然而这方面研究在黄土高原还未引起足够的重视。在黄土高原不同地点采集了16种多年生草本物种的根部年轮样品,通过根部解剖结构识别年轮结构,并分析了这些物种的年轮宽度和导管大小随年龄的变化趋势特征。研究结果表明调查样品中共有14个草本物种(87.5%)具有清晰可识别的年轮结构,平均年龄为7年左右;草本年轮宽度随年龄均有不断减小的趋势,这主要是由于随年龄不断增强的水分胁迫导致的。自然草本物种导管直径(导水能力)随年龄有不断变大的趋势,生长具有可持续性;人工草本物种导水能力随年龄有不断减弱趋势,生长趋于衰退;而分布于黄土高原北缘至半荒漠地区的二色补血草导水能力则随年龄有先上升后下降的趋势,表现出输水效率和安全的权衡策略。本研究阐述了黄土高原多年生草本的年轮学价值和对胁迫生境条件下的生活史策略,能为黄土高原草地植被的生态恢复提供科学依据。     

Evapotranspiration over the Grassland Field in the Liudaogou Basin of the Loess Plateau,China

Severe desertification on the Loess Plateau of China since the 17th century as a result of improper land use has caused critical soil erosion and water shortages in the lower reaches of the Yellow River. To prevent further soil erosion, it is very important to cover the bare land surface with natural vegetation. Evapotranspiration (ET) over the grassland (Stipa bungeana) in Shenmu County of the Loess Plateau during the growing season is estimated to be about 1 mm day^–1, and the ratio of ET to reference Evapotranspiration (ET/ET₀) is below 0.3. Evaporation from the bare soil surface simulated by a three-layer soil model is less than ET; that is, ET is 1.5 times greater than evaporation from the soil surface during the growing season.This study examines the relationships among the surface resistance r_s in the Penman–Monteith equation, solar radiation, vapor-pressure deficit, temperature, wind speed, and soil water content. Surface resistance (r_s) is strongly affected by the vapor-pressure deficit and soil water content.     

Comparative analysis of annual rings of perennial forbs in the Loess Plateau,China

Although recent studies have demonstrated that annual growth rings are present among perennial forbs species at high northern latitudes, little is known about whether there are demarcated growth rings of perennial forbs in the Loess Plateau of China where plant growth is strongly limited by dry climate conditions and severe soil erosion. In this study, we collected the main roots of 11 perennial forbs species along the precipitation gradient in the Loess Plateau, and analyzed the growth rings in the secondary root xylem. We found that ten species showed distinct annual growth rings, and the anatomical patterns, including vessel size and density, varied considerably among different families. Our results suggest, for forbs species in the Loess Plateau, that vessel diameter in the root xylem was strongly correlated with growth rate of the forb’s roots. Ring widths of the forbs showed a significant declining trend, reflecting the deteriorating signal of growth condition with age. In comparison to other families, forb species of Fabaceae usually have the evidently larger vessels that link directly to higher hydraulic capacity and growth rate. In terms of annual ring width patterns, this study provides an applicable approach to detecting effects of limited climatic conditions and life history strategies on herbaceous vegetation in the Loess Plateau.     

黄土高原-青藏高原过渡带农户生产系统的碳平衡

黄土高原-青藏高原过渡带是我国农业生产方式变化最剧烈、碳平衡效应最敏感的区域之一.本文分析了海拔梯度上通渭-渭源-夏河样带农业系统的碳平衡.结果表明: 随海拔增加,单位面积作物的碳排放、碳固定和碳汇能力逐渐降低,户均家畜碳排放与碳固定、碳源能力递增,综合生产系统由碳汇渐变为碳源,户均碳排放上升,碳固定变化趋势与之相反.黄土高原-青藏高原过渡带的农户占比随碳平衡的变化可用Logistic方程拟合,随海拔升高,在通渭、渭源与夏河3个区域农户占比50.0%拐点处,作物系统的碳排放和碳固定分别为1491、857、376 kg CE·household^-1和6187、3872、778 kg CE·household^-1,家畜系统碳排放和碳固定分别为2218、3725、49511 kg CE·household^-1和138、230、2706 kg CE·household^-1,综合系统碳排放和碳固定分别为3615、4583、49918 kg CE·household^-1和6289、4113、3819 kg CE·household^-1,这些是区域碳平衡调控的关键点.     

Assessing the Ecological Success of Restoration by Afforestation on the Chinese Loess Plateau

Afforestation has been accepted as a key measure for preventing soil erosion on the Chinese Loess Plateau for 40 years. In this study, we assessed the ecological success of afforestation by comparing afforested with pre‐afforested (croplands) and natural recovery sites in a typical watershed on the Loess Plateau. We evaluated the ecosystem response in terms of vegetation structure, plant diversity, and several key ecological processes of soil moisture, soil nutrients, and soil anti‐erodibility. Compared with the croplands, we found that the following indexes were significantly enhanced in afforested sites: vegetation structure and species diversity (species richness, Margalef index, Shannon–Wiener index, and Sorensen's similarity index), soil nutrients (organic carbon, total nitrogen, extractable ammonium nitrogen, available potassium, and available phosphorous), and soil anti‐erodibility indexes (water‐stable soil aggregates, mean weight diameter, and the ratio of soil structure dispersion). Afforestation offered few additional advantages when compared with natural recovery sites. More importantly, afforestation had significant negative effects on soil desiccation, with negative impacts on the long‐term sustainability of these ecosystems. In order to develop self‐sustaining and functional ecosystems, our results suggest that natural revegetation offers a more adaptive and appropriate method of ecological restoration on the Loess Plateau.     

A comparison of soil qualities of different revegetation types in the Loess Plateau, China

Serious soil erosion has resulted in widespread land degradation in the Loess Plateau of China. In the past two decades, great efforts have been made to restore degraded soil such as reconverting croplands into forestlands or grasslands. A comparison of soil qualities of different revegetation types has important implications in soil reclamation. Our study investigated the effect of different revegetation types on the physicochemical and microbial soil properties in the Loess Plateau, with the aim of determining which revegetation type has the best capacity for soil recovery. The vegetation types included two shrublands (Caragana korshinskii and Hippophae rhamnoides), two grasslands (Astragalus adsurgens and Panicum virgatum), and two species from croplands that were abandoned for natural recovery (Artemisia capillaries and Heteropappus altaicus). Among the plants studied, H. altaicus and A. capillaries had the highest values of soil organic C, total N, total P, available N, available P, moisture content, microbial biomass C (MBC), substrate-induced respiration, saccharase, urease, catalase, and peroxidase. Soil sampled from the A. adsurgens plot had the highest bulk density and microbial biomass N, and soil from the H. rhamnoides plot had the highest metabolic quotient (basal respiration/MBC). The soil quality index, which was obtained based on the available N, metabolic quotient, MBC, urease, polyphenol oxidase, and bulk density, shows that the abandoned cropland for natural recovery had the highest soil quality, followed by grassland, and then shrubland. Vegetation types affect the physicochemical and microbial properties of soils in arid climatic conditions. Abandoned cropland for natural recovery has the best capacity for improving soil quality in the Loess Plateau among all studied revegetation types. Our study suggests that in the Loess Plateau, natural recovery is the best choice for soil revegetation of sloping croplands.