豆科灌木－小叶锦鸡儿在我国北方半干旱沙地中的作用

Caragana microphylla Lam., a pioneer leguminous shrub species for vegetation re-establishment, is widely distributed in the semi-fixed and fixed sandy lands of the Horqin region. Some soil chemical and physical properties were measured under the canopy of C. microphylla and in the adjacent open areas to determine the effects of individual shrubs on soil properties. The influence of isolated C. microphylla on chemical and physical properties of the topsoil was significantly different between plots under the shrub canopy and in the shrub interspaces. Beneath the shrub canopy greater amounts of fine particle fractions, a higher water-holding capacity, and a lower bulk density, as well as higher aboveground and belowground litter biomass were found. Soil organic C and total N concentrations were 23%-31.6% and 14%-27.2% higher under the shrub canopies than in the shrub interspaces, respectively, giving rise to ＂islands of fertility＂. In a desertified sandy grassland ecosystem, C. microphylla was believed to play a major role in organic C sequestration, N accumulation, and the hydrologic cycle. Additionally, it has been found to be of ecological importance for vegetative restoration and reversal of desertification.     

Shrub encroachment does not reduce the activity of some soil enzymes in Mediterranean semiarid grasslands

Shrub encroachment is a worldwide phenomenon with implications for desertification and global change. We evaluated its effects on the activities of urease, phosphatase and β-glucosidase in Mediterranean semiarid grasslands dominated by Stipa tenacissima by sampling 12 sites with and without resprouting shrubs along a climatic gradient. The presence of shrubs affected the evaluated enzymes at different spatial scales. Soils under S. tenacissima tussocks and in bare ground areas devoid of vascular plants had higher values of phosphatase and urease when the shrubs were present. For the β-glucosidase, this effect was site-specific. At the scale of whole plots (30 m × 30 m), shrubs increased soil enzyme activities between 2% (β-glucosidase) and 22% (urease), albeit these differences were significant only in the later case. Our results indicate that shrub encroachment does not reduce the activity of extracellular soil enzymes in S. tenacissima grasslands.     

小叶锦鸡儿灌丛化对退化沙质草地土壤孔隙特征的影响

以内蒙古太卜寺旗地区退化沙质草地为研究对象,对该地区的小叶锦鸡儿灌丛化草地中的灌丛斑块和草地斑块分别取原状土柱各三个进行CT扫描,利用Fiji软件分析土壤孔隙结构特征的差异。研究结果表明,小叶锦鸡儿灌丛化对土壤的孔隙结构有较大影响,灌丛斑块土壤的总孔隙数、大孔隙数、总孔隙度、大孔隙度和孔隙等效直径均大于草地斑块土壤,灌丛斑块土壤的平均大孔隙度是草地斑块土壤的3倍。草地斑块土壤的大孔隙主要分布在0~50 mm土层深度,而灌丛斑块土壤的大孔隙在0~400 mm深度都有分布,这与土壤中灌丛的丰富根系分布有关。     

Coupled land-atmosphere modeling of the effects of shrub encroachment on nighttime temperatures

Changes in vegetation cover affect the interactions between the land surface and the overlying atmosphere with important impacts on surface energy balance and microclimate conditions. A major ongoing change in vegetation cover has been observed in dryland regions around the world, where desert shrubs are encroaching into arid grasslands. However, the impact of shrub encroachment on local climate has not been investigated. We used a mesoscale model coupled with a Land Surface Model to simulate the effects of shrub encroachment on nighttime temperatures. These effects can have an important effect on the establishment of shrubs and need to be represented well by land surface parameterization schemes that are also used in long-term climate simulations. Idealized 2-dimensional simulations were conducted with vegetation types corresponding to shrubland and grassland typical of the Northern Chihuahuan Desert. Simulated surface energy and radiation fluxes and near-ground air temperature were analyzed and compared with observations. Results show a good comparison between the simulations and observations as long as vegetation parameters are adjusted in the model to be in better agreement with the observed parameters. The sensitivity of the nighttime air temperatures to green vegetation fraction, albedo, emissivity and roughness length is investigated. The results indicate that the green vegetation fraction is the key factor that causes the higher nighttime temperature in shrubland than in adjacent grassland, mainly by its effects on soil surface insulation, soil thermal diffusivity, and therefore on ground heat fluxes.     

内蒙古灌丛化草原分布特征的遥感辨识

灌丛化草原在中国内蒙古干旱、半干旱草原区广为分布。为了探究灌丛化草原的分布状况,该文利用高空间分辨率(5.8 m)卫星资源三号遥感影像,结合地面调查,研究了内蒙古镶黄旗境内灌丛化草原的分布特征。以归一化植被指数(normalized differential vegetation index,NDVI)阈值法提取植被覆盖区域后,分别采用基于像元的监督分类方法(支持向量机、最大似然和马氏距离)和面向对象方法进行灌草镶嵌斑块和草地斑块的辨识,并对分类结果进行对比分析。结果表明:在3种基于像元光谱信息的监督分类算法中,支持向量机算法对灌丛化草地的识别精度相对较高,表现在这一类型的生产者精度和用户精度均大于另外2种算法,并且,该算法的总体分类精度也最高(81.15%),明显优于最大似然(73.33%)和马氏距离(61.77%)。然而,融入了空间信息进行分类的面向对象方法(合并尺度97)的总体识别精度高达89.24%,并且随着对象合并尺度的增大,灌丛化草地的错分和漏分比例明显降低。这一结果表明利用草本与灌丛像元的空间纹理属性差异,能够有效削弱噪声,提高识别精度。     

不同沙地生境下柠条灌丛化对草地土壤有机碳含量及分布的影响

为揭示不同沙地生境下灌丛化草地土壤有机碳及其组分的分布特征,以宁夏盐池县沙化草原不同沙地生境(丘间低地、固定沙地、半固定沙地、流动沙地)下不同发育期的柠条灌丛斑块及其对应的草地斑块为研究对象,对土壤颗粒组成、土壤有机碳(soil organic carbon,SOC)、颗粒有机碳(particulate organic carbon,POC)及易氧化有机碳含量(labile organic carbon,LOC)进行分析。结果表明:1)各沙地生境发育中期灌丛斑块的SOC、POC、LOC及POC/SOC极显著高于草地斑块(P0.01),而LOC/SOC在灌丛和草地斑块间差异性不显著;2)从丘间低地、固定沙地、半固定沙地到流动沙地,灌丛斑块及其对应的草地斑块SOC、POC、LOC及LOC/SOC均在固定沙地出现峰值,然后呈下降趋势,表明固定沙地及不同沙地生境发育中期的灌丛斑块和草地斑块是SOC、LOC及POC变化的临界点;3)相关分析发现,发育中期2种斑块SOC与POC及LOC间及SOC与LOC/SOC间均呈极显著相关(P0.01),但土壤黏粉粒与各组分有机碳及其分配比率间没有显著相关,因此LOC和POC可作为表征草地退化最敏感的指标。研究可为沙化草原土壤恢复研究提供理论依据。     

内蒙古典型草原区退耕方式对植物群落特征与土壤特性的影响

退耕后不恰当的植被建设会严重影响植物群落演替及土壤性质.本文以内蒙古太仆寺旗境内典型草原为研究区,以天然草地为对照,研究退耕后自然恢复与人工种草2种退耕方式对植物群落特征及土壤性状的影响,揭示不同退耕方式的生态恢复效应.通过样方法调查不同退耕方式草地的盖度、生物量和多样性特征,并对土壤密度、机械组成及养分含量等进行了室内测定分析.结果表明:1)植物群落多样性、盖度、地上及地下生物量均表现为人工种草＜自然恢复＜天然草地,且相比于人工种草,自然恢复草地的物种组成与天然草地更为相似;2)不同退耕方式影响下土壤性质的差异主要集中在表层0～10 cm;3)在表层0～ 10 cm,土壤密度及砂粒含量表现为人工种草＞自然恢复＞天然草地,而土壤黏粒、有机质(SOM)及全氮(TN)含量则表现为人工种草＜自然恢复＜天然草地.以上结果说明,在内蒙太仆寺旗退耕后采用自然恢复方式比人工种草更有助于改善土壤理化性质、建立稳定的植被系统.经过12年的恢复,退耕草地(人工种草与自然恢复草地)仍未恢复到天然草地的水平.     

土壤调节剂对土壤物理性质的改善

Effects of non-ionic polyacrylamide(PAM),anionic polyacrylamide(PHP),cationic polyacrylamide(PCAM),non-ionic polyvinylalcohol(PVA),anionic hydrolyzed polyacrylonitrile(HPAN)and polyethleneoxide(PEO)on the physical properties of three different soil stpes were studied.content of water-stable aggregates larger than 0.25mm increased to varying extents for different soils and soil conditioners,Among the six kinds of condiftioners,non-ionic polyacrylamide(PAM) was the most effective for red soil while polyethyleneoxide(PEO)the least effective for Chao soil,red soil and yellow-brown soil.Water-stable aggregates with the molecular weight of PEO within a certain range.Only evaporation rate of Chao soil decreased after aplication of PAM and HPAN to Chao soil and red soil.     

科尔沁沙地小叶锦鸡儿人工固沙区土壤理化性质的变化

选取科尔沁沙地不同年龄的小叶锦鸡儿固沙林为研究对象,研究了在人工固沙林发育过程中土壤的颗粒组成、容重、孔隙度、持水性、透水性、养分和水分含量以及土壤酶活性等理化性质的变化。结果表明,随着林龄的增长,固沙林内土壤理化性质均得到较好的改善,土壤粘粒含量增加,表层容重变小,孔隙度增大,土壤持水性和渗透性能均有所提高,有机质、速效N、P、K的含量大幅度增加,但土壤水分含量却出现了下降的趋势。同时,随着林龄的增长小叶锦鸡儿固沙林土壤酶活性逐渐提高,20年生的土壤酶活性基本接近于天然群落,表明小叶锦鸡儿是本地区优良的固沙树种。固沙林内结皮层的酶活性总体上不高,但均高于其毗邻下层土壤,其中转化酶活性高出近20倍。     

Effects of grazing on soil physical properties and soil erodibility in semiarid grassland of the Northern Loess Plateau (China)

Grazing animals provide a livelihood for farmers, but they may also produce adverse environmental effects. We investigated whether grazing leads to deterioration of soil physical properties that subsequently increases topsoil erodibility. We sampled three sites (an ungrazed grassland, a continuously grazed grassland, and a track trampled by stock) on the northern Loess Plateau of China. The bulk density, water content, proportion of stable aggregates, infiltration rate, and resistance to scouring were determined for each soil sample. The results showed that the track had the highest soil bulk density and the lowest soil water content, proportion of stable aggregates, infiltration rate, and ability to resist scouring. The ungrazed plots had the best results for these parameters, in terms of reduced erosion. Soil bulk density and the proportion of stable aggregates differed significantly with depth beneath the track. However, the effect of depth on water content, infiltration rate, and the soil resistance to scouring was not significant at any sampling site. The ability of the soil to resist scouring was negatively correlated with the soil's bulk density and positively correlated with the soil's water content, infiltration rate, and proportion of stable aggregates. Thus, soil physical properties played an important role in determining soil erodibility. Grazing and trampling by livestock therefore appear to cause deterioration of soil physical properties and to increase soil erodibility.     

内蒙古草原碳、氮储量:气候与土壤质地的关系

Understanding the spatial variability of soil carbon(C) storage and its relationship with climate and soil texture is critical for developing regional C models and for predicting the potential impact of climate change on soil C storage. On the basis of soil data from a transect across the Inner Mongolian grasslands, we determined the quantitative relationships of C and nitrogen(N) in bulk soil and particle-size fractions(sand, silt, and clay) with climate and soil texture to evaluate the major factors controlling soil C and N storage and to predict the effect of climate changes on soil C and N storage. The contents of C and N in the bulk soil and the different fractions in the 0–20 and 20–40 cm soil layers were positively correlated with the mean annual precipitation(MAP) and negatively correlated with the mean annual temperature(MAT). The responses of C storage in the soil and particle-size fractions to MAP and MAT were more sensitive in the 0–20 cm than in the 20–40 cm soil layer. Although MAP and MAT were both important factors influencing soil C storage, the models that include only MAP could well explain the variation in soil C storage in the Inner Mongolian grasslands. Because of the high correlation between MAP and MAT in the region, the models including MAT did not significantly enhance the model precision. Moreover, the contribution of the fine fraction(silt and clay) to the variation in soil C storage was rather small because of the very low fine fraction content in the Inner Mongolian grasslands.     

Moderate sheep grazing in semiarid shrubland alters small-scale soil surface structure and patch properties

We investigated whether long-term moderate livestock grazing by sheep (ca. 10 animal unit days/ha) in a semiarid shrubland with a long-term average annual rainfall of 200 mm causes changes in soil surface structure and dimensions of shrub and intershrub patches. We examined grazing-induced changes in landscape patchiness, patch structure, and soil moisture in three grazed and three ungrazed plots of 4 m × 4 m on a south-facing slope and the opposite, more productive north-facing slope. The measurements were done in early spring 2001 and 2002 before grazing started, in two surveys, one using two parallel transects and one using sample quadrats of 20 cm × 30 cm under three shrubs per plot and on an adjacent part of the intershrub matrix. On the north-facing slope, the sheep reduced shrub patch size as they trampled the soil mounds under the shrubs and browsed the shrub canopy. Reduced shrub patch size decreases the area and resources available for plant production. On the south-facing slope, the sheep mainly disrupted the soil crust in the intershrub area. This may increase soil erosion, but also seedling establishment. The contrast in impacts on the two slopes is due to the interaction between environment (productivity, exposure and vegetation) and sheep behavior (herbivory and trampling). On both slopes, the changes due to grazing are significant, though small. Changes in patch size and properties induced by moderate grazing can have positive and negative effects on productivity and diversity, but may also be viewed as early signs of landscape degradation as is often caused by heavy grazing.     

Biological soil crust and surface soil properties in different vegetation types of Horqin Sand Land,China

Physical and chemical properties (including coverage, thickness, hardness, moisture, particle size distribution, organic matter and nutrient contents etc.) of biological soil crust and 0–5.0 cm surface soil under the crust in three types of vegetation (semi-shrub Artemisia frigida, shrub Salix gordejevii and tree Populus simonii) were surveyed in 2005 and 2006 in Horqin Sand Land to understand the effects of different vegetation types on development of soil crust and surface soil properties under crust. The results showed that 1) no physical soil crust or biological soil crust (BSC) formed on mobile dunes without vegetation, though most ground surface in originally mobile dunes had been covered by BSC fifteen years after planted vegetation was established; 2) BSC development was best in shrub S. gordejevii sites, second in semi-shrub A. frigida sites, and weakest in tree P. simonii sites; 3) development of BSC was better in moss crust distributed mainly beneath or near plant canopies than in lichen crust distributed mainly between plant canopies in all three vegetation types; 4) surface soil properties 0–5.0 cm under BSC were improved significantly in all three vegetation types compared to those in mobile sand land. The magnitude of improvement was greater in S. gordejevii sites than in A. frigida and P. simonii sites, and greater in moss crust sites than lichen crust sites, but the magnitude of improvement decreased significantly with increasing surface soil depth; 5) based on the above-mentioned results, we suggest that S. gordejevii should be favored in future planting in Horqin Sand Land.     

红壤稻田土壤理化及生物学性状的动态变化特征

Rice production plays a crucial role in the food supply of China and a better understanding of the changes in paddy soil fertility and the management effects is of practical importance for increasing rice productivity. In this study, field sampling in a typical red soil region of subtropical China, Jiangxi Province, was used to observe changes in the soil physical, chemical, and biological properties in a cultivation chronosequence of paddy fields. After cultivation, clay (< 0.002 mm) content in the soil, which was 39% in the original uncultivated wasteland, decreased, to 17% in the 80-year paddy field, while silt (0.02--0.002 mm) content increased. Additionally, macroporosity increased and pore shapes became more homogeneous. Soil Ph generally increased. Soil organic C and total N content of the 0-10 cm layer increased from 4.58 and 0.39 g kg-1 to 19.6 and 1.62 g kg-1, respectively in the paddy fields after 30-year cultivation and then remained stable. Soil total P content increased from 0.5 to 1.3 g kg-1 after 3 years of rice cultivation, indicating that application of phosphate fertilizer could accelerate phosphorous accumulation in the soil. Total K content in the 0--10 cm soil layer for the 80-year paddy fields decreased by 28% compared to that of the uncultivated wasteland land. Total Fe and free Fe contents declined with years of cultivation. The bacterial population increased and urease activity noticeably intensified after years of cultivation. In this chronosequence it appeared that it took 30 years to increase soil fertility to a relatively constant value that was seen after 80 years of cultivation.     

黄土丘陵区柠条人工林土壤有机碳动态及其影响因子

以黄土丘陵区柠条人工林为研究对象,采用野外调查与室内分析相结合的方法,探讨柠条生长过程中土壤有机碳储量的变化规律。结果表明:1)土壤有机碳主要分布在0～20 cm土层,占0～50 cm土层总储量的49%～63%;2)相对于对照地,柠条林地土壤有机碳储量随柠条生长年限的增加先减小再升高最后趋于稳定,10、26、40、50 a柠条林地土壤总有机碳储量分别为1.555、3.236、2.775、2.444 kg/m2,26 a林地土壤有机碳储量最高,随林龄增大其变化趋于稳定;3)相关性分析结果表明,土壤有机碳质量分数与土壤密度之间呈显著负相关关系,各林地土壤密度随柠条生长年限的增加而减小,说明柠条可以通过改变土壤性质间接增加土壤总有机碳储量,土壤有机碳质量分数与根系生物量、土壤全氮质量分数之间呈极显著正相关关系,说明柠条的根系生长和固氮特性有助于有机碳的积累。     

土壤调理剂对土壤理化性质及甘蓝生理特性的影响

试验研究了土壤调理剂对土壤结构性质和甘蓝根系活力、光合指标的影响.结果表明,施用调理剂后,处理两次、处理一次分别使20 cm和30 cm土层的容重下降7.3%、1.9%和4.6%、1.3%,孔隙度分别提高9.3%、2.8%和5.9%、1.9%;与对照相比,处理两次后的阳离子交换量在0～27 cm、27～45 cm土层分别增加5.7%和10.9%;甘蓝的根系活力,处理与对照相比达到1%的显著差异水平;改变了Pn的光合日变化曲线,提高了甘蓝对光强的适应能力,光合能力加强.     

Structural and functional diversity of soil bacterial and fungal communities following woody plant encroachment in the southern Great Plains

In the southern Great Plains (USA), encroachment of grassland ecosystems by Prosopis glandulosa (honey mesquite) is widespread. Mesquite encroachment alters net primary productivity, enhances stores of C and N in plants and soil, and leads to increased levels of soil microbial biomass and activity. While mesquite’s impact on the biogeochemistry of the region is well established, it effects on soil microbial diversity and function are unknown. In this study, soils associated with four plant types (C₃ perennial grasses, C₄ midgrasses, C₄ shortgrasses, and mesquite) from a mesquite-encroached mixed grass prairie were surveyed to in an attempt to characterize the structure, diversity, and functional capacity of their soil microbial communities. rRNA gene cloning and sequencing were used in conjunction with the GeoChip functional gene array to evaluate these potential differences. Mesquite soil supported increased bacterial and fungal diversity and harbored a distinct fungal community relative to other plant types. Despite differences in composition and diversity, few significant differences were detected with respect to the potential functional capacity of the soil microbial communities. These results may suggest that a high level of functional redundancy exists within the bacterial portion of the soil communities; however, given the bias of the GeoChip toward bacterial functional genes, potential functional differences among soil fungi could not be addressed. The results of this study illustrate the linkages shared between above- and belowground communities and demonstrate that soil microbial communities, and in particular soil fungi, may be altered by the process of woody plant encroachment.     

土壤物理性质对供水能力的影响

The water-supplying capacity of two agricltural soils red soil in Jiangxi Province and meadow sol in Henan Province,was assessed mainly using physical investigations.The reticulated mottling horizon in the red soil was a horizon limiting roots distribution due to its high density and hardness in structure and low pH(pH5.05),The reistance of the red soil to drought hazard was poor because of its low water-supply capacity and poor hydraulic conductivity.The meadow soil had superior profile infiltration to that of the red soil and great available water-storage capacity,which resulted in low run-off loss,espectially in the wheat-growth season.It was difficult for water stored in the deep layers of the meadow soil to reach the surface due to the low unsaturated hydraulic conductivity of its clay-rich horizon in subsoil,Howver,water stored in deep layers was still available because the roots could extend to the deep layers due to the relatively low density in soil structure.