科尔沁沙地东南部植被类型变化对土壤磷素状况的影响

In the past 50 years, large areas of the Horqin sandy land were afforested to prevent desertification. Although the afforestation policy appears successful, many people now doubt whether it is suitable to plant trees with high density on the poor soils in semiarid regions. Little is known about the impacts of afforestation on the sandy soil properties, although the evaluation of these impacts is fundamental to judge the rationality of afforestation policy. Soil phosphorus （P） fractions, acid phosphomonoesterase activities, and other soil chemical properties were compared among five adjoining typical ecosystems on poor sandy soils in southeastern Horqin sandy land. The ecosystems studied are natural elm savanna, degraded grassland, Mongolian pine （Pinus sylvestris var. mongolica） plantation, Chinese pine （Pinus tabulaeformis） plantation, and mixed plantation of Mongolian pine and poplar （Populus simonii）. The results showed that organic P dominated soil P （47%-65%） was the principal source of available P. The degradation of elm savanna to grassland significantly reduced soil pH and resulted in an overall reduction in soil fertility, although slightly increased labile inorganic P. Grassland afforestation had no significant influence on soil pH, organic carbon, and total N but significantly reduced total P. Impacts of grassland afforestation on soil P fractions depended on tree species. Natural elm savanna had higher soil P conserving ability than artificial plantations. Therefore, with the aim of developing a sustainable ecosystem, we suggested that vegetations with low nutrient demand （particularly P） and efficient nutrient cycling would be more suitable for ecosystem restoration in the semiarid region.     

Soil properties following cultivation and non-grazing of a semi-arid sandy grassland in northern China

Cultivation and overgrazing are widely recognized as the primary causes of desertification of sandy grassland in the semi-arid region of northern China. Very little is known about the effect of cultivation and overgrazing on soil physical, chemical and biological properties in this region. The objective of this study was to quantitatively evaluate the magnitude of changes in soil properties due to 3 years of cultivation (3CGS) and 5 years of ungrazed exclosure (5RGS) in a degraded grassland ecosystem of the semi-arid Horqin sandy steppe. Short-term cultivation resulted in a 18–38% reduction in concentration of soil organic C, and total N and P in the 0–15 cm plow layer. Cultivation had a significant influence on N and P availability and soil biological properties, with lower basal soil respiration (BSR) and enzyme activities than the grassland soils. This was mostly due to strong wind erosion when sandy grassland was cultivated. Data indicated a considerable difference in soil particle size distribution between the cultivated and grassland soils, and fine fraction (<0.1 mm) in the cultivated soil was lower than that in the grassland soils. Moreover, grassland vegetation recovery in the 5RGS resulted in significant improvement in soil properties measured at the 0–7.5 cm depth. From the perspective of soil resource management and environmental conservation, a viable option for these sandy grasslands would be to stop conversion of grassland to cropland and adopt proper fencing practices to limit overgrazing.     

放牧干扰后自然恢复的退化沙质草地土壤性状的空间分布

用地统计学的方法 ,研究了科尔沁沙质退化草地不同强度放牧干扰 (重度放牧和适度放牧 )后自然恢复过程中 0～ 15cm土层土壤有机碳、全氮、pH和电导率在 10m尺度上的空间异质性特征。结果表明 ,重牧后的恢复草地比适度放牧后的恢复草地呈现出显著低的有机碳和全氮含量及其显著高的变异性。在取样尺度的空间分布上均表现出显著的空间结构特征 ,自相关尺度分别为 2 2 2～ 2 9 4m和 2 5 5～ 39m ,结构性方差占样本方差的 87 2 %～ 88 2 %和 6 5 5 %～ 85 9%。全氮的自相关尺度大于有机碳。土壤pH和电导率在取样的尺度内不存在局部格局 ,而可能受更大尺度的格局控制。放牧引起的植被斑块状分布和沙化裸斑的出现是土壤碳、氮空间变异的主要因素 ;土壤异质性尺度的改变又可能影响着植被的恢复演替和分布格局。     

Vegetation characteristics and soil properties in grazing exclusion areas of the Inner Mongolia desert steppe

In arid and semi-arid desert steppe areas, grazing exclusion with fencing is widely regarded as an effective strategy for restoring degraded vegetation and enhancing the quality of degraded soil. In this study, we hypothesized that grazing exclusion caused by fencing enhances both vegetation and soil properties, and that the longer an area is fenced, the more considerable the improvement. We conducted an observational study wherein random sampling was utilized to select 9 plots fenced for ten or more years, 25 plots fenced for four to nine years, 25 plots fenced for one to three years and 29 free-grazing plots within an area of approximately 63,000 km² of Inner Mongolia desert steppe. A one-way ANOVA revealed no significant differences in the characteristics of grassland vegetation or soil properties between grasslands fenced for one to three years and free-grazing grassland. After 4 years of fencing, noticeable increases in above-ground biomass, litter content, Simpson index, soil organic carbon, and available nitrogen were observed. Significant positive differences in vegetation coverage, height, species richness, soil available phosphorus, and available potassium were associated with plots with a minimum of 10 years of fencing. The soil layer with the greatest difference in the fenced-in areas for soil organic carbon was at 0–25 cm. For available nitrogen and available phosphorus, fencing produced the most significant differences in the 0–20 cm soil layer, while for available potassium, fencing produced the most significant differences in the 0–30 cm soil layer. However, the fencing did not indicate any statistically significant differences in terms of clay, silt, and sand content in any soil layer. The data support our hypothesis that grazing exclusion improves both vegetation and soil properties, and that longer periods of grazing exclusion result in greater degrees of improvement. This research offers technical guidance for the reasonable choice of fencing time across a vast area of the Inner Mongolian desert steppe.     

Grassland degradation reduces the carbon sequestration capacity of the vegetation and enhances the soil carbon and nitrogen loss

Abstract

Grassland degradation not only results in soil degradation and severe decreases in land productivity, but also can promote the emission of soil carbon and nitrogen compounds as greenhouse gases into the atmosphere. The primary objective of this study was to characterize the impact of grassland degradation on carbon and nitrogen budgets in Inner Mongolia, China. We investigated the changes of total carbon, organic carbon, inorganic carbon and total nitrogen that occur in a grassland ecosystem (including vegetation and top 30 cm soil layer) in the course of grassland degradation. Total carbon stored in the grassland ecosystem was reduced by up to 14%, depending on the severity of the degradation. Total nitrogen storage was reduced by almost 10% under severe degradation, but was slightly increased at light and intermediate degradation, indicating that grazing exclusion would not lead to an increase in nitrogen storage in the ecosystem. Over 98% of the total carbon and nitrogen stored in the grassland ecosystem was bound in the soil which provides the dominant and most stable carbon and nitrogen pool in the ecosystem. Most of the soil carbon and nitrogen storage was present in soil water-stable aggregates and was released as soil water-stable aggregates break in the course of grassland degradation. In conclusion, the carbon sequestration capacity of the vegetation decreased significantly, and substantial proportions of soil carbon and nitrogen were lost in the course of grassland degradation, resulting in unbalanced carbon and nitrogen budgets. Strategies to restore degraded grassland must be designed to increase the carbon and nitrogen storage potential of grassland ecosystems.     

退化沙质草地自然恢复过程中土壤-植物系统的变化特征

研究了科尔沁沙地封育5a后退化沙质草地自然恢复过程中土壤—植物系统的变化特征,同时分析了土壤性状与植物特征之间的相互影响程度。(1)从流动沙地恢复到固定沙地,沙质草地植物群落的物种多样性、植被盖度、地下根量和地表枯落物残留量均趋于增大。β多样性测度值表明,在半流动沙地恢复到半固定沙地阶段,植物种周转速率大,群落结构变化明显。(2)在退化沙质草地的自然恢复过程中,表层土壤的结构性能明显改善,土壤养分的有效性相应提高。(3)相关分析显示,沙质草地表层土壤的理化性状与植物特征值之间存有密切的相关性(R2=0.33～0.84,P<0.01,n=20),表明退化沙质草地的恢复过程实质上是土壤—植物系统协同演变的过程,在该过程中,植物多样性的关键恢复期滞后于土壤环境的关键恢复期。     

退化演替对高山草地植被和土壤理化特性影响

[目的]分析3种不同草地退化阶段(轻度退化,中度退化和重度退化)草地植被和土壤理化特性的变化规律,为类似区域退化草地植被恢复提供有效途径。[方法]野外植被调查、土壤取样和室内分析。[结果]草地退化不同阶段草地植物群落组成和物种多样性均有差异,退化对草地土壤理化特性有明显影响。重度退化草地土壤容重显著高于轻度退化草地(p0.05)。轻度和中度退化样地0—10cm土壤空隙度显著高于重度退化草地。重度退化草地的土壤有机质、全碳、全钾、全磷和有效钾均明显小于轻度退化草地(p0.05),但土壤pH值和有效氮含量没有显著变化。[结论]高山草地退化演替对该区土壤物理特性具有显著影响。     

Effects of crop abandonment and grazing exclusion on available soil water and other soil properties in a semi-arid Mongolian grassland

Improper cropping and overgrazing have led to land degradation in semi-arid regions, resulting in desertification. During desertification, vegetation changes have been widely observed, and are likely controlled to some extent by soil water. The purpose of this study was to investigate changes in soil physical properties, organic C, and vegetation induced by land-use changes, with special reference to the dynamics of available soil water. We selected four study sites in a typical Mongolian steppe grassland: grassland protected from grazing, grazed grassland, abandoned cropland, and cultivated cropland. Grazing exclusion increased the cover of perennial grass, with little increase in the root weight. Since there was no difference in available water between the grasslands with and without grazing, there appears to be no serious soil compaction due to overgrazing. On the other hand, vegetation cover and the number of species were poor in both abandoned cropland and cultivated cropland. However, the root weight was greater in abandoned cropland. Although the abandonment of cultivation appeared to increase organic C, available water did not differ significantly in comparison with cultivated cropland. The silt contents were significantly lower in abandoned and cultivated cropland than in both grasslands, suggesting the effects of wind erosion. In addition, the silt contents were positively correlated with the volume fraction of storage pores for available water. Therefore, the lower silt contents may constrain the volume of available water in abandoned cropland. Moreover, the unsaturated hydraulic conductivity results indicated that the diameters of storage pores for available water at the present study sites were smaller than those suggested by previous studies. Although the differences in vegetation cover by different land-use types were observed at every site, differences in the volume of available water were observed at between abandoned cropland and cultivated cropland. The reason why the no differences in available water between grazed grassland and grasslands protected from grazing may be short time of grazing exclusion for 2 years for evaluating the effects of exclusion on soil properties.     

退化草地土壤农化性状与微生物区系研究

通过对三种退化程度不同的草地土壤农化性状与微生物区系进行研究，结果表明，草地退化后，其土壤肥力水平、土壤微生物数量和微生物种类有随退化程度增高而下降的趋势；退化草地存在不同的程度的营养元素比例失调，表现为少氮、缺磷、富钾和高有机质含量，且退化程度接近的草地间，在土壤微生物区系和农化性状有部分类似的特征。     

Spatial pattern and heterogeneity of soil properties in sand dunes under grazing and restoration in Horqin Sandy Land, Northern China

Applying a combination of classical and geostatistical methods, we identified soil properties and their spatial variation in a 5-year grazed sand dune (GSD5) and a 20-year recovered sand dune (RSD20) in Horqin Sandy Land, northern China. The paper assesses the effect of grazing, topography and vegetation restoration on spatial heterogeneity of soil properties. The results showed that soil organic carbon, total nitrogen, very fine sand (0.1–0.05 mm) content and their coefficients of variation were lower in GSD5 than in RSD20, while soil water contents (0–20 cm and 20–40 cm depths) were higher in GSD5 than in RSD20. Geostatistical analysis revealed that the spatial structured variance accounted for the largest proportion of total sample variance in soil properties at the measured scale under grazing and restoration. The spatial autocorrelation ranges were 66.30 m for soil organic carbon and 50.80 m for total nitrogen in GSD5 less than those in RSD20 (70.00 m and 76.10 m, respectively), while the spatial autocorrelation ranges of soil particle size fractions and soil water contents in RSD20 were less than those in GSD5. Kriging-interpolated maps also showed that the heterogeneity of soil organic carbon and total nitrogen and their degree of patch fragmentation were higher in GSD5 than in RSD20. These results suggested that continuous grazing resulted in an increase in spatial variability of soil nutrient and a decrease in spatial variability of soil particle size fractions and soil water content. Soil organic carbon and total nitrogen of sand dunes are associated closely with soil particle size fractions, relative height of sampling site and vegetation cover. Spatial patterns of soil properties are most strongly related to grazing, topography and plant-induced heterogeneity in sand dune ecosystems prone to wind erosion.     

Impacts of grazing on montane heath vegetation in Wales and implications for the restoration of montane areas

The impact of long-term heavy grazing pressure on montane vegetation and soils was investigated on the Carneddau plateau in North Wales. At this site, historical information suggests that formerly extensive Racomitrium- and Vaccinium-dominated heaths have become degraded and reduced in extent over the last 40-50 years. This coincides with a period when both sheep numbers and atmospheric deposition of nitrogen have greatly increased. Vegetation composition, plant tissue chemistry, soil chemistry and sheep presence were compared between areas of ‘good’ condition Racomitrium and Vaccinium heath and degraded areas. Comparison of species composition data with sheep presence and environmental data showed no significant link between current grazing distribution and species composition in the areas investigated, with all habitats having sheep presence above the recommended maximum for this habitat. Soil chemistry showed several differences between degraded and ‘good’ condition habitats, suggesting that degraded areas had experienced loss of soil organic matter and upper organic horizons. Comparison of soil and vegetation nitrogen content with data from other UK sites suggests a build up of nitrogen has occurred in Carneddau vegetation and soils, possibly related to high levels of nitrogen deposition. It is concluded that restoration of severely degraded areas of montane vegetation may be retarded by deleterious changes in soil properties which could slow recolonisation by montane species. Reductions in stocking density aiming to restore montane communities might have more immediate impact on less degraded areas.     

宁夏河东沙地农牧交错区不同放牧方式对土壤环境的影响

研究了宁夏河东沙地农牧交错区不同放牧方式对土壤环境的影响。结果表明，不同放牧方式下的土壤含水量以6区轮牧的较高，自由放牧和封育地的土壤含水量较低，且不同放牧方式和封育地的土壤含水量随季节降雨量的变化呈一致性；封育、6区轮牧、4区轮牧和2区轮牧地土壤容重方别比自由放牧地的土壤容重下降了6％，7．77％，1．96％，1．43％；封育、6区轮牧、4区轮牧和2区轮牧地土壤总孔隙度分别比自由放牧的增加了7．38％，4．67％，3．79％，4．72％；土壤有机质、全氮、全磷、全钾的变化以自由放牧较高，不同放牧方式之间的差异不显著。土壤速效钾以6区轮牧地较高，自由放牧地较低。     

青藏高原三江源区不同恢复期高寒草甸土壤线虫群落演变

青藏高原三江源地区的高寒草甸面临着严峻的退化问题，人工建植是三江源地区退化草地的重要修复方式。为探究地下生物对草地人工恢复措施的响应，本研究比较了三江源地区高寒草甸不同恢复期人工草地(建植1、5和10 a)的土壤线虫群落变化。结果显示：与原生植被样地相比，所有恢复期样地的植物地下生物量降低，土壤容重、pH、全磷、全钾和硝态氮含量升高，表明人工草地系统的初级生产力和土壤特性尚未恢复到原生草地状态。不同恢复期样地中土壤线虫的均匀度和多样性指数均显著高于原生植被样地。此外，不同恢复期样地的线虫多度、代谢足迹以及成熟度指数均随恢复年限的增加而增加。相关性分析结果表明，土壤线虫多度与植物地下生物量、土壤有机质、全氮、全磷、矿质氮和速效氮含量显著正相关(P<0.05)，与土壤pH、全钾和容重显著负相关(P<0.05)。尽管三江源区退化草地的人工恢复措施尚未完全恢复牧草生产力至原生植被状态，但土壤生物结构及功能具有改善的趋势，显示该地区退化草地生态系统具有较强的恢复潜力。     

科尔沁沙地旱作农田土壤退化的过程和特征

在一个较小的时空尺度上对科尔沁沙地典型旱作农田土壤物理和化学特性在风蚀沙化过程中的演变特征及其退化过程进行了的探讨。结果表明 :旱作农田由于周边沙质草地的开垦而发生风蚀沙化 ,3～ 5年的时间就会使 5 %～ 15 %的细粒物质吹蚀 ,表土粗化 ,向风沙沉积特征发展 ,土体结构破坏 ,容重增加 0 .0 5～ 0 .15 g/ cm3,总孔隙度降低 3%～ 5 % ,持水性能变劣 ,养分也随之丧失 ;<0 .0 5 mm的粘粉粒吹蚀 1% ,土壤有机质和全氮含量下降 0 .2 5 9g/ kg和 0 .0 16 4 g/ kg;土壤退化的演变 ,既有系统本身的自然属性决定的内在原因 ,更重要的是人为的外部干扰体系的驱动 ;退化的过程既有渐变型 ,又有跃变型     

科尔沁沙地草地退化过程中的物种组成及功能多样性变化特征

科尔沁沙地草地退化、沙漠化过程存在着疏林草地、沙质草场、半流动沙地和流动沙地等明显的逆行演替阶段，并且不同的阶段对应着适合本生境的典型群落类型，每一群落优势种的作用明显。草地退化过程中，原生地带性群落及演替早期群落物种丰富、多样性高．结构复杂，随着草地退化、沙漠化过程，群落组成物种数、科属减少．禾本科植物衰退，物种多样性降低，草地群落结构趋于简单、质量下降。在退化的各个阶段，一年生、二年生和旱生植物功能群在各个阶段始终保持着较高的优势地位．对群落生态功能的发挥和维持起着重要作用。草地退化过程中不同群落的组成变化是物种适应性和群落环境变化相互作用的结果．物种、功能群组成的变化，基本反映草地生态系统退化、群落结构简单化和环境基质稳定性减弱等一系列植被与生境系统变化的趋向。     

放牧模式对内蒙古典型草原生长季土壤呼吸速率的影响

【目的】放牧改变了典型草原生产力和土壤养分循环,影响了植被和土壤微生物的生长状况,进而使草原土壤碳排放量发生变化。本研究通过分析不同放牧措施下内蒙古典型草原生长季土壤呼吸速率 (Rs) 的差异,了解不同放牧管理模式影响草原碳交换和碳平衡的主要途径。【方法】基于内蒙古典型草原全年放牧、休牧及禁牧三种放牧措施,于2014和2015年的7月和9月对Rs进行原位测定,并分析了不同放牧措施下Rs及其影响因子的差异。【结果】1) 三种放牧措施下,Rs表现为休牧样地 [CO₂ 2.00 μmol/(m2·s)] > 禁牧样地 [CO₂ 1.94 μmol/(m2·s)]> 全年放牧样地 [CO₂ 1.56 μmol/(m2·s)]。放牧对Rs的影响还存在季节效应,7月份放牧降低了Rs,而9月份放牧则提高了Rs。2) 与禁牧措施相比,放牧和休牧管理均降低了地上生物量(70.6%和47.3%)、土壤总碳含量(34.5%和32.0%)、土壤总氮含量(37.0%和34.5%),但休牧显著提高了根系生物量(37.2%)。全年放牧样地中土壤可溶性有机碳提高,但微生物磷脂脂肪酸含量下降。3) 7月份Rs主要与土壤湿度和地上生物量显著正相关,而9月份则与土壤温度和土壤PLFAs含量显著正相关。结构方程模型 (SEM) 结果显示,土壤温度 (0.905) 和湿度 (0.188) 通过影响微生物和根系的代谢环境对生长季Rs起主导作用,放牧通过降低土壤湿度和地上生物量对Rs有抑制作用 (–0.137)。【结论】全年放牧通过抑制微生物的生长降低了土壤呼吸速率,休牧通过提高根系生物量增加了土壤呼吸速率,说明放牧对内蒙古典型草原生长季土壤呼吸速率的影响途径因放牧模式的不同而不同。     

聚丙烯酰胺促进沙化退化草场植被恢复效果研究

东北黑土区农牧交错带严重的水土流失破坏了草场资源,降低了土地承载能力,导致草场沙化退化严重。为了以最快的速度最大程度地实现沙化退化草场的植被恢复与重建,通过野外小区对比试验和室内分析,采用二因素完全随机设计,研究了在不同植被条件下施用不同剂量聚丙烯酰胺后草场植被的生物学性状及物种组成的变化,分析探讨了聚丙烯酰胺促进沙化退化草场植被恢复的效果。结果表明:聚丙烯酰胺对植被盖度、株高、生物量和植物多样性的提高均具有明显的促进作用,特别是剂量在120 kg/hm2时,聚丙烯酰胺促进草场植被恢复的效果最为突出。     

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.     

围封禁牧对退化草原土壤性状的影响

以希拉穆仁草原为研究对象,通过对比分析不同围封年限草原土壤机械组成、含水率、容重、孔隙度、有机质含量、碱解氮及速效磷、钾等各项指标,探讨了围封对低山丘陵退化草原土壤性状的影响。结果表明,随着围封年限的增加,草原0-20 cm土层土壤黏粒含量、孔隙度逐年增大,容重和含水率逐渐降低。随着围封时间的延长,土壤速效钾含量逐年降低,土壤有机质、速效磷、碱解氮含量逐渐增加。回归分析结果表明,土壤有机质、碱解氮、速效磷以及速效钾含量的变化同围封年限有显著的相关性。由此可见,围封是促进退化草原土壤改良及植被恢复的一项有效措施。     

春季休牧对内蒙古羊草草原有机碳储量的影响

为了揭示休牧对羊草草原有机碳储量的影响,以休牧3年（RG3a）、6年（RG6a）和9年（RG9a）的羊草草原为对象,采用重铬酸一浓硫酸外加热法,研究了不同休牧年限草原植物群落和土壤的有机碳储量变化。结果表明,地上植被生物量、凋落物量和根系生物量随着休牧年限的延长而逐渐增加。与长期自由放牧草地相比,植物群落和土壤有机碳储量均随休牧年限的延长而增多。长期自由放牧草地（RG0）、休牧3年、休牧6年和休牧9年植物群落地上部有机碳储量为65．17～98．69gC·m^-2,地表凋落物有机碳储量为3．07～10．84gC·m^-2;植物群落0～100cm地下根系有机碳储量为397．13～1480．28gC·m^-2,0～100cm土壤有机碳储量为28306．39～38372．46gC·m^-2。从固碳成本角度,总固碳成本随着休牧年限的延长而增加,最高为8710．20元·hm^-2,固碳成本分别为0．09、0．11、0．08元·kg^-1C。从现有数据显示,休牧9年的固碳量最高,固碳成本最低。春季休牧可以使草地植被得到有效的恢复与更新,有利于草地的可持续利用;随休牧年限的增加,草地有机碳储量增加,固碳成本基本呈现降低趋势。因此,综合现有指标的测定数据,春季休牧是一个非常好的草地利用措施,在休牧过程中草地是一个碳汇,应该鼓励持续进行。