不同强度牦牛放牧对青藏高原高寒草地土壤和植物生物量的影响

放牧作为家畜饲养方式之一,是草地最简单、有效的利用方式,放牧中的家畜对草地生态系统的影响是全球畜牧生态学研究的焦点。过度放牧导致草地退化严重,虽然在青藏高原地区已有较多放牧对草地影响的研究,但探究连续4年放牧对高寒草地生态系统影响的定位实验却鲜见报道。本研究在青藏高原东缘选取典型高寒草地,使用高原特有且分布最广的牦牛作为大型草食放牧家畜,设置了4个牦牛放牧强度（禁牧：无放牧、轻牧：1头/hm²、中牧：2头/hm²和重牧：3头/hm²）以研究其对高寒草地土壤和植物功能的影响。开展4年试验后的结果表明：放牧条件下土壤含水率显著增加;而土壤容重、全磷和有机质含量对放牧强度均无显著性响应;土壤全氮和pH的响应主要在表层0-20 cm,其中全氮为轻牧和重牧处理分别显著高于中牧,中牧处理下的土壤pH为显著高于轻牧;土壤全钾含量在禁牧处理中显著高于放牧处理;而土壤有效氮和速效钾均为中牧处理显著高于禁牧;放牧可以显著降低植物地上生物量。牦牛放牧强度显著影响土壤含水率、有效养分和植物地上生物量,而对其它土壤理化性质影响较弱。本研究结果揭示放牧对高寒草地土壤理化性质和植物地上生物量的影响,为青藏高原高寒草甸生态系统保护、可持续管理和合理放牧率提供理论依据。     

Vegetation and soil responses to livestock grazing in Central Asian grasslands: a review of Chinese literature

Grasslands in northern China and the Qinghai-Tibetan plateau are particularly important to both ecosystem functioning and pastoral livelihoods. Although there are numerous degradation studies on the effect of livestock grazing across the region, they are largely only published in Chinese, and most focus on single sites. Based on case studies from 100 sites, covering a mean annual precipitation gradient of 95–744 mm, we present a comprehensive, internationally accessible review on the impact of livestock grazing on vegetation and soils. We compared ungrazed or slightly grazed sites with moderately and heavily grazed sites by evaluating changes in two indicator groups: vegetation (plant species richness, vegetation cover, aboveground biomass, belowground biomass and root/shoot ratio) and soil (pH, bulk density, organic C, total N, total P and available P). Most indicators declined with intensified grazing, while soil pH, bulk density and belowground biomass increased. Available P showed no clear response. Variables within indicator groups were mostly linearly correlated at a given grazing intensity. Relative grazing effects on different indicators varied along specific abiotic gradients. Grazing responses of plant species richness, aboveground biomass, soil bulk density, total N and available P interacted with precipitation patterns, while grazing effects on belowground biomass were influenced by temperature. Elevation had impact on grazing responses of aboveground biomass and soil organic carbon. Complex grazing effects reflect both methodological inconsistency and ecological complexity. Further assessments should consider specific characteristics of different indicators in the context of the local environment.     

放牧强度对高寒草甸土壤理化性状和植物功能群的影响

为明晰放牧强度对植物功能群落的物种分布特征和土壤理化性状的影响。在青藏高原东北缘高寒草甸设置6块放牧强度样地开展试验。采用多元排序和方差分解等方法,分析放牧强度作用下植物功能群落物种分布与土壤物理结构和化学养分因子的定量关系。结果表明:(1)随放牧强度增加,禾本科、莎草科和多年生杂类草植物群落的物种丰富度、盖度和实际重要值均显著降低,而一年生杂类草无显著变化。(2)对于土壤化学养分,不同放牧强度区,土壤速效钾、全氮和有机质含量均随土层深度的增加而降低,土壤速效磷在不同放牧强度区变化规律不一致。随放牧强度增加,土壤速效钾和全氮含量增加,而土壤速效磷和有机质含量无明显变化。(3)对于土壤物理性状,不同放牧强度区,随土层深度增加,土壤紧实度和容重均增加,而土壤含水量和通气孔隙度均降低。随放牧强度增加,0—30 cm各土层深度的土壤紧实度和容重均增加,土壤含水量和通气孔隙度均降低。(4)以功能群为基本单元对植物群落进行方差分解得出,土壤物理性状可单独解释群落功能群分布总方差的58.10%。(5)基于物种尺度对不同功能群落与环境因子进行定量研究表明,土壤紧实度是决定每种功能群物种分布格局的最主要因子。禾本科、莎草科和多年生草本植物均受土壤物理性状的显著影响,贡献率分别为26.3%、31.0%和16.5%。而一年生草本植物不受土壤物理和化学性状的显著影响。综上所述,放牧强度对土壤化学性状的影响具有不确定性,而对土壤物理性状和群落特征的影响具有确定性。土壤物理结构性状主导了高寒草甸植物功能群落的物种分布格局。     

Managing Semi-Arid Rangelands for Carbon Storage: Grazing and Woody Encroachment Effects on Soil Carbon and Nitrogen

High grazing intensity and wide-spread woody encroachment may strongly alter soil carbon (C) and nitrogen (N) pools. However, the direction and quantity of these changes have rarely been quantified in East African savanna ecosystem. As shifts in soil C and N pools might further potentially influence climate change mitigation, we quantified and compared soil organic carbon (SOC) and total soil nitrogen (TSN) content in enclosures and communal grazing lands across varying woody cover i.e. woody encroachment levels. Estimated mean SOC and TSN stocks at 0–40 cm depth varied across grazing regimes and among woody encroachment levels. The open grazing land at the heavily encroached site on sandy loam soil contained the least SOC (30 ± 2.1 Mg ha^-1) and TSN (5 ± 0.57 Mg ha^-1) while the enclosure at the least encroached site on sandy clay soil had the greatest mean SOC (81.0 ± 10.6 Mg ha^-1) and TSN (9.2 ± 1.48 Mg ha^-1). Soil OC and TSN did not differ with grazing exclusion at heavily encroached sites, but were twice as high inside enclosure compared to open grazing soils at low encroached sites. Mean SOC and TSN in soils of 0–20 cm depth were up to 120% higher than that of the 21–40 cm soil layer. Soil OC was positively related to TSN, cation exchange capacity (CEC), but negatively related to sand content. Our results show that soil OC and TSN stocks are affected by grazing, but the magnitude is largely influenced by woody encroachment and soil texture. We suggest that improving the herbaceous layer cover through a reduction in grazing and woody encroachment restriction are the key strategies for reducing SOC and TSN losses and, hence, for climate change mitigation in semi-arid rangelands.     

Warming and grazing increase mineralization of organic P in an alpine meadow ecosystem of Qinghai-Tibet Plateau, China

Background and aims

Little is known about the soil phosphorus (P) biogeochemical cycling in response to combined warming and grazing, especially in the alpine meadow ecosystem of the Qinghai-Tibet Plateau. Here, we used a free-air temperature enhancement system in a controlled warming-grazing experiment to test the hypothesis that combined warming and grazing would significantly accelerate mineralization of soil organic P.

Methods

A two factorial design of warming (1.2–1.7°C temperature increase) and moderate grazing was utilized. A fractionation method was applied to investigate the sizes of different soil inorganic and organic P fractions.

Results

Results showed that both warming and grazing significantly decreased the quantity of organic P extracted by first NaOH (N(I)Po), as well as the total extractable organic P (TPo) at the 0–10?cm depth. Warming also decreased the total P of soil at 0–10?cm. The combined warming and grazing treatment (WG) led to the reduction of major soil organic P fractions (N(I)Po, TPo) by 40–48% and 28–32%, respectively compared with other treatments at 0–10?cm. The activities of acid and alkaline phosphomonoesterase (AcPME and AlPME) were both enhanced by warming and grazing, and their interaction. Decreased concentrations of soil N(I)Po and TPo were accompanied by increased AcPME activity (P?<?0.01) and soil temperature (P?<?0.05), indicating the enhanced mineralization of organic P under rising temperature. Meanwhile, leaf biomass P of two major species (Potentilla anserine and Gentiana straminea) within these plots were significantly enhanced by either grazing or warming.

Conclusions

The microbial mineralization of soil organic P could be strongly increased under combined warming and grazing conditions as driven by increasing plant demand for P and enhanced microbial activities.     

Comparison of aboveground vegetation and soil seed bank composition at sites of different grazing intensity around a savanna-woodland watering point in West Africa

Grazing removes a plant’s aboveground vegetative and reproductive tissues and can modify the soil seed bank, potentially impacting the restoration of preferred species. Knowledge about aboveground vegetation and species composition of soil seed bank and the processes that contribute to vegetation recovery on and surrounding watering points subjected to grazing is lacking. Successful restoration strategies hinge on addressing these knowledge gaps. We assessed the effects of livestock grazing on aboveground vegetation and soil seed bank characteristics along a river bank and surrounding areas subject to different grazing intensities and draw implications for restoration. Plots (50?×?50 m) were established along five transects representing differing levels of grazing intensity. Soil samples were taken from three layers within each plot to determine soil properties and species composition of soil seed bank using the seedling emergence method. Heavy grazing resulted in the disappearance of perennial grasses, a reduction in species diversity and a decrease in soil nutrients with increased soil depth. Overall, the similarity between the extant aboveground vegetation and flora within the soil seed bank was low. The soil seed bank was dominated by herbaceous species and two woody species, suggesting that many woody species are not accumulating in the soil. With increasing soil depth, the seed density and richness declined. Canonical correspondence analyses (CCAs) showed that emerged seedlings from the soil seed bank were significantly influenced by soil carbon, organic matter, total nitrogen, total potassium and soil cation exchange capacity. This finding suggests that current grazing practices have a negative impact on the vegetation surrounding watering points; hence there is a need for improved grazing management strategies and vegetation restoration in these areas. The soil seed bank alone cannot restore degraded river banks; active transfer of propagules from adjacent undisturbed forest areas is essential.     

短期氮素添加和模拟放牧对青藏高原高寒草甸生态系统呼吸的影响

氮沉降和放牧是影响草地碳循环过程的重要环境因子,但很少有研究探讨这些因子交互作用对生态系统呼吸的影响。在西藏高原高寒草甸地区开展了外源氮素添加与刈割模拟放牧实验,测定了其对植物生物量分配、土壤微生物碳氮和生态系统呼吸的影响。结果表明:氮素添加显著促进生态系统呼吸,而模拟放牧对其无显著影响,且降低了氮素添加的刺激作用。氮素添加通过提高微生物氮含量和土壤微生物代谢活性,促进植物地上生产,从而增加生态系统的碳排放;而模拟放牧降低了微生物碳含量,且降低了氮素添加的作用,促进根系的补偿性生长,降低了氮素添加对生态系统碳排放的刺激作用。这表明,放牧压力的存在会抑制氮沉降对高寒草甸生态系统碳排放的促进作用,同时外源氮输入也会缓解放牧压力对高寒草甸生态系统生产的负面影响。     

内蒙古高原典型草原区河漫滩湿地植物群落退化表征

草原区河流河漫滩草甸是生物多样性表现最充分和生物生产力最高的地段, 但由于过度放牧利用, 绝大部分草甸处于退化状态。该文以锡林河流域中游的河漫滩草甸为研究对象, 比较分析了围封保育湿地与放牧退化湿地的群落组成、地上生物量, 以及共有植物种的植株高度、节间长、叶长、叶宽, 土壤含水量、容重, 群落地下根量及根的分布, 土壤微生物生物量碳、氮的变化。结果表明: 1)放牧使得湿地植物群落优势种发生变化, 原有湿生植物逐渐向旱生化转变, 同时地上及地下生物量明显降低。2)退化湿地的植物呈现显著小型化现象。3)放牧退化湿地的土壤含水量较围封保育湿地低, 其垂直分布及地下根的垂直分布也发生变化。在低河漫滩, 土壤水分随土层的增加而增加, 根量也趋于深层化。但在高河漫滩湿地, 土壤含水量接近典型草原, 根未出现深层化分布趋势。4)放牧践踏引起土壤容重和土壤紧实度增加。5)放牧使得低河漫滩湿地土壤微生物生物量增加, 而在过渡区及高河漫滩湿地, 放牧使得土壤微生物生物量碳、氮含量显著降低。     

Recovery of short tussock and woody species guilds in ungrazed

Soil characteristics were examined within and adjacent to two vegetation exclosures near Porters Pass, Canterbury retired from grazing 45 years ago. Soils were analysed for a range of simple physical (topsoil depth, bulk density), chemical (pH, exchangeable cations, P, S, total C and N) and biochemical (microbial carbon) properties to determine whether the vegetation recovery inside the exclosures was reflected in soil differences. At both sites there were few significant differences between the exclosure and the surrounding grazed area, despite vegetation recovery since exclusion of grazing. At Starvation Gully topsoil depth and Na were higher, and bulk density, pH, K, total C, total N and microbial C mass, and the microbial C to total C ratio were lower in the exclosure. At Cloudy Knell Ca, Mg, total C and N were higher and Na was lower in the exclosure. There was a marked contrast in the trends at the two sites, with slightly lower nutrient status and organic matter in the exclosure at Starvation Gully, and the reverse at Cloudy Knell. The differences between the sites probably reflect differences in the partitioning of nutrients and organic matter between vegetation, litter and soil at the two sites. The results suggest a slow rate of change of soil properties following cessation of grazing and the need to sample soils, litter and vegetation when determining trends in organic matter and chemical fertility.     

中国东黄海海岛5种常见草本的碳氮磷化学计量特征

研究不同纬度海岛共有植物种的碳(C)氮(N)磷(P)化学计量变异特征,有助于剔除植物谱系的影响,揭示植物对海岛环境条件变化的适应策略.本研究以中国东部9个典型海岛的5种常见共有草本植物艾草、狗尾草、葎草、麦冬、酢浆草为研究对象,测定和分析了其地上部分和根系的C、N、P化学计量比,及其与土壤C、N、P含量,温度和降水的关系.结果表明: 9个海岛5种草本地上部分C、N、P含量分别为352.16～518.16、10.81～34.43、0.58～2.38 mg·g^-1,C∶N、N∶P、C∶P分别为11.98～38.99、4.67～27.47、133.39～748.54;根系C、N、P含量分别为312.28～493.34、9.26～23.27、0.40～2.10 mg·g^-1,C∶N、N∶P、C∶P分别为18.18～46.79、8.53～37.38、174.45～1120.40.海岛常见草本的地上部分N、P含量均随着纬度的升高而增高,而N∶P随着纬度的升高而减小;P含量较N含量具有更高的变异性和环境依赖性,气候因子可以解释草本地上部分N、P、N∶P变异的60%;但草本的根系N、P及N∶P不依赖纬度变化而变化,气候因子只解释了根系中的N、P变异的6%～10%.气候因子和土壤养分对植物地上部分及根系的变异贡献率不同,土壤N与P含量对草本植物根系的P含量有显著影响,植物地上部分P含量与土壤P含量呈显著正相关,土壤特性解释了根系N、P变异的37%.研究表明,在剔除植物谱系的影响后,纬度差异导致的环境变化是5种海岛常见草本地上部分的N、P及N∶P变异的主要原因,土壤养分是根系P变异的主要原因.     

放牧强度对内蒙古荒漠草原土壤有机碳及其空间异质性的影响

放牧是内蒙古荒漠草原主要利用方式之一,研究不同放牧强度下土壤有机碳分布规律对退化草原恢复以及推广精准放牧技术具有重要的指导意义。基于不同放牧强度长期放牧样地（0、0.93、1.82、2.71羊单位hm^-2（a/2）^-1）,采用高样本数量的取样设计并结合地统计学分析方法,研究荒漠草原土壤有机碳及其空间异质性。结果表明：中度放牧会显著降低0-30 cm土层全氮含量（P<0.05）,全磷含量随放牧强度增强出现先降低后升高趋势;放牧样地土壤有机碳含量均显著低于对照样地（P<0.05）,不同放牧强度处理土壤有机碳含量没有显著差异;土壤有机碳密度受放牧影响在0-20 cm土层出现显著下降（P<0.05）,变化趋势同有机碳含量相似,碳氮比在重度放牧区0-10 cm土层显著降低（P<0.05）。土壤有机碳空间异质性和异质性斑块的破碎程度随放牧强度增加而增大;土壤有机碳含量与海拔高度在对照、轻度放牧和中度放牧区均呈极显著负相关（P<0.01）,在重度放牧区土壤有机碳含量和海拔无显著相关性;土壤有机碳含量与土壤全氮、全磷含量均呈极显著正相关（P<0.01）。综上所述,放牧降低土壤有机碳含量,提高土壤有机碳空间异质性,土壤有机碳含量的空间变异受海拔和土壤养分含量等因素的共同影响。     

Influence of Grazing on Soil Seed Banks Determines the Restoration Potential of Aboveground Vegetation in a Semi‐arid Savanna of Ethiopia

Species composition, number of emerging seedlings, species diversity and functional group of the soil seed banks, and the influence of grazing on the similarity between the soil seed banks and aboveground vegetation, were studied in 2008 and 2009 in a semi‐arid savanna of Ethiopia. We tested whether the availability of persistent seeds in the soil could drive the transition from a degraded system under heavy grazing to healthy vegetation with ample perennial grasses. A total of 77 species emerged from the soil seed bank samples: 21 annual grasses, 12 perennial grasses, 4 herbaceous legumes, 39 forbs, and 1 woody species. Perennial grass species dominated the lightly grazed sites, whereas the heavily grazed sites were dominated by annual forbs. Heavy grazing reduced the number of seeds that can germinate in the seed bank. Species richness in the seed bank was, however, not affected by grazing. With increasing soil depth, the seed density and its species richness declined. There was a higher similarity in species composition between the soil seed bank and aboveground vegetation at the lightly grazed sites compared with the heavily grazed sites. The mean similarity between the seed banks and aboveground vegetation was relatively low, indicating the effect of heavy grazing. Moreover, seeds of perennial grasses were less abundant in the soil seed banks under heavy grazing. We concluded that restoration of grass and woody species from the soil seed banks in the heavily grazed areas could not be successful in semi‐arid savannas of Ethiopia.     

Ungulate and topographic control of nitrogen: phosphorus stoichiometry in a temperate grassland; soils, plants and mineralization rates

Although the link between the nitrogen (N): phosphorus (P) stoichiometry of biota and availability has received considerable attention in aquatic systems, there has been relatively little effort to compare the elemental composition of biota and supply in terrestrial habitats. In this study, I explored the effects of a prominent topo-edaphic gradient, from dry hilltop to wet slope-base, and native ungulates on N and P of soils, plants, and rates of in situ net mineralization in grasslands of Yellowstone National Park. Nitrogen and P measurements were made May–September, 2000, in paired, grazed and 38–42 year fenced, ungrazed grassland at five topographically variable sites. Similar to findings from other grassland ecosystems, several site factors associated with organic activity, including soil moisture, C, and plant biomass, covaried with soil N concentration and/or net N mineralization. Soil P concentration and net P mineralization, however, were unrelated to those factors. Instead, net P mineralization was negatively related to soil pH, which is known to control the form of inorganic P and its availability, and soil P was uncorrelated with any soil or plant variable measured in the study. Because of being influenced by different soil properties, N and P net mineralization were unrelated among grasslands. Furthermore, supply and plant N:P ratios were uncorrelated in this grassland system. Based on critical N:P ratios reflecting nutritional limitation of plants, Yellowstone grassland vegetation ranged from being N limited to N-P co-limited. Grazers increased N-P co-limitation by enhancing plant N concentrations and the soil pH gradient across grassland sites regulated plant nutritional limitation by affecting plant-available P. These findings showed how ungulates and a landscape factor, i.e. soil pH, determined plant nutrient status among YNP grasslands differently by influencing plant N concentration versus plant P concentration, respectively.     

Does grazing mediate soil carbon and nitrogen accumulation beneath C4, perennial grasses along an environmental gradient?

An experiment was conducted to evaluate the influence of long-term (>25 yrs) grazing on soil organic carbon (SOC) and total soil nitrogen (N) accumulation beneath individual plants of three perennial grasses along an environmental gradient in the North American Great Plains. The zone of maximum SOC and N accumulation was restricted vertically to the upper soil depth (0-5 cm) and horizontally within the basal area occupied by individual caespitose grasses, which contributed to fine-scale patterning of soil heterogeneity. Long-term grazing mediated SOC and N accumulation in the tall-, mid- and shortgrass communities, but the responses were community specific. SOC and N were lower beneath Schizachyrium scoparium plants in long-term grazed sites of the tall- and midgrass communities, but higher beneath Bouteloua gracilis plants in the long-term grazed site of the shortgrass community. SOC, but not N, was greater in soils beneath compared to between S. scoparium plants in an abandoned field seeded in 1941, indicating that this caespitose grass accumulated SOC more rapidly than N. SOC and N were greater in the 0-5 cm soil depth beneath a caespitose grass (S. scoparium) compared to a rhizomatous grass (Panicum virgatum) in the tallgrass community, with no significant accumulation of either SOC or N beneath P. virgatum plants. Grazing appears to indirectly mediate nutrient accumulation beneath caespitose grasses along the environmental gradient by modifying the size class distribution of plants. Populations with a greater proportion of large plants have a greater potential for biomass incorporation into soils and may more effectively capture redistributed organic matter from between plant locations. Contrasting plant responses to grazing at various locations along the environmental gradient conform to the predictions of the generalized grazing model, as the selection pressures of grazing and aridity may have also influenced the ability of caespitose grasses to accumulate nutrients in soils beneath them by mediating grazing resistance, competitive ability and population structure.     

Recovery of Tawa-dominated forest fragments in the Rotorua Basin, New Zealand, after cessation of livestock grazing

Summary   Tawa ( Beilschmiedia tawa )-dominated forest fragments on farms within the Rotorua Basin were surveyed to quantify the likely recovery processes following exclusion of domestic livestock grazing, using a space-for-time substitution approach. Vegetation structure, plant diversity and soil fertility were measured at 24 sites within 15 forest fragments on six farms, covering a range in time since exclusion from grazing of 1–53 years. The forest fragments were compared with a large area of ungrazed forest in the nearby Lake Okataina Scenic Reserve. As time since exclusion from grazing increased, indigenous plant species diversity increased (up to 30–35 years); ground fern and epiphyte abundance increased (up to 30–35 years); tree seedling and sapling numbers, and litter cover also increased (up to 10–15 years); and overall tree numbers increased, while average tree diameter at breast height and overall tree basal area did not differ significantly. The soil fertility status was highly variable, obscuring clear patterns, although Olsen P status decreased with time since grazing exclusion. Once grazing of forest fragments ceases, significant changes in their diversity, structure and soil characteristics can be expected, which indicate recovery of these plant communities towards the conditions observed in ungrazed forest.     

人类活动对锡林郭勒地区主要草原土壤有机碳分布的影响

 内蒙古锡林郭勒地区3类主要草原土壤有机碳含量呈现规律性变化,其顺序为：黑钙土>栗钙土>棕钙土。同时,有机碳沿土壤剖面自上而下逐渐降低,且主要分布在0～15cm处。草甸草原植被下的黑钙土不同层次有机碳含量因农垦分别损失34％～38％,损失主要发生在0～35cm处。分析结果表明,放牧强度在短时期内对典型草原植被下的栗钙土有机碳含量没有显著影响。     

放牧制度对荒漠草原生态系统土壤养分状况的影响

从土壤N,P,K及土壤有机质等方面研究了在连续进行了7 a的放牧制度试验对荒漠草原生态系统土壤养分含量的影响。研究结果表明:放牧制度对土壤的养分状况有明显的影响。划区轮牧区和禁牧提高了土壤有机质、土壤氮素、土壤全钾和土壤速效钾含量。土壤表层磷含量划区轮牧区最高。放牧导致碳氮比减少。同时,土壤养分含量随土壤深度的变化在不同处理没有表现出较为一致的变化趋势。禁牧区土壤全氮含量随土壤深度的增加而增加;不同处理土壤速效氮、土壤速效钾含量均随土壤深度的增加逐渐降低;土壤全磷在自由放牧区随土壤深度的增加逐渐升高;土壤速效磷、全钾含量在划区轮牧区随土壤深度的增加逐渐降低;土壤养分含量与土壤深度的拟合曲线为二次幂函数。研究表明,禁牧和划区轮牧较自由放牧可以提高荒漠草原土壤养分元素的含量,有利于遏制草原土壤的退化。     

藏北古露高寒草地生态系统对短期围封的响应

过度放牧导致高寒草地生态系统退化,围封是生态保护和恢复的管理手段。以青藏高原那曲县古露镇过牧退化高寒草地为对象,系统分析了高寒草地生态系统的植被特征及土壤理化特性、土壤酶活性、土壤微生物生物量和群落结构对围封的响应。结果表明,短期围封后,(1)植被平均高度、盖度和地上生物量均有极显著增加(P0.01),而生物多样性指数则显著降低(P0.01);(2)土壤的水溶性有机碳含量、土壤物理结构(沙土与粉土的比例)及pH有显著变化(P0.05);(3)土壤酶活性没有明显改善;(4)土壤微生物生物量(细菌、放线菌、真菌)均呈显著增加(P0.05);(5)土壤中细菌的多样性有增加的趋势,其群落组成在门水平上也发生了变化;(6)Manteltest分析显示与土壤细菌群落结构的呈正相关性的环境因子主要为土壤有机碳含量(TOC)、总氮含量(TN)、碳磷比(C/P)与氮磷比(N/P)(P0.05)。这表明围栏封育有利于藏北草地植被、土壤理化特性的恢复,还能维持土壤微生物多样性,促进高寒草地生态系统的可持续发展。     

Microbial C, N and P in soils of Mediterranean oak forests: influence of season, canopy cover and soil depth

In Mediterranean ecosystems the effect of aboveground and belowground environmental factors on soil microbial biomass and nutrient immobilization-release cycles may be conditioned by the distinctive seasonal pattern of the Mediterranean-type climates. We studied the effects of season, canopy cover and soil depth on microbial C, N and P in soils of two Mediterranean forests using the fumigation-extraction procedure. Average microbial values recorded were 820 μg C g^?1, 115 μg N g^?1 and 19 μg P g^?1, which accounted for 2.7, 4.7 and 8.8% of the total pools in the surface soil, respectively. Microbial N and P pools were about 10 times higher than the inorganic N and P fractions available for plants. Microbial C values differed between forest sites but in each site they were similar across seasons. Both microbial and inorganic N and P showed maximum values in spring and minimum values in summer, which were positively correlated with soil moisture. Significant differences in soil microbial properties among canopy cover types were observed in the surface soil but only under favourable environmental conditions (spring) and not during summer. Soil depth affected microbial contents which decreased twofold from surface to subsurface soil. Microbial nutrient ratios (C/N, C/P and N/P) varied with seasons and soil depth. Soil moisture regime, which was intimately related to seasonality, emerged as a potential key factor for microbial biomass growth in the studied forests. Our research shows that under a Mediterranean-type climate the interaction among season, vegetation type and structure and soil properties affect microbial nutrient immobilization and thus could influence the biogeochemical cycles of C, N and P in Mediterranean forest ecosystems.     

放牧对荒漠草原克氏针茅种群和土壤生态化学计量特征的影响

该研究选取内蒙古荒漠草原,设计无牧区(NG)、中度放牧(MG)、重度放牧(HG)3个处理,测定分析不同放牧强度处理5年后,优势植物克氏针茅以及土壤的C、N、P营养元素的化学计量特征及其协同关系,以揭示放牧生态系统养分循环的影响机制,为区域草地的利用以及修复提供理论依据。结果表明:(1)轻度放牧下荒漠草原的物种多样性均显著高于中度和重度放牧条件(P<0.05)。(2)土壤中C、N含量以及C∶N、N∶P、C∶P,均随着放牧强度的增加呈先升高后降低的变化趋势,土壤P含量随放牧强度的增加而升高。(3)随放牧强度增加,克氏针茅地上部分C含量降低,N、P含量以及N∶P先升高后降低,C∶P则先减少后升高;克氏针茅地下部分的C、N含量以及N∶P一直呈增加的趋势,P含量先减少后升高,而C∶N、C∶P则是与P含量规律相反。(4)与地上部分各元素含量相比,克氏针茅地下部分各元素含量及其比值与土壤中各元素含量的相关性更高,说明放牧条件下荒漠草原优势植物的根系与其所处的土壤环境具有一定的协同变化能力。