不同土地利用类型下土壤粒径分形分析——以黄土丘陵沟壑区为例

土壤粒径分布影响土壤的水力特性、土壤肥力状况以及土壤侵蚀等,是重要土壤物理特性之一。在水蚀严重的黄土丘陵沟壑区,不同的土地利用类型对水土流失的阻截作用不同,因而进一步导致其土壤粒径分布的差异。对不同土地利用类型下土壤粒径分布的分形和多重分形分析发现：黄绵土土壤粒径分布包含有3个无标度区间,分别为粘粒域、粉粒域和砂粒域;土壤粒径分布的分形维数D、粉粒域维数Dsilt、砂粒域维数Dsand、信息维数D1、信息维数/容量维数D1/D0与土壤细颗粒含量和有机质含量成显著的正相关关系;土地利用对分形维数D、粉粒域维数Dsilt、砂粒域维数Dsand、容量维数D0、信息维数D1、信息维数/容量维数比值D1/D0的影响较显著。这表明这些分形和多重分形参数可以作为反映土壤物理性质和土壤质量的潜在性指标,其实用性有待进一步探讨。     

江河源区高寒草甸退化序列土壤粒径分布及其分形维数

江河源区高寒草甸退化日益严重,恢复治理已进行了大量工作,但收效甚微,主要是对退化机理认识不清.为阐明退化草地的形成机制,
本文以江河源区高寒草甸为对象,分析退化序列土壤粒径的分布特征、分形维数,以及分形维数与土壤侵蚀模数的关系.结果表明: 随着高寒草甸退化加剧,土壤的黏粒百分含量呈增加趋势,粉砂和极细砂呈减小趋势;退化序列土壤粒径分形维数与黏粒百分含量呈显著正相关,与极细砂和粉砂呈显著负相关;各粒级土壤侵蚀模数与分形维数呈二次函数关系,分形维数2.81为土壤侵蚀发生的阈值.以土壤粒径分形维数2.81作为草地恢复指标,选择使分形维数小于2.81的相应措施,是恢复退化草地的有力保证.     

宁夏荒漠草原沙漠化过程中土壤粒径分形特征

研究宁夏荒漠草原沙漠化过程中土壤性状、土壤粒径分形维数的变化特征,以及分形维数与土壤性状的关系.结果表明: 草地沙漠化对土壤分形维数(D)影响显著,D值为1.69～2.62.除在10～20 cm土层出现较小波动外,随着沙漠化程度加剧,0～30 cm土层D值整体呈减小趋势.在荒漠草原沙漠化过程中,荒漠草地D值最大,黏粒和粉粒体积百分含量最高,极细砂粒和细砂粒体积百分含量最低;流动沙地D值最小,黏粒和粉粒体积百分含量最小,极细砂粒和细砂粒体积百分含量最高.D与<50 μm和>50 μm粒径的土壤颗粒存在显著正相关和负相关,表明50 μm粒径是决定草地沙漠化过程中土壤分形维数与土壤粒径关系的临界粒径.随着荒漠草原沙漠化加剧,土壤有机质和全氮含量逐渐降低,土壤容重逐渐升高,固定沙地至半固定沙地是荒漠草原沙漠化的质变过程,其中土壤粘粒体积百分含量、粉粒体积百分含量、土壤有机质含量、土壤全氮含量骤减,极细砂粒体积百分含量、细砂粒体积百分含量和土壤容重骤增.分形维数与土壤有机质、土壤全氮和土壤容重显著相关,固定沙地与半固定沙地分形维数的临界值为2.58,因此分形维数2.58可作为荒漠草原沙漠化的退化指标.     

封育对荒漠草原苦豆子群落土壤粒径分形特征的影响

该研究以宁夏盐池荒漠草原区苦豆子(Sophora alopecuroides)群落为研究对象,通过野外采样和实验室分析,研究了围封对苦豆子群落土壤颗粒分形维数的变化特征以及分形维数与土壤理化性质的关系。结果表明:(1)与围栏外相比,围栏处理样地的黏粒(2μm)体积百分比含量增加,在0~10、10~20和20~40cm土层差异显著;粉粒(2~50μm)体积百分比含量在0~10cm土层显著增加;而砂粒(50~250μm)体积百分比含量减少,在0~10和10~20cm土层差异显著,围封可促使土质细粒化。(2)与围栏外相比,围栏内土壤有机碳、全N、全P、碱解氮、速效磷含量均有所提高,其中0~10cm土层分别增加了177.70%、155.70%、60.11%、120.42%、179.40%,10~20cm土层土壤有机碳、全N、全P、速效磷含量增加比例分别为202.80%、36.50%、27.78%和s37.30%,20~40cm土层土壤养分变化不显著,说明围栏封育使土壤养分主要富集在0~20cm土层,其中0~10cm土层富集达到显著水平。(3)苦豆子群落围栏内的土壤粒径分形维数在2.64~2.69之间,围栏外的分形维数在2.59~2.64之间;与围栏外相比,围栏内土壤粒径分形维数在0~10和10~20cm土层增加显著。(4)土壤粒径分形维数与土壤粒径分布、土壤有机碳、全N、全P、碱解氮、速效P含量均呈显著的线性关系,说明分形维数可以作为一个衡量土壤肥力、土壤结构以及退化土壤恢复程度的综合性指标。     

退化沙质草地开垦和围封过程中的土壤颗粒分形特征

研究了科尔沁退化沙质草地开垦和围封过程中土壤颗粒分形维数的变化特征,以及分形维数与土壤性状的关系.结果表明,不同开垦和围封年限的土壤颗粒分形维数(0～30cm)介于2.387～2.588之间.随着开垦年限的增加,0～15 cm层土壤颗粒分形维数从2.441降至2.387;围封11年后,0～15 cm层土壤颗粒分形维数增加到2.588.15～30 cm层土壤颗粒分形维数无明显变化.土壤颗粒分形维数是反映土壤质地的一个较好指标,重点反映粘粒含量,其次是粉粒含量.分形维数的变化能够很好地表征退化沙质草地土壤的化学、物理和生物学性状的变化趋势,可以作为评价退化沙质草地土壤性状的一个综合指标.     

半干旱矿区排土场苜蓿恢复过程中土壤颗粒分形的演变特征

种植苜蓿恢复模式在半干旱矿区植被恢复中占重要地位。为掌握其恢复过程中土壤颗粒分形的演变特征,选择恢复年限分别为2 a、4 a、6 a和10 a(M2、M4、M6和M10)的苜蓿种植地为研究对象,通过野外分层采样与室内测定,依据颗粒体积分形理论,研究了排土场苜蓿恢复过程中土壤颗粒分形的演变特征及与土壤特性的关系。结果表明:研究区土壤各粒径含量以砂粒为主,粉粒次之,粘粒最少;随着苜蓿恢复过程,粘粒与粉粒含量整体表现为先增加后下降的趋势,且在M4阶段达到最佳,砂粒反之。土壤分形维数变化在2.09—2.57,在苜蓿恢复过程中先增大后减小,在M4阶段达到最大。土壤分形维数与粘粒、粉粒具有极显著正相关性(P<0.01),与砂粒具有极显著负相关性(P<0.01);土壤分形维数与电导率呈极显著负相关关系(P<0.01),与pH值和速效钾含量呈显著负相关关系(P<0.05),与碱解氮含量呈显著正相关关系(P<0.05)。在半干旱矿区排土场采用苜蓿恢复模式,可用土壤分形维数表征土壤特性,应重视恢复年限的调控,适时进行适宜的利用与改造,确保矿区生态恢复的可持续性。     

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。     

南亚热带不同林分土壤颗粒分形与水分物理特征

以广西国有高峰林场的6种不同林分(马尾松林Pinus massoniana、杉木林Cunninghamia lanceolata、尾巨桉林Eucalyptus urophylla×E. grandis、米老排林Mytilaria laosensis、红锥林Castanopsis hystrix和天然次生林)为对象,运用分形学和森林水文学的理论和方法,研究了不同林分类型土壤的颗粒组成以及水分物理特征。结果表明:研究区不同林分类型的土壤颗粒组成以黏粒为主,其次为粉粒和细砂粒,粗砂粒的含量相对较低,土壤颗粒分形维数从大到小依次表现为天然次生林、杉木林、米老排林、红锥林、马尾松林和尾巨桉林;不同林分类型土壤的水分物理特征存在差异,蓄水性能大小依次表现为天然次生林、米老排林、杉木林、红锥林、马尾松林和尾巨桉林,且土壤表层(0～10 cm)的蓄水能力要好于下层(20～50 cm);土壤颗粒分形维数主要受黏粒含量的影响,分形维数与黏粒含量呈极显著正相关,与总孔隙度、饱和蓄水量显著正相关,与土壤密度显著负相关,而与非毛管孔隙度、非毛管蓄水量和有机质含量相关性不显著。土壤颗粒分布的分形维数可作为反映南亚...     

农牧交错区草地利用方式导致的土壤颗粒组分变化及其对土壤碳氮含量的影响

 以位于农牧交错带的内蒙古多伦县6种主要草地利用方式为研究对象,对0～ 30 cm土层的土壤颗粒组分、植物地下根系生物量、土壤有机碳 （Soil organic carbon, SOC）和土壤全氮（Total nitrogen, TN）含量进行了测定分析。6种草地利用方式分别为自由放牧、刈割、围封禁牧 、弃耕、人工牧草（紫花苜蓿（Medicago sativa））和青储作物玉米(Zea mays)）栽培。对土壤粒径分布的分维分析表明,自由放牧样地的土 壤分维数明显低于其余5种类型的草地利用样地,表现出较大的土壤质地异质性。在土壤颗粒组分方面,弃耕样地和人工牧草样地的土壤粘粒（ <0.005 mm）和粉粒(0.005～0.05 mm)含量要明显高于其它草地利用方式,而自由放牧样地呈现相反的变异趋势。除人工牧草样地和自由放牧样 地之外,代表其余4种类型草地利用方式的样地的粘、粉粒含量均随土层加深而降低。6种草地利用方式中,土壤砂粒(0.05～1 mm)含量均与土 壤碳氮含量呈负相关关系;除自由放牧样地和人工牧草样地外,其余4种草地利用方式的土壤粘粒与土壤碳氮含量均表现为显著正相关;植物根 系生物量与土壤碳氮含量和粘、粉粒含量均呈显著正相关;地上生物量和凋落物仅与粘粒含量存在显著正相关关系。以上差异说明草地利用变 化有可能通过影响植被而改变土壤物理性状,同时土壤碳氮含量和土壤颗粒组分的分布特征以及它们之间的相关关系受土地利用方式的影响较 大。根系生物量和土壤粘粒含量可以共同解释土壤碳氮含量变异的70%,自变量的独立解释量约为20%。回归方程为：SOC = 1.08×［粘粒含量 ］+0.01×［根系生物量］-19.45,TN=0.079 ×［粘粒含量］+0.001×［根系生物量］-1.143。     

退化沙质草地开垦和围封过程中的土壤颗粒分形特征

研究了科尔沁退化沙质草地开垦和围封过程中土壤颗粒分形维数的变化特征,以及分形维数与土壤性状的关系.结果表明,不同开垦和围封年限的土壤颗粒分形维数(0～30cm)介于2.387～2.588之间.随着开垦年限的增加,0～15 cm层土壤颗粒分形维数从2.441降至2.387;围封11年后,0～15 cm层土壤颗粒分形维数增加到2.588.15～30 cm层土壤颗粒分形维数无明显变化.土壤颗粒分形维数是反映土壤质地的一个较好指标,重点反映粘粒含量,其次是粉粒含量.分形维数的变化能够很好地表征退化沙质草地土壤的化学、物理和生物学性状的变化趋势,可以作为评价退化沙质草地土壤性状的一个综合指标.     

Impact of historic grazing on steppe soils on the northern Tibetan Plateau

Aims

Few studies have focused on changes in the physical and chemical properties of soils that are induced by grazing at high altitudes. Our aim was to identify potential responses of soil to grazing pressure on the semiarid steppe of the northern Tibetan Plateau and their probable causes.

Methods

Fractal geometry to describe soil structure, soil dynamics, and physical processes within soil is becoming an increasingly useful tool that allows a better understanding of the performance of soil systems. In this study, we sampled four experimental areas in the northern part of the Tibetan Plateau under different grazing intensities: ungrazed, lightly grazed, moderately grazed and heavily grazed plots. Fractal methods were applied to characterise particle-size distributions and pore patterns of soils under different grazing intensities.

Results

Our results reveal a highly significant decrease in the fractal dimensions of particle size distributions (D ₁ ) and the fractal dimensions of all pores (D ₂ ) with increasing grazing intensity. Soil organic carbon (SOC), total N and total P concentrations increased significantly with decreasing grazing intensity. We did not find differences in soil pH in response to grazing.

Conclusions

Grazing induced a significant deterioration of the physical and chemical topsoil properties in the semiarid steppe of the northern Tibetan Plateau. Fractal dimensions can be a useful parameter for quantifying soil degradation due to human activities.     

生长季放牧对高寒草甸传粉网络的影响

植物-传粉者相互作用面临人类活动的威胁。在青藏高原地区,放牧是一项主要的人类活动干扰,过度放牧导致高寒草甸植被严重退化。然而在该区域放牧如何影响植物-传粉者相互作用网络还不得而知。在青藏高原东部的高寒草甸选取了两个研究样点,每个样点包括一块禁牧样地（生长季禁牧）和放牧样地（全年放牧）。在2016年至2018年每年的生长季（7月和8月）进行了连续3年观测,共构建16个传粉网络。结果发现,在研究区域的高寒草甸生态系统中,传粉者群落的物种组成以双翅目昆虫为主。放牧后双翅目、鳞翅目以及鞘翅目传粉者的种类数减少,但膜翅目传粉者的种类数未受到放牧的影响。放牧干扰显著降低了群落中植物、传粉者以及它们之间相互作用的多样性,但对传粉网络的嵌套性和特化程度（H₂''）没有显著影响,说明网络的稳定性和恢复力没有受到放牧的影响。探讨了放牧对传粉网络的影响,发现区域放牧强度过大,降低了传粉昆虫和传粉网络的多样性。未来需要进一步深入研究高寒草甸生态系统中放牧强度对传粉网络的影响模式,以期为合理的放牧制度模式提供理论依据。     

不同恢复方式对退化高寒草甸土壤nifH和chiA微生物群落结构的影响

生物固氮和有机氮降解是土壤有效氮的主要来源,固氮和有机氮降解微生物对土壤氮素供应和地力维持具有重要作用。本研究以青藏高原4种不同利用方式的高寒草甸(未扰动、放牧、围封和围封+补播草甸)为对象,结合荧光实时定量和扩增子测序技术,研究了不同恢复方式对nifH固氮菌和chiA几丁质降解菌基因丰度及其微生物群落结构的影响。结果表明: 4种草甸的nifH和chiA基因丰度大小排序为: 未扰动草甸＞放牧草甸＞围封草甸＞围封+补播草甸,其中未扰动草甸的nifH和chiA基因丰度分别是其他3种草甸的3.4～6.3倍和3.3～8.3倍;固氮菌α多样性在放牧、围封和围封+补播草甸中显著高于未扰动草甸,而几丁质降解菌的α多样性在未扰动和放牧草甸中最高;放牧显著提高了变形菌的丰度而降低了蓝细菌和放线菌丰度;土壤含水量、养分和植被特征对nifH和chiA的基因丰度和群落结构均有显著影响。与未扰动草甸相比,放牧降低了高寒草甸的固氮和有机氮降解潜力,而10年的围封禁牧和补播植草措施对固氮和有机氮降解功能的改善作用不明显。草甸恢复时应综合考虑功能微生物特征及其影响因素,放牧草甸恢复至未扰动水平可能需要更长的封育时间或者采用更加合理的管护措施。     

Effect of fencing and grazing on a Kobresia-dominated meadow in the Qinghai-Tibetan Plateau

Grazing is one of the most important factors influencing community structure and productivity in natural grasslands. Fencing to exclude grazers is one of the main management practices used to protect grasslands. Can fencing improve grassland community status by restraining grazing? We conducted a field community study and indoor soil analyses to determine the long-term effects of fencing and grazing on the above-ground community and soil in a Kobresia-dominated meadow in the Qinghai-Tibetan Plateau, NW China. Our results showed that fencing significantly improved above-ground vegetation productivity but reduced plant density and species diversity. Long-term fencing favored the improvement of forage grass functional groups and restrained the development noxious weed functional groups. There were significant positive effects of fencing on below-ground organic matter, total nitrogen, available nitrogen, total phosphorus and available phosphorus. The productivity of grazed meadow showed a weak decrease over time. There were long-term decreasing trends for plant density both in fenced and grazed meadows. Our study suggests that grazing can be considered as a useful management practice to improve species diversity and plant density in long-term fenced grasslands and that periodic grazing and fencing is beneficial in grassland management.     

Relationship of plant diversity with litter and soil available nitrogen in an alpine meadow under a 9-year grazing exclusion

Grazing exclusion is widely used globally to restore degraded grasslands. Plant diversity has important impacts on grassland ecosystem functions, including grassland productivity and carbon storage. In this study, we selected a Kobresia meadow on the Qinghai–Tibetan Plateau to investigate how grazing exclusion affects plant diversity. Inorganic nitrogen (NH₄ ⁺ and NO₃ ^?) was also measured because its availability impacts plant growth. We found that plant diversity in the meadow was significantly lower under grazing exclusion (fenced meadow) for 9 years compared with moderate grazing. Accumulated litter was significantly higher under grazing exclusion (386.41 g m^?2) compared with grazing (58.77 g m^?2). Soil inorganic nitrogen at 0–5 cm depth was significantly higher under grazing exclusion (13.60 × 10^?2 g kg^?1) than under grazing (9.40 × 10^?2 g kg^?1). The composition of the four functional groups (grasses, sedges, legumes, and forbs) might alter in response to significant changes in the amount of litter and soil available nitrogen content under grazing exclusion compared with grazing. However, the enhanced soil available nitrogen content showed weak feedbacks on plant diversity. In conclusion, light limitation induced by increased amounts of litter may be the main factor causing decreased plant diversity in grazing-excluded meadows compared with moderately grazed meadows.     

Grazing exclusion reduced soil respiration but increased its temperature sensitivity in a Meadow Grassland on the Tibetan Plateau

Understanding anthropogenic influences on soil respiration (R_s) is critical for accurate predictions of soil carbon fluxes, but it is not known how R_s responds to grazing exclusion (GE). Here, we conducted a manipulative experiment in a meadow grassland on the Tibetan Plateau to investigate the effects of GE on R_s. The exclusion of livestock significantly increased soil moisture and above‐ground biomass, but it decreased soil temperature, microbial biomass carbon (MBC), and R_s. Regression analysis indicated that the effects of GE on R_s were mainly due to changes in soil temperature, soil moisture, and MBC. Compared with the grazed blocks, GE significantly decreased soil carbon release by 23.6% over the growing season and 21.4% annually, but it increased the temperature sensitivity (Q₁₀) of R_s by 6.5% and 14.2% for the growing season and annually respectively. Therefore, GE may reduce the release of soil carbon from the Tibetan Plateau, but under future climate warming scenarios, the increases in Q₁₀ induced by GE could lead to increased carbon emissions.     

Methanotrophic community structure and activity under warming and grazing of alpine meadow on the Tibetan Plateau

Knowledge about methanotrophs and their activities is important to understand the microbial mediation of the greenhouse gas CH₄ under climate change and human activities in terrestrial ecosystems. The effects of simulated warming and sheep grazing on methanotrophic abundance, community composition, and activity were studied in an alpine meadow soil on the Tibetan Plateau. There was high abundance of methanotrophs (1.2–3.4 × 10⁸ pmoA gene copies per gram of dry weight soil) assessed by real-time PCR, and warming significantly increased the abundance regardless of grazing. A total of 64 methanotrophic operational taxonomic units (OTUs) were obtained from 1,439 clone sequences, of these OTUs; 63 OTUs (98.4%) belonged to type I methanotrophs, and only one OTU was Methylocystis of type II methanotrophs. The methanotroph community composition and diversity were not apparently affected by the treatments. Warming and grazing significantly enhanced the potential CH₄ oxidation activity. There were significantly negative correlations between methanotrophic abundance and soil moisture and between methanotrophic abundance and NH₄–N content. The study suggests that type I methanotrophs, as the dominance, may play a key role in CH₄ oxidation, and the alpine meadow has great potential to consume more CH₄ under future warmer and grazing conditions on the Tibetan Plateau.     

围栏禁牧对滇西北高寒湿地土壤活性有机碳的影响

过度放牧导致滇西北高寒湿地碳汇功能逐渐丧失,围栏禁牧作为一种有效的湿地恢复方式,其对滇西北高寒湿地土壤碳库的影响尚缺乏研究。为探明围栏禁牧对滇西北高寒湿地土壤活性有机碳的影响,以纳帕海湿地不同禁牧年限(未禁牧、禁牧3年、禁牧8年、禁牧10年)的草甸和沼泽化草甸作为研究对象,对比分析不同禁牧年限草甸和沼泽化草甸土壤总有机碳(TOC)、颗粒有机碳(POC)、溶解性有机碳(DOC)、易氧化有机碳(EOC)和微生物生物量碳(MBC)含量特征。研究结果表明,随着禁牧年限的增加(<10 a),草甸和沼泽化草甸土壤TOC、DOC、EOC、MBC含量显著增加(P<0.05);随着土壤深度的增加,草甸和沼泽化草甸土壤TOC、EOC和MBC含量逐渐下降,而POC和DOC含量逐渐增加。土壤理化性质显著影响土壤活性有机碳各组分含量,其中总氮(TN)是影响草甸和沼泽化草甸土壤活性有机碳各组分含量的主导因素。围栏禁牧有利于滇西北高寒湿地土壤质量和固碳能力的恢复,且随着禁牧年限的增加,恢复效果越明显。相同恢复年限,纳帕海沼泽化草甸土壤恢复效果比草甸土壤显著。研究可以为放牧湿地恢复研究提供理论基础。     

Moderate grazing increased alpine meadow soils bacterial abundance and diversity index on the Tibetan Plateau

The response of grassland soil bacterial community characteristics to different grazing intensities is central ecological topics. However, the underlying mechanisms between bacterial abundance, diversity index, and grazing intensity remain unclear. We measured alpine meadow soil bacterial gene richness and diversity index under four grazing intensities using 16S rDNA sequence analysis on the Tibetan Plateau. The results suggest that extreme grazing significantly decreased alpine meadow both bacterial gene abundance and diversity index (p < .05). The lowest operational taxonomic unit numbers were 3,012 ± 447 copies under heavy grazing in the growing season. It was significantly lower than heavy grazing with approximately 3,958 ± 119 copies (p < .05). The Shannon index for medium and high grazing grassland bacterial diversity was slightly higher than for light grazing in the growing season. Furthermore, the lowest index was approximately 9.20 ± 0.50 for extreme grazing of grassland in the growing season. The average bacterial gene abundance and diversity index in the dormancy period were slightly higher than that in the growing season. Soil bulk density, pH, ammonium, and nitrate nitrogen were the main positive factors driving grazed grassland bacterial communities. Our study provides insight into the response of alpine meadows to grazing intensity, demonstrating that moderate grazing increases bacterial community diversity in grazed grasslands.