Cesium‐137‐based erosion‐rate determination of a steep mountainous region

Data on quantification of erosion rates in alpine grasslands remain scarce but are urgently needed to estimate soil degradation. We determined soil‐erosion rates based on ¹³⁷Cs in situ measurements. The method integrates soil erosion over the last 22 y (time after the Chernobyl accident). Measured erosion rates were compared with erosion rates modeled with the Universal Soil Loss Equation (USLE). The comparison was done in order to find out if the USLE is a useful tool for erosion prediction in steep mountainous grassland systems. Three different land‐use types were investigated: hayfields, pasture with dwarf shrubs, and pasture without dwarf shrubs. Our test plots are situated in the Urseren Valley (Central Switzerland) with a mean slope steepness of 37°. Mean annual soil‐erosion rates determined with ¹³⁷Cs of the investigated sites ranged between the minimum of 4.7 t ha^–1 y^–1 for pastures with dwarf shrubs to >30 t ha^–1 y^–1 at hayfields and pastures without dwarf shrubs. The determined erosion rates are 10 to 20 times higher compared to previous measurements in alpine regions. Our measurements integrated over the last 22 y, including extreme rainfall events as well as winter processes, whereas previous studies mostly reported erosion rates based on summer time and short‐term rainfall simulation experiments. These results lead to the assumption that heavy‐rainfall events as well as erosion processes during winter time and early spring do have a considerable influence on the high erosion amounts that were measured. The latter can be confirmed by photographs of damaged plots after snowmelt. Erosion rates based on the USLE are in the same order of magnitude compared to ¹³⁷Cs‐based results for the land‐use type “pasture with dwarf shrubs”. However, erosion amounts on hayfields and pasture without dwarf shrubs are underestimated by the USLE compared to ¹³⁷Cs‐based erosion rates. We assume that the underestimation is due to winter processes that cause soil erosion on sites without dwarf shrubs that is not considered by the USLE. Dwarf shrubs may possibly prevent from damage of soil erosion through winter processes. The USLE is not able to perform well on the affected sites. Thus, a first attempt was done to create an alpine factor for the USLE based on the measured data.     

Snow removal alters soil microbial biomass and enzyme activity in a Tibetan alpine forest

Projected future decreases in snow cover associated with global warming in alpine ecosystems could affect soil biochemical cycling. To address the objectives how an altered snow removal could affect soil microbial biomass and enzyme activity related to soil carbon and nitrogen cycling and pools, plastic film coverage and returning of melt snow water were applied to simulate the absence of snow cover in a Tibetan alpine forest of western China. Soil temperature and moisture, nutrient availability, microbial biomass and enzyme activity were measured at different periods (before snow cover, early snow cover, deep snow cover, snow cover melting and early growing season) over the entire 2009/2010 winter. Snow removal increased the daily variation of soil temperature, frequency of freeze–thaw cycle, soil frost depth, and advanced the dates of soil freezing and melting, and the peak release of inorganic N. Snow removal significantly decreased soil gravimetric water, ammonium and inorganic N, and activity of soil invertase and urease, but increased soil nitrate, dissolve organic C (DOC) and N (DON), and soil microbial biomass C (MBC) and N (MBN). Our results suggest that a decreased snow cover associated with global warming may advance the timing of soil freezing and thawing as well as the peak of releases of nutrients, leading to an enhanced nutrient leaching before plant become active. These results demonstrate that an absence of snow cover under global warming scenarios will alter soil microbial activities and hence element biogeochemical cycling in alpine forest ecosystems.     

祁连山林区苔藓垂直分布特征与水文功能分析

苔藓是祁连山林区地被层植物的主要建群种，具有保持林区环境湿润、调节地表径流和涵养水源的功能。通过野外调查，结合苔藓植物的分布情况和环境特征，将研究区苔藓植物垂直分布划分为低山苔藓植物带、乔木林苔藓分布带、亚高山灌丛林苔藓分布带，对各带的主要苔藓种类和分布情况做了较详细的描述。由于各带苔藓厚度有明显的不同，导致含水量有明显的差异。当苔藓最大厚度达到7．4cm时，苔藓的最大持水率为519．44％，随厚度降低持水率变小。林区苔藓在5月含水量最大，7月最小，从5月到9月含水量呈递减趋势；并对林内无苔藓覆盖和林内有苔藓覆盖的土壤水分蒸发做了比较分析，得到这两者蒸发大小的顺序是：林内无苔藓覆盖〉林内有苔藓覆盖。     

Microbial community composition and activity in different Alpine vegetation zones

In alpine environments, climate change may alter vegetation composition as well as the quantity and quality of plant litter, which in turn may affect microbial community composition and functioning. In this study, we analyzed soil microbial community composition and its activity along a vegetation gradient (900-1900 m above sea level (a.s.l.)) in the Austrian Limestone Alps. Soil pH and C:N ratios were significantly different under different plant communities and ranged from 3.9 to 6.1 and from 29 to 17, respectively. The highest amounts of microbial biomass, estimated by the sum of microbial phospholipid fatty acids (total PLFAs), were found at sites with high pH and low C:N ratio, i.e. in alpine grassland and beech forest sites (3.9 ± 0.05 and 3.4 ± 0.7 μmol per g organic carbon (OC), respectively), and the lowest amounts were found at sites with low pH and high C:N ratio, i.e. sites with high percentage of conifers and acidophilic vegetation (around 2 μmol (g OC)⁻¹). Total and bacterial PLFAs as well as microbial activity (dimethyl sulphoxide reduction) did not show consistent altitudinal trends. The fungal PLFA 18:2ω6,9 was significantly higher in the forest sites (between 9.2 and 6.7 mol%) compared to the shrubland and grassland sites (between 4.5 and 2.3 mol%). A similar trend was found for ergosterol contents. As a consequence, the bacterial to fungal biomass ratio increased significantly from forest sites to shrubland and grassland sites. Expected future upward migration of the tree line in alpine environments in response to climate warming will therefore increase the abundance of fungi in these ecosystems.     

Organic matter dynamics in a temperate forest as influenced by soil frost

In the future, climate models predict an increase in global surface temperature and during winter a changing of precipitation from less snowfall to more raining. Without protective snow cover, freezing can be more intensive and can enter noticeably deeper into the soil with effects on C cycling and soil organic matter (SOM) dynamics. We removed the natural snow cover in a Norway spruce forest in the Fichtelgebirge Mts. during winter from late December 2005 until middle of February 2006 on three replicate plots. Hence, we induced soil frost to 15 cm depth (at a depth of 5 cm below surface up to –5°C) from January to April 2006, while the snow‐covered control plots never reached temperatures < 0°C. Quantity and quality of SOM was followed by total organic C and biomarker analysis. While soil frost did not influence total organic‐C and lignin concentrations, the decomposition of vanillyl monomers (Ac/Ad)_V and the microbial‐sugar concentrations decreased at the end of the frost period, these results confirm reduced SOM mineralization under frost. Soil microbial biomass was not affected by the frost event or recovered more quickly than the accumulation of microbial residues such as microbial sugars directly after the experiment. However, in the subsequent autumn, soil microbial biomass was significantly higher at the snow‐removal (SR) treatments compared to the control despite lower CO₂ respiration. In addition, the water‐stress indicator (PLFA [cy17:0 + cy19:0] / [16:1ω7c + 18:1ω7c]) increased. These results suggest that soil microbial respiration and therefore the activity was not closely related to soil microbial biomass but more strongly controlled by substrate availability and quality. The PLFA pattern indicates that fungi are more susceptible to soil frost than bacteria.     

Benefactor and allelopathic shrub species have different effects on the soil microbial community along an environmental severity gradient

Patches where shrubs have either positive or negative effects on their understory plant community are common in arid ecosystems. The intensity and balance of these effects change along environmental severity gradients but, despite the major role of soil microbes in plant interactions, little is known about the differences among soil microbial communities under these species and their possible influence on such contrasting shrub effects. We hypothesized that microbial communities associated to benefactor and allelopathic shrubs would differ among them and that differences would increase with environmental severity. To test these hypotheses we characterized soil microbial biomass, activity and community composition under a benefactor shrub species, Retama sphaerocarpa, an allelopathic shrub species, Thymus hyemalis, and in bare soil among plants (gaps) at three sites along an environmental severity gradient. Shrubs promoted an increase in soil bacterial diversity, being bacterial communities associated to benefactor shrubs, allelopathic shrubs and gaps different in composition. Microbial enzymatic activity and biomass increased under shrubs and under more mesic conditions; nonetheless, they were highest under benefactor shrubs at the most arid site and under allelopathic shrubs at the less severe site. Compared to gaps, the presence of shrubs induced changes in microbial activity and community composition that were larger at the most severe site than at the less severe site. Along the gradient, benefactor shrubs enhanced the abundance of bacterial groups involved in organic matter decomposition and N fixation as well as plant pathogens, which could contribute to Retama's outstanding positive effects on understory plant biomass and diversity. Plant patches mitigate the effects of extreme conditions on associated plant and soil microbial communities and promote soil biodiversity and ecosystem functioning in arid ecosystems, with shrubs actively selecting for specific microbial groups in their understory.     

Patterns and drivers of fungal diversity along an altitudinal gradient on Mount Gongga,China

Purpose

Fungi are essential components of soil microbial communities and have a crucial role in biogeochemical processes. Alpine regions are sensitive to climate change, and the importance of changes in fungal community composition along altitudinal gradients in alpine regions is hotly debated.

Materials and methods

We used 454 pyrosequencing approaches to investigate the fungal communities at 1600, 2300, 2800, 3000, and 3900 m above sea level along an altitudinal gradient on Mount Gongga.

Results and discussion

The results showed that Agaricomycetes, Sordariomycetes, and Tremellomycetes are the dominant classes at all sampling sites. Operational taxonomic unit richness decreased with increasing altitude, and the fungal communities were clustered into three groups that corresponded to altitudes of, i.e., 1600, 2300, and above 2800 m. The evenness of fungi was not significantly correlated with altitude, whereas beta diversities were significantly correlated with altitude. The distance-based redundancy analysis and Mantel test indicated that the composition of fungal assemblages was mostly driven by altitude and temperature.

Conclusions

Our results indicated that ecological processes possibly related to altitude and temperature play an important role in structuring fungal biodiversity along the elevational gradient. Our results highlight that different microbes may respond differently to environmental gradients.

     

Land Use and Cover Dynamics Since 1964 in the Afro‐Alpine Vegetation Belt: Lib Amba Mountain in North Ethiopia

Human‐induced land use and land cover (LUC) changes threaten the ecosystem services of the vulnerable tropical afro‐alpine vegetation. Several LUC change studies are available for the Ethiopian highlands, but relatively little is known about LUC change in the afro‐alpine zones. In this study, LUC changes between 1964 and 2012 were mapped for the afro‐alpine zone of Lib Amba Mountain, part of the Abune Yosef Mountains in North Ethiopia. Historical LUC was derived from georeferenced aerial photographs of 1964 and 1982, and the present LUC (2012) from Bing Map satellite imagery. Based on these successive LUC maps a time‐depth map, LUC proportions, LUC transition matrices and LUC change trajectories were calculated. Two main phases of LUC change could be distinguished linked to the neo‐Boserupian perspective. (i) Between 1964 and 1982, there were large‐scale deforestation and general degradation of the vegetation above 3500 m, in a period of low population pressure; (ii) Between 1982 and 2012, an intensification of land use prevailed accompanied with a slight regeneration of the vegetation and the Erica arborea L. forest, under increased population pressure. Depth interviews indicated that local and governmental land management measures are very important for the protection against vegetation depletion and soil degradation. Quick recovery of the forest on Lib Amba provides confidence that degraded afro‐alpine areas would benefit in a short time from complete protection, given the vicinity of remaining patches of afro‐alpine vegetation. Management interventions are thus vital to restore the important ecosystem services of the afro‐alpine vegetation belt. Copyright © 2015 John Wiley & Sons, Ltd.     

土壤有机碳活性组分沿中国长白山海拔坡度的分布情况

Understanding the responses of soil organic carbon(SOC) fractions to altitudinal gradient variation is important for understanding changes in the carbon balance of forest ecosystems.In our study the SOC and its fractions of readily oxidizable carbon(ROC),water-soluble carbon(WSC) and microbial biomass carbon(MBC) in the soil organic and mineral horizons were investigated for four typical forest types,including mixed coniferous broad-leaved forest(MCB),dark coniferous spruce-fir forest(DCSF),dark coniferous spruce forest(DCS),and Ermans birch forest(EB),along an altitudinal gradient in the Changbai Mountain Nature Reserve in Northeast China.The results showed that there was no obvious altitudinal pattern in the SOC.Similar variation trends of SOC with altitude were observed between the organic and mineral horizons.Significant differences in the contents of SOC,WSC,MBC and ROC were found among the four forest types and between horizons.The contents of ROC in the mineral horizon,WSC in the organic horizon and MBC in both horizons in the MCB and EB forests were significantly greater than those in either DCSF or DCS forest.The proportion of soil WSC to SOC was the lowest among the three main fractions.The contents of WSC,MBC and ROC were significantly correlated(P < 0.05) with SOC content.It can be concluded that vegetation types and climate were crucial factors in regulating the distribution of soil organic carbon fractions in Changbai Mountain.     

Snow removal and its influence on temperature and N dynamics in alpine soils (Vallée d'Aoste,northwest Italy)

The effect of a lack of snow cover in winter was investigated in two soils, beneath larch and meadow, in NW Italy (Vallée d'Aoste Region). During the late 1980s and early 1990s and 2000s, this region experienced extreme climatic conditions including a low snow pack and lack of snow cover for extended periods with important effects on soil temperature and nutrient dynamics. In particular, the mountain belt in the Alps may be extremely sensitive to these phenomena, in relation to the rise in average snowline projected under a warmer global climate. The study area is located at an elevation of 1450 m asl in the Italian Alps (Mont Mars Natural Reserve). During the winter 2003/04, snow was continuously removed in a treatment plot while a reference plot was maintained undisturbed. Soil temperature was measured at 10 cm depth by data loggers (UTL‐1). Soil N transformations in the topsoil (10 cm depth) were determined by the buried‐bag technique. The removal of the snow cover caused a significant decrease in soil temperature, related to concurrent decreases in air temperature. The lowest soil temperatures recorded were –4.3°C and –4.5°C beneath larch and meadow, respectively, on January 31, 2004. Soil temperature in the undisturbed plots was maintained above the freezing point when the snow cover was present. The snow removal caused significant increases in net ammonification in both soils and net nitrification only under meadow, but did not affect microbial biomass N which decreased in both plots. Our results suggest that the lower temperature reached in the plot without snow favored the production of inorganic N by physical rather than microbial degradation of soil organic matter (SOM). Soil freezing could enhance soil‐aggregate disruption releasing physically protected SOM and fragmentation of OM itself.     

Modelling the transformations and sequestration of soil organic matter in two contrasting ecosystems of the Andes

The mechanisms linking soil respiration to climate and soil physical properties are important for modelling transformation and sequestration of C and N in the soil. We investigated them by incubating ¹⁴C and ¹⁵N labelled straw in soils of the dry puna (Bolivian altiplano, semi‐arid shrubland at 3789 m above sea level) and the humid paramo (Venezuelan tropical alpine vegetation at 3400 m). These two ecosystems of the high Andes are comparable in terms of altitude, mean temperature and land use, but are very different regarding organic matter content, rainfall patterns and soil physical properties. Total ¹⁴C and ¹⁵N, microbial‐biomass ¹⁴C and ¹⁵N, soil moisture and meteorological data were recorded over 2 years. Daily soil moisture was predicted from a water balance model. The data from the paramo site were used to calibrate MOMOS‐6, a model of organic matter decomposition based on microbial activity and requiring only kinetic constant parameters to describe: (i) inputs to microbial biomass from plant debris and microbial metabolites, and (ii) losses from the biomass by mortality and respiration (respiration coefficient and microbial metabolic quotient qCO₂). The simulated qCO₂–¹⁴C agrees well with qCO₂–¹⁴C and qCO₂ measured at the calibration site and with published data. To apply MOMOS‐6 to the puna site, only the respiration coefficient of the biomass was re‐estimated. The dynamics of ¹⁴C and ¹⁵N were very different in the two systems. In the puna, the transformation processes stop during the long dry periods, though total annual mineralization is greater than in the paramo. The change in the value of the respiration coefficient enables us to predict that the amount of C and N sequestered in the stable humus is greater in the paramo than in the puna. The data in this paper can be used to estimate values of the respiration coefficient so that MOMOS‐6 can be applied to other systems.     

Climate dependence of heterotrophic soil respiration from a soil‐translocation experiment along a 3000 m tropical forest altitudinal gradient

Tropical ecosystems play a key role in the global carbon cycle, but their response to global warming is not well understood. Altitudinal gradients offer the unique possibility of undertaking in situ experimental studies of the influence of alterations in climate on the carbon (C) cycle. In a soil‐translocation experiment we took replicate soil cores at 3030 m, 1500 m, 1000 m and 200 m above sea level along an altitudinal gradient in tropical forest in Peru, and exchanged (i.e. translocated) them among these sites to observe the influence of altered climatic conditions on the decomposition of soil organic matter under natural field conditions. Soil respiration rates of the translocated soil cores and adjacent undisturbed soils were measured twice a month from April 2007 to October 2007. The temperature sensitivity of heterotrophic respiration in each core was examined using a Lloyd & Taylor function and a simple modified third‐order polynomial fit. Calculated Q₁₀ values decreased with decreasing altitude using both mathematical functions (2.53–1.24 according to the Lloyd & Taylor function, and 2.56–0.63 using the polynomial fit). Soil organic C‐stocks increased markedly and linearly with altitude, but surprisingly the average total soil respiration rate did not vary significantly with altitude along the transect (3.98–4.31 μmol CO₂ m⁻² s⁻¹). This implies an increase with elevation of absolute C allocation to below‐ground allocation.     

藏西南高原植被NDVI时空变化及其与海拔梯度的关系

青藏高原植被分布不仅与区域水热条件密切相关,而且受海拔和地形的共同影响,认知植被与海拔梯度的关系对青藏高原生态保护具有重要科学和现实意义。基于MODIS NDVI数据和植被类型数据,分析了藏西南高原近21年来不同植被类型生长季NDVI时空变化特征,探讨了植被覆盖与海拔梯度的关系。结果表明:藏西南高原植被类型有森林、荒漠、草原、草甸、高山植被、栽培植被、灌丛和其他植被8种; 随时间推移,各植被类型NDVI均显著增加且在2017年达到最大值。研究区草原、草甸、灌丛和高山植被的增加速率依次为0.006/10 a,0.004/10 a,0.01/10 a和0.006/10 a。除了局地植被呈退化趋势外,绝大部分植被覆盖不断改善。草原、草甸、灌丛和高山植被主要集中分布在海拔4 000 m以上的地区,NDVI在各海拔梯度上均存在较大差异。不同植被类型NDVI随海拔升高均呈现不同的减小趋势,不同年份间同种植被NDVI随海拔梯度变化具有相似的变化趋势。研究结果可为藏西南高原生态建设、植被恢复和畜牧业发展提供一定的科学依据和决策支持。     

小浪底库区不同水位高程下消落带落干期土壤微生物量碳分布特征

  目的  探究小浪底库区不同水位高程下消落带落干期土壤微生物量碳（SMBC）分布特征,为库区土壤碳循环研究及消落带受损植被系统恢复与重建提供理论依据。  方法  采用定位试验的方法,监测并分析了小浪底库区对照高程（275 m）和3个淹水高程（265、255、245 m）下消落带落干期SMBC含量及土壤理化性质变化。  结果  小浪底库区消落带表层SMBC含量的变化区间为29.25 ~ 204.97 mg kg?1,平均值为112.81 mg kg?1;消落带SMBC含量在各高程间差异明显,与对照相比,中短期淹水高程下（265和255 m）SMBC含量显著升高（P < 0.05）,而长期淹水高程下（245 m）SMBC含量则显著降低（P < 0.05）;消落带落干期SMBC含量随时间总体呈下降的变化趋势,并且前期下降更为明显,后期则较为平缓;不同土层间消落带SMBC含量的变化规律较为相似,其差异性主要体现在SMBC含量大小的变化上,表现为上土层（0 ~ 10 cm） > 下土层（10 ~ 20 cm）;Pearson相关分析得出消落带SMBC含量在水位高程、时间及土层尺度上均与土壤含水率、温度、有机质和全氮之间存在显著相关性（P < 0.05）,但与土壤黏粒含量和全磷之间的相关性并不显著（P > 0.05）;同一高程草本植被下消落带SMBC含量明显高于灌丛,且混生植被类型下SMBC含量较相应的单一植被类型明显升高,表现为草本混生 > 单一草本,或灌丛－草本混生 > 灌丛。  结论  小浪底库区消落带土壤微生物量碳含量在不同研究尺度上的分布特征显著,并对土壤理化性质及植被类型的变化响应明显,因此可根据土壤环境条件,考虑采取不同植被混植的修复方式,开展小浪底库区消落带受损植被系统的恢复与重建。     

岷江干旱河谷植物群落生态梯度分析

 为干旱河谷地区的植被恢复和生物多样性的保育提供科学依据,运用数量排序方法DCCA,就岷江干旱河谷调查的植被和环境数据进行排序分析,研究该地区植物群落分布与环境梯度之间的关系,并用主成分分析法,研究该地区灌丛地上生物量与环境因子之间的关系。DCCA排序结果表明,该地区植被的分布是土壤水分、土壤养分和微地形三者综合作用的结果;主成分分析结果表明,影响灌丛群落地上生物量的第1主成分中,土壤pH值、速效P、全N、有机质含量和坡向的影响较大,影响灌丛群落地上生物量的第2主成分因子,主要是土壤含水量和海拔,第3主成分因子,主要是土壤速效K,第4主成分因子,主要是地形中的坡度因子。灌丛地上生物量,也受土壤养分、水分、地形三者共同的影响和作用。     

Soil properties and tree growth along an altitudinal transect in Ecuadorian tropical montane forest

In tropical montane forests, soil properties change with increasing altitude, and tree‐growth decreases. In a tropical montane forest in Ecuador, we determined soil and tree properties along an altitudinal transect between 1960 and 2450 m asl. In different vegetation units, all horizons of three replicate profiles at each of eight sites were sampled and height, basal area, and diameter growth of trees were recorded. We determined pH and total concentrations of Al, C, Ca, K, Mg, Mn, N, Na, P, S, Zn, polyphenols, and lignin in all soil horizons and in the mineral soil additionally the effective cation‐exchange capacity (CEC). The soils were Cambisols, Planosols, and Histosols. The concentrations of Mg, Mn, N, P, and S in the O horizons and of Al, C, and all nutrients except Ca in the A horizons correlated significantly negatively with altitude. The C : N, C : P, and C : S ratios increased, and the lignin concentrations decreased in O and A horizons with increasing altitude. Forest stature, tree basal area, and tree growth decreased with altitude. An ANOVA analysis indicated that macronutrients (e.g., N, P, Ca) and micronutrients (e.g., Mn) in the O layer and in the soil mineral A horizon were correlated with tree growth. Furthermore, lignin concentrations in the O layer and the C : N ratio in soil affected tree growth. These effects were consistent, even if the effect of altitude was accounted for in a hierarchical statistical model. This suggests a contribution of nutrient deficiencies to reduced tree growth possibly caused by reduced organic‐matter turnover at higher altitudes.     

Factors Affecting Herbaceous Richness and Biomass Accumulation Patterns of Reclaimed Coal Mines

Open‐cast mining reclamation strategies are focused on the identification of the environmental factors at different scales that facilitate the vegetation establishment and development. Here, we characterised the environmental factors at macro‐scale and micro‐scale that influenced the herbaceous richness and biomass accumulation patterns trough a 32‐year chronosequence. Herbaceous richness and biomass were influenced at macro‐scale by successional and soil development gradients whereas at micro‐scale by shrub cover and coarseness gradients. Indeed, certain environmental factors at macro‐scale and micro‐scale contributed simultaneously to determine these gradients. Explicitly, the successional gradient was related to carbon and nitrogen ratio, grazing intensity and Shannon diversity. Across this successional gradient, total herb biomass and Fabaceae biomass were reduced as well as main taxonomical groups richness. Soil development gradient was related to total nitrogen, pH and erosion severity. This gradient only influenced species richness and produced a richness reduction when pH and erosion severity increased. At micro‐scale, the shrub cover gradient was related to organic matter thickness, producing a Poaceae biomass and bryophytes cover increase when shrub cover and organic matter increased. The coarseness gradient was related to the cover of rocks and bare soil, producing a reduction of herb biomass and richness when rocks and bare soil increased. These results emphasise the need to incorporate in the management plans the influence of soil development, successional, shrub cover and coarseness gradients over herbaceous richness and biomass to improve mine reclamation strategies. Copyright © 2013 John Wiley & Sons, Ltd.     

东祁连山高寒草甸土壤“固-液-气”三相组成对海拔和坡向的响应

为探究不同海拔和坡向下高寒草甸土壤"固—液—气"三相组成变化特征,以东祁连山高寒草甸为研究对象,分析了不同海拔(2 800,3 000,3 200,3 400,3 600,3 800,4 000 m)、坡向(阳坡、阴坡)高寒草甸的植被特征和土壤物理特征,结合植被指标拟合探讨高寒草甸"固—液—气"三相的最佳组成比例。结果表明:植被盖度、草层高度和地上生物量均随海拔升高呈先升高后降低,在海拔3 200 m处达最大值,同一海拔的阴坡植被盖度、草层高度、地上生物量均高于阳坡;土壤容重随海拔和坡向的变化规律与植被盖度相反,而土壤含水量、孔隙度和持水性变化规律与植被盖度类似;经方程拟合发现,土壤"固—液—气"三相比例为31∶33∶36时,高寒草甸生产力最优。综上所述,在海拔3 200 m处是东祁连山高寒草甸分布的中心典型区域,海拔和坡向是影响高寒草甸土壤物理质量和"固—液—气"三相组成的重要环境因子,且该区域高寒草甸土壤"固—液—气"最佳比例为31∶33∶36。     

Soil organic‐matter stocks and characteristics along an Alpine elevation gradient

Mountain regions are known to be especially vulnerable to climatic changes; however, information on the climate sensitivity of alpine ecosystems is still scarce to date. In this study, we investigate the impacts of climate and vegetation composition on soil organic‐matter (SOM) stocks and characteristics along an elevation gradient (900 to 1900 m asl) in the Austrian Limestone Alps. The soils classified as Leptic Histosols, i.e., organic soils directly overlying the calcareous bedrock. Soil organic‐carbon stocks (SOC; mean ± standard deviation) to bedrock increased in the low‐elevation forest sites from 19 ± 3 kg m^–2 (900 m asl) to 31 ± 3 kg m^–2 (1300 m asl), reached a maximum (38 ± 5 kg m^–2) in the shrubland at 1500 m asl, but decreased again in the high‐elevation grassland sites (26 ± 3 kg m^–2 at 1700 m asl and 13 ± 3 kg m^–2 at 1900 m asl). Thermogravimetic measurements and Fourier‐transform infrared spectroscopy (FTIR) suggest that the upper soil layers were dominated by more labile organic compounds, whereas more persistent materials increased with depth. Along the studied climosequence, the aliphatic FTIR band (2920 cm^–1) was lower in the low‐elevation forest sites compared to the high‐elevation grassland sites. Most other FTIR bands did not change with altitude, but were related to specific site conditions, such as vegetation composition and associated differences in soil pH. Our results demonstrate that differences in SOM stocks and characteristics are not consistently related to variations in climatic conditions along the studied elevation gradient, but are strongly affected by the vegetation composition, their C input and litter quality. This, in turn, is expected to shift in response to climate change.     

Below‐ground and above‐ground production of vegetational organic matter along a climosequence in alpine grasslands

The distribution of vegetational organic matter above‐ and below‐ground and its productivity was analyzed in an alpine area along a climosequence ranging from subalpine to alpine climates. Emphasis is placed on the quantification of carbon (C) and nitrogen (N) fixed in the above‐ground and below‐ground vegetation and its annual input. Annual C‐input ranged from 17.9 to 60.2 g m^—2 year^—1 and the N‐input from 0.74 to 2.48 g m^—2 year^—1. Above‐ground phytomass and the annual production rate of organic matter showed a distinct correlation with the altitude and, thus, the climate. However, the measurement of the above‐ground phytomass is bound to methodological problems: the commonly used harvesting method seems to underestimate the real situation. The harvesting method yielded in its average 100 to 300 g m^—2 phytomass which was 35—83% of the values obtained by the soil core method. Thus, the calculation of turnover times of above‐ground vegetation greatly depends on the method used. Calculated turnover times based on the harvesting method did not correlate with the climate while a clear tendency of lower turnover times with increasing altitude could be observed using the soil core method. The amount of below‐ground phytomass was in the range of 1880 to 2469 g m^—2 and the corresponding annual C‐input (fixation in the roots) between 91.1 and 162 g m^—2 year^—1 and the N‐input between 2.68 and 4.99 g m^—2 year^—1. The below‐ground phytomass and its production rate in high alpine zones are of greater importance and exceed the above‐ground ones. With increasing altitude, furthermore, the importance of the below‐ground phytomass increases with respect to the biomass and to the C‐ and N‐input. For high alpine areas, the phytomass is concentrated in the uppermost soil horizons. About 88.7 to 94.5% of the below‐ground phytomass was found in the soil compartment 0‐20 cm. The below‐ground production rate of phytomass in alpine grassland is fundamental in order to calculate any C or N budgets and potential inputs to SOM: its neglection would introduce most significant errors in modeling any C or N cycles.