Upscaling as ecological information transfer: a simple framework with application to Arctic ecosystem carbon exchange

Transferring ecological information across scale often involves spatial aggregation, which alters information content and may bias estimates if the scaling process is nonlinear. Here, a potential solution, the preservation of the information content of fine-scale measurements, is highlighted using modeled net ecosystem exchange (NEE) of an Arctic tundra landscape as an example. The variance of aggregated normalized difference vegetation index (NDVI), measured from an airborne platform, decreased linearly with log(scale), resulting in a linear relationship between log(scale) and the scale-wise modeled NEE estimate. Preserving three units of information, the mean, variance and skewness of fine-scale NDVI observations, resulted in upscaled NEE estimates that deviated less than 4% from the fine-scale estimate. Preserving only the mean and variance resulted in nearly 23% NEE bias, and preserving only the mean resulted in larger error and a change in sign from CO₂ sink to source. Compressing NDVI maps by 70–75% using wavelet thresholding with the Haar and Coiflet basis functions resulted in 13% NEE bias across the study domain. Applying unique scale-dependent transfer functions between NDVI and leaf area index (LAI) decreased, but did not remove, bias in modeled flux in a smaller expanse using handheld NDVI observations. Quantifying the parameters of statistical distributions to preserve ecological information reduces bias when upscaling and makes possible spatial data assimilation to further reduce errors in estimates of ecological processes across scale.     

Tundra plants protect the soil surface from UV

In the Arctic, seasonal ozone depletion is resulting in periods of enhanced UV-B radiation at ground level while regional climate change is associated with increasing temperatures. These changes are likely to alter plant distribution, biodiversity and morphology, which may have knock-on effects for microbially driven biogeochemical cycling and other soil processes. Our study examined the transmission of solar UV radiation through arctic tundra plants using a portable UV radiometer and the DLR-biofilm biological UV dosimeter. A strong negative correlation was found between vegetation cover and UV transmission to the soil surface. Penetration of UV to the soil beneath tundra plants varied depending upon plant morphology, being greater through low creeping plants than cushion plants, grasses or mosses. UV transmission to the soil surface beyond the foliage edge also varied with plant morphology and the presence of flowers.     

Carbon cycling in subarctic tundra; seasonal variation in ecosystem partitioning based on in situ C pulse-labelling

Carbon assimilation and allocation were studied in a tundra ecosystem in northern Scandinavia. Seasonal variation in the below-ground carbon allocation to dissolved organic carbon (DOC), coarse-, fine-, and hair roots was investigated using in situ ¹⁴C pulse-labelling, adding 2-3 MBq ¹⁴CO₂ dm⁻² to the above-ground vegetation. Combining the allocation data with regression models of the seasonal carbon flux made it possible to estimate a temporally explicit ecosystem carbon allocation budget.The ecosystem was a net source of CO₂, losing on average 0.97 g C m⁻² d⁻¹ to the atmosphere, with little variation through the season. There was, however, significant temporal variation in partitioning of recently assimilated carbon. Allocation to below-ground compartments over 32 days following labelling increased from 18% in June to 55% in September. Above-ground allocation showed the opposite trend. Hair roots and DOC were strong sinks in the autumn. Transport of newly assimilated carbon occurred rapidly throughout the season, ¹⁴C appearing in all sampled pools within 4 h of labelling.The seasonal variation in carbon partitioning observed in this study has implications for the residence time of assimilated carbon in the ecosystem. A relatively greater allocation to rapidly decomposing pools, such as hair roots and DOC, would tend to reduce incorporation into woody tissue, increasing the overall rate of carbon cycling and decreasing ecosystem storage. The results of this study will be of value for building and validating mechanistic models of ecosystem carbon flow in tundra and subarctic ecosystems.     

大兴安岭不同冻土带土壤动物生态地理研究

2003年6月、8月、10月对大兴安岭不同冻土带选择沼泽、柳丛、耕地、次生林群落进行土壤动物调查，共获土壤动物39225只，隶属于4门8纲24目。由对大型、中小型及湿生三类土壤动物的数量分析可知，三类土壤动物数量的变化在群落间并不总是成正相关的关系。水平分布调查表明，中小型土壤动物的个体数量和类群数量从岛状冻土带到连续多年冻土带逐渐减少，该分布与土壤动物分布的一般规律（土壤动物分布通常符合纬度地带性分布规律，即由低纬向高纬逐渐减少）一致，但大型土壤动物的个体数量、类群数和生物量基本上从岛状冻土带到连续多年冻土带逐渐增加（即由低纬向高纬逐渐增加），湿生动物的数量也如此分布，这与土壤动物分布的一般规律不一致甚至相悖，这一特点表现出生态系统局部-区域相互关系的复杂性；土壤动物的类群数、个体数量与土壤有机质、全氮的含量呈明显的正相关；垂直分布调查表明，中小型土壤动物的个体数量和类群数量分布表现出明显的表聚性，但大型土壤动物的个体数量与生物量最大值出现在第二层；土壤动物多样性分析表明，中小型土壤动物的多样性指数从岛状冻土带到连续多年冻土带逐渐减小，而大型土壤动物的多样性指数在不同冻土带间的变化规律不明显。     

Influence of N and non-N salts on atmospheric methane oxidation by upland boreal forest and tundra soils

 The short-term (24 h) and medium-term (30 day) influence of N salts (NH₄Cl, NaNO₃ and NaNO₂) and a non-N salt (NaCl) on first-order rate constants, k (h^–1) and thresholds (C_Th) for atmospheric CH₄ oxidation by homogenized composites of upland boreal forest and tundra soils was assessed at salt additions ranging to 20 μmol g^–1 dry weight (dw) soil. Additions of NH₄Cl, NaNO₃ and NaCl to 0.5 μmol g^–1 dw soil did not significantly decrease k relative to watered controls in the short term. Higher concentrations significantly reduced k, with the degree of inhibition increasing with increasing dose. Similar doses of NH₄Cl and NaCl gave comparable decreases in k relative to controls and both soils showed low native concentrations of NH₄ ⁺-N (≤1 μmol g^–1dw soil), suggesting that the reduction in k was due primarily to a salt influence rather than competitive inhibition of CH₄ oxidation by exogenous NH₄ ⁺-N or NH₄ ⁺-N released through cation exchange. The decrease in k was consistently less for NaNO₃ than for NH₄Cl and NaCl at similar doses, pointing to a strong inhibitory effect of the Cl^– counter-anion. Thresholds for CH₄ oxidation were less sensitive to salt addition than k for these three salts, as significant increases in C_Th relative to controls were only observed at concentrations ≥1.0 μmol g^–1 dw soil. Both soils were more sensitive to NaNO₂ than to other salts in the short term, showing a significant decrease in k at an addition of 0.25 μmol NaNO₂ g^–1 dw soil that was clearly attributable to NO₂ ^–. Soils showed no recovery from NaCl, NH₄ ⁺-N or NaNO₃ addition with respect to atmospheric CH₄ oxidation after 30 days. However, soils amended with NaNO₂ to 1.0 μmol NaNO₂ g^–1 dw showed values of k that were not significantly different from controls. Recovery of CH₄-oxidizing ability was due to complete oxidation of NO₂ ^–-N to NO₃ ^–-N. Analysis of soil concentrations of N salts necessary to inhibit atmospheric CH₄ oxidation and regional rates of N deposition suggest that N deposition will not decrease the future sink strength of upland high-latitude soils in the atmospheric CH₄ budget. Received: 30 April 1999     

Quality and potential biodegradability of soil organic matter preserved in permafrost of Siberian tussock tundra

Soil organic matter (SOM) quality and biodegradability the permafrost underlying Siberian wet tussock tundra (Kolyma river basin, northeast Siberia) were analyzed and compared to the characteristics of the contemporary active layer. For this purpose, three permafrost affected soil cores (down to 3 m depth) and seven active layer soil cores (down to 0.3 m depth) were sampled. The samples were divided into particular layers, which were analyzed separately. SOM stability was assessed using a simple chemical fractionation (sequential extraction by cold and hot water, and hot acid). SOM biodegradability and soil mineralization potentials were tested in short-term laboratory incubations. The active layer contained 24 kg C m⁻² and 70 kg C m⁻² was preserved in 3 m of permafrost. The chemical quality and biodegradability of permafrost SOM were very similar to that of the active layer mineral horizon, and independent from depth. The only exceptions were (1) higher solubility of permafrost SOM in water, indicating its higher mobility and potential leakage after permafrost thawing and (2) higher nutrient (N, P) concentrations available to a dense permafrost microbial community, which could support decomposition of more complex substrates under suitable temperature conditions after thawing. The mineralization potential of the upper 1 m deep permafrost, which could melt by 2100 according to permafrost degradation models, was 6.7 g C m⁻² d⁻¹ (optimum conditions of 20 °C, field water capacity), which is comparable to that of the contemporary active layer of 0.5 m depth (7.5 g C m⁻² d⁻¹). Under field conditions, SOM mineralization rate would reasonably be significantly lower due to prevailing anoxia (high water table) and diffusion constraints in the deep and flooded soil profile.We conclude from our results that the permafrost (1) cryopreserves a high SOM amount, which is distributed to considerable depths, being of similar chemical quality and biodegradability to that of the active layer mineral horizon SOM, and (2) contains a dense living microbial community, which is able to decompose the present SOM rapidly without any obvious chemical limitation under suitable conditions.     

Effects of tracked vehicles on the morphological and physical properties of tundra soils

The agricultural lands of typic tundra of the Yamal Peninsula in Russia are pastures for reindeer (Rangifer tarandus sibiricus Murr.) herds. Currently, degradation of tundra soil cover is mainly caused by mechanical impacts of tracked vehicles used in construction operations. The objective of this study was to evaluate changes in morphological, micro-structural, and physical properties of Cryozems and Cryogenic peaty soils affected by these tracked vehicles. Soil samples were taken from the surface and underlying horizons before and 5 years after four and 100 passes of tracked vehicles. Surface horizons (0–10 cm) of the undisturbed Cryozems and Cryogenic peaty soils were organogenic. Passage of tracked vehicles caused mixing of these horizons with lower sandy loam and loam mineral horizons. Properties of the organomineral horizons formed in this way differed essentially from those of the surface horizons of the undisturbed soils. Microaggregates were completely disturbed, even after only four passes of tracked vehicles. Large inter-aggregate pores disappeared and thin pores or cracks formed as a result of vehicle-induced mechanical impacts. Humification of plant residues was observed to be faster in the compacted organomineral horizons of disturbed soils compared with undisturbed ones. The organic substances formed in the compacted organomineral horizons readily moved downward within the soil profile or were lost during runoff events. High correlation coefficients of organic carbon content with both specific surface area and water retention showed that the above-mentioned organic substances were hydrophilic. Specific surface area and water retention of the disturbed soils rose with increasing organic carbon content. The results obtained in this study demonstrated a high susceptibility of Cryozems and Cryogenic peaty soils to mechanical impacts.     

Phosphorus compounds in subarctic Fennoscandian soils at the mountain birch (Betula pubescens)—tundra ecotone

Nutrient availability will partly regulate the response of high latitude ecosystems to climate warming, but phosphorus biogeochemistry is poorly understood in Arctic soils. We used NaOH-EDTA extraction and solution ³¹P nuclear magnetic resonance (NMR) spectroscopy to determine phosphorus compounds in subarctic soils from three locations in the Fennoscandian mountains contrasting in latitude and continentality. Soils were taken from open tundra and mountain birch (Betula pubescens Ehrh.) forest at each location. Between 87 and 95% of the total phosphorus was extracted from the surface 2 cm of the organic soil horizons. Most of the extracted phosphorus was orthophosphate monoesters (44-55%), with smaller concentrations of inorganic orthophosphate (15-24%), orthophosphate diesters (12-16%), pyrophosphate (3-18%), inorganic polyphosphate (0-15%) and phosphonates (0-4%). The orthophosphate diesters were further subclassified into DNA (9-13% extracted phosphorus) and phospholipids (1-6% extracted phosphorus), although strong signals in the orthophosphate monoester region of the spectra, consistent with the degradation of phosphatidyl choline in alkaline solution, suggested that phospholipid concentrations were substantially underestimated. The phosphorus composition was broadly similar among soils from the three locations, although no phosphonates were detected in tundra soils from the most southerly site. Deeper organic horizons tended to contain a greater proportion of orthophosphate monoesters than at the surface. The abundance of phosphorus compounds that would be considered readily degradable in temperate environments probably reflects the slow organic matter decomposition in these cold, acidic soils, and suggests that phosphorus availability is unlikely to limit ecosystem productivity on mesic soils at the birch-tundra ecotone during changes induced by climate warming.     

Microbial carbon dynamics in nitrogen amended Arctic tundra soil: Measurement and model testing

We examined the responses of grazers (protozoa and nematodes) and their main food sources to low levels of nitrogen (N) fertilisation and applied carbon (C) flux models to our data. Replicate plots of tundra soil adjacent to the Kongsfjorden (Svalbard 78°N) were amended with ammonium and nitrate at concentrations of 1 and 5 kg N ha⁻¹ to assess the impact of anthropogenic N deposition over three summers. Bacterial abundance as determined using the fluorochrome SYBR Green and epifluorescence microscopy ranged between 9.73×10⁸ and 102.49×10⁸ cells/g dry wt of soil, with a significant response to N addition occurring only during the second sampling in 2001. Despite little change in bacterial biomass, bacterial production (measured by the incorporation of ³H thymidine into DNA) during the second sampling in 2002, increased in NH₄ enriched plots compared to control and NO₃ amended plots, indicating that NH₄ was the preferred source of inorganic N. The main bacterial predators were heterotrophic flagellates (HNAN) and naked amoebae, which showed no significant response to the N addition. HNAN showed a correlation with bacterial abundance suggesting a dependence on bacteria as a food source. The inability of a microbial C flux model to fit our data (RWSS/data=18.6, r²=0.088) was at least partly due to insufficient bacterial production to meet the C demands of predator taxa, and high variability in the data over time. This is reflected in the performance statistics for model variants where select microbial taxa and data were removed. The optimal model in terms of predictive utility was a model with data from 2002 only, minus naked amoebae (RWSS/data=2.45, r²=0.806).     

Methane turnover and temperature response of methane-oxidizing bacteria in permafrost-affected soils of northeast Siberia

The abundance, activity, and temperature response of aerobic methane-oxidizing bacteria were studied in permafrost-affected tundra soils of northeast Siberia. The soils were characterized by both a high accumulation of organic matter at the surface and high methane concentrations in the water-saturated soils. The methane oxidation rates of up to 835 nmol CH₄ h⁻¹ g⁻¹ in the surface soils were similar to the highest values reported so far for natural wetland soils worldwide. The temperature response of methane oxidation was measured during short incubations and revealed maximum rates between 22 °C and 28 °C. The active methanotrophic community was characterized by its phospholipid fatty acid (PLFA) concentrations and with stable isotope probing (SIP). Concentrations of 16:1ω8 and 18:1ω8 PLFAs, specific to methanotrophic bacteria, correlated significantly with the potential methane oxidation rates. In all soils, distinct 16:1 PLFAs were dominant, indicating a predominance of type I methanotrophs. However, long-term incubation of soil samples at 0 °C and 22 °C demonstrated a shift in the composition of the active community with rising temperatures. At 0 °C, only the concentrations of 16:1 PLFAs increased and those of 18:1 PLFAs decreased, whereas the opposite was true at 22 °C. Similarly, SIP with ¹³CH₄ showed a temperature-dependent pattern. When the soils were incubated at 0 °C, most of the incorporated label (83%) was found in 16:1 PLFAs and only 2% in 18:1 PLFAs. In soils incubated at 22 °C, almost equal amounts of ¹³C label were incorporated into 16:1 PLFAs and 18:1 PLFAs (33% and 36%, respectively). We concluded that the highly active methane-oxidizing community in cold permafrost-affected soils was dominated by type I methanotrophs under in situ conditions. However, rising temperatures, as predicted for the future, seem to increase the importance of type II methanotrophs, which may affect methane cycling in northern wetlands.