C:N:P stoichiometry in Australian soils with respect to vegetation and environmental factors

Aims

We estimate organic carbon (C): total nitrogen (N): total phosphorus (P) ratios in soils under Australia’s major native vegetation groups.

Methods

We use digital datasets for climate, soils, and vegetation created for the National Land and Water Resources Audit in 2001. Analysis-of-variance is used to investigate differences in nutrient ratios between ecosystems. Linear discriminant analysis and logistic regression are used to investigate the relative importance of climatic variables and soil nutrients in vegetation patterns.

Results

We find that the N:P and C:P ratios have a greater range of values than the C:N ratio, although major vegetation groups tend to show similar trends across all three ratios. Some apparently homeostatic groupings emerge: those with very low, low, medium, or high N:P and C:P. Tussock grasslands have very low soil N, N:P, and C:P, probably due to frequent burning. Eucalypt woodlands have low soil N:P and C:P ratios, although their total P level varies. Rainforests and Melaleuca forests have medium soil N:P and C:P ratios, although their total P level is different. Heathlands, tall open eucalypt forests, and shrublands occur on soils with low levels of total P, and high N:P and C:P ratios that reflect foliar nutrient ratios and recalcitrant litter.

Conclusions

Certain plant communities have typical soil nutrient stoichiometries but there is no single Redfield-like ratio. Vegetation patterns largely reflect soil moisture but for several plant communities, eucalypt communities in particular, soil N and P (or N:P) also play a significant role. Soil N:P and the presence of Proteaceae appear indicative of nutrient constraints in ecosystems.     

Understorey plant and soil responses to disturbance and increased nitrogen in boreal forests

Question: How do N fertilization and disturbance affect the understorey vegetation, microbial properties and soil nutrient concentration in boreal forests? Location: Kuusamo (66°22′N; 29°18′E) and Oulu (65°02′N; 25°47′E) in northern Finland. Methods: We conducted a fully factorial experiment with three factors: site (two levels), N fertilization (four levels) and disturbance (two levels). We measured treatment effects on understorey biomass, vegetation structure, and plant, soil and microbial N and C concentrations. Results: The understorey biomass was not affected by fertilization either in the control or in the disturbance treatment. Fertilization reduced the biomass of deciduous Vaccinium myrtillus. Disturbance had a negative effect on the biomass of V. myrtillus and evergreen Vaccinium vitis‐idaea and decreased the relative proportion of evergreen species. Fertilization and disturbance increased the biomass of grass Deschampsia flexuosa and the relative proportion of graminoids. The amount of NH₄⁺ increased in soil after fertilization, and microbial C decreased after disturbance. Conclusions: Our results suggest that the growth of slow‐growing Vaccinium species and soil microbes in boreal forests are not limited by N availability. However, significant changes in the proportion of dwarf shrubs to graminoids and a decrease in the biomass of V. myrtillus demonstrate the susceptibility of understorey vegetation to N enrichment. N enrichment and disturbance seem to have similar effects on understorey vegetation. Consequently, increasing N does not affect the rate or the direction of recovery after disturbance. Moreover, our study demonstrates the importance of understorey vegetation as a C source for soil microbes in boreal forests.     

Quantitative phytogeography of the Yukon Territory (NW Canada) on a chorological-phytosociological basis

This study is based on the analysis of the chorological spectra from 19 vegetation types obtained from a numerical classification of ca. 400 phytosociological relevés taken during a vegetation survey in the Yukon Territory (NW Canada).All vegetation types are well characterized in terms of their chorological features. This allowed an ecological-historical interpretation of the vegetation in the study area. The distribution of the various chorological categories within the vegetation types is strongly correlated with the main environmental influences, whose action led to the present floristical and vegetational characteristics of the area, such as glaciation, fire, permafrost and water availability.The results show how the phytosociological approach constitutes an effective methodological tool for clarifying the phytogeographical aspects in the historical-ecological interpretation of a large area.Nomenclature follows Hultén (1968), otherwise author names are specified.The field work was completed in the summer of 1978. We are grateful to Dr W. Stanek, Canadian Forestry Service, for coordination of the survey and for soil data, and to Prof. L. Orlóci for organization. Partial financial support was received from the Italian C.N.R.     

Spatial variation in a grassland on soil rich in heavy metals

Abstract. The vegetation in a grassland area in the prefecture of Kilkis (N. Greece), known for its surface Cu-mineralization, was studied. 43 quadrats were established along a transect through an area where the vegetation formed patches of different size. Cover-abundance and frequency estimates for all species were made. Normal Association Analysis revealed five quadrat groups characterized by Trifolium scabrum, Linaria pelisseriana, Anthoxanthum ovatum, Gypsophila muralis and Minuartia hirsuta ssp. falcata. 43 soil samples were analysed for pH, organic C, CaCO₃, total content of Fe, Zn, Pb, Cu, Mn, Ca, Mg, K, Na and soil texture. From a discriminant analysis performed on soil data five soil groups resulted, which are highly related to the five vegetation groups. Thymus sibthorpii, Minuartia hirsuta ssp. falcata and Rumex acetosella are the most important taxa with respect to physiognomy and patchi-ness of the vegetation. The number of species in each group of quadrats is affected by the relative favourableness or severity of the soil conditions. Metal contents, mainly Zn, Cu, Mg and Na, and soil texture are considered to be among the main factors controlling the structure and physiognomy of the vegetation.     

Refining vegetation simulation models: From plant functional types to bioclimatic affinity groups of plants

Question: How to refine simulations based on a global vegetation model in order to apply it to regional scale? Location: Europe from 35° N to 71° N and 25° W to 70° E. Methods: Geographical ranges of European plants were georeferenced and used with monthly mean climatic data (diurnal temperature ranges, ground frost frequencies, precipitation, relative humidity, rain frequencies, amount of sunshine hours and temperature) and growing degree days to infer climatic boundaries for 320 taxa. We performed a discriminant analysis to define their potential geographic ranges. Hierarchical clustering was computed on potential ranges. Results: Clustering provided 25 Bioclimatic Affinity Groups (BAG) of plants consisting of 13 tree, seven shrub and five herb groups. These B AGs are characterized by different geographical ranges and climatic tolerances and requirements. Conclusion: The use of monthly data instead of annual values improved the prediction of potential distribution ranges and highlighted the importance of climate seasonality for defining the plant groups with accuracy. The B AGs are detailed enough to provide finer reconstructions and simulations of the vegetation at the regional scale.     

Detecting complex relations among vegetation,soil and geomorphology. An in-depth method applied to a case study in the Apennines (Italy)

Physical environment is the ruling factor of vegetation patterns in mountain areas, where vegetation mosaics are determined by a complex interplay among topography, geomorphology and soil. A deep analysis of such interplay is pivotal in order to build vegetation anamnesis and make sound projections. Instead, even recent cartographic models are still linked to standard statistical methods which are not on top of an efficient uncovering of knotty associations among these kinds of data. To this aim, in this study we propose a novel approach for: (a) assessing the associations among vegetation, soil, topography and geomorphology; (b) measuring the frequency and strength of these associations; (c) define in a rigorous way land units based on vegetation–soil–geomorphology associations; (d) advance hypotheses on the causes and prospects of the existing spatial pattern. In order to test the strength of the proposed methodology we applied it to a case study in the above-tree-line glacial cirque of Mount Prado (Northern Apennines, N Italy). In this area, the vegetation mosaic is still strongly conditioned by physical features but in a lower measure with respect to the higher alpine sites. We have been able to detect and weight 168 kinds of associations among vegetation, soil and geomorphological types, 1092 kinds of associations among vegetation and topographic variables and 12 land units with inner dominance of a particular association. The analysis of associations between vegetation types, soils, topography and landforms produced considerable insights into the ecology of the occurring plant communities. This proposed analytic methodology can be extended to other regions (e.g. mountain and alpine areas) and can also be considered a tool for interpreting present landscape heterogeneity also in a historical perspective.     

Soil macrofauna and nitrogen on a sub-Antarctic island

Summary The densities, diets and habitat preferences of the soil macrofaunal species on sub-Antarctic Marion Island (47°S, 38°E) are described. Their role in N cycling on the island is assessed, using a mire-grassland community as an example. Primary production on the island is high and this leads to a substantial annual requirement of nutrients by the vegetation. This requirement must almost wholly be met by mineralization of nutrient reserves in the organic matter. Rates of peat nitrogen mineralization mediated by microorganisms alone are much too low to account for rates of N uptake by the vegetation. Although soil macroinvertebrates, and bacteria represent a very small fraction of the total N pool, their interaction accounts for most of the peat N mineralization, as indicated by the amounts of inorganic N released into solution in microcosms. Extrapolation of the microcosm results shows that the soil macrofauna (mainly earthworms) stimulate the release of enough N from the mire-grassland peat to account for maximum N mineralization rates calculated from temporal changes in peat inorganic N levels and plant uptake during the most active part of the growing season. Considering that large numbers of mesoand microinvertebrates occur and must also contribute to nutrient mineralization, the soil faunal component is clearly of crucial importance to nutrient cycling on Marion Island. This is probably true of all sub-Antarctic islands.     

Ecosystem health assessment on the hill and gully area of loess Plateau in Inner Mongolia, China

Maintenance of ecosystem health is the primary focus of a sound ecological restoration. Yet methods involved in quantifying and assessing the health level remain a challenge to the ecological community. In this study, we selected the hill and gully area of Loess Plateau, Inner Mongolia, China, as our study area. The soil and water erosions in this area continue to be responsible for many environmental problems in northern China because of its fragility and long disturbance history. In this study, we developed an assessment method of indicator system (AMIS) based on analytical hierarchy process (AHP), fuzzy mathematics, and the theory of net-hierarchy. At ecosystem or catchment scale, three sample areas, that is (1) intact vegetation (i.e., Aguimiao Natural Reserve, 110°45′E, 39°28′N), (2) reconstructed vegetation (Wufendigou Soil and Water Conservation Experimental Area, 111°07′E, 39°45′N), and (3) severely degraded vegetation (Yangquangou Catchment, 111°06′E, 39°45′N) in the hill and gully area of Loess Plateau in Inner Mongolia, China, were selected to examine ecosystem vigor, organizational structure, service function, and soil health. We applied the AMIS for all three landscapes by categorizing each ecosystem into five health levels. We found that the health index for reconstructed vegetation were at levels of IV, II, IV, and III, while those of degraded vegetation were ranked at V, IV, V, and IV. Overall, the comprehensive ecosystem health index of reconstructed vegetation was lower than that of intact vegetation but higher than that of degraded vegetation. The health index for reconstructed vegetation was at level III, and that of degraded vegetation was still at level IV. The contributing values were: organization structure > soil health > vigor > service function. Based on our results and assessments, we proposed several management recommendations and methods for restoring the regional ecosystems. __________ Translated from Acta Ecologica Sinica, 2005, 25(5): 1048–1056 [译自: 生态学报, 2005, 25(5): 1048–1056]     

Links between plant community composition,soil organic matter quality and microbial communities in contrasting tundra habitats

Plant communities, soil organic matter and microbial communities are predicted to be interlinked and to exhibit concordant patterns along major environmental gradients. We investigated the relationships between plant functional type composition, soil organic matter quality and decomposer community composition, and how these are related to major environmental variation in non-acid and acid soils derived from calcareous versus siliceous bedrocks, respectively. We analysed vegetation, organic matter and microbial community compositions from five non-acidic and five acidic heath sites in alpine tundra in northern Europe. Sequential organic matter fractionation was used to characterize organic matter quality and phospholipid fatty acid analysis to detect major variation in decomposer communities. Non-acidic and acidic heaths differed substantially in vegetation composition, and these disparities were associated with congruent shifts in soil organic matter and microbial communities. A high proportion of forbs in the vegetation was positively associated with low C:N and high soluble N:phenolics ratios in soil organic matter, and a high proportion of bacteria in the microbial community. On the contrary, dwarf shrub-rich vegetation was associated with high C:N and low soluble N:phenolics ratios, and a high proportion of fungi in the microbial community. Our study demonstrates a strong link between the plant community composition, soil organic matter quality, and microbial community composition, and that differences in one compartment are paralleled by changes in others. Variation in the forb-shrub gradient of vegetation may largely dictate variations in the chemical quality of organic matter and decomposer communities in tundra ecosystems. Soil pH, through its direct and indirect effects on plant and microbial communities, seems to function as an ultimate environmental driver that gives rise to and amplifies the interactions between above- and belowground systems. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Vegetation and Soil 15N Natural Abundance in Alpine Grasslands on the Tibetan Plateau: Patterns and Implications

The natural abundance of nitrogen (N) stable isotopes (δ¹⁵N) has the potential to enhance our understanding of the ecosystem N cycle at large spatial scales. However, vegetation and soil δ¹⁵N patterns along climatic and edaphic gradients have not yet been fully understood, particularly for high-altitude ecosystems. Here we determined vegetation and soil δ¹⁵N in alpine grasslands on the Tibetan Plateau by conducting four consecutive regional surveys during 2001–2004, and then examined their relationships with both climatic and edaphic variables. Our results showed that both vegetation and soil N in Tibetan alpine grasslands were more ¹⁵N-enriched than global averages. Vegetation δ¹⁵N did not exhibit any significant trend along the temperature gradient, but decreased significantly with an increase in precipitation amount. In contrast, soil δ¹⁵N did not vary with either mean annual temperature or precipitation. Our results also indicated that soil δ¹⁵N exhibited a slight increase with clay content, but decreased with soil carbon:nitrogen ratio. A general linear model analysis revealed that variations in vegetation δ¹⁵N were dominantly determined by climatic variables, whereas soil δ¹⁵N was related to edaphic variables. These results provide clues for potential climatic and edaphic regulations on ecosystem N cycle in these high-altitude regions.     

Effects of Herbivory,Fire and N<Subscript>2</Subscript>-fixation on Nutrient Limitation in a Humid African Savanna

The quantities and spatial distribution of nutrients in savanna ecosystems are affected by many factors, of which fire, herbivory and symbiotic N₂-fixation are particularly important. We measured soil nitrogen (N) pools and the relative abundance of N and phosphorus (P) in herbaceous vegetation in five vegetation types in a humid savanna in Tanzania. We also performed a factorial fertilization experiment to investigate which nutrients most limit herbaceous production. N pools in the top 10 cm of soil were low at sites where fires were frequent, and higher in areas with woody legume encroachment, or high herbivore excretion. Biomass production was co-limited by N and P at sites that were frequently burnt or heavily grazed by native herbivores. In contrast, aboveground production was limited by N in areas receiving large amounts of excreta from livestock. N₂-fixation by woody legumes did not lead to P-limitation, but did increase the availability of N relative to P. We conclude that the effects of fire, herbivory and N₂-fixation upon soil N pools and N:P-stoichiometry in savanna ecosystems are, to a large extent, predictable. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Author Contributions  P.C., H.O.V. and P.E. designed the study and wrote the paper. P.C. and T.K. performed the research and analyzed the data.     

Production and structure in the early stages of vegetation development in the Lauwerszee-polder

Summary In this study on vegetation development in the newly enclosed polder of the former Lauwerszee-estuary, data are presented on a qualitative and quantitative analysis of the pioneer vegetation of five experimental areas over the first four years. The methods used and the background to the study are briefly outlined. Data are given on structure, in terms of density and biomass, involving the speciesSalicornia spp., Suaeda maritima, Atriplex hastata andSpartina × townsendii and on soil factors (carbonate, organic matter, texture, K, P, total N, mineral N, pH and salt). Pattern and process in the pioneer stages are discussed, especially the underlying changes in environmental conditions and the behaviour of species in relation to these conditions. Only the halophytes mentioned could cope with the conditions of high salinity. It was found that in the initial phase plant densities are determined by the available amount of seeds, while after three years the total number and biomass is limited by environmental factors, especially those affecting soil-fertility. Thanks are due to Prof. Dr. D. Bakker for his stimulating and continuous interest in all stages of the present study and to Dr. A. J. Gray for critical reading and correcting of the English text. The project was realized by financial support of the Netherlands Organisation for the Advancement of Pure Research (Z.W.O.).     

Temporal changes in soil C‐N‐P stoichiometry over the past 60 years across subtropical China

Controlled experiments have shown that global changes decouple the biogeochemical cycles of carbon (C), nitrogen (N), and phosphorus (P), resulting in shifting stoichiometry that lies at the core of ecosystem functioning. However, the response of soil stoichiometry to global changes in natural ecosystems with different soil depths, vegetation types, and climate gradients remains poorly understood. Based on 2,736 observations along soil profiles of 0–150 cm depth from 1955 to 2016, we evaluated the temporal changes in soil C‐N‐P stoichiometry across subtropical China, where soils are P‐impoverished, with diverse vegetation, soil, and parent material types and a wide range of climate gradients. We found a significant overall increase in soil total C concentration and a decrease in soil total P concentration, resulting in increasing soil C:P and N:P ratios during the past 60 years across all soil depths. Although average soil N concentration did not change, soil C:N increased in topsoil while decreasing in deeper soil. The temporal trends in soil C‐N‐P stoichiometry differed among vegetation, soil, parent material types, and spatial climate variations, with significantly increased C:P and N:P ratios for evergreen broadleaf forest and highly weathered Ultisols, and more pronounced temporal changes in soil C:N, N:P, and C:P ratios at low elevations. Our sensitivity analysis suggests that the temporal changes in soil stoichiometry resulted from elevated N deposition, rising atmospheric CO₂ concentration and regional warming. Our findings revealed that the responses of soil C‐N‐P and stoichiometry to long‐term global changes have occurred across the whole soil depth in subtropical China and the magnitudes of the changes in soil stoichiometry are dependent on vegetation types, soil types, and spatial climate variations.     

Characterization of spatial scaling relationships between vegetation pattern and topography at different directions in Gurbantunggut desert,China

Vegetation striped pattern is a common feature in semiarid and arid landscapes, which is seen as mosaics including vegetated and non-vegetated patches. Identifying scales of pattern in ecological systems and referring patterns to multi-scaled processes that create them are ongoing challenges. The aim of this paper is to study the vegetation patterns and their across-scale relationships between the vegetation and anisotropic topography (W–E and N–S) in 12 transects at Gurbantunggut desert. We used wavelet-based across-scale analysis for extracting information on scales of pattern for those transect data, evaluating their inherent structure, and inferring characteristics of the processes that imposed those patterns at across scales. The results show that, in W–E direction, the scales of vegetation pattern (C. ewersmanniana is at the scale 40 m, H. ammodendron, at 35 m) correspond to the dune ridge/dune valley sequences (appearing at distance of 40 m), and vegetation on mesoscale and large scale are significant cross-scale correlation with topography on mesoscale and large scale in all W–E transects. In N–S direction, there is an irregular pattern of vegetation along the N–S irregular topography, and no unified cross-scale relationships between topography and vegetation on different scales in different transects. Moreover, cross-scale correlation analysis between topography and vegetation provides further detail on hierarchical structure and specific scales in space that strongly influenced the larger patterns. Knowledge of the cross-scale relationships between topography and vegetation could lead to better understanding and management of biological resources in that region.     

Variation in nutrient characteristics of surface soils from the Luquillo Experimental Forest of Puerto Rico: A multivariate perspective

We assessed the effects of landscape features (vegetation type and topography), season, and spatial hierarchy on the nutrient content of surface soils in the Luquillo Experimental Forest (LEF) of Puerto Rico. Considerable spatial variation characterized the soils of the LEF, and differences between replicate sites within each combination of vegetation type (tabonuco vs. palo colorado vs. dwarf vs. pasture) and topographic position (ridge vs valley) accounted for 11–60% of the total variation in soil properties. Nevertheless, mean soil properties differed significantly among vegetation types, between topographic positions, and between seasons (wet vs dry). Differences among vegetation types reflected soil properties (e.g., bulk density, soil moisture, Na, P, C, N, S) that typically are related to biological processes and inputs of water. In forests, differences between topographic positions reflected elements (e.g., Ca, Mg, K, and Al) that typically are associated with geochemical processes; however, the nutrients and elements responsible for topographic differences in dwarf forest were different from those in other forest types. In pastures, differences between topographic positions were associated with the same soil properties responsible for differences among the other vegetation types. Pastures also had reduced N levels and different soil characteristics compared to undisturbed tabonuco forest. The only soil parameter that differed significantly between seasons was soil moisture. Soils of the LEF do not support the contention that N becomes limiting with an increase in elevation, and suggest that absolute pool sizes of N and P are not responsible for the reduction in productivity with elevation.     

Nitrogen limitation and microbial diversity at the treeline

Tree growth limitation at treeline has mainly been studied in terms of carbon limitation while effects and mechanisms of potential nitrogen (N) limitation are barely known, especially in the southern hemisphere. We investigated how soil abiotic properties and microbial community structure and composition change from lower to upper sites within three vegetation belts (Nothofagus betuloides and N. pumilio forests, and alpine vegetation) across an elevation gradient (from 0 to 650 m a.s.l.) in Cordillera Darwin, southern Patagonia. Increasing elevation was associated with a decrease in soil N‐NH₄⁺ availability within the N. pumilio and the alpine vegetation belt. Within the alpine vegetation belt, a concurrent increase in the soil C:N ratio was associated with a shift from bacterial‐dominated in lower alpine sites to fungal‐dominated microbial communities in upper alpine sites. Lower forested belts (N. betuloides, N. pumilio) exhibited more complex patterns both in terms of soil properties and microbial communities. Overall, our results concur with recent findings from high‐latitude and altitude ecosystems showing decreased nutrient availability with elevation, leading to fungal‐dominated microbial communities. We suggest that growth limitation at treeline may result, in addition to proximal climatic parameters, from a competition between trees and soil microbial communities for limited soil inorganic N. At higher elevation, soil microbial communities could have comparably greater capacities to uptake soil N than trees, and the shift towards a fungal‐dominated community would favour N immobilization over N mineralization. Though evidences of altered nutrient dynamics in tree and alpine plant tissue with increasing altitude remain needed, we contend that the measured residual low amount of inorganic N available for trees in the soil could participate to the establishment limitation. Finally, our results suggest that responses of soil microbial communities to elevation could be influenced by functional properties of forest communities for instance through variations in litter quality.     

Vegetation Leachate During Arctic Thaw Enhances Soil Microbial Phosphorus

Leachate from litter and vegetation penetrates permafrost surface soils during thaw before being exported to aquatic systems. We know this leachate is critical to ecosystem function downstream and hypothesized that thaw leachate inputs would also drive terrestrial microbial activity and nutrient uptake. However, we recognized two potential endpoint scenarios: vegetation leachate is an important source of C for microbes in thawing soil; or vegetation leachate is irrelevant next to the large background C, N, and P pools in thaw soil solution. We assessed these potential outcomes by making vegetation leachate from frozen vegetation and litter in four Arctic ecosystems that have a variety of litter quality and soil C, N, and P contents; one of these ecosystems included a disturbance recovery chronosequence that allowed us to test our second hypothesis that thaw leachate response would be enhanced in disturbed ecosystems. We added water or vegetation leachate to intact, frozen, winter soil cores and incubated the cores through thaw. We measured soil respiration throughout, and soil solution and microbial biomass C, N, and P pools and gross N mineralization immediately after a thaw incubation (?10 to 2°C) lasting 6 days. Vegetation leachate varied strongly by ecosystem in C, N, and P quantity and stoichiometry. Regardless, all vegetated ecosystems responded to leachate additions at thaw with an increase in the microbial biomass phosphate flush and an increase in soil solution carbon and nitrogen, implying a selective microbial uptake of phosphate from plant and litter leachate at thaw. This response to leachate additions was absent in recently disturbed, exposed mineral soil but otherwise did not differ between disturbed and undisturbed ecosystems. The selective uptake of P by microbes implies either thaw microbial P limitation or thaw microbial P uptake opportunism, and that spring thaw is an important time for P retention in several Arctic ecosystems.     

Biotic and Abiotic Controls Over Canopy Function and Structure in Humid Hawaiian Forests

Foliar nitrogen (N) plays a key role in ecosystem function and dynamics, including processes such as photosynthesis, productivity, and decomposition. Aboveground carbon density (ACD Mg C ha^?1) represents a cumulative functional outcome of these and other ecosystem processes and is an important metric for monitoring current carbon stocks. Despite their importance, multiple interacting controls over landscape-level variation in foliar N and ACD are poorly understood. We assessed the relative importance of individual ecologically important state factors (climate, substrate, age, vegetation, and topography) associated with canopy foliar N and ACD throughout a humid forest landscape. We combined high-resolution remotely sensed data, machine learning, and field data to map and assess canopy foliar N and ACD patterns across a 5016-ha forest reserve in Hawai‘i. Distance to non-native forests had the largest relative influence on canopy foliar N concentration, followed by mean annual temperature (MAT), vegetation type, precipitation, soil, canopy height, and substrate age. In contrast, soil type was the strongest determinant of spatial variability in ACD, followed by precipitation, MAT, and vegetation type. Similar to foliar N, climate and vegetation variables were associated with ACD. However, soil type was found to be much more important in the ACD model (30%) than in the foliar N model (4%). Landscape-scale patterns in canopy foliar N and ACD are the result of shifts in vegetation type and composition, most likely due to species’ responses to past disturbances, current climate conditions, and available nutrients. Degradation of native forests and future climate changes could result in highly altered biogeochemical cycles.     

Hydrology,water chemistry and nutrient accumulation in the Biebrza fens and floodplains (Poland)

The composition, structure and above-ground biomass production of floodplain- and fen-vegetation of the Biebrza valley (N.E. Poland) are strongly correlated with water flow characteristics and water chemistry. Groundwater flow and flooding are the major conditioning factors for the vegetation in the valley.The highly productive vegetation is restricted to the dynamic floodplain where it receives nutrient-rich river water during spring floods. The non-flooded parts of the valley contain rich fen and transitional fen vegetation that have a lower biomass production. The rich fen is fed by calcareous and phosphate-poor groundwater coming from the moraines. In the transitional fen, where rainwater infiltrates, phosphate availability is large.Annual nutrient accumulation in the above-ground biomass of the floodplains is estimated to be about 8–9 § 10³ kg/km² for N and K and 1 § 10³ kg/km² for P. For the less-productive fens these figures are 60 to 70% lower. The total annual nutrient accumulation by vegetation of both floodplains and fens for the entire Biebrza valley is estimated to be about 5600 × 10³ kg N, 560 × 103 kg P and 4500 × 10³ kg K. This is high compared to the loading rates in the river near to where the Biebrza River discharges into the Narew River (N-, P- and K-loading rates are c. 900, 200 and 3000 × 103 kg/y, respectively). This implies that floodplain and fen vegetation are important sinks for nutrients, especially for N and P.This paper was presented at the INTECOL IV International Wetlands Conference in Columbus, Ohio, 1992, as part of a session organized by Prof. S. E. Jørgensen and sponsored by the International Lake Environment Committee.Corresponding Editor: J. Kvt     

半干旱黄土小流域不同植被类型植物与土壤生态化学计量特征

生态化学计量学是研究生态系统元素平衡与能量流动的有效方法,明确不同植被恢复类型下植物与土壤化学计量特征对揭示黄土高原植被恢复中生态系统养分循环具重要意义,可为黄土高原植被恢复类型的选择提供可行性依据。以典型半干旱黄土小流域3种植被恢复方式下（天然荒草、自然恢复、人工恢复）的5种植被类型（长芒草草地、赖草草地、苜蓿草地、柠条灌丛、山杏林）为研究对象,分析不同植被类型下叶、茎、根及土壤碳（C）、氮（N）、磷（P）含量及化学计量特征。结果表明：1）植物不同器官和植被类型对植物生态化学计量特征都具有显著影响,C、N、P含量在5种典型植被中均表现为叶>茎>根。人工恢复植被各器官C、N含量及N ∶ P均显著高于天然荒草地,与自然恢复植被无显著差异;其中,在人工恢复植被中山杏各器官C含量最高,柠条各器官N含量最高。叶、茎、根的C ∶ N则表现为自然恢复植被显著高于人工恢复植被与天然荒草地。P含量、C ∶ P则在不同植被恢复类型间无显著差异。2）不同植被恢复类型下土壤C、N、P含量及化学计量特征具一定差异。人工恢复植被土壤C、N、P含量及C ∶ P、N ∶ P均为最高,显著高于自然恢复植被土壤;人工恢复植被中柠条土壤C、N含量及C ∶ P、N ∶ P均显著高于其他植被土壤。土壤C ∶ N在各植被类型间无显著差异。3）不同植被恢复类型下C、N、P含量在植物叶片与土壤间的相关性存在差异,说明植物自身生长特性影响着养分在植物与土壤间转化与传递。以5种典型植被整体来看,植物叶、茎、根的生态化学计量特征在彼此间均呈显著正相关。在植物与土壤间,植物各器官N含量与土壤C、N、P含量呈显著正相关,植物各器官N ∶ P与土壤N ∶ P呈显著正相关,表明该黄土小流域生态系统中植物与土壤生态化学计量特征的变化是相互制约,相互影响的。