Nutrient turnover studies in alpine ecosystems

Summary The nutrient relations of five treeless plant communities on acid soils above siliceous rock of the Central Alps are investigated. Three of these communities, situated on Mt. Patscherkofel, are dominated by dwarf shrubs of the Ericaceae family: Loiseleurietum (P 1, 2175 m NN), Loiseleuria heath (P 2, 2000 m NN), and Vaccinium heath (P 3, 1980 m NN). The other two are bound to higher elevations (2500 m NN, at Timmelsjoch): Caricetum curvulae (T 1), forming the mats, and Salicetum herbaceae (T 2), covering the snow-beds.Phytomass productivity decreases with increasing altitude in the sequence P 3-P 2, P 1-T 1-T 2.Compared with the turf communities of the Northern Calcareous Alps, nitrogen reserves and experimental net-mineralization of the soils (0–15 cm) are extremely low in P 1, P 2, and P 3 (<0.5 g N/m² mineralized per GS¹). The fluctuation of N in the living above-ground phytomass during the GS is also low (about 1.6 g/m² in P 1 and P 2; 2.2 g/m² in P 3, although it exceeds the values of net mineralization. Additional uptake through mycorrhizal fungi or activation of mineralizing microbes in the rhizosphere by exudation is assumed.The P- and K-reserves are extremely small in the humic soils of P 2 and P 3, but somewhat higher in the more mineral soil of P 1. Mean lactatesoluble P of the three sites is low (0.3 g/m² or less) whereas K_lact (2.7–3.3 g/m²) is higher than the lowest level found in some turf communities, e.g. Caricetum firmae. The amounts of P in the phytomass are in the range of those of the turf communities and agree with the gradation in the mean P_lact values (P 1 and P 3>P 2). There are, however, almost no discernible fluctuations of P in the phytomass, and the K-fluctuations are far below the mean K_lact level.The Timmelsjoch communities generally have higher N/C-, P/C-, and K/C-ratios in the soils compared with those of Mt. Patscherkofel, although the N-reserves (g/m²) and the K-reserves (of T 1 only) are lower. The P_lact values are higher than those from Mt. Patscherkofel and also exceed those of the calcareous turf communities. K_lact is low in T 1 whereas in T 2 it is in the range of P 1, P 2, and P 3. Compared with T 1, T 2 has distinctly higher amounts of the three nutrients in the soils and a higher net mineralization of N, as well as higher values in the phytomass components and in the fluctuation of the latter.In conclusion, a general view is given (Fig. 9) of the most important nutrient parameters of the communities represented in this series, including some others of lower altitudes.     

Nutrient turnover studies in alpine ecosystems

Summary Two plant communities, both dominated by Carex sempervirens but growing at different altitudes of the Northern Calcareous Alp region (IS: 600 m; KS: 1200 m) and one Carex ferruginea — dominated community (KC: 1200 m) are compared as to changes in dry matter, nitrogen, phosphorus, and potassium content of living and dead overground and underground phytomass.The soils of the montanic sites KS and KC are better provided with water and the three nutrients than that of the prealpine site IS. KC has the highest potassium content in the soil and in the phytomass.The dry matter increase (g/m²) of the living overground phytomass during the growing season is about 200 in IS, 360 in KS, and 340 in KC with maxima of 365 in IS, 550 in KS and 375 in KC.The increase of dead overground phytomass is highest in KS, indicating that the total annual overground production exceeds the mere increase in living parts. Furthermore, there is an increase of underground phytomass in KS and KC. The average ratio of total underground/living overground phytomass is 4.6 in IS, 3.7 in KS, but 7.5 in KC.The annual fluctuation of nitrogen (g/m²) in the living overground phytomass increases from 2.5 in IS to 3.8 in KS and to 5.9 in KC. For KS and KC these values approach the nitrogen mineralization values of the soils observed during the growing season. There is an obvious increase of nitrogen in the underground phytomass of KS and KC toward the end of the growing season. It is concluded that in KC, there is a more pronounced annual oscillation of nitrogen between overground and underground phytomass, which is not observed in IS, and which in KS is intermediate.     

Groundwater influence on alpine stream ecosystems

1. Spatial and temporal variability of relative snow‐melt, glacier‐melt and groundwater contributions to streams play important roles in shaping alpine freshwater ecosystems. Although meltwater (particularly glacier‐fed) streams have received much attention in recent years, the influence of groundwater on alpine freshwater ecosystems remains poorly understood. 2. This study tested the hypotheses that increased groundwater contributions to meltwater‐dominated alpine streams would yield increases in water temperature, channel stability, electrical conductivity and particulate organic matter (POM) and decreases in suspended sediment concentration (SSC). These more favourable habitat conditions were hypothesised to result in increased macroinvertebrate abundance and diversity. 3. Groundwater contributions, physicochemical habitat variables and benthic macroinvertebrates were sampled throughout the 2002 and 2003 summer‐melt seasons in three streams in the French Pyrénées. 4. Increased groundwater contributions were significantly correlated with higher discharge, water temperature, electrical conductivity, POM and channel stability, but lower SSC. 5. Macroinvertebrate total abundance, taxonomic richness, number of Ephemeroptera, Plecoptera and Trichoptera genera, and per cent Plecoptera all increased significantly with greater groundwater contributions to streamflow. However, beta diversity and Trichoptera relative abundance decreased. 6. Abundance of most macroinvertebrate taxa was highest under groundwater‐dominated conditions but a gradient of optimum groundwater preferences was evident across all taxa. Some taxa were found only where groundwater contributions were low (i.e. in predominantly meltwater‐fed streams). 7. This study provides evidence that water source, physicochemical habitat and stream biota are strongly linked. Therefore, an interdisciplinary approach is necessary for future studies aiming to develop conservation strategies or predict the response of alpine river ecosystems to global climate change.     

Nutrient dynamics within amazonian forest ecosystems

Summary A comparative analysis on the rate of fine litterfall and its associated nutrient fluxes was carried out in a mixed forest on Tierra Firme, a tall Amazon Caatinga and a Bana on podsolized sands near San Carlos de Rio Negro. There was seasonality in leaf fall and total litterfall in mixed forest and tall Amazon Caatinga forest but no definite trend in the Bana. Litterfall curves were significantly correlated among sites indicating common regulating factors in the three forests. Leaf litter from mixed forest on Tierra Firme was richer in N with extremely low Ca and Mg concentrations; tall Amazon Caatinga litter had higher P and Mg concentration, while Bana litter was low in N but K concentration was twice as high as in the other two forests. Annual fine litterfall in Tierra Firme mixed forest was nearly 4 times higher than in Bana, But N flux was 10 times higher, while Ca and Mg fluxes were similar. Tall Amazon Caatinga had Ca and Mg fluxes in litterfall 2–3 times higher than the other two forests. Within-stand efficiency of nitrogen, calcium and magnesium use, as measured by biomass/nutrient ratios, differentiates Tierra Firme from Caatinga and Bana forest: Tierra Firme has the lowest N, but the highest Ca and Mg use efficiencies. Higher P use efficiency was measured in Bana followed by Tierra Firme and Caatinga; while Tierra Firme and Caatinga showed similar higher K use efficiencies than Bana. N/P ratios indicates that Tierra Firme forest is limited by P availability, while low N availability predominates in Caatinga. Bana appears limited by both N and P. These differences probably relate to variations in degree of sclerophylly and leaf duration which determine leaf nutrient concentrations in the ecosystems studied.     

Higher plant diversity enhances soil stability in disturbed alpine ecosystems

Genotypic differences in acquiring immobile P exist among species or cultivars within one species. We investigated the P-efficiency mechanisms of rapeseed (Brassica napus L.) in low P soil by measuring plant growth, P acquisition and rhizosphere properties. Two genotypes with different P efficiencies were grown in a root-compartment experiment under low P (P15: 15 mg P kg^?1) and high P (P100: 100 mg P kg^?1) treatments. The P-efficient genotype produced more biomass, and had a high seed yield and high P acquisition efficiency under low P treatment. Under both P treatments, both genotypes decreased inorganic P (Pi) and organic P (Po) fractions in the rhizosphere soil. However there was no decrease in NaHCO₃-Po at P100. For the P15 treatment, the concentrations of NaHCO₃-Po and NaOH-Po were negatively correlated with soil acid phosphatase activity. The P-efficient genotype 102 differed from the P-inefficient genotype 105 in the following ways. In the rhizosphere the soil pH was lower, acid phosphatase activity was higher, and depletion of P was greater. Further the depletion zones were wider. These results suggested that improving P efficiency based on the character of P efficiency acquisition in P-efficient genotype would be a potential approach for maintaining rapeseed yield potential in soils with low P bioavailability.     

Nutrient addition accelerates leaf breakdown in an alpine springbrook

This study assessed the effect of nutrient enrichment on organic matter breakdown in an alpine springbrook, using alder leaf packs to which phosphorus and nitrogen were added in the form of slow-release fertilizer briquettes. The breakdown of leaf packs with nutrients added (k=0.0284 day^–1) was significantly faster than that of unfertilized packs (k=0.0137 day^–1), resulting in a 30% higher mass loss after 42 days. Unfertilized leaves enclosed in fine-mesh bags broke down at an even slower rate (k=0.0062 day^–1). Phosphorus and nitrogen concentrations were initially higher in leaf packs with nutrients added, but this difference disappeared within 3 weeks. Fungal biomass developing in decomposing leaves was substantial (c. 55 mg dry mass per 1 g leaf dry mass) although similar between fertilized and unfertilized packs, as was the sporulation activity of aquatic hyphomycetes. There was a significantly greater number and higher biomass of macroinvertebrates (shredding nemourid stoneflies in particular) on the fertilized packs, suggesting that the increased leaf mass loss was brought about by shredder feeding. Received: 11 March 1999 / Accepted: 6 September 1999     

Global patterns of root turnover for terrestrial ecosystems

Root turnover is a critical component of ecosystem nutrient dynamics and carbon sequestration and is also an important sink for plant primary productivity. We tested global controls on root turnover across climatic gradients and for plant functional groups by using a database of 190 published studies. Root turnover rates increased exponentially with mean annual temperature for fine roots of grasslands ( r ² = 0.48) and forests ( r ² = 0.17) and for total root biomass in shrublands ( r ² = 0.55). On the basis of the best-fit exponential model, the Q ₁₀ for root turnover was 1.4 for forest small diameter roots (5 mm or less), 1.6 for grassland fine roots, and 1.9 for shrublands. Surprisingly, after accounting for temperature, there was no such global relationship between precipitation and root turnover. The slowest average turnover rates were observed for entire tree root systems (10% annually), followed by 34% for shrubland total roots, 53% for grassland fine roots, 55% for wetland fine roots, and 56% for forest fine roots. Root turnover decreased from tropical to high-latitude systems for all plant functional groups. To test whether global relationships can be used to predict interannual variability in root turnover, we evaluated 14 yr of published root turnover data from a shortgrass steppe site in northeastern Colorado, USA. At this site there was no correlation between interannual variability in mean annual temperature and root turnover. Rather, turnover was positively correlated with the ratio of growing season precipitation and maximum monthly temperature ( r ² = 0.61). We conclude that there are global patterns in rates of root turnover between plant groups and across climatic gradients but that these patterns cannot always be used for the successful prediction of the relationship of root turnover to climate change at a particular site.     

Carbon and nitrogen turnover in adjacent grassland and cropland ecosystems

The effects of cultivation and soil texture on net and gross N mineralization, CO₂ evolution and C and N turnover were investigated using paired grassland and cropped sites on soils of three textures. Gross N mineralization and immobilization were measured using¹⁵N-isotope dilution. Grassland soils had high CO₂ evolution and gross N mineralization rates, and low net N mineralization rates. Cropland soils had low CO₂ evolution rates but had high net and gross N mineralization rates. Grassland soils thus had high immobilization rates and cropland soils had low immobilization rates. Cultivation increased N turnover but reduced C turnover. The data suggest that the microflora in grassland soils are N limited, while those of cropland soils are limited by C availability. Increasing clay content reduced N turnover. C turnover was less clearly related to texture. Differences in the immobilization potential of substrates help explain why agricultural soils have higher N losses than do grassland soils.     

Nutrient limitation of bacterial production in clear water Amazonian ecosystems

The aim of this research was to determine the main limiting nutrient (carbon, nitrogen or phosphorus) to bacterial production in different clear water Amazonian ecosystems during the high water period, when there is influence of the flooded land, mainly as sources of organic matter. Five stations were sampled in three clear water ecosystems: Trombetas River, Lake Batata and Caranã Stream. We estimated in each station the nutrient concentration, bacterial production and bacterial abundance. The experiment was set up with GF/F filtered water from all stations together with additions of glucose (400 M C), KNO₃ (15 M N) and KH₂PO₄ (5 M P) in accordance with each treatment (C, N, P ,CN, CP, NP, CNP and no amends). Bacterial production was estimated after 24 h of incubation. We observed that the values of bacterial production after additions of phosphate alone (P treatment) were 2- to 6-fold greater than the values measured in control flasks. Additions of nitrate (N treatment) and glucose alone (C treatment) had no effect on the bacterial production in four out of five ecosystems studied. However, additions of glucose with phosphate (CP treatment) strongly stimulated bacterial production in all ecosystems studied, including treatments with phosphate addition only. We conclude that phosphorus is the main limiting nutrient to bacterioplankton production in these clear water Amazonian ecosystems during the high water period. In addition, we conclude that, together with phosphorus, additions of glucose stimulated the bacterial production mainly due to the low quality of the carbon pool present in these ecosystems.     

Nutrient flows between ecosystems can destabilize simple food chains

Dispersal of organisms has large effects on the dynamics and stability of populations and communities. However, current metacommunity theory largely ignores how the flows of limiting nutrients across ecosystems can influence communities. We studied a meta-ecosystem model where two autotroph-consumer communities are spatially coupled through the diffusion of the limiting nutrient. We analyzed regional and local stability, as well as spatial and temporal synchrony to elucidate the impacts of nutrient recycling and diffusion on trophic dynamics. We show that nutrient diffusion is capable of inducing asynchronous local destabilization of biotic compartments through a diffusion-induced spatiotemporal bifurcation. Nutrient recycling interacts with nutrient diffusion and influences the susceptibility of the meta-ecosystem to diffusion-induced instabilities. This interaction between nutrient recycling and transport is further shown to depend on ecosystem enrichment. It more generally emphasizes the importance of meta-ecosystem theory for predicting species persistence and distribution in managed ecosystems.     

In situ determination of sulfide turnover rates in a meromictic alpine lake

A push-pull method, previously used in groundwater analyses, was successfully adapted for measuring sulfide turnover rates in situ at different depths in the meromictic Lake Cadagno. In the layer of phototrophic bacteria at about 12 m in depth net sulfide consumption was observed during the day, indicating active bacterial photosynthesis. During the night the sulfide turnover rates were positive, indicating a net sulfide production from the reduction of more-oxidized sulfur compounds. Because of lack of light, no photosynthesis takes place in the monimolimnion; thus, only sulfide formation is observed both during the day and the night. Sulfide turnover rates in the oxic mixolimnion were always positive as sulfide is spontaneously oxidized by oxygen and as the rates of sulfide oxidation depend on the oxygen concentrations present. Sulfide oxidation by chemolithotrophic bacteria may occur at the oxicline, but this cannot be distinguished from spontaneous chemical oxidation.     

Enzymology under global change: organic nitrogen turnover in alpine and sub-Arctic soils

Understanding global change impacts on the globally important carbon storage in alpine, Arctic and sub-Arctic soils requires knowledge of the mechanisms underlying the balance between plant primary productivity and decomposition. Given that nitrogen availability limits both processes, understanding the response of the soil nitrogen cycle to shifts in temperature and other global change factors is crucial for predicting the fate of cold biome carbon stores. Measurements of soil enzyme activities at different positions of the nitrogen cycling network are an important tool for this purpose. We review a selection of studies that provide data on potential enzyme activities across natural, seasonal and experimental gradients in cold biomes. Responses of enzyme activities to increased nitrogen availability and temperature are diverse and seasonal dynamics are often larger than differences due to experimental treatments, suggesting that enzyme expression is regulated by a combination of interacting factors reflecting both nutrient supply and demand. The extrapolation from potential enzyme activities to prediction of elemental nitrogen fluxes under field conditions remains challenging. Progress in molecular '-omics' approaches may eventually facilitate deeper understanding of the links between soil microbial community structure and biogeochemical fluxes. In the meantime, accounting for effects of the soil spatial structure and in situ variations in pH and temperature, better mapping of the network of enzymatic processes and the identification of rate-limiting steps under different conditions should advance our ability to predict nitrogen fluxes.     

Nutrient leaching in dry heathland ecosystems: effects of atmospheric deposition and management

Atmospheric nutrient deposition has contributed to widespread changes in sensitive seminatural ecosystems throughout Europe. For an understanding of underlying processes it is important to quantify input–output flows in relation to ongoing atmospheric inputs and current management strategies. In this study we quantified losses of N, P, Ca, Mg, and K via leaching in heathland ecosystems (Lüneburger Heide, NW Germany) as a function of current deposition rates and different management measures (mowing, prescribed burning, choppering, sod-cutting) which aim to prevent shrub and tree encroachment. Leaching was only moderately related to atmospheric input rates, indicating that leaching was mostly affected by internal turnover processes. Leaching significantly increased for most of the nutrients after the application of management measures, particularly in the choppered and sod-cut plots. However, atmospheric nutrient inputs exceeded leaching outputs for most of the nutrients, even in the plots subjected to management. Despite high deposition rates (20–25 kg N ha⁻¹ year⁻¹), retention of atmospheric N input ranged between 74% and 92% in the control plots. In the treated plots, N retention decreased to 59–80%. However, in the study area mean N leaching in the controls has almost doubled since 1980 and currently amounts to 3.7 kg ha⁻¹ year⁻¹, indicating an early stage of N saturation. Our study provides evidence that leaching did not compensate for atmospheric nutrient deposition, particularly as regards N. Management, thus, will be an indispensable tool for the maintenance of the low-nutrient status as a prerequisite for the long-term preservation of heathland ecosystems.     

Drought alters carbon fluxes in alpine snowbed ecosystems through contrasting impacts on graminoids and forbs

? Climate change is predicted to increase the frequency of drought events in alpine ecosystems with the potential to affect carbon turnover. ? We removed intact turfs from a Nardus stricta alpine snowbed community and subjected half of them to two drought events of 8 d duration under controlled conditions. Leachate dissolved organic carbon (DOC) was measured throughout the 6 wk study period, and a (13)CO(2) pulse enabled quantification of fluxes of recent assimilate into shoots, roots and leachate and ecosystem CO(2) exchange. ? The amount of DOC in leachate from droughted cores was 62% less than in controls. Drought reduced graminoid biomass, increased forb biomass, had no effect on bryophytes, and led to an overall decrease in total above-ground biomass compared with controls. Net CO(2) exchange, gross photosynthesis and the amount of (13)CO(2) fixed were all significantly less in droughted turfs. These turfs also retained proportionally more (13)C in shoots, allocated less (13)C to roots, and the amount of dissolved organic (13)C recovered in leachate was 57% less than in controls. ? Our data show that drought events can have significant impacts on ecosystem carbon fluxes, and that the principal mechanism behind this is probably changes in the relative abundance of forbs and grasses.     

Nutrient uptake as a contributing explanation for deep rooting in arid and semi-arid ecosystems

Explanations for the occurrence of deep-rooted plants in arid and semi-arid ecosystems have traditionally emphasized the uptake of relatively deep soil water. However, recent hydrologic data from arid systems show that soil water potentials at depth fluctuate little over long time periods, suggesting this water may be rarely utilized or replenished. In this study, we examine the distributions of root biomass, soil moisture and nutrient contents to 10-m depths at five semi-arid and arid sites across southwestern USA. We couple these depth distributions with strontium (Sr) isotope data that show deep (>1 m) nutrient uptake is prevalent at four of the five sites. At all of the sites, the highest abundance of one or more of the measured nutrients occurred deep within the soil profile, particularly for P, Ca²⁺ and Mg²⁺. Phosphate contents were greater at depth than in the top meter of soil at three of five sites. At Jornada, for example, the 2–3 m depth increment had twice the extractable P as the top meter of soil, despite the highest concentrations of P occurring at the surface. The prevalence of such deep resource pools, and our evidence for cation uptake from them, suggest nutrient uptake as a complementary explanation for the occurrence of deep-rooted plants in arid and semi-arid systems. We propose that hydraulic redistribution of shallow surface water to deep soil layers by roots may be the mechanism through which deep soil nutrients are mobilized and taken up by plants.Electronic Supplementary Material Supplementary material is available for this article at     

高山植物繁殖策略的研究进展

高山地区通常被认为是陆地上最为极端的生境之一,但却拥有许多形态特化的植物和较高的物种多样性。高山植物如何在严酷的环境中实现成功繁殖,这一问题倍受研究者们的关注。本文综合了国内外高山植物在资源分配、花形态对非生物环境因子的响应、动物传粉及其适应机制、果实和种子及克隆繁殖等繁殖策略方面的文献。为应对低温多雨雪的恶劣环境,一些高山植物采取花向日性、花冠闭合及花序保温结构等繁殖策略。高山植物的传粉者类群也发生了改变,主要为蜂类和蝇类。熊蜂(Bombusspp.)传粉的高效性,减少了高山环境对植物传粉造成的不利影响。当传粉者不可得时,植物不仅通过延迟自交和自助自交等机制来提供繁殖保障,还借助克隆繁殖及其他传粉机制(风媒或风虫媒)来维持种群的繁衍。依赖动物传粉的高山植物,可以采取增加繁殖构件的资源分配、加大广告投入以及较大的花展示或较长的花寿命来提高传粉者的拜访几率,以及借助泛化的花结构和选择合适的开花时间等策略来提高繁殖成功率。此外,大部分高山植物产生干果且具有持久的种子库,有利于种子的传播以及种子寻找萌发及幼苗生长的最佳外界环境。在今后的研究中,可着重探讨以下几个问题:(1)非生物环境因子对花形态的选择;(2)季节变化与繁殖策略;(3)群落水平上植物与传粉者的关系;(4)高山生态系统对全球变暖的响应。     

Limnological studies of and primary production in temple pond ecosystems

Three temple ponds with permanent blooms of blue green algae were highly productive. They all showed high alkalinity, hardness, electrical conductivity and pH. Organic carbon and nitrogen were highest in Sarvatheertham pond—60 to 79.6 mg./l. C and 4.10 to 7.60 mg./l. N. In Tamaraikulam it was 16.5 to 20.3 mg. C/l. and 1.03 to 1.32 mg. N/l. In Sarvatheertham, the gross production ranged from 2.85 to 20.72 g. O₂/m.²/d. Self shading by blanket algae of blue greens reduced productivity in Sarvatheertham, where a persistent thermal and biochemical stratification was noted. Very high organic carbon and nitrogen contents were noted in Sarvatheertham pond. The dry weight of plankton in this pond ranged from 430 to 900 mg./l. Productivity computed from diurnal changes in alkalinity and dissolved oxygen also revealed a high rate in Ayyankulam, Tamaraikulam and Sarvatheertham in descending order. Very wide fluctuations in pH, both diurnally and depth-wise, were recorded in Sarvatheertham and to a lesser extent in the other two ponds. Photosynthetic efficiency was 4.03% in Ayyankulam, 2.09% in Tamaraikulam and 1.56% in Sarvatheertham. By the diurnal oxygen curve method, a gross primary production of 97.5 g. O₂/m.²/d was recorded in Ayyankulam.