Nutrient removal and biomass production in land treatment systems receiving domestic effluent

Land application of pre-treated wastewater is increasingly practiced to achieve both treatment and beneficial reuse of applied effluent. Vegetation is an important component of these systems, affecting hydraulic loading and nutrient uptake and hence treatment efficiency. This work investigated the effect of plant species (Acacia cyanophylla, Eucalyptus camaldulensis, Populus nigra and Arundo donax), on water requirements, nutrient removal, water use efficiency (WUE) and biomass production in land treatment systems (LTS) in which pre-treated wastewater was applied at rates to meet crop evapotranspiration. Vegetation had a strong effect on all the parameters monitored during this trial. A. cyanophylla produced the greatest amount of biomass and showed the highest irrigation requirements and WUE, followed by E. camaldulensis, A. donax and P. nigra. In addition, A. cyanophylla and A. donax achieved a higher leaf-N content compared to other species. As a result of the differences in tissue nutrient content and biomass, A. cyanophylla accumulated 23, 20, and 70% more N in hypergeous biomass than E. camaldulensis, A. donax and P. nigra, respectively. A. cyanophylla and E. camaldulensis accumulated 57 and 53% respectively more P than did P. nigra and A. donax. Therefore substantial improvement of the performance of the LTS in terms of nutrient removal can be achieved through the selection of appropriate plant species. Despite the enhanced growth rates observed in the study nutrient recovery by vegetation did not exceed 31 and 35% of the applied N and P, respectively. The relatively low percentages of removal are attributed to increased concentration of nutrients in effluent and the high ET rates prevailing in the study area. These findings suggest that additional practices are required to mitigate environmental impacts arising from excessive nutrient loads when effluent is applied at rates to meet crop water requirements.     

Seedling growth and soil nutrient availability in exotic and native tree species: implications for afforestation in southern China

Background and aims

The relationship between tree species and soil nutrient availability is critical for evaluating plantation succession and promoting forest restoration. This study was conducted to evaluate the impact of exotic and native tress species on soil nutrient availability.

Methods

Four exotic species (Eucalyptus urophylla, E. tereticornis, Acaia auriculaeformis, A. mangium) and four native species (Castanopsis fissa, Schima superba, C. hystrix, Michelia macclurei) were planted and grown for one-year. Soil solution (DOC, DON, NH₄?N, NO₃?N) was sampled and analyzed during the study. After the experiment, soil properties were determined, and plant tissues were analyzed.

Results

DOC levels were greater in soils with trees planted than controls without trees. Compared to native species, exotic species had much faster growth rates and greatly reduced DON and NO₃?N concentrations. Exotic species always had less P concentrations in leaves and stems than native species. Furthermore, N-fixing A. auriculaeformis led to greater soil available P compared to other species.

Conclusions

Based on these findings, we provide some recommendations for afforestation practice. This study highlights that a better understanding of the pros and cons of exotic species would be beneficial to advance afforestation in China and the world.     

Restoration of rocky slopes based on planted gabions and use of drought-preconditioned woody species

The restoration of steep rock faces with shrubs and trees is difficult due to extreme microclimatic and edaphic conditions. In this study, we tested the applicability of free-standing planted gabions to improve the landscape and achieve protection against rockfall, erosion and enhanced surface flow. Furthermore, we analyzed the effect of preconditioning on drought tolerance of several planted species (Ligustrum vulgare, Viburnum lantana, Juniperus communis and Pinus sylvestris).Planted gabions showed sufficient mechanical stability, but survival rates of planted shrubs and trees were reduced by drought stress. Soil water potential on the gabions decreased several times below ?1.4 MPa and soil temperature increased up to 30 °C in summer and decreased below ?6 °C in winter. The percentage of surviving individuals was correlated with the species’ resistance to drought-induced embolism. Drought tolerance was overall higher in conifer species, while angiosperm species were able to shift their vulnerability thresholds upon preconditioning.We conclude that free-standing planted gabions may be an alternative technique for restoration and securing of critical parts of steep rocky slopes. Preconditioning of plant material used for restoration of drought-prone sites can increase the drought tolerance of some species.     

Growth and physiological response of Arundo donax L. to controlled drought stress and recovery

Soil water deficit constrains crop growth more than any other abiotic stress, both per se and in combination with other factors, making drought resistance a key element for the successful exploitation of marginal areas. Arundo donax (Poaceae), is a mesophyte that can adapt to a wide variety of ecological conditions, although its growth can be retarded by a shortage of water. The objective of the present research is to draw a comprehensive picture of the integrated response mechanisms of A. donax to controlled drought conditions, and characterize its ability to recover upon rewatering in terms of photochemical efficiency. Plants were subjected to a gradually applied drought stress for a period of three weeks, after which they were returned to fully hydrated soil conditions for one week. Overall, plant dry weight and key growth parameters were not significantly affected. However, detrimental effects were visible in the form of impaired leaf gas exchange, which influences the performance of photosynthesis, and pre-dawn leaf water potential (pdΨ_W), ?92.1% of net CO₂ assimilation rate and ?0.36 MPa, respectively at the cessation of stress. Nonetheless, a rapid restoration of A. donax physiological functions was observed upon rewatering, testifying to the environmental plasticity of this species.     

Resource-use efficiencies of three indigenous tree species planted in resource islands created by shrubs: implications for reforestation of subtropical degraded shrublands

Shrub resource islands are characterized by resources accumulated shrubby areas surrounded by relative barren soils. This research aims to determine resource-use efficiency of native trees species planted on shrub resource islands, and to determine how the planted trees may influence the resource islands in degraded shrublands in South China. Shrub (Rhodomyrtus tomentosa) resource islands were left unplanted or were planted with 0.5-year-old indigenous tree species Schima superba, Castanopsis fissa, and Michelia macclurei. The results indicate that, after 2.5?years, the tree seedlings did not modify the physical traits (light, air temperature, and soil water) but tended to increase soil nutrients (soil organic carbon and soil nitrogen) and soil microbial biomass of the resource islands. Relative to S. superba and M. macclurei, C. fissa had greater effects on soil nutrients and microbial biomass but showed lower plant growth, survival, and resource-use efficiencies (for water, light, energy, and nitrogen). These results rejected our initial assumption that shrub resource islands would effectively promote the growth and resource utility of all the indigenous tree species and shorten the reforestation course in subtropical degraded shrubland. C. fissa performed poorly when growing on shrub resource islands, but its role in soil nutrient accumulation might have long-term impacts on the restoration of degraded shrubland. In contrast, S. superba and M. macclurei could make better use of the shrub resource islands therefore accelerating the construction of native plantations.     

Ecological correlates of invasion by <Emphasis Type="Italic">Arundo donax</Emphasis> in three southern California riparian habitats

Arundo donax L. (Poaceae) is an aggressive invader in California’s riparian habitats. Field experiments were conducted to examine invader and site attributes important in early invasion. One hundred A. donax rhizomes were planted along five transects into each of three southern California riparian habitats. Pre-planting rhizome weight was recorded, along with site variables including percent bare ground, litter depth, PAR, soil moisture, soil temperature, incidence of herbivory, native canopy cover, and plant community richness and diversity. A. donax shoot emergence, survival time, and shoot height were recorded for approximately 10 months. The experiment was repeated over three years in different locations within each site. When years and sites were pooled to reveal large-scale patterns, A. donax performance was explained by rhizome weight, soil moisture, bare ground, soil temperature, and herbivory. When each site was considered singly, A. donax was positively correlated with different variables in each location. Species richness was correlated with A. donax performance in only one site. Our results indicate that A. donax establishment in riparian habitats is promoted by both vegetative reproduction and favorable abiotic environmental factors and relatively unaffected by the composition of the native community. The positive response of A. donax to disturbance (bare ground) and high resource availability (soil moisture), combined with a competitive perennial habit suggest that this species takes advantage of a competitive-ruderal life history. The ability of A. donax to respond to different conditions in each site combined with low genetic and phenotypic variation seen in other studies also suggests that a high degree of environmental tolerance contributes to invasion success.     

Plant N capture from pulses: effects of pulse size,growth rate,and other soil resources

In arid ecosystems, the ability to rapidly capture nitrogen (N) from brief pulses is expected to influence plant growth, survival, and competitive ability. Theory and data suggest that N capture from pulses should depend on plant growth rate and availability of other limiting resources. Theory also predicts trade-offs in plant stress tolerance and ability to capture N from different size pulses. We injected K¹⁵NO₃, to simulate small and large N pulses at three different times during the growing season into soil around the co-dominant Great Basin species Sarcobatus vermiculatus, Chrysothamnus nauseosus ssp. consimilis, and Distichlis spicata. Soils were amended with water and P in a partial factorial design. As predicted, all study species showed a comparable decline in N capture from large pulses through the season as growth rates slowed. Surprisingly, however, water and P availability differentially influenced the ability of these species to capture N from pulses. Distichlis N capture increased up to tenfold with water addition while Chrysothamnus N capture increased up to threefold with P addition. Sarcobatus N capture was not affected by water or P availability. Opposite to our prediction, Sarcobatus, the most stress tolerant species, captured less N from small pulses but more N from large pulses relative to the other species. These observations suggest that variation in N pulse timing and size can interact with variable soil water and P supply to determine how N is partitioned among co-existing Great Basin species.     

Establishment of Vesicular-Arbuscular Mycorrhizal Fungi and Other Microorganisms on a Beach Replenishment Site in Florida

Beach replenishment is a widely used method of controlling coastal erosion. To reduce erosional losses from wind, beach grasses are often planted on the replenishment sands. However, there is little information on the microbial populations in this material that may affect plant establishment and growth. The objectives of this research were to document changes in the populations of vesicular-arbuscular mycorrhizal (VAM) fungi and other soil microorganisms in replenishment materials and to determine whether roots of transplanted beach grasses become colonized by beneficial microbes. The study was conducted over a 2-year period on a replenishment project in northeastern Florida. Three sampling locations were established at 1-km intervals along the beach. Each location consisted of three plots: an established dune, replenishment sand planted with Uniola paniculata and Panicum sp., and replenishment sand left unplanted. Fungal and bacterial populations increased rapidly in the rhizosphere of beach grasses in the planted plots. However, no bacteria were recovered that could fix significant amounts of N₂. The VAM fungi established slowly on the transplanted grasses. Even after two growing seasons, levels of root colonization and sporulation were significantly below those found in the established dune. There was a shift in the dominant VAM fungi found in the planted zone with respect to those in the established dunes. The most abundant species recovered from the established dunes were Glomus deserticola, followed by Acaulospora scrobiculata and Scutellospora weresubiae. The VAM fungi that colonized the planted zone most rapidly were Glomus globiferum, followed by G. deserticola and Glomus aggregatum.     

Biogeochemical consequences of winter flooding in brook valleys

Climatic change has great impacts on stream catchments and their ecology. Expectations are that more extreme climate events will result in undesired flooding in stream catchments. In the Netherlands, former floodplains with a history of agricultural use are put into use again as flooding areas for the purpose of water retention. This study focuses on the effects of winter flooding on various plant site conditions in the soil, such as redox, nutrient, pH, and base status. We compared the effects on groundwater- and rainwater-dominated floodplains. Water chemistry (pH, EC, HCO₃, SO₄, Cl, Ca, Mg, Na, K, , NO₃, NH₄, and PO₄) and soil nutrients (Total N and P, and bio-available P) were monitored for one year, including a 3–4 month period with winter flooding. In both floodplains no direct effect of the flood-water chemistry was detected in the pore water, because the soil pores had become saturated with groundwater or rainwater, respectively, just before flooding, flood-water did not penetrate the soil. We found that the increase in pH and ammonium concentration in the rainwater floodplain were due to changes in redox status, resulting from the completely water-filled state of the soil pores during the flooding event. Furthermore, we noticed an increase in soil nutrient contents and a shift in plant species composition in the rainwater floodplain: the vegetation included more plant species characteristic for N-richness. Finally, we conclude that winter flooding has more drastic effects on biogeochemical conditions and vegetation composition in the atmotrophic conditions characteristic for low-order subcatchments than in lithotrophic conditions in the larger, higher-order subcatchments of the stream basin.     

Local soil characteristics determine the microbial communities under forest understorey plants along a latitudinal gradient

The soil microbial community is essential for maintaining ecosystem functioning and is intimately linked with the plant community. Yet, little is known on how soil microbial communities in the root zone vary at continental scales within plant species. Here we assess the effects of soil chemistry, large-scale environmental conditions (i.e. temperature, precipitation and nitrogen deposition) and forest land-use history on the soil microbial communities (measured by phospholipid fatty acids) in the root zone of four plant species (Geum urbanum, Milium effusum, Poa nemoralis and Stachys sylvatica) in forests along a 1700 km latitudinal gradient in Europe.Soil microbial communities differed significantly among plant species, and soil chemistry was the main determinant of the microbial community composition within each plant species. Influential soil chemical variables for microbial communities were plant species-specific; soil acidity, however, was often an important factor. Large-scale environmental conditions, together with soil chemistry, only explained the microbial community composition in M. effusum and P. nemoralis. Forest land-use history did not affect the soil microbial community composition.Our results underpin the dominant role of soil chemistry in shaping microbial community composition variation within plant species at the continental scale, and provide insights into the composition and functionality of soil microbial communities in forest ecosystems.     

Effects of salinity on growth,membrane permeability and root hydraulic conductivity in three saltbush species

The species of the genus Atriplex have been introduced in West Asia and North Africa to determine their adaptability for use as fodder species. These halophytes are well adapted to extreme environmental conditions and may possess interesting properties for soil rehabilitation. The effect of NaCl stress on growth, water relation and mineral nutrition were investigated in three xero-halophyte species of Atriplex used for rehabilitation of arid steppe in Algeria. Atriplex halimus, Atriplex canescens and Atriplex nummularia, were cultivated in hydroponic conditions and treated with increasing doses of NaCl (0–300 mM). All species showed positive plant growth for low and moderate levels of salinity. A. halimus had higher dry weight production than A. nummularia and A. canescens in high salinity concentration. Increasing concentration of salinity induced decrease in chlorophyll content (Chl a and b) and root hydraulic conductivity (L₀) in all species, especially in A. canescens. All three species showed marked increase in electrolyte leakage across the salinity gradient. In addition all species were able to accumulate a large quantity of sodium (Na), chloride (Cl) and proline and to maintain higher relative water content, which was probably associated with a greater capacity for osmotic adjustment, whereas potassium (K) and calcium (Ca) decreased with increase salinity. The data suggest that salt tolerance strategies in all Atriplex species could involve a delicate balance among ion accumulation, osmotic adjustment, production of osmotica and maintenance of relative water content and growth.     

鄱阳湖湿地景观恢复的物种选择及其对环境因子的响应

湿地是重要的生态系统,对人类和野生生物都具有极其重要的价值。由于自然因素的变化和人类活动的干扰,湿地退化严重。近年来,湿地恢复已成为世界环境问题改善的重要工具之一。选择适用的湿地植物是退化湿地恢复的关键途径。本文以鄱阳湖湿地为研究对象,通过专家赋值、野外调查、定位观测等方法,筛选了苦草、野菱、芦苇、苔草等25种鄱阳湖常见植物作为湿地景观恢复的优先物种。对苦草、黑藻、菹草、菖蒲、芦苇等5种植物对环境因子的响应进行观测。结果表明,苦草在清水环境130-140cm处的生长最好;黑藻在清水环境中100-110cm处的生长最好;菹草在不同水深(50-160cm)下都能够生长,菹草高度随水深增加而增加;菖蒲具有一定的耐淹能力(< 80cm),但完全淹水(水深100-120cm)明显影响到菖蒲根状茎萌发、幼苗生长和生物量的积累;芦苇根状茎萌发对水深要求严格,土壤要湿润且透气性良好才是芦苇萌发的最好条件,芦苇根状茎萌发前淹水超过20 cm其萌发将会受到明显抑制,淹水超过30 cm则无法萌发。通过对沉水植物的透明度研究表明,植物对水质的透明度都有一定的要求,透明度较好更利于湿地植物的生长发育。     

Effects of Plant Biomass, Plant Diversity, and Water Content on Bacterial Communities in Soil Lysimeters: Implications for the Determinants of Bacterial Diversity

Soils may comprise tens of thousands to millions of bacterial species. It is still unclear whether this high level of diversity is governed by functional redundancy or by a multitude of ecological niches. In order to address this question, we analyzed the reproducibility of bacterial community composition after different experimental manipulations. Soil lysimeters were planted with four different types of plant communities, and the water content was adjusted. Group-specific phylogenetic fingerprinting by PCR-denaturing gradient gel electrophoresis revealed clear differences in the composition of Alphaproteobacteria, Betaproteobacteria, Bacteroidetes, Chloroflexi, Planctomycetes, and Verrucomicrobia populations in soils without plants compared to that of populations in planted soils, whereas no influence of plant species composition on bacterial diversity could be discerned. These results indicate that the presence of higher plant species affects the species composition of bacterial groups in a reproducible manner and even outside of the rhizosphere. In contrast, the environmental factors tested did not affect the composition of Acidobacteria, Actinobacteria, Archaea, and Firmicutes populations. One-third (52 out of 160) of the sequence types were found to be specifically and reproducibly associated with the absence or presence of plants. Unexpectedly, this was also true for numerous minor constituents of the soil bacterial assemblage. Subsequently, one of the low-abundance phylotypes (beta10) was selected for studying the interdependence under particular experimental conditions and the underlying causes in more detail. This so-far-uncultured phylotype of the Betaproteobacteria species represented up to 0.18% of all bacterial cells in planted lysimeters compared to 0.017% in unplanted systems. A cultured representative of this phylotype exhibited high physiological flexibility and was capable of utilizing major constituents of root exudates. Our results suggest that the bacterial species composition in soil is determined to a significant extent by abiotic and biotic factors, rather than by mere chance, thereby reflecting a multitude of distinct ecological niches.     

Microbially mediated CH4 consumption and N2O emission is affected by elevated CO2, soil water content, and composition of semi-arid grassland species

Elevated CO₂ affects plant productivity, but also water availability and plant species composition in semi-arid grasslands, thereby potentially causing complex effects on CH₄ consumption and N₂O emission. We studied the effects of atmospheric CO₂ concentration (400 vs 780 μL L^?1), water content (15 vs 20% gravimetric soil moisture), and composition of semi-arid grassland species (perennial grasses Bouteloua gracilis, Hesperostipa comata, and Pascopyrum smithii; sub-shrub Artemisia frigida; invasive forb Linaria dalmatica grown in monoculture and all five species together) on CH₄ consumption and N₂O emission in a full factorial greenhouse experiment. We used a unique method where we measured microbial effects on CH₄ consumption and N₂O emission in isolation from effects of gas diffusivity. Microbially mediated CH₄ consumption was significantly higher under elevated CO₂ (by 20%), but was not affected by soil water content or plant species composition. Microbially mediated N₂O emission was not significantly affected by elevated CO₂, but was significantly higher with high water content (by 67%) and differed significantly among species. Treatment effects on CH₄ consumption and N₂O emission often could not be explained simply by differences in soil moisture, suggesting that treatment-induced changes in other soil and microbial properties played a role in causing these effects.     

Understory vegetation as an indicator of soil characteristics in the Hyrcanian area,N. Iran

The mesic Caspian (Hyrcanian) forest and ecotone communities provide a marked contrast to the arid and semiarid landscapes associated with most of the territory of Iran. To date, the ecological characteristics of these habitats, threatened and of conservation importance, have been little studied. Accordingly, ecological profiles of some important plant species of these communities have been assessed along two altitudinal gradients (300–2300 m a.s.l.). Vegetation and soils were sampled every 100 m in elevation, with the data subsequently analyzed using TWINSPAN and corrected frequency (CF) analyses. Relationships between soil variables (subdivided into three classes, the lowest, the middle and the upper third of all values) and herbaceous and shrub species (presence/absence data) were analyzed by the polythetic divisive classification method. 379 plant species and eleven soil variables – N, P, K, CaCO₃, EC, pH, organic matter, C/N ratio and percentage of sand, clay and silt – were considered. The ecological profile method was used to evaluate the affinity and significance of associations between the probability of species’ occurrence and topsoil characteristics found by the polythetic method. Five vegetation groups were identified: two groups, with Acer campestre and Quercus macranthera in the tree layer and Veronica mazanderanae and Phuopsis stylosa as herbs, were restricted to forest-steppe ecotones and the upper mountain areas. Three groups, with Acer velutinum, Ruscus hyrcanus, Carpinus betulus, Danae racemosa, Fagus orientalis and Aruncus vulgaris as indicator species, occurred in the forest itself. Of the 42 plant species assessed as being of particular importance, 13 had significant relationships with eight soil factors. Thus, certain species, including endemic plant species of restricted distribution and conservation importance, can be used as indicators of particular soil conditions in the Hyrcanian forest area.     

Restoring degraded arid Mediterranean areas with exotic tree species: Influence of an age sequence of Acacia salicina on soil and vegetation dynamics

Acacia salicina Lindl. is an Australian leguminous tree widely planted outside its original distribution as a multi-purpose species, and successfully establishes on degraded areas. The objective of this study was to determine how an age sequence of 3, 5, 9 and 13-year-old A. salicina plantations affected soil properties and flora diversity of an arid Mediterranean steppe. Soil samples were taken from the upper 10 cm of soil under tree canopies and in the associated open spaces. The results showed that tree establishment and development enhanced soil contents of total C, total N, available P and exchangeable K⁺, Ca²⁺, Mg²⁺ and Na⁺. These trends increased significantly with increasing plantation age. At the same time A. salicina facilitated the colonization and development of understory vegetation. Indeed, the number of plant species, the total plant cover, the perennial species density, the plant biomass and the diversity all attained higher values under tree canopies and increased with increasing plantation age. The soil dynamic under 13-year-old A. salicina plantations reflected two phases in the restoration sequence, characterized by nominal changes during tree establishment (0–5 years) and showing marked and rapid changes associated with the start of canopy closure (5–13 years). A. salicina establishment could be an effective and applicable measure to restore soil and vegetation and control desertification in the Mediterranean arid steppes.     

Effect of slight vegetation degradation on soil properties in Brachypodium pinnatum grasslands

Water is the most important factor controlling plant growth, primary production, and ecosystem stability in arid and semi-arid grasslands. Here we conducted a 2-year field study to explore the contribution of winter half-year (i.e. October through April) and summer precipitation (May through September) to the growth of coexisting plant species in typical steppe ecosystems of Inner Mongolia, China. Hydrogen stable isotope ratios of soil water and stem water of dominant plant species, soil moisture, and plant water potential were measured at three steppe communities dominated by Stipa grandis, Caragana microphylla, and Leymus chinensis, respectively. The fraction of water from winter half-year precipitation was an important water source, contributing 45% to plant total water uptake in a dry summer after a wet winter period (2005) and 15% in a summer where subsoil moisture had been exploited in the previous year (2006). At species level, Caragana microphylla exhibited a complete access to deep soil water, which is recharged by winter precipitation, while Cleistogenes squarrosa completely depended on summer rains. Leymus chinensis, Agropyron cristatum, and Stipa grandis showed a resource-dependent water use strategy, utilizing deep soil water when it was well available and shifting to rain water when subsoil water had been exploited. Our findings indicate that differentiation of water sources among plants improves use of available soil water and lessens the interspecific competition for water in these semi-arid ecosystems. The niche complementarity in water sources among coexisting species is likely to be the potential mechanism for high diversity communities with both high productivity and high resilience to droughts.     

乡土植物生活型构成对川渝地区边坡植被水土保持效益的影响

乡土植物灌木化建植是高速公路边坡防护的重要生态模式。为了探讨生态恢复过程中乡土植物的生活型构成对边坡植被水土保持效益的影响,揭示乡土植物生活型-物种多样性-生态系统功能间的偶合关系,借助3个物种配置试验,于2009年4月构建了以草本、灌木或乔木为主体的草本型、灌木型、乔木型绿化配置及草-灌-乔混合型试验区。自建植次年(2010年)起,对试验区进行持续5a生态监测。结果表明:1)边坡植被的物种丰富度与乡土植物的生活型有关,呈现乔木型灌木型草-灌-乔混合型草本型趋势;2)植被的物种多样性(Shannon-Wiener指数、Pielou指数)与乡土植物生活型构成及建植年限有关:建植后第1、第2年,多样性水平呈草本型草-灌-乔混合型灌木型乔木型变化趋势;自建植后第三起(2012—2014年),呈草-灌-乔混合型草本型灌木型乔木型波动;3)植被的水土保持性能(径流系数、侵蚀模数)与群落的物种多样性密切相关:多样性水平越高,水土保持性能越强。可见,乡土植物的生活型构成对提高边坡植被的物种多样性、改善生态性能至关重要。     

Does pre-dawn water potential reflect conditions of equilibrium in plant and soil water status?

Variation in base water potential (Ψ_b, a daily maximum level of plant water potential, which is presumed to correspond to the equilibrium between soil and plant water potentials) was examined in shoots of Picea abies and Vaccinium myrtillus with respect to soil (available water storage, water potential, temperature) and atmospheric (temperature, relative humidity, vapour pressure deficit) conditions. The available soil water storage (W_tr) accounted for 77% of the dynamics of Ψ_b, while the influence of atmospheric factors became evident under high evaporative demand. Ψ_b was not always observable immediately before dawn, but on 30% of observation days, the recovery continued up to an hour or two after dawn. Full equilibrium between soil and plant water potentials in P. abies in northern conditions is rather improbable by dawn in summer-time, because of the shortness of the dark period and probable night-time transpiration in the case of high atmospheric vapour pressure deficit.     

Effect of soil moisture content on the deformation behaviour of root-reinforced soils subjected to shear

The effects of plant species which frequently occur in set-aside arable land on rhizosphere soil properties were assessed and compared to rhizosphere soil of Secale cereale (Rye) grown on an intensively managed arable soil (sandy Cambisol, Saxony, NE-Germany). On a 6 year old set-aside arable land rhizosphere soil samples were taken under Agropyron repens, Cirsium arvense and Rumex acetosa, the most frequent plant species, and under the leguminous plant species Vicia villosa. Phospholipid fatty acid analysis (PLFA) has been used to characterise the structure of the soil microbial community. Carbon mineralisation rates as well as gross (¹⁵N isotope pool dilution method) and net nitrogen mineralisation rates were determined as indicator of microbial activity. In intensive managed plots a rhizosphere effect was obvious in higher nutrient contents, gross N mineralisation rates and higher relative abundances of fungi and protozoa in Rye rhizosphere compared to bulk soil. Plant species altered rhizosphere microbial activity. Lowest gross N mineralisation and gross NH₄ consumption rates were detected in Rye rhizosphere soil. Both rates revealed high positive correlations with dissolved organic carbon (extracted with KCl) and soil pH. The rhizosphere soil microbial communities of the three dominant plant species of the set-aside arable land (Agropyron, Cirsium, Rumex) were more similar to each other than to Vicia grown on the same set-aside plots and Rye grown on intensive managed plots. The highest number of non-identified PLFAs detected in Vicia rhizosphere soil suggests that microbial diversity was highest. Differences in quantity and quality of Vicia rhizodeposition, especially higher N contents, seem to induce the higher microbial activity and different microbial community structure. The rhizosphere soil of the dominant plant species on the set-aside and intensively managed arable land reflected the differences in bulk soil properties (obtained in a previous study) between the two management systems (e.g. pH, gross N mineralisation, metabolic quotient, PLFA marker characteristic of G? bacteria and fungi).