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Purpose: Sulfur (S) deposition as a global change issue causes worldwide soil acidification, nutrient mobilization and marked changes in plant nutrition. Here, we hypothesize that S deposition would reduce leaf nutrient resorption with this effect varies with yearly fluctuations in precipitation. Methods: In a semiarid meadow exposed to S addition, we determined nitrogen (N), phosphorus (P) and S concentrations and nutrient resorption efficiencies (NuRE) of a grass and a sedge across two years with contrasting precipitation difference. Results: Concentrations of N, P, and S in green and senescent leaves generally increased with S addition across the two years, with the exception of N and P concentrations in green leaves of the grass that showed no response or even decreased with S addition. The coupling relationships between N and P concentrations were stronger in senescent leaves than in green leaves in the wet year. Leaf NuRE decreased with S addition across the two years as driven by increasing soil N, P and S availability. However, NuRE was higher in the wet year due to lower soil nutrient availability herein as compared with the dry year. Conclusions: This study provides new evidence on the role of nutrient resorption in tightening stoichiometric N:P relationships, and that plant nutrient resorption may be favored by higher precipitation to sharpen its tradeoff with soil nutrient availability. [ABSTRACT FROM AUTHOR]

Zhang et al. ([29]) determined that linkages between community assembly processes and the abundance of soil nematode communities under nutrient enrichment may play a major role in the C cycling of meadow steppe ecosystems. China's meadow grasslands possess a total area of some 1.1 million km SP 2 sp , including meadow steppes (60,851 km SP 2 sp ), lowland meadows (252,196 km SP 2 sp ), montane meadows (167,189 km SP 2 sp ), and alpine meadows (637,206 km SP 2 sp ) (Liao and Jia [15]). 1 Outline map of the Chinese meadow steppe vegetation (adapted from Li et al. [11]) Of the 15 papers presented in this Special Issue, 12 concern meadow steppe communities at local and regional scales, based on either long-term stationary manipulative experiments, or off-site incubation tests, and transect surveys. Overgrazing has long been regarded as the most significant factor causing grassland degradation in China, while cultivation of grasslands has been most substantial in the meadow steppe region of Inner Mongolia and meadows in northeast China. [Extracted from the article]

Purpose: In nitrogen (N)-fertilized grasslands, mowing removes large quantity of nutrients from ecosystems due to plant biomass removal at higher levels. This study tested the hypothesis that if mowing could counteract the synergistic interactions of exogenous zinc (Zn) and N supply on plant Zn uptake. Methods: Our hypothesis was tested with three dominant species (Leymus chinensis, Carex duriuscula, and Stipa baicalensis) in a field experiment exposed to Zn addition, N addition and mowing treatments. A pot experiment using a low-Zn soil was further conducted to explore mechanisms of N-driven changes in plant-soil Zn dynamics. Results: Zinc addition increased soil available Zn across all treatments. However, effects of Zn addition on plant Zn uptake were treatment- and species-specific given by higher Zn contents in L. chinensis under N addition, in C. duriuscula under mowing, and in S. baicalensis under mowing and N addition. Nitrogen addition synergistically interacted with Zn addition to increase Zn uptake of L. chinensis. Meanwhile, N addition reduced Zn uptake of C. duriuscula without Zn addition, mainly due to plant biomass suppression in the presence of more dominant L. chinensis. Mowing counteracted the synergistic effect of combined N and Zn addition on Zn content of L. chinensis through biomass removal and lowering soil moisture. Conclusion: Our results indicated that plant Zn uptake was mainly driven by soil Zn availability and species-specific responses of biomass to N addition and mowing. Moreover, counteractive mowing effect on the synergisms between Zn and N addition might necessitate grassland Zn fertilization. [ABSTRACT FROM AUTHOR]

Aims: Livestock grazing is one of the most common utilization methods and exerts a significant effect on the carbon allocations between the above- and belowground components of a grassland ecosystem. The major aim of this study were to evaluate the proportions of 13C allocation to various C pools of the plant-soil system of a meadow steppe ecosystem in response to changes of stocking rate. Methods: In situ stable 13C isotope pulse labeling was conducted in a long-term grazing experiment with 4 stocking rate. Plant materials and soil samples were taken at eight occasions (0, 3, 10, 18, 31, 56 and 100 days after labeling) to analyze the decline in 13C over time, and their composition signature of 13C were analyzed by the isotope ratio mass spectrometer technique. Results: We found a significantly greater decline in assimilated 13C of shoot and living root for the heavily grazed swards compared to other stocking rates, with the highest relocation rate of 13C into soil C pool compared to other fractions. In addition, light grazing significantly allocated 13C assimilates in the belowground pool compared to other stocking rates, especially in the live root and topsoil C-pools. Conclusions: In this study, the effects of grazing on the carbon transfers and stocks within the plant-soil system of the meadow steppe were highly grazing pressure dependent. Plant-soil system in light stocking rate presented the highest C utilization efficiency, however, plants allocated more C to soil C pools with heavily stocking rate. [ABSTRACT FROM AUTHOR]

Aims: Changes caused by single herbivore species grazing to soil and plant interfaces can significantly affect the leaf litter decomposition rates within ecosystems. However, we intended to study how grazing by multiple herbivore species regulate the litter decomposition process and associated soil or plant properties in Leymus chinensis dominant meadow steppe. Methods: Two consecutive randomized field experiments were conducted between May 2017 and May 2019: 1) a grazing experiment with four (control or no, sheep, cattle, and mixed (sheep + cattle)) grazing treatments to explore the effects of moderate grazing on soil properties and L. chinensis litter quality and 2) the litter decomposition experiment to evaluate the decay rate in grazed or non-grazed litter by using litter bag technique. Results: Litter decay rate was the highest in mixed grazed litter as compared to litter grazed by individual herbivore species. Both herbivore grazing and incubation time affected decay rate of L. chinensis litter by modifying soil moisture and nitrogen (N) content, as well as, litter N and lignin contents. Plant litter quality has been displayed to be a dominant regulator of litter decay rate than soil physical or chemical properties in mixed grazed litter. Conclusions: Livestock diversification benefited litter decomposition indirectly by modifying plant litter quality with time. Therefore, herbivore assemblages should be given more importance in future research on litter decomposition process to mediate nutrient cycling in grassland. [ABSTRACT FROM AUTHOR]

Background and aims: Understanding the effects of livestock grazing on the ecosystem biomass and soil nitrogen processes of grassland ecosystems is critical to improving knowledge on the mechanisms underlying grassland degradation and accurately assessing the influence of grazing management on grassland functions. Methods: We examined the interannual patterns of ecosystem biomass and soil nitrogen mineralization in response to cattle grazing in a Chinese meadow steppe. The soil core incubation method was employed for soil N transfer estimation, whilst the fumigation extraction method, a modified Baermann funnel method and harvest method were used for various measurements of ecosystem biomass parameters. Results: We found that cattle grazing caused consistent significant increases in soil temperature, irrespective of the stocking rate and year, whereas significant effects on soil moisture and edaphic properties were observed only in individual years and/or at specific stocking rates. Consistent positive effects at moderate stocking rates were observed for aboveground net primary production and soil nematode biomass in all study years. The across stocking rate pattern of N mineralization in response to cattle stocking appeared to be year-specific, although negative effects were found in most cases. In contrast, the interannual pattern of N mineralization was determined principally by the interannual patterns in precipitation and soil moisture and was much less affected by cattle grazing. Conclusions: Soil N mineralization in this meadow steppe was affected by cattle grazing via two major mechanisms, i.e., its effects on the aboveground net primary production (ANPP) and thus the quantity of plant litter input into the soil and its effects on soil temperature and moisture. Overall, our study spanned the longest consecutive years with the broadest range of stocking rates thus far of its kind, which revealed for the first time that the soil nitrogen mineralization pattern with respect to stocking rate was year-specific. Our findings have important implications for adaptive management and sustainable utilization of Chinese grasslands. [ABSTRACT FROM AUTHOR]

Aims: Soil nematodes, as key bioindicators, play crucial roles in soil ecological process. Management of grasslands, such as meadow steppes in northeast China, is often done by mowing, which has an impact on soil nematode communities. However, few studies have explored effects of mowing frequency on the community structure and biomass of soil nematodes. Methods: Routine field and laboratory methods concerning plant community, soil properties, and soil nematodes were applied in this study. Soil nematode community structure was analyzed by using nonmetric multidimensional scaling (NMDS) and principal component analysis (PCA). The relationships between nematode genus and biotic and abiotic factors were analyzed by redundancy analysis (RDA). Results: High mowing frequency significantly reduced abundance, biomass, and functional or metabolic regimes of soil nematodes in this ecosystem, whereas moderate mowing frequency enhanced those indices and regimes. Conclusions: Our findings showed that changing patterns in nematode indices across the mowing frequency conformed with the intermediate disturbance theory. Variations in soil nematode community were related to changes in belowground biomass, aboveground litter, soil available nitrogen and acidity, and the effects of edaphic and vegetal traits appeared to be trophic or genus-specific. This study has potential benefits for grassland restoration in northeast China. [ABSTRACT FROM AUTHOR]

Background and aims: Soil microorganisms play key roles in soil nutrient turnover and plant community composition; however, the soil microbial community composition and species diversity are often influenced by nutrient enrichment which may affect how soil microbes influence nutrient cycles and the plant community structure. The resistance of soil fungal and bacterial communities to nitrogen (N) and phosphorus (P) additions and whether the responses of the soil microbes and the plant community are simultaneous in a N-limited temperate meadow ecosystem are still unclear. Methods: We carried out a 7-year experiment with N and P additions in a temperate meadow. The community structures of soil bacteria and fungi were examined based on high-throughput sequencing targeting the 16S rRNA and ITS genes, respectively. Results: Nitrogen addition did not influence the community composition or species richness of bacteria, but it did alter the soil fungal community composition and increased fungal operational taxonomic unit (OTU) richness. Phosphorus addition significantly altered the soil fungal and bacterial community compositions, decreased the richness of bacterial OTUs, and increased the OTU richness of fungi. Proteobacteria (38.5%) and Acidobacteria (22.3%) were the most dominant bacteria. Ascomycota were the dominant fungi (42.6%) across all samples. The enrichment of available P in the soil due to P addition reduced the bacterial β-diversity, while the β-diversity of soil fungi was mainly influenced by the concentrations of soil N and P, as well as soil moisture. Conclusions: The sensitivity of soil fungi and bacteria to P addition was stronger than that of N addition, and the response of the soil microbes to N and P additions was more sensitive than that of the plant community. Our results highlight the unequal sensitivity of the soil fungal and bacterial community composition and structure to N and P additions, thereby causing changes in above and belowground community composition and structures in the studied temperate meadow ecosystem. [ABSTRACT FROM AUTHOR]

Aims: Reveal the soil organic carbon (SOC) stock change in the Qinghai-Tibetan Plateau (QTP) alpine wetlands in the past fifty years. The Qinghai-Tibetan Plateau (QTP) has a large area of alpine marshland and wet meadows. Artificial drainage, overgrazing and climate change have caused severe degradation of the alpine wetlands. However, little is known about the effects of wetland degradation on SOC stock, and studies only focused on the Zoige marshland, the biggest marshland of China. Direct SOC observations from the extensively distributed wet meadows remain scarce. Methods: SOC in the soil surface layer (0–50 cm) were investigated at four wetland sites where degradation has continued for decades. One site is in marshland, and three are in wet meadows of the QTP. Using datasets from the literature and the field measurements of the present study, we estimated the loss of alpine wetland SOC. Results and conclusions: Initially, marshland degradation to wet meadows prompted the accumulation of SOC; however, grazing in wet meadows reduced SOC accumulation. Wetland degradation to dried meadows led to a much greater SOC loss than that in the initial degradation stage, and grazing exacerbated the loss of SOC. An exponential decay rate of SOC was found in the grazed dried meadows. The wetlands of the QTP, have lost 141 ± 25 Tg in 1966–2016, representing 15% of the SOC stock. [ABSTRACT FROM AUTHOR]

Aims: Soil aggregates constitute spatially-separated microbial habitats and architectural units for biogeochemical reactions. However, little is known about how aggregates varying in size can affect soil carbon (C) storage and mediate the direction of plant-soil interactions. Methods: In a meadow steppe, we assessed soil aggregate C storage affected by nitrogen (N) addition and mowing and to what degree plant-soil interactions differed among soil aggregate-size classes. Results: Nitrogen addition increased plant biomass, soil C concentration in macroaggregates and relative abundance of bacteria, but decreased fungal relative abundance and the activity of oxidative enzymes. However, mowing counteracted N effects on plant productivity and enzyme activity. In macroaggregates, close linkages with plant biomass and species richness were found for soil available nutrients and ratio of fungi to bacteria (F:B ratio). In contrast, strong physical protection and restricted fungal dominance and activity contributed to C stabilization in microaggregates, where plant community and soil properties were less linked with each other. Conclusions: Our study clearly demonstrated that stronger plant-soil linkages occurred in macro- vs. microaggregates. This linkage was associated with a rise in plant biomass and soil C accumulation but a drop in F:B ratio in macroaggregates under N addition. [ABSTRACT FROM AUTHOR]

Background and aims: Understanding the influences of environmental variation and anthropogenic disturbance on soil respiration (RS) is critical for accurate prediction of ecosystem C uptake and release. However, surprisingly, little is known about how soil respiration and its components respond to grazing in the context of global climate change (i.e., precipitation or nitrogen deposition increase). Methods: We conducted a field manipulative grazing experiment with water and nitrogen addition treatments in a meadow grassland on the Songnen Plain, China, and assessed the combined influences of grazing and global change factors on RS, autotrophic respiration (RA), and heterotrophic respiration (RH). Results: Compared with the control plots, RS, RA and RH all exhibited positive responses to water or nitrogen addition in the wet year, while a similar effect occurred only for RH in the dry year. The responses of RS to precipitation regimes were dominated by both frequency and amount. However, grazing significantly inhibited both soil respiration and its components in all subplots. Further analysis demonstrated that the plant root/shoot ratio, belowground biomass and microbial biomass played dominant roles in shaping these C exchange processes. Conclusion: These findings suggest that changes in precipitation regimes, nitrogen deposition, and land utilization may significantly alter soil respiration and its component processes by affecting local carbon users (roots and soil microorganism) and carbon substrate supply in meadow steppe grasslands. The future soil carbon sequestration in the studied meadow steppe will be benefited more by the moderate grazing disturbance. [ABSTRACT FROM AUTHOR]

Aims: Determining base cation and trace element dynamics in plant-soil systems is important for sustainable utilization of grasslands affected by global ecosystem nitrogen (N) enrichment. Methods: A 4-year field experiment was conducted with urea addition rates of 0, 2.5, 5, 7.5, 10, 15, 20, and 30 g N m−2 yr.−1 to investigate the dynamics of base cations (Ca, Mg, K) and trace elements (Fe, Mn, Cu and Zn) in soil and a dominant species Leymus chinensis in a semi-arid meadow grassland of northeast China. Results: Soil showed a significant decrease in exchangeable Ca and increases in extractable Fe, Mn and Zn concentrations, while plant Ca and Zn remained unchanged and plant Fe decreased with N addition. For both plant and soil compartments, stoichiometric ratios of trace elements were more variable than base cations, mainly driven by plant physiological requirements, plant nutrient uptake intensity, and elemental interactions. Excessive soil Mn mobilization and plant uptake affected concentrations of Fe, Cu and Zn in the plant and even inhibited Fe absorption (antagonistic interactions), resulting in a plant Fe:Mn ratio lower than 1.5 with high N addition rates, indicating Mn phytotoxicity or Fe deficiency. As a result, plant elemental stoichiometry did not remain homeostatic and was even more variable than in soil. Conclusions: Our results provided direct evidence of decoupled plant-soil elemental responses, stricter homeostatic control of macronutrients than trace elements in plants, and altered stoichiometric variability in the plant-soil system, and suggest that N addition enhances metal nutrient imbalances in the meadow steppe grassland. [ABSTRACT FROM AUTHOR]

Background and aims: Plant breeding usually focuses on conspicuous above-ground plant traits, yet roots fundamentally underpin plant fitness. Roots show phenotypic plasticity in response to soil conditions but it is unclear whether domesticated plants respond like their ancestors. We aimed to determine how root traits differed between ancestral and domesticated types of a meadow grass (Microlaena stipoides) under altered regimes of precipitation and soil silicon availability.Methods: We subjected the two grass types to three simulated precipitation regimes (ambient, +50%/deluge and −50%/drought) in soil with (Si+) and without (Si−) silicon supplementation and then characterised root biomass, architectural complexity and toughness in addition to shoot traits.Results: Domestication increased root tissue density, decreased specific root length (SRL) and decreased root architectural complexity. Domestication also increased root strength under Si− conditions but not Si+ conditions. Fine roots, SRL, architectural complexity and the force required to tear the roots all decreased under deluge. The ancestral and domesticated grasses responded similarly to precipitation, except that the latter had weaker roots (decreased fracture strain) under drought.Conclusions: Domestication and increased precipitation caused changes in M. stipoides root traits that could be beneficial against some stresses (e.g. soil compaction, herbivory) but not others (e.g. drought). [ABSTRACT FROM AUTHOR]

The following articles are part of the Special Issue "Challenges and opportunities in Chinese meadow grasslands: perspectives in a land-use change context" Guest Edited Tang Huajun, Li Linghao and Xin Xiaoping and were inadvertently published in a different issue: Li, H., Li, T., Sun, W. et al. Effects of grazing intensity on soil nematode community structure and function in different soil layers in a meadow steppe. [Extracted from the article]

We conducted a field experiment in two alpine meadows to investigate the short-term effects of nitrogen enrichment and plant litter biomass on plant species richness, the percent cover of functional groups, soil microbial biomass, and enzyme activity in two alpine meadow communities. The addition of nitrogen fertilizer to experimental plots over two growing seasons increased plant production, as indicated by increases in both the living plant biomass and litter biomass in the Kobresia humilis meadow community. In contrast, fertilization had no significant effect on the amounts of living biomass and litter biomass in the K. tibetica meadow. The litter treatment results indicate that litter removal significantly increased the living biomass and decreased the litter biomass in the K. humilis meadow; however, litter-removal and litter-intact treatments had no impact on the amounts of living biomass and litter biomass in the K. tibetica meadow. Litter production depended on the degree of grass cover and was also influenced by nitrogen enrichment. The increase in plant biomass reflects a strong positive effect of nitrogen enrichment and litter removal on grasses in the K. humilis meadow. Neither fertilization nor litter removal had any impact on the grass biomass in the K. tibetica meadow. Sedge biomass was not significantly affected by either nutrient enrichment or litter removal in either alpine meadow community. The plant species richness decreased in the K. humilis meadow following nitrogen addition. In the K. humilis meadow, microbial biomass C increased significantly in response to the nitrogen enrichment and litter removal treatments. Enzyme activities differed depending on the enzyme and the different alpine meadow communities; in general, enzyme activities were higher in the upper soil layers (0–10 cm and 10–20 cm) than in the lower soil layers (20–40 cm). The amounts of living plant biomass and plant litter biomass in response to the different treatments of the two alpine meadow communities affected the soil microbial biomass C, soil organic C, and soil fertility. These results suggest that the original soil conditions, plant community composition, and community productivity are very important in regulating plant community productivity and microbial biomass and activity. [ABSTRACT FROM AUTHOR]

Few studies have examined plant–soil relationships in competitive arenas between exotic and native plants in the western United States. A pair-wise competitive design was used to evaluate plant–soil relationships between seedlings of the exotic annual grasses Bromus tectorum and Taeniatherium caput-medusae and the native perennial grasses Elymus elymoides and Pseudoroegneria spicata. Two soils were tested: an arid soil (argid) occupied by E. elymoides and presently invaded by B. tectorum and a high elevation, high organic matter, soil (aquept) where none of the tested species would typically occur. Plant growth proceeded for 85 days at which time above-ground biomass and tissue nutrient concentrations were quantified. Soil also was collected from the rooting zone beneath each species and analyzed for various nutrient pools. The exotic species had significantly greater above-ground biomass than the natives and grew far better in the aquept soil than the argid soil. Growth of B. tectorum, and to some degree, T. caput-medusae was suppressed in intraspecific competition and enhanced, especially in the aquept soil, when competing with the natives. Although not significant, biomass of natives strongly trended downward when competing with the exotic grasses. Overall, concentrations of tissue nutrients were minimally affected by competition, but natives tended to be more negatively affected by competition with exotics. Except for phosphorus (P), all species had significantly greater nutrient concentrations when growing in the aquept soil compared to the argid soil. In both soils, exotics had significant greater tissue concentrations of manganese (Mn), magnesium (Mg), and iron (Fe), while natives had significantly greater nitrogen (N). Species affects on soil nutrient pools occurred mostly in the aquept soil with exotic species significantly decreasing pools of available N, potentially available N, and soil-solution pools of calcium (Ca2+), potassium (K+), and magnesium (Mg2+) relative to natives. Overall, the data suggest that, in the seedling state, B. tectorum is a superior competitor. Moreover, when the natives compete intra- or interspecifically, particularly in the aquept soil, availability of N and other nutrients in their rooting zone is consistently greater than when they compete interspecifically with the exotic grasses. These data suggest the exotics are able to co-opt nutrients in the rooting zone of the natives and perhaps gain a competitive advantage. [ABSTRACT FROM AUTHOR]

Rates and patterns of nitrogen transformation differ in divergently managed pasture soils. In pastures with low nutrient inputs, N is utilized efficiently and it is assimilated by plants and soil microorganisms for synthesis of biomass. In more intensive pastures, characterized with higher N inputs, significant amounts of N can be lost from the ecosystem in various forms. Two soils of a cattle overwintering area with different levels of cattle disturbance were supplied with a solution of KNO3 in various levels corresponding in range to 0–500 kg N ha−1. Emissions of N2O were measured during 24 h after a NO3 −-N application. We hypothesized that under a low disturbance small additions of up to 5 kg NO3 −-N are used by plants and soil microbes without an increase in N2O emissions, while a pasture adapted to a moderate disturbance will increase N2O emissions. Results showed that in both soils, the addition of N always increased N2O emissions, while emissions were more pronounced in soil at the location with a higher intensity of cattle traffic. Contrary to our hypothesis, however, NO3 ––N was not fully metabolized in the soil with low disturbance by the cattle. Probable explanations of such a result were lower intensity of N transformations in this soil and low utilisation of N by grass. Our results suggest that under certain conditions relatively low nitrate-N inputs can also stimulate N2O fluxes from soils. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) emission was measured in a Kobresia humilis meadow and a Potentilla fruticosa meadow in the Qinghai–Tibet Plateau from June 2003 to July 2006. Five treatments were setup in the two alpine meadows. Two bare soil treatments were setup in the K. humilis meadow (BSK) and in the P. fruticosa meadow (BSP) by removing the above- and belowground plant biomass. Three plant community treatments were setup with one in the K. humilis meadow (herbaceous community in the K. humilis meadow-HCK) and two in the P. fruticosa meadow (herbaceous community in the P. fruticosa meadow-HCP, and shrub community in the P. fruticosa meadow-SCP). Nitrous oxide emission from BSP was estimated to be 38.1 ± 3.6 μg m−2 h−1, significantly higher than from BSK (30.2 ± 2.8 μg m−2 h−1) during the whole experiment period. Rates from the two herbaceous blocks (HCK and HCP) were close to 39.5 μg m−2 h−1 during the whole experimental period whereas shrub community (SCP) showed significant high emission rates of N2O. Annual rate of N2O emission was estimated to be 356.7 ± 8.3 and 295.0 ± 11.6 mg m−2 year−1 from the alpine P. fruticosa meadow and from the alpine K. humilis meadow, respectively. These results suggest that alpine meadows in the Qinghai–Tibetan Plateau are an important source of N2O, contributing an average of 0.3 Tg N2O year−1. We concluded that N2O emission will decrease, due to a predicted vegetation shift from shrubs to grasses imposed by overgrazing. [ABSTRACT FROM AUTHOR]

Root hemiparasites like Rhinanthus angustifolius C.C. Gmel and R. minor L. have a potential to accelerate the restoration of semi-natural grasslands because they may decrease above-ground biomass of the vegetation. This, in turn, may be beneficial for species diversity. It is known that hemiparasites often accumulate high nutrient concentrations in their above-ground parts, resulting in high quality litter. Because of the short life cycle of many parasitic plants, litter is released early in the season and the main part is not removed from the grassland by hay-making. This has been shown to yield an increased nutrient availability locally. We performed an introduction experiment with R. angustifolius and R. minor in three semi-natural grasslands in Flanders (Belgium). In the second year after sowing, the above-ground nitrogen (N) content of the grasses and of the potential host vegetation (excluding the hemiparasite), was increased in the parasitized plots. The reduction of grass (and legume) above-ground biomass in parasitized plots resulted in a decrease in the total above-ground N uptake of grasses, host and total vegetation (ex- and including the parasite, respectively) of the parasitized plots compared to the control. Furthermore, with a tracer experiment (15N), we demonstrated that the N from the added tracer was relatively less available in parasitized plots, suggesting larger soil N pools in these treatments. This is probably the consequence of increased mineralization, resulting from the high-quality, parasitic litter. Further experiments should be conducted to investigate the impact of hemiparasitic Rhinanthus spp., e.g. on the availability of other nutrients such as phosphorus. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine whether a planted mesocosm mimics a natural habitat in terms of N2O and CH4 fluxes, soil characteristics and potential nitrification and denitrification activities. We compared mesocosms in unchambered open-field plots and in open-top chambers with nonfiltered ambient air with three natural meadows that had similar soil characteristics and species composition. The N2O fluxes in the mesocosms were very similar to the fluxes in the three natural meadows. There were no marked differences in potential nitrification and denitrification activities between the mesocosms and the natural meadows, either. Only the CH4 fluxes differed slightly between the mesocosms and some of the natural meadows. Therefore, it seems that the mesocosms compared rather well to natural habitats. The open-top chambers modified only the soil water content, the values being higher in the unchambered plots than in the chambered plots. These results thus suggest that the open-top chamber experiment enables estimates of greenhouse gas and potential activities of nitrifying and denitrifying bacteria in unfertilized Finnish meadows, in spite of the chamber effects on the soil water content. [ABSTRACT FROM AUTHOR]

Nitrogen acquisition is one of the most important factors for plant production, and N contribution from biological N2 fixation can reduce the need for industrial N fertilizers. Perennial forages are widespread in temperate and boreal areas, where much of the agriculture is based on livestock production. Due to the symbiosis with N2-fixing rhizobia, perennial forage legumes have great potential to increase sustainability in such grassland farming systems. The present work is a summary of a large number of studies investigating N2 fixation in three perennial forage legumes primarily relating to ungrazed northern temperate/boreal areas. Reported rates of N2 fixation in above-ground plant tissues were in the range of up to 373 kg N ha-1 year-1 in red clover (Trifolium pratense L.), 545 kg N ha-1 year-1 in white clover (T. repens L.) and 350 kg N ha-1 year-1 in alfalfa ( Medicago sativa L.). When grown in mixtures with grasses, these species took a large fraction of their nitrogen from N2 fixation (average around 80%), regardless of management, dry matter yield and location. There was a large variation in N2 fixation data and part of this variation was ascribed to differences in plant production between years. Studies with experiments at more than one site showed that also geographic location was an important source of variation. On the other hand, when all data were plotted against latitude, there was no simple correlation. Climatic conditions seem therefore to give as high N2 fixation per ha and year in northern areas (around 60°N) as in areas with a milder climate (around 40°N). Analyzing whole plants or just above-ground plant parts influenced the estimate of N2 fixation, and most reported values were underestimated since roots were not included. Despite large differences in environmental conditions, such as N fertilization and geographic location, N2 fixation (Nfix; kg N per ha and year) was significantly (P<0.001) correlated to legume dry matter yield (DM; kg per ha and year). Very rough, but nevertheless valuable estimations of Nfix in legume/grass mixtures (roots not considered) are given by Nfix = 0.026ċDM + 7 for T. pratense, Nfix = 0.031ċDM + 24 for T. repens, and Nfix = 0.021ċDM + 17 for M. sativa. [ABSTRACT FROM AUTHOR]