Unfertilized Plots Research Articles

Aboveground biomass and root/shoot ratio regulated drought susceptibility of ecosystem carbon exchange in a meadow steppe

Nitrogen deposition and altered precipitation regime are likely to change plant growth, biomass allocation and community structure, which may influence susceptibility of ecosystem functions (i.e. ecosystem carbon exchange) to extreme climatic events, such as drought. In a meadow steppe, we deployed a drought treatment on a long-term water and nitrogen addition experiment to investigate resource abundance changes induced variation in the sensitivity of ecosystem carbon exchange to extreme drought. Compared to the control plots, long-term water and nitrogen addition caused a strong increase in biomass, and a reduction in diversity and root/shoot ratio. Net ecosystem CO2 exchange (NEE) in water and nitrogen addition plots were more sensitive to drought stress than the control plots. The enhanced NEE drought sensitivity (SNEE) in nitrogen fertilization habitat is associated with changes in aboveground biomass and root/shoot ratio, rather than variation in species diversity, while SNEE in the unfertilized plots was controlled by root/shoot ratio. Compared to the water and nitrogen addition plots, the control plots had the highest percentage recovery of ecosystem carbon exchange (RNEE) during the rehydration period. RNEE is likely determined by aboveground biomass and level of damage in the photosynthetic organ. These findings suggest that long-term changes in precipitation regimes and nitrogen deposition may significant alter the susceptibility of key ecosystem processes to drought stress.

УРОЖАЙНІСТЬ ПШЕНИЦІ ОЗИМОЇ ЗАЛЕЖНО ВІД СИСТЕМ ОСНОВНОГО ОБРОБІТКУ ҐРУНТУ ТА УДОБРЕННЯ

УРОЖАЙНІСТЬ ПШЕНИЦІ ОЗИМОЇ ЗАЛЕЖНО ВІД СИСТЕМ ОСНОВНОГО ОБРОБІТКУ ҐРУНТУ ТА УДОБРЕННЯ

Facultative bacterial endosymbionts shape parasitoid food webs in natural host populations: A correlative analysis

Facultative bacterial endosymbionts can protect their aphid hosts from natural enemies such as hymenopteran parasitoids. As such, they have the capability to modulate interactions between aphids, parasitoids and hyperparasitoids. However, the magnitude of these effects in natural aphid populations and their associated parasitoid communities is currently unknown. Moreover, environmental factors such as plant fertilization and landscape complexity are known to affect aphid–parasitoid interactions but it remains unclear how such environmental factors affect the interplay between aphids, parasitoids and endosymbionts.Here, we tested whether facultative endosymbionts confer protection to parasitoids in natural populations of the English grain aphid, Sitobion avenae, and if this is affected by plant fertilization and landscape complexity. Furthermore, we examined whether the effects of facultative endosymbionts can cascade up to the hyperparasitoid level and increase primary‐hyperparasitoid food web specialization.Living aphids and mummies were collected in fertilized and unfertilized plots within 13 wheat fields in Central Germany. We assessed the occurrence of primary parasitoid, hyperparasitoid and endosymbiont species in aphids and mummies using a newly established molecular approach.Facultative endosymbiont infection rates were high across fields (~80%), independent of whether aphids were parasitized or unparasitized. Aphid mummies exhibited a significantly lower share of facultative endosymbiont infection (~38%). These findings suggest that facultative endosymbionts do not affect parasitoid oviposition behaviour, but decrease parasitoid survival in the host. Facultative endosymbiont infection rates were lower in mummies collected from fertilized compared to unfertilized plants, indicating that plant fertilization boosts the facultative endosymbiont protective effect. Furthermore, we found strong evidence for species‐specific and negative cascading effects of facultative endosymbionts on primary and hyperparasitoids, respectively. Facultative endosymbionts impacted parasitoid assemblages and increased the specialization of primary‐hyperparasitoid food webs: these effects were independent from and much stronger than other environmental factors.The current findings strongly suggest that facultative endosymbionts act as a driving force in aphid–parasitoid–hyperparasitoid networks: they shape insect community composition at different trophic levels and modulate, directly and indirectly, the interactions between aphids, parasitoids and their environment.

English

The NP fertilizer or organic resources alone may not provide sufficient amounts or may be unsuitable for alleviating specific constraints to crop production. Therefore, a field experiment was conducted at Maitsebri Research Station of Shire-Maitsebri Agricultural Research Center (SMARC) to study the effect of inorganic NP fertilizers and vermicompost on growth, seed yield and yield components of red onion (Allium cepa L.) variety during 2016/17 dry season under irrigation. The treatments consisted of five NP fertilizer rates {0, 25, 50, 75 and 100% of recommended NP rates (69 kg N and 92 kg P2O5 ha-1)} and four rates of vermicompost (0, 2.5, 5.0, 7.5 t ha-1). The experiment was laid out in a factorial arrangement using randomized complete block design (RCBD) with three replications. Results of the analysis revealed that the interaction effects on inorganic NP fertilizer and vermicompost significantly (P<0.05) affected plant height. Days to bolting, days to 50% flowering, flower stalk diameter and days to maturity were significantly (P<0.05) affected by the main effect of NP fertilizer rates and vermicompost. Similarly, numbers of umbels per plant, umbel diameter, number of seeds per umbel and seed weight per umbel were significantly affected by the main effect of NP fertilizer rates and vermicompost. The highest seed yield per hectare (1462.5 kg ha-1) was obtained from the plants grown at 75% of RDF with vermicompost at 2.5 t ha-1 which was about 263% higher than seed yield from unfertilized control plot. It can, thus, be concluded that the combined application of 75% of RDF with vermicompost at 2.5 t ha-1can improve growth, seed yield and yield components of Bombay red onion variety in the study area. Key words: Growth, onion, NP fertilizers, parameters, seed yield, vermicompost.

Why does mineral fertilization increase soil carbon stocks in temperate grasslands?

Globally, grasslands are a major land cover type and store significant amounts of soil organic carbon (SOC). Fertilization with the major plant nutrients nitrogen (N), phosphorus (P), and potassium (K) may affect SOC stocks, e.g., by altering aboveground and belowground plant productivity, species composition, litter composition and decomposition, and microbial metabolism. However, belowground responses to fertilization in grasslands are not fully understood, hampering accurate predictions of SOC dynamics. In this study, seven different long-term grassland fertilization experiments (16–58 years) in Germany and the Netherlands were sampled to determine the effects of mineral fertilization (i.e., N, P, K, PK, and NPK) compared with unfertilized plots (Control) on SOC stocks and root C stocks. Soils were sampled to a depth of 100 cm or to the maximum depth possible. Potential litter decomposition was assessed using Lipton Rooibos and Lipton Green teas as standardized and well-characterized litter materials. In the topsoil (0–30 cm depth), PK, NPK, and NPK+ (increased NPK) fertilization had significant positive effects on SOC stocks, with annual sequestration rates of 0.28, 0.13, and 0.37 Mg ha−1 yr−1, respectively, within an average time span of 34 (PK, NPK) or 20 (NPK+) years. For NPK fertilization, 1.15 kg of N was needed to sequester 1 kg SOC. Increased SOC stocks could not be explained by altered belowground C inputs or decomposition rates, since root C stocks were not affected by fertilization and potential litter decomposition was unchanged. The highly significant increases in dry matter yield with PK and NPK fertilization and resulting higher aboveground C inputs were also unlikely to explain the observed SOC stock changes, since increases were only observed at soil depths >10 cm. However, significantly narrower root C:N ratios were observed for the N (26.9), PK (36.5), NPK (36.8), and NPK+ (33.2) treatments than for the Control (41.8), which may have caused increased microbial C use efficiency, positively affecting SOC storage. The narrower C:N ratios in PK treatments were explained by significantly increased abundance of legumes. We concluded that the carbon footprint of fertilization-induced SOC sequestration needs to be considered when the latter should be accounted for as a climate mitigation measure. Thereby, PK fertilization has much lower CO2 costs than NPK fertilization due to N input via legumes.

Seasonality promotes grassland diversity: Interactions with mowing, fertilization and removal of dominant species

Abstract Current biodiversity declines in species‐rich grasslands are connected with the cessation of management, eutrophication and the expansion of dominant grass species. One of the theoretical mechanisms limiting biodiversity loss is the ability of subordinate species to avoid competitive exclusion by seasonal niche separation from dominant species. Here, we explore how seasonality underpins the maintenance of diversity in temperate meadows under different management regimes and competition intensities in relation to species functional traits. We studied eight different communities in a long‐term meadow experiment that manipulated mowing, fertilization and dominant species (Molinia caerulea) removal. In each community, species‐specific trait and biomass data were taken five times during the year to test whether seasonal variation in species composition and functional strategies enable species to coexist. Mown unfertilized meadows exhibited pronounced seasonal variations in community composition and structure, linked to differences in resource‐use strategies between mid‐summer dominants and the spring and autumn subordinates. Higher specific leaf area and foliar nitrogen concentration in the fast‐growing dominants, and increased water use (δ13C) and nutrient acquisition (δ15N) efficiency in resource‐retentive subordinates, best predicted their temporal niche separation. Seasonal segregation of species with contrasting strategies increased after mowing cessation, and the resulting summer dominance of Molinia. Conversely, the seasonal dynamics were markedly reduced by fertilization, promoting tall grasses over sedges and forbs throughout the entire year, thereby decreasing the overall taxonomic and functional diversity. When Molinia was removed the compositional changes during the season became less pronounced, being significant only in mown unfertilized plots. Synthesis. Seasonal shifts in community composition reduced the competitive interactions and promoted the coexistence of dominant and subordinate species. Seasonality reversed the negative mid‐summer diversity‐productivity relationship with a positive one during the spring and autumn, and seasonality only prevented diversity loss in unfertilized conditions possibly because competition is most intense in summer. In fertilized meadows, subordinate species are not able to escape competitive exclusion by shifting their phenological peaks to the spring or autumn periods because asymmetric competition is intense over the entire growing season. Studying seasonal dynamics is key to understanding the maintenance of grassland diversity under ongoing land use change.

Impacts of surface-applied residues on N-cycling soil microbial communities in miscanthus and switchgrass cropping systems

The production of biomass crops such as the perennial grasses (PGs) miscanthus (Miscanthus spp.) and switchgrass (Panicum virgatum L.) has increased considerably. The repeated annual harvest of aboveground PG biomass removes organic inputs from the soil and may influence soil health and soil microbial communities, which drive terrestrial nitrogen (N) cycling, influencing the ecosystem services provided by these feedstock systems. Our objective was to assess soil bacterial N-cycling communities as influenced by the return or removal of aboveground plant biomass (residues) to soils in PG biomass feedstock systems at different N fertilization (0 or 160 kg N ha−1) rates. Soil was collected from a field trial and quantitative PCR was used to enumerate bacterial 16S rRNA and denitrifying (nirS and nosZ) genes and transcripts. Denitrifier gene expression (nirS and nosZ) was significantly higher in N-fertilized compared to unfertilized plots, indicating that applying fertilizer in these systems may shift the activity of the denitrifying populations and possibly lead to associated N losses with no return in yield. Returning biomass residues resulted in significantly higher nosZ transcripts than in soils with residues removed but did not influence nirS gene expression. The removal of plant residues in these systems may influence the activity of the nitrous-oxide reducing microbial community, resulting in potential changes in the ecosystem services moderated by soil microbial communities, which may need to be incorporated into future soil health assessments of bioenergy feedstock systems.

Trichoderma-Based Biostimulants Modulate Rhizosphere Microbial Populations and Improve N Uptake Efficiency, Yield, and Nutritional Quality of Leafy Vegetables.

Microbial inoculants such as Trichoderma-based products are receiving great interest among researchers and agricultural producers for their potential to improve crop productivity, nutritional quality as well as resistance to plant pathogens/pests and numerous environmental stresses. Two greenhouse experiments were conducted to assess the effects of Trichoderma-based biostimulants under suboptimal, optimal and supraoptimal levels of nitrogen (N) fertilization in two leafy vegetables: Iceberg lettuce (Lactuca sativa L.) and rocket (Eruca sativa Mill.). The yield, nutritional characteristics, N uptake and mineral composition were analyzed for each vegetable crop after inoculation with Trichoderma strains T. virens (GV41) or T. harzianum (T22), and results were compared to non-inoculated plants. In addition, the effect of the Trichoderma-based biostimulants on microbes associated with the rhizosphere in terms of prokaryotic and eukaryotic composition and concentration using DGGE was also evaluated. Trichoderma-based biostimulants, in particular GV41, positively increased lettuce and rocket yield in the unfertilized plots. The highest marketable lettuce fresh yield was recorded with either of the biostimulant inoculations when plants were supplied with optimal levels of N. The inoculation of rocket with GV41, and to a lesser degree with T22, elicited an increase in total ascorbic acid under both optimal and high N conditions. T. virens GV41 increased N-use efficiency of lettuce, and favored the uptake of native N present in the soil of both lettuce and rocket. The positive effect of biostimulants on nutrient uptake and crop growth was species-dependent, being more marked with lettuce. The best biostimulation effects from the Trichoderma treatments were observed in both crops when grown under low N availability. The Trichoderma inoculation strongly influenced the composition of eukaryotic populations in the rhizosphere, in particularly exerting different effects with low N levels in comparison to the N fertilized plots. Overall, inoculations with Trichoderma may be considered as a viable strategy to manage the nutrient content of leafy horticulture crops cultivated in low fertility soils, and assist vegetable growers in reducing the use of synthetic fertilizers, developing sustainable management practices to optimize N use efficiency.

Agronomic effects of biochar and wastewater irrigation in urban crop production of Tamale, northern Ghana

Agricultural production needs to increase, particularly in sub-Saharan Africa, many rural people are undernourished, and the urban population is growing rapidly. It is worrisome that on many West African soils with low cation exchange capacity and soil organic carbon content, mineral fertilization is rather inefficient. Under these conditions, wherever available untreated wastewater is used for irrigation despite the potential health risks to producers and consumers. For intensively cultivated soils with high mineralization rates, biochar application has been advocated as a promising management option. However, the agronomic benefits of wastewater reuse in agriculture and its interaction with biochar have received only limited attention. This study therefore investigated the effects of mineral fertilizer application and biochar amendment at two water quality and quantity levels on soil moisture, plant nutrition and biomass production on a Petroplinthic Cambisol over 2 years. Rice husk biochar applied at 20 t ha−1 significantly increased fresh matter yields in the first five cropping cycles by 15%, and by 9% by the end of 2 years. Compared with clean water, wastewater irrigation increased yields 10–20-fold on unfertilized plots during the dry seasons, while a fourfold increment was observed in the wet seasons. This seasonal difference is likely a result of the high sequence of irrigation events during the dry season. In this study, fertigation with wastewater contributed significantly to plant nutrition and nutrient recovery while yield-increasing biochar effects disappeared over time. Soil moisture was enhanced by up to 9% due to biochar amendments under unfertilized conditions.

Nitrous Oxide Emissions from Turfgrass Receiving Different Irrigation Amounts and Nitrogen Fertilizer Forms

Nitrous oxide is an important greenhouse gas associated with global climate change. Turfgrasses emit N2O when fertilized with N and irrigated. The development of management practices such as use of controlled‐release N fertilizers and/or deficit irrigation may reduce N2O emissions in turf soils. The objectives of this study were (i) to quantify the magnitude and patterns of N2O emissions in turfgrass, and (ii) to determine how irrigation and N fertilization may be managed to reduce N2O fluxes. Nitrous oxide emissions were measured for 2 yr in ‘Meyer’ zoysiagrass (Zoysia japonica Steud.) under an automated rainout shelter in Manhattan, KS, using static chambers. Two irrigation levels (66 [medium] and 33% [low] reference evapotranspiration replacement), and three N fertilization treatments (urea and polymer‐coated urea [PCU], both applied at a rate of 98 kg N ha−1 yr−1, and an unfertilized plot) were included. During two summers, N2O emissions were reduced by 6% with low (2.71 kg ha−1) vs. medium irrigation (2.88 kg ha−1) (P ≤ 0.001). Over the 2 yr, cumulative N2O emissions averaged 4.06 kg ha−1 in unfertilized turf and 4.5 kg ha−1 in PCU‐treated turf, which represent reductions of 28 and 20%, respectively, from urea‐treated turf (5.62 kg ha−1) (P ≤ 0.01). Results from this study indicate that the use of a controlled‐release fertilizer, such as PCU, and/or lower irrigation reduces N2O emissions in turfgrass.

Long-term nutrient addition increases respiration and nitrous oxide emissions in a New England salt marsh.

Salt marshes may act either as greenhouse gas (GHG) sources or sinks depending on hydrological conditions, vegetation communities, and nutrient availability. In recent decades, eutrophication has emerged as a major driver of change in salt marsh ecosystems. An ongoing fertilization experiment at the Great Sippewissett Marsh (Cape Cod, USA) allows for observation of the results of over four decades of nutrient addition. Here, nutrient enrichment stimulated changes to vegetation communities that, over time, have resulted in increased elevation of the marsh platform. In this study, we measured fluxes of carbon dioxide (CO 2), methane (CH 4) and nitrous oxide (N2O) in dominant vegetation zones along elevation gradients of chronically fertilized (1,572 kg N ha−1 year−1) and unfertilized (12 kg N ha−1 year−1) experimental plots at Great Sippewissett Marsh. Flux measurements were performed using darkened chambers to focus on community respiration and excluded photosynthetic CO 2 uptake. We hypothesized that N‐replete conditions in fertilized plots would result in larger N2O emissions relative to control plots and that higher elevations caused by nutrient enrichment would support increased CO 2 and N2O and decreased CH 4 emissions due to the potential for more oxygen diffusion into sediment. Patterns of GHG emission supported our hypotheses. Fertilized plots were substantially larger sources of N2O and had higher community respiration rates relative to control plots, due to large emissions of these GHGs at higher elevations. While CH 4 emissions displayed a negative relationship with elevation, they were generally small across elevation gradients and nutrient enrichment treatments. Our results demonstrate that at decadal scales, vegetation community shifts and associated elevation changes driven by chronic eutrophication affect GHG emission from salt marshes. Results demonstrate the necessity of long‐term fertilization experiments to understand impacts of eutrophication on ecosystem function and have implications for how chronic eutrophication may impact the role that salt marshes play in sequestering C and N.

Effect of Sodic Irrigation Water on Organic Carbon and Nitrogen Concentrations, Fluxes and Exports from Newly Installed St. Augustine Grass Sod in South-Central Texas

Population growth in towns and cities requires new construction of homes and conversion of native land use to urban and suburban landscapes. Municipal tap water is generally used for irrigating these urban and suburban landscapes and its water quality can differ globally dependent on whether it is sourced from ground or surface waters. We examined runoff dissolved organic carbon (DOC) and organic nitrogen (DON) concentrations, fluxes and exports from newly installed, fertilized and unfertilized St. Augustine (Stenotaphrum secundatum (Walt.) Kuntze ‘Raleigh’) sod irrigated with a sodic municipal tap water during two 5-week establishment periods (August and September). In unfertilized plots, concentrations of DOC in runoff significantly increased from 20.5 to 73.7 mg L-1 and from 29.6 to 113.3 mg L-1 Runoff concentrations of DOC in fertilized plots significantly increased from 27.3 to 72.0 mg L-1 and from 30.0 to 120.3 mg L-1. Concentrations of DON in runoff did not increase in either unfertilized or fertilized plots. Total DOC exports were 2036 ± 803 kg km-2 and 3341 ± 227 kg km-2 and DON exports were 99 ± 43 kg km-2 and 134 ± 15 kg km-2 respectively for the two turfgrass installation dates for the unfertilized plots. Fertilization had no significant effect on DOC and DON exports (p = 0.29 and 0.18). Na+, K+, Mg2+ and Ca2+ were implicated in both DOC and DON fluxes suggesting that as resources for irrigation water for urban landscapes decline and alternative irrigation water supplies such as grey and black water are utilized we would expect, due to their higher Na+ content that DOC and DON fluxes to urban watersheds will increase.

Low-intensity management promotes bryophyte diversity in grasslands

Bryophytes constitute an important and permanent component of the grassland flora and diversity in Europe. As most bryophyte species are sensitive to habitat change, their diversity is likely to decline following land-use intensification. Most previous studies on bryophyte diversity focused on specific habitats of high bryophyte diversity, such as bogs, montane grasslands, or calcareous dry grasslands. In contrast, mesic grasslands are rarely studied, although they are the most common grassland habitat in Europe. They are secondary vegetation, maintained by agricultural use and thus, are influenced by different forms of land use. We studied bryophyte species richness in three regions in Germany, in 707 plots of 16 m2 representing different land-use types and environmental conditions. Our study is one of the few to inspect the relationships between bryophyte richness and land use across contrasting regions and using a high number of replicates.Among the managed grasslands, pastures harboured 2.5 times more bryophyte species than mead-ows and mown pastures. Similarly, bryophyte cover was about twice as high in fallows and pastures than in meadows and mown pastures. Among the pastures, bryophyte species richness was about three times higher in sheep grazed plots than in the ones grazed by cattle or horses. In general, bryophyte species richness and cover was more than 50% lower in fertilized than in unfertilized plots. Moreover, the amount of suitable substrates was linked to bryophyte diversity. Species richness of bryophytes growing on stones increased with stone cover, and the one of bryophytes growing on bark and deadwood increased with larger values of woody plant species and deadwood cover. Our findings highlight the importance of low-intensity land use and high structural heterogeneity for bryophyte conservation. They also caution against an intensification of traditionally managed pastures. In the light of our results, we recommend to maintain low-intensity sheep grazing on sites with low productivity, such as slopes on shallow soils.

Responses of herbage yield and soil phosphorus fractions to phosphorus fertilisation on a degraded arid steppe

Low plant-available phosphorus (P) in degraded arid steppes greatly limits plant yields. However, whether exterior P addition will improve the soil P availability and thus increase plant yield in these degraded arid steppes is still not certain. In the current study, a severely degraded arid steppe in Inner Mongolia, China, with soil-available P &lt;5 mg/kg, was fertilised annually with chemical or manure P for two years (2014, dry year; 2015, wet year). There were six fertilisation treatments: 0, 30 kg P/ha, 60 kg P/ha, 90 kg P/ha, 4000 kg sheep manure/ha (equalling 16.4 kg P/ha) and 8000 kg sheep manure/ha (32.8 kg P/ha). A pot experiment with Stipa krylovii (the dominant plant species in the tested steppe) and five P application rates (0, 30, 60, 90 and 120 kg P/ha) was also conducted, under well-watered and nitrogen-fertilised conditions, using surface soils from unfertilised plots in the field. Results indicated that the tested soils had strong P adsorption capacity and weaker desorption capacity, and that the labile P fractions were quickly transformed into less labile fractions, reducing P availabilities. Overall, chemical P fertiliser resulted in the accumulation of Ca10-P and occluded P, whereas sheep manure resulted in the accumulation of moderately resistant organic P and highly resistant organic P. Phosphorus fertilisation was associated with an increase in plant P concentrations in both 2014 and 2015, and a low P rate (30 kg P/ha in the current study) was able to improve the aboveground biomass in both the field experiment in the wet year and the pot experiment under well-watered conditions. Thus, in degraded arid steppes, P fertilisation may be unnecessary in dry years. A low rate of P fertilisation is recommended in wet years to improve soil P status and steppe plant productivity.

Low-intensity management promotes bryophyte diversity in grasslands

Bryophytes constitute an important and permanent component of the grassland flora and diversity in Europe. As most bryophyte species are sensitive to habitat change, their diversity is likely to decline following land-use intensification. Most previous studies on bryophyte diversity focused on specific habitats of high bryophyte diversity, such as bogs, montane grasslands, or calcareous dry grasslands. In contrast, mesic grasslands are rarely studied, although they are the most common grassland habitat in Europe. They are secondary vegetation, maintained by agricultural use and thus, are influenced by different forms of land use. We studied bryophyte species richness in three regions in Germany, in 707 plots of 16 m2 representing different land-use types and environmental conditions. Our study is one of the few to inspect the relationships between bryophyte richness and land use across contrasting regions and using a high number of replicates.Among the managed grasslands, pastures harboured 2.5 times more bryophyte species than mead-ows and mown pastures. Similarly, bryophyte cover was about twice as high in fallows and pastures than in meadows and mown pastures. Among the pastures, bryophyte species richness was about three times higher in sheep grazed plots than in the ones grazed by cattle or horses. In general, bryophyte species richness and cover was more than 50% lower in fertilized than in unfertilized plots. Moreover, the amount of suitable substrates was linked to bryophyte diversity. Species richness of bryophytes growing on stones increased with stone cover, and the one of bryophytes growing on bark and deadwood increased with larger values of woody plant species and deadwood cover. Our findings highlight the importance of low-intensity land use and high structural heterogeneity for bryophyte conservation. They also caution against an intensification of traditionally managed pastures. In the light of our results, we recommend to maintain low-intensity sheep grazing on sites with low productivity, such as slopes on shallow soils.

Stabilizing effects in temporal fluctuations: management, traits, and species richness in high‐diversity communities

The loss of biodiversity is thought to have adverse effects on multiple ecosystem functions, including the decline of community stability. Decreased diversity reduces the strength of the portfolio effect, a mechanism stabilizing community temporal fluctuations. Community stability is also expected to decrease with greater variability in individual species populations and with synchrony of their fluctuations. In semi-natural meadows, eutrophication is one of the most important drivers of diversity decline; it is expected to increase species fluctuations and synchrony among them, all effects leading to lower community stability. With a 16-year time series of biomass data from a temperate species-rich meadow with fertilization and removal of the dominant species, we assessed population biomass temporal (co)variation under different management types and competition intensity, and in relation to species functional traits and to species diversity. Whereas the effect of dominant removal was relatively small (with a tendency toward lower stability), fertilization markedly decreased community stability (i.e., increased coefficient of variation in the total biomass) and species diversity. On average, the fluctuations of individual populations were mutually independent, with a slight tendency toward synchrony in unfertilized plots, and a tendency toward compensatory dynamics in fertilized plots and no effects of removal. The marked decrease of synchrony with fertilization, contrary to the majority of the results reported previously, follows the predictions of increased compensatory dynamics with increased asymmetric competition for light in a more productive environment. Synchrony increased also with species functional similarity stressing the importance of shared ecological strategies in driving similar species responses to weather fluctuations. As expected, the decrease of temporal stability of total biomass was mainly related to the decrease of species richness, with its effect remaining significant also after accounting for fertilization. The weakening of the portfolio effect with species richness decline is a crucial driver of community destabilization. However, the positive effect of species richness on temporal stability of total biomass was not due to increased compensatory dynamics, since synchrony increased with species richness. This shows that the negative effect of eutrophication on community stability does not operate through increasing synchrony, but through the reduction of diversity.

Potassium fertilisation reduces radiocesium uptake by Japanese cypress seedlings grown in a stand contaminated by the Fukushima Daiichi nuclear accident

We analysed suppressive effects of potassium (K) fertilisation on radiocesium (137Cs) uptake by hinoki cypress (Chamaecyparis obtusa) seedlings from soils contaminated after the Fukushima Daiichi Nuclear Power Plant accident. Three-year-old seedlings were planted in a clear-cut forest (ca. 4 ha) during June–July 2014, and potassium chloride fertiliser (83 kg K ha−1) was applied twice (August 2014 and April 2015). 137Cs concentrations in the needles in the fertilised plots were one-eighth of those in the control (unfertilised) plots at the end of the second growing season (October 2015). Our results clearly indicated that K fertilisation reduced radiocesium transfer from soil to planted cypress seedlings. A linear mixed model analysis revealed that 137Cs concentrations in the needles were significantly affected by 137Cs inventory in the soil (Bq m−2) adjacent to the sampled seedlings, exchangeable K concentrations in surface mineral soils (0–5 cm) and fertilisation. The exchangeable K concentrations in surface soils in October 2015 did not differ from those in August 2014 (before fertilisation) in the fertilised plots and in the control plots. These results suggested that the levels of exchangeable K would temporarily increase by fertilisation during the growing season, and radiocesium uptake by tree roots was suppressed.

Leaf, canopy and agronomic water‐use efficiency of field‐grown sugar beet in response to potassium fertilization

AbstractPotassium (K) fertilization is important to maintain adequate concentrations of plant available K in agricultural soils to achieve best yields and improve crop stress tolerance and water‐use efficiency (WUE). Water‐use efficiency (WUE) can be expressed on various spatiotemporal scales, and it is known that responses of WUE to external stress are not uniform across scales. Multiscale evaluations of the impact of varying K fertilization on the WUE of C3 crops under field conditions are missing so far. In the present field study, we evaluated effects of K fertilization on WUE of sugar beet (Beta vulgaris L.) on short‐termed leaf‐ (WUELeaf) and canopy‐scales (WUECanopy) and as the agronomic ratio of white sugar yield (WSY) to in‐season water use (i.e. WUEWSY). In K‐fertilized plots, WUEWSY was enhanced by 15.9%. This effect is attributed to increased beet yield and WSY, as no differences in total in‐season water use between fertilized and unfertilized plots were observed. Potassium (K) fertilization significantly enhanced the leaf area index, resulting in a more efficient depletion of soil moisture by roots in K‐fertilized plots. As a consequence, WUELeaf was increased due to stomatal adjustment. Potassium (K) improved WUECanopy only by tendency. It is concluded that K fertilization improves the WUE of field‐grown sugar beet across scales, but processes that regulate WUE are highly scale dependent.

The effect of oil shale ash and mixtures of wood ash and oil shale ash on the above- and belowground biomass formation of Silver birch and Scots pine seedlings on a cutaway peatland

Use of biofuel ashes for the afforestation of cutaway peatlands helps to balance the content of nutrients in peat substrate, which improves the survival of planted seedlings and increases significantly bio-production. The purpose of this study was to investigate the effect of fertilization with alkaline ashes on the above- and belowground biomass formation of four-year-old Silver birch (Betula pendula Roth) and five-year-old Scots pine (Pinus sylvestris L.) stands on a cutaway peatland. Five treatments were established: three mixtures with different proportions of wood ash (10–15tha−1) and oil shale ash (10–15tha−1), pure oil shale ash (10tha−1) and control (unfertilized plot). Three years after fertilization with ashes the content of phosphorus was up to 150 times and that of potassium 23 times higher in the peat substrate treated with ashes than on the control plot. The growth and biomass formation varied among treatments and depends strongly on the content of P and K in the growth substrate. The best results were observed on plots of Silver birch treated with mixed ashes; there the seedlings annual height increment was 2–3 times (first year), 5–7 times (second year) and 8–9 times (third year) greater than on the control plot. The effect of mixed ashes on the annual height increment of Scots pine was weaker: the annual height increment was 1.4 times (first year), 3 times (second year) and 5 times (third year) greater than on the control plot. The effect of pure oil shale ash on the growth and biomass formation of trees was the smallest. The greatest root collar diameter increment of birch and pine was observed on the third vegetation period. Roots formed the largest part of the total Silver birch biomass, followed by stem, branches and leaves. At the end of the third year after treatment the largest part of the biomass of Scots pine was allocated to the needles, followed by roots, stem and branches. The biomass and biomass production were the greatest on the plots treated with mixed ashes, especially on the WA15+OSA10 and WA15+OSA10 treatments. The total bio-productivity of birch was until 4 times intense than in the case of pine. The average current annual biomass production of Silver birch and Scots pine stands were respectively 0.17–0.21t ha−1 and 0.3–0.56t ha−1 (mixed ashes), 0.04t ha−1 and 0.16t ha−1 (OSA10) and 0.02t ha−1 (control).

Effects of precision conservation agriculture in a maize-wheat-mungbean rotation on crop yield, water-use and radiation conversion under a semiarid agro-ecosystem

In recent years, water resources have decreased and water saving has become an important issue in the Indo-Gangetic Plains (IGP) of South Asia. Maize-wheat-mungbean (MWMb), is an alternate to traditional rice-wheat cropping system, can mitigate the effects of the frequency, intensity, and duration of rainfall due to climate change on food security in the semi arid-region of north-western IGP. The objective of this research was to determine the productivity, water-use efficiency (WUE) and incident radiation conversation efficiency (IRCE) of MWMb cropping system under 3 tillage practices [zero tillage (ZT), permanent beds (PB) and conventional tillage (CT) and 4 nutrient management strategies [Control (unfertilized), farmers’ fertilizer practice (FFP), recommended dose of fertilizers (Ad-hoc) and a site specific nutrient management (SSNM” using the Nutrient Expert® decision support tool). Results of multi-year trial showed that among tillage practices, ZT and PB practices reduced the system irrigation water requirement by 140–200mmha−1 and 200–300mmha−1 respectively, compared to CT system, resulting an enhanced grain yield by 5.7–24.6%, biomass yield by 4.6–20.8%, WUE by 18.4–39.0%, and IRCE by 9.9–34.4%, respectively. Significant (P≤0.05) improvement in system WUE, grain and biomass yield, and IRCE (by 30.6–59.9, 38.3–80.5, 34.3–64.7 and 13.5–48.5%, respectively) was observed in SSNM compared to the unfertilized plots. Significant (P≤0.05) interactions between tillage practices and nutrient management strategies was measured with respect to water–use, WUE, grain and biomass yield, and IRCE of MWMb system. Combinations of ZT/PB practices+SSNM/Ad-hoc nutrient management strategies registered significantly (P<0.05) higher system WUE and IRCE, grain and biomass yield compared to CT+unfertilized/FFP. Results of present study showed that SSNM/Ad-hoc based nutrient application coupled with CA-based tillage practices in MWMb system has complementarity to attain higher system productivity, WUE and IRCE compared to the use of these crop management practices in isolation.