Grassland Field Research Articles

Environmentally-friendly and organic management practices enable complementary diversification of plant–bumblebee food webs

Plant and pollinator diversity have declined concurrently in Europe in the last half century. We studied plant–bumblebee food webs to understand the effects of two agri-environmental schemes (AES, organic farming and environmentally-friendly management practice) vs. conventional farming as control group, landscape structure (heterogeneous vs. homogeneous landscapes) and seasonality (June, July, and August) interactions using Estonian AES monitoring data. In the summer of 2014, we observed foraging bumblebees (20 species) on 64 farms that varied in agricultural management and landscape structure, yielding a total of 2303 flower visits on 76 plant species. We found that both management practice and landscape structure influenced the generality (redundancy in the use of flower resources) of food webs. In homogeneous landscapes, environmentally-friendly management practices, including restrictions on the application of glyphosates, enhancement of bumblebee habitats, such as permanent grassland field margins, the allocation of a minimum of 15% of arable land (including rotational grasslands) to legumes, contributed to a higher number of visited plant species (generality) in July, whereas organic farming did so in August. Therefore, both environmentally-friendly and organic management practices are needed to support plant–bumblebee food webs in agricultural landscapes. Food web generality and diversity (Shannon index) are affected by a significant interaction between landscape structure and seasonality: food web diversity varied in homogeneous landscapes between the three different survey months, whereas food webs were more diverse in heterogeneous landscapes. We did not find any significant interaction effect of management, landscape structure and seasonality on linkage density and vulnerability. A full list of the most visited plant species by bumblebees based on species-specific flower visitation was also assembled. In homogeneous landscapes, resource limitation is an issue for bumblebees in certain time periods. For supporting bumblebees in the agricultural landscapes, avoiding resource limitation is important and this can be secured with a combination of AES management practices.

Population Status, Habitat Use and Breeding Biology of the Endangered Colombian Horned Lark in an Andean Wetland

The Colombian Horned Lark Eremophila alpestris peregrina is an endemic bird of the Colombian Andean Plateau that is endangered due to habitat loss. Information on the population status, habitat use and reproductive biology of this species is therefore vital. We studied these aspects in the La Copa reservoir, where the largest population of this species is found. First, we determined at which locations around the reservoir it was present. At these locations, we used fixed-width transects to estimate its abundance and densities in different habitats for eight months. We monitored its reproductive biology, through behavioural observations and nest tracing during 12 months. The species was only present in plain areas with sparse short vegetation, using grassland, cropland or a mix of the two. Population densities varied significantly between habitats, being high (5.7 birds/ha) in extensive grasslands and medium to low in mixed cropland-grassland (1.1 birds/ha) and cropland (0.41 birds/ha). These differences may be related to the presence of grazing, flooding dynamics, the density of perennial forbs, the size of the grassland fields and the detrimental effect of toxic pesticides used for crop production. We estimated that 133 to 230 (95% CI) individuals (mostly adults), inhabit the entire reservoir. This is a significant number since it may represent 13–23% of the Colombian Horned Lark population. Finally, we present our data on the reproductive cycle of these larks.

Natural estrogen emissions to subsurface tile drains from experimental grassland fields in Switzerland after application of livestock slurries and free compounds.

Natural estrogens are present in high concentrations in livestock slurries, which are often applied to agricultural fields in large quantities. As such, the export of slurry-derived natural estrogens from tile-drained fields is a potential source for estrogenic pollution in surface waters. Yet despite the abundance of tile-drained fields in Central Europe, export of natural estrogens from agricultural fields receiving livestock slurries is rarely studied in this region. In an effort to fill this knowledge gap, here we applied natural estrogens to Swiss experimental fields in the form of cattle slurry, pig slurry or dissolved in water, and quantified them in flow-proportionally collected drainage water over 18months. After pig and cattle slurry applications, concentration maxima in drainage water of 73, 8, 37, and 60ngL-1 for 17α-estradiol (E2α), 17β-estradiol (E2β), estrone (E1), and estriol (E3), respectively, were observed shortly after rain events. The exported fractions of individual natural estrogens to tile drains were on average 0.26% (ranging from 0.08 to 0.41%) after cattle, and 0.18% (0.03-0.40%) after pig slurry applications. Such numbers were higher than expected from the leaching potential based on substance properties, and comparable to those of more mobile micropollutants previously studied on the same fields. Natural estrogens were mainly exported to tile drains through preferential flow. Exported fractions were lower when applied in aqueous solution than when applied in slurry, pointing to particle-facilitated transport to tile drains when applied in slurry. In Switzerland, the estimated 6.3, 0.6, 7.4, and 7.7g of E2α, E2β, E1, and E3, respectively, exported through the tile-drained agricultural area per year contribute little to the total natural estrogen load received by surface waters. However, after slurry applications in highly drained catchments, natural estrogen emissions to tile drains can cause short term (i.e. less than 1week) estrogenic exposure in nearby streams.

Balance between geographic, soil, and host tree parameters to shape soil microbiomes associated to clonal oak varies across soil zones along a European North-South transect.

Tree root-associated microbiomes are shaped by geographic, soil physico-chemical, and host tree parameters. However, their respective impacts on microbiome variations in soils across larger spatial scales remain weakly studied. We out-planted saplings of oak clone DF159 (Quercus robur L.) as phytometer in four grassland field sites along a European North-South transect. After four years, we first compared the soil microbiomes of the tree root zone (RZ) and the tree root-free zone (RFZ). Then, we separately considered the total microbiomes of both zones, besides the microbiome with significant affinity to the RZ and compared their variability along the transect. Variations within the microbiome of the tree RFZ were shaped by geographic and soil physico-chemical changes, whereby bacteria responded more than fungi. Variations within both microbiomes of the tree RZ depended on the host tree and abiotic parameters. Based on perMANOVA and Mantel correlation tests, impacts of site specificities and geographic distance strongly decreased for the tree RZ affine microbiome. This pattern was more pronounced for fungi than bacteria. Shaping the microbiome of the soil zones in root proximity might be a mechanism mediating the acclimation of oaks to a wide range of environmental conditions across geographic regions.

A new net primary productivity model and new management strategy of grassland classification based on CSCS in China

The discovery of grassland field, form and biomass in China was central to the sustainable development of grassland. In this study, the realistic spatial distribution patterns of grasslands were clarified through the combination of the International Geosphere-Biosphere Program (IGBP) and the Comprehensive and Sequential Classification System (CSCS). An optimal net primary productivity (NPP) model suitable for Chinese grasslands was introduced by integrating the classification indices-based model (CIM) with the Normalised Difference Vegetation Index (NDVI), and comparing it with the standard classical model (Miami, Schuur, CIM, CASA model). Using the optimal model as the algorithm basis, the net primary production spatial pattern of grassland in China was determined. The results showed that: (1) the total area of grassland was ~374.3 × 104 km2 in 2018, mainly distributed in north-western China. Among the grassland super-class groups, Tundra and alpine steppe were largest, and Warm desert smallest; (2) the optimal modified CIM had the highest prediction efficiency, and the overall accuracy was higher than the standard classical model (Miami, Schuur, CIM, CASA model). It achieved the accurate calculation of grassland NPP in China; (3) different grassland super-class groups had different carbon fixation efficiency per unit area, resulting in huge differences in total NPP. Among the various grassland super-class groups, the temperate humid grassland, steppe, tundra and alpine steppe had high conversion efficiency per unit area of NPP, whereas that for warm desert and the savanna was low. The total NPP was 388.04 × 1012 g C/year in the study area in 2018. The results provide a basis for the rational arrangement of grassland ecological and productive functions, and are significant for developing a new strategy of grassland classification management in China.

Spatial Variability of Soil Phosphorus Indices under Two Contrasting Grassland Fields in Eastern Canada

Phosphorus (P) is an essential nutrient for grassland production systems. However, continuous applications of P fertilizers result in soil P accumulations, increasing the risk of P losses in runoff and erosion. This study aims to investigate the field-scale variability of soil-test P (STP) in two contrasting grassland fields using descriptive statistics and geostatistics for accurate recommendations on soil sampling strategy and sustainable approaches to P management. A young grassland (YG; 2 years) and an old grassland (OG; 10 years under permanent pasture) were classified as humo-ferric podzol and received organic fertilizers. Soil samples were collected in 16-m by 16-m triangular grids at two depths (0–5 and 5–20 cm). They were analyzed for available P and other soil elements extracted using the Mehlich-3 method (M3). The agri-environmental P saturation index (P/Al)M3 was calculated. Phosphorus accumulation was observed in OG (0–5 cm) as a result of long-term manure applications. Repeated applications of organic fertilizers can impact the long-term buildup of soil P, thus decreasing soil P va-riability and spatial dependence in permanent grasslands. A soil sampling strategy focusing on the 0–5 cm layer should be retained in permanent grasslands for sustainable P recommendations in Eastern Canada.

A novel 13 C pulse-labelling method to quantify the contribution of rhizodeposits to soil respiration in a grassland exposed to drought and nitrogen addition.

Rhizodeposition plays an important role in below-ground carbon (C) cycling. However, quantification of rhizodeposition in intact plant-soil systems has remained elusive due to methodological issues. We used a 13 C-CO2 pulse-labelling method to quantify the contribution of rhizodeposition to below-ground respiration. Intact plant-soil cores were taken from a grassland field, and in half, shoots and roots were removed (unplanted cores). Both unplanted and planted cores were assigned to drought and nitrogen (N) treatments. Afterwards, shoots in planted cores were pulse labelled with 13 C-CO2 and then clipped to determine total below-ground respiration and its δ13 C. Simultaneously, δ13 C was measured for the respiration of live roots, soils with rhizodeposits, and unplanted treatments, and used as endmembers with which to determine root respiration and rhizodeposit C decomposition using two-source mixing models. Rhizodeposit decomposition accounted for 7-31% of total below-ground respiration. Drought reduced decomposition of both rhizodeposits and soil organic carbon (SOC), while N addition increased root respiration but not the contribution of rhizodeposit C decomposition to below-ground respiration. This study provides a new approach for the partitioning of below-ground respiration into different sources, and indicates that decomposition of rhizodeposit C is an important component of below-ground respiration that is sensitive to drought and N addition in grassland ecosystems.

Effects of manipulated precipitation on aboveground net primary productivity of grassland fields: Controlled rainfall experiments in Inner Mongolia, China

AbstractRecovery from grassland degradation caused by climate change and human disturbance is critical to the sustainable development of drylands. Grassland in China accounts for 13% of the global grassland area, and more than half of it is still recovering from degradation. How climate change will contribute to the recovery of degraded grassland has not been clarified through field experiments. Here, we report the effects of manipulated precipitation regimes on above ground net primary productivity (ANPP) in five grassland fields along a degradation gradient using a 3‐year controlled rainfall manipulation experiment in Inner Mongolia, China. We found that differences of approximately 20–30% in growing season precipitation have limited impacts on the ANPP of grasslands, and the responses can depend crucially on the degradation status indicated by vegetation and soil features. ANPP sensitivity to spring drought increased with increasing degradation level, which was mainly determined by vegetation composition. ANPP was generally insensitive to summer drought except for mature grassland, in which drought led to severe soil water deficit, mainly mediated by soil water holding capacity. Our results suggest that the recovery of degraded grassland is expected to be delayed by increasing drought early in the growing season, and mature grassland would be more vulnerable to extreme summer drought. These findings highlight the negative impacts of seasonal drought on degraded grassland and emphasize the importance of accounting for climate change and degradation status in future grassland ecosystem restoration and management policies.

Estimating Plant Pasture Biomass and Quality from UAV Imaging across Queensland’s Rangelands

The aim of this research was to test recent developments in the use of Remotely Piloted Aircraft Systems or Unmanned Aerial Vehicles (UAV)/drones to map both pasture quantity as biomass yield and pasture quality as the proportions of key pasture nutrients, across a selected range of field sites throughout the rangelands of Queensland. Improved pasture management begins with an understanding of the state of the resource base, UAV based methods can potentially achieve this at improved spatial and temporal scales. This study developed machine learning based predictive models of both pasture measures. UAV-based structure from motion photogrammetry provided a measure of yield from overlapping high resolution visible colour imagery. Pasture nutrient composition was estimated from the spectral signatures of visible near infrared hyperspectral UAV sensing. An automated pasture height surface modelling technique was developed, tested and used along with field site measurements to predict further estimates across each field site. Both prior knowledge and automated predictive modelling techniques were employed to predict yield and nutrition. Pasture height surface modelling was assessed against field measurements using a rising plate meter, results reported correlation coefficients (R2) ranging from 0.2 to 0.4 for both woodland and grassland field sites. Accuracy of the predictive modelling was determined from further field measurements of yield and on average indicated an error of 0.8 t ha−1 in grasslands and 1.3 t ha−1 in mixed woodlands across both modelling approaches. Correlation analyses between measures of pasture quality, acid detergent fibre and crude protein (ADF, CP), and spectral reflectance data indicated the visible red (651 nm) and red-edge (759 nm) regions were highly correlated (ADF R2 = 0.9 and CP R2 = 0.5 mean values). These findings agreed with previous studies linking specific absorption features with grass chemical composition. These results conclude that the practical application of such techniques, to efficiently and accurately map pasture yield and quality, is possible at the field site scale; however, further research is needed, in particular further field sampling of both yield and nutrient elements across such a diverse landscape, with the potential to scale up to a satellite platform for broader scale monitoring.

Assessment of selected soil physicochemical properties on different land-use systems and landscape positions at Hamesa watershed, Wolayita zone, Southern Ethiopia

The investigation was undertaken at Hamesa watershed of Wolayita Zone with the aim to assess the consequences of land-use systems and topography on the physical and chemical properties of selected soils. Surface soil samples taken at 0-15 and 15-30 cm depths from three land-use systems (enset, grassland and maize fields) were collected under three slope positions (upper, middle and lower). Both the clay and bulk density increased with depth, while total nitrogen (N), OC, available P and micro-nutrients (Fe, Zn, Mn, and Cu) decreased. On the landscape positions, increase in exchangeable Ca and K, pH, bulk density and available Mn down the slope was observed; whereas total N, OC, available P and available Fe showed decreasing trend down the slope. At 0-15 cm soil depth, grassland soils exhibited higher bulk density and lower porosity as a result of livestock movement which was compacted. Grasslands had higher OC and TN compared to the other two land-use systems, due to the accumulation of humus in the root system in the grassland. Application of household refuses and manure contribute to increasing available P, TN, Zn, Ca and K contents in enset farmland. On the contrary, maize land use had lower CEC, K, PBS, Mg, TN and OC, which might be due to crop removal, erosion phenomena, and excessive tillage activities. These results suggest that for sustainable crop production, proper management practices should be in place by considering different slope positions and land-use systems. Key words: Land use system, slope position, physical, chemical soil properties.

Transferability of a soil variogram for sampling design: A case study of three grasslands in Ireland

AbstractIt is commonly accepted that an estimated soil variogram can be transferred to another similar area for deriving the tolerable spacing of a sampling grid or, more generally, the sample size, given a requirement on the quality of the soil property map of the recipient area. The quality of the derived tolerable grid spacing depends on how similar the population variograms of the donor area and recipient area are. In practice we are uncertain about the variograms of both areas due to sampling errors. Ideally, the uncertainty about the variogram of the donor area is accounted for in deriving the tolerable grid spacing. To assess the transferability, we should also account for uncertainty in the estimated variogram of the recipient area. In this study the transferability of variograms of soil pH, P, Mg and K is analysed for three grassland fields in Ireland, which are similar in soil‐forming factors. One field served as donor area, the other two as recipient area. For all three fields and for each soil property, 500 variograms were sampled from the posterior distribution of the variogram parameters. Results showed that the estimated variogram parameters of the recipient fields differed largely from those of the transferred variograms. The ranges of estimated mean kriging variance values for the various grid spacings, as obtained with the two sets of variograms (one set of the donor field, one set of the recipient field), did not overlap. Even after scaling the transferred variogram with an estimate of the variance of the recipient field, the transferred variogram was of no use for determining the tolerable grid spacing. The difference in the variograms can possibly be explained by the difference in historical land use.Highlights Transferability of variograms to derive tolerable grid spacing for mapping grassland fields is assessed Transferability should be based on the uncertainty distributions of the tolerable grid spacings Due to difference in historical land use, local and transferred variograms differed largely Transferability of a variogram is very poor, even after scaling the transferred variogram

WEPP model prediction evaluation of soil water content in northeast Uruguay

WEPP is a process-based model that estimates runoff and water erosion at slope level, maintaining a soil water balance at daily pace. The objective of this work is to adjust and validate the water balance component of the WEPP model in two watershed management situations (afforestation and natural grassland field) to obtain an adjusted tool that determines runoff and erosion. Soil water content data measured with neutron probe 4 times in the year down to 1.3 m depth during 10 years were used, and were compared with WEPP estimates. The results indicate that the WEPP estimations were not good (Efficiency coefficient (E) = 0.03, -1.29, -0.01, -1.74, 0.17 and -0.08 for the profiles) in high slope (C), average slope (D) and low slope (F), in the Grassland and afforested watershed, respectively, with an E considered insufficient and with periods of over and underestimation water content for both management situations. A better fit was obtained by eliminating the data outside of the calibration line in the profile C, with no improvement for the D and F profiles in both management situations. The results indicate that parameters such as evapotranspiration and WEPP equations must be adjusted to achieve better performance.

Decomposition disentangled: A test of the multiple mechanisms by which nitrogen enrichment alters litter decomposition

AbstractNitrogen (N) enrichment has direct effects on ecosystem functioning by altering soil abiotic conditions and indirect effects by reducing plant diversity and shifting plant functional composition from dominance by slow to fast growing species. Litter decomposition is a key ecosystem function and is affected by N enrichment either by a change in litter quality (the recalcitrance of the plant material) or through a change in soil quality (the abiotic and biotic components of the soil that affect decomposition). How the direct and indirect effects of N alter soil and litter quality remains poorly known.We designed a large grassland field experiment manipulating N enrichment, plant species richness and functional composition in a full factorial design. We used three complementary litterbag experiments, combined in a structural equation model (SEM), to quantify the effects of the treatments and various measures of functional composition and diversity on litter and soil quality and overall decomposition.Our results revealed multiple drivers of litter quality and showed that nutrient concentrations (N and calcium) were about twice as important as structural components (leaf dry matter content, fibres) in determining litter quality. Overall the experimental results suggest that N enrichment increases litter decomposition mostly indirectly through a shift in functional composition toward faster growing plant species, producing higher quality litter. N enrichment also altered soil quality and thereby litter decomposition, through its effects on vegetation cover.Our approach provides a mechanistic tool to test the drivers of litter decomposition across different ecosystems. Our results show that litter quality is determined by several nutrient and structure traits and highlight the importance of considering shifts in plant species composition when assessing the effects of N enrichment on decomposition.

Genetic structure and gene flow among populations of Encholirium magalhaesii, a rocky grassland fields bromeliad

Encholirium is a genus of 31 xerophytic terrestrial or epilithic bromeliad species endemic to eastern Brazil. Together with Dyckia and Deuterocohnia, it forms the so-called xeric clade of the Pitcairnioideae subfamily of Bromeliaceae. Encholirium species are adapted to rocky landscapes, and many of them are found in the rocky grassland fields of the Espinhaco in the state of Minas Gerais, which is considered the diversity center of the genus. Encholirium species and other bromeliads growing on isolated, island-like habitats like rock outcrops and “inselbergs” are often characterized by high levels of genetic structure and limited gene flow among populations, but there are also exceptions. In the present study, we applied nuclear and chloroplast microsatellite markers to investigate the genetic diversity and population structure of E. magalhaesii L.B.Sm., an endemic species of the Espinhaco, collected in four localities of the Diamantina municipality in southeastern Brazil. Moderate genetic differentiation among localities was revealed by the nuclear markers (Fst = 0.199), whereas genetic structuring was much higher with plastid markers (Fst = 0.496). Estimations of pollen/seed flow ratios suggest that pollen flow is more efficient in maintaining the genetic connectivity among E. magalhaesii populations than seed flow.

Can flooding-induced greenhouse gas emissions be mitigated by trait-based plant species choice?

Intensively managed grasslands are large sources of the potent greenhouse gas nitrous oxide (N2O) and important regulators of methane (CH4) consumption and production. The predicted increase in flooding frequency and severity due to climate change could increase N2O emissions and shift grasslands from a net CH4 sink to a source. Therefore, effective management strategies are critical for mitigating greenhouse gas emissions from flood-prone grasslands. We tested how repeated flooding affected the N2O and CH4 emissions from 11 different plant communities (Festuca arundinacea, Lolium perenne, Poa trivialis, and Trifolium repens in monoculture, 2- and 4-species mixtures), using intact soil cores from an 18-month old grassland field experiment in a 4-month greenhouse experiment. To elucidate potential underlying mechanisms, we related plant functional traits to cumulative N2O and CH4 emissions. We hypothesized that traits related with fast nitrogen uptake and growth would lower N2O and CH4 emissions in ambient (non-flooded) conditions, and that traits related to tissue toughness would lower N2O and CH4 emissions in flooded conditions. We found that flooding increased cumulative N2O emissions by 97 fold and cumulative CH4 emissions by 1.6 fold on average. Plant community composition mediated the flood-induced increase in N2O emissions. In flooded conditions, increasing abundance of the grass F. arundinacea was related with lower N2O emissions; whereas increases in abundance of the legume T. repens resulted in higher N2O emissions. In non-flooded conditions, N2O emissions were not clearly mediated by plant traits related with nitrogen uptake or biomass production. In flooded conditions, plant communities with high root carbon to nitrogen ratio were related with lower cumulative N2O emissions, and a lower global warming potential (CO2 equivalent of N2O and CH4). We conclude that plant functional traits related to slower decomposition and nitrogen mineralization could play a significant role in mitigating N2O emissions in flooded grasslands.

Effect of management and weather variations on the greenhouse gas budget of two grasslands during a 10-year experiment

While many studies have measured the CO2 and N2O exchange of grassland ecosystems and analysed the influence of relevant drivers, only few reported the entire carbon budget over multiple years, which is most relevant for the net greenhouse gas (GHG) source or sink effect. When analysing eddy-covariance-based flux measurements for management and weather related drivers, this is commonly done by comparing either different measurement years at one site or data from different sites distributed regionally or globally. However this procedure makes it usually difficult to clearly attribute observed differences in the carbon exchange to management effects or meteorological drivers.In this study we present results of the carbon and GHG budget of a 10-year paired grassland field experiment in Switzerland comparing intensive and extensive management. We focus on the inter-annual variability of the entire 10-year dataset and especially on the effect of a renovation activity in the intensive field after seven years. By comparing the results of the paired plots, we attempted to disentangle the effects of management including renovation from the effect of seasonal weather conditions on the carbon and greenhouse gas budget. The annual carbon budgets of the two paired fields showed clear systematic differences attributable to the different management. The inter-annual variation (IAV) of the carbon budget was determined as residuals from linear trends. Due to the high correlation of the IAV between the two parallel fields, it was assigned mainly to variations in seasonal weather conditions. The total range of weather attributed variations of annual NECB values was similar in magnitude to the systematic management induced difference between the two fields (100–200 gC m−2 yr-1). In contrast to previous studies on grassland renovation, a large net carbon loss and enhanced N2O emission over 2–3 years was observed here. The excess N2O emission after renovation could be well explained by the IPCC default emission factor approach when considering the additional N input by plant residues and the net soil organic matter mineralisation. Concerning the total GHG budget effect the cumulated GHG uptake by the INT field in the first six years of the experiment was more than compensated by the release in the three post-renovation years.

Land-use history impacts functional diversity across multiple trophic groups.

Land-use change is a major driver of biodiversity loss worldwide. Although biodiversity often shows a delayed response to land-use change, previous studies have typically focused on a narrow range of current landscape factors and have largely ignored the role of land-use history in shaping plant and animal communities and their functional characteristics. Here, we used a unique database of 220,000 land-use records to investigate how 20-y of land-use changes have affected functional diversity across multiple trophic groups (primary producers, mutualists, herbivores, invertebrate predators, and vertebrate predators) in 75 grassland fields with a broad range of land-use histories. The effects of land-use history on multitrophic trait diversity were as strong as other drivers known to impact biodiversity, e.g., grassland management and current landscape composition. The diversity of animal mobility and resource-acquisition traits was lower in landscapes where much of the land had been historically converted from grassland to crop. In contrast, functional biodiversity was higher in landscapes containing old permanent grasslands, most likely because they offer a stable and high-quality habitat refuge for species with low mobility and specialized feeding niches. Our study shows that grassland-to-crop conversion has long-lasting impacts on the functional biodiversity of agricultural ecosystems. Accordingly, land-use legacy effects must be considered in conservation programs aiming to protect agricultural biodiversity. In particular, the retention of permanent grassland sanctuaries within intensive landscapes may offset ecological debts.

Evaluating Soil-Borne Causes of Biomass Variability in Grassland by Remote and Proximal Sensing.

On a grassland field with sandy soils in Northeast Germany (Brandenburg), vegetation indices from multi-spectral UAV-based remote sensing were used to predict grassland biomass productivity. These data were combined with soil pH value and apparent electrical conductivity (ECa) from on-the-go proximal sensing serving as indicators for soil-borne causes of grassland biomass variation. The field internal magnitude of spatial variability and hidden correlations between the variables of investigation were analyzed by means of geostatistics and boundary-line analysis to elucidate the influence of soil pH and ECa on the spatial distribution of biomass. Biomass and pH showed high spatial variability, which necessitates high resolution data acquisition of soil and plant properties. Moreover, boundary-line analysis showed grassland biomass maxima at pH values between 5.3 and 7.2 and ECa values between 3.5 and 17.5 mS m−1. After calibrating ECa to soil moisture, the ECa optimum was translated to a range of optimum soil moisture from 7% to 13%. This matches well with to the plant-available water content of the predominantly sandy soil as derived from its water retention curve. These results can be used in site-specific management decisions to improve grassland biomass productivity in low-yield regions of the field due to soil acidity or texture-related water scarcity.

Evidence of low response of soil carbon stocks to grassland intensification

Grasslands cover more than a third of the European agricultural area and are often intensively managed to support the livestock-farming sector. Despite grassland intensification can greatly influence soil carbon (C) cycling, changes in soil C stocks both across years and at increasing soil depths remain difficult to quantify simultaneously. Here we measured spatial and temporal changes in soil C stocks to assess C stocks’ response to intensive grassland management. We measured soil C stocks (a) in a long-term nutrient fertilization experiment on permanent grassland (established in 1970), and (b) in 126 grassland fields distributed across 11 lowland farms in Northern Ireland (UK), which are associated with different frequencies of soil tillage. Using 45 years of data from the plot-scale grassland experiment we found evidence that significant changes in soil C stocks mainly occurred in the soil top 20 cm (not in deeper soils) and only between ‘extreme’ nutrient treatments (i.e. unfertilized vs. highly fertilized soils). Soil physical fractionation, radiocarbon and stable nitrogen isotope analyses all suggest that new C has accumulated in these soils but perhaps not fast enough to affect C stocks in deeper soil layers. Results at the field-scale from intensively managed grasslands show how the frequency of soil tillage neither affected soil C stocks between 0–20, 20–40 or 40–60 cm depth layers nor the C pool of different soil physical fractions at increasing soil depths. Our findings demonstrate how the response of soil C stocks to grassland intensification (i.e. C stocks response to different rates of nutrient fertilization or frequency of soil tillage) can be very slow both in time and space under cool and humid climate conditions. We suggest how the persistence of these soil C stocks under intensive grassland management offers the unique opportunity to improve nutrient use efficiency and cycling thus promoting the delivery of multiple ecosystem processes.

When history matters: The overlooked role of priority effects in grassland overyielding

Abstract Biodiversity–ecosystem functioning experiments have shown that plant species and functional group richness are important drivers of grassland productivity, but the impact that plant order of arrival (i.e. priority effects) has on grassland overyielding and its drivers (complementarity and dominance effects) has been overlooked so far. Using species‐specific plant biomass data collected in mixture and monoculture plots of a grassland field experiment (Jülich Priority Effect experiment) that manipulated the order of arrival of three plant functional groups (forbs, grasses and legumes), we quantified net biodiversity effects (overyielding) as well as complementarity and dominance effects in mixtures one and 2 years after sowing. In this experiment, priority effects were created by sowing one functional group 6 weeks before the two others. First, we tested whether plant order of arrival affected overyielding, complementarity and dominance effects. Second, we investigated whether the magnitude of net biodiversity, complementarity and dominance effects was dependent on the strength and direction of priority effects. We found that complementarity and dominance effects were affected by plant order of arrival during community assembly. In addition, we found that moving from negative to positive priority effects increased grassland overyielding, mainly via increased complementarity effects. These results highlight the need to combine biodiversity and assembly approaches in future ecosystem functioning research, as this will increase the predictive power of community ecology in conservation and ecological restoration. A free Plain Language Summary can be found within the Supporting Information of this article.