Resident Vegetation Research Articles

Enhancement of palatable perennial grasses by disturbance and seed addition in degraded native grasslands of the dry pampas in Central Argentina

Land use has changed the original composition of the natural grasslands in the dry pampas of central Argentina, to the detriment of palatable perennial grasses (PPG). Long-term elimination of anthropogenic disturbances has not been enough to effectively recover the PPG, which suggests that availability of seeds and/or habitats may be limiting their recruitment. Therefore, our objectives in a degraded grassland site were to assess: (1) the germinable soil seed bank and (2) changes in botanical composition after addition of PPG seed following canopy disturbance. In autumn 2015, we randomly selected 10-paired plots, measured the aboveground biomass and took soil samples to assess the germinable soil seed bank. Afterwards, we disturbed the resident vegetation in each paired plot and either added PPG seeds or left the plot without any seed addition as a control. We quantified the seedling density of seeded and spontaneous species in the spring of 2015 and 2016, and the aboveground biomass at the end of 2017. Annual grasses and forbs (AGFS) dominated the soil seed bank, while PPG and unpalatable perennial grasses (UPG) occurred at low seed density and richness. Addition of PPG seeds resulted in the successful establishment of one key seeded PPG (Poa ligularis). In the spring 2017, the aerial biomass of PPG was highest in the seeded plots, where P. ligularis accounted for 94%. Our results showed that PPG were poorly represented in the soil seed bank of the degraded grassland and that disturbance of the resident vegetation combined with PPG seed addition enabled successful recruitment of a key PPG. So, enhancement of the pastoral value of degraded dry pampas grasslands would be possible through disturbance of the resident vegetation and addition of PPG seed.

Understanding the importance of spatial scale in the patterns of grassland invasions

The invasion of alien plant species is a serious problem for conservation and the maintenance of biodiversity in grasslands. Therefore, it is important to find environmental factors correlated with the distribution of invasive species in such areas. In this study, we examined the impacts of environmental factors operating at different spatial scales on the distribution of invasive species. The study area were located in the Sudetes Mountains, Poland (3800 km2). We sampled field data from 163 random plots located in grassland, among which there were 94 plots with invasive species and 69 plots without invasive species. For each plot, we collected data on resident vegetation (species richness, community structure), geodiversity (topography, soil type), environmental heterogeneity (landscape structure) and climate (temperature and precipitation). Since the factors examined are likely to operate at different spatial scales, we calculated values of environmental variables with different spatial scopes (10m2 plot and buffers with 50, 250 and 1250 m radii). The probability of invasive plant presence was modeled using boosted regression trees (BRT). The results of our study showed that the distribution of invasive species is explained by factors operated at different spatial scale: in the finer scale the presence of invasive species was driven predominantly by the average Ellenberg's Indicator Values for soil moisture, in medium-scale by the average topographic wetness index and sum of edges, while at coarse-scale by temperature. It was also presented that the effect of drivers operating at fine-spatial scale is overwhelming by effect of drivers operating at coarse scale. From a practical point of view, the results demonstrate that effective grassland management should be planned on a larger spatial context, because focussing on the management of a single site cannot be successful.

Large differences in biomass quantity and quality between invasive Reynoutria japonica and resident vegetation are not reflected in topsoil physicochemical properties

Biological invasions are an important element of ongoing global change. Reynoutria japonica is one of the most invasive plant species in Europe and North America, potentially affecting recipient ecosystems. However, little is known about the relationships between its senescing biomass and element concentrations/pools in soil. The aim of this study was to compare the quantity and quality of aboveground and belowground plant biomass, and the quality of topsoil between plots with invasive R. japonica and resident plant communities. The study was conducted at 25 paired R. japonica-native plots in southern Poland. Harvested biomass was dried and weighted, and characterized in terms of C, Ca, K, Mg, N and P concentrations and pools, as well as C/N and C/P ratios. These parameters were also measured in soil along with texture, bulk soil density, moisture and pH. R. japonica produced greater amounts of aboveground and belowground biomass relative to resident species. The concentrations and pools of most elements in plant biomass were affected by invasion (R. japonica vs. resident), biomass type (aboveground vs. belowground) and/or their interactions. Senescing aboveground biomass of R. japonica was characterized by poor quality – lower N, P, K, greater C, Ca concentrations and greater C/N, C/P ratios compared to resident vegetation. Belowground R. japonica biomass had either greater or similar element concentrations (with the exception of P) or ratios. Element pools were greater in R. japonica than in resident species, with the exception of N and P in aboveground biomass. Despite these differences, topsoil generally did not differ in physicochemical properties when analyzed across all study sites; only total N and H2O-extractable K pools were lower under R. japonica than resident vegetation. Our data suggest that ecosystem response to invasion may be site-specific and depend on initial ecosystem properties.

Impacts of weed management on ladybird (Coleoptera: Coccinellidae) abundance and diversity on resident vegetation in a citrus orchard

Citrus fruits are markedly affected by aphids on the island of Réunion (France). These pests are generally controlled with pesticides, which have adverse effects on human and environmental health. Furthermore, resident vegetation in orchards is often eliminated with herbicides due to suspected competition with citrus trees for resources. Yet this resident vegetation could serve as a habitat for natural enemies of crop pests, particularly ladybirds (Coleoptera: Coccinellidae), which are well-known aphid predators, thus reducing the need for pesticide treatments. Results of a 2-year study conducted in an experimental citrus orchard, on the impacts of four different weed management treatments on ladybird populations, viz: i) M: hedge-trimmer mowing; ii) T: disk harrow tilling; iii) HM: hammer mill crushing/mulching; iv) H: herbicide spraying are presented. Ladybirds were captured over a 5 week period each year using Malaise-derived flight interception traps. A total of 690 ladybird specimens, belonging to 12 species distributed across four subfamilies, were captured. These were mainly aphidophagous, with Scymnus constrictus Mulsant being largely dominant. There was a significant effect of distance to a field border with diversified vegetation on ladybird abundance and diversity. Ladybirds were also significantly more abundant on tall vegetation cover than on short cover. Although proportionately fewer ladybirds were trapped in the ‘H’ treatment than in the other three, there were no clearcut effects of weed management treatments on ladybird abundance. This study nevertheless confirmed the efficacy of interception traps for assessment of ladybird population abundance and diversity. It also demonstrated the potential of these natural enemies as bioindicators of habitat disturbance.

At a Microsite Scale, Native Vegetation Determines Spatial Patterns and Survival of Pinus contorta Invasion in Patagonia

Research Highlights: The invasive species Pinus contorta, has become a new component of the vegetation in the Patagonian Steppe, invading the complex matrix of bare ground, tussock grasses and cushion plants. At a microsite scale, the type of native vegetation is one of the multiple factors determining the establishment of P. contorta and in some cases, increasing its survival, and as a result, the invasion of the species. Background and Objectives: The presence of trees, particularly pines, where they are naturally absent, represents a clear threat to Patagonian steppe ecosystems. Thus, understanding the interaction between pines and native plant species may be the key to understanding the invasion and applying management actions. Pinus contorta is considered one of the most aggressive among the pines species, with recognized impacts on regions in the southern hemisphere and Europe, and it is one of the main invaders in the Patagonian steppe. Our aim in this study is to determine the influence of surrounding vegetation on P. contorta spatial distribution, its establishment and future development in the Chilean Patagonia. Materials and Methods: We used point pattern analysis to determine the existence of spatial associations between P. contorta and the resident vegetation of the Patagonian steppe. Further, a seeding experiment was carried out to assess the influence of the surrounding vegetation during P. contorta establishment and first growing season. Results: We found that young P. contorta individuals are positively associated with the native cushion plant B. magellanica and also to tussock grasses. Seeding experiments showed that P. contorta is influenced by resident plant species during establishment and is able to establish on any ground cover type in the Patagonian steppe, but some resident plant species increase P. contorta survival chances. Conclusions: Pinus contorta is interacting with native vegetation and becoming an active component of the Patagonian steppe mosaic. Although pines can establish in any type of vegetation in the Patagonian steppe mosaics, native cushion and tussock grasses may be facilitating the process and promoting pine survival, allowing it to survive and thrive in this stressful environment.

Soil carbon content and its stratification at the medium-term (5 and 8 years) in a semi-arid vineyard with cover crops

There is little information available on the evolution and stratification of soil C content (SCC) at the medium- to long-term in semiarid vineyards with cover crops. The objective was to determine SCC at different depths in the medium term (5 and 8 years) in a semiarid vineyard with different cover crops. The field experiment was conducted on Typic Haploxerept soil with a loam texture, pH 8.2, situated in a vineyard (cv. Tempranillo) located in the La Rioja region (northeast Spain) on Miocene sandstones, siltstones, clays and marlstones. Two different soil managements were evaluated: conventional tillage (CT) and continuous cover crop of resident vegetation (RV). Soil samples were collected from four soil layers (at depths of 0-2.5, 2.5-5, 5-15, and 15-25 cm) in June 2009 and June 2012, 5 and 8 years respectively after cover crop establishment. The SCC was determined and the SCC variation with respect to tillage treatment was determined considering the percentage of soil < 2 mm and soil bulk density. The results showed that the greatest increase in SCC occurred at 0-2.5 cm soil depth, increasing less with depth. The SCC annual increment in the whole soil sampled (0-25 cm) was 2.78 Mg C ha<sup>-1</sup> year<sup>-1 </sup>after 5 years and decreased to 1.98 Mg C ha<sup>-1</sup> year<sup>-1</sup> after 8 years of cover crop establishment. The lower SCC annual increase was not due to the maximum increase being reached in the whole of the sampled soil (0-25 cm). From 2009 to 2012, the SCC did not increase at the soil surface (0-2.5 cm), but did so in the subsurface zone (2.5-5 cm), although with an annual increment lower than that found at soil surface (0-2.5 cm). In conclusion, the steady state in SCC would not have been reached in the medium term (8 years) under cover crop, since there is still a increment of SCC in the subsurface layers.

Seed local adaptation and seedling plasticity account for Gleditsia triacanthos tree invasion across biomes.

Phenotypic plasticity and local adaption can contribute to the success of invasive species. While the former is an environmentally induced trait, the latter involves a selection process to filter the best genotype for a location. We examined the evidence for phenotypic plasticity and local adaptation for seed and seedling traits of the invasive tree Gleditsia triacanthos, with three origins distributed along an approx. 10° latitude gradient across three biomes. In sub-tropical forests, dry woodlands and secondary temperate grasslands in Argentina, we harvested seeds from clusters of neighbouring trees (i.e. families) distributed within 15-20 km in each origin (biome). We manipulated the environmental conditions relevant to each biome, assuming that propagule availability did not represent an ecological barrier. In growth chambers, we evaluated seed imbibition and seed germination under different light, temperature and water potential. In a 2 year common garden, we evaluated the impact of resident vegetation removal on seedling survival and growth. Mean time to complete seed imbibition differed among origins; seeds from temperate grasslands reached full imbibition before seeds from dry woodlands and sub-tropical forests. Germination was always >70 %, but was differentially affected by water potential, and light quantity (dark-light) and quality (red-far red) among origins, suggesting local adaptation. In the common garden, vegetation removal rather than origin negatively affected seedling survival and enhanced seedling growth. Vegetation removal increased basal diameter, leaves per plant and spine number, and reduced the height:basal diameter ratio. We conclude that local adaptation in seed germination traits and plastic changes in seedling allometry (e.g. height:diameter) may allow this tree to respond over the short and long term to changes in environmental conditions, and to contribute to shape G. triacanthos as a successful woody invader. Overall, our study revealed how local adaptation and plasticity can explain different aspects of tree invasion capacity across biomes.

Impact of the alien plant Impatiens glandulifera on species diversity of invaded vegetation in the northern foothills of the Tatra Mountains, Central Europe

The impact of exotic annual Impatiens glandulifera on invaded European vegetation is ambiguous; there are studies reporting considerable negative as well as weak or even no impact of this invader on species richness and diversity of the invaded communities. The effect of invasion by I. glandulifera on species richness, diversity and the composition of resident vegetation was studied in the northern foothills of the Tatra Mountains in southern Poland. Two approaches were used: comparing diversity measures of the invaded and uninvaded plots and analysing changes in species richness and diversity in plots grouped according to increasing cover percentage of I. glandulifera. Invaded plots harboured 0.27 fewer species per 4 m2 and had significantly reduced values of the Shannon and Simpson diversity indices and Pielou’s measure of evenness. Analysis of changes in diversity measures with the increase in I. glandulifera cover revealed that an increase in I. glandulifera cover was from the onset related to a decrease in the diversity of the invaded plant communities, but after exceeding a 80% cover, this species dramatically reduced the diversity of the invaded vegetation. Non-metric multidimensional scaling analysis indicated a significant shift in the composition of invaded plots in relation to uninvaded plots, which resulted from the proportional increase in the more shade tolerant and nutrients demanding species. Our results suggest that in species-rich vegetation, such as fresh meadows and related communities, I. glandulifera may suppress weak competitors and, thus, negatively impact plant diversity.

Disentangling the carbon budget of a vineyard: The role of soil management

The environmental sustainability of viticulture can be enhanced with the application of conservative management practices (e.g. resident vegetation or cover crop on the inter-row), which can lead to an increase of soil carbon (C) sequestration. However, studies disentangling the vineyard C budget are still very scarce. In this context, comparing vineyard net ecosystem CO2 exchange (NEE) with soil fluxes is especially useful. From January 2015 to August 2016, we continuously monitored vineyard NEE with the eddy covariance method and ground CO2 fluxes with an automated chamber system in a commercial vineyard in North Eastern Italy. At the site, inter-rows are covered with resident herbaceous vegetation, however, due to low soil permeability, soil cultivation (ripping or tillage) was performed on alternate alleys in autumn and, sometimes, spring in order to improve water infiltration. Measured annual soil respiration was comparable, but lower, to values estimated by previous studies in vineyards and the net uptake of the grass cover laid in the middle of yearly C budget range reported in the literature for grasslands. At the end of the measurement period, the vineyard ecosystem showed to be a net sink of CO2, absorbing around −233 gC m−2. However, the C sequestration could have been much greater if no soil cultivation had been applied. Indeed, the ground compartment was a source of CO2, but without inter-row cultivation it could have been a net sink, with an overall vineyard C budget of about −421 gC m−2. This confirms that grass cover of the inter-rows can play an important role in the C budget of woody crops. Additionally, the pattern of C fluxes reveals that the activity of herbaceous vegetation in summer decreased well before vines, thus reducing water competition during dry periods. These results provide important information for the tuning of management practices aimed at improving the environmental sustainability of viticulture.

Rootstock and soil management effects on productive characteristics of ‘Princess Seedless®’ table grapes in Apulia region (southern Italy): first results

The use of rootstocks on table grape cultivars is required due to phylloxera, nematodes or soil difficulties, like high lime or salt content, drought or high ground water level. The use of inter-row cover crops (permanent or temporary) in viticulture has many advantages, such as reduction of water runoff and soil erosion, restriction of evaporation from the soil surface, improvement in soil water holding and soil organic matter, reduction of temperature fluctuations in the soil, as well as regulation of the vine growth and vigor, with influence on grape quality and quantity. The trial was carried out in 2012-2013 at an experimental vineyard, trained to “tendone trellis system” on ‘Princess®’, (Vitis vinifera L.) a white mid-season muscat-flavored seedless table grape, grafted onto 3 rootstocks: Vitis riparia × Vitis cinerea var. helleri 161.49 C., 34 E.M. and Vitis rupestris × Vitis cinerea var. helleri 140 Ruggeri. Two different soil inter-row space management treatments, tilled cultivation and permanent resident cover crop, were applied in a split-plot design. At commercial harvest, cluster and berry mass, berry diameter, yield per vine, berry chemical composition, skin berry color and berry mechanical parameters were determined. ‘Princess®’ vines exhibited a good performance on all three rootstocks tested. No significant interactions were detected between soil management/rootstocks with regard to cluster weight, berry weight and number per cluster. The soil management/rootstocks interaction was significant for all parameters of chemical composition and skin color coordinates. The highest and statistically different sugar juice content onto 140 Ruggeri and 161.49 rootstocks was noted. Finally, a temporary cover crop with resident vegetation had no negative effects on vine growth and productivity of ‘Princess®’ seedless table grape, with clear benefits of the cover crops in relation to soil compaction, soil water storage and organic matter. Moreover, the rootstocks/soil management interaction affected firmness and berry detachment force.

Mulch and groundcover effects on soil temperature and moisture, surface reflectance, grapevine water potential, and vineyard weed management.

The objectives of this research were to identify alternatives to glyphosate for intra-row (under-trellis) vineyard floor management and to evaluate the potential for intra-row and inter-row (alleyway) groundcovers to reduce vegetative vigor of ‘Marquette’ grapevines (Vitis spp.) in a southeast Nebraska vineyard. The experiment was a randomized factorial design with five intra-row treatments (crushed glass mulch [CG], distillers’ grain mulch [DG], creeping red fescue [CRF], non-sprayed control [NSC], and glyphosate [GLY]) and three inter-row treatments (creeping red fescue [CRF], Kentucky bluegrass [KB], and resident vegetation [RV]). Treatments were established in 2010–2011 and measurements were conducted during 2012 and 2013 on 5- and 6-year-old vines. Soil temperatures were mostly higher under mulches and lower under intra-row groundcovers, compared to GLY. Weed cover in CG, DG, and CRF treatments was the same or less than GLY. At most sampling dates, inter-row soil moisture was lowest under KB. Intra-row soil moisture was highest under DG mulch and lowest under CRF and NSC; CG had the same or lower soil moisture than GLY. Surprisingly, we did not detect differences in mid-day photosynthetically active radiation (PAR) reflectance, despite visual differences among the intra-row treatments. Mid-day vine water potential did not differ among treatments. We concluded it is not necessary to maintain a bare soil strip under established vines in this region, where soil fertility and moisture are non-limiting.

Abiotic constraints and biotic resistance control the establishment success and abundance of invasive Humulus japonicus in riparian habitats

Dispersal, abiotic and biotic constraints are all involved in explaining the success of invasive plants but how these factors influence the different life stages of an invader remains poorly known. Focusing on highly invaded riparian habitats we asked: (1) how do propagule pressure, resource availability and resident vegetation influence the success of the invasive Asian vine Humulus japonicus at different stages of its life cycle (i.e. seedling, vegetative and flowering) (2) what is the influence of increasing resource availability on the performance and trait plasticity of H. japonicus compared to a functionally similar co-occurring native species? To answer the first question we performed a repeated field survey along the Gardon River (S France) with detailed measurements of distance to the riverbed, soil characteristics, light availability, and resident vegetation cover. To answer the second question we used a greenhouse experiment to compare the biomass and three functional traits of H. japonicus and Galium aparine along a gradient of increasing water and nitrogen availability. Initial germination success was only determined by abiotic constraints, while the role of biotic resistance increased for later stages with establishment success favoured by the interaction of low resident vegetation cover and high soil fertility, and final integrated success favoured by high light availability. H. japonicus performed better and showed higher plasticity in plant height than G. aparine under increased resource availability while their biomass did not differ in the lower part of the resource gradient. Our study demonstrates that by combining field and experimental studies and analysing responses at different life stages we can gain a more complete understanding of how ecological filters shape successful invasions in the course of the life cycle.

Impact of vineyard cover cropping on carbon dioxide and nitrous oxide emissions in Portugal

Scarce studies have been published reporting field measurements of nitrous oxide (N2O) emissions from vineyards, particularly for European conditions. The aim this study was to assess the effect of conventional tillage and no-tillage cover crops on direct N2O emission factor from vineyards (Vitis vinifera L.) in Portugal. A two-year field study was carried out in central Portugal (Nelas, Portugal). The experiment was established in a mature non-irrigated vineyard. The following four treatments with three replications were considered: soil tillage of the inter-row (Till), treatment Till followed by application of mineral fertiliser (50 kg N ha−1) (Till + N), permanent resident vegetation in the inter-row (NoTill), and treatment No-Till followed by application of mineral fertiliser (50 kg N ha−1) (NoTill + N). The carbon dioxide (CO2) and N2O fluxes were measured by the closed chamber technique and analyzed by gas chromatography during two consecutive growing seasons (March-September of 2015 and 2016) of the grapevine crop. The results showed that the average direct N2O EF for vineyards managed with conventional soil tillage in the inter-row was 0.57 ± 0.12% of N input and cover cropping by permanent resident vegetation in the inter-row reduces N2O emission in 60% (0.23 ± 0.29% of N input). Thus, the vineyard cover cropping was recommended as mitigation measure in order to reduce N2O emissions. The defaults direct N2O EF currently recommended by IPCC was not appropriated for vineyards and N2O emissions are currently potentially overestimated in the Portuguese inventory.

Weeds as Emerging Threat to Biodiversity:A Consequence of Spread of <i>Ludwigia peruviana</i> in Dhansiri and Kopili Catchment Areas of Assam, North East India

Wetlands seem to be more vulnerable to invasions compared to terrestrial ecosystems. The alien invasive weed, Ludwigia peruviana , invading the wetlands of the Dhansiri catchment and eastern part of Kopili in Assam has threatened the resident biodiversity and has also posed possibilities of spreading to other wetlands of North East India. The present study was conducted to measure the impact of the weed on the biodiversity of this region, to find out the causes for increasing invasiveness and to suggest a suitable management strategy. The weed has already damaged the marshland plant community and offered severe competition to the plants of peatland ecosystems in nearly 700 sq. km in the affected areas. Pre-monsoon temperature and monsoon rainfall had strong positive correlation with the frequency of occurrence of the weed. L. peruviana showed the highest (nearly 52%) frequency of occurrence in the wetlands of the area in comparison to other troublesome weeds. It has already formed its pure-stand in the ecotone zone replacing resident vegetation and is severely hampering normal food webs. Birds and animals either nest or graze in L. peruviana -dominant areas, and the abundant waterways exhibit high probability of spreading the weed from the gullies and furrows and settlement areas in the near future. The seriousness of the problem calls for effective and timely management strategy.

The effect of exurban development on wintering birds in Colorado

ABSTRACT Large-scale land-use change driven by residential development has degraded native ecosystems and altered the composition of species communities. Concern over the loss of habitat for human-sensitive species has led to questions about how housing impacts bird communities along the urban to rural gradient. Yet most studies of birds in residential ecosystems are limited to the breeding season, thus the effects of housing on avian habitat use in winter are not well understood. We surveyed winter resident birds, vegetation cover and structure, and human activity along a housing gradient in a Colorado landscape undergoing exurban development. Using an occupancy-based approach, we evaluated models for species with sufficient detections (n = 8). We found that habitat use by six species [American Robin (Turdus migratorius), Black-billed Magpie (Pica hudsonia), Dark-eyed Junco (Junco hyemalis), Downy Woodpecker (Picoides pubescens), Pygmy Nuthatch (Sitta pygmaea), Townsend's Solitaire (Myadestes townsendi)]...

Methods to test the interactive effects of drought and plant invasion on ecosystem structure and function using complementary common garden and field experiments.

Abiotic global change drivers affect ecosystem structure and function, but how they interact with biotic factors such as invasive plants is understudied. Such interactions may be additive, synergistic, or offsetting, and difficult to predict. We present methods to test the individual and interactive effects of drought and plant invasion on native ecosystems. We coupled a factorial common garden experiment containing resident communities exposed to drought (imposed with rainout shelters) and invasion with a field experiment where the invader was removed from sites spanning a natural soil moisture gradient. We detail treatments and their effects on abiotic conditions, including soil moisture, light, temperature, and humidity, which shape community and ecosystem responses. Ambient precipitation during the garden experiment exceeded historic norms despite severe drought in prior years. Soil moisture was 48% lower in drought than ambient plots, but the invader largely offset drought effects. Additionally, temperature and light were lower and humidity higher in invaded plots. Field sites spanned up to a 10‐fold range in soil moisture and up to a 2.5‐fold range in light availability. Invaded and resident vegetation did not differentially mediate soil moisture, unlike in the garden experiment. Herbicide effectively removed invaded and resident vegetation, with removal having site‐specific effects on soil moisture and light availability. However, light was generally higher in invader‐removal than control plots, whereas resident removal had less effect on light, similar to the garden experiment. Invasion mitigated a constellation of abiotic conditions associated with drought stress in the garden experiment. In the field, where other factors co‐varied, these patterns did not emerge. Still, neither experiment suggested that drought and invasion will have synergistic negative effects on ecosystems, although invasion can limit light availability. Coupling factorial garden experiments with field experiments across environmental gradients will be effective for predicting how multiple stressors interact in natural systems.

Influence of cover cropping on water uptake dynamics in an irrigated Mediterranean vineyard

AbstractAs a result of its physiological characteristics, vine's yield and quality responses are greatly affected by water availability in the soil. Knowledge about water uptake of grapevines in pedoclimatic conditions of high water availability is essential when considering the increasing use of irrigation in a previously rainfed crop. We studied the water uptake of irrigated grapevines under different soil covers. The study was carried out over 2 years in southern Portugal, a Mediterranean climate region, in ‘Aragonez’ grapevines planted in Vertisols. A cover crop was sown in half the area while maintaining the permanent resident vegetation in the remaining area. Five levels of annual irrigation supply were applied: 200, 150, 100 and 50 mm, and no irrigation. Soil moisture was monitored every 2 or 3 weeks, and weekly after the start of irrigation. Results show that water uptake in the interrows did not cease after the beginning of irrigation. Water uptake by the vines occurred to depths of approximately 3 m, hence 7.5 times greater than the cover crop root system depth. Results suggest that over time, the presence of the cover crop forces the vine root system, mainly its thinner roots, to seek water in increasingly deeper soil compartments. Copyright © 2017 John Wiley & Sons, Ltd.

Net ecosystem CO2 exchange in an irrigated olive orchard of SE Spain: Influence of weed cover

No-till management and the establishment of plant cover have been implemented in olive crops in recent years in order to prevent soil erosion and increase soil organic carbon. However, the effect of these conservation practices on the net CO2 exchange at the ecosystem scale has not been explored so far. In this study, we analyze the influence of resident vegetation cover (hereafter weeds) on the net ecosystem CO2 exchange (NEE) in an irrigated olive orchard located in Jaén (SE Spain) by using the eddy covariance technique. NEE was measured in the olive orchard under two treatments, one with weed cover in the alleys from autumn to spring, and another where weed growth was avoided by the application of a glyphosate herbicide. Our study demonstrates that the presence of weeds in the alleys increased carbon assimilation in the weed-cover treatment during the weed growing period (from December to April). However, the net ecosystem CO2 uptake decreased in the weed-cover treatment during late spring (May and June), after weeds were cut and left on the soil, compared to the weed-free treatment, probably due to an increase in soil respiration. On an annual basis, weed removal decreased net carbon uptake by 50% compared to the weed-cover treatment. The annual NEE was −140gCm−2y−1 in the weed-cover treatment and −70gCm−2y−1 in the weed-free treatment. In summary, our study demonstrates that, during the first year of differential treatment, maintenance of weed cover in olive groves has a positive effect on CO2 uptake and enhances the capacity of the agro-system to act as a net CO2 sink.

Enriching plant diversity in grasslands by large-scale experimental sward disturbance and seed addition along gradients of land-use intensity

Aims The relationship between biodiversity and ecosystem functioning is among the most active areas of ecological research. Furthermore, enhancing the diversity of degraded ecosystems is a major goal in applied restoration ecology. In grasslands, many species may be locally absent due to dispersal or microsite limitation and may therefore profit from mechanical disturbance of the resident vegetation. We established a seed addition and disturbance experiment across several grassland sites of different land use to test whether plant diversity can be increased in these grasslands. Additionally, the experiment will allow us testing the consequences of increased plant diversity for ecosystem processes and for the diversity of other taxa in real-world ecosystems. Here we present details of the experimental design and report results from the first vegetation survey one year after disturbance and seed addition. Moreover, we tested whether the effects of seed addition and disturbance varied among grassland depending on their land use or pre-disturbance plant diversity. Methods A full-factorial experiment was installed in 73 grasslands in three regions across Germany. Grasslands were under regular agricultural use, but varied in the type and the intensity of management, thereby representing the range of management typical for large parts of Central Europe. The disturbance treatment consisted of disturbing the top 10 cm of the sward using a rotavator or rotary harrow. Seed addition consisted of sowing a high-diversity seed mixture of regional plant species. These species were all regionally present, but often locally absent, depending on the resident vegetation composition and richness of each grassland. Important findings One year after sward disturbance it had significantly increased cover of bare soil, seedling species richness and numbers of seedlings. Seed addition had increased plant species richness, but only in combination with sward disturbance. The increase in species richness, when both seed addition and disturbance was applied, was higher at high land-use intensity and low resident diversity. Thus, we show that at least the early recruitment of many species is possible also at high land-use intensity, indicating the potential to restore and enhance biodiversity of species-poor agricultural grasslands. Our newly established experiment provides a unique platform for broad-scale research on the land-use dependence of future trajectories of vegetation diversity and composition and their effects on ecosystem functioning.

Surface Soil Properties Influence Carbon Oxide Pulses After Precipitation Events in a Semiarid Vineyard Under Conventional Tillage and Cover Crops

In semiarid regions of the Mediterranean basin, a rainfall event can induce a respiratory pulse that releases a large amount of soil carbon dioxide (CO2) into the atmosphere; this pulse can significantly contribute to the annual ecosystem carbon (C) balance. The impacts of conventional tillage and two different cover crops, resident vegetation and Bromus catharticus L., on soil CO2 efflux were evaluated in a Vitis vinifera L. vineyard in La Rioja, Spain. Soil CO2 efflux, gravimetric water content, and temperature were monitored at a depth of 0–5 cm after rainfall precipitation events approximately every 10 d in the period from May 17 to July 27, 2012, during which the cover crops had withered. Additionally, on June 10, 2012, soil organic C, microbial biomass C, and β-glucosidase activity were determined at soil depths of 0–2.5, 2.5–5, 5–15, and 15–25 cm. The results show that pulses of soil CO2 were related to the increase in soil water content following precipitation events. Compared to the conventional tillage treatment, both cover crop treatments had higher soil CO2 efflux after precipitation events. Both cover crop treatments had higher soil organic C, microbial biomass C, and β-glucosidase activity at the soil surface (0–2.5 cm) than the conventional tillage treatment. Each pulse of CO2 was related to the surface soil properties. Thus, this study suggests that the enhancement of soil organic C and microbiological properties at the soil surface under cover crops may increase soil CO2 efflux relative to conventional tillage immediately after precipitation events during the dry season.