Increased Nitrogen Availability Research Articles

Clay soil amendment suppressed microbial enzymatic activities while increasing nitrogen availability in sandy soils

AbstractConservation management practices often produced positive but limited desirable outcomes in US Southeast sandy soils, likely due to their intrinsically low clay contents that constrain the soil's capacity to preserve organic carbon (C) and nutrients. In the field, we tested the effectiveness of a novel approach, that is, clay soil amendment, to improve sandy soils. In October 2017, clay‐rich soils (25% clay) were spread at 25 metric tons ha−1 and tilled onto a sandy soil (1.9% clay) in the field, which was further mixed by light tillage at 0‐ to 15‐cm depth, followed by planting winter cover crop mixtures (cereal rye, crimson clover, and winter pea). The crop rotation was cotton and corn with cover crop mixtures planted in the winter fallow season. Soils (0–15 cm) were collected in August 2021 and subjected to physio‐biochemical analyses. Clay amendment increased soil clay content to 3.4%, which improved nitrogen (N) availability by 51% but inhibited the activities of C (β‐d‐cellubiosidase [CB]; β‐xylosidase [BX]; N‐acetyl‐β‐glucosaminidase [NAG]) and N (leucine aminopeptidase [LAP]) cycling enzymes, resulting in up to 78% reduction in microbial respiration. A follow‐up kinetic study on BG and LAP enzymes suggested that clay addition can have different impacts on enzymes with diverse biological origins through distinct mechanisms. Clay addition can potentially improve sandy soils by stabilizing the organic inputs in soils. However, more research is required to understand its long‐term impacts making this approach practical.

Nitrogen addition alleviates the adverse effects of drought on plant productivity in a temperate steppe.

Drought and nitrogen enrichment could profoundly affect the productivity of semiarid ecosystems. However, how ecosystem productivity will respond to different drought scenarios, especially with a concurrent increase in nitrogen availability, is still poorly understood. Using data from a 4-year field experiment conducted in a semiarid temperate steppe, we explored the responses of aboveground net primary productivity (ANPP) to different drought scenarios and nitrogen addition, and the underlying mechanisms linking soil properties, plant species richness, functional diversity (community-weighted means of plant traits, functional dispersion) and phylogenetic diversity (net relatedness index) to ANPP. Our results showed that completely excluding precipitation in June (1-month intense drought) and reducing half the precipitation amount from June to August (season-long chronic drought) both significantly reduced ANPP, with the latter having a more negative impact on ANPP. However, reducing half of the precipitation frequency from June to August (precipitation redistribution) had no significant effect on ANPP. Nitrogen addition increased ANPP irrespective of drought scenarios. ANPP was primarily determined by soil moisture and nitrogen availability by regulating the community-weighted means of plant height, rather than other aspects of plant diversity. Our findings suggest that precipitation amount is more important than precipitation redistribution in influencing the productivity of temperate steppe, and nitrogen supply could alleviate the adverse impacts of drought on grassland productivity. Our study advances the mechanistic understanding of how the temperate grassland responds to drought stress, and implies that management strategies to protect tall species in the community would be beneficial for maintaining the productivity and carbon sequestration of grassland ecosystems under climate drought.

Growth‐chemical defence‐metabolomic expression trade‐off is relaxed as soil nutrient availability increases for a tropical passion vine

Abstract Abiotic resource limitation presents organisms with a dilemma about how to use resources when they become available. Characterizing how resource allocation affects investment in growth or defensive traits that affect organismal survival strategies allows us to understand the environmental contexts in which species interact. Our goal was to measure how macronutrient availability drives nitrogen and phosphorus allocation towards functional growth and defensive chemical traits of the Neotropical passion vine, Passiflora biflora. We investigated this question with a paired field study in La Selva, Costa Rica and a full factorial greenhouse experiment to determine whether the concentration of a key secondary chemical defence is driven by nitrogen availability. We correlated defensive chemical concentration with soil nitrogen availability in naturally occurring plants, measured the effects of nitrogen and phosphorus availability on growth and secondary chemical defence traits in the greenhouse and characterized the P. biflora leaf metabolome to assess how nutrient availability affected shifts in metabolism related to plant fitness. We found that nutrient allocation increased the magnitude of both growth and defence traits. Increased nitrogen availability resulted in higher concentrations of toxic leaf secondary chemicals, longer vines, greater biomass and more leaves with a superior ability to capture sunlight. In addition, plants from high nitrogen environments had metabolomes with significantly greater secondary metabolite richness and biochemical pathway diversity, as well as increases in the number of metabolites from several chemical classes related to basic cell function and defence. Nutrient availability had no significant effect on the richness and diversity of primary metabolites involved in basic cell functions. A direct comparison of the relative strength of quantitative growth and secondary defence traits indicated that P. biflora favours nutrient allocation to growth at low nitrogen levels but invests in both strategies more evenly as nitrogen availability increases. These findings lead us to predict that passion vines are better prepared to tolerate and resist herbivory when nutrients are plentiful and experience a trade‐off between growth and chemical defence against natural enemies when they are scarce. These findings are consistent with both the ‘escape’ and ‘defend’ syndromes that are often used to describe tropical plant survival strategies. This is one of the only studies to measure nutrient allocation in vines, a group comprising a significant percentage of global plant diversity. Moreover, this work demonstrated the power of leveraging untargeted metabolomics to characterize how nutrient addition affects plant growth and defence, highlighting its potential for understanding functional trait variation. Read the free Plain Language Summary for this article on the Journal blog.

Fertilization during mineland rehabilitation may shift competitive outcomes toward invasive species

Managing invasive species is essential for achieving mineland rehabilitation goals and ensuring the long‐term provision of critical ecosystem services while preventing new dispersion sources to neighboring areas. Traditional techniques include chemical and manual weeding, but frequent reinvasion limits their long‐term success. Therefore, additional integrated tools, such as stimulating natural competitors, may become necessary, especially where sensitive ecosystems, e.g. the ferruginous savanna ecosystem (cangas) from the Carajás National Forest, Eastern Amazon, Brazil, are found nearby rehabilitation sites. Here, we investigate the influence of different substrates and fertilization levels on the biotic interactions between two native canga grasses (Axonopus longispicus and Paspalum cinerascens) and the invasive molasses grass (Melinis minutiflora), which is frequently found in anthropized and natural ecosystems in Latin America. Nutrient application significantly influenced the growth, resource use strategies, and competitive outcomes of M. minutiflora. Nutrient application has positive effects on the growth of native species when cultivated in isolation but reduces plant development when subjected to competition with molasses grass, potentiating the invader. Although neither of the tested native species exhibited competitive advantages over M. minutiflora, increased nitrogen availability favored the competitive ability of this invasive grass. Thus, eliminating fertilization during mineland rehabilitation may be important for reducing the cover of M. minutiflora in the Carajás region, as sensitive canga ecosystems lack natural barriers against invasion. This strategic approach mitigates the operational risks and costs associated with combating invasive species from rehabilitating minelands, reducing propagule pressure on neighboring canga areas.

The effect of shrub cover on conifer water-use patterns, growth and response to precipitation variability in the southern Sierra Nevada.

As wildfires increase in size and severity, large areas of forest are undergoing substantial increases in shrub cover. In forests where water is the limiting resource, the partitioning of soil water between shrubs and young trees may determine how shrubs affect tree growth and water-stress. Here we evaluated juvenile trees (average age=32years) of two dominant conifer species in the southern Sierra Nevada of California (Abies concolor (white fir) and Pinus jeffreyi (Jeffrey pine)) growing in the presence or absence of shrubs. The two shrub species included Arctostaphylos patula and Ceanothus cordulatus, a nitrogen-fixing species. We analyzed the δ2H and δ18O values of xylem water for both tree and shrub species to assess how shrub cover affects the water-uptake patterns of conifers and whether there is niche partitioning between trees and shrubs. We found that growing near shrubs did not have a significant effect on the water source dynamics of either tree species, with similar source water contributions calculated for conifers growing in both the presence and absence of shrubs. Using a tree-ring analysis of growth and δ13C from 2016 to 2021, a period of high precipitation variability, we found that shrub cover had a positive effect on tree growth while decreasing carbon discrimination, which may be due to increased nitrogen availability from Ceanothus cordulatus. Overall, our results suggest that growing in the presence of shrubs does not alter the water uptake patterns of white fir and Jeffrey pine and instead may have a positive effect on the growth rates of these species during both wet and dry years.

The effect of nitrogen source and levels on hybrid aspen tree physiology and wood formation.

Nitrogen can be taken up by trees in the form of nitrate, ammonium and amino acids, but the influence of the different forms on tree growth and development is poorly understood in angiosperm species like Populus. We studied the effects of both organic and inorganic forms of nitrogen on growth and wood formation of hybrid aspen trees in experimental conditions that allowed growth under four distinct steady-state nitrogen levels. Increased nitrogen availability had a positive influence on biomass accumulation and the radial dimensions of both xylem vessels and fibers, and a negative influence on wood density. An optimal level of nitrogen availability was identified where increases in biomass accumulation outweighed decreases in wood density. None of these responses depended on the source of nitrogen except for shoot biomass accumulation, which was stimulated more by treatments complemented with nitrate than by ammonium alone or the organic source arginine. The most striking difference between the nitrogen sources was the effect on lignin composition, whereby the abundance of H-type lignin increased only in the presence of nitrate. The differential effect of nitrate is possibly related to the well-known role of nitrate as a signaling compound. RNA-sequencing revealed that while the lignin-biosynthetic genes did not significantly (FDR <0.01) respond to added NO3 - , the expression of several laccases, catalysing lignin polymerization, was dependent on N-availability. These results reveal a unique role of nitrate in wood formation and contribute to the knowledge basis for decision-making in utilizing hybrid aspen as a bioresource.

Long-term effects of nitrogen enrichment in pollen chemistry of a plant species from Brazilian savannas, Pavonia rosa campestris

Human activities have substantially increased soil nutrient availability during the past decades, affecting plant community composition and plants' nutritional content. Several amino acids found in pollen, the main source of larval diet for bees, affect the development, health, and behaviour of this important group of pollinators. A better understanding of the consequences of global changes on pollen amino acid content can help explain and predict future impacts on bee populations and diversity. This is particularly relevant in regions that are highly exposed to fertilizers due to their importance for global food production, such as the Brazilian savannas (Cerrado), where soils are mostly dystrophic. Here, we use a long-term controlled fertilization experiment conducted in Cerrado and demonstrate that even after 10 years since the last fertilization addition, effects were still detectable on leaf and pollen chemical content. More specifically, pollen amino acid content of Pavonia rosa-campestris (Malvaceae), a species known to be important for the diet of several native bee species, changed because of nitrogen (N) addition. Not only did the overall amino acid content increase with N addition, but its profile was also affected, with the proportion of some amino acids increasing (e.g. isoleucine, leucine, serine, threonine), while decreasing for others (e.g. cysteine). These amino acids can have important effects on larval development and flower visitor behaviour. Further studies evaluating the effects on a diverse set of plant species and the consequent impacts on flower visitation and bee fitness are essential to better understand the full consequences of increased nitrogen availability in nutrient-limited ecosystems such as Cerrado.

Plant-Plant Interdependence and Mutualism Interactions in Heterogeneous Ecosystems still hide a lot of secrets

Plant-Plant Interdependence and Mutualism Interactions in Heterogeneous Ecosystems still hide a lot of secrets

Nitrogen addition improves drought tolerance in Camellia japonica (Naidong) seedlings

The northernmost population of Camellia japonica globally is a unique ecotype within the species. Water deficit and atmospheric nitrogen deposition are two critical environmental factors that influence plant growth and primary productivity, particularly in the context of environmental change. However, the interactive effects of drought and nitrogen deposition on the physiology and growth of Naidong seedlings have not been investigated. To address this gap, we conducted a greenhouse experiment to investigate the individual and combined influences of different water and nitrogen (N) levels on growth, leaf morphology and physiology, and biomass and carbohydrate allocation of three-year-old Naidong seedlings. The results demonstrated that drought reduced height, basal diameter, specific leaf area, biomass accumulation, net photosynthesis, and non-structural carbohydrate (NSC) pool in the root of seedlings. However, water use efficiency (WUE) increased under slight drought conditions. Moderate (6 g N m−2 year−1) nitrogen addition enhanced seedling biomass accumulation, carbon fixation capacity, and WUE. Furthermore, a significant interaction between water and nitrogen deposition on Fv/Fm, soluble sugars concentration in the stem, and starch concentration in the root of Naidong seedlings was discovered. Drought and nitrogen deposition exhibited antagonistic effects on seedling biomass accumulation and photosynthetic capacity. The adverse impact of drought on growth and physiological responses could be partially compensated by increased nitrogen availability. This study highlights the need to include more variables when assessing a species' vulnerability to shifts in environmental conditions in the context of global change studies. Furthermore, our findings provide supportive data for the survival of C. japonica under future climate scenarios.

Nitrogen cycle pattern variations during seawater-groundwater-river interactions enhance the nitrogen availability in the coastal earth critical zone

Hydrological interaction in highly vital and productive coastal earth critical zone (CECZ) significantly impacts the nitrogen cycle and availability, which is the essential foundation for agricultural production. The results of isotopes and microbial sequencing showed that nitrogen fixation and nitrite oxidation are enhanced in the palaeo-saltwater intrusion process. The weakening AmoCAB and Hao impedes the normal nitrogen cycling pathway, promoting the input of organic nitrogen, thus increasing nitrogen availability flux. In the river into the sea, nitrogen fixation is enhanced, while nitrite oxidation, denitrification, and DNRA are weakened. The whole intensity of the nitrogen cycle decreases. In addition, the oxidation of NH4-N to NO2-N in this process is inaccessible, which means that the nitrogen cycle flux is substantially reduced. In the river recharge to groundwater, nitrite oxidation, nitrogen fixation, and ammonia oxidation are enhanced. In the submarine groundwater discharge, the whole intensity of the nitrogen cycle gradually weakens and the nitrogen cycle flux greatly reduces. As the final pool of coastal groundwater and surface water, the significant reduction of the nitrogen cycle intensity and the absence of the pathway link allows nitrogen in seawater to flow out of the inorganic nitrogen cycle by the conversion to organic nitrogen, thus the net flux of nitrogen availability trapped in the hydrological systems increases. The hydrological interaction enhances the breadth of nitrogen sources, the diversity of pathways, and the flux of nitrogen in CECZ, thereby promoting more nitrogen being trapped in system and increasing nitrogen availability.

Warming, permafrost thaw and increased nitrogen availability as drivers for plant composition and growth across the Tibetan Plateau

Permafrost-affected ecosystems are subject to warming and thawing, which can increase the availability of subsurface nitrogen (N) with consequences in otherwise N-limited tundra and alpine vegetation. Here, we quantify the extent of warming and permafrost thawing and the corresponding effects on nitrogen availability and plant growth based on a 20-year survey across 14 sites on the Tibetan Plateau. The survey showed that most sites have been subject to warming and thawing and that the upper permafrost zone across all sites was rich in inorganic N, mainly as ammonium. We further explore the efficiency of plants to utilize 15N-labelled inorganic N over five years following 15N addition at the permafrost table far below the main root zone. The 15N experiment showed that deep-rooted plant species were able to utilize the labelled N. A SEM model suggests that changes in vegetation can be explained by both active layer warming and permafrost thawing and the associated changes in inorganic nitrogen availability. Our results highlight a feedback mechanism of climate warming, in which released plant-available N may favour deep-rooted plants. This can explain important changes in plant composition and growth across the sites on the Tibetan Plateau.

Anthropogenic sodium influences butterfly responses to nitrogen-enriched resources: implications for the nitrogen limitation hypothesis

Humans are increasing the environmental availability of historically limited nutrients, which may significantly influence organismal performance and behavior. Beneficial or stimulatory responses to increases in nitrogen availability (i.e., nitrogen limitation) are generally observed in plants but less consistently in animals. One possible explanation is that animal responses to nitrogen enrichment depend on how nitrogen intake is balanced with sodium, a micronutrient crucial for animals but not plants. We tested this idea in the cabbage white butterfly (Pieris rapae), a species that frequently inhabits nutrient-enriched plants in agricultural settings and roadside verges. We asked (1) whether anthropogenic increases in sodium influence how nitrogen enrichment affects butterfly performance and (2) whether individuals can adaptively adjust their foraging behavior to such effects. Larval nitrogen enrichment enhanced growth of cabbage white larvae under conditions of low but not high sodium availability. In contrast, larval nitrogen enrichment increased egg production of adult females only when individuals developed with high sodium availability. Ovipositing females preferred nitrogen-enriched leaves regardless of sodium availability, while larvae avoided feeding on nitrogen-enriched leaves elevated in sodium. Our results show that anthropogenic increases in sodium influence whether individuals benefit from and forage on nitrogen-enriched resources. Yet, different nitrogen-to-sodium ratios are required to optimize larval and adult performance. Whether increases in sodium catalyze or inhibit benefits of nitrogen enrichment may depend on how evolved nutrient requirements vary across stages of animal development.

Differential response of two acidophytic lichens to increased reactive nitrogen availability

Lichens are one of the most responsive components of the ecosystem to reactive forms of nitrogen. In this work, we selected the lichen genera Cladonia and Usnea, composed of terricolous and epiphytic lichens respectively, and described as sensitive to nitrogen, to test the effects of different doses of nitrogen on lichen physiological parameters (photobiont and mycobiont vitality, chitin quantification, nitrogen content and stable isotopes analysis). The main objectives were to check if the activation of protective mechanisms could be stimulated in case of chronic stress (low nitrogen increase for prolonged time), and, if so, if a toxicity threshold could be identified above which these mechanisms fail. The two lichen genera were generally affected by prolonged exposure to increased nitrogen availability. However, Cladonia rangiformis was able to maintain physiological functioning at the lowest nitrogen doses used, whereas thalli of Usnea become overwhelmed. Moreover, the mycobiont appeared to be more sensitive than the photobiont responding to lower nitrogen doses. Although only studies of longer duration and testing more nitrogen doses will be able to determine an accurate toxicity threshold, these results give important clues on the use of lichens as biomonitors for the establishment of environmental policies.

Excess labile carbon promotes diazotroph abundance in heat-stressed octocorals.

Nitrogen limitation is the foundation of stable coral-algal symbioses. Diazotrophs, prokaryotes capable of fixing N2 into ammonia, support the productivity of corals in oligotrophic waters, but could contribute to the destabilization of holobiont functioning when overstimulated. Recent studies on reef-building corals have shown that labile dissolved organic carbon (DOC) enrichment or heat stress increases diazotroph abundance and activity, thereby increasing nitrogen availability and destabilizing the coral-algal symbiosis. However, the (a)biotic drivers of diazotrophs in octocorals are still poorly understood. We investigated diazotroph abundance (via relative quantification of nifH gene copy numbers) in two symbiotic octocorals, the more mixotrophic soft coral Xenia umbellata and the more autotrophic gorgonian Pinnigorgia flava, under (i) labile DOC enrichment for 21 days, followed by (ii) combined labile DOC enrichment and heat stress for 24 days. Without heat stress, relative diazotroph abundances in X. umbellata and P. flava were unaffected by DOC enrichment. During heat stress, DOC enrichment (20 and 40 mg glucose l-1) increased the relative abundances of diazotrophs by sixfold in X. umbellata and fourfold in P. flava, compared with their counterparts without excess DOC. Our data suggest that labile DOC enrichment and concomitant heat stress could disrupt the nitrogen limitation in octocorals by stimulating diazotroph proliferation. Ultimately, the disruption of nitrogen cycling may further compromise octocoral fitness by destabilizing symbiotic nutrient cycling. Therefore, improving local wastewater facilities to reduce labile DOC input into vulnerable coastal ecosystems may help octocorals cope with ocean warming.

Partição de fotoassimilados em plantas de quiabo submetidas a doses de nitrogênio

ABSTRACT Nitrogen (N) is the third nutrient more absorbed by okra. Therefore, an adequate supply of this element is essential for okra growth through the accumulation of dry matter in the leaves, stem, root and fruit. The objective was to evaluate the influence of N doses on growth, photoassimilates partition and yield of okra. The experiment was carried out in a Red-Yellow Argisol. A randomized complete block design with four replicates was used. The treatments consisted of N doses applied as topdressing (0, 60, 120, 240, 360 kg/ha). Samples of plants were held at 60, 75, 90, 105, 120, 135, 150 and 165 DAS for determination of the plant’s dry weight. The plant showed slow growth until 70 days, and after that time, intensified its growth until the end of the cycle. Total dry mass and absolute plant growth rate increased with increasing N availability, reaching the maximum marketable fruit yield of 10,665 kg/ha with 346 kg/ha N. The growth and partition of photoassimilates among the organs of the okra plant ‘Santa Cruz’ are altered with increasing nitrogen availability applied in topdressing.

A research agenda for nonvascular photoautotrophs under climate change.

Nonvascular photoautotrophs (NVP), including bryophytes, lichens, terrestrial algae, and cyanobacteria, are increasingly recognized as being essential to ecosystem functioning in many regions of the world. Current research suggests that climate change may pose a substantial threat to NVP, but the extent to which this will affect the associated ecosystem functions and services is highly uncertain. Here, we propose a research agenda to address this urgent question, focusing on physiological and ecological processes that link NVP to ecosystem functions while also taking into account the substantial taxonomic diversity across multiple ecosystem types. Accordingly, we developed a new categorization scheme, based on microclimatic gradients, which simplifies the high physiological and morphological diversity of NVP and world-wide distribution with respect to several broad habitat types. We found that habitat-specific ecosystem functions of NVP will likely be substantially affected by climate change, and more quantitative process understanding is required on (1) potential for acclimation, (2) response to elevated CO2 , (3) role of the microbiome, and (4) feedback to (micro)climate. We suggest an integrative approach of innovative, multimethod laboratory and field experiments and ecophysiological modelling, for which sustained scientific collaboration on NVP research will be essential.

The Effect of Aplication Zeolit, and Urea, Chicken Manure Fertilizer in Increasing Nitrogen Availability and Growth of Maize (Zea mays L.)

This research was performed to learn the effect of Zeolit, Urea Fertilizer and Chicken Manure Fertilizer in Increasing Nitrogen Availability and Growth of Corn Plant (Zea mays L.). This study used factorial randomized block design (RBD) method with three treatment factors and three replications. The first factor was zeolit with four treatment (0, 5.000, 10.000, dan 15.000 kg/ha), the second factor was urea fertilizer with two treatment (0 and 400 kg/ha), the third factor was chicken manure fertilizer with two treatment (0 and 30.000 kg/ha). The parameters measured were pH H2O, C-Organic, Total N, plant height, number of leaves, canopy dry weight, root dry weight and plant dry weight. The results showed that aplication of zeolit was able to increase N-total value, number of leaves and canopy dry weight. Aplication of urea fertilizer wasn’t able to increase all of parameters however can increase that’s value. Aplication of manure fertilizer was able to increase C-organic, total N, plant height and plant dry weight. Aplication of zeolit and urea fertilizer was able to increase total N and plant height. Aplication of zeolit and manure fertilizer was able to increase total N and root dry weight. Aplication of urea fertilizer and manure fertilizer was able to increase total N. Aplication of zeolit, urea fertilizer and manure fertilizer was able to increase total N of Ultisol.

Local vehicles add nitrogen to moss biomonitors in a low-traffic protected wilderness area as revealed by a long-term isotope study

Public use of protected areas is typically encouraged, but visitors arriving by vehicles may alter the natural areas they seek. Vehicle emissions add nitrogen oxides (NOx) and ammonia (NH3) to the air, which can increase the amount of plant-available (reactive) nitrogen, a limiting nutrient. Changes in ecosystem processes as a result of increases in nitrogen availability are at odds with the goals of many protected wilderness areas that are typically accessed by vehicles. In this multi-year study (2003–2019), we tested whether emissions from local vehicles entered the forest ecosystem adjacent to a highway in a protected wilderness valley near a mid-sized city (Calgary, Alberta, Canada). We examined the concentration of NO2 in the air and the abundance of combustion-derived nitrogen isotopes (δ15N) in naturally-occurring forest moss (Hylocomium splendens and Pleurozium schreberi) within 20 m of the highway as a function of traffic levels that varied independently at two scales: along the highway and among years. Within the valley, we observed a gradient in the number of vehicles that was greatest where vehicles enter the valley, with a corresponding pattern for NO2 concentrations in air. Traffic volume also varied among years, with the highest year having almost twice as many vehicles in the summer as the lowest year. δ15N values in forest moss displayed similar patterns as traffic both within and among years, signalling that nitrogen from vehicle emissions entered the local ecosystem corresponding to local traffic levels. Because vehicle emissions enter natural ecosystems that are intended to be conserved, vehicle use must be considered in the management of protected natural areas.

Effect of Different Cover Crops, Mass-Trapping Systems and Environmental Factors on Invertebrate Activity in Table Olive Orchards—Results from Field Experiments in Crete, Greece

Background: Although the negative effects of insecticides and herbicides on beneficial and non-target invertebrates are well documented, there is limited information on potential negative impacts of pest and weed management practices used in organic farming on invertebrate activity. Methods: Using established field experiments designed to compare different ground cover crops (used to suppress weeds and increase nitrogen availability and soil health) and mass-trapping systems (used for olive fly control) in organic olive production systems, we monitored the impact of these practices on invertebrate activity. Results: When different ground cover crops were compared, ground cover crops established from a vetch/pea/barley seed mixtures resulted in significantly higher parasitic wasps activity than ground cover vegetation in control plots (plots in which Medicago seed were sown and failed to establish) that were dominated by the weed Oxalis pes-caprae. When two bottle based mass-trapping systems were compared, the traps caught similar numbers of olive flies and some non-target invertebrates (mainly other Diptera, Neuroptera and Lepidotera and Formicidae), although no parasitic wasps or pollinators (bees; bumble bees) were caught in traps. Analyses of invertebrate profiles found in McPhail monitoring traps showed that invertebrate activity profiles were similar in plots with and without mass-trapping devices. In addition, as expected, redundancy analyses showed that climatic parameters (temperature, rainfall, humidity, wind direction) are significant explanatory variables/drivers for invertebrate activity in olive orchards. Conclusions: The results presented indicate that mixed legume/cereal ground cover crops may increase the activity of parasitic wasps and may act as a reservoir for natural enemies of agricultural pest and that olive fly mass-trapping systems may lure and kill some non-target invertebrates, but do not affect the activity of two main groups of beneficial invertebrates namely pollinators and parasitic wasps.

Nitrogen-based symbioses, phosphorus availability, and accounting for a modern world more productive than the Paleozoic.

Evolution of high-productivity angiosperms has been regarded as a driver of Mesozoic ecosystem restructuring. However, terrestrial productivity is limited by availability of rock-derived nutrients such as phosphorus for which permanent increases in weathering would violate mass balance requirements of the long-term carbon cycle. The potential reality of productivity increases sustained since the Mesozoic is supported here with documentation of a dramatic increase in the evolution of nitrogen-fixing or nitrogen-scavenging symbioses, including more than 100 lineages of ectomycorrhizal and lichen-forming fungi and plants with specialized microbial associations. Given this evidence of broadly increased nitrogen availability, we explore via carbon cycle modeling how enhanced phosphorus availability might be sustained without violating mass balance requirements. Volcanism is the dominant carbon input, dictating peaks in weathering outputs up to twice modern values. However, times of weathering rate suppression may be more important for setting system behavior, and the late Paleozoic was the only extended period over which rates are expected to have remained lower than modern. Modeling results are consistent with terrestrial organic matter deposition that accompanied Paleozoic vascular plant evolution having suppressed weathering fluxes by providing an alternative sink of atmospheric CO2 . Suppression would have then been progressively lifted as the crustal reservoir's holding capacity for terrestrial organic matter saturated back toward steady state with deposition of new organic matter balanced by erosion of older organic deposits. Although not an absolute increase, weathering fluxes returning to early Paleozoic conditions would represent a novel regime for the complex land biota that evolved in the interim. Volcanism-based peaks in Mesozoic weathering far surpass the modern rates that sustain a complex diversity of nitrogen-based symbioses; only in the late Paleozoic might these ecologies have been suppressed by significantly lower rates. Thus, angiosperms are posited to be another effect rather than proximal cause of Mesozoic upheaval.