Jesús Pascual

Prognosis and correction of iron chlorosis in peach trees: Influence on fruit quality

Abstract A floral analysis for iron (Fe) content allowed for the prognosis of the incidence of the Fe chlorosis on peach (Prunus persica L. Batsch) trees (c.v. ‘Babygold 7’ grafted on seedlings) with high reliability. From a total of 35 peach trees analyzed, six of them had floral Fe dry matter concentrations less than 133 ppm and these six trees later developed severe Fe chlorosis in their leaves. The early detection and correction of Fe deficiency permitted us to measure the influence of Fe chlorosis on fruit quality as Fe correction resulted in a doubling of frait size and avoidance of the delay of frait ripeness that occurred on the Fe‐deficient trees.

Prognosis of iron chlorosis in apple trees by floral analysis

Abstract In populations of apple trees (Malus pumila Mill) affected by iron (Fe) chlorosis, the floral analyses permit to establish relationships between the Fe concentration in flowers and the chlorophyll content in leaves at 60 and 120 days after full bloom. The relationships between both parameters were highly significant with correlation coefficients of 0.603*** and 0.872***, respectively. As from previous research with peach trees, these high correlations permitted us to predict at a very early stage, the appearance of the Fe deficiency and its intensity. In our experimental conditions, the first visual symptoms of the Fe chlorosis appear in apple leaves with floral Fe concentrations below 310 ppm in dry matter.

Climate modifies response of non-native and native species richness to nutrient enrichment

Ecosystem eutrophication often increases domination by non-natives and causes displacement of native taxa. However, variation in environmental conditions may affect the outcome of interactions between native and non-native taxa in environments where nutrient supply is elevated. We examined the interactive effects of eutrophication, climate variability and climate average conditions on the success of native and non-native plant species using experimental nutrient manipulations replicated at 32 grassland sites on four continents. We hypothesized that effects of nutrient addition would be greatest where climate was stable and benign, owing to reduced niche partitioning. We found that the abundance of non-native species increased with nutrient addition independent of climate; however, nutrient addition increased non-native species richness and decreased native species richness, with these effects dampened in warmer or wetter sites. Eutrophication also altered the time scale in which grassland invasion responded to climate, decreasing the importance of long-term climate and increasing that of annual climate. Thus, climatic conditions mediate the responses of native and non-native flora to nutrient enrichment. Our results suggest that the negative effect of nutrient addition on native abundance is decoupled from its effect on richness, and reduces the time scale of the links between climate and compositional change.

Herbivory affects salt marsh succession dynamics by suppressing the recovery of dominant species

Disturbance can generate heterogeneous environments and profoundly influence plant diversity by creating patches at different successional stages. Herbivores, in turn, can govern plant succession dynamics by determining the rate of species replacement, ultimately affecting plant community structure. In a south-western Atlantic salt marsh, we experimentally evaluated the role of herbivory in the recovery following disturbance of the plant community and assessed whether herbivory affects the relative importance of sexual and clonal reproduction on these dynamics. Our results show that herbivory strongly affects salt marsh secondary succession by suppressing seedlings and limiting clonal colonization of the dominant marsh grass, allowing subordinate species to dominate disturbed patches. These results demonstrate that herbivores can have an important role in salt marsh community structure and function, and can be a key force during succession dynamics.

Local loss and spatial homogenization of plant diversity reduce ecosystem multifunctionality

Biodiversity is declining in many local communities while also becoming increasingly homogenized across space. Experiments show that local plant species loss reduces ecosystem functioning and services, but the role of spatial homogenization of community composition and the potential interaction between diversity at different scales in maintaining ecosystem functioning remains unclear, especially when many functions are considered (ecosystem multifunctionality). We present an analysis of eight ecosystem functions measured in 65 grasslands worldwide. We find that more diverse grasslands—those with both species-rich local communities (α-diversity) and large compositional differences among localities (β-diversity)—had higher levels of multifunctionality. Moreover, α- and β-diversity synergistically affected multifunctionality, with higher levels of diversity at one scale amplifying the contribution to ecological functions at the other scale. The identity of species influencing ecosystem functioning differed among functions and across local communities, explaining why more diverse grasslands maintained greater functionality when more functions and localities were considered. These results were robust to variation in environmental drivers. Our findings reveal that plant diversity, at both local and landscape scales, contributes to the maintenance of multiple ecosystem services provided by grasslands. Preserving ecosystem functioning therefore requires conservation of biodiversity both within and among ecological communities.Analysis of 65 grasslands worldwide from the Nutrient Network experiment reveals that plant communities with higher α- and β-diversity have higher levels of ecosystem multifunctionality, and that this effect is amplified across scales.

Physical stress modifies top-down and bottom-up forcing on plant growth and reproduction in a coastal ecosystem

Bottom-up and top-down effects act together to exert strong control over plant growth and reproduction, but how physical stress modifies those interactive forces remains unclear. Even though empirical evidence is scarce, theory predicts that the importance of both top-down- and bottom-up forces may decrease as physical stress increases. Here, we experimentally evaluate in the field the separate and interactive effect of salinity, nutrient availability, and crab herbivory on plant above- and belowground biomass, as well as on sexual and clonal reproduction in the salt marsh plant Spartina densiflora. Results show that the outcome of the interaction between nutrient availability and herbivory is highly context dependent, not only varying with the abiotic context (i.e., with or without increased salinity stress), but also with the dependent variable considered. Contrary to theoretical predictions, our results show that, consistently across different measured variables, salinity stress did not cancel bottom-up (i.e., nutrients) or top-down (i.e., consumers) control, but has additive effects. Our results support emerging theory by highlighting that, under many conditions, physical stress can act additively with, or even stimulate, consumer control, especially in cases where the physical stress is only experienced by basal levels of the trophic chain. Abiotic stress, as well as bottom-up and top-down factors, can affect salt marsh structure and function not only by affecting biomass production but also by having other indirect effects, such as changing patterns in plant biomass allocation and reproduction.

Small Mammals Along SW-Atlantic Marshes: Diversity Correlates with Inland Habitats but Abundance Correlates with Marsh Characteristics

Tidal marshes are narrow wetlands distributed worldwide between the ocean and a variety of inland-habitats. The high diversity of interacting terrestrial habitats may influence terrestrial species composition and abundance in marshes. We investigated if characteristics of small mammal assemblages inhabiting the South-West-Atlantic (SWA) marshes are influenced by marsh characteristics, or if they vary in relation to changes in the inland biogeographic context. Sampling at five-Spartina marshes across the SWA-coast showed that plant cover, richness and height (ANOVA analysis) and small mammal assemblages (PERMANOVA analysis) differed between habitats (marsh or inland) depending on the site. Generalized Linear Models (GLMs) showed that abundance of small mammals in marshes is related to vegetation cover and diversity. However, its richness was related to the richness of small mammal at the inland habitats. In fact, species present in each marsh were also recorded in adjacent inland habitats. Species composition differed among similar marshes surrounded by different landscapes, while those in the same landscape did not. Consequently, regional abundance of small mammals in SWA-marshes is consistent with ecological sorting of abundance ranges along environmental gradients (e.g., plant-cover and richness). In contrast, landscape composition and configuration strongly affect marsh small mammal species assemblages, even if the marsh-habitats are quite similar.

Herbivory and trampling by small mammals modify soil properties and plant assemblages

Question Do trampling and herbivory by small mammals affect salt marshes physical and biological properties? Location Upper salt marsh at the Mar Chiquita coastal lagoon (37o 44′ 52′′ S, 57o 26′ 6′′ W, Argentina). Methods A field experiment was placed from autumn to early summer in runways made by the wild Guinea pig Cavia aperea. Segments of runways were randomly assigned to different treatments: control (herbivory and trampling), total exclusion (without herbivory or trampling) and reduced trampling (herbivory without trampling). After eight months of experiment, soil hardness, runway depth, maximum plant height, aboveground biomass, plant assemblages, diversity and richness were measured and compared between treatments. Results Runways of C. aperea covered 14.5% of the area. Through trampling, C. aperea compacted the soil, increasing soil hardness and runway depth. Herbivory, in turn, reduced aboveground biomass and plant species richness, and affected species composition. Both, herbivory and trampling decreased the maximum plant height. Conclusion Our results show how small herbivores, through trampling, are able to drive soil compaction, an effect previously described only for large mammals. Results also show that small mammals can control salt marsh primary production, reduce species richness and modify the composition of plant species through herbivory. Small mammal herbivores, thus, can modify physical and biological properties of salt marsh communities through both trophic and non-trophic mechanisms. This article is protected by copyright. All rights reserved.

Nutrients and Abiotic Stress Interact to Control Ergot Plant Disease in a SW Atlantic Salt Marsh

Over the last decades, human activities have strongly affected ecosystems, with pervasive increases in nutrient loadings, abiotic stress, and altered herbivore pressure. The evaluation of how those environmental factors interact to influence plant–pathogen interactions under natural conditions becomes essential to fully understand the ecology of diseases and anticipate the possible effects of global change on natural and agricultural systems. In a SW Atlantic salt marsh, we performed a field factorial experiment to evaluate the effect of herbivory, salinity, and nutrient availability, three main limiting factors for salt marsh plant growth, on the infection of the fungus Claviceps purpurea (ergot) upon the cordgrass Spartina densiflora. Results show that herbivory has no effect but both nutrients and salinity increase fungal infection. The combined effect of salinity and nutrients is not additive but interactive. Salinity stress increases infection at ambient nutrient levels but in combination with fertilizer it buffers the higher infection produced by increased nutrient availability. Since both, nitrogen availability and salinity are factors predicted to globally increase due to human impact on ecosystems, this interaction between environmental factors and ergot infection can have strong effects on natural and productive agricultural systems.

Herbivory and presence of a dominant competitor interactively affect salt marsh plant diversity

Question Do herbivory and the presence of a dominant grass competitor interactively affect herbaceous communities and assembly rules in a SW Atlantic salt marsh? Location Upper salt marsh at the Mar Chiquita coastal lagoon (37o 44′ 52′′ S, 57o 26′ 6′′ W, Argentina). Methods We performed a field factorial experiment, during 4 years, to evaluate the separate and interactive effects of (1) herbivory and (2) competition with the dominant grass species (i.e. Spartina densiflora) on salt marsh subordinate plant community. The factorial design includes dominant grass removal and herbivory manipulation. Results Our results show that herbivory and presence of the dominant competitor interactively affect subordinate plant cover and diversity. Results further indicate that, in the presence of the dominant competitor, patch-to-patch variation in subordinate species composition is lower than expected at random, a result consistent with the expected outcomes of deterministic exclusion following light competition. Removal of the dominant grass, nevertheless led to patch-to-patch dissimilarity in subordinate species composition far from the dissimilarity expected at random, indicating an increased importance of deterministic processes that drive communities to diverge. Conclusion Our results show that the conditional effect of herbivory on plant diversity can be determined by the presence of a single plant species. Dominant plant species, in addition, may not only affect plant species diversity by determining the number and identity of subordinate species in a given patch (i.e. α diversity) but also by affecting spatial variability by means of habitat homogenization. This article is protected by copyright. All rights reserved.