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  • Author or Editor: S. Mazzoleni x
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Belowground soil characteristics are recognised as possible key factors in affecting plant species coexistence and community organisation. In this study, soil heterogeneity was generated by the growth of different herbaceous plants under controlled conditions, and thus related to growth and competitive ability of three naturally co-occurring species (Holcus lanatus, Inula viscosa and Pulicaria dysenterica). Soil changes induced by all species caused significant specific effects on the performance of these species and on their competitive hierarchies. Holcus lanatus was the strongest competitor on disturbed soil, but showed a dramatic negative feedback in monoculture. The experimental results are relevant for understanding community ecology and suggest that the investigation of species coexistence should take into account the possible role of plant-soil feedback processes.to the agricultural.

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Allelopathic effects of Calluna vulgaris have been extensively studied, but little attention has been given to the dynamics of phytotoxicity during the decomposition of its litter. Strong evidence from vegetation dynamics and management strategies indicate that Calluna litter inhibits its own seed regeneration. This work investigates the hypotheses that Calluna tissues are autotoxic and that decomposition processes moderate this effect. Water extracts of fresh Calluna shoots, litter and surface soil from a burned stand were used in both aerobic and anaerobic conditions to test for phytotoxicity in Lepidium sativum and Calluna vulgaris seeds and seedlings. Phytotoxicity varied for undecomposed Calluna materials with the following rank: shoots ?? litter ? burned soil. Moreover, phytotoxicity on Lepidium and Calluna of all tested materials sharply decreased during aerobic decomposition, but it remained high in anaerobic conditions. This paper confirms that Calluna shoots and litter are autotoxic, and demonstrates clear patterns related to decomposition processes. The potential consequences for vegetation dynamics are discussed.

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Community ecologists have become increasingly interested in analyzing the phylogenetic diversity of species assemblages. Species that co-occur in the same habitats often share a common phylogenetic history such that at coarse spatial scales a species assemblage with a locally clustered phylogenetic structure is usually associated with the presence of habitat filtering mechanisms. However, more recently it has been hypothesized that environmental filters act primarily on the relative abundance of species rather than on their simple presences and absences, reducing the species’ probabilities to persist in given environmental conditions. This process may produce a non-random distribution of species abundances in the regional phylogeny even in the absence of a locally clustered phylogenetic structure. In this paper, using data from the urban flora of Brussels (Belgium) we tested for the presence of non-randomness in the distribution of abundances among the species phylogenetic structure. We argue that the observed pattern of low species phylogenetic distinctiveness at increasing species abundances is compatible with environmental filtering processes.

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Species-specificity of facilitative interactions is ecologically relevant for community organization and dynamics. The prevalence of heterospecific facilitation which is found between higher plants seems an evolutionary paradox since beneficiary heterospecifics can compete with, and even replace, their nurse. An extensive review on facilitative interactions for both higher plants and sessile aquatic organisms is presented. The study reports on the occurrence of positive interactions between conspecifics and heterospecifics, in relation to different growth forms and facilitative mechanisms in terrestrial and aquatic environments. Four hypotheses are considered to explain the observed rarity of conspecific compared to heterospecific facilitation: 1) the occurrence of plant-induced unsuitable recruitment conditions (negative conspecific plant-soil feedback and hump-shaped recruitment distribution), 2) higher competition levels between conspecifics, 3) the prevalence of non-facilitated regeneration niche for nurses, and, 4) differences in the research effort. Self-facilitation is reported much more rarely in terrestrial vegetation (5.3% of 1554 cases of facilitiative interactions), than in aquatic ecosystems (36.2%, n = 130). In absolute terms, far more occurrences of heterospecific facilitative interactions are reported for all growth forms. However, when the occurrences of facilitative interactions are expressed as a percentage of the total con- and heterospecific interactions, annual and perennial herbaceous nurse plants show prevailing conspecific interactions, while woody (trees and shrubs) nurse species mostly show heterospecific facilitation. Increase of soil nutrient fertility, improvement of above-ground microclimate, associational refuge and seed trapping are the most common mechanisms of heterospecific interactions. Differently, conspecific facilitation is mostly due to improved soil biotic conditions, changes in fire regimes and reduction of heterospecific competition. Given the frequently reported occurrence of non-facilitated regeneration niche for nurse species, conspecific negative feedback and hump-shaped recruitment distribution in terrestrial plants, these processes are suggested as significantly contributing to explain the observed rarity of conspecific facilitation.

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Diversity of forest trees ranges from monospecific stands to the astonishing richness of tierra firma tropical forests. Such patterns are observed along gradients of latitude, altitude, soil fertility and rainfall. So far, the proposed coexisting mechanisms do not provide a comprehensive and unequivocal explanation of these patterns at the community level. We propose a new theory linking species diversity with organic matter cycle and negative plant-soil feedback induced by litter autotoxicity. This approach focuses on resource-waste rather than resource-only dynamics. High diversity does occur where litter decomposition is rapid and ecosystem nutrient cycles are closed. On the other hand, single species dominance is found where litter decomposition is slow and/or autotoxicity is removed from the nutrient cycle pathway. Unlike previous theoretical views, the one we present proves potentially capable of explaining differences in species diversity both along environmental gradients and within the tropics.

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Community Ecology
Authors: G. Bonanomi, G. Incerti, A. Stinca, F. Cartenì, F. Giannino and S. Mazzoleni

Ring shaped patches of clonal plants fascinated plant ecologists since long time. In this work we review the reports on the occurrence of ring pattern in different environmental conditions, the growth forms of ring-forming plants, the mechanisms underlying ring formation, and the consequences for species diversity at community scale. Rings formed by 83 species of clonal vascular plants have been found in grasslands, deserts, bare substrates of lava flow, harvested peat lands, salt marshes, and sand dunes. Four causal hypotheses have been proposed for the emergence of ring patterns: i. occurrence of architectural constraints for ramets development; ii. induction by fire, drought, trampling or overgrazing; iii. nutrient and water depletion by competition inside the ring; and iv. onset of species-specific negative plant-soil feedback in the inner zone of the clone. Since almost all the available studies are observations of ring structure or modelling exercises, none of the putative mechanisms for ring formation emerged from the literature as either generally applicable or suitable for rejection. Therefore, long-term field experiments are needed to investigate the relative prevalence of different mechanisms in different environments. Ring formation bears important consequences at community scale, because ring forming plants often act as “nurses”, enhancing the recruitment and development of different plant species. In fact, ring establishment modifies above- and below-ground environmental conditions, providing specialized safe sites for beneficiaries in the inner zone of the clones. Such interspecific facilitation by ring forming plants, particularly in chronically stressed environments, contributes to increase plant species richness and can locally promote the successional dynamics.

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Unlike vagile organisms, plants perform a wide range of phenotypic responses to cope with environmental stresses. A special case of interaction with external factors is the ability of plants to recognize genetic relatedness of neighbour plants, actually well known as kin recognition. The present work aimed to provide a valuable contribution to the field of kin recognition in plants through a common garden experiment. To avoid bias involved in pot experiments, we perform an experiment in unconstrained root growth conditions comparing the development of coupled kin, non-kin and solitary plants of Xanthium italicum. Biometrics of plants with different genetic relatedness were measured, then architecture and competitive interaction were assessed using the relative interaction index (RII) for above and belowground portions of plants. X. italicum showed different allocation depending on the neighbourhood. Root biomass was declined in plants growing with kin compared to non-kin coupled plants, while plants coupled with kin allocated more shoot than roots compared to solitary plants. RII explains phenotypic response of decreased competition in roots rather than in shoots. Despite high values of RII for the aboveground portion, the architectural analysis of shoot, number, angle and length of branches and roots reveals dramatic but indistinctive change in the structure of plants growing near kin or non kin compared to a solitary plant. These results confirm phenotypic responses of kin recognition in unconstrained environment.

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The consequences of decline in biodiversity for ecosystem functioning is a major concern in soil ecology. Recent research efforts have been mostly focused on terrestrial plants, while, despite their importance in ecosystems, little is known about soil microbial communities. This work aims at investigating the effects of fungal and bacterial species richness on the dynamics of leaf litter decomposition. Synthetic microbial communities with species richness ranging from 1 to 64 were assembled in laboratory microcosms and used in three factorial experiments of decomposition. Thereafter, the functionality of the different microcosms was determined by measuring their capability to decompose materials with different chemical properties, including two species of litter (Quercus ilex L. and Hedera helix L.), cellulose strips and woody sticks. Incubation was done in microcosms at two temperatures (12°C and 24°C) for 120 days. The number of microbial species inoculated in the microcosms positively affected decomposition rates of Q. ilex and H. helix litters, while relationships found for cellulose and wood were not statistically significant. Diversity effect was greater at higher incubation temperature. We found lower variability of decay rates in microcosms with higher inoculated species richness of microbial communities. Our study pointed out that the relationships between inoculum microbial diversity and litter decomposition is dependent on temperature and litter quality. Therefore, the loss of microbial species may adversely affects ecosystem functionality under specific environmental conditions.

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Community Ecology
Authors: C. Ricotta, E. Ari, G. Bonanomi, F. Giannino, D. Heathfield, S. Mazzoleni and J. Podani

The increasing availability of phylogenetic information facilitates the use of evolutionary methods in community ecology to reveal the importance of evolution in the species assembly process. However, while several methods have been applied to a wide range of communities across different spatial scales with the purpose of detecting non-random phylogenetic patterns, the spatial aspects of phylogenetic community structure have received far less attention. Accordingly, the question for this study is: can point pattern analysis be used for revealing the phylogenetic structure of multi-species assemblages? We introduce a new individual-centered procedure for analyzing the scale-dependent phylogenetic structure of multi-species point patterns based on digitized field data. The method uses nested circular plots with increasing radii drawn around each individual plant and calculates the mean phylogenetic distance between the focal individual and all individuals located in the circular ring delimited by two successive radii. This scale-dependent value is then averaged over all individuals of the same species and the observed mean is compared to a null expectation with permutation procedures. The method detects particular radius values at which the point pattern of a single species exhibits maximum deviation from the expectation towards either phylogenetic aggregation or segregation. Its performance is illustrated using data from a grassland community in Hungary and simulated point patterns. The proposed method can be extended to virtually any distance function for species pairs, such as functional distances.

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Community Ecology
Authors: M. Idbella, M. Zotti, G. Cesarano, T. Fechtali, S. Mazzoleni and G. Bonanomi

Abstract

Plant litter decomposition is a crucial process of nutrient cycling within ecosystems. However, many studies have shown that, apart from its several beneficial effects, organic matter decomposition can be disadvantageous to seed germination, seedling growth, and physiological activity of plants. Litter decomposition was reported to affect both plants and their associated soil microbial communities. The aim of this work was to test the relationships between seed-associated endophytic fungi on the either positive or negative plant's response to different litter types. Leaf material of four species was collected and used in a decomposition experiment inside a growth chamber for 120 days. The plant growth experiment was set in a greenhouse using Trifolium repens and Triticum durum with and without their associated endophytic fungi in the presence of the different litter species at two decay levels (fresh litter and after 120 days of decomposition). Results demonstrated that fresh litter exerted a strong inhibition effect on the plant total biomass when compared to decomposed litter. Moreover, seed-associated endophytic fungi enhanced the inhibitory effect of litter in the observed experimental conditions. The removal of seed-associated endophytic fungi improved the capacity of tested plants to resist to litter inhibitory effect.

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