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Gomez-Aparicio L.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville | Valiente-Banuet A.,National Autonomous University of Mexico
Proceedings of the Royal Society B: Biological Sciences | Year: 2012

Biotic interactions assembling plant communities can be positive (facilitation) or negative (competition) and operate simultaneously. Facilitative interactions and posterior competition are among the mechanisms triggering succession, thus representing a good scenario for ecological restoration. As distantly related species tend to have different phenotypes, and therefore different ecological requirements, they can coexist, maximizing facilitation and minimizing competition. We suggest including phylogenetic relatedness together with phenotypic information as a predictor for the net effects of the balance between facilitation and competition in nurse-based restoration experiments. We quantify, by means of a Bayesian meta-analysis of nurse-based restoration experiments performed worldwide, the importance of phylogenetic relatedness and life-form disparity in the survival, growth and density of facilitated plants. We find that the more similar the life forms of neighbouring plants are the greater the positive effect of phylogenetic distance is on survival and density. This result suggests that other characteristics beyond life form are also contained in the phylogeny, and the larger the phylogenetic distance, the less is the niche overlap, and therefore the less is the competition. As a general rule, we can maximize the success of the nurse-based practices by increasing life-form disparity and phylogenetic distances between the neighbour and the facilitated plant. © 2012 The Royal Society.

Kraft N.J.B.,University of Maryland University College | Godoy O.,University of California at Santa Barbara | Godoy O.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville | Levine J.M.,ETH Zurich
Proceedings of the National Academy of Sciences of the United States of America | Year: 2015

Understanding the processes maintaining species diversity is a central problem in ecology, with implications for the conservation and management of ecosystems. Although biologists often assume that trait differences between competitors promote diversity, empirical evidence connecting functional traits to the niche differences that stabilize species coexistence is rare. Obtaining such evidence is critical because traits also underlie the average fitness differences driving competitive exclusion, and this complicates efforts to infer community dynamics from phenotypic patterns. We coupled fieldparameterized mathematical models of competition between 102 pairs of annual plants with detailed sampling of leaf, seed, root, and whole-plant functional traits to relate phenotypic differences to stabilizing niche and average fitness differences. Single functional traits were often well correlated with average fitness differences between species, indicating that competitive dominance was associated with late phenology, deep rooting, and several other traits. In contrast, single functional traits were poorly correlated with the stabilizing niche differences that promote coexistence. Niche differences could only be described by combinations of traits, corresponding to differentiation between species in multiple ecological dimensions. In addition, several traits were associated with both fitness differences and stabilizing niche differences. These complex relationships between phenotypic differences and the dynamics of competing species argue against the simple use of single functional traits to infer community assembly processes but lay the groundwork for a theoretically justified trait-based community ecology.

Knicker H.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville
Soil Biology and Biochemistry | Year: 2011

The availability of Soil Organic Nitrogen (SON) determines soil fertility and biomass production to a great extent. SON also affects the amounts and turnover rates of the soil organic carbon (SOC) pools. Although there is increasing awareness of the impact of the nitrogen (N) cycle on the carbon (C) cycle, the extent of this interaction and the implications for soil organic matter (SOM) dynamics are still under debate. Therefore, present knowledge about the inter-relationships of the soil cycles of C and N as well as current ideas about SON stabilization are summarized in this paper in order to develop an advanced concept of the role of N on C sequestration. Modeling global C-cycling, it was already recognized that SON and SOC are closely coupled via biomass production and degradation. However, the narrow C/N ratio of mature soil organic matter (SOM) shows further that the impact of SON on the refractory SOM is beyond that of determining the size of the active cycling entities. It affects the quantity of the slow cycling pool and as a major contributor it also determines its chemical composition. Although the chemical nature of SON is still not very well understood, both improved classical wet chemical analyses and modern spectroscopic techniques provide increasing evidence that almost the entire organic N in fire-unaffected soils is bound in peptide-like compounds and to a lesser extent in amino sugars. This clearly points to the conclusion, that such compounds have greater importance for SOM formation than previously assumed. Based on published papers, I suggest that peptides even have a key function in the C-sequestration process. Although the mechanisms involved in their medium and long-term stabilization are far from understood, the immobilization of these biomolecules seems to determine the chemistry and functionality of the slow cycling SOM fraction and even the potential of a soil to act as a C sink. Pyrogenic organic N, which derives mostly from incomplete combustion of plant and litter peptides is another under-rated player in soil organic matter preservation. In fire-prone regions, its formation represents a major N stabilization mechanism, leading to the accumulation of heterocyclic aromatic N, the stability of which is still not elaborated. The concept of peptide-like compounds as a key in SOM-sequestration implies that for an improved evaluation of the potential of soils as C-sinks our research focus as to be directed to a better understanding of their chemistry and of the mechanisms which are responsible for their resistance against biochemical degradation in soils. © 2011 Elsevier Ltd.

Fernandez J.-E.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville
Environmental and Experimental Botany | Year: 2014

In this work we give an overview of both morphological characteristics and physiological mechanisms responsible for the high adaptability of olive to harsh environments, and how this knowledge is currently used to design new sustainable and efficient crop management practices. We first describe the biennial vegetative and reproductive cycle of olive, and how these are affected by environmental conditions. Then we address main morphological, functional and physiological traits of olive that may contribute to stress tolerance. We also summarize innovative crop management practices that have been developed from our understanding of the mechanisms of response to abiotic stresses. © 2013 Elsevier B.V.

Knicker H.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville
Organic Geochemistry | Year: 2010

The chemical and thermal stability of organic nitrogen (N) in pyrogenic organic matter (PyOM) was examined by charring casein at 350 °C and 450 °C. The alteration was compared with that observed for char derived from lignin, cellulose, grass and wood. With respect to heating, casein showed a considerably higher stability than cellulose. Comparable proportions of carbon (C) and N were recovered, supporting the idea that black nitrogen (BN) represents an integral part of the char structure. Although some amides were still present, they lost importance with increasing temperature. Charring of grass revealed an enrichment in N compounds because of the low thermal stability of cellulose. The similarity in the resulting nuclear magnetic resonance (NMR) spectra to those of casein char confirmed that BN can play a major role in the chemical composition of plant char. Subjecting the chars to oxidation with acidic dichromate demonstrated that, in spite of their relatively high resistance to heat, the N-containing compounds of the chars were less recalcitrant than the components of the cellulose char. Thus, in soil, N-rich chars are likely to be underestimated on the basis of this method. On the other hand, for an ancient paddy soil whose N-containing char compounds were calculated to account for ca. 25% of the total organic C in the soil. This clearly underlines the pedogenic stability of BN and confirms that it has the potential to contribute significantly to the refractory soil organic matter pool. © 2010 Elsevier Ltd.

Hilscher A.,TU Munich | Knicker H.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville
Soil Biology and Biochemistry | Year: 2011

The present study focuses on the microbial recalcitrance of pyrogenic organic material (PyOM) on a molecular scale. We performed microcosm incubation experiments using 13C- and 15N-enriched grass-derived PyOM mixed with a sub soil material taken from a Haplic Cambisol. Solid-state 13C and 15N NMR studies were conducted to elucidate the humification processes at different stages of PyOM degradation. The chemical structure of the remaining PyOM after incubation was clearly different from the initial pyrogenic material. The proportion of O-containing functional groups was increased, whereas that of aryl C and of N-containing heterocyclic structures had decreased, probably due to mineralisation and conversion to other C and N groups. After 20 months of incubation the aryl C loss reached up to 40% of the initial amount and up to 29% of the remaining PyOM C was assigned to carboxyl/carbonyl C and O-aryl C. These reactions alter the chemical and physical properties of the char residue and make it more available for further microbial attack but also for adsorption processes. Our study presents direct evidence for the degradation of N-heterocyclic domains in charred plant remains adding new aspects to the understanding of the N cycling in fire-affected ecosystems. © 2010 Elsevier Ltd.

Posada-Baquero R.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville | Ortega-Calvo J.-J.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville
Environmental Pollution | Year: 2011

The microbial accessibility of native phenanthrene and pyrene was determined in soils representing background scenarios for pollution by polycyclic aromatic hydrocarbons (PAHs). The soils were selected to cover a wide range of concentrations of organic matter (1.7-10.0%) and total PAHs (85-952 μg/kg). The experiments included radiorespirometry determinations of biodegradation with 14C-labeled phenanthrene and pyrene and chemical analyses to determine the residual concentrations of the native compounds. Part of the tests relied on the spontaneous biodegradation of the chemicals by native microorganisms; another part also involved inoculation with PAH-degrading bacteria. The results showed the recalcitrance of PAHs already present in the soils. Even after extensive mineralization of the added 14C-PAHs, the concentrations of native phenanthrene and pyrene did not significantly decrease. We suggest that aging processes operating at background concentrations may contribute to recalcitrance and, therefore, to ubiquitous pollution by PAHs in soils. © 2011 Elsevier Ltd. All rights reserved.

Hilscher A.,TU Munich | Knicker H.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville
Organic Geochemistry | Year: 2011

The microbial recalcitrance of char accumulated after vegetation fires and its transport within a soil column were studied in microcosms using 13C- and 15N-enriched pyrogenic organic material (PyOM). The PyOM from rye grass (Lolium perenne L.) was produced by charring at 350°C under oxic conditions for 1 and 4min to examine the impact of the charring degree. After 28months, 13C recovery decreased to values between 62% and 65%, confirming that this material can be attacked by microorganisms and that the degradation occurs rapidly after accumulation of PyOM at the soil surface. The respective 15N recovery followed the same trend but tended to be higher (between 67% and 80%). Most of the added PyOM isotopic labels were recovered in the particulate organic matter (POM) fraction, containing between 84% and 65% of the added 13C and 15N after the first 2months, being reduced by half at the end of the experiment. After 1month, up to 13.8% of the 13C label and 12.4% of the 15N label were detected in the POM-free mineral fractions. This fast association of PyOM with the mineral phase indicates that physical soil properties have to be considered for the elucidation of PyOM stability. Addition of fresh unlabelled grass material as co-substrate resulted in comparable trends as for the pure PyOM but the total recovery of the isotopic labels clearly increased with respect to the amount of mineral-associated PyOM. Between 73% and 82% of the mineral-associated PyOM occurred in the clay separates (<2μm) for which the highest values were obtained for the experiment with the more intensively charred PyOM and co-substrate addition. In summary, the study demonstrates the degradability of grass-derived PyOM. The addition of fresh plant material as an easily degradable co-substrate promoted the formation of partially decomposed PyOM and subsequently its association with the mineral phase, but did not increase the respective mineralisation rates. Detection of 13C and 15N content at different depths of the microcosm column demonstrated an additional loss of PyOM from top soil by way of mobilisation and transport to deeper horizons. All these processes have to be taken into account in order to obtain a more realistic view about the behaviour of PyOM in environmental systems and for estimation of the C and N sequestration potential. © 2010 Elsevier Ltd.

Trigo C.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville
Journal of agricultural and food chemistry | Year: 2010

Pesticide formulations based on organoclays have been proposed to prolong the efficacy and reduce the environmental impact of pesticides in soil. This research addressed the question of whether atrazine in organoclay-based formulations is irreversibly sorbed or is bioavailable for bacterial degradation in soil. Different cations of l-carnitine (CAR), tyramine (TYRAM), hexadimethrine (HEXADIM), phenyltrimethylammonium (PTMA), hexadecyltrimethylammonium (HDTMA), and Fe(III) were incorporated into Na-rich Wyoming montmorillonite (SWy-2) and Ca-rich Arizona montmorillonite (SAz-1) at 100% of the cation exchange capacity (CEC) of the clays as a strategy to enhance the affinity of the clay minerals for atrazine. A Buse loam soil from Becker, MN, was treated with three organoclay-based formulations of 14C-atrazine or free herbicide and incubated for 2 weeks. To determine the bioavailability of 14C-atrazine, the soil was inoculated with Pseudomonas sp. strain ADP, which rapidly mineralizes atrazine. At day 0, and after a 2 week incubation, mineralization and the amount of 14C-atrazine residues distributed between the aqueous-extractable, methanol-extractable, and bound fractions in the soil were determined to characterize the availability of nonaged and aged atrazine residues. By the end of the 2 week incubation, the microorganisms had mineralized >80% of the initial readily available (water-extractable) and >70% of the less readily available (methanol-extractable) 14C-atrazine in the soil. Bound residues increased from <4% at day 0 to ∼17% after the 2 week incubation for both the formulated and free forms of atrazine. The results of these incubation experiments show that the bioavailabilities of atrazine were similar in the case of the organoclay formulations and as free atrazine. This indicated that whereas more atrazine was sorbed and less likely to be transported in soil, when formulated as organoclay complexes, it was ultimately accessible to degrading bacteria, so that the herbicide is likely to be naturally attenuated by soil microorganisms.

Fernandez J.E.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville
Agricultural Water Management | Year: 2014

Despite their potential for water stress monitoring, sap flow (SF), trunk diameter variation (TDV) and leaf turgor pressure (LTP) related measurements are rarely used in commercial orchards. The reasons for this lack of popularity are analysed here, as well as possible solutions for the identified limitations. I worked with data collected from different olive orchards as well as with findings from the literature reported for other fruit tree species. SF sensors are difficult to install but easy to maintain. TDV sensors are easier to install, but require greater maintenance. Both methods are highly demanding in terms of data processing, especially sap flow. The usefulness of SF records for monitoring water stress is curtailed on recovery periods, due to the delayed recovery of stomatal conductance. TDV records, on the other hand, depend on plant water status, but also on plant age, phenological stage and crop load, among other factors. For correct data interpretation, therefore, a deep understanding of the response of the monitored variable to plant and environmental conditions is required. For LTP related measurements we used ZIM probes. They showed to be easy to install and use, and robust enough to withstand field conditions for long irrigation seasons. Severe water stress, however, limited their performance. New approaches are being developed to increase the potential of the tested methods for being used in commercial orchards. These include combining the plant-based methods with remote imagery, deriving more user-friendly water stress indices from the collected records and hiring the services of specialized companies which provide the user with easy-to-interpret summaries of the collected information. With the help of new tools and applications, and the hiring of specialized companies if required, the assessed plant-based methods can be reliable and profitable tools for monitoring water stress and scheduling irrigation in commercial orchards. © 2014 Elsevier B.V.

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