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Rhizosphere: a communication between plant and soil
No full text• Plant survival and crop productivity are strictly dependent on the capability of plants to adapt to different environments. This adaptation is the result of the interaction among roots and biotic components of soil. The research on plant soil interaction is focused on the processes that take place in the rhizosphere, the soil environment surrounding the root. Many of these processes can control plant growth, microbial infections and nutrient uptake.
• Our understanding of the biology, biochemistry and genetic development of roots has considerably improved during the last decade. In contrast, the processes mediated by roots in the rhizosphere such as secretion of root border cells and root exudates are not yet well understood. Nevertheless, the ability to secrete a vast array of compounds into the rhizosphere is one of the most remarkable metabolic features of plant roots, with nearly 5% to 21% of all photosynthetically fixed carbon being transferred to the rhizosphere through root exudates.
• On the other hand, it is known that the rhizosphere is a densely populated area in which the roots must compete with different plant species, for space, water, mineral nutrients and with soil-borne microrganisms including bacteria, fungi and insects. Root-root, root-microbe and root-insect communications are likely continuous occurrences in this biological active soil zone. Thus, if plant roots are in communication with different organisms, how do roots effectively carried out this communication process within the rhizosphere?
• Many papers suggest that root exudates may act as messengers that communicate and initiated biological physical interactions between roots and soil organisms. As already described, plant survival depends primarily on the ability of the plant to perceive change in the local environment. In other studies it has been found the presence of strong feed backs between plant community structures and soil attributes. In this way plants modify soils, making and maintaining the habitat more favourable for growth and survival in stress conditions. Therefore, exudation of organic substances by roots is not a wasteful C and energy losses for the plants, but an evolutionary developed mechanism by which plants “speak” to micro-organisms or to soil. In the light of this, the mobilisation of bioactive organic/humic substances from the bulk soil or the bulk humus is a result of prominent importance
I suoli forestali
No full textI suoli forestali, come pure la vegetazione
sovrastante, hanno un ruolo di primaria importanza nel tamponare gli effetti delle
attività antropiche sull’emissione di anidride carbonica nell’atmosfera, da qui la
necessità di sviluppare le nostre conoscenze sulle interazioni tra suolo, piante ed
ambiente.La crescita degli alberi e la produttività delle foreste sono direttamente
influenzate dalla quantità, qualità e giacitura del suolo. Nei suoli forestali l’accumulo
superficiale di sostanza organica svolge un ruolo importante nella dinamica della
fertilità. La lettiera, che presenta caratteristiche differenti a seconda delle condizioni
climatiche e della vegetazione sotto cui si forma, è contemporaneamente sia fonte di
carbonio e azoto per le piante e i microrganismi che luogo di stoccaggio o di accumulo
attraverso il quale gli elementi nutritivi entrano nel terreno (source e sink
rispettivamente nella letteratura anglosassone). L’evoluzione della sostanza organica nel
terreno regola processi come la nitrificazione e denitrificazione e influenza la dotazione
di macro e micro elementi lungo tutto il profilo. Le trasformazioni chimiche e
biologiche dei composti organici mediano i diversi processi pedogenetici dando luogo
alla formazione di orizzonti diversi il cui riconoscimento è essenziale per distinguere le
diverse forme di humus. Il tipo di humus che si forma è una conseguenza delle
condizioni ecologiche locali: infatti le alterazioni degli equilibri idrici e i processi
erosivi si ripercuotono sul ciclo, detto anche turnover, della sostanza organica e sulla
quantità e qualità dell’humus, deprimendo così la produttività dei suoli a lungo termine.
Il selvicoltore nella gestione di un bosco deve quindi operare per la conservazione della
sostanza organica in modo non solo da incrementare la produttività dei suoli a medio e
lungo termine, ma anche per favorire lo stoccaggio dell’anidride carbonica atmosferica
nel suolo.
10.1. Dinamica degli elementi nutritivi nei suoli forestal
Hormone-like activities of humic substances in different forest ecosystems
No full textIn order to understand the phytohormone-like activity of humic substances (HS) with respect to vegetation, different forest ecosystems were considered. For this study, 32 soil horizons from a large area of northern Italy typical for silver fir (Abies alba) were evaluated. The development of organic and humic matter in the five silver fir forest types was assessed by quantifying chemical and biochemical parameters. Phytohormone-like activity of HS was evaluated by measuring auxin-like (indoleacetic acid (IAA)-like) and gibberellin-like (GA-like) activities as well as invertase and peroxidase activities. Differences between ecosystems were obtained by comparing the five silver fir types with previous work in beech forests, which investigated three large groups: thermophilous, mesophilous and acidophilous. In these eight forests it was reconfirmed that acid conditions were essential for the release of the IAA-like activity, whereas neutral conditions promoted GA-like activity. Humic substances are of ecological importance because their phytohormone-like activity stands out not only within the five silver fir forest types, but also between the silver fir and beech types. Our results demonstrated a different collocation of the hormone-like activity along the profile in accordance with the different growth conditions, seed germination and the first stage of seedling growth. Humic substances evoke the greatest response on seed germination and on the first stage of seedling growth, particularly in stressed environmental conditions. © New Phytologist (2002)
Cà Tron (Saggio 8): prelievo di campioni di terreno per un’analisi del contenuto in fosforo, in La Tenuta di Ca’Tron (Roncade-Tv/Meolo-Ve): le indagini su un edificio rustico (a cura di Maria Stella Busana), in QdAV, XXI, 2005,
No full textHormone-like activity of humic substances in Fagus sylvaticae forests
No full text• Soil A horizons from a large area typical for beech ( Fagus sylvatica ) in northern Italy were investigated to understand the phyto-hormone-like activity of humic
substances (HS) with respect to the vegetation. These soils had developed under thermophilous ( Cephalonthero–Fagion with Carici albae–Fagetum ), mesophilous ( Fagion sylvaticae with Dentario pentaphylli–Fagetum and Galio-odourati–Fagetum ) or acidophilous ( Luzulo–Fagion with Luzulo niveae–Fagetum
) beech forests. • The development of organic and humic matter in the three forest types was assessed by quantifying chemical parameters. Phyto-hormone-like activity of HS was evaluated by measuring auxin-like (IAA like ) and gibberellin-like (GA like ) activity as well as IAA concentration, invertase and peroxidase activities. • Soil pH differed between the forest types. Soil C: N distinguished the thermophilous
and the mesophilous from the acidophilous types but did not distinguish thermophilous from the mesophilous types. Phyto-hormone-like activity of HS varied significantly across the beech forests. Acid conditions were essential for the release of IAA like activity whereas neutral conditions promoted GA
like activity. Plant isoenzymatic poly - morphism confirmed the different auxin activities of HS.
• The phyto-hormone-like activity of HS is highly suitable, and better than soil
chemical parameters, for differentiating between these ecosystems
Produttività delle foreste e attività biologica della sostanza organica disciolta nella soluzione del suolo
No full textIl ruolo biologico della sostanza organica disciolta (DOM) nella soluzione circolante del suolo è ancora poco conosciuto, nonostante vi siano numerosi studi sulle proprietà chimico-fisiche della DOM. Inoltre è nota l’influenza delle specie arboree e della vegetazione del sottobosco sulle proprietà quantitative e qualitative della sostanza organica solubile.
Con questo lavoro abbiamo studiato la fertilità di 59 siti forestali, suddivisi in 8 alleanze appartenenti all’ordine Fagetalia sylvaticae Pawl., considerando la composizione floristica, l’altezza e il diametro degli alberi dominanti e alcuni parametri biochimici della DOM.
I risultati evidenziano che le caratteristiche chimico-vegetazionali del sito influenzavano sia l’altezza che il diametro degli alberi dominanti. In particolare, nei siti ad abieteto il diametro risultava correlato all’attività auxino-simile della sostanza organica disciolta, mentre nei siti a faggete l’altezza era correlata al contenuto di acidi fenolici. Inoltre, l’attività auxino-simile, a seconda del raggruppamento vegetazionale, risultava essere modulata in maniera diversa da acidi organici e fenoli della soluzione circolante.
Gli acidi fenolici, inoltre, influenzavano la crescita di plantule di abete rosso (Picea abies). A concentrazioni tra 1 e 100 μM, l’acido fenilacetico e l’acido protocatechico inibivano la crescita della radice come l’acido indolacetico, mentre l’acido p-idrossibenzoico stimolava similmente all’acido gibberellico.
Da questi studi appare che gli acidi organici e fenolici a basso peso molecolare presenti nella soluzione del suolo possono essere considerati come indicatori biologici del funzionamento di un ecosistema
The role of organic acids in the breaking out humic substances and in the releasing of biomolecules active in the rhizosphere
No full textLow-molecular-weight organic acids and hormone-like activity of dissolved organic matter in two forest soils in N Italy
No full textConcentrations of aliphatic acids, phenolic acid, and inorganic nutrients,
as well as hormone-like activity, were determined in soil dissolved organic
matter (DOM) from two forest sites in N Italy showing differing degrees of
silver fir regeneration. In the site where silver fir recruitment was abundant, humification
processes prevailed, and the soil DOM had a high content in aliphatic
and phenolic acids. This enhanced the hormone-like activity in the soil, which
could in turn promote growth of silver fir seedlings. In the site with poor fir
recruitment, the soil DOM underwent rapid mineralization and was richer in inorganic
nutrients, but had lower concentrations of aliphatic and phenolic acids,
and lower hormone-like activity
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