Klement Rejšek

Non-protein amino acids: plant, soil and ecosystem interactions

Non-protein amino acids are a significant store of organic nitrogen in many ecosystems, but there is a lack of knowledge relating to them. Research has indicated that they play important roles as metabolites, as allelopthic chemicals, in nutrient acquisition, in signalling and in stress response. They are also thought to be responsible for significant medical issues in both invertebrate and vertebrate animals. This review attempts to appraise the literature related to non-protein amino acids, both in terms of their metabolism, plant–soil interactions and at the level of the ecosystem, where they are seen as significant drivers of structure and function. Finally, important areas for future research are discussed.

The significance of D-amino acids in soil, fate and utilization by microbes and plants: review and identification of knowledge gaps

BackgroundD-amino acids are far less abundant in nature than L-amino acids. Both L- and D-amino acids enter soil from different sources including plant, animal and microbial biomass, antibiotics, faeces and synthetic insecticides. Moreover, D-amino acids appear in soil due to abiotic or biotic racemization of L-amino acids. Both L- and D-amino acids occur as bound in soil organic matter and as “free“ amino acids dissolved in soil solution or exchangeably bound to soil colloids. D-amino acids are mineralized at slower rates compared to the corresponding L-enantiomers. Plants have a capacity to directly take up “free“ D-amino acids by their roots but their ability to utilize them is low and thus D-amino acids inhibit plant growth.ScopeThe aim of this work is to review current knowledge on D-amino acids in soil and their utilization by soil microorganisms and plants, and to identify critical knowledge gaps and directions for future research.ConclusionAssessment of “free“ D-amino acids in soils is currently complicated due to the lack of appropriate extraction procedures. This information is necessary for consequent experimental determination of their significance for crop production and growth of plants in different types of managed and unmanaged ecosystems. Hypotheses on occurrence of “free“ D-amino acids in soil are presented in this review.

Aliphatic, cyclic, and aromatic organic acids, vitamins, and carbohydrates in soil: a review.

Organic acids, vitamins, and carbohydrates represent important organic compounds in soil. Aliphatic, cyclic, and aromatic organic acids play important roles in rhizosphere ecology, pedogenesis, food-web interactions, and decontamination of sites polluted by heavy metals and organic pollutants. Carbohydrates in soils can be used to estimate changes of soil organic matter due to management practices, whereas vitamins may play an important role in soil biological and biochemical processes. The aim of this work is to review current knowledge on aliphatic, cyclic, and aromatic organic acids, vitamins, and carbohydrates in soil and to identify directions for future research. Assessments of organic acids (aliphatic, cyclic, and aromatic) and carbohydrates, including their behaviour, have been reported in many works. However, knowledge on the occurrence and behaviour of D-enantiomers of organic acids, which may be abundant in soil, is currently lacking. Also, identification of the impact and mechanisms of environmental factors, such as soil water content, on carbohydrate status within soil organic matter remains to be determined. Finally, the occurrence of vitamins in soil and their role in biological and biochemical soil processes represent an important direction for future research.

Significance of the natural occurrence of L- versus D-pipecolic acid: a review.

Pipecolic acid naturally occurs in microorganisms, plants, and animals, where it plays many roles, including the interactions between these organisms, and is a key constituent of many natural and synthetic bioactive molecules. This article provides a review of current knowledge on the natural occurrence of pipecolic acid and the known and potential significance of its L- and D-enantiomers in different scientific disciplines. Knowledge gaps with perspectives for future research identified within this article include the roles of the L- versus the D-enantiomer of pipecolic acid in plant resistance, nutrient acquisition, and decontamination of polluted soils, as well as rhizosphere ecology and medical issues.

Effect of Elevated CO2, O3, and UV Radiation on Soils

In this work, we have attempted to review the current knowledge on the impact of elevated CO2, O3, and UV on soils. Elevated CO2 increases labile and stabile soil C pool as well as efficiency of organic pollutants rhizoremediation and phytoextraction of heavy metals. Conversely, both elevated O3 and UV radiation decrease inputs of assimilates to the rhizosphere being accompanied by inhibitory effects on decomposition processes, rhizoremediation, and heavy metals phytoextraction efficiency. Contrary to elevated CO2, O3, or UV-B decreases soil microbial biomass, metabolisable C, and soil Nt content leading to higher C/N of soil organic matter. Elevated UV-B radiation shifts soil microbial community and decreases populations of soil meso- and macrofauna via direct effect rather than by induced changes of litter quality and root exudation as in case of elevated CO2 or O3. CO2 enrichment or increased UV-B is hypothesised to stimulate or inhibit both plant and microbial competitiveness for soluble soil N, respectively, whereas O3 favours only microbial competitive efficiency. Understanding the consequences of elevated CO2, O3, and UV radiation for soils, especially those related to fertility, phytotoxins inputs, elements cycling, plant-microbe interactions, and decontamination of polluted sites, presents a knowledge gap for future research.

Effect of soil sieving on respiration induced by low-molecular-weight substrates

Abstract The mesh size of sieves has a significant impact upon soil disturbance, affecting pore structure, fungal hyphae, proportion of fungi to bacteria, and organic matter fractions. The effects are dependent upon soil type and plant coverage. Sieving through a 2 mm mesh increases mineralization of exogenously supplied carbohydrates and phenolics compared to a 5 mm mesh and the effect is significant (p<0.05), especially in organic horizons, due to increased microbial metabolism and alteration of other soil properties. Finer mesh size particularly increases arabinose, mannose, galactose, ferulic and pthalic acid metabolism, whereas maltose mineralization is less affected. Sieving through a 5 mm mesh size is suggested for all type of experiments where enhanced mineralization of low-molecular-weight organic compounds needs to be minimalized.

Natural Occurrence of Enantiomers of Organic Compounds Versus Phytoremediations: Should Research on Phytoremediations Be Revisited? A Mini‐review

Decontamination of polluted soils using plants is based on the ability of plant species (including transgenic plants) to enhance bioavailability of pollutants in the rhizosphere and support growth of pollutant-degrading microorganisms via root exudation and plant species-specific composition of the exudates. In this work, we review current knowledge of enantiomers of low-molecular-weight (LMW) organic compounds with emphasis on their use in phytoremediation. Many research studies have been performed to search for plants suitable for decontamination of polluted soils. Nevertheless, the natural occurrence of L- versus D-enantiomers of dominant compounds of plant root exudates which play different roles in the complexation of heavy metals, chemoattraction, and support of pollutant-degrading microorganisms were not included in these studies. D-enantiomers of aliphatic organic acids and amino acids or L-enantiomers of carbohydrates occur in high concentrations in root exudates of some plant species, especially under stress, and are less stimulatory for plants to extract heavy metals or for rhizosphere microflora to degrade pollutants compared with L-enantiomers (organic acids and amino acids) or D-carbohydrates. Determining the ratio of L- versus D-enantiomers of organic compounds as a criterion of plant suitability for decontamination of polluted soils and development of other types of bioremediation technologies need to be subjects of future research.

How enzymes are adsorbed on soil solid phase and factors limiting its activity: A Review

Abstract A majority of biochemical reactions are often catalysed by different types of enzymes. Adsorption of the enzyme is an imperative phenomenon, which protects it from physical or chemical degradation resulting in enzyme reserve in soil. This article summarizes some of the key results from previous studies and provides information about how enzymes are adsorbed on the surface of the soil solid phase and how different factors affect enzymatic activity in soil. Many studies have been done separately on the soil enzymatic activity and adsorption of enzymes on solid surfaces. However, only a few studies discuss enzyme adsorption on soil perspective; hence, we attempted to facilitate the process of enzyme adsorption specifically on soil surfaces. This review is remarkably unmatched, as we have thoroughly reviewed the relevant publications related to protein adsorption and enzymatic activity. Also, the article focuses on two important aspects, adsorption of enzymes and factors limiting the activity of adsorbed enzyme, together in one paper. The first part of this review comprehensively lays emphasis on different interactions between enzymes and the soil solid phase and the kinetics of enzyme adsorption. In the second part, we encircle various factors affecting the enzymatic activity of the adsorbed enzyme in soil.

Determination of the Proportion of Total Soil Extracellular Acid Phosphomonoesterase (E.C. 3.1.3.2) Activity Represented by Roots in the Soil of Different Forest Ecosystems

The aim of this study is to present a new method for determining the root-derived extracellular acid phosphomonoesterase (EAPM) activity fraction within the total EAPM activity of soil. EAPM activity was determined for roots, organic and mineral soil. Samples were collected using paired PVC cylinders, inserted to a depth of 15u2009cm, within seven selected forest stands. Root-derived EAPM formed between 4 and18% of the total EAPM activity of soil from forests of differing maturity. A new approach, presented in this work, enables separation of root-derived EAPM activity from total soil EAPM. Separation of root-derived EAPM from soil provides a better understanding of its role in P-cycling in terrestrial ecosystems. The method presented in this work is a first step towards the separation of root- and microbe-derived EAPM in soils, which are thought to possess different kinetic properties and different sensitivity to environmental change.

A methodological contribution to use of Ground-Penetrating Radar (GPR) as a tool for monitoring contamination of urbansoils with road salt

The use of Ground-Penetrating Radar as a tool for monitoring urban soils contaminated with road salt was tested. Data obtained from GPR measurements were compared with the results of laboratory analyses of soil samples collected during selected measurements and evaluated in relation to weather (esp. temperature and precipitation sums) prevailing prior to the individual measurements. It was proved that GPR technology can be used to indicate presence of road salt in soil to a certain extent. However, the radar also reacted sensitively to other irregularities within soil horizons such as type of soil freezing and thawing, changes in soil moisture content and probably also varying activity of soil biota. Further research is necessary to screen out these influences in order to improve practical applicability of this technology in research of soil salinity in urban environment.