Multi-chemical analysis combined with chemometrics to characterize PDO and PGI Italian apples.

BACKGROUND: The use of PDO (protected designation of origin) and PGI (protected geographical indication) labels allows to protect and promote agricultural products characterized by unique features related to the place of origin and traditional know-how. However, the presence of non-authentic products in the market represents a fraud that can be tackled applying analytical techniques combined with chemometric analysis. In this study, we applied multi-element and multi-isotope analysis to characterize PDO and PGI apples cultivated in northern Italy, comparing them with Italian apples without labels of geographical indications. RESULTS: The multi-element and multi-isotope approach allowed to characterize the apples cultivated in northern Italy. Despite a significant effect of the sampling sites on the apple composition, the comparison of the multi-chemical fingerprint of the apples significantly varied among cultivation areas. Results of this characterization were used to classify samples according to their cultivation area applying a linear discriminant analysis (LDA). Outputs of the LDA showed that correct sample classification can be successfully achieved (balanced accuracy > 96%). Moreover, using a selection of variables, it was possible to correctly classify samples also at regional level. CONCLUSION: The presented evidences indicate that the multi-element and multi-isotope fingerprint can be successfully applied to traceability studies. The combination of this characterization with chemometric tools allows the classification of Italian apples based on their origin both on a national and regional scale. This approach represents an interesting tool to enhance and protect PDO and PGI Italian products. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Sr isotope composition of Golden Delicious apples in Northern Italy reflects the soil 87 Sr/86 Sr ratio of the cultivation area.

BACKGROUND: Apples have a leading role in the Italian fruit sector, and high-quality apples, including the Golden Delicious variety, are cultivated mainly in the Northern mountain districts. In the present study, Golden Delicious apples from PDO (Protected Designation of Origin) and PGI (Protected Geographical Indication) cultivation districts were characterized according to their Sr isotope composition and compared with apples from other Northern Italian districts. RESULTS: Apples collected in two consecutive years (2017 and 2018) confirmed the low annual variability of the 87 Sr/86 Sr ratio. The isotope ratio of apples was highly correlated with that of the soil extracts of the respective orchards. Statistical differences were highlighted between cultivation districts. However, because similar geological features characterized some areas, their ratios overlapped and a complete separation of the districts was not possible. CONCLUSION: The 87 Sr/86 Sr ratio is an excellent marker for studies of food traceability because it retains the information about the place of origin. However, its strength is limited when comparing products from cultivation areas sharing similar geological features. In the perspective of geographical traceability, a multichemical characterization can overcome the limits of single-parameter approach. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Assessing the ecophysiological response of a mountain grassland community to ski slope management through isotopic composition.

A scarce natural snow cover forces an increasing use of artificial snow on ski slopes and returns a small amount of snowmelt water available to plants outside the pistes at the beginning of the growing season. We tested if the use of artificial snow on the ski slopes and the decreased natural snow cover outside the ski slopes lead to changes in the leaf ecophysiology of dominant species in a ski area located in Northern Italy. Using carbon (13C/12C) and oxygen (18O/16O) stable isotope ratios in plant leaves, we estimated the intrinsic water use efficiency (iWUE) and we speculated about changes in photosynthesis and stomatal conductance. Furthermore, carbon and nitrogen concentration, pigments and dry matter content, and the specific area of leaves were measured. We found a higher iWUE of the plants on the ski slopes than outside, probably because the plants on the ski piste are exposed to a condition close to waterlogging that can lead them to regulate their stomata differently than the plants outside the pistes. This behaviour was observed particularly in Ranunculus acris and in Tussilago farfara, for these species the water surplus on the piste may have affected the plants' gas exchanges.

Intra- and Intertree Variability of the 87Sr/86Sr Ratio in Apple Orchards and Its Correlation with the Soil 87Sr/86Sr Ratio.

The 87Sr/86Sr ratio of horticultural products mostly derives from that of the bioavailable Sr fraction of the soil where they grow and, therefore, varies according to the local geolithological features. This study investigated the intra- and intertree variability of the 87Sr/86Sr ratio in two apple orchards in South Tyrol and its relation with the soil 87Sr/86Sr ratio. In both orchards, a moderate homogeneity of the 87Sr/86Sr ratio was observed among subsamples of the same tree part (shoot axes, leaves, apple peels, and pulps). Moreover, the 87Sr/86Sr ratio homogeneity among tree parts was high intratree and low intertree. The variability of the 87Sr/86Sr ratio within the tree and within the orchard is explained in light of the 87Sr/86Sr ratios of the soil. This 87Sr/86Sr variability within orchards does not preclude its use as a geographical tracer; however, this aspect should be evaluated to correctly design a sampling campaign or to generalize the results.

Plant Sr Isotope Ratios As Affected by the Sr Isotope Ratio of the Soil and of the External Sr Inputs.

The 87Sr/86Sr ratio of a produce is generally linked with the soil geological features of the growing areas. This study aimed at assessing to which extent the addition of external Sr by agricultural practices, like irrigation and mineral nutrient supply, influences this relationship. In a first experiment, oat plants in two soils reflected the 87Sr/86Sr of the soil. However, this link was significantly altered at increasing levels of external Sr soil supplies. In a second experiment, apple trees transplanted in pots modified their original 87Sr/86Sr, which became progressively closer to the soil Sr isotope ratio. The addition of tap water and fertilizers, with different Sr isotopic signatures, slightly affected plant 87Sr/86Sr. Results confirm the potential of the 87Sr/86Sr ratio as a geographical tracer of agricultural commodities, but whenever the range of 87Sr/86Sr variability among soils from different geographical areas is narrow, the influence of external Sr-sources may smooth over these diversities.

Comparison of pore water samplers and cryogenic distillation under laboratory and field conditions for soil water stable isotope analysis.

We used pore water samplers (PWS) to sample for isotope analysis (1) only water, (2) soil under laboratory conditions, and (3) soil in the field comparing the results with cryogenic extraction (CE). In (1) and (2), no significant differences between source and water extracted with PWS were detected with a mean absolute difference (MAD) always lower than 2 ‰ for δ2H and 1 ‰ for δ18O. In (2), CE water was more enriched than PWS-extracted water, with a MAD respect to source water of roughly 8 ‰ for δ2H and 4 ‰ for δ18O. In (3), PWS water was enriched relative to CE water by 3 ‰ for δ2H and 0.9 ‰ for δ18O. The latter result may be due to the distinct water portions sampled by the two methods. Large pores, easily sampled by PWS, likely retain recent, and enriched, summer precipitation while small pores, only sampled by CE, possibly retain isotopically depleted water from previous winter precipitation or irrigation inputs. Accuracy and precision were greater for PWS relative to CE. PWS is therefore suggested as viable tool to extract soil water for stable isotope analysis, particularly for soils used in this study (sandy and silty loams).

Recently fixed carbon allocation in strawberry plants and concurrent inorganic nitrogen uptake through arbuscular mycorrhizal fungi.

Most crop species form a symbiotic association with arbuscular mycorrhizal (AM) fungi, receiving plant photosynthate and exchanging nutrients from the soil. The plant carbon (C) allocation to AM fungi and the nitrogen feedback are rarely studied together. In this study, a dual (13)CO2 and (15)NH4(15)NO3 pulse labeling experiment was carried out to determine the allocation of recent photosynthates to mycorrhizal hyphae and the translocation of N absorbed by hyphae to strawberry plants. Plants were grown in pots in which a 50 µm mesh net allowed the physical separation of the mycorrhizal hyphae from the roots in one portion of the pot. An inorganic source of (15)N was added to the hyphal compartment at the same time of the (13)CO2 pulse labeling. One and seven days after pulse labeling, the plants were destructively harvested and the amount of the recently fixed carbon (C) and of the absorbed N was determined. (13)C allocated to belowground organs such as roots and mycorrhizal hyphae accounted for an average of 10%, with 4.3% allocated to mycorrhizal hyphae within the first 24h after the pulse labeling. Mycorrhizae absorbed labeled inorganic nitrogen, of which almost 23% was retained in the fungal mycelium. The N uptake was linearly correlated with the (13)C fixed by the plants suggesting a positive correlation between a plant photosynthetic rate and the hyphal absorption capacity.

Special Issue: Mycorrhizal Fungi in Sensitive Environments.

The scope of this special issue is to understand whether and how mycorrhizal symbiosis can be included as an agriculture and agroforestry tool that promotes more environmentally friendly practices, and whether it promotes the protection of sensitive areas. Three papers are included in this special issue, each dealing with a different sensitive environment. These papers present fundamental aspects that should be taken into account when planning or reporting studies related to mycorrhizal fungi in sensitive environments.

Tracing metabolic pathways of lipid biosynthesis in ectomycorrhizal fungi from position-specific 13C-labelling in glucose.

Six position-specific (13)C-labelled isotopomers of glucose were supplied to the ectomycorrhizal fungi Suillus pungens and Tricholoma flavovirens. From the resulting distribution of (13)C among fungal PLFAs, the overall order and contribution of each glucose atom to fatty acid (13)C enrichment was: C6 (approximately 31%) > C5 (approximately 25%) > C1 (approximately 18%) > C2 (approximately 18%) > C3 (approximately 8%) > C4 (approximately 1%). These data were used to parameterize a metabolic model of the relative fluxes from glucose degradation to lipid synthesis. Our data revealed that a higher amount of carbon is directed to glycolysis than to the oxidative pentose phosphate pathway (60% and 40% respectively) and that a significant part flows through these pathways more than once (73%) due to the reversibility of some glycolysis reactions. Surprisingly, 95% of carbon cycled through glyoxylate prior to incorporation into lipids, possibly to consume the excess of acetyl-CoA produced during fatty acid turnover. Our approach provides a rigorous framework for analysing lipid biosynthesis in fungi. In addition, this approach could ultimately improve the interpretation of isotopic patterns at natural abundance in field studies.

Structure of reaction intermediates formed during Saccharomyces cerevisiae Rad51-catalyzed strand transfer.

The process by which the Saccharomyces cerevisiae strand transfer protein, Rad51, seeks out homologous sequences in vivo can be modeled by an in vitro reaction between a single-stranded DNA circle and a double-stranded linear DNA. In addition to the substrates and products, electrophoresis of reaction mixtures resolves two groups of low mobility bands. Here we show that the low mobility bands formed during strand transfer by Rad51 (or Escherichia coli RecA) represent joint molecules (JM) between the two substrates. One group, which we name JM1, is an obligatory reaction intermediate in which the complementary strand from the duplex substrate has been partially transferred to the single-stranded circle. Our assignment is based on pulse-chase and restriction enzyme digestion experiments and verified by electron microscopy. The slower moving group of bands, designated JM2, is formed by an unexpected reaction between JM1 and a second double-stranded linear substrate. Strand transfer of the second duplex initiates noncanonically from the end where the complementary strand is recessed. Thus JM2 is formed by two strand transfer reactions with the same single-stranded circular substrate but with opposite polarities. Finally, we show that the multiple sharp bands in JM1 and JM2 are the result of substrate sequences that pause strand transfer.