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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.

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 (

Recent studies applying stable isotopes of hydrogen and oxygen showed that different methods for extracting water from plant tissues can return different isotopic composition. One of the most used methods to extract plant water is the cryogenic vacuum distillation (CVD), which tends to extract total plant water. Conversely, the Scholander pressure chamber (SPC), which is commonly used by tree physiologists to measure water potential in plant tissues, likely accesses only the mobile plant water (i.e., xylem and inter-cellular water). However, only few studies reported the application of SPC to extract plant water for isotopic analyses, and therefore, an inter-method comparison between SPC and CVD is needed.In this study, we analyzed the variability in the isotopic signature of plant water extracted by SPC and CVD. Furthermore, we considered the potential variability in the isotopic composition of the plant water extracted from various tissues by CVD (i.e., leaves, twig without bark, twig with bark, twig close to the trunk of the tree, and wood core), and from different tree species (i.e., alder, apple, chestnut and beech) located in three different study areas in northern Italy.Results indicate that plant waters extracted by SPC and CVD were significantly different, likely due to the extraction of different plant water domains. The difference in the isotopic composition obtained by the two extraction methods was smaller in the beech samples compared to alder, apple and chestnut samples. The signature of alder, apple and chestnut plant water extracted by SPC was more enriched in heavy isotopes than the samples obtained by CVD (except for the leaf water obtained by CVD, which also had a marked evaporative signature). We conclude that plant water extraction by SPC does not represent an alternative for CVD, as SPC likely extracts mostly the mobile plant water, whereas CVD tends to retrieve all water stored in the sampled tissues. However, studies aiming to quantify the relative contribution of the water sources to transpiration should rely more on the isotopic composition of xylem water transpiring during the sampling day (theoretically sampled by SPC), than the isotopic composition of total plant water (sampled by CVD), which also contains a fraction of water that could be stored in plant tissues for a long time. Keywords: stable isotopes of hydrogen and oxygen; cryogenic vacuum distillation; Scholander pressure chamber; plant water; xylem water.

The WATSON COST Action (CA19120; https://watson-cost.eu/) started in September 2020. It aims to integrate and synthesize current interdisciplinary scientific knowledge on the use of the stable isotopes of water to understand the mixing and partitioning of water in the Earth’s Critical Zone. The network is organized into working groups that focus on a major scientific challenge: 1) groundwater recharge and soil water mixing processes; 2) vegetation water uptake and transpiration; and 3) catchment-scale residence time and travel times. A fourth working group organizes the network and dissemination activities.WATSON aims at better connecting academia and stakeholders from industry, non-profit organizations, and government agencies. WATSON fosters the exchange of information and expertise among scientists and stakeholders, builds capacity in the use of the latest isotope approaches and translates scientific cutting-edge knowledge into tangible outputs and recommendations on how to use stable water isotopes to effectively address water management needs. Our poster describes the WATSON network, as well as its activities. These include the preparation of an open-access database of water isotope-based studies in the Critical Zone, the development of protocols for water sampling and stable isotope analysis, the organization of virtual and in-person meetings, seminars, training schools, and the exchange of students, researchers, and technicians via short term scientific missions.

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.

Die meisten Konsumenten interessieren sich immer stärker für die Herkunft ihrer Lebensmittel. Eine vielversprechende Methode, um die Herkunft von landwirtschaftlichen Produkten zu prüfen ist die Analyse des Strontium (87Sr/86Sr)-Isotopenverhältnisses. Das 87Sr/86Sr-Verhältnis einer Pflanze spiegelt jenes des Bodens auf dem sie wächst wider. Der folgende Beitrag zeigt einige Aspekte des 87Sr/86Sr-Verhältnisses, untersucht während eines 3-jährigen Projektes, und seiner Verwendung als geographischen Indikator für Äpfel auf. In einem ersten Experiment betrachteten wir den Einfluss von landwirtschaftlichen Praktiken und des dadurch extern eingebrachten Strontiums, auf das Isotopenverhältnis der Apfelbäume im Gewächshaus. Die Bäume passten sich langsam an das Isotopenverhältnis im Boden an. Die landwirtschaftlichen Anwendungen hatten nur einen geringen Einfluss auf das 87Sr/86Sr-Verhältnis der Pflanze. Im zweiten Experiment wurden Unterschiede im Isotopenverhältnis zwischen Teilproben eines Pflanzenbestandteiles derselben Pflanze („intra-part“), Unterschiede zwischen den verschiedenen Pflanzenbestandteilen desselben Baumes („intra-tree“), die Unterschiede zwischen den verschieden Pflanzenbestandteilen unterschiedlicher Bäume derselben Obstanlage („inter-tree“) und ihr Zusammenhang mit dem Isotopenverhältnis im Boden, in jeweils zwei Südtiroler Obstanlagen untersucht. „Intra-part“ und „intra-tree“ war das 87Sr/86Sr Verhältniss homogen, allerdings konnten wir Unterschiede zwischen den Bäumen („inter-tree“) der beiden Obstanlagen beobachten. Im letzten Experiment wurden die Analysen auf 41 Obstanlagen in Norditalien ausgeweitet. Das 87Sr/86Sr-Verhältnis von Äpfeln mit geographischer Kennzeichnung aus verschiedenen Gebieten, wurde mit jenen ohne Kennzeichnung verglichen. Das Isotopenverhältnis im Apfel korrelierte stark mit jenem des jeweiligen Bodens der entsprechenden Obstanlage. Einige Gebiete hatten ähnliche geologische Eigenschaften und Isotopenverhältnis, wodurch eine eindeutige Unterscheidung nicht für alle Ortschaften möglich war. Trotzdem kann das 87Sr/86Sr-Verhältnis als geographischer Indikator verwendet werden, jedoch sollten in zukünftigen Studien weitere Parameter miteinbezogen werden.

Understanding the dynamics and sources of root water uptake in agricultural systems is becoming increasingly important for implementing efficient and sustainable water resources management and, at the same time, for optimizing crop yield and quality under changing climatic conditions. In this work, we adopted the stable isotope approach to investigate the water sources accessed by apple trees in two orchards growing in the upper Etsch/Adige valley (South Tyrol, Eastern Italian Alps). We tested the general hypothesis that soil water, composed of a mixture of rain and irrigation water, was the main source for tree transpiration but that river water and groundwater mixed with soil water and contributed to root uptake for trees growing close to the river and with higher water table. Our results revealed that apple trees during the 2015 and 2016 growing seasons relied mostly on soil water present in the upper 20-40 cm of soils, with an apparently negligible contribution of groundwater and river water, irrespective of the field position across the valley bottom. The isotopic composition of xylem water did not reflect the one of irrigation water (and neither that of groundwater) but rather of rainfall and throughfall, as well as that of soil water. We related this “hidden” tracer signature of irrigation water to the effect of soil evaporation that strongly modified its original isotopic composition: irrigation and rain water infiltrated into the soil and mixed with isotopically fractionated soil water, and trees took up a mixture of water with different isotopic composition compared to the one of the original irrigation source. This work contributes to improve the understanding of water uptake strategies in Alpine apple orchards and paves the way for further analysis on the proportion of irrigation and rain water used by apple trees in mountain agroecosystems.

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.

Recent tracer-based studies using stable isotopes of hydrogen and oxygen showed that different methods for extracting water from plant tissues can return different isotopic compositions due to the presence of organic compounds and because they extract different plant water domains. One of the most used methods to extract plant water is the cryogenic vacuum distillation (CVD), which tends to extract total plant water. Conversely, the Scholander-type pressure chamber (SPC), which is commonly used by tree physiologists to measure water potential in plant tissues and determine plant water stress, is expected to extract only the more mobile plant water (i.e., xylem and inter-cellular water). However, only few studies reported the application of SPC to extract plant water for isotopic analyses, and therefore, inter-method comparisons between SPC and CVD are of great value. In this work, we analyzed the variability in the isotopic composition of plant water extracted by SPC and CVD, also considering the potential variability in the isotopic signature of the plant water extracted by CVD from various tissues (i.e., leaves, twig without bark, twig with bark, twig close to the trunk of the tree, and wood core) and from different plant species (i.e., alder, apple, chestnut, and beech). The extraction of plant water by SPC is simple, can be carried out in the field, and it does not require specific laboratory work as in the case of CVD. However, the main limitation of SPC is the very small water volume that can be extracted from the lignified twigs under water stress conditions compared to CVD. Our results indicated that plant water extracted by SPC and CVD were significantly different. The difference in the isotopic composition obtained by the two extraction methods was smaller in the beech samples compared to alder, apple, and chestnut samples. The isotopic signature of alder, apple, and chestnut plant water extracted by SPC was more enriched in δ2H and δ18O, respectively, than the samples obtained by CVD. We conclude that plant water extraction by SPC is not an alternative for CVD as SPC mostly extracts the mobile plant water, whereas CVD tends to retrieve all water stored in the sampled tissue from both living and dead cells. However, studies aiming to quantify the relative contribution of the soil water sources to transpiration should rely more on the isotopic composition of xylem water (which is theoretically sampled by SPC) than the isotopic composition of total plant water (sampled by CVD), which also contains a fraction of water that could be stored in plant tissues for a longer time.

Improving the efficiency and sustainability in water resources management in agricultural and agroforestry systems is becoming increasingly important in the light of the increasing pressure on agro-food production due to the growing world population growth and the changing climatic conditions. In this context, achieving an accurate quantification of the proportions of different water sources (including irrigation) taken up by plants has important ecological and economic implications for water saving and utilization. Stable isotopes of hydrogen and oxygen in the water molecule are powerful and, nowadays, affordable tracers that can greatly help to identify and quantify the seasonal water uptake patterns by plants. This tool is largely adopted in natural systems (e.g., in ecohydrological applications in forested environments) but has not been fully exploited in agricultural and agroforestry ecosystems. Here, we outline the advantages and limitations of this technique and report some examples on how it can support more traditional approaches to understand root water uptake dynamics in agricultural and agroforestry systems. Finally, we present a vision for future challenges and new research lines using isotope tracers to investigate crop water use.

To be economically and environmentally sound, the nitrogen (N) supply in orchards needs to be finely tuned according to crop needs. This requires knowledge of the amount and the dynamics of N uptake by roots and of its allocation. This paper reports two experiments, carried out on the same set of trees, in order to: 1) study the uptake dynamics of N derived from fertiliser (N dff ) and its allocation to tree organs and, 2) quantify its N remobilization in spring from storage organs to new growth. The study was carried out using field-grown adult orange trees (cv. Tarocco nucellare grafted on Troyer Citrange), one of the most important fruit tree crops in the Mediterranean area. Nitrogen was supplied as ammonium nitrate in 10 applications with equal doses evenly distributed from March to November 2009. Four groups of 5 trees each received 15 N-enriched N starting from March, July, September, and November, respectively, while they received unlabelled N in the remaining periods. The results show that trees absorbed roughly 30% of the fertiliser N. Fertiliser-N use efficiency (NUE) was generally low in spite of the fact that readily available N sources were regularly supplied and the trees were irrigated; the later the fertiliser N was supplied, the lower was the NUE. Uptake rate was rather constant from April to November, but relatively less N was partitioned to fruits when the fertiliser was supplied later in the season. Remobilization of N from one-year-old leaves provided more than 60% of the N required by shoots in spring. By the end of April, most of the N had already been transferred from storage to growing organs. We estimated that, during the vegetative season, trees absorbed 94 kg N ha −1 from the soil and half of this amount derived from fertiliser. Spring remobilisation of winter stored N contributed for additional 40 kg N ha −1 to the N needs.

The

Soil respiration ( R soil ) partitioning into its components is pivotal to understand C cycling in ecosystems. Notwithstanding the importance of mycorrhizal fungi in the belowground C cycle, their respiration ( R myc ) is poorly studied in agricultural ecosystems. In this study, we applied a modified trenching method and the 13 C natural abundance technique to distinguish R myc from root respiration ( R root ) and from the respiration due to soil organic matter (SOM) degradation ( R som ) in an apple orchard ( Malus domestica Borkh.) located in Northern Italy. Membranes with different mesh size were used to physically exclude roots or mycorrhizae from soil cores with a different δ 13 C than the orchard average value. The CO 2 efflux from soil cores was determined with an infrared gas analyser, and isotopic measurements were performed on the soil-emitted CO 2 . The different R soil components were determined both by difference and by the isotopic mass balance. Mycorrhizal contribution to soil respiration (11 ± 6%) was of similar magnitude to that of roots (12 ± 4%) while R som accounted for 73 ± 3% of R soil . In presence of apple roots, respiration of SOM and mycorrhizae ( R som+myc ) significantly increased in late summer and autumn, likely because of a priming effect of roots on SOM degradation or to a stimulation of mycorrhizal respiration. Our results suggest that respiration of mycorrhizal fungi can significantly contribute to R soil , and need to be considered to correctly partition soil respiration. Furthermore, as roots increased R som+myc , the root exclusion method for soil respiration partitioning may overestimate R root .

Understanding water sources for crop water uptake in agricultural and agroforestry systems is an essential step to develop more efficient and sustainable water management strategies, which is increasingly important in the light of current world population growth, changing climatic conditions and consequent growing pressures on agricultural- and agroforestry production. Stable isotopes of hydrogen and oxygen in the water molecule are powerful and, nowadays, affordable tracers that can help to define the proportion of water sources accessed by plants. Yet, contrary to natural environments, their application is still relatively limited in agricultural and agroforestry research. In this work, we synthesize the advantages and the current knowledge deriving from the use of the stable isotopes of hydrogen and oxygen, in support of more traditional techniques, to understand root water uptake dynamics in agricultural and agroforestry systems. We also underline the practical implications related to the application of this technique for management purposes, and provide a vision for new challenges and future research opportunities in exploring crop and plant water use based on isotopic data.

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.

In this commentary, we build on discussions that emerged during the workshop "Isotope-based studies of water partitioning and plant-soil interactions in forested and agricultural environments" held in San Casciano Val di Pesa, Italy, in September 2017. Quantifying and understanding how water cycles through the Earth's critical zone is important to provide society and policy makers with the scientific background to manage water resources sustainably, especially considering the ever-increasing worldwide concern about water scarcity. Stable isotopes of hydrogen and oxygen in water have proven to be a powerful tool to track water fluxes in the critical zone. However, both mechanistic complexities (e.g., mixing and fractionation processes, heterogeneity of natural systems) and practical methodological issues (e.g., lack of standard protocols to sample specific compartments, such as soil water and xylem water) limit the application of stable water isotopes in critical zone science. In this commentary, we examine some of the opportunities and critical challenges of using isotope-based ecohydrological applications, and outline new perspectives focused on interdisciplinary research opportunities for this important tool in water and environmental science.

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.

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 CO 2 and 15 NH 4 15 NO 3 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 CO 2 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 24 h 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.

Fruit tree ecosystems represent an important land use type in Southern Europe. Nevertheless, limited information and large uncertainty currently exist about their potential role as a sink of atmospheric CO2, which is measured through an index that accounts for all inputs and outputs of C, namely the net ecosystem carbon balance (NECB). In this paper, we studied the fluxes of C assimilation, the C release and the lateral C and their contribution to the NECB in an apple orchard at different time scales. Data of net ecosystem productivity (NEP) were recorded by eddy covariance and converted into ecosystem respiration and gross primary productivity (GPP). The net primary productivity (NPP) and the C partitioning among tree organs were also biometrically assessed. The study was carried out in the period 2009–2012 in a commercial apple orchard located in an intensive fruit production district of South Tyrol, Italy. We found a positive NEP from March to October and yearly NEP values of 403 g C m−2. GPP (1346 g C m−2 year−1 on average) was highest between May and September, when leaves intercepted the highest amount of PPFD. Tree growth accounted for more than 90% of the total new biomass produced in the orchard, the remaining part being represented by the herbaceous vegetation covering the orchard floor. Trees allocated to fruits approximately half of the yearly NPP, while they increased only to a limited extent their standing biomass. A significant fraction of NPP was also allocated to organs (leaves, pruned woody organs, etc.,) that feed the detritus cycle. The NECB was on average positive (69 g C m−2) but showed high variation among years, and in the year when fruit yields was very high (74 t fruits/ha), the NECB was even negative. NECB was accounted to a greater extent by the yearly increase of tree woody organs and to a minor extent by the C transfer to the soil from the decomposing litter. The most relevant agronomical suggestion of this study is that tree vegetative growth resulting into either increasing standing biomass and/or increasing tree litter should not be reduced if we aim at maintaining the CO2 sink capacity of the apple orchard.

Arbuscular mycorrhizal fungi (AMF) are beneficial microrganisms which establish mutualistic symbioses with the roots of most food crops, improving plant performance, nutrient uptake and tolerance to biotic and abiotic stresses. A better understanding of the factors affecting AMF occurrence and diversity is fundamental to implement sustainable agricultural managements effectively profiting from beneficial plant symbionts. Here, we investigated AMF occurrence, diversity and community composition in the roots of apple trees from 21 orchards in South Tyrol, as affected by location, management (organic vs integrated) and altitude, by PCR cloning and sequencing and PCR-DGGE of partial 18S rRNA gene. The screening of 448 clones from 21 clone libraries allowed the identification of 6 native AMF at the species level: Glomus indicum , Sclerocystis sinuosa, Funneliformis mosseae , Rhizoglomus irregulare , Septoglomus constrictus and Claroideoglomus lamellosum . The most abundant genera were represented by Glomus (29.7% of the sequences), Paraglomus (19.4%), Claroideoglomus (17.2%), Sclerocystis (16.1%) and Rhizoglomus (12.3%). Septoglomus , Diversispora and Funneliformis sequences corresponded to less than 4% of total sequences. Although the degree of root colonization was unaffected by treatments, ANOSIM analysis of PCR-DGGE clusters revealed significant differences in apple root AMF diversity between sites and agricultural managements. Species richness was significantly higher in organically managed orchards than in integrated ones. Our findings provide insights into important factors affecting native AMF communities of apple trees, which could be exploited in sustainable fruit production systems, where beneficial soil biota boost biogeochemical cycles, energy fluxes and crop productivity.

From 2004 to 2012 carbon (C) fluxes between the soil-vegetation system and the atmosphere in apple, grape, olive and orange orchards planted in different Italian regions were measured. Above-ground net primary productivity (ANPP) ranged from 4 (olive) to 9 (apple) Mg C ha-1. Alley grass contribution to total ANPP significantly varied among the systems, reaching a maximum of 60% in vineyards. The harvest index ranged from 46% for apple, to 58% for orange, 60% for grape and 41% for olive, while abscised leaves accounted for 30% of ANPP, on average. Soil respiration fluxes ranged from 6 (orange) to 10 (grape) Mg C ha-1. Results indicate the potential of these fruit crop to sequester atmospheric C.

Orchards and vineyards are important land use types in Southern Europe. In spite of their potential to sequester atmospheric C and to mitigate climate change, relatively little is known regarding the influx and outflux of C in these systems. The aim of this work is to provide data on the C budget, including net primary production (NPP), C removal through production, and C sequestration potential for the vineyards and the main fruit tree species (apple, citrus, olive, and peach) grown in Italy. Standing biomass and NPP were measured, and net ecosystem exchange and net C balance assessed directly, through either eddy covariance technique, or considering NPP and heterotrophic respiration. Aboveground NPP ranged between 10 and 20 t ha-1 while, when directly assessed, belowground NPP was less than 20% of the total NPP. The C leaving the system through fruit production ranged between 2 and 3 t ha-1. Mature fruit tree ecosystems had positive net ecosystem productivity (ranging from 4.30 in Apple-2 to 7.5 in Grape-1.) and net ecosystem carbon balance (ranging from 0.6 to 5.9 t C ha-1 y-1), indicating the potential of these systems to store C.

Background and aims Fruit orchards potential as carbon (C) sinks is virtually unknown. Moreover, despite their importance in the Mediterranean area, few data are available about the effect of the reduction in water availability on fruit tree productivity. Here we report the effect of two different irrigation regimes on net primary (NPP) and net ecosystem (NEP) productivities of an apple orchard in northern Italy in 2006.

Soil CO 2 efflux ( E soil ), the main pathway of C movement from the biosphere to the atmosphere, is critical to the terrestrial C cycle but how precipitation and soil moisture influence E soil remains poorly understood. Here, we irrigated a longleaf pine wiregrass savanna for six years; this increased soil moisture by 41.2%. We tested how an altered precipitation regime affected total belowground carbon allocation (TBCA), root growth, soil carbon, and E soil . We used two methods to quantify E soil : daytime biweekly manual measurements and automated continuous measurements for one year. We hypothesized that the low-frequency manual method would miss both short- and long-term (i.e., subdaily to annual, respectively) effects of soil moisture on E soil while the high-frequency data from the automated method would allow the effects of soil moisture to be discerned. Root growth was significantly higher in irrigated plots, particularly at 0–20 cm depth. Irrigated annual E soil was significantly greater than that of the control when estimated with the continuous measurements but not when estimated from biweekly measurements. The difference in annual E soil estimates is likely due to (1) the delayed increase in E soil following irrigation pulses of soil moisture (i.e., variation that the biweekly manual measurements missed) and (2) the diel timing of biweekly manual measurements (they were completed early to mid-day before peak efflux). With irrigation, estimates of TBCA increased almost two-fold with automated measurements but only 36% with intermittent measurements. Relative to controls, irrigated treatments stored almost 2 Mg C ha −1 year −1 more in soils and 0.26 Mg C ha −1 year −1 more in roots. High-frequency measurements of E soil were essential to estimate total belowground carbon allocation. With irrigation, soil carbon pools were not at steady-state, so shifts in soil carbon storage must be considered in TBCA estimates.

Sustainable management of mineral nutrition in vineyards, as well as in other fruit plantations, should aim at exploiting the use of internal sources of nutrients, in order to reduce the need for external nutrient inputs. In this paper we explore the potential of the grassed alleys to provide nutrients to the vines. We followed for one vegetative season the decomposition of ryegrass and clover, frequently present as floor vegetation in vineyards, using litter bags filled with 15N-enriched grass material. In addition, we quantified the amount of nitrogen (N) transferred from the decomposing litter to field-grown grapevines. Ryegrass and clover had a relatively rapid decomposition rate, with a loss of C approaching 80% in only 16 weeks. The release of nutrients was particularly fast for potassium (95% in 16 weeks) followed by nitrogen (80%), calcium (70–80%), phosphorous (65–85%), magnesium (70–75%), and sulfur (60–70%). In spite of the rapid release of N from decomposing material, the N uptake by grapevines was on average less than 4% of the initial amount of N present in the litter of ryegrass and clover. Even if N release during the decomposition of mowed perennial ryegrass and white clover little contributed to the N nutrition of grapevine in the same growing season, most N from mowed grassed was still recovered in the soil.

We identified the role of various soil parameters and root density as drivers of soil respiration (Rs) in an apple orchard, measured during different periods of the year and at a range of distances from trees, in plots with a different history of nutrient supply. Rs was measured in April, May, August and December and studied in relation to soil temperature and moisture, total soil C and N, as well as to fine root density and medium-, and large-sized root density and root N concentration. The study also aimed to partition Rs by applying the root regression technique. Rs ranged from 0.06 in December to 1.49 g CO2 m−2 h−1 in August. Average soil temperature alone explained up to 71% of the annual variability of Rs, while soil water content was negatively correlated to Rs. Fertilization, soil C and N concentration and root N had negligible effects on Rs. Fine root density, but not medium- and large-sized root density, contributed to explaining part of the yearly variability of Rs and proved to be a good predictor in December, when the statistical significance of the regression made it possible to estimate the autotrophic component of Rs as being about 35% of total soil respiration.

Modern agriculture requires both, attention to crop yield and quality and to environmental issues. Among farmers' practices, fertilization can play a pivotal role in alleviating environmental pressure without affecting the production. In this work we present the study of nutrients budget spanning six years of apple trees cultivation and we propose a model for tree nutrient uptake as a tool to guide fruit trees fertilization. The survey has been carried on a typical apple orchard of the Po Valley, Italy, with Gala/M9 planted in February 1997 at a density of 2632 trees/ha. Each year trunk diameter, fruit yield and pruning wood production were recorded. The biomass of abscised leaves was estimated. A sample of 3 trees was excavated in November 2002. Nutrient concentration has been obtained for fruits, pruning wood, leaves and the whole excavated trees. In 6 years from planting, trees accumulated 16 Mg ha -1 of dry biomass in the framework, 8.5 in the pruning wood, 28 in fruits, and 8.3 in the abscised leaves. Nutrients absorbed in higher amounts were Ca (462 kg ha -1 ) and K (406 kg ha -1 ), but most of them returned to soil by abscised leaves and pruning wood. Potassium was mostly partitioned to fruits. Nitrogen was also absorbed in high amounts (345 kg ha ). The results of this study have been integrated in an electronic spreadsheet (www.isafruit.org) able to estimate apple tree nutrient uptake.

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.

The decomposition of plant residues has a pivotal role in carbon and nutrient cycles in agricultural ecosystems, where it can contribute to the sustainable management of the crops. In this paper we report a study on the release of C and nutrients during the decomposition of peach abscised leaves in northern Italy. Litter bags containing a representative amount of leaf material were installed under tree canopies either on the soil surface under open field conditions or on the soil surface in pots under partially controlled conditions. Potted leaf litter was pre-labelled with 15N. We observed that in 3 years, peach leaves lost 85% of their initial mass mostly attributable to cellulose decomposition, while new lignin or lignin-like compounds were synthesised during the first stages of the decomposition process. Nutrient dynamics differed depending on the considered element. Nitrogen and sulphur were initially immobilized into the litter to be released only starting after 44 weeks from the beginning of the decomposition. Potassium and magnesium were rapidly released in the winter following leaf abscission, reaching an amount that remained constant up to the end of the trial. Calcium and phosphorus release was slow, but constant throughout the three-year study period. With the only exception of Mg, 80–90% of initial amounts of mineral elements had released from decomposing peach leaves after 3 year from leaf abscission. Since in mature stands leaf litters of different ages coexist on the soil surface 80–90% of the nutrients contained in the abscised leaves are expected to return annually to the soil and potentially be available for subsequent root and/or microbial uptake.

Sustainable agriculture requires assessments of nitrogen fluxes and monitoring of potential nitrate losses. Watershed studies are particularly valuable to calculate nitrogen balances and quantify the relative importance of different sources of inputs and outputs. A nitrogen balance was calculated from September 2004 to October 2006 in an agricultural watershed named Valle Volta (Northern Italy) located in a Nitrate Vulnerable Zone. The area, consisting of 17.4 km 2 of arable land, with limited presence of urban areas and roads, is entirely below the sea level (3 m b.s.l. in average). Soils are typically Vertic Cambisols and Thionic Fulvisols with fine texture (silty clay or silty clay loam). About 45% of the agricultural soil is pipe-drained. The ground water level is maintained at 4.6 m b.s.l. by the activity of pumps that raise excess waters into a river. Water fluxes in and out from the basin were daily registered, and dissolved inorganic nitrogen concentration (N–NO 3 + N–NH 4 ) analyzed periodically. Data about fertilizers applications, seeds and crop yield were obtained from farmers’ interviews. Biological nitrogen fixation (BNF) was estimated on the base of dry matter yield. Major N inputs derived from fertilizers (174–188 Mg watershed −1 year −1 ), followed by BNF (126–131 Mg watershed −1 year −1 ). Maize was the crop receiving the highest fertilization rates, accounting for more than 40% of total fertilizer inputs. Saleable products were the main form of N leaving the watershed (317–338 Mg watershed −1 year −1 ). Nitrate was the main N form in irrigation and efflux water; its concentration was higher from autumn to spring, with peaks of 10–20 mg N L −1 in efflux water, while it was low in summer. Nitrogen losses with efflux water were higher in spring and in autumn. Overall, losses of nitrate by efflux water were limited if compared with literature data. Water balance in the area remained near zero at the beginning and the end of the first year, confirming the suitability of the area for this kind of study. The potential net contribution of each hectare of agricultural soil of Valle Volta basin to the N load toward the Adriatic sea is about 5.5 kg N. Our study demonstrated that in the Valle Volta watershed, total N outputs and inputs are of similar magnitude, indicating that crop management and especially N fertilization techniques has reached good levels of ecological sustainability.

Each year, significant fractions of nutrients absorbed by trees and orchard grasses, return to the soil by abscised leaves and mowed biomass. Using litter bag technique and labelled ( 15 N) litter, we assessed the decay dynamics and the related nutrient releases in a mature, drip irrigated, apple ( Malus domestica ) orchard located in the Eastern Po Valley (Italy) on a silty clay loam soil. Litter bags containing abscised apple leaves were placed in December 2001 on the soil surface and collected over a 2-year period, while the decomposition of perennial ryegrass was studied over a 6-month period from May 2002. The dynamics of mass and C losses from decomposing apple leaves fitted to a single exponential decay model. At 1 year from their placement, about 50% of original mass was lost, while and additional 20% was not recovered in the second year. Initial C losses were not accompanied by degradation of cellulose which started only in the spring of the year after their placement on the soil. Along with the decomposition process, the remaining litter was progressively enriched in lignin-like compounds. Net N and S immobilization occurred during the winter–spring period and net release of these nutrients occurred only in the second year. Ryegrass lost about half their mass and original N content after 6 weeks and most of sward derived N was recovered in the underneath soil volume. Both apple and ryegrass released most their initial K content during the period of decomposition. The knowledge of the dynamics of nutrient release on the orchard floor will be useful for predicting nutrient availability for tree uptake and therefore for managing amounts and dynamics of nutrient supply.

Temperature is often used as the primary driver to model soil respiration (RS) and several models based only on temperature have been used to estimate it, with a variable degree of accuracy. An adequate availability of photosynthates translocated from the canopy also affects root respiration (RR) and therefore RS. In this work, carried out in an apple orchard for three years, we assessed the role of temperature to RS and its autotrophic (RR) and heterotrophic (RH) components. We also determined the variation over the season of RS at a reference temperature and related it to concurrent data of gross primary productivity at ecosystem level (GPP), light (PPFD), air temperature (Tair), orchard net primary productivity (NPP) and root growth rate. Several of these factors were then incorporated into a model to estimate RS. Data showed that temperature alone explained less than 50 % of RS variability at yearly scale. GPP, NPP, PPFD and Tair were correlated to RS at a reference temperature. The contribution of root respiration to RS increased with increasing photosynthetic activity, total tree and root growth, PPFD and Tair. On a diurnal scale, the time lag between the pattern of GPP and the pattern of RR was between 2.5 and 3 h during the growing season, decreasing to 1.5 after fruit harvest. Including GPP, NPP, PPFD and Tair to a temperature-based model improved its predicting power of RS. The results confirm the existence of a tight coupling between plant metabolism and root-derived soil respiration in the apple orchard.

Rhizodeposition plays an important role in nitrogen (N) cycling within ecosystems, but it is understudied in agroecosystems, especially in orchards. In this study, we quantified N flux from peach root to soil in two soils with different texture. Seedlings were grown for 1 year in sand and fertilized with 15N-enriched ammonium nitrate. Trees were then transplanted into pots filled with a coarse-textured (CT) or a fine-textured (FT) soil with natural 15N abundance. The isotopic mass balance technique was applied to quantify the uptake and the release of N by roots. At the end of the experimental year tree growth was 431 g tree−1 in CT soil and 188 g tree−1 in FT soil, and root N concentration was 0.98% in CT soil and 0.73% in FT soil. Leaf chlorophyll was always higher in trees grown in CT than in FT soil. Nitrogen uptake in CT soil was more than double that in FT soil (4471 mg tree−1 vs. 2106 mg tree−1), but its allocation was not affected by soil texture (57% aboveground and 43% belowground). Nitrogen flux from roots to soil was 453 and 412 mg N tree−1 year−1 for trees in CT and in FT soil, respectively, 70% of which transferred in the winter. Our data suggest that root mortality is more important than root exudation in N transfer from roots to soil. Rhizodeposition was similar for both soils but tree growth was greater in CT soil than in FT soil. As a consequence, trees in FT soil allocated belowground (root biomass and rhizodeposition) a higher proportion of the absorbed N compared to trees in CT soil. Data also indicate that rhizodeposition can account for a major fraction (25–41%) of the photosynthate flux to the root system and therefore it should be considered to accurately estimate BNPP. A deeper knowledge of the belowground orchard processes is necessary to understand a balanced tree nutrient uptake. Rhizodeposition can also contribute to nutrient mobilization, heavy metal detoxification, root exploitation of soil, and drought tolerance. This work can thus provide information enabling horticulturists to develop management practices to optimise tree growth.

The mass transfer from root to soil by means of rhizodeposition has been studied in grasses and forest trees, but its role in fruit trees is still unknown. In this study, N fluxes from roots to soil were estimated by applying a 15N mass balance technique to the soil–tree system. Apple (Malus domestica) trees were pre-labelled with 15N and then grown outdoors in 40 L pots for one vegetative season in (1) a coarse-textured, low organic matter soil, (2) a coarse-textured, high organic matter soil, and (3) a fine-textured, high organic matter soil. At tree harvest the 15N abundance of the soils was higher than at transplanting, but the total amount of 15N present in the tree–soil system was similar at transplanting and tree harvest. The soils had a strong effect on N fluxes from and to the soil. In the fine-textured soil, 11% of the total plant-derived nitrogen was transferred to the soil, compared with 2–5% in the two coarse-textured soils. Rhizodeposition was higher in the fine soil (18% of the primary production) than in the coarse-textured soils, whereas higher soil organic matter depressed rhizodeposition. Nitrogen uptake was almost double in the coarse-textured, high organic matter soil versus the other soils. Our results indicate that belowground primary productivity is significantly underestimated if based on root production data only. Rhizodeposition represents a major process, whose role should not be underestimated in carbon and nitrogen cycles in orchard ecosystems.

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.