Soil management affects carbon and nitrogen concentrations and stable isotope ratios in vine products

Weeds reduce vineyard productivity and affect grape quality by competing with grapevines (Vitis vinifera L.) for water and nutrients. The increased banning of herbicides has prompted the evaluation of alternative soil management strategies. Cover cropping seems to be the best alternative for weed management. However, it may impact vine growth, grape yield, and quality. Quantitative studies on these changes are scarce. Our study aimed to investigate the combined effect of grass cover and water availability on vines of three cultivars, the white Chasselas and Petite Arvine and the red Pinot noir field-grown under identical climatic and pedological conditions and grafted onto the same rootstock. Soil management and irrigation experiments were performed during the 2020-2021 seasons. Two extreme soil management practices were established in the vineyard, based on 100 % bare soil (BS) by the application of herbicides with glufosinate or glyphosate as active ingredients and 100 % grass-covered soil (GS) by cover cropping with a mixture of plant species. Two water statuses were imposed by drip irrigation (DI) and no irrigation (NI). The level of vine-weed competition for water and nitrogen (N) was assessed in the vine, must, and wine solid residues (WSRs) by comparing measurements, i.e., the yeast assimilable N content, C/N_WSR, carbon and N isotope ratios (δ¹³C_grape-sugars, δ¹³C_WSR, and δ¹⁵N_WSR) among the different treatments (BS-DI, BS-NI, GS-DI, GS-NI). The increase in the δ¹³C_grape-sugars and δ¹³C_WSR values with increasing plant water deficit mimicked the observations in irrigation experiments on BS. The N_WSR content and δ¹⁵N_WSR values decreased with water stress and much more strongly in vines on GS. The dramatic N deficit in rainfed vines on GS could be alleviated with irrigation. The present study provides insights from chemical and stable isotope analyses into the potential impact of cover cropping in vineyards in the context of the banning of herbicides in a time of global water scarcity due to climate change.

Carbon and nitrogen stable isotope variations in leaves of two grapevine cultivars (Chasselas and Pinot noir): Implications for ecophysiological studies

We investigated the within- and between-leaf variability in the carbon and nitrogen isotope composition (δ¹³C and δ¹⁵N) and total nitrogen (TN) content in two grapevine cultivars (Vitis vinifera cv. Chasselas and Pinot noir) field-grown under rain-fed conditions. The within-leaf variability was studied in discs sampled from base-to-tip and left and right regions from the margin to midrib. The intra- and interplant variability was studied by comparing leaves at different positions along the shoot (basal, median, apical). In leaves from both cultivars, a decrease in δ¹³C from base to tip was observed, which is in line with an upward gradient of stomatal density and chlorophyll concentration. Less important, but still significant differences were observed between the right and left discs. The leaf TN and δ¹⁵N values differed between cultivars, showed smaller variations than the δ¹³C values, and no systematic spatial trends. The intraleaf variations in δ¹³C, δ¹⁵N, and TN suggest that stomatal behavior, CO₂ fixation, chlorophyll concentrations, and the chemical composition of leaf components were heterogeneous in the leaves. At the canopy scale, the apical leaves had less ¹³C and more ¹⁵N and TN than the basal leaves, indicating differences in their photosynthetic capacity and remobilizations from old, senescing leaves to younger leaves. Overall, this study demonstrates patchiness in the δ¹³C and δ¹⁵N values of grapevine leaves and species-specificity of the nitrogen assimilation and ¹⁵N fractionation. These findings suggest that care must be taken not to overinterpret foliar δ¹³C and δ¹⁵N values in studies based on fragmented material as markers of physiological and biochemical responses to environmental factors.

Shifts in carbon and nitrogen stable isotope composition and epicuticular lipids in leaves reflect early water-stress in vineyards

Changes in leaf carbon and nitrogen isotope composition (δ¹³C and δ¹⁵N values) and the accumulation of epicuticular lipids have been associated with plant responses to water stress. We investigated their potential use as indicators of early plant water deficit in two grapevine (Vitis vinifera L.) cultivars, Chasselas and Pinot noir, that were field-grown under well-watered and water-deficient conditions. We tested the hypothesis that the bulk δ¹³C and δ¹⁵N values and the concentrations of epicuticular fatty acids may change in leaves of similar age with the soil water availability. For this purpose, leaves were sampled at the same position in the canopy at different times (phenological stages) during the 2014 growing season. Bulk dry matter of young leaves from flowering to veraison had higher δ¹³C values, higher total nitrogen content, and lower δ¹⁵N values than old leaves. In both cultivars, δ¹⁵N values were strongly correlated with plant water deficiency, demonstrating their integration of the plant water stress response. δ¹³C values recorded the water deficiency only in those plants that had not received foliar organic fertilization. The soil water deficiency triggered the accumulation of C_>26 fatty acids in the cuticular waxes. The compound-specific isotope analysis (CSIA) of fatty acids from old leaves showed an increase in δ¹³C among the C₁₆-C₂₂ chains, including stress signaling linoleic and linolenic acids. Our results provide evidence for leaf ¹³C-enrichment, ¹⁵N-depletion, and enhanced FA-chain elongation and epicuticular accumulation in the grapevine response to water stress. The leaf δ¹³C and δ¹⁵N values, and the concentration of epicuticular fatty acids can be used as reliable and sensitive indicators of plant water deficit even when the level of water stress is low to moderate. They could also be used, particularly the more cost-efficient δ¹³C and δ¹⁵N measurements, for periodic biogeochemical mapping of the plant water availability at the vineyard and regional scale.

Corrigendum to: Impact of crop load on nitrogen uptake and reserve mobilisation in Vitis vinifera

Nitrogen deficit affects both crop production and composition, particularly in crops requiring an optimal fruit N content for aroma development. The adaptation of cultural practices to improve N use efficiency (NUE) (i.e. N uptake, assimilation and partitioning) is a priority for the sustainable production of high-quality crops. A trial was set on potted grapevines (Vitis vinifera L. cv. Chasselas) to investigate the potential of crop limitation (via bunch thinning) to control plant NUE and ultimately fruit N composition at harvest. A large crop load gradient was imposed by bunch thinning (0.5-2.5 kg m^-2) and N traceability in the plant was realised with an isotope-labelling method (10 atom % ¹⁵N foliar urea). The results indicate that the mobilisation of root reserves plays a major role in the balance of fruit N content. Fertiliser N uptake and assimilation appeared to be strongly stimulated by high-yielding conditions. Fertilisation largely contributed to fulfilling the high fruit N demand while limiting the mobilisation of root reserves under high yield conditions. Plants were able to modulate root N reserve mobilisation and fertiliser N uptake in function of the crop load, thus maintaining a uniform N concentration in fruits. However, the fruit free amino N profile was modified, which potentially altered the fruit aromas. These findings highlight the great capacity of plants to adapt their N metabolism to constraints, crop thinning in this case. This confirms the possibility of monitoring NUE by adapting cultural practices.

Impact of crop load on nitrogen uptake and reserve mobilisation in Vitis vinifera

Nitrogen deficit affects both crop production and composition, particularly in crops requiring an optimal fruit N content for aroma development. The adaptation of cultural practices to improve N use efficiency (NUE) (i.e. N uptake, assimilation and partitioning) is a priority for the sustainable production of high-quality crops. A trial was set on potted grapevines (Vitis vinifera L. cv. Chasselas) to investigate the potential of crop limitation (via bunch thinning) to control plant NUE and ultimately fruit N composition at harvest. A large crop load gradient was imposed by bunch thinning (0.5-2.5 kg m-2) and N traceability in the plant was realised with an isotope-labelling method (10 atom % 15N foliar urea). The results indicate that the mobilisation of root reserves plays a major role in the balance of fruit N content. Fertiliser N uptake and assimilation appeared to be strongly stimulated by high-yielding conditions. Fertilisation largely contributed to fulfilling the high fruit N demand while limiting the mobilisation of root reserves under high yield conditions. Plants were able to modulate root N reserve mobilisation and fertiliser N uptake in function of the crop load, thus maintaining a uniform N concentration in fruits. However, the fruit free amino N profile was modified, which potentially altered the fruit aromas. These findings highlight the great capacity of plants to adapt their N metabolism to constraints, crop thinning in this case. This confirms the possibility of monitoring NUE by adapting cultural practices.

Past and future of sustainable viticulture in Switzerland

Switzerland is a pioneer country in the development of integrated production (IP) and integrated pest management (IPM). The overall goal is sustainability at the ecological, economic and social level to produce high quality grapes. In 1993, the IP-IPM head-organisation VITISWISS was created. The starting points were the improvement of pest management by the biocontrol of spider mites and the control of grape berry moths by mating disruption and an optimal soil management, followed over the years by state-of-the-art sprayer calibration, development of disease forecasting models (AgroMeteo, VitiMeteo), leaf-area adapted dosage of plant protection products, enhanced biodiversity, water and cover crop management. The efforts and the results gained in a continuous education process by the growers are considerable, but not enough for consumers and politics concerned by the use of plant protection products. The absence of acaricides and insecticides as well as forecasting systems available on the internet (www.agrometeo.ch) for the control of downy and powdery mildew, represent the major progresses. Where mechanisation is possible, herbicides can progressively be replaced by mechanical technics, which is not possible in steep vineyards. The general irrational unscientific trend against “synthetic” plant protection products requests alternatives for the control of fungal diseases and for cover crop management under the vine rows to avoid excessive water-nitrogen competition particularly in the actual context of climate change.

Changes in soil water availability in vineyards can be traced by the carbon and nitrogen isotope composition of dried wines

The grapevine is one of the most important edible fruit plants cultivated worldwide, and it is highly sensitive to changes in the soil water content. We studied the total carbon and nitrogen contents and stable isotope compositions (C/N_WSR, δ¹³C_WSR and δ¹⁵N_WSR values) of the solid residues obtained by freeze-drying wines produced from two white grapevine cultivars (Vitis vinifera L. cv Chasselas and Petite Arvine) field grown under different soil water regimes while maintaining other climatic and ecopedological conditions identical. These experiments simulated the more frequent and extended climate change-induced periods of soil water shortage. The wines were from the 2009-2014 vintages, produced using the same vinification procedure. The plant water status, reflecting soil water availability, was assessed by the predawn leaf water potential (Ψ_pd), monitored in the field during the growing seasons. For both wine varieties, the δ¹³C_WSR values are highly correlated with Ψ_pd values and record the soil water availability set by soil water holding capacity, rainfall and irrigation water supply. These relationships were the same as those observed for the carbon isotope composition of fruit sugars (i.e., must sugars) and plant water status. In Chasselas wines, the nitrogen content and δ¹⁵N_WSR values decreased with soil water deficit, indicating control of the flux of soil-water soluble nutrients into plants by soil water availability. Such a correlation was not found for Petite Arvine, probably due to different N-metabolism processes in this genetically atypical cultivar. The results presented in this study confirm and generalize what was previously found for red wine (Pinot noir); the carbon isotope composition of wine solid residues is a reliable indicator of the soil and the plant water status and thus can be used to trace back local climatic conditions in the vineyard's region. In most wines (except Petite Arvine) the C/N_WSR and δ¹⁵N_WSR values are indicators of the origin of the nitrogen supplied to the plant's fruit (grape) that can be used to assess the N dynamics in the soil-water-plant system.

Grapevine red blotch virus: Absence in Swiss Vineyards and Analysis of Potential Detrimental Effect on Viticultural Performance

Grapevine red blotch virus (GRBV) is a recently described virus that infects grapevine. Little information is available on the possible occurrence and distribution outside North America. Therefore, we surveyed commercial vineyards from the three major grape-growing regions in Switzerland to determine the presence or absence of GRBV. In total, 3,062 vines were analyzed by polymerase chain reaction. None of the vines tested positive for GRBV, suggesting the absence of GRBV from Swiss vineyards. We also investigated whether GRBV was present in 653 grapevine accessions in the Agroscope grapevine virus collection at Nyon, including dominantly Swiss (457) but also international accessions. Only six referential accessions were infected by GRBV, all originating from the United States, whereas all others from 10 European and 8 non-European origins tested negative. High-throughput sequencing analysis of Zinfandel A2V13, in the collection since 1985, confirmed close similarity of GRBV isolate Z_A2V13 to American isolates according to genomes deposited in GenBank. Because the Zinfandel A2V13 reference was also maintained grafted on the leafroll virus indicator Vitis vinifera 'Gamay', we evaluated the effect of GRBV on viticultural performance over a 3-year period. Our results showed clear detrimental effects of GRBV on grapevine physiology (vine vigor, leaf chlorophyll content, and gas exchange) and fruit quality. These findings underscore the importance of implementation of GRBV testing worldwide in certification and quarantine programs to prevent the dissemination of this virus.

Changes in leaf stomatal conductance, petiole hydraulics and vessel morphology in grapevine (Vitis vinifera cv. Chasselas) under different light and irrigation regimes

Hydraulic conductance and water transport in plants may be affected by environmental factors, which in turn regulate leaf gas exchange, plant growth and yield. In this study, we assessed the combined effects of radiation and water regimes on leaf stomatal conductance (gs), petiole specific hydraulic conductivity (Kpetiole) and anatomy (vessel number and size); and leaf aquaporin gene expression of field-grown grapevines at the Agroscope Research Station (Leytron, Switzerland). Chasselas vines were subjected to two radiation (sun and shade) levels combined with two water (irrigated and water-stressed) regimes. The sun and shade leaves received ~61.2 and 1.48molm-2day-1 of photosynthetically active radiation, respectively, during a clear-sky day. The irrigated vines were watered weekly from bloom to veraison whereas the water-stressed vines did not receive any irrigation during the season. Water stress reduced gs and Kpetiole relative to irrigated vines throughout the season. The petioles from water-stressed vines showed fewer large-sized vessels than those from irrigated vines. The shaded leaves from the irrigated vines exhibited a higher Kpetiole than the sun leaves at the end of the season, which was partially explained by a higher number of vessels per petiole and possibly by the upregulation of some of the aquaporins measured in the leaf. These results suggest that not only plant water status but also the light environment at the leaf level affected leaf and petiole hydraulics.

The influence of water stress on grapevine (Vitis vinifera L.) shoots in a cool, humid climate: growth, gas exchange and hydraulics

Recent climatic trends of higher average temperatures and erratic precipitation patterns are resulting in decreased soil moisture availability and, consequently, periods of water stress. We studied the effects of seasonal water stress on grapevine (Vitis vinifera L. cv. Riesling grafted onto 101-14 (Vitis riparia Michx.×Vitis rupestris Scheele) rootstock) shoot growth, leaf gas exchange, xylem morphology and hydraulic performance in the cool-climate Finger Lakes region of New York. A plastic rain exclusion tarp was installed on the vineyard floor to create a soil moisture deficit and consequently induce vine water stress. Weekly measurements of predawn leaf and midday stem water potentials (Ψmd) were made, and two contrasting shoot length classes, long (length >2.0m) and short (length <1.0m), were monitored. Growth of both long and short shoots was positively correlated with Ψmd but no difference in water status was found between the two. Compared with rain-fed vines, water-stressed vines had lower photosynthesis and stomatal conductance later in the season when Ψmd dropped below -1.2MPa. Long shoots had three-fold higher xylem-specific hydraulic conductivity values than short shoots. Long shoots experiencing water stress were less vulnerable to xylem cavitation than shorter shoots even though they had more large-diameter vessels. The lower vulnerability to cavitation of long shoots may be attributed to less xylem intervessel pitting being found in long shoots, consistent with the air-seeding hypothesis, and suggests that a hydraulic advantage enables them to maintain superior growth and productivity under water stress.

Are needles of Pinus pinaster more vulnerable to xylem embolism than branches? New insights from X-ray computed tomography

Plants can be highly segmented organisms with an independently redundant design of organs. In the context of plant hydraulics, leaves may be less embolism resistant than stems, allowing hydraulic failure to be restricted to distal organs that can be readily replaced. We quantified drought-induced embolism in needles and stems of Pinus pinaster using high-resolution computed tomography (HRCT). HRCT observations of needles were compared with the rehydration kinetics method to estimate the contribution of extra-xylary pathways to declining hydraulic conductance. High-resolution computed tomography images indicated that the pressure inducing 50% of embolized tracheids was similar between needle and stem xylem (P50 needle xylem  = -3.62 MPa, P50 stem xylem  = -3.88 MPa). Tracheids in both organs showed no difference in torus overlap of bordered pits. However, estimations of the pressure inducing 50% loss of hydraulic conductance at the whole needle level by the rehydration kinetics method were significantly higher (P50 needle  = -1.71 MPa) than P50 needle xylem derived from HRCT. The vulnerability segmentation hypothesis appears to be valid only when considering hydraulic failure at the entire needle level, including extra-xylary pathways. Our findings suggest that native embolism in needles is limited and highlight the importance of imaging techniques for vulnerability curves.

Stomatal behaviour of irrigated Vitis vinifera cv. Syrah following partial root removal

We examined stomatal behaviour of a grapevine cultivar (Vitis vinifera L. cv. Syrah) following partial root removal under field conditions during progressively developing water deficits. Partial root removal led to an increase in hydraulic resistances along the soil-to-leaf pathway and leaf wilting symptoms appeared in the root-pruned plants immediately following root removal. Leaves recovered from wilting shortly thereafter, but hydraulic resistances were sustained. In comparison with the non-root pruned vines, leaves of root-pruned vines showed an immediate decrease in both pre-dawn (ψPD) and midday (ψleaf) leaf water potential. The decline in ψPD was unexpected in as much as soil moisture was not altered and it has been shown that axial water transport readily occurs in woody perennials. Only ~30% of the functional root system was removed, thus leaving the system mainly intact for water redistribution. Stem water potential (ψStem) and leaf gas exchanges of CO2 (A) and H2O (E) also declined immediately following root pruning. The lowering of ψPD, ψleaf, ψStem, A and E was sustained during the entire growing season and was not dependent on irrigation during that time. This, and a close relationship between stomatal conductance (gs) and leaf-specific hydraulic conductance (Kplant), indicated that the stomatal response was linked to plant hydraulics. Stomatal closure was observed only in the root-restricted plants and at times of very high evaporative demand (VPD). In accordance with the Ball-Berry stomatal control model proposed by Ball et al. (1987), the stomatal sensitivity factor was also lower in the root-restricted plants than in intact plants as soil water availability decreased. Although ψPD, ψStem and ψLeaf changed modestly and gradually following root removal, gs changed dramatically and abruptly following removal. These results suggest the involvement of stomatal restricting signals being propagated following removal of roots.

Diurnal cycles of embolism formation and repair in petioles of grapevine (Vitis vinifera cv. Chasselas)

The impact of water deficit on stomatal conductance (g(s)), petiole hydraulic conductance (K(petiole)), and vulnerability to cavitation (PLC, percentage loss of hydraulic conductivity) in leaf petioles has been observed on field-grown vines (Vitis vinifera L. cv. Chasselas). Petioles were highly vulnerable to cavitation, with a 50% loss of hydraulic conductivity at a stem xylem water potential (Ψ(x)) of -0.95 MPa, and up to 90% loss of conductivity at a Ψ(x) of -1.5 MPa. K(petiole) described a daily cycle, decreasing during the day as water stress and evapotranspiration increased, then rising again in the early evening up to the previous morning's K(petiole) levels. In water-stressed vines, PLC increased sharply during the daytime and reached maximum values (70-90%) in the middle of the afternoon. Embolism repair occurred in petioles from the end of the day through the night. Indeed, PLC decreased in darkness in water-stressed vines. PLC variation in irrigated plants showed the same tendency, but with a smaller amplitude. The Chasselas cultivar appears to develop hydraulic segmentation, in which petiole cavitation plays an important role as a 'hydraulic fuse', thereby limiting leaf transpiration and the propagation of embolism and preserving the integrity of other organs (shoots and roots) during water stress. In the present study, progressive stomatal closure responded to a decrease in K(petiole) and an increase in cavitation events. Almost total closure of stomata (90%) was measured when PLC in petioles reached >90%.