Effect of Leaf Removal and Insecticide Applications on Population Densities of Leafhoppers and Mites Associated with Grapevines.

In this study, we tested the effects of mechanical leaf removal, insecticide application, and their interaction on leafhoppers and phytophagous and predatory mites occurring in two vineyards over three growing seasons. Leaf removal was performed in the fruit zone using a two-head pulsed air leaf remover, while insecticides were applied with a tunnel air-assisted sprayer at the maximum dose/ha recommended on the product label. Results demonstrated the efficacy of insecticide application in reducing the population densities of leafhoppers but also their detrimental effects on predatory mites. In a number of case studies, leaf removal reduced leafhopper and predatory mite densities. In one vineyard, phytophagous mite populations increased some weeks after leaf removal and insecticide application, highlighting the need to carefully consider the potential impact of vineyard management practices on non-target arthropods in the IPM framework.

Monitoring of carbon-water fluxes at Eurasian meteorological stations using random forest and remote sensing.

Simulating the carbon-water fluxes at more widely distributed meteorological stations based on the sparsely and unevenly distributed eddy covariance flux stations is needed to accurately understand the carbon-water cycle of terrestrial ecosystems. We established a new framework consisting of machine learning, determination coefficient (R2), Euclidean distance, and remote sensing (RS), to simulate the daily net ecosystem carbon dioxide exchange (NEE) and water flux (WF) of the Eurasian meteorological stations using a random forest model or/and RS. The daily NEE and WF datasets with RS-based information (NEE-RS and WF-RS) for 3774 and 4427 meteorological stations during 2002-2020 were produced, respectively. And the daily NEE and WF datasets without RS-based information (NEE-WRS and WF-WRS) for 4667 and 6763 meteorological stations during 1983-2018 were generated, respectively. For each meteorological station, the carbon-water fluxes meet accuracy requirements and have quasi-observational properties. These four carbon-water flux datasets have great potential to improve the assessments of the ecosystem carbon-water dynamics.

Uncovering the critical soil moisture thresholds of plant water stress for European ecosystems.

Understanding the critical soil moisture (SM) threshold (θcrit ) of plant water stress and land surface energy partitioning is a basis to evaluate drought impacts and improve models for predicting future ecosystem condition and climate. Quantifying the θcrit across biomes and climates is challenging because observations of surface energy fluxes and SM remain sparse. Here, we used the latest database of eddy covariance measurements to estimate θcrit across Europe by evaluating evaporative fraction (EF)-SM relationships and investigating the covariance between vapor pressure deficit (VPD) and gross primary production (GPP) during SM dry-down periods. We found that the θcrit and soil matric potential threshold in Europe are 16.5% and -0.7 MPa, respectively. Surface energy partitioning characteristics varied among different vegetation types; EF in savannas had the highest sensitivities to SM in water-limited stage, and the lowest in forests. The sign of the covariance between daily VPD and GPP consistently changed from positive to negative during dry-down across all sites when EF shifted from relatively high to low values. This sign of the covariance changed after longer period of SM decline in forests than in grasslands and savannas. Estimated θcrit from the VPD-GPP covariance method match well with the EF-SM method, showing this covariance method can be used to detect the θcrit . We further found that soil texture dominates the spatial variability of θcrit while shortwave radiation and VPD are the major drivers in determining the spatial pattern of EF sensitivities. Our results highlight for the first time that the sign change of the covariance between daily VPD and GPP can be used as an indicator of how ecosystems transition from energy to SM limitation. We also characterized the corresponding θcrit and its drivers across diverse ecosystems in Europe, an essential variable to improve the representation of water stress in land surface models.

Susceptibility to Xylella fastidiosa and functional xylem anatomy in Olea europaea: revisiting a tale of plant-pathogen interaction.

Xylella fastidiosa is a xylem-limited bacterium causing the Olive Quick Decline Syndrome, which is currently devastating the agricultural landscape of Southern Italy. The bacterium is injected into the xylem vessels of leaf petioles after the penetration of the insect vector's stylet. From here, it is supposed to colonize the xylem vasculature moving against water flow inside conductive vessels. Widespread vessel clogging following the bacterial infection and causing the failure of water transport seemed not to fully supported by the recent empirical xylem anatomical observations in infected olive trees. We tested the hypothesis that the higher susceptibility to the X. fastidiosa's infection in Cellina di Nardò compared with Leccino is associated to the higher vulnerability to air embolism of its larger vessels. Such hypothesis is motivated by the recognized ability of X. fastidiosa in degrading pit membranes and also because air embolism would possibly provide microenvironmental conditions more favourable to its more efficient aerobic metabolism. We revised the relevant literature on bacterium growth and xylem physiology, and carried out empirical field, mid-summer measurements of xylem anatomy and native embolism in olive cultivars with high (Cellina di Nardò) and low susceptibility (Leccino) to the infection by X. fastidiosa. Both cultivars had similar shoot mass traits and vessel length (~80 cm), but the highly susceptible one had larger vessels and a lower number of vessels supplying a given leaf mass. Native air embolism reduced mean xylem hydraulic conductance by ~58 % (Cellina di Nardò) and ~38 % (Leccino). The higher air-embolism vulnerability of the larger vessels in Cellina di Nardò possibly facilitates the X. fastidiosa's infection compared to Leccino. Some important characteristics of the vector-pathogen-plant interactions still require deep investigations acknowledging both the pathogen metabolic pathways and the biophysical principles of xylem hydraulics.

Sensitivity of gross primary productivity to climatic drivers during the summer drought of 2018 in Europe.

In summer 2018, Europe experienced a record drought, but it remains unknown how the drought affected ecosystem carbon dynamics. Using observations from 34 eddy covariance sites in different biomes across Europe, we studied the sensitivity of gross primary productivity (GPP) to environmental drivers during the summer drought of 2018 versus the reference summer of 2016. We found a greater drought-induced decline of summer GPP in grasslands (-38%) than in forests (-10%), which coincided with reduced evapotranspiration and soil water content (SWC). As compared to the 'normal year' of 2016, GPP in different ecosystems exhibited more negative sensitivity to summer air temperature (Ta) but stronger positive sensitivity to SWC during summer drought in 2018, that is, a stronger reduction of GPP with soil moisture deficit. We found larger negative effects of Ta and vapour pressure deficit (VPD) but a lower positive effect of photosynthetic photon flux density on GPP in 2018 compared to 2016, which contributed to reduced summer GPP in 2018. Our results demonstrate that high temperature-induced increases in VPD and decreases in SWC aggravated drought impacts on GPP. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

The total path length hydraulic resistance according to known anatomical patterns: What is the shape of the root-to-leaf tension gradient along the plant longitudinal axis?

Xylem conduit diameter widens from leaf tip to stem base and how this widening affects the total hydraulic resistance (RTOT) and the gradient of water potential (Ψxyl) has never been thoroughly investigated. Data of conduit diameter of Acer pseudoplatanus,Fagus sylvatica and Picea abies were used to model the axial variation of RTOT and Ψxyl. The majority of RTOT (from 79 to 98%) was predicted to be confined within the leaf/needle. This means that the xylem conduits of stem and roots, accounting for nearly the total length of the hydraulic path, theoretically provide a nearly negligible contribution to RTOT. Consequently, a steep gradient of water potentials was predicted to develop within the leaf/needle base, whereas lower in the stem water potentials approximate those of rootlets. Our results would suggest that the strong partitioning of RTOT between leaves/needles coupled with basal conduit widening is of key importance for both hydraulic safety against drought-induced embolism formation and efficiency, as it minimizes the exposure of stem xylem to high tensions and makes the total plant's conductance substantially independent of body size.

Comprehensive transcript profiling of two grapevine rootstock genotypes contrasting in drought susceptibility links the phenylpropanoid pathway to enhanced tolerance.

In light of ongoing climate changes in wine-growing regions, the selection of drought-tolerant rootstocks is becoming a crucial factor for developing a sustainable viticulture. In this study, M4, a new rootstock genotype that shows tolerance to drought, was compared from a genomic and transcriptomic point of view with the less drought-tolerant genotype 101.14. The root and leaf transcriptome of both 101.14 and the M4 rootstock genotype was analysed, following exposure to progressive drought conditions. Multifactorial analyses indicated that stress treatment represents the main factor driving differential gene expression in roots, whereas in leaves the genotype is the prominent factor. Upon stress, M4 roots and leaves showed a higher induction of resveratrol and flavonoid biosynthetic genes, respectively. The higher expression of VvSTS genes in M4, confirmed by the accumulation of higher levels of resveratrol in M4 roots compared with 101.14, was coupled to an up-regulation of several VvWRKY transcription factors. Interestingly, VvSTS promoter analyses performed on both the resequenced genomes highlighted a significantly higher number of W-BOX elements in the tolerant genotype. It is proposed that the elevated synthesis of resveratrol in M4 roots upon water stress could enhance the plant's ability to cope with the oxidative stress usually associated with water deficit.

Sulfadiazine uptake and effects in common hazel (Corylus avellana L.).

Soil contamination by antibiotics is a possible consequence of animal husbandry waste, sewage sludge, and reclaimed water spreading in agriculture. In this study, 1-year-old hazel plants (Corylus avellana L.) were grown in pots for 64 days in soil spiked with sulfadiazine (SDZ) in the range 0.01-100 mg kg(-1) soil. Leaf gas exchanges, fluorescence parameters and plant growth were measured regularly during the experiment, whereas plant biomass, sulfonamide concentrations in soil and plant tissues, and the quantitative variation of culturable bacterial endophytes in leaf petiole were analyzed at the end of the trial. During the experiment, photosynthesis and leaf transpiration as well as fluorescence parameters were progressively reduced by the antibiotic. Effects were more evident for leaf transpiration and for the highest SDZ spiking concentrations, whereas growth analyses did not reveal negative effects of the antibiotic. At the end of the trial, a high number of culturable endophytic bacteria in the leaf petiole of plants treated with 0.1 and 0.01 mg kg(-1) were observed, and SDZ was extractable from soil and plant roots for spiking concentrations ≥1 mg kg(-1). Inside plants, the antibiotic was mainly stored at the root level with bioconcentration factors increasing with the spiking dose, and the hydroxylated derivate 4-OH-SDZ was the only metabolite detected. Overall results show that 1-year-old hazel plants can contribute to the reduction of sulfonamide concentrations in the environment, however, sensitive reactions to SDZ can be expected at the highest contamination levels.

Variability with xylem depth in sap flow in trunks and branches of mature olive trees.

Knowledge of sap flow variability in tree trunks is important for up-scaling transpiration from the measuring point to the whole-tree and stand levels. Natural variability in sap flow, both radial and circumferential, was studied in the trunks and branches of mature olive trees (Olea europea L., cv Coratina) by the heat field deformation method using multi-point sensors. Sapwood depth ranged from 22 to 55 mm with greater variability in trunks than in branches. Two asymmetric types of sap flow radial patterns were observed: Type 1, rising to a maximum near the mid-point of the sapwood; and Type 2, falling continuously from a maximum just below cambium to zero at the inner boundary of the sapwood. The Type 1 pattern was recorded more often in branches and smaller trees. Both types of sap flow radial patterns were observed in trunks of the sample trees. Sap flow radial patterns were rather stable during the day, but varied with soil water changes. A decrease in sap flow in the outermost xylem was related to water depletion in the topsoil. We hypothesized that the variations in sap flow radial pattern in a tree trunk reflects a vertical distribution of water uptake that varies with water availability in different soil layers.