Cavitation fatigue in conifers: a study on eight European species.

After drought-induced embolism and repair, tree xylem may be weakened against future drought events (cavitation fatigue). As there are few data on cavitation fatigue in conifers available, we quantified vulnerability curves (VCs) after embolism/repair cycles on eight European conifer species. We induced 50% and 100% loss of conductivity (LC) with a cavitron, and analyzed VCs. Embolism repair was obtained by vacuum infiltration. All species demonstrated complete embolism repair and a lack of any cavitation fatigue after 50% LC . After 100% LC, European larch (Larix decidua), stone pine (Pinus cembra), Norway spruce (Picea abies), and silver fir (Abies alba) remained unaffected, while mountain pine (Pinus mugo), yew (Taxus baccata), and common juniper (Juniperus communis) exhibited 0.4-0.9 MPa higher vulnerability to embolism. A small cavitation fatigue observed in Scots pine (Pinus sylvestris) was probably biased by incomplete embolism repair, as indicated by a correlation of vulnerability shifts and conductivity restoration. Our data demonstrate that cavitation fatigue in conifers is species-specific and depends on the intensity of preceding LC. The lack of fatigue effects after moderate LC, and relevant effects in only three species after high LC, indicate that conifers are relatively resistant against cavitation fatigue. This is remarkable considering the complex and delicate conifer pit architecture and may be important considering climate change projections.

Anatomical, Phytochemical, and Histochemical Study of Juniperus rigida Needles at Different Altitudes.

Needles of Juniperus rigida are used in Chinese traditional medicine for the treatment of brucellosis, dropsy, skin disease, and rheumatoid arthritis. This is the first study that reports anatomical structures of the J. rigida needles collected at different altitudes. The most common anatomical, phytochemical, and histochemical techniques and methods are used. The results show that anatomical structures and chemical composition change significantly at different altitudes. The main anatomical characters are significant xeromorphic structures (thick epidermis, hypodermis, and cuticle), a stomatal band, a developed vascular bundle, and a marginal resin duct. The xeromorphic structures become more pronounced with increasing altitude. The phytochemical and histochemical results demonstrate that the content of the main chemical compounds (phenols and terpenoids) basically increases at a higher elevation. Histochemical analysis localizes the phenols in epidermal cells, sponge tissue, endothelial layer cells, and stomatal bands, and the terpenoids in palisade tissue, sponge tissue, and the edge of the resin duct. This work reveals the relation between anatomy and chemistry in J. rigida needles, contributes to the quality control of its ethno-medicine, and provides the evidence to develop the commercial cultivation.

Effects of feeding juniper as a roughage on feedlot performance, carcass measurements, meat sensory attributes, and volatile aroma compounds of yearling Rambouillet wethers1,2.

The majority of U.S. lambs are born during late winter or early spring, which can create downstream variability in carcass quality if commercial lamb harvest is to be relatively constant throughout the year. Flavor is an important quality determining characteristic of sheep meat and is influenced, in part, by animal age at harvest. However, management practices to mitigate the risk of objectionable flavors in meat from old crop lambs or yearlings are not well known. Yearling (16.8 ± 0.14 mo) Rambouillet wethers were assigned to 1 of 3 treatment groups, which consisted of feeding a 20% ground sorghum-sudangrass hay diet for 40 d (JUN0; n = 10), a 20% ground juniper diet for 40 d (JUN40; n = 10), or a 20% ground hay diet for 20 d followed by a 20% ground juniper diet for 20 d (JUN20; n = 10). Wethers were harvested on day 41 and a whole bone-in loin and a boneless inside leg roast were fabricated from one side each of carcass. After grilling (loin chop) or convection air roasting (leg roast), trained sensory panel evaluation and measurement of aroma volatiles by gas chromatography/mass spectrometry were performed. Treatment diet did not affect (P ≥ 0.17) wether feedlot performance, dressing percentage, or loin eye area. However, wethers fed JUN0 tended (P = 0.06) to have greater back fat depth than wethers fed JUN20 or JUN40. No trained sensory panel trait of loin chop samples was affected (P > 0.10) by treatment. Leg roasts from JUN0 and JUN20 wethers had greater (P = 0.01) lamb identification sensory score than JUN40. Benzaldehyde, 1-heptanol, and 1-octanol concentrations were greater (P < 0.05) and decanal and nonenal concentrations were less (P < 0.05) in loin chops from JUN0 compared with JUN40 wethers. Additionally, the terpenes cedr-8-ene, gamma muurolene, and widdrene tended to be greater (P < 0.07) in loin chops from JUN20 and JUN40 than JUN0 wethers. The 2-pentyl-furan concentrations were greatest (P = 0.03) in leg roasts from JUN40 wethers. Like the loin chops, cedr-8-ene, gamma-muurolene, toluene, and widdrene were greater (P < 0.05) in leg roasts from wethers fed either of the juniper diets compared with JUN0. Yearling wethers can be finished on a feedlot diet containing 20% juniper for up to 40 d prior to harvest with no impact on feedlot performance, carcass characteristics, nor negative impact on sensory attributes or volatile compounds of either grilled loin chops or roasted legs.

Lack of acclimation of leaf area:sapwood area ratios in piñon pine and juniper in response to precipitation reduction and warming.

The leaf area to sapwood area ratios of trees (Al:AS) can shift to maintain homeostatic gas exchange per unit leaf area in response to climate variability. We tested the hypothesis that trees alter their Al:AS ratios in response to long-term warming and reduced precipitation in order to maintain leaf-specific gas exchange rates under more stressful conditions. Whole-tree Al:AS was measured on mature piñon pine (Pinus edulis Engelm.) and one-seed juniper (Juniperus monosperma (Engelm.) Sarg.) trees after 5 years (2012-16) of chronic exposure to increased temperature (+4.8 °C), precipitation reduction (-45%), or both simultaneously. No difference was found in Al:As among treatments for either species. Associated with this lack of shift in Al:As were large changes in pre-dawn leaf water potential and stomatal conductance, consistent with theoretical expectations of interactions between leaf and whole-tree hydraulic supply. Our results suggest that a lack of whole-tree acclimation in Al:As results in the reductions in plant gas exchange and water status associated with long-term warming and reduced precipitation in semi-arid woodlands.

Is desiccation tolerance and avoidance reflected in xylem and phloem anatomy of two coexisting arid-zone coniferous trees?

Plants close their stomata during drought to avoid excessive water loss, but species differ in respect to the drought severity at which stomata close. The stomatal closure point is related to xylem anatomy and vulnerability to embolism, but it also has implications for phloem transport and possibly phloem anatomy to allow sugar transport at low water potentials. Desiccation-tolerant plants that close their stomata at severe drought should have smaller xylem conduits and/or fewer and smaller interconduit pits to reduce vulnerability to embolism but more phloem tissue and larger phloem conduits compared with plants that avoid desiccation. These anatomical differences could be expected to increase in response to long-term reduction in precipitation. To test these hypotheses, we used tridimensional synchroton X-ray microtomograph and light microscope imaging of combined xylem and phloem tissues of 2 coniferous species: one-seed juniper (Juniperus monosperma) and piñon pine (Pinus edulis) subjected to precipitation manipulation treatments. These species show different xylem vulnerability to embolism, contrasting desiccation tolerance, and stomatal closure points. Our results support the hypothesis that desiccation tolerant plants require higher phloem transport capacity than desiccation avoiding plants, but this can be gained through various anatomical adaptations in addition to changing conduit or tissue size.

Impacts of long-term precipitation manipulation on hydraulic architecture and xylem anatomy of piñon and juniper in Southwest USA.

Hydraulic architecture imposes a fundamental control on water transport, underpinning plant productivity, and survival. The extent to which hydraulic architecture of mature trees acclimates to chronic drought is poorly understood, limiting accuracy in predictions of forest responses to future droughts. We measured seasonal shoot hydraulic performance for multiple years to assess xylem acclimation in mature piñon (Pinus edulis) and juniper (Juniperus monosperma) after 3+ years of precipitation manipulation. Our treatments consisted of water addition (+20% ambient precipitation), partial precipitation-exclusion (-45% ambient precipitation), and exclusion-structure control. Supplemental watering elevated leaf water potential, sapwood-area specific hydraulic conductivity, and leaf-area specific hydraulic conductivity relative to precipitation exclusion. Shifts in allocation of leaf area to sapwood area enhanced differences between irrigated and droughted KL in piñon but not juniper. Piñon and juniper achieved similar KL under ambient conditions, but juniper matched or outperformed piñon in all physiological measurements under both increased and decreased precipitation treatments. Embolism vulnerability and xylem anatomy were unaffected by treatments in either species. Absence of significant acclimation combined with inferior performance for both hydraulic transport and safety suggests piñon has greater risk of local extirpation if aridity increases as predicted in the southwestern USA.

Sex determines xylem anatomy in a dioecious conifer: hydraulic consequences in a drier world.

Increased drought frequency and severity may reshape tree species distribution in arid environments. Dioecious tree species may be more sensitive to climate warming if sex-related vulnerability to drought occurs, since lower performance of one sex may drive differential stress tolerance, sex-related mortality rates and biased sex ratios. We explored the effect of sex and environment on branch hydraulic (hydraulic conductivity and vulnerability to embolism) and trunk anatomical traits in both sexes of the dioecious conifer Juniperus thurifera L. at two sites with contrasting water availability. Additionally, we tested for a trade-off between hydraulic safety (vulnerability to embolism) and efficiency (hydraulic conductivity). Vulnerability to embolism and hydraulic conductivity were unaffected by sex or site at branch level. In contrast, sex played a significant role in xylem anatomy. We found a trade-off between hydraulic safety and efficiency, with larger conductivities related to higher vulnerabilities to embolism. At the anatomical level, females' trunk showed xylem anatomical traits related to greater hydraulic efficiency (higher theoretical hydraulic conductivity) over safety (thinner tracheid walls, lower Mork's Index), whereas males' trunk anatomy followed a more conservative strategy, especially in the drier site. Reconciling the discrepancy between branch hydraulic function and trunk xylem anatomy would require a thorough and integrated understanding of the tree structure-function relationship at the whole-plant level. Nevertheless, lower construction costs and higher efficiency in females' xylem anatomy at trunk level might explain the previously observed higher growth rates in mesic habitats. However, prioritizing efficiency over safety in trunk construction might make females more sensitive to drought, endangering the species' persistence in a drier world.

Taxonomy of prickly juniper (Juniperus oxycedrus group): A phytochemical-morphometric combined approach at the contact zone of two cryptospecies.

Based on different essential oil composition paralleling different genotypes, Juniperus deltoides was recently segregated from Juniperus oxycedrus. Despite a clear phytochemical and molecular differentiation, J. deltoides resulted not clearly morphologically discernible from J. oxycedrus, so that it was defined as a cryptospecies. Italy represents the contact zone of their distribution, but the ranges of the two species are not sufficiently known, due to unsatisfactory morphological characterisation. To further complicate the picture, a third closely related species (ecotype), J. macrocarpa, occurs all across the Mediterranean coasts. After a preliminary phytochemical analysis to ascertain the (chemo-)identities of the studied populations, we performed a morphometric investigation to test the degree of morphological distinctiveness among the taxa. According to our analysis, some character (e.g. leaf mucro length, leaf width, seed-cone size and seed size) resulted useful to discriminate these cryptic taxa. Finally, based on these characters, an extensive revision of herbarium specimens allowed us to redefine the distribution pattern of the investigated species in the Central Mediterranean area.

Facilitation promotes changes in leaf economics traits of a perennial forb.

Optimal allocation of resources is crucial to maximize plant success. Plants modify their economic strategies by adjusting functional traits in response to shifts in environmental conditions. Facilitation has been recognized as a major biotic filter of trait distribution in communities, although the effect of facilitation on intraspecific variability has been scarcely explored. We evaluated intraspecific shifts in leaf functional traits of a perennial forb (Helleborus foetidus) in relation to the presence of a nurse plant (Juniperus sabina) in two sites with contrasting abiotic stress levels. The effects of abiotic (site) and biotic (juniper presence, microsite) environments on specific leaf area (SLA), leaf area (LA), lamina/petiole length ratio (LPR), intrinsic water use efficiency (iWUE) and leaf nutrient content (N, P and N:P) per mass were evaluated. Alleviation of drought stress associated with nurse plant presence was reflected in SLA, LA, LPR and iWUE at the high-stress site. Individuals growing in open areas showed more resource-conservative traits, supporting the argument that this strategy is advantageous in environments that limit opportunities for rapid carbon gain. Leaf nutrients were unrelated to other traits. The large amount of intraspecific variation in leaf functional traits related to facilitative processes highlights the importance of facilitation as a major source of plant trait variation. Both positive and negative biotic interactions, as well as intraspecific trait variability, should be considered in mechanistic models of plant communities' functional responses to environmental changes.

The effects of leaf area density variation on the particle collection efficiency in the size range of ultrafine particles (UFP).

Carbonaceous particles were generated during a "sooting burn" experiment to explore how heterogeneity in horizontal leaf area density (LAD) within the canopy impacts the ultrafine particle (UFP) collection efficiency at the branch-scale. To address this goal, wind tunnel experiments and a particle-size resolving model, which couples the turbulent flow field within the vegetated volume and the collection efficiency, were presented. Three scenarios were examined in a wind-tunnel packed with Juniperus chinensis branches: An LAD that was uniformly distributed, linearly increasing and linearly decreasing along the longitudinal or mean wind direction. The concentration measurements were conducted at multiple locations within the vegetated volume to evaluate the performance of the proposed model needed in discerning the role of LAD heterogeneity on UFP collection. Differences not exceeding 20% were found between modeled and measured concentration for all particle sizes across a wide range of wind speeds. The overall particle collection efficiency was found to be primarily governed by the spatially integrated LAD when differences in aerodynamic attributes (e.g., foliage drag) were accounted for. When combined with earlier studies, the results suggest that one parameter linking the laminar boundary layer conductance to the Schmidt number depends on particle size.

New star on the stage: amount of ray parenchyma in tree rings shows a link to climate.

Tree-ring anatomy reflects the year-by-year impact of environmental factors on tree growth. Up to now, research in this field has mainly focused on the hydraulic architecture, with ray parenchyma neglected despite the growing recognition of its relevance for xylem function. Our aim was to address this gap by exploring the potential of the annual patterns of xylem parenchyma as a climate proxy. We constructed ring-width and ray-parenchyma chronologies from 1965 to 2004 for 20 Juniperus thurifera trees growing in a Mediterranean continental climate. Chronologies were related to climate records by means of correlation, multiple regression and partial correlation analyses. Ray parenchyma responded to climatic conditions at critical stages during the xylogenetic process; namely, at the end of the previous year's xylogenesis (October) and at the onset of earlywood (May) and latewood formation (August). Ray parenchyma-based chronologies have potential to complement ring-width chronologies as a tool for climate reconstructions. Furthermore, medium- and low-frequency signals in the variation of ray parenchyma may improve our understanding of how trees respond to environmental fluctuations and to global change.

Annual increments of juniper dwarf shrubs above the tree line on the central Tibetan Plateau: a useful climatic proxy.

BACKGROUND AND AIMS: Dendroclimatology is playing an important role in understanding past climatic changes on the Tibetan Plateau. Forests, however, are mainly confined to the eastern Tibetan Plateau. On the central Tibetan Plateau, in contrast, shrubs and dwarf shrubs need to be studied instead of trees as a source of climate information. The objectives of this study were to check the dendrochronological potential of the dwarf shrub Wilson juniper (Juniperus pingii var. wilsonii) growing from 4740 to 4780 m a.s.l. and to identify the climatic factors controlling its radial growth. METHODS: Forty-three discs from 33 stems of Wilson juniper were sampled near the north-eastern shore of the Nam Co (Heavenly Lake). Cross-dating was performed along two directions of each stem, avoiding the compression-wood side as far as possible. A ring-width chronology was developed after a negative exponential function or a straight line of any slope had been fit to the raw measurements. Then, correlations were calculated between the standard ring-width chronology and monthly climate data recorded by a weather station around 100 km away. KEY RESULTS: Our study has shown high dendrochronological potential of Wilson juniper, based on its longevity (one individual was 324 years old), well-defined growth rings, reliable cross-dating between individuals and distinct climatic signals reflected by the ring-width variability. Unlike dwarf shrubs in the circum-arctic tundra ecosystem which positively responded to above-average temperature in the growing season, moisture turned out to be growth limiting for Wilson juniper, particularly the loss of moisture caused by high maximum temperatures in May-June. CONCLUSIONS: Because of the wide distribution of shrub and dwarf shrub species on the central Tibetan Plateau, an exciting prospect was opened up to extend the presently existing tree-ring networks far up into one of the largest tundra regions of the world.

Hydraulic lift and tolerance to salinity of semiarid species: consequences for species interactions.

The different abilities of plant species to use ephemeral or permanent water sources strongly affect physiological performance and species coexistence in water-limited ecosystems. In addition to withstanding drought, plants in coastal habitats often have to withstand highly saline soils, an additional ecological stress. Here we tested whether observed competitive abilities and C-water relations of two interacting shrub species from an arid coastal system were more related to differences in root architecture or salinity tolerance. We explored water sources of interacting Juniperus phoenicea Guss. and Pistacia lentiscus L. plants by conducting physiology measurements, including water relations, CO2 exchange, photochemical efficiency, sap osmolality, and water and C isotopes. We also conducted parallel soil analyses that included electrical conductivity, humidity, and water isotopes. During drought, Pistacia shrubs relied primarily on permanent salty groundwater, while isolated Juniperus plants took up the scarce and relatively fresh water stored in upper soil layers. As drought progressed further, the physiological activity of Juniperus plants nearly stopped while Pistacia plants were only slightly affected. Juniperus plants growing with Pistacia had stem-water isotopes that matched Pistacia, unlike values for isolated Juniperus plants. This result suggests that Pistacia shrubs supplied water to nearby Juniperus plants through hydraulic lift. This lifted water, however, did not appear to benefit Juniperus plants, as their physiological performance with co-occurring Pistacia plants was poor, including lower water potentials and rates of photosynthesis than isolated plants. Juniperus was more salt sensitive than Pistacia, which withstood salinity levels similar to that of groundwater. Overall, the different abilities of the two species to use salty water appear to drive the outcome of their interaction, resulting in asymmetric competition where Juniperus is negatively affected by Pistacia. Salt also seems to mediate the interaction between the two species, negating the potential positive effects of an additional water source via hydraulic lift.

Tree ring imprints of long-term changes in climate in western Himalaya, India.

Tree-ring analyses from semi-arid to arid regions in western Himalaya show immense potential for developing millennia long climate records. Millennium and longer ring-width chronologies of Himalayan pencil juniper (Juniperus polycarpos), Himalayan pencil cedar (Cedrus deodara) and Chilgoza pine (Pinus gerardiana) have been developed from different sites in western Himalaya. Studies conducted so far on various conifer species indicate strong precipitation signatures in ring-width measurement series. The paucity of weather records from stations close to tree-ring sampling sites poses diffi culty in calibrating tree-ring data against climate data especially precipitation for its strong spatial variability in mountain regions. However, for the existence of strong coherence in temperature, even in data from distant stations, more robust temperature reconstructions representing regional and hemispheric signatures have been developed. Tree-ring records from the region indicate multi-century warm and cool anomalies consistent with the Medieval Warm Period and Little Ice Age anomalies. Signifi cant relationships noted between mean premonsoon temperature over the western Himalaya and ENSO features endorse utility of climate records from western Himalayan region in understanding long-term climate variability and attribution of anthropogenic impact.

The hydraulic architecture of Juniperus communis L. ssp. communis: shrubs and trees compared.

Juniperus communis ssp. communis can grow like a shrub or it can develop a tree-like habit. In this study, the hydraulic architecture of these contrasting growth forms was compared. We analysed the hydraulic efficiency (leaf-specific conductivity, k(l); specific conductivity, k(s); Huber value, HV) and the vulnerability to cavitation (the water potential corresponding to a 50% loss of conductivity, Psi(50)), as well as anatomical parameters [mean tracheid diameter, d; mean hydraulic diameter, d(h); cell wall reinforcement (t/b)(h)(2)] of shrub shoots, tree stems and tree branches. Shrub shoots were similar to tree branches (especially to lower branches) in growth form and conductivity (k(l) = 1.93 +/- 0.11 m(2) s(-1) MPa(-1) 10(-7), k(s) = 5.71 +/- 0.19 m(2) s(-1) MPa(-1) 10(-4)), but were similar to tree stems in their vulnerability to cavitation (Psi(50) = -5.81 +/- 0.08 MPa). Tree stems showed extraordinarily high k(l) and k(s) values, and HV increased from the base up. Stem xylem was more vulnerable to cavitation than branch xylem, where Psi(50) increased from lower (Psi(50) = -6.44 +/- 0.19 MPa) to upper branches (Psi(50) = -5.98 +/- 0.13 MPa). Conduit diameters were correlated with k(l) and k(s). Data indicate that differences in hydraulic architecture correspond to changes in growth form. In some aspects, the xylem hydraulics of tree-like Juniperus communis differs from that of other coniferous tree species.

[The multistemmed structure of Juniperus thurifera: adaptive advantage in a severe environment?]. / La structure multicaule du genévrier thurifère: avantage adaptatif à un environnement sévère?

A comparative study of radial growth and biomass between multistemmed trees with variable number of stems and single-stemmed trees was carried out to better understand determinism and organisation of multicaulis structure of a juniper species (Juniperus thurifera L.) growing in high Mediterranean mountains (High Atlas, Morocco). It appears that all the stems of the same tree have similar ages and so simultaneous development. Their mean annual radial increments show significant differences because of probable competition for water and nutrient supply and obvious physical competition for space. The multistemmed trees characterized by low number of stems have the same mean annual radial growth as single-stemmed trees and more generally all multistemmed junipers have a higher biomass. The multicaulis structure of Juniperus thurifera thus could be considered as an adaptation to severe environment, characterized not only by hard topographical, edaphic and climatic conditions, but by strong human pressure too.