A major environmental pollution problem is the release into the atmosphere of particulate matter, including nanoparticles (NPs), which causes serious hazards to human and ecosystem health, ...particularly in urban areas. However, knowledge about the uptake, translocation and accumulation of NPs in plant tissues is almost completely lacking. The uptake of silver nanoparticles (Ag-NPs) and their transport and accumulation in the leaves, stems and roots of three different tree species, downy oak (Quercus pubescens Willd.), Scots pine (Pinus sylvestris L.) and black poplar (Populus nigra L.), were assessed. In the experiment, Ag-NPs were supplied separately to the leaves (via spraying, the foliar treatment) and roots (via watering, the root treatment) of the three species. Uptake, transport and accumulation of Ag were investigated through spectroscopy. The concentration of Ag in the stem was higher in the foliar than in the root treatment, and in poplar more than in oak and pine. Foliar treatment with Ag-NPs reduced aboveground biomass and stem length in poplars, but not in oaks or pines. Species-specific signals of oxidative stress were observed; foliar treatment of oak caused the accumulation of H2O2 in leaves, and both foliar and root treatments of poplar led to increased O2- in leaves. Ag-NPs affected leaf and root bacteria and fungi; in the case of leaves, foliar treatment reduced bacterial populations in oak and poplar and fungi populations in pine, and in the case of roots, root treatment reduced bacteria and increased fungi in poplar. Species-specific mechanisms of interaction, transport, allocation and storage of NPs in trees were found. We demonstrated definitively that NPs enter into the tree stem through leaves faster than through roots in all of the investigated tree species.
Warming and drought alter plant phenology, photosynthesis and growth with important consequences for the global carbon cycle and the earth's climate. Yet, few studies have attempted to tease apart ...their effects on tree phenology, particularly leaf senescence, and on source and sink activity.
We experimentally assessed the single and combined effects of warming and reduced soil moisture on the phenology (leaf‐out and senescence date, growing season length) and above‐ground sink (height and diameter growth, leaf area and Huber values) and source activity (net photosynthesis, photosynthetic efficiency, chlorophyll concentration and total carbon C uptake) of two tree species with distinct strategies to deal with drought: European beech and pubescent oak.
Warming advanced leaf‐out, irrespective of soil moisture levels, particularly in oak and to a lower extent in beech, leading to a prolonged growing season in oak but not beech. No impacts of warming on senescence timing were found for both species. Reduced moisture had little impact on the phenology of both species. Warming‐induced advances in phenology and higher photosynthetic efficiency increased the annual C uptake for oak and compensated for the reduced photosynthetic activity in the presence of reduced moisture. Conversely, for beech, source activity, including yearly C uptake, was lower in all treatments than the control, indicating no compensation of the C budget by phenological shifts.
Synthesis. Our results demonstrate that a warming‐driven earlier activity and higher photosynthetic efficiency compensates for reduced photosynthesis during hot and dry periods, but only for pubescent oak, which is a rather drought‐tolerant species. Current predictions of warming‐induced mitigation effects through extended C uptake seem incorrect for beech.
Our results demonstrate that a warming‐driven earlier activity and higher photosynthetic efficiency compensates for reduced photosynthesis during hot and dry periods, but only for pubescent oak, which is a rather drought‐tolerant species. Current predictions of warming‐induced mitigation effects through extended C uptake seem incorrect for beech.
The variability of branch-level hydraulic properties was assessed across 12 Scots pine populations covering a wide range of environmental conditions, including some of the southernmost populations of ...the species. The aims were to relate this variability to differences in climate, and to study the potential tradeoffs between traits. Traits measured included wood density, radial growth, xylem anatomy, sapwood- and leaf-specific hydraulic conductivity (KS and KL), vulnerability to embolism, leaf-to-sapwood area ratio (AL : AS), needle carbon isotope discrimination (Δ¹³C) and nitrogen content, and specific leaf area. Between-population variability was high for most of the hydraulic traits studied, but it was directly associated with climate dryness (defined as a combination of atmospheric moisture demand and availability) only for AL : AS, KL and Δ¹³C. Shoot radial growth and AL : AS declined with stand development, which is consistent with a strategy to avoid exceedingly low water potentials as tree size increases. In addition, we did not find evidence at the intraspecific level of some associations between hydraulic traits that have been commonly reported across species. The adjustment of Scots pine's hydraulic system to local climatic conditions occurred primarily through modifications of AL : AS and direct stomatal control, whereas intraspecific variation in vulnerability to embolism and leaf physiology appears to be limited.
Quercus petraea (Matt.) Liebl., Q. pubescens Willd., and Q. frainetto Ten. grow naturally in sympatry in the Landscape of Outstanding Features "Kosmaj" (Mt. Kosmaj) in Serbia, in the Western Balkans. ...The levels of genetic diversity and genetic structure in populations of these species (160 trees in total) was assessed by means of 14 nuclear microsatellites. The number of alleles detected in overall sample was 314, with the locus QrZAG90 being the most informative one in all three species (31, 35 and 36 alleles in Q. frainetto, Q. pubescens and Q. petraea, respectively). The levels of genetic diversity of all three species were relatively high (HE = 0.824, 0.834, and 0.794 in Q. petraea, Q. pubescens and Q. frainetto, respectively). Low but statistically significant inbreeding was detected in all three species (F = 0.100, 0.131 and 0.065 in Q. petraea, Q. pubescens and Q. frainetto, respectively), which, however, most likely reflects population substructure, which was observed in the STRUCTURE analysis. The optimal number of genetic groups revealed by Bayesian clustering analysis did not coincide with the number of analyzed species as it amounted to four (one gene pool was observed in each of the two species, Q. petraea and Q. pubescens, while two gene pools were observed in Q. pubescens). Furthermore, a higher level of hierarchical genetic structure, with six gene pools was found, with Q. frainetto being the only oak species in which population substructure was not observed. Genetic differentiation of three sympatric oak species was relatively low but statistically significant, with the highest FST value found among Q. petraea and Q. frainetto (FST = 0.047, P = 0.001), and the lowest between Q. petraea and Q. pubescens (FST = 0.032, P = 0.001). Our results reveal rather high levels of genetic diversity in all three studied oak species, which retained their genetic integrity despite sympatric distribution, indicating low levels of interspecific hybridization, and pronounced genetic structure of Q. pubescens and Q. petraea.
Natural landscapes in the Mediterranean ecosystem have experienced extensive changes over the last two centuries due to wildfire activity. Resulting interactions between climatic warming, vegetation ...species, soil natural, and meteorological condition before and after a wildfire create substantial abrupt landscape alterations. This study investigates the evolution (2 days, 3, 6, 9, and 12 months after a fire) of topsoil (0–5 cm) chemical properties in burned Cambisols (Zadar County, Croatia) with respect to different wildfire severities (HS—high severity, MS—medium severity, C—unburned) and vegetation species (Quercus pubescens Willd. and Juniperus communis L.). Soil pH, electrical conductivity (EC), calcium carbonates (CaCO3), total organic carbon (TOC), total nitrogen (TN), total sulphur (TS), copper (Cu) and zinc (Zn) were significantly higher in HS than in MS and C. Total soil potassium (TK), Fe and Ni were significantly higher in C than in HS. The increase of TOC and TN was more pronounced in Quercus p. than Juniperus c., especially in the first three months. Soil pH, EC, CaCO3, TOC, TN, and TS were most affected by wildfire severity. The distinction between C, MS and HS categories was less visible 9 and 12 months post-fire, indicating the start of the recovery of the soil system. Post-fire management and temporal recovery of the soil system should consider the obvious difference in soil disturbance under HS and MS between vegetation species.
Key message
Warming will induce an upward displacement of Scots pine, but this can be partially mitigated by maintaining a more intense land use.
Context
Scots pine is currently declining in most ...inner alpine sectors of southern Europe. The relative contribution of climate, land use change, and disturbances on the decline is poorly understood. What will be the future distribution of the species? Is vegetation shifting toward oak-dominated forests? What is the role of extreme drought years?
Aims
The aims of the study were to determine drivers of current distribution of Scots pine and downy oak in Aosta valley (SW Alps), to extrapolate species distribution models to year 2080 (Special Report on Emissions Scenarios (SRES) A1B), and to assess the correlation between pine vitality after the extreme droughts of 2003 and 2006, and modeled longterm vegetation changes.
Methods
Ensemble distribution models were created using climate, topography, soil, competition, natural disturbances, and land use. Species presence was derived from a regional forest inventory. Pine response to drought of 2003–2006 was assessed by Normalized Difference Vegetation Index (NDVI) differencing and correlated to modeled cover change between 2080 and present.
Results
Scots pine and downy oak were more likely to occur under higher climatic aridity. Scots pine was also associated to higher wildfire frequency, land use intensity, and lack of competition. In a warming scenario, pine experienced an elevational displacement. This was partially counteracted if no land abandonment was hypothesized. Downy oak cover increased in all scenarios. Short- and long-term drought responses of pine were unrelated.
Conclusion
Warming will induce an upward displacement of pine, but this can be partially mitigated by maintaining a more intense land use. The drought-induced decline in pine vitality after extreme years did not overlap to the modeled species response under climate warming; responses to short-term drought must be more thoroughly understood in order to predict community shifts.
Currently, studies on land use in territorial planning are of interest, the purpose of which was previously to analyze the aptitude of each type of land for a specific use, based on its ability to ...assume impacts and the potential that the land may have had. The analysis of erosive risks constitutes a parameter to take into account in said management.The scientific community, given the enormous social interest in monitoring and controlling the environment, is developing methodologies that allow such control that is more efficient. One of the environmental factors to consider is the soil, which constitutes the support for life and is one of the basic natural elements, which is evident in the European Soil Charter, of the Council of Europe, which says, in its first point: “The soil is one of the most precious goods of Humanity. It allows the life of plants, animals and man on the surface of the Earth”. This European charter also highlights the scarcity and fragility of the edaphic resource, indicating that it must be protected through a greater effort in scientific research and interdisciplinary collaboration to ensure the rational use and conservation of soil.
Background and Aims Plant roots' growth direction has important implications for plant development and survival; moreover it plays an effective and vital role in stabilizing weathered soil on a steep ...slope. The aim of this work was to assess the influence of slope on the architecture of woody root systems. Methods Five mature, single-stemmed Quercus pubescens trees growing on a steep slope and five on a shallow slope were excavated to a root diameter of 1 cm. A very precise numeric representation of the geometry and topology of structural root architecture was gained using a low-magnetic-field digitizing device (Fastrak, Polhemus). Several characteristics of root architecture were extracted by macros, including root volume, diameter, length, number, spatial position and branching order. Key Results The diameter at breast height (dbh) was the best predictor of the root volume but had no correlation with length and number of roots. The slope affected the root volume for each branching order, and the basal cross-sectional area (CSA), number and length of the first-order roots. Number and length of the second- and third-order laterals were closely related in both conditions, although this relationship was closer in the shallow trees, suggesting the influence of a genetic control. Sloping trees showed a clustering tendency of the first- and second-order lateral roots in the up-slope direction, suggesting that the laterals rather than the taproots provide much of the anchorage. In a steep-slope condition, the taproot tapering was positively correlated with the asymmetry magnitude of first-order roots, indicating compensation between taproot and main lateral roots' clustering tendency. Conclusions These results suggest that on a slope, on clayey soils, root asymmetry appears to be a consequence of several environmental factors such as inclination, shallow-slides and soil compactness. In addition, this adaptive growth seems to counteract the turning moment induced by the self-loading forces acting in slope conditions, and as a consequence improves the tree stability.
This paper casts light on the events taking place in the root system when seedlings of two deciduous woody Mediterranean species,
Quercus pubescens Willd. and
Fraxinus ornus L., are stressed by ...drought or fire or both. Stress treatment mimicked the conditions that often occur in natural Mediterranean ecosystems during dry summers. Allocation of resources to the root system is affected as shown by the fact that taproot biomass decreases under stress conditions only in
Fraxinus ornus whereas lateral roots undergo a decrease in length, dry weight, number of apices in both species. An increase in electrolyte leakage from roots of both species during treatments suggests that morphological variations in the root system are associated with damages occurring in root tissue. All the effects observed are reversible if a critical threshold of stress duration is not reached but recovery starts when the aboveground parts are fully replaced. The alteration of a number of root traits suggests that both drought and fire affect root growth and root turnover. Differences in recovery patterns between the two species are observed and attributed to specific tolerances of the root systems. The knowledge of the events taking place at root level might help to understand better the tolerance mechanism to drought or fire characterizing species living in Mediterranean ecosystems.
The seasonal patterns of xylem embolism and xylem transport properties
in Quercus pubescens Willd. and Quercus
ilex L. trees growing in a natural mixed coppice stand in
conditions of severe water ...stress were investigated. Xylem
embolism was evaluated in both dehydrating branches and in
apical twigs during a whole year. Measurements of
xylem water potential were conducted from predawn to sunset
on selected sunny days. On the same days, diurnal
courses of leaf conductance were monitored. Measurements of
half-hourly sap flow were made by the heat-pulse
technique throughout the summer. At the onset of summer, a
sharp decrease in water potential was observed in
both species. Full recovery of water potentials was observed
for both species after the first major rainfall event in
September. Both experienced serious embolism throughout the year,
ranging between minima of c. 60%
(expressed as percentage loss of hydraulic conductivity) after
the rains in autumn and after bud burst in spring,
and maxima of c. 80% during summer and after freezing-thawing
events during the winter season. A significant
negative linear relationship was found between water potential
and xylem embolism in branches dehydrating in
air for Q. pubescens and Q. ilex. Q. pubescens
had greater
efficiency in hydraulic transport (higher specific
conductivity and leaf specific conductivity) by the xylem than
Q. ilex. In June, leaf conductance was high early in
the morning and decreased gradually during the day. Midday
depression of leaf conductance, as a result of high
evaporative demand combined with water deficit, was observed in
both species. In August, leaf conductance of
both species was greatly reduced, as water potential dropped to
extremely low values, and the stomata were almost
completely closed during the afternoon. No hysteresis resulting
from plant capacitance was observed in the
relationship between shoot water potential and sap flow. Q.
pubescens exhibited very high values of whole-tree
hydraulic resistance between July and September, whereas
Q. ilex generally showed lower values. The effect of soil
moisture depletion on the relationship between sap flow and
shoot water potential appears as a lowering of water
potential at zero flow. A significant decrease of whole-tree
hydraulic resistance in both species was observed with
the onset of the autumn, preceding the partial recovery of twig
hydraulic conductivity. The results demonstrate
that both Q. pubescens and Q. ilex, although highly tolerant
of
severe water stress and tissue dehydration, operate
at the limits of safety which are surpassed under severe droughts,
and prolonged climatic stress might predispose
these Quercus species to decline.
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