Responses of Contrasting Tree Functional Types to Air Warming and Drought (original) (raw)
Related papers
Xylem hydraulic adjustment and growth response of Quercus canariensis Willd. to climatic variability
Tree Physiology, 2012
Global change challenges forest adaptability at the distributional limit of species. We studied ring-porous Quercus canariensis Willd. xylem traits to analyze how they adjust to spatio-temporal variability in climate. Trees were sampled along altitudinal transects, and annual time series of radial growth (ring width (RW)) and several earlywood vessel (EV) traits were built to analyze their relationships with climate. The trees responded to increasing water constraints with decreasing altitude and changes in climate in the short term but the analyses showed that xylem did not acclimate in response to long-term temperature increase during the past 30 years. The plants' adjustment to climate variability was expressed in a different but complementary manner by the different xylem traits. At low elevations, trees exhibited higher correlations with water stress indices and trees acclimated to more xeric conditions at low elevations by reducing radial growth and hydraulic diameter (D H) but increasing the density of vessels (DV). Average potential conductivity (K H) was similar for trees at different altitudes. However, intertree differences in xylem traits were higher than those between altitudes, suggesting a strong influence of individual genetic features or micro-site conditions. Trees exhibited higher RW those years with larger D H and particularly the linear density of vessels (DV l), but partly, climatic signals expressed in RW differed from those in EVs. Trees produced larger D H after cold winters and wet years. Ring width responded positively to wet and cool weather in fall and spring, whereas the response to climate of DV and K H was generally opposite to that of RW. These relationships likely expressed the negative impact of high respiration rates in winter on the carbon pools used to produce the EVs in the next spring and the overall positive influence of water availability for trees. Our results showed that trees at different sites were able to adjust their hydraulic architecture to climatic variability and temperature increase during recent decades coordinating several complementary traits. Nonetheless, it should be monitored whether they will succeed to acclimate to future climatic scenarios of increasing water stress.
Plant, Cell & Environment, 2015
Relatively anisohydric species are predicted to be more predisposed to hydraulic failure than relatively isohydric species, as they operate with narrower hydraulic safety margins. We subjected co-occurring anisohydric Juniperus monosperma and isohydric Pinus edulis trees to warming, reduced precipitation, or both, and measured their gas exchange and hydraulic responses. We found that reductions in stomatal conductance and assimilation by heat and drought were more frequent during relatively moist periods, but these effects were not exacerbated in the combined heat and drought treatment. Counter to expectations, both species exhibited similar g s temporal dynamics in response to drought. Further, whereas P. edulis exhibited chronic embolism, J. monosperma showed very little embolism due to its conservative stomatal regulation and maintenance of xylem water potential above the embolism entry point. This tight stomatal control and low levels of embolism experienced by juniper refuted the notion that very low water potentials during drought are associated with loose stomatal control and with the hypothesis that anisohydric species are more prone to hydraulic failure than isohydric species. Because direct association of stomatal behavior with embolism resistance can be misleading, we advocate consideration of stomatal behavior relative to embolism resistance for classifying species drought response strategies.
Plant, Cell & Environment, 2013
Although climate change will alter both soil water availability and evaporative demand, our understanding of how future climate conditions will alter tree hydraulic architecture is limited. Here, we demonstrate that growth at elevated temperatures (ambient +5°C) affects hydraulic traits in seedlings of the deciduous boreal tree species Populus tremuloides, with the strength of the effect varying with the plant organ studied. Temperature altered the partitioning of hydraulic resistance, with greater resistance attributed to stems and less to roots in warm-grown seedlings (P < 0.02), and a 46% (but marginally significant, P = 0.08) increase in whole plant conductance at elevated temperature. Vulnerability to cavitation was greater in leaves grown at high than at ambient temperatures, but vulnerability in stems was similar between treatments. A soil-plant-atmosphere (SPA) model suggests that these coordinated changes in hydraulic physiology would lead to more frequent drought stress and reduced water-use efficiency in aspen that develop at warmer temperatures. Tissue-specific trade-offs in hydraulic traits in response to high growth temperatures would be difficult to detect when relying solely on whole plant measurements, but may have large-scale ecological implications for plant water use, carbon cycling and, possibly, plant drought survival.
Tree Physiology, 2016
Adjustment in leaf water status parameters and modification in xylem structure and functioning can be important elements of a tree's response to continued water limitation. In a growth trial with saplings of five co-occurring temperate broad-leaved tree species (genera Fraxinus, Acer, Carpinus, Tilia and Fagus) conducted in moist or dry soil, we compared the drought acclimation in several leaf water status and stem hydraulic parameters. Considering the extremes in the species responses, Fraxinus excelsior L. improved its leaf tissue hydration in the dry treatment through osmotic, elastic and apoplastic adjustment while Fagus sylvatica L. solely modified its xylem anatomy, which resulted in increased embolism resistance at the cost of hydraulic efficiency. Our results demonstrate the contrasting response strategies of coexisting tree species and how variable trait plasticity among species can be. The comparison of plants grown either in monoculture or in five-species mixture showed that the neighbouring species diversity can significantly influence a tree's hydraulic architecture and leaf water status regulation. Droughted Carpinus betulus L. (and to a lesser extent, Acer pseudoplatanus L.) plants developed a more efficient stem hydraulic system in heterospecific neighbourhoods, while that of F. sylvatica was generally more efficient in conspecific than heterospecific neighbourhoods. We conclude that co-occurring tree species may develop a high diversity of drought-response strategies, and exploring the full diversity of trait characteristics requires synchronous study of acclimation at the leaf and stem (and possibly also the root) levels, and consideration of physiological as well as morphological and anatomical modifications.
Annals of Forest Science, 2006
The extreme drought event that occurred in Western Europe during 2003 highlighted the need to understand the key processes that may allow trees and stands to overcome such severe water shortages. We therefore reviewed the current knowledge available about such processes. First, impact of drought on exchanges at soil-root and canopy-atmosphere interfaces are presented and illustrated with examples from water and CO 2 flux measurements. The decline in transpiration and water uptake and in net carbon assimilation due to stomatal closure has been quantified and modelled. The resulting models were used to compute water balance at stand level basing on the 2003 climate in nine European forest sites from the CARBOEUROPE network. Estimates of soil water deficit were produced and provided a quantitative index of soil water shortage and therefore of the intensity of drought stress experienced by trees during summer 2003. In a second section, we review the irreversible damage that could be imposed on water transfer within trees and particularly within xylem. A special attention was paid to the inter-specific variability of these properties among a wide range of tree species. The inter-specific diversity of hydraulic and stomatal responses to soil water deficit is also discussed as it might reflect a large diversity in traits potentially related to drought tolerance. Finally, tree decline and mortality due to recurrent or extreme drought events are discussed on the basis of a literature review and recent decline studies. The potential involvement of hydraulic dysfunctions or of deficits in carbon storage as causes for the observed long term (several years) decline of tree growth and development and for the onset of tree dieback is discussed. As an example, the starch content in stem tissues recorded at the end of the 2003's summer was used to predict crown conditions of oak trees during the following spring: low starch contents were correlated with large twig and branch decline in the crown of trees.
Drought stress responses of seedlings of two oak species (Quercus cerris and Quercus robur)
TURKISH JOURNAL OF AGRICULTURE AND FORESTRY
Introduction Global warming and climate change are among the most prominent threats to the world. It is expected that there will be several regional and global effects of global climate change, especially on agriculture, forests, freshwater reserves, sea level, energy, human health, biodiversity (Doğan and Tüzer, 2011), and forest trees (Provost et al., 2013). Therefore, understanding the adaptation responses of tree species is quite important for plant production and sustainable forests. The plant drought resistant mechanism has been identified on a morphological, physiological, and molecular basis. Several strategies of management have been suggested for coping with drought stress (Farooq et al., 2009). Plants rely on genetically changeable mechanisms of droughtavoidance and drought-tolerance for coping with periods of drought (Chaves et al., 2002). Morphological adaptations in leaves, stems, and roots exhibit drought avoidance and tolerance. Physiological adaptations include the control of stomatal conductance, leaf water potential, osmotic adjustment, and photosynthetic carbon fixation (Dickson and Tomlinson 1996). Water stress has decreased stomatal conductance and photosynthesis in quite a few species (Peguero-Pina et al., 2009). As stomatal conductance decreases, plant water loss also decreases (Raftoyannis and Radoglou, 2002) and photosynthesis efficiency declines. This decrease affects plant growth and development due to the fact that carbohydrate molecules and energy, which are used in plant growth and development, are produced by photosynthesis (Öztürk, 2015). Essentially, drought tolerance is a tool for maintaining the turgor pressure and it is related to the elasticity of the cell wall and osmotic adjustment (Xu et al., 2010). Osmotic adjustment seems to be one of the critical stages for a plant's adaptation to drought. It is because of that, osmotic adjustments sustain the metabolic activity of the tissue and help for regrowth after rewetting. For osmotic adjustment, proline and water-soluble sugar are the most important compatible solutes in plants (Chaves et al., 2003). Oaks are considered tolerant to drought and heat, and this feature is beneficial in warmer and drier climates (Arend et al., 2012). Success of oaks on drought-prone sites is related to diversity of oaks in their morphological and physiological characteristics (Abram, 1990; Arend et al., 2011). Tolerance to drought may differ between oak species and their origins (Dickson and Tomlinson, 1996). The forest ecosystem in Turkey contains significant diversity with regard to oak species. Quercus robur L. and Quercus cerris L. are quite important species of forest trees. According to several recent studies, adaptation of oak species to drought Abstract: Effects of drought stress on growth, predawn xylem water potential (Ψ pd), osmotic solutes (soluble sugar and proline), and stomatal conductance were assessed in two oak (Quercus cerris L. and Quercus robur L.) seedlings. Seedlings of both species were subjected to three drought treatments with the following irrigation intervals: well-watered (control: irrigation every 2-3 days), moderate drought stress (irrigation every 15 days), and severe drought stress (irrigation every 30 days). Drought-stressed seedlings of Q. cerris and Q. robur had more negative predawn xylem water potential than their well-watered seedlings. In Q. cerris, root collar diameter and root dry weights were negatively influenced by drought, while height, shoot dry weight, and root:shoot ratios were unaffected. Height and shoot dry weight of drought-stressed Q. robur were decreased, while root:shoot ratio increased. Drought caused significant decreases in stomatal conductance of both species. Q. cerris seedlings sustained higher stomatal conductance compared with Q. robur. Proline and soluble sugar increased in response to drought stress. Q. robur had a higher proline accumulation than Q. cerris. These findings suggested that the Q. cerris and Q. robur seedlings showed a drought stress adaptive mechanism either by restricting their growth or increasing root:shoot ratio or by decreasing water loss (reduced stomatal conductance) and accumulating of osmotic solutes.
Leaf specific conductivity (LSC; the ratio of stem conductivity (KP) to leaf area (AL)), a measure of the hydraulic capacity of the stem to supply leaves with water, varies with soil water content. Empirical evidence for LSC responses to drought is ambiguous, because previously published results were subject to many confounding factors.We tested howLSC of similar-sized trees of the same population, under similar climatic conditions, responds to persistently wet or dry soil. Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescensWilld.) trees were compared between a dry site and a wet site in theValais, an inner alpine valley in Switzerland. Soilwater strongly influenced AL and KP and the plant components affecting KP, such as conduit radius, conduit density and functional sapwood area. Trees at the dry site had lower LSC than trees with the same stem diameter at the wet site. Low LSC in trees at the dry site was associated with a smaller functional sapwood area and narrower conduits, resulting in a stronger reduction in KP than in AL. These observations support the hypothesis that trees maintain a homeostatic water pressure gradient. An alternative hypothesis is that relatively high investments in leaves compared with sapwood contribute to carbon gain over an entire season by enabling rapid whole-plant photosynthesis during periods of high water availability (e.g., in spring, after rain events and during morning hours when leafto- air vapor pressure deficit is small). Dynamic data and a hydraulic plant growth model are needed to test how investments in leaves versus sapwood and roots contribute to transpiration and to maximizing carbon gain throughout entire growth seasons.
Trees, 2024
Key message Norway spruce operates with larger hydraulic safety margins (HSM) than beech and Douglas-fir despite the known drought sensitivity of spruce, questioning a pivotal role of HSM in drought tolerance. Abstract The exceptional 2018/2019 drought exposed Central Europe's forests to severe stress, highlighting the need to better understand stomatal regulation strategies and their relationship to xylem safety under extreme drought. We studied diurnal, seasonal, and inter-annual variation in stomatal conductance (g s) and leaf water potential (Ψ Leaf) in co-occurring European beech (F. sylvatica), Norway spruce (P. abies), and Douglas-fir (P. menziesii) trees in the two summers and related them to hydraulic traits characterizing drought resistance. In 2018, F. sylvatica exhibited a continuous Ψ Leaf decline from June to September, as is characteristic for an anisohydric strategy, while P. abies closed stomata early and reached the least negative Ψ Leaf-values at the end of summer. P. menziesii showed low Ψ Leaf-values close to P 12 (the xylem pressure at onset of embolism) already in July. Both conifers closed stomata when approaching P 12 and maintained low g s-levels throughout summer, indicative for isohydric regulation. In 2019, all three species showed a linear decline in Ψ Leaf , but F. sylvatica crossed P 12 in contrast to the conifers. The three species exhibited similar water potentials at turgor loss point (− 2.44 to − 2.51 MPa) and branch P 50 (xylem pressure at 50% loss of hydraulic conductance; − 3.3 to − 3.8 MPa). Yet, F. sylvatica and P. menziesii operated with smaller hydraulic safety margins (HSM means: 0.79 and 0.77 MPa) than P. abies (1.28 MPa). F. sylvatica reduced leaf size and specific leaf area in 2019 and increased Huber value. Our species comparison during extreme drought contradicts the general assumption that conifers operate with larger HSMs than angiosperm trees. Contrary to expectation, P. abies appeared as hydraulically less vulnerable than Douglas-fir.
2017
This study aimed to compare the hydraulic drought resistance capabilities of different tree species in the Northern temperate deciduous forest. Species differ in the ability of their xylem to resist embolism and hydraulic failure caused by the dramatic decreases in water potential during droughts. Climate change is predicted to increase the frequency of droughts in these areas of the Northern hemisphere, so having an understanding of the ability of individual species to resist drought is essential for anticipating how these forest communities could change in the future. We sampled three gymnosperm species and three angiosperm species using a vacuum apparatus to measure embolism and a pressure chamber to measure water potential. These measurements were used to construct xylem vulnerability curves to compare the water potential at which 50% of hydraulic conductivity was lost (Ψ50) as well as the hydraulic safety margins of these species. We found that, contrary to our original hypothe...