Drier Future Climate Research Articles

High flow management as climate change adaptation for freshwater ecosystems in regulated rivers

ABSTRACT Rivers worldwide have been disconnected from their floodplains through anthropogenic modifications, leading to a reduction in ecosystem services and decline in condition. These issues will be exacerbated by climate change. We assessed the effectiveness of relaxing river operating constraints to provide managed high flows to improve freshwater ecosystem outcomes in the Goulburn River basin in Victoria, Australia. We used a simplified, integrated ecohydrological modelling framework to help reduce the decision space of options in multiple river reaches, to highlight key thresholds of ecological responses, and to assess the robustness of options to an uncertain future climate. Constraints relaxation was shown to provide overall ecological benefits in the current climate, and to result in adaptation benefits for freshwater ecosystems in drier future climates. Our approach offers a practical way to assess multiple potential intervention options to improve ecosystem outcomes and be robust to uncertain climate change for complex regulated river systems.

Elevation‐dependent patterns of borer‐mediated snow‐gum dieback are associated with subspecies' trait differences and environmental variation

AbstractSubalpine forests worldwide face the synergistic threats of global warming and increased biotic attack, and the collapse or transition of subalpine forests is predicted in south‐eastern Australia under future climates. The recent widespread dieback of subalpine snow‐gum forests due to increased activity of a native wood‐boring longicorn beetle, Phoracantha mastersii, suggests this process may already be underway. We investigated how variation in tree tissue traits and environmental conditions correlated with elevation‐dependent spatial patterns of forest mortality. We hypothesized that increased vulnerability of subalpine snow gums to wood‐borer‐mediated dieback at intermediate elevations was associated with poorly resolved differences in traits between montane (Eucalyptus pauciflora subsp. pauciflora) and subalpine (E. pauciflora subsp. niphophila) snow‐gum subspecies. We first sought to characterize variation and elevation‐dependent transitions in 20 structural and drought‐related functional traits among 120 healthy trees distributed along a 1000 m elevation transect that spanned the subspecies transition zone. Secondly, we surveyed 774 trees across 53 sites between 1280 and 1980 m a.s.l. to explore associations between borer‐damage severity, elevation, subspecies and a subset of traits that differed between subspecies. We observed evidence for both continuous trait variation in response to changing elevation (10/20 traits) and discrete shifts in mean trait values across the transition between subspecies distributions (5/20 traits). Increased borer‐damage severity across the montane‐to‐subalpine subspecies transition was correlated with lower bark thickness, whereas reduced borer damage at the highest elevations was associated with greater precipitation and lower temperatures. Our results suggest that due to possessing distinct traits associated with increased borer susceptibility, subalpine snow‐gum forests may be subject to an increased risk of severe borer‐mediated forest dieback under warmer and drier future climates. Identifying traits contributing to species' distribution limits and biotic‐agent vulnerability remains critical for predicting, monitoring and possibly mitigating forest and vegetation declines under future climates.

Effects of Multiple Drivers of Environmental Change on Native and Invasive Macroalgae in Nearshore Groundwater Dependent Ecosystems

AbstractGroundwater dependent ecosystems (GDE) are increasingly recognized as critical components of sustainable groundwater management, but are threatened by multiple drivers of environmental change. Despite this importance, data that link drivers of hydrologic change to GDEs are scarce. This study adapts a land‐sea modeling framework by calibrating marine models with macroalgal experiments to quantitatively assess impacts of climate and land use change on submarine groundwater discharge (SGD) and subsequent habitat suitability for a native (Ulva lactuca) and an invasive (Hypnea musciformis) macroalgae in nearshore GDEs in Kona, Hawai'i. Lab analyses demonstrate that while U. lactuca grows optimally in low‐salinity, high‐nutrient waters, H. musciformis appears constrained to a salinity threshold and exhibits low growth in low salinity despite high nutrient concentrations. Land‐sea model results predict that while a dry future climate (Representative Concentration Pathway 8.5 mid‐century) coupled with increased urban development will likely reduce SGD, protecting native forests may prevent further loss of SGD quantity. This prevention thus partially mitigates the decline in habitat suitability of U. lactuca due to the combined effects of climate and land use change. Findings also suggest that, in contrast to the native U. lactuca, reductions in SGD may favor H. musciformis growth if introduced to Kona. Collectively, this study demonstrates the importance of considering multiple drivers of environmental change on GDEs. This study bridges experiments with models to spatially map changes in species abundance beyond their current habitat conditions, and thus informs management actions that can explicitly incorporate future human and climate‐related impacts.

Combined effect of ambient temperature and solar radiation on maned sloths' behaviour and detectability

AbstractChanges in ambient temperature and solar radiation may affect sloths' metabolic rate and body temperature, with consequent changes in activities, postures and microhabitat selection. Although the separate effect of temperature and solar radiation on sloth's behaviour have been previously studied, the combined effect of these climatic factors on behavioural aspects of sloths has never been systematically evaluated in field conditions. Here we evaluated the influence of hourly ambient temperature variation on maned sloth (Bradypus torquatus) activities, postures and tree crown positions, under sunny and cloudy conditions; and tested if any of the animal posture and position increase their exposure to human detection. We performed 350 h of visual observation on eight maned sloths, equipped with radio‐backpacks, in northern Bahia, Brazil, recording their activities, and their resting postures and positions on tree crowns. We also recorded the time taken to visualize the sloths on 58 days to analyse if sloths' detection is affected by posture and position. Higher ambient temperature, within a range of 21–33°C, increased the sloths' activity levels in cloudy conditions but reduced their activity in sunny conditions. Increasing ambient temperature also reduced the frequency of huddled posture and increased the frequency of extended posture and permanence in the inner tree crown. Lastly, the postures and positions did not influence sloths' detectability. Thus, the direction of the temperature–activity relationship depends on climatic conditions (sunny/cloudy), and individuals rely on resting postures and positions to thermoregulate. The warmer and drier future climate, expected to occur in the northern Atlantic Forest, may impose change in the diurnal activity levels and postural pattern for this threatened species, leading maned sloths to reduce its activity on sunny and warmer days and adopting an extended posture.

Quantifying the grapevine xylem embolism resistance spectrum to identify varieties and regions at risk in a future dry climate

Maintaining wine production under global warming partly relies on optimizing the choice of plant material for a given viticultural region and developing drought-resistant cultivars. However, progress in these directions is hampered by the lack of understanding of differences in drought resistance among Vitis genotypes. We investigated patterns of xylem embolism vulnerability within and among 30 Vitis species and sub-species (varieties) from different locations and climates, and assessed the risk of drought vulnerability in 329 viticultural regions worldwide. Within a variety, vulnerability to embolism decreased during summer. Among varieties, we have found wide variations in drought resistance of the vascular system in grapevines. This is particularly the case within Vitis vinifera, with varieties distributed across four clusters of embolism vulnerability. Ugni blanc and Chardonnay featured among the most vulnerable, while Pinot noir, Merlot and Cabernet Sauvignon ranked among the most resistant. Regions possibly at greater risk of being vulnerable to drought, such as Poitou–Charentes, France and Marlborough, New Zealand, do not necessarily have arid climates, but rather bear a significant proportion of vulnerable varieties. We demonstrate that grapevine varieties may not respond equally to warmer and drier conditions, and highlight that hydraulic traits are key to improve viticulture suitability under climate change.

Tree-ring growth varies with climate and stand density in a red pine plantation forest in the Great Lakes region of North America

Red pine (Pinus resinosa Ait.) was widely planted across the Great Lakes region of North America in the early 20th century to restore tree cover to degraded forest and agricultural lands. In this study, a dendrochronological assessment of radial growth response to climate was conducted in an 82-year-old, previously thinned red pine plantation forest in southern Ontario, Canada. Climate-growth relationships were analyzed at multi-monthly and annual time scales using a 72-year residual growth chronology (1942–2013). Warmer temperatures and periodic drought during the current and previous growing seasons were associated with decreased growth, while higher precipitation during the early part of the current growing season was associated with increased growth. Moving interval correlation analysis of long-term trends indicated that climate-growth relations were temporally unstable due to thinning and variation in climate over the length of the chronology. The correlation between climate and growth was stronger when stand density was relatively high and diminished in the two decades following thinning. These results indicate that growth of red pine plantations near the species’ southern range limit may be much reduced if exposed to a warmer, drier future climate and that periodic thinning can help mitigate the impacts of future climate change on these plantations.

A multi-variable constrained ensemble of regional climate projections under multi-scenarios for Portugal – Part I: An overview of impacts on means and extremes

Climate projections are a powerful tool that can help decision makers to timely prepare adaptation policies, which may then be efficiently implemented. In this study, a comprehensive analysis of how climate change may affect Portugal (located in a climate change hotspot) is conducted, providing the foundations to the first National Roadmap for Adaptation 2100. A multi-variable ensemble was built and tested, being the baseline for assessing future projections for three different emission scenarios (RCP2.6, RCP4.5, and RCP8.5) throughout the 21st century, accounting for the model’s ability to simulate a set of variables. A warmer and drier future climate is projected for the mainland, being more severe in the interior regions. Even for the optimistic RCP2.6 scenario, results indicate increases in temperature between 1 and 2 °C in comparison with the historical period and can surpass 6 °C in some regions for RCP8.5. Extreme hot events will be more frequent and severe, with maximum temperatures above 45 °C being more common throughout the 21st century. A decline in precipitation is expected mostly in summer and intermediate seasons, with losses above 40 % for the end-of-century. However, an intensification of heavy short-term rainfall events is projected to increase in northern regions. A rising of maximum wind gusts is also expected in these regions. Such projections call for an urgent planning and adaptation measures to safeguard critical sectors of the Portuguese society. Finally, the information here produced and examined constitutes a key example of climate services for mitigation and adaptation in Portugal.

Drought then wildfire reveals a compound disturbance in a resprouting forest.

The frequency and intensity of forest disturbances, such as drought and fire, are increasing globally, with an increased likelihood of multiple disturbance events occurring in short succession. Disturbances layered over one another may influence the likelihood or intensity of subsequent events (a linked disturbance) or impact response and recovery trajectories (a compound disturbance), with substantial implications for ecological spatiotemporal vulnerability. This study evaluates evidence for disturbance interactions of drought followed by wildfire in a resprouting eucalypt-dominated forest (the Northern Jarrah Forest) in southwestern Australia. Sites were stratified by drought (high, low), from previous modeling and ground validation, and fire severity (high, moderate, unburnt), via remote sensing using the relative difference normalized burn ratio (RdNBR). Evidence of a linked disturbance was assessed via fine fuel consumption and fire severity. Compound disturbance effects were quantified at stand scale (canopy height, quadratic mean diameter, stem density) and stem scale (mortality). There was no evidence of prior drought influencing fine fuel consumption or fire severity and, hence, no evidence of a linked disturbance. However, compound disturbance effects were evident; stands previously affected by drought experienced smaller shifts in canopy height, quadratic mean diameter, and stem density than stands without prior drought impact. At the stem scale, size and fire severity were the strongest determinants of stem survival. Proportional resprouting height was greater in high drought sites than in low drought sites (p < 0.01), meaning, structurally, the low drought stands decreased in height more than the high drought stands. Thus, a legacy of the drought was evident after the wildfire. Although these resprouting eucalypt forests have been regarded as particularly resilient, this study illustrates how multiple disturbances can overwhelm the larger tree component and promote an abundance of smaller stems. We suggest that this is early evidence of a structural destabilization of these forests under a more fire-prone, hotter, and drier future climate.

Will the grass be greener on the other side of climate change? (with corrigendum)

Increasing atmospheric [CO2] is stimulating photosynthesis and plant production, increasing the demand for nitrogen relative to soil supply with declining global foliar nitrogen concentrations as a consequence. The effects of such oligotrophication on the forage quality of sweetveld, mixed veld, and sourveld grasslands in South Africa, which support livestock production and native ungulates, are unknown. Soil characteristics and the herbage quality of an abundant grass are described from baseline historical (mid- 1980s) data collected across a sweet-mixed-sour grassland gradient in KwaZulu-Natal. Sourveld occurred on the most acidic, dystrophic soils and exhibited a pronounced decline in leaf nitrogen, digestibility, and other macronutrients during winter, in sharp contrast to sweetveld, on nutrient-rich soils, where forage quality varied little seasonally. In a carbon-enriched, warmer, and most likely drier future climate, we predict that forage quality will not be substantially altered in sweetveld where soil nutrients and temperature are not limiting but that sourveld could become ‘sourer’ because soil nutrients will be inadequate to match higher plant production promoted by elevated [CO2] and warmer and longer growing seasons. Reassessing historical data and seasonal and spatial monitoring of forage quality will enable assessment of past and future impacts of climate change on grassland forage quality. Significance: Grassland forage quality will likely decline with elevated [CO2] and warming, particularly in sourveld. Climate change could deepen and widen the sourveld winter forage bottleneck, necessitating greater supplementary feeding of livestock.

Physiological traits and response strategies of four subtropical tree species exposed to drought

World-wide, forests are experiencing drought-induced mortality. However, physiological adaptation to drought is highly variable, which may lead to differential mortality patterns and alter community structure. In this study, saplings of four common tree species ( Ormosia pinnata , Dalbergia odorifera , Castanopsis fissa and Michelia macclurei ) grown in subtropical plantations in southern China were subjected to average rainfall and three drought treatments, consisting of low (25% rainfall reduction), moderate (50% rainfall reduction) and high (75% rainfall reduction) drought. To investigate their drought response strategies and select tree species with higher drought tolerance, we examined plant traits, including tree growth, stomatal regulation, water relations, carbon dynamics and morphology, that might contribute to drought tolerance. We found that O. pinnata adapted to drought by decreasing turgor loss point (TLP) and increasing leaf dry matter content and leaf mass per area (LMA). D. odorifera exhibited low leaf minimum conductance and high LMA as the key drought traits to reduce water loss. C. fissa was slowest to initiate stomatal closure but completed stomatal closure more rapidly than the other species. Drought reduced light-saturated photosynthetic rates (A sat ) for O. pinnata , D. odorifera and C. fissa primarily due to declining stomatal conductance (g s ), with lesser limitations due to the biochemical capacity of Rubisco carboxylation (V cmax ) and electron transport (J max ). M. macclurei was the first species to close stomata. Drought did not affect A sat for M. macclurei due to stable photosynthetic biochemical processes; however, V cmax regulation of A sat increased with drought intensity. There was trait variation in the capacity of study trees to tolerate drought, with M. macclurei exhibiting the highest capacity to tolerate drought due to key stomatal (earlier stomatal closure) and hydraulic (lower TLP) traits reducing plant water loss with progressive drought stress. • Selecting species with morphological and physiological traits that confer high drought tolerance and resistance will be critical for designing and managing plantations. • M. macclurei might be the best adapted plantation tree for growth in future drier climates. • M. macclurei exhibited high drought avoidance and resistance, and maintained photosynthesis.

QTL mapping for early root and shoot vigor of upland rice (Oryza sativa L.) under P deficient field conditions in Japan and Madagascar.

Upland rice production is limited by the low phosphorus (P) availability of many highly weathered tropical soils and P deficiency is likely to become increasingly limiting in future drier climates because P mobility decreases sharply with soil moisture. Good seedling root development will be crucial to cope with the combined effects of low P and water availability. Upland rice genebank accession DJ123 was used as a donor for P efficiency and root vigor traits in a cross with inefficient local variety Nerica4 and a set of backcross lines were used to characterize the seedling stage response of upland rice to low P availability and to identify associated QTL in field trials in Japan and Madagascar. Ten QTL were detected for crown root number, root, shoot and total dry weight per plant in a highly P deficient field in Japan using the BC1F3 generation. Of these, qPef9 on chromosome 9 affected multiple traits, increasing root number, root weight and total biomass, whereas a neighboring QTL on chromosome 9 (qPef9-2) increased shoot biomass. Field trials with derived BC1F5 lines in a low-P field in Madagascar confirmed a highly influential region on chromosome 9. However, qPef9-2 appeared more influential than qPef9, as the shoot and root biomass contrast between lines carrying DJ123 or Nerica4 alleles at qPef9-2 was +23.8% and +13.5% compared to +19.2% and +14.4% at qPef9. This advantage increased further during the growing season, leading to 46% higher shoot biomass at the late vegetative stage. Results suggest an introgression between 8.0 and 12.9 Mb on chromosome 9 from P efficient donor DJ123 can improve plant performance under P-limited conditions. The QTL identified here have practical relevance because they were confirmed in the target genetic background of the local variety Nerica4 and can therefore be applied directly to improve its performance.

GIS-based modelling of climate variability impacts on groundwater quality: Cape Flats aquifer, Cape Town, South Africa

The need to improve groundwater security remains critical, especially in urban areas where demand for groundwater as an alternative source of water supply is increasing following unprecedented population growth. Climate change continues to threaten groundwater resources in such areas. This study assessed and analysed data from a variety of sources that required holistic analytical tools to demonstrate the impacts of climate change on groundwater quality at the local level. We evaluated how climate conditions affect groundwater quality using a hydrological model (WaterWorld model) in a GIS context. The Cape Flats Aquifer in the city of Cape Town in South Africa was chosen as a case study. The WaterWorld model was used to calculate hydrologic scenarios based on climate change factors and groundwater quality parameters for the period 1950–2000. Mean annual precipitation and temperature were simulated using the multi-model mean and Representative Concentration Pathway 8.5 for the years 2041–2060. Simulation results showed that annual precipitation will increase until 2041 and then decrease until 2060. A significant temperature increase of 1.9 °C–2.3 °C was predicted. Water balance simulations showed a decrease of about 8.6% per year under the future dry climate. ArcGIS 10.3 was used to combine geospatial data and develop a groundwater vulnerability map. Modelling analysis based on GIS showed that the southern and central suburbs of the study area are more susceptible to groundwater contamination and have high surface runoff and higher average temperatures. The groundwater vulnerability index and electrical conductivity concentrations showed a strong positive correlation when the model was validated using linear regression analysis (R2 = 0.99, P < 0.05). In this article, we recommend the use of the WaterWorld model in a GIS environment to simulate hydrologic scenarios on climate change and groundwater quality parameters to provide practical and feasible insights for actions to improve groundwater management.

Growth of 19 conifer species is highly sensitive to winter warming, spring frost and summer drought.

Background and AimsConifers are key components of many temperate and boreal forests and are important for forestry, but species differences in stem growth responses to climate are still poorly understood and may hinder effective management of these forests in a warmer and drier future.MethodsWe studied 19 Northern Hemisphere conifer species planted in a 50-year-old common garden experiment in the Netherlands to (1) assess the effect of temporal dynamics in climate on stem growth, (2) test for a possible positive relationship between the growth potential and climatic growth sensitivity across species, and (3) evaluate the extent to which stem growth is controlled by phylogeny.Key resultsEighty-nine per cent of the species showed a significant reduction in stem growth to summer drought, 37 % responded negatively to spring frost and 32 % responded positively to higher winter temperatures. Species differed largely in their growth sensitivity to climatic variation and showed, for example, a four-fold difference in growth reduction to summer drought. Remarkably, we did not find a positive relationship between productivity and climatic sensitivity, but instead observed that some species combined a low growth sensitivity to summer drought with high growth potential. Both growth sensitivity to climate and growth potential were partly phylogenetically controlled.ConclusionsA warmer and drier future climate is likely to reduce the productivity of most conifer species. We did not find a relationship between growth potential and growth sensitivity to climate; instead, some species combined high growth potential with low sensitivity to summer drought. This may help forest managers to select productive species that are able to cope with a warmer and drier future.

Landscape Conservation Forecasting for Data-Poor at-Risk Species on Western Public Lands, United States

Managing vast federal public lands governed by multiple land use policies creates challenges when demographic data on at-risk species are lacking. The U.S. Bureau of Land Management Cedar City Field Office used this project in the Black Mountains (Utah) to inform vegetation management supporting at-risk greater sage-grouse and Utah prairie dog planning. Ecological systems were mapped from satellite remote sensing imagery and used to model species habitat suitability under two levels of management activity (custodial, preferred) and climate scenarios for historic and two global circulation models. Spatial state-and-transition models of ecological systems were simulated for all six scenarios up to 60 years while coupled with expert-developed habitat suitability indices. All ecological systems are at least moderately departed from reference conditions in 2012, whereas habitat suitability was 50.5% and 48.4% for sage-grouse and prairie dog, respectively. Management actions replaced non-native annual grasslands with perennial grasses, removed conifers, and controlled exotic forbs. The drier climate most affected ecological departure and prairie dog habitat suitability at 30 years only. Different climates influenced spatial patterns of sage-grouse habitat suitability, but nonspatial values were unchanged. Climate impacts on fire, vegetation succession, and restoration explain many results. Front-loading restoration is predicted to benefit under future drier climate.

Effects of land-cover and watershed protection futures on sustainable groundwater management in a heavily utilized aquifer in Hawai\u2018i (USA)

Groundwater sustainability initiatives, including sustainable yield and watershed policy protection policies, are growing globally in response to increasing demand for groundwater, coupled with concerns about the effects of climate and land-cover change on groundwater supply. Improved understanding of the impacts of watershed management on groundwater yields and management costs—particularly in the broader context of climate and land-cover change—is critical to inform these initiatives and facilitate integrated land and water management. This study develops a novel, spatially explicit groundwater hydrologic ecosystem services framework, which combines stakeholder-defined land-cover scenarios, sustainable yield estimation using a groundwater simulation optimization approach, and economic valuation, and applies it in the most heavily utilized aquifer Hawai‘i (USA). Sustainable yield estimates and resulting differences in replacement costs are estimated for six land-cover scenarios (with varying levels of urban development and watershed management) crossed with two water demand scenarios in a context of a dry future climate (Representative Concentration Pathway [RCP] 8.5 mid-century). Land-cover change is found to be an important, though less significant drive of changes in groundwater recharge than climate change. The degree of watershed protection, through preventing the spread of high-water-use, invasive plant species, is projected to be a much stronger land-cover signal than urban development. Specifically, full forest protection increases sustainable yield by 7–11% (30–45 million liters per day) and substantially decreases treatment costs compared with no forest protection. Collectively, this study demonstrates the hydrologic and economic value of watershed protection in a context of a dry future climate, providing insights for integrated land and water policy and management in Hawai‘i and other regions, particularly where species invasions threaten source watersheds.

Compensation effect of winter snow on larch growth in Northeast China

Winter snow plays a crucial role in regulating tree growth during the subsequent growing season in regions suffering seasonal or even annual drought stress, but the mechanisms of the potential compensation effect of winter snow on subsequent growing-season tree growth are not well understood. In this study, we establish tree-ring chronologies of six larch forest stands along a marked drought gradient across Northeast China. We identify the spatial pattern in the compensation effects of winter snow on subsequent growing-season tree radial growth and uncover a potentially enhanced compensation effect in drier climates. Our results indicate that in snow-rich sites, winter snow tends to exert a significantly positive effect on tree growth during the growing season, whereas this growth compensation effect is reduced in drier sites. More importantly, our findings identify a much higher compensation effect of winter snow on growing-season larch growth in drier years (24.4–48.0%) than in wetter years (6.1–8.1%) at snow-rich sites. Given the projected increase in both severity and duration of droughts in temperate regions, the potential compensation effect of winter snow could play a crucial role in mediating the adaptation ability of boreal/hemi-boreal forest ecosystems in response to a warmer and drier future climate in these regions.

Best of both worlds: hybrids of two commercially important pines (Pinus contorta × Pinus banksiana) combine increased growth potential and high drought tolerance

Over 18 million hectares of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) forests have been affected by a massive mountain pine beetle outbreak in western Canada. The ensuing need for reforestation compels forest managers to deploy more drought-resistant stock in anticipation of a hotter and drier future climate. Recent studies suggest that naturally occurring lodgepole pine × jack pine (Pinus banksiana Lamb.) hybrids may be more drought-resistant than pure lodgepole pine. We used single-nucleotide polymorphism markers to determine the level of jack pine introgression present in the region J lodgepole pine seed orchard, in northwest Alberta, and we identified six hybrid genotypes with 10%–18% jack pine introgression for further study. We compared the performance of open-pollinated seedlings of lodgepole, jack, and hybrid pines under well-watered and drought conditions in a greenhouse experiment. Seedlings were subjected to repeg ated drought cycles, withholding water for either 2 or 3 weeks. We found that hybrid pines grew significantly faster than lodgepole pine under well-watered conditions while retaining the high tolerance to prolonged drought exhibited by lodgepole pine seedlings, a particularly beneficial combination of traits during the critical stage of establishment. We therefore suggest the deployment of hybrid lodgepole pine as a strategy to promote adaptation to hotter and drier future climates.

Intraspecific plasticity in hydraulic and stomatal regulation under drought is linked to aridity at the seed source in a wild pear species

Adaptations of fruit trees to future climate are a current research priority due to the rapid increase in air temperature and changes in precipitation patterns. This is aimed at securing sustainable food production for our growing populations. Key physiological traits in trees conferring drought tolerance are resistance to embolism and stomatal control over water loss. Recently, we have shown in the field that a native wild pear species performs better under drought than two cultivated pear species. A comparative greenhouse study was conducted to investigate traits associated with drought tolerance in four ecotypes of a wild pear species (Pyrus syriaca Boiss), compared with a wild pear species (Pyrus betulifolia Bunge) commonly used as a pear rootstock. Seed sources were collected from semi-arid, sub-humid and humid sites across northern Israel. Measurements of water relations, leaf physiology, hydraulic conductivity and percent loss of hydraulic conductivity (PLC) were conducted under standard irrigation, drought and recovery from drought. The four P. syriaca ecotypes maintained significantly higher leaf gas exchange values and water-use efficiency and had lower PLC than the rootstock species under prolonged drought as well as during recovery. Across the four ecotypes, stomatal closure occurred at stem water potential (Ψ) around -3.5MPa; however, Ψ at 50% PLC ranged from -4.1MPa in the humid ecotype to -5.2MPa in one of the semi-arid ecotypes, rendering the latter with a higher hydraulic safety margin (the Ψ difference between stomatal closure and 50% PLC). Divergence of the ecotypes in xylem vulnerability to embolism closely matched the mean annual precipitation at their seed sources. Thus, selection of pear ecotypes from populations in semi-arid sites may be better than the currently used plant material for preparing our cultivated species for hotter and drier future climate.

Drought shrinks terrestrial upland resilience to climate change

AbstractAimDrought has been shown to alter terrestrial ecosystem carbon (C) and nitrogen (N) dynamics, and thus feedback to future climate. However, drought‐induced changes in terrestrial upland C and N pools and the drought response of soil carbon dioxide (CO2) and nitrous oxide (N2O) fluxes are yet to be quantified.LocationGlobal upland ecosystems.Time period2000–2018.Major taxa studiedTerrestrial C and N fluxes.MethodsA meta‐analysis was conducted that compiled 1,344 measurements from 128 manipulative studies worldwide to obtain a general picture of terrestrial C and N cycling responses to soil drought stress and identify the primary driving factors.ResultsWe showed that drought significantly decreased plant C pools, with stronger negative responses of aboveground than belowground C components. Drought significantly decreased soil respiration (RS) and N2O fluxes by 19% and 29%, respectively. There were non‐significant changes in soil organic C and N pools in response to drought; in contrast to a considerable decrease in soil dissolved organic C (−22%), there was a robust increase in soil nitrate‐N (26%) following short‐term drought impact. By relating net ecosystem productivity (NEP) to the difference between net primary production (NPP) and soil heterotrophic respiration (RH), drought was found to drive a decrease up to −37% in NEP, being equivalent to a reduction in terrestrial net C uptake of 2.91 t C/ha.Main conclusionsOur study provides insights into soil release of CO2 and N2O with a linkage to the changes in terrestrial C and N pools in response to drought across upland biomes. Our findings highlight that, despite the lowered soil C release rate, the capacity of upland biomes as a C sink to slow climate change would still be weakened due to a robust decline of plant‐derived C input to soil in a future drier climate.

The shifting influence of future water and temperature stress on the optimal flowering period for wheat in Western Australia

An optimal flowering period (OFP) minimises the long-term combined risk of extreme weather events on crop yield and exists in all environments. With climate change, the frequency, timing and intensity of these events are likely to change, which in turn may shift the OFP. It is important to explore how the OFP would change under a future climate. Knowledge of the OFP is important for formulating breeding strategies and developing suitable varieties. Here, a simulation analysis was conducted at 4 sites in Western Australia to quantify any shift in the OFP due to climate change, by accounting for the effects of frost, heat and water stress on wheat yield. Three global climate models that projected the greatest precipitation decrease under the Representative Concentration Pathways 8.5 during 2061–2100 were ensembled to represent a dry future climate condition (dry scenario); and 3 models that predicted the smallest decrease in precipitation were ensembled to represent a wet future climate condition (wet scenario). The simulation results predicted that the timing of OFPs for wheat in Western Australia would occur earlier than the current OFP. On average the OFP was 29 days earlier in the dry scenario and 11 days earlier in the wet scenario. Early sowing of long-season varieties would be preferable to achieve the OFP in both climate scenarios due to greater yield potential. Early sowing opportunities were very limited under the dry scenario, and therefore fast maturing varieties for late sowing would also be necessary.