Dry Summer Research Articles

Eco-physiological behaviors of some apple genotypes (Malus x domestica Borkh.) in the hot-and-dry climate of an inner area of Southern Italy

The Italian internal areas are distant from the main trade flows and service centers, but have important environmental and cultural resources. The Italian “National Strategy for Inner Areas” represents a novel policy aimed at contrast the abandon of these territories by supporting multiple activities aimed at stimulating economic development and promoting territorial cohesion. The condition of marginality offers the chance to pursue economic development according to the principles of sustainability. These internal areas are often distinguished by a purely rural vocation. Genotypes of fruit crops traditionally grown in inland areas cope often with difficult climatic conditions and low-input farming techniques, showing generally a good tolerance to abiotic tresses. Exploring their eco-physiological behaviors in response to the agri-environmental context is useful for identifying crops capable of stimulating the recovery and expansion of a sustainable agriculture system in inland areas. The present work reports some results of a research conducted on three traditional local apple genotypes grown in an internal hot-arid summer area of Southern Italy, evaluating their water status and the intensity of leaf gas exchange compared to those of a well-known “standard” cultivar, in a hot, dry summer period. The local genotypes tested in this case study proved to be more eco-physiologically performing. The experiment allowed to estimate their probable relative eco-physiological advantages compared to the “standard” apple genotype taken as reference.

Strong coupling between soil moisture and temperature intensifies warming and humidification on the Tibetan Plateau: Evidence from 200-year tree ring records

In recent times, the warming and humidification of the Tibetan Plateau have become more pronounced. However, research on soil moisture on the Tibetan Plateau has been limited by the late initiation of data acquisition, thereby constraining the study of its driving mechanisms. Hence, there is an urgent need for historical time series to fill this research gap. To address this issue, we analyzed four spruce (Picea likiangensis) chronologies collected in high-altitude regions of the Tibetan Plateau, and we found that soil moisture during the dry season was a critical limiting factor for tree growth. The first principal component of a principal component analysis, accounting for 56.21% of the variance in all chronologies, was then used to reconstruct soil moisture variations from October of the previous year to May of the current year in the southeastern Tibetan Plateau from 1778 to 2020. We found significant relationships between soil moisture changes and the El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Variability (AMV). We also found a strong linkage between dry season soil moisture and summer temperature, suggesting that this relationship contributes to the intensification of warming and humidification on the Tibetan Plateau.

Multi-year time series of daily solute and isotope measurements from three Swiss pre-Alpine catchments

Time series analyses of solute concentrations in streamwater and precipitation are powerful tools for unraveling the interplay of hydrological and biogeochemical processes at the catchment scale. While such datasets are available for many sites around the world, they often lack the necessary temporal resolution or are limited in the number of solutes they encompass. Here we present a multi-year dataset encompassing daily records of major ions and a range of trace metals in both streamwater and precipitation in three catchments in the northern Swiss Pre-Alps. These time series capture the temporal variability observed in solute concentrations in response to storm events, snow melt, and dry summer conditions. This dataset additionally includes stable water isotope data as an extension of a publicly available isotope dataset collected concurrently at the same locations, and together these data can provide insights into a range of ecohydrological processes and enable a suite of analyses into hydrologic and biogeochemical catchment functioning.

Effect of Harvest Management on Biomass Yield, Forage Quality, and Nutrient Removal by Bioenergy Grasses in Mid-Central Virginia

The increasing cost of fossil-based energy sources has driven research in bio-based alternatives, such as perennial grasses for feedstock. The mid-Atlantic receives appreciable summer rainfall that may support a two-cut-per-year−1 harvest. At Virginia State University, a study on annual forage sorghum and two one-year stand perennials, miscanthus, and selected switchgrass ecotypes was carried out. The experimental design was a split-plot with harvest systems and feedstock grass species randomly assigned to the main and sub-plots, respectively. Only perennial grasses were assigned to the two-cut-per-year−1 system. The first cut occurred in early summer, and the second and single cut occurred after the frost-kill. Under the two-cut system, in 2022, the first-cut dry matter (DM) yield ranged from 8.9 Mg ha−1 in Blackwell to 14.7 Mg ha−1 in BoMaster. Additionally, except for BoMaster, the regrowth DM yields were within 10% of the first-cut DM yield. Under the one-cut system, the yield ranged from 10.8 Mg ha−1 in Blackwell to 23.2 Mg ha−1 in sorghum. Under the two-cut system, in 2023, miscanthus produced the greatest first-cut DM yield of 18.4 Mg ha−1, while other perennials averaged 10.1 Mg ha−1. Compared to the first cut, the hot and dry summer significantly reduced regrowth for all feedstock species, with the miscanthus DM yield dropping by 64%. While forage attributes differ among feedstock species, in general, both the first cut and regrowth showed greater crude protein and mineral elements, as well as lower ADF contents compared to a single cut following a killing freeze. Sorghum had better forage quality for the one-cut-per-year−1 feedstock material, and, along with the first cut and regrowth, it may have the potential for use as forage for maintenance energy in animal systems. For perennials, the two-cut-per-year−1 system removed the greatest quantities of nutrients during both years, with the first-cut harvest contributing about 65% of all removed N and K. Sorghum removed the greatest quantities of nutrients compared to the perennial under a one-cut-per-year−1 system. Therefore, while a two-cut-per-year−1 system can result in the greatest DM yields for dual-purpose use, its adoption calls for a critical analysis of economic benefits that considers feedstock bioenergy processing approaches, stand persistence, and fertilizer management strategies to address potential soil fertility depletion due to mineral element mining.

Drought- and heat-induced mortality of conifer trees is explained by leaf and growth legacies.

An increased frequency and severity of droughts and heat waves have resulted in increased tree mortality and forest dieback across the world, but underlying mechanisms are poorly understood. We used a common garden experiment with 20 conifer tree species to quantify mortality after three consecutive hot, dry summers and tested whether mortality could be explained by putative underlying mechanisms, such as stem hydraulics and legacies affected by leaf life span and stem growth responses to previous droughts. Mortality varied from 0 to 79% across species and was not affected by hydraulic traits. Mortality increased with species' leaf life span probably because leaf damage caused crown dieback and contributed to carbon depletion and bark beetle damage. Mortality also increased with lower growth resilience, which may exacerbate the contribution of carbon depletion and bark beetle sensitivity to tree mortality. Our study highlights how ecological legacies at different time scales can explain tree mortality in response to hot, dry periods and climate change.

Does lower water availability limit stem CO2 efflux of oak and hornbeam coppices?

Recent changes in water availability can be crucial for the development, growth and carbon budget of forests. Therefore, our aim was to determine the effect of reduced throughfall and severe summer drought on stem CO2 efflux as a function of temperature and stem increment. Stem CO2 efflux was measured using the chamber method on oak and hornbeam under four treatments: coppice, thinned coppice, and both coppice and thinned coppice with 30 %-reduced throughfall. The first year of the experiment had favourable soil water availability and the second year was characterized by a dry summer. While reduced throughfall had no effect on stem CO2 efflux, the summer drought decreased efflux by 43-81 % during July and August. The stem CO2 efflux was reduced less severely (by 13-40 %) in September when the drought persisted but the stem increment was already negligible. The stem increment was also strongly affected by the drought, which was reflected in its paired relationship with stem CO2 efflux over the two experimental years. The study showed that summer dry periods significantly and rapidly reduce stem CO2 efflux, whereas a constant 30 % rainfall reduction needs probably a longer time to affect stem properties, and indirectly stem CO2 efflux.

Fuzzy Inference System For Mapping Forest Fire Susceptibility In Northern Rondônia, Brazil

Forest fires are global phenomena that pose an accelerating threat to ecosystems, affect the population life quality and contribute to climate change. The mapping of fire susceptibility provides proper direction for mitigating measures for these events. However, predicting their occurrence and scope is complicated since many of their causes are related to human practices and climatological variations. To predict fire occurrences, this study applies a fuzzy inference system methodology implemented in R software and using triangular and trapezoidal functions that comprise four input parameters (temperature, rainfall, distance from highways, and land use and occupation) obtained from remote sensing data and processed through GIS environment. The fuzzy system classified 63.27% of the study area as having high and very high fire susceptibility. The high density of fire occurrences in these classes shows the high precision of the proposed model, which was confirmed by the area under the curve (AUC) value of 0.879. The application of the fuzzy system using two extreme climate events (rainy summer and dry summer) showed that the model is highly responsive to temperature and rainfall variations, which was verified by the sensitivity analysis. The results obtained with the system can assist in decision-making for appropriate firefighting actions in the region.

Shaded streams with permeable watersheds provide naturally resilient fish habitat refugia during heatwaves

AbstractStreamflow, dissolved oxygen, and water temperature underpin stream fish habitat suitability, so climate change could cause widespread habitat deterioration. Identifying stream characteristics that mediate habitat resilience to heatwaves will allow conservation effort prioritisation. Here, a set of readily applied metrics were used to assess hydrological and oxythermal responses of neighbouring salmonid streams, with distinctive geologies, soil‐types, and localised riparian shading, to periods of anomalously warm conditions. During heatwaves, low flows, warm‐water temperatures, and diel oxygen variability, associated with biogenic production and respiration, predominated. In a low‐shade stream lacking significant catchment water storage, high daytime (>22°C) and night‐time (>19°C) water temperatures and low early morning O2 concentrations (<5 mg L−1) accumulated oxythermal stress for salmonids throughout summer. A stream with localised shading and a higher proportion of underlying aquifers and permeable soils throughout its watershed experienced considerably less cumulative oxythermal stress (O2 > 6 mg L−1; temperatures <19°C), whilst slower release of subsurface water bolstered base flows during dry spells. Our findings support conservation of shaded streams with permeable watersheds characterised by higher soil infiltration rates and aquifer storage capacity as salmonid sanctuaries under a warmer, drier summer climate. Preventing water quality and hydromorphological deterioration are paramount for safeguarding their role as climate refugia.

Genetic Potential of Newly Developed Maize Hybrids under Different Water-Availability Conditions in an Arid Environment.

Drought is a crucial environmental stress that tremendously impacts maize production, particularly under abrupt climate changes. Consequently, breeding drought-tolerant and high-yielding maize hybrids has become decisive in sustaining its production and ensuring global food security under the global fast-growing population. The present study aimed to explore drought tolerance and agronomic performance of newly developed maize inbred lines and their hybrids. Ten newly developed maize inbred lines were crossed with two high-yielding testers using a line × tester mating design. The developed twenty hybrids alongside two high-yielding commercial hybrids were evaluated under water-deficit (5411 m3/ha) and well-watered (7990 m3/ha) conditions in dry summer climate conditions. Highly significant variations were detected among the evaluated hybrids for all studied agronomic traits under well-watered and water-deficit conditions. The inbred lines L10 and L6 were particularly notable, demonstrating the most significant negative general combining ability (GCA) effects for earliness, which is crucial for stress avoidance in both environmental settings. Inbred lines L11, L7, L6, and L1 also showed the highest positive and most significant GCA effects for key yield traits, indicating their potential as parents in breeding programs. The crosses L-10×T-1 and L-6×T-2 were outstanding for their heterotic effects on earliness in days to tasseling and silking. Similarly, the crosses L-4×T-2 and L-1×T-1 excelled in plant and ear heights under both irrigation regimes. The hybrids L-1×T-2 and L-7×T-1 demonstrated superior heterosis for chlorophyll content, number of rows per ear, and overall grain yield. Additionally, hybrids L-11×T-1 and L-11×T-2 exhibited remarkable heterotic effects for the number of grains per row, number of rows per ear, 100-kernel weight, and grain yield, highlighting their potential in breeding for productivity. Based on drought tolerance indices and cluster analysis, the cross combinations L-11×T-1, L-11×T-2, L-7×T-1, and L-1×T-2 were classified as the most drought-tolerant crosses. The principal component analysis highlighted traits such as days to tasseling, days to silking, chlorophyll content, plant height, ear height, number of grains per row, number of rows per ear, and 100-kernel weight can be taken as selection criteria for improving grain yield in maize breeding programs under limited water conditions. Based on the summarized results, the identified genetic materials could be considered promising under both conditions and hold potential for future breeding programs.

Added value of seasonal hindcasts to create UK hydrological drought storylines

Abstract. The UK has experienced recurring periods of hydrological droughts in the past, including the drought declared in summer 2022. Seasonal hindcasts, consisting of a large sample of plausible weather sequences, can be used to create drought storylines and add value to existing approaches to water resources planning. In this study, the drivers of winter rainfall in the Anglian region in England are investigated using the ECMWF SEAS5 hindcast dataset, which includes 2850 plausible winters across 25 ensemble members and 3 lead times. Four winter clusters are defined using the hindcast winters based on possible combinations of various atmospheric circulation indices (such as the North Atlantic Oscillation, NAO; East Atlantic, EA, pattern; and El Niño–Southern Oscillation). Using the 2022 drought as a case study, we demonstrate how storylines representing alternative ways the event could have unfolded can be used to explore plausible worst-case scenarios over winter 2022/23 and beyond. The winter clusters span a range of temperature and rainfall response in the study region and represent circulation storylines that could have happened over winter 2022/23. River flow and groundwater level simulations with the large sample of plausible hindcast winters show that drier-than-average winters characterised by predominantly NAO−/EA− and NAO+/EA− circulation patterns could have resulted in the continuation of the drought with a high likelihood of below-normal to low river flows across all selected catchments and boreholes by spring and summer 2023. Catchments in Norfolk were particularly vulnerable to a dry summer in 2023 as river flows were not estimated to recover to normal levels even with wet winters characterised predominantly by NAO−/EA+ and NAO+/EA+ circulation patterns, due to insufficient rainfall to overcome previous dry conditions and the slow response nature of groundwater-dominated catchments. Through this analysis, we aim to demonstrate the added value of this approach to create drought storylines during an ongoing event. Storylines constructed in this way supplement traditional weather forecasts and hydrological outlooks, in order to explore a wider range of plausible outcomes.

Influence of Transboundary Pollution on the Variability of Surface Ozone Concentrations in the Desert Southwest of the U.S.: Case Study for Arizona

Arizona, a rapidly growing state in the southwestern U.S., faces ozone pollution challenges, including nonattainment areas in Yuma and Maricopa counties influenced by neighboring state pollution transport. In this study, we use five-year (2017–2021) hourly back-trajectories and O3 concentration data for concentration-weighted trajectory (CWT) analysis to identify transport pathways and potential source regions of O3 at six monitoring sites in Arizona. We divide the data into five seasons (winter, spring, dry summer, monsoon summer, and fall) to examine variations in O3 concentration and transport across sites and seasons. The highest mean O3 concentrations occur during spring (37–49 ppb), dry summer (39–51 ppb), and monsoon summer (34–49 ppb), while winter (19–41 ppb) exhibits the lowest seasonal mean. The CWT results reveal that high O3 concentrations (≥40 ppb) in Arizona, with the exception of Phoenix and Tucson sites, are influenced significantly by regional and international transport, especially in spring (14.9–35.4%) and dry summer (12.7–26.9%). The major potential source areas (excluding the Phoenix and Tucson sites) are predominantly located outside Arizona. This study highlights the critical role of pollution transport in influencing O3 variability within Arizona and will be valuable in shaping pollution control strategies in the future.

Northward shift of Indian summer monsoon and intensifying winter westerlies cause stronger precipitation seasonality over Pamirs and its downstream basins in the 21st century

Hydroclimate will change over Pamirs and its downstream basins (PDB), including Indus River, Tarim River, Amu Darya and Syr Darya Basins, in response to the variation of Indian summer monsoon (ISM) and mid-latitude westerlies. However, the precipitation variation and its mechanism over PDB in the 21st century are yet not fully understood. Here, the best models ensemble selected from 25 CMIP6 models under SSP2–4.5 and SSP5–8.5 scenarios is applied to detect the precipitation variations over PDB in the 21st century. A remarkable dipolar pattern is found in both summer and winter precipitation over PDB, particularly in the central Indus River Basin and upper Amu and Syr Darya Basins. The central Indus River Basin (upper Amu and Syr Darya Basins) will experience an increasingly wet (dry) summer in response to northward ISM and a dry (wet) winter driven by mid-latitude westerlies. The amplifying dipolar pattern of seasonal precipitation thus increases the water resource vulnerability over PDB and emphasizes the role of Pamirs in modulating the water resources over surrounding basins, especially the Amu Darya and Syr Darya Basins in the future. The findings underscore the need for prioritizing policies by considering the impacts of precipitation seasonality on social planning.

Effects of selected biostimulants on qualitative and quantitative parameters of nine cultivars of the genus Capsicum spp.

Abstract Despite the growing popularity of biostimulants among farmers, a major problem remains with their variable effects on individual species and varieties of cultivated crops. Therefore, it is important to know how to choose a suitable product for the given growing conditions while simultaneously considering species and varietal variability in crop cultivation. The goal of this study is to highlight different reactions of plants to the applied preparations within the monitored representatives of the Capsicum genus, with an emphasis on intervarietal variability. The experiments with two monitored and one control variants occurred during the growing seasons of 2020 and 2022 in Slovakia’s southwest region, characterized by a European continental climate with warm and dry summers. Seven varieties of Capsicum annuum and two varieties of Capsicum chinense were chosen based on actual growers’ preferences: “Žitava,” “Szegedi 80,” “Karkulka,” “Hodoníska sladká,” “Habanero Orange,” “Habanero Chocolate,” “Kristián,” “Damián” and “Kurtovska kápia.” In the present study, we observed the effects of selected commercial biostimulants – the combination of Energen Fulhum Plus and Energen Fruktus Plus in the first variant and the biostimulant Humix® Universal in the second variant – on bell pepper fruits. We evaluated three productivity parameters: fresh fruit weight per variety, weight of one fruit and number of bell pepper fruits per plant. From the qualitative parameters, we evaluated the content of ascorbic acid, capsaicin, carotenoids, and the American Spice Trade Association color value. The monitored biostimulants had variable effects in all pepper varieties, while some of them statistically significantly increased and others significantly decreased the monitored parameters. In conclusion, we state that the application of verified biostimulants did not have a uniform effect on the observed varieties of the Capsicum genus. Therefore, based on our results, we cannot generalize the effect of a specific biostimulant on a specific crop genus or species.

Trends of the Global Burden of Disease Linked to Ground-Level Ozone Pollution: A 30-Year Analysis for the Greater Athens Area, Greece

The Greater Athens Area (GAA), situated in the southern part of the European continent (in Greece), has a Mediterranean climate characterized by hot, dry summers and mild, wet winters. As a result of increased sunshine and high temperatures, exceedances in ozone concentrations are often recorded during the hot period. In the present study, the monthly as well as daily variations of O3 concentrations at thirteen stations in the GAA were investigated for the period 1987–2019. Moreover, the impact of O3 on the people’s health in Greece was examined by using data from the Global Burden of Disease (GBD) study with the socio-economic conditions of the country. Ozone concentrations were found to be particularly high during the summer months, especially in suburban stations. Values ranged from 65 μg/m3 to 90 μg/m3 during the night, in contrast to urban areas and remain high for several hours. Comparing estimates from GBD, it was found that exposure to ozone can impair respiratory function, leading to death or susceptibility to respiratory diseases that reduce quality of life, especially for people over 55 years of age. Finally, since 2009, when the economic crisis began in Greece, an upward trend was observed for deaths and disability adjusted life years.

Factors influencing migration of short-finned eels (Anguilla australis) over 3 years from a wetland system, Lake Condah, south-east Australia, downstream to the sea.

Anguillid eel populations are under threat globally. A particularly vulnerable life-cycle stage is the migration of mature adult eels downstream from freshwater habitats through estuaries into the sea to spawn. This study investigated the factors associated with downstream migration of the short-finned eel Anguilla australis (Richardson 1841) from a coastal wetland (Lake Condah) in south-east Australia, using acoustic telemetry. Migration was associated with time of the year, higher water level and river flows, decreasing water temperature, and darker moon phases. Larger individuals and those in better condition were more likely to migrate from the wetland. Downstream migration peaked in spring, in contrast to the typical autumn migration period for other temperate anguillids. Variable responses, in comparison to other studies, highlight how migration cues may not be universal. In south-east Australia, short-finned eels may have evolved to migrate in multiple phases by first migrating to the estuary during typical seasonal spring flow pulses (e.g., to avoid being stranded in upland reaches during dry summer periods) and then migrating into the ocean in autumn. More research is needed to unravel these processes and causes, especially considering that the relationship between migration and hydrology may be complex and confounded (e.g., by human-induced disruptions to migratory pathways).

Leaf traits of Central-European beech (Fagus sylvatica) and oaks (Quercus petraea/robur): Effects of severe drought and long-term dynamics

In 2018—2020, Central-European forests suffered from extremely hot and dry summers. We used data from long-term forest monitoring of six stands of European beech (Fagus sylvatica) and two stands of oak (Quercus petraea/Q. robur) growing on different geological substrates in the climatically uniform state of Saarland (south-western Germany) for analyzing leaf traits of the period 2004—2021. We aimed at detecting overall effects of the drought on foliar morphology, nutrient concentrations, and injury, and long-term alterations in these traits. Across sites, drought resulted in a decrease in leaf size and specific leaf area (SLA) and increased fruiting in the beech and a decrease in the foliar nitrogen (N) concentrations in both tree genera. During drought, foliar calcium and manganese concentrations were lower and potassium (K) concentrations higher across the beech stands, whereas in the oak stands, drought led to a reduction in the foliar phosphorus (P) and magnesium (Mg) concentrations. High rates of anthropogenic N deposition during recent decades have resulted in high foliar N concentrations and low to deficient concentrations of P and, in the beech, of Mg. However, a significant (negative) long-term trend in leaf traits across the study sites was only found for the K concentration and necroses of the beech leaves. Foliar N correlated positively with SLA in the beech and with leaf size in the oak but was not related to herbivory. Chlorosis was the only leaf trait that, in the beech, correlated (negatively) with the climatic water balance. We conclude that even severe drought during three consecutive years does not seem to critically affect the nutrient supply to the two most important deciduous forest tree genera of Central Europe. In the beech, a decrease in leaf size and SLA might be used as an early indication of severe drought stress effects in regular monitoring programs.

FIRE WEATHER INDEX AND FOREST FIRE DANGER MAPPING: INSIGHTS FROM A CASE STUDY IN ANTALYA - MANAVGAT FOREST, TURKIYE

Abstract. Forest fires in Türkiye, like in other regions, have detrimental effects on wildlife habitats, water quality, air pollution, climate change, and the economy. These fires become particularly concerning during the dry summer months. In 2021, forest fires affected over 150 thousand hectares of land across the country, with the Manavgat district in Antalya province alone witnessing the burning of approximately 60 thousand hectares of forest area. This study aims to assess the applicability and suitability of Fire Weather Index (FWI) data derived from meteorological station data in the Antalya region, as well as EFFIS FWI data generated using satellite-based meteorological information, for fire danger mapping during the Manavgat forest fire that occurred between 28 July and 6 August 2021. Additionally, correlation analyses were performed between the two FWI datasets and other relevant variables, including the difference in Normalized Burn Ratio (dNBR), the difference in Land Surface Temperature (dLST), and Fire Radiative Power (FRP) data detected from MODIS and VIIRS satellites. The results of the correlation analysis indicated that the FWI values obtained using in-situ meteorology station data showed much higher correlations than FWI values obtained from EFFIS, with the highest correlation (73%) observed with dLST data. Consequently, the fire danger map was created using the in-situ meteorological data, given its stronger correlation. The results prominently revealed a widespread high-risk level across the entire Antalya province, with the Manavgat district classified into the "Extreme" and "Very Extreme" FWI classes, emphasizing the critical importance of utilizing in-situ meteorological data for precise fire danger assessments and proactive fire management strategies.

Low Resource Competition, Availability of Nutrients and Water Level Fluctuations Facilitate Invasions of Australian Swamp Stonecrop (Crassula helmsii)

Australian swamp stonecrop (Crassula helmsii (Kirk) Cockayne) is invasive in Western Europe. Its small size and high potential for regeneration make it difficult to eliminate. Short-term experiments have demonstrated that the growth of C. helmsii depends on nutrient availability and resource competition. In order to confirm those mechanisms in the field, we studied the abundance of C. helmsii in Northern Europe over a longer period of time in relation to nutrient availability and co-occurring plant communities and plant species. C. helmsii impacted native species mainly by limiting their abundance. The native plant species present indicated that previous or periodic elevated nutrient availability were likely responsible for the proliferation of C. helmsii. When growing in submerged conditions, the dominance of C. helmsii depended on a high availability of CO2. A series of exceptionally dry summers allowed C. helmsii to increase in cover due to weakened biotic resistance and a loss of carbon limitation. Only Littorella uniflora (L.) Asch. and Juncus effusus L. were able to remain dominant and continue to provide biotic resistance. Based on our findings, minimizing nutrient (C and N) availability and optimizing hydrology provides native species with stable growth conditions. This optimizes resource competition and may prevent the proliferation of C. helmsii.

Width undulation drives flow convergence routing in five flashy ephemeral river types across a dry summer subtropical region

AbstractDuring the last decade, meter‐resolution topo‐bathymetric digital elevation models (DEMs) have become increasingly utilized within fluvial geomorphology, but most meter‐scale geomorphic analyses are done on just one to a few rivers. While such analyses have contributed greatly to our collective understanding of river discharge‐topography interactions, which is applicable in both river restoration design and environmental flow regulation contexts, their generalizability across a range of river types remains largely unevaluated. This study assessed the dominance of a single hydro‐morphodynamic mechanism, flow convergence routing, in 35 ephemeral rivers divided among five river types in California's South Coast region by answering five questions. Geomorphic covariance structure (GCS) analysis was performed on longitudinal standardized width and standardized, detrended bed elevation spatial series from meter‐resolution DEMs. All river types had coherent, multi‐scalar structures of longitudinal fluvial topography, implicating a process‐morphology link. GCS metrics revealed that landform patterning was consistent with the requirements of the morphodynamic mechanism of flow convergence routing. Thus, that process was found to be a broadly relevant channel altering mechanism among sites, but its relationship with water stage differed between river types. Specifically, river types in unconfined valleys exhibited a strong bankfull width control over base flow bed undulations, with no obvious flood‐stage control over bankfull landform patterning. River types in partially confined valleys also exhibited strong bankfull width control over base flow bed undulations, but their bankfull landform patterns appear to have coalesced with coherent width and bed elevation undulations during flood flows. Finally, metrics for confined river types showed that it takes higher magnitude, less frequent floods to set their coherent width and bed elevation undulations, but even these channels do exhibit flow convergence routing when given enough discharge for sufficient duration.

Assessing the impact of drought on water cycling in urban trees via in-situ isotopic monitoring of plant xylem water

Urban trees are an integral part of sustainable cities. They regulate the local microclimate and enhance the urban water cycle. Increasing periods of drought can impair urban trees by affecting their water uptake, transpiration and growth patterns. In this study, we used a multi-proxy approach to assess how non-irrigated urban trees react to changing water supply throughout the full vegetative period of 2022 including a major drought in Berlin, Germany. Our work focused on individual mature trees in an urban green space; examining daily mean in-situ isotopes in plant xylem water (δxyl) while also monitoring vegetation dynamics via sap flow, stem increments, LAI, as well as groundwater, and soil moisture at different depths. The monitoring period was characterised by a spring with average precipitation inputs, followed by an extremely dry period from July until mid-August, then a gradual rewetting from the end of August until October. At the beginning of the growing period, changes in the ecohydrological dynamics of the investigated maple and birch trees were high with increases in stem size and LAI, but also decreasing soil moisture. In spring, δxyl signatures were high in both trees, with the effect more marked in the maple hinting at a dependence of δxyl on species specific-storage effects and a distinct start of transpiration. During summer, drought stress was apparent in the ecohydrological fluxes of the monitored trees in the reduction of stem growth, LAI, midday water potential and soil moisture. Yet sap flow rates were relatively stable and tree transpiration maintained. We noted a midsummer enrichment of δxyl in both species. Most importantly, the measured δxyl signatures were isotopically in the range of deep soil waters and groundwater implying that deeper sources were sustaining the trees’ water supply during the drought. We also detected fractionation of δxyl, which is possibly induced by heterogenous water uptake strategies and biochemical processes in the tree xylem, including CH4 transport. Our results suggest that urban trees rely on deep water supply and internal storage during drought. We conclude urban trees and shrubs with shallow root development would be more vulnerable to dry summers with a particular threat during future accelerated summer droughts combined with insufficient autumn rewetting causing deep soil layers to dry out.