Mediterranean springs: Keystone ecosystems and biodiversity refugia threatened by global change.

Mediterranean spring ecosystems are unique habitats at the interface between surface water and groundwater. These ecosystems support a remarkable array of biodiversity and provide important ecological functions and ecosystem services. Spring ecosystems are influenced by abiotic, biotic, and anthropogenic factors such as the lithology of their draining aquifers, their climate, and the land use of their recharge area, all of which affect the water chemistry of the aquifer and the spring discharges. One of the most relevant characteristics of spring ecosystems is the temporal stability of environmental conditions, including physicochemical features of the spring water, across seasons and years. This stability allows a wide range of species to benefit from these ecosystems (particularly during dry periods), fostering an unusually high number of endemic species. However, global change poses important threats to these freshwater ecosystems. Changes in temperature, evapotranspiration, and precipitation patterns can alter the water balance and chemistry of spring water. Eutrophication due to agricultural practices and emergent pollutants, such as pharmaceuticals, personal care products, and pesticides, is also a growing concern for the preservation of spring biodiversity. Here, we provide a synthesis of the main characteristics and functioning of Mediterranean spring ecosystems. We then describe their ecological value and biodiversity patterns and highlight the main risks these ecosystems face. Moreover, we identify existing knowledge gaps to guide future research in order to fully uncover the hidden biodiversity within these habitats and understand the main drivers that govern them. Finally, we provide a brief summary of recommended actions that should be taken to effectively manage and preserve Mediterranean spring ecosystems for future generations. Even though studies on Mediterranean spring ecosystems are still scarce, our review shows there are sufficient data to conclude that their future viability as functional ecosystems is under severe threat.

Detecting Streamflow in Dryland Rivers Using CubeSats.

Determining the flow regime of non-perennial rivers is critical in hydrology. In this study, we developed a new approach using CubeSat imagery to detect streamflow presence using differences in surface reflectance for areas within and outside of a river reach. We calibrated the approach with streamflow records in the Hassayampa River of Arizona over 3 years (2019-2021), finding good agreement in the annual fractions of flowing days at stream gages (R 2 = 0.82, p < 0.0001). Subsequently, annual fractions of flowing days were derived at 90 m intervals along the Hassayampa River, finding that 12% of reaches were classified as intermittent, with the remaining as ephemeral. Using a Hovmöller diagram, streamflow presence was visualized in unprecedented spatiotemporal detail, allowing estimates of daily fraction of flowing channel and annual fractions of flowing days. This new tool opens avenues for detecting streamflow and studying hydrological and biogeochemical processes dependent on water presence in drylands.

Landscape-scale restoration minimizes tree growth vulnerability to 21st century drought in a dry forest.

Increasing aridity is a challenge for forest managers and reducing stand density to minimize competition is a recognized strategy to mitigate drought impacts on growth. In many dry forests, the most widespread and common forest management programs currently being implemented focus on restoration of historical stand structures, primarily to minimize fire risk and enhance watershed function. The implications of these restoration projects for drought vulnerability are not well understood. Here, we examined how planned restoration treatments in the Four Forests Restoration Initiative, the largest forest restoration project in the United States, would alter landscape-scale patterns of forest growth and drought vulnerability throughout the 21st century. Using drought-growth relationships developed within the landscape, we considered a suite of climate and treatment scenarios and estimated average forest growth and the proportion of years with extremely low growth as a measure of vulnerability to long-term decline. Climatic shifts projected for this landscape include higher temperatures and shifting seasonal precipitation that promotes lower soil moisture availability in the early growing season and greater hot-dry stress, conditions negatively associated with tree growth. However, drought severity and the magnitude of future growth declines were moderated by the thinning treatments. Compared to historical conditions, proportional growth in mid-century declines by ~40% if thinning ceases or continues at the status quo pace. By comparison, proportional growth declines by only 20% if the Four Forest Restoration Initiative treatments are fully implemented, and <10% if stands are thinned even more intensively than currently planned. Furthermore, restoration treatments resulted in dramatically fewer years with extremely low growth in the future, a recognized precursor to forest decline and eventual tree mortality. Benefits from density reduction for mitigating drought-induced growth declines are more apparent in mid-century and under RCP4.5 than under RCP8.5 at the end of the century. Future climate is inherently uncertain, and our results only reflect the climate projections from the representative suite of models examined. Nevertheless, these results indicate that forest restoration projects designed for other objectives also have substantial benefits for minimizing future drought vulnerability in dry forests and provide additional incentive to accelerate the pace of restoration.

Response of bean cultures' water use efficiency against climate warming in semiarid regions of China.

Farm crop growing and high efficiency water resource utilizing are directly influenced by global warming, and a new challenge will be given to food and water resource security. A simulation experiment by farm warming with infrared ray radiator was carried out, and the result showed photosynthesis of broad bean was significantly faster than transpiration during the seedling stage, ramifying stage, budding stage, blooming stage and podding stage when the temperate was increased by 0.5-1.5 °C. But broad bean transpiration was faster than photosynthesis during the budding stage, blooming stage and podding stage when the temperature was increased by 1.5 °C above. The number of grain per hill and hundred-grain weight were significantly increased when the temperature was increased by 0.5-1.0 °C. But they significantly dropped and finally the yield decreased when the temperature was increased by 1.0 °C above. The broad bean yield decreased by 39.2-88.4% when the temperature was increased by 1.5-2.0 °C. The broad bean water use efficiency increased and then decreased with temperature rising. The water use efficiency increased when the temperature was increased by 1.0 °C below, and it quickly decreased when the temperature was increased by 1.0 °C above. In all, global warming in the future will significantly influence the growth, yield and water use efficiency of bean cultures in China's semiarid regions.

Phylogenetic relationships of North American western chubs of the genus Gila (Cyprinidae, Teleostei), with emphasis on southern species.

Species of Gila comprise a heterogeneous and widespread group of freshwater fishes inhabiting drainage systems of western North America. The classification of species of Gila and relatives has been complicated and sometimes compromised by differences in body shapes, sizes, habitats, variable taxonomic placement by early taxonomists, and instances of hypothesized hybridization. While most attention on Gila has focused on hybridization in USA, little is actually know about their intra and intergeneric relationships. We present a molecular phylogeny using 173 specimens for all 19 recognized species of Gila, covering their entire distributions in 31 major drainages. Using one mitochondrial and three nuclear genes, specimens of Gila were analyzed with 10 other North American genera that comprise the Revised Western Clade. All analyses identified most species of Gila in a lineage that always included the monotypic genera Moapa and Acrocheilus, and we recommend the synonymy of both genera with Gila. The composition of this Gila lineage varied depending on the genes analyzed. Within the Gila lineage, similar morphotypes (forms adapted to fast currents vs. general forms) were not resolved as closest relatives. Analyses of mitochondrial DNA resolved all species of Gila from Mexico in reciprocally monophyletic clades except G. modesta. Most species of Gila in the USA were nested in 3 major clades, potentially indicating some level of historic or contemporary interspecific hybridization. Herein, we redefine the ranges for all species of Gila in Mexico. Relevant taxonomic and conservation implications stemming from the results are discussed.

Land degradation neutrality assessment and factors influencing it in China's arid and semiarid regions.

The ecosystems in China's arid and semiarid regions are notably fragile and experiencing dramatic land degradation. At the 12th Conference of the Parties (COP12) to the United Nations Convention to Combat Desertification (UNCCD) in October 2015, a definition for land degradation neutrality (LDN) was proposed and subsequently integrated into the Sustainable Development Goals (SDGs). Research on LDN has developed in terms of conceptual framework constructions, quantitative assessments, and empirical studies. However, LDN and its drivers must be clarified in China's arid and semiarid regions since some representative processes have yet to be fully considered in the assessment. Here, we develop an LDN indicator system specialised for the area, assess their LDN status, and determine the impacts of human activities and climate change on LDN. Our research aims to refine the LDN indicator system tailored for China's arid and semiarid regions by incorporating the trends of wind and water erosion. We also identify the influence of human activity and climate change on LDN, which provides insightful strategies for ecological restoration and sustainable development in drylands with climate-sensitive ecosystems. The results show that: (1) In 2020, more than half of areas of China's arid and semiarid regions achieved LDN, with more pronounced success in the southeastern areas compared to the central regions. (2) For LDN drivers, elevation shows negligible influence on LDN, whereas increased temperature promotes LDN achievement. Conversely, factors like vapour pressure deficit and v-direction wind speed hinder it. In conclusion, China's arid and semiarid regions achieved LDN, and the dominant factor that substantially influences LDN varies across geographical zones, with higher wind speeds and elevated GDP levels generally obstructing LDN in most areas.

Applicability of hybrid bionic optimization models with kernel-based extreme learning machine algorithm for predicting daily reference evapotranspiration: a case study in arid and semiarid regions, China.

The accurate prediction of daily reference crop evapotranspiration (ETO) enables effective management decision-making for agricultural water resources; this is crucial for developing water-efficient agriculture. To improve the accuracy of ETO forecasts in data-deficient areas, this study uses a decision tree algorithm (classification and regression tree [CART]) to obtain the effects of various factors on ETO at typical stations in arid and semiarid regions of China. A combination of factors with considerable influence on the model was selected as the input for constructing a kernel-extreme-learning-machine (KELM) daily reference evapotranspiration prediction model, and three bionic optimization algorithms (i.e., sparrow search optimization algorithm, Harris Hawks optimization algorithm, and lion swarm optimization algorithm) were integrated to optimize KELM prediction model parameters and improve the accuracy of daily reference evapotranspiration prediction. The results indicate that temperature (maximum or minimum temperature) is the primary factor influencing ETO, and the range of importance is 0.399-0.554. RH and Ra are also key factors influencing ETO; the hybrid model optimized using the bionic optimization algorithm provides advantages over the independent KELM model, and the SSA-KELM model has the highest accuracy among hybrid models, with a root-mean-square error of 0.408-1.964, R2 of 0.545-0.982, mean absolute error of 0.273-1.086, and Nash-Sutcliffe efficiency coefficient of 0.658-0.967. The top five factors extracted using the CART algorithm are recommended as inputs for constructing the SSA-KELM model for ETO estimation in arid and semiarid regions of China, and this model can also serve as a reference for ETO forecasting in similar regions.

Sap Flow Velocity in Fraxinus pennsylvanica in Response to Water Stress and Microclimatic Variables.

In arid and semiarid regions with water shortage, forestry development is limited by water availability. Understanding how tree sap flow responds to water stress and microclimatic variables is essential for the management of trees and the understanding of the eco-physiological properties of trees in arid areas. In the city of Tianjin in northern China, we measured the sap flow of Fraxinus pennsylvanica, a widely distributed urban greening tree species in semiarid regions of China. We measured the sap flow in four F. pennsylvanica trees over 6 months (April-September 2021), using a thermal diffusion probe method, and simultaneously monitored microclimatic variables and soil moisture. Results indicated that high nighttime sap flow velocity might be produced under the water stress condition. In addition, the nighttime sap flow velocity under the water stress condition was more susceptible to the combined effects of meteorological factors at night. The daytime sap flow velocity exerted a highly significant positive effect on the nighttime sap flow velocity during the whole research period, and the model fit was higher in the early growing season than that in the late growing season (early growing season: R 2 = 0.51, P < 0.01; late growing season: R 2 = 0.36, P < 0.01). Vapor pressure deficit had a positive effect on daytime sap flow. However, net vapor pressure deficit restrained daytime sap flow velocity when the intercorrelation between the microclimatic variables was removed. Our study highlights that drought areas perhaps have higher nighttime sap flow and that more emphasis should be placed on nighttime sap flow and the response of nighttime sap flow to microclimatic variables. In addition, the influence of other microclimatic variables on vapor pressure deficit needs to be considered when analyzing the relationship between daytime sap flow and vapor pressure deficit. An increase in net VPD can suppress the daytime sap flow.

Greywater in Egypt: the sustainable future of non-conventional water resources.

Egypt is a country with limited water resources. Egypt water needs are growing rapidly as a result of the population increase, climate change and development activities. The aim of the study is to analyse how Egypt can sustain its mega urban projects by utilizing greywater as a non-conventional water resource. A quantitative-based assessment has been conducted to investigate the overall evaluation of the greywater resources in Egypt. Greywater accounts for between 40 and 80% of the total water discharged from the house, and the total use of water for drinking and health use can be estimated at 10.4 billion cubic meters per year. The results show that the greywater resources may support a sustainable future of non-conventional water resources in a very positive way. Greywater can provide Egypt with about 4.15-8.30 billion cubic meters annually, which is a good support for water resources in Egypt. The paper concluded that greywater is an important resource to facilitate the success of the new mega urban projects. Egypt should maximize the share of greywater resources, especially in its new mega urban projects. Greywater resources can support Egypt and other arid and semiarid regions and countries in transition to a sustainable future.

Inter-comparison of stable isotope mixing models for determining plant water source partitioning.

Water sources used for plant identification coupled with stable isotopes are essential to improving the understanding of eco-hydrological processes and ecological management in water-limited ecosystems. Many approaches associated with stable isotopes have been used to determine plant water source apportionment. However, inter-comparisons of different methods are still limited, especially for Bayesian mixing models. In this study, we tested linear mixing models (IsoSource) and Bayesian models (SIAR, MixSIR and MixSIAR) to identify sources of water absorbed by Vitex negundo and Sophora viciifolia (shrubs) and Artemisia gmelinii (subshrub) during the growing season in the semiarid Loess Plateau. The results showed that there was no significant difference in the predicted plant water source fractions using only stable hydrogen isotope (δ2H) and only stable oxygen isotope (δ18O) with the IsoSource model. No significant difference was found in plant water source apportionment by the three Bayesian mixing models combined with δ2H and δ18O except for individual months. The SIAR and MixSIAR models detected no pronounced seasonal variations in plant water uptake, while the MixSIR model did detect seasonal variations. Overall, the SIAR and MixSIAR models exhibited relatively better water source apportionment performances than that of the MixSIR model. This discrepancy may be attributed to the difference in the post distribution simulation algorithm. This study provides critical insights into choosing a suitable method for identifying plant water source apportionment in arid and semiarid regions.

Seed germination and seedling growth of five desert plants and their relevance to vegetation restoration.

Due to significant decreases in precipitation in northern China, knowledge of the response of seed germination and plant growth characteristics to key limiting factors is essential for vegetation restoration. We examined seed germination under different temperatures and water potentials, and we examined seedling growth under different amounts of water supply. Experiments were carried out in automatic temperature-, humidity-, and light-controlled growth chambers. Under low water potentials, the final germination percentages of four herbaceous species were high, while seed germination of the shrub species Caragana microphylla was significantly inhibited. Under the different water supply amounts, seedlings of Agropyron cristatum allocated more biomass to the root and had a higher growth rate than those of Elymus dahuricus and C. microphylla. In light of these results and drier environmental conditions (annual mean precipitation is 366 mm, which falling mainly between June and August), potential selections for revegetation of different landscapes include the following: A. cristatum for shifting sand dunes, the establishment of the pioneer species Agriophyllum squarrosum, C. microphylla for semifixed sand dunes, E. dahuricus for fixed sand dunes, and Melilotus suaveolens and Medicago sativa for cultivation.

Environmental Groundwater Depth for Groundwater-Dependent Terrestrial Ecosystems in Arid/Semiarid Regions: A Review.

Groundwater in arid/semiarid regions plays crucial roles in providing drinking water supply, supporting irrigated agriculture, and sustaining important native terrestrial ecosystems. Groundwater depth controls water availability to vegetation and is essential for conserving groundwater-dependent terrestrial ecosystems. Environmental groundwater depth can be defined as a mean depth or a range of depths, satisfying the growth of natural vegetation that is not under stress, either due to lack of water or anoxia or soil salinization. Five methodologies have been reported to estimate environmental groundwater depth: the direct ones rely on response functions that relate vegetation condition, e.g., physiological parameters, appearance frequency, community structure, and remotely sensed physical indexes, to changes in groundwater depth; the indirect one estimates environmental groundwater depth based on the threshold of soil moisture content. To fill a knowledge gap of unique recognized methodology, a conceptual framework was proposed, which involves initial estimation (data collection, response assessment, and estimation) and feedback adjustment (implementation and modification). A key component of the framework is to quantify the linkage between ecological conditions and geohydrological features. This review may provide references for groundwater resources management, ecological conservation, and sustainable development in arid/semiarid regions.

Two new genera of metalmark butterflies of North and Central America (Lepidoptera, Riodinidae).

Two new genera of Riodinidae (Insecta: Lepidoptera) are described, Neoapodemia Trujano-Ortega, gen. n. (Neoapodemia nais (W. H. Edwards, 1876), comb. n., N. chisosensis Freeman, 1964, comb. n.) and Plesioarida Trujano-Ortega & García-Vázquez, gen. n. (Plesioarida palmerii palmerii (W. H. Edwards, 1870), comb. n., P. palmerii arizona (Austin, [1989]), comb. n., P. palmerii australis (Austin, [1989]), comb. n., P. hepburni hepburni (Godman & Salvin, 1886), comb. n., P. hepburni remota (Austin, 1991), comb. n., P. murphyi (Austin, [1989]), comb. n., P. hypoglauca hypoglauca (Godman & Salvin, 1878), comb. n., P. hypoglauca wellingi (Ferris, 1985), comb. n., P. walkeri (Godman & Salvin, 1886), comb. n., P. selvatica (De la Maza & De la Maza, 2017), comb. n.). Neoapodemia Trujano-Ortega, gen. n. is distributed in the southwestern USA and northeastern Mexico, while Plesioarida Trujano-Ortega & García-Vázquez, gen. n. is present from the southern USA to Central America. Species of these genera were previously classified as Apodemia C. Felder & R. Felder but molecular and morphological evidence separate them as new taxa. Morphological diagnoses and descriptions are provided for both new genera, including the main distinctive characters from labial palpi, prothoracic legs, wing venation and genitalia, as well as life history traits. A molecular phylogeny of one mitochondrial gene (COI) and two nuclear genes (EF-1a and wg) are also presented of most species of Apodemia, Neoapodemia Trujano-Ortega, gen. n., Plesioarida Trujano-Ortega & García-Vázquez, gen. n., and sequences of specimens from all tribes of Riodinidae. We compare the characters of Apodemia, Neoapodemia Trujano-Ortega, gen. n. and Plesioarida Trujano-Ortega & García-Vázquez, gen. n. and discuss the differences that support the description of these new taxa. This is a contribution to the taxonomy of the Riodinidae of North America of which the generic diversity is greater than previously recognized.

Seed filling in maize and hormones crosstalk regulated by exogenous application of uniconazole in semiarid regions.

In semiarid regions, deficit and unpredictable precipitation results in yield losses. Uniconazole is a plant growth regulator and its application is beneficial in water saving agriculture and improves maize production in semiarid regions. In order to determine the effects of uniconazole application on seed filling and hormonal changes of maize, a field study was conducted in the summer of 2015 and 2016. Seeds were soaked in uniconazole at concentration of 0 (SCK), 25 (S25), 50 (S50), and 75 (S75) mg kg-1, while in the second experiment, uniconazole was applied to the foliage at concentration of 0 (FCK), 25 (F25), 50 (F50), and 75 (F75) mg L-1 at the eight-leaf. Uniconazole application significantly improves the seed filling rates by regulating the endogenous hormones contents. Uniconazole seed soaking treatments improved significantly the seed filling rate of superior, middle, and inferior seeds compared with foliar application treatments. Uniconazole improved significantly the zeatin (Z) + zeatin riboside (ZR) and abscisic acid (ABA) contents while reducing the gibberellic acid (GA) content in the seeds during the process of seed filling. The Z + ZR and ABA contents were significantly positively correlated while the GA content was negatively correlated with maximum seed weight, maximum seed filling rates, and mean seed filling rates. Treatments S25 and F25 significantly improved the above dry matter accumulation plant-1, seed filling rates, ABA, Z + ZR contents, characters of ear, and grain yield while reduced the GA content. It is concluded from our results that the uniconazole application at concentration of 25 mg kg-1 as seed soaking or 25 mg L-1 foliar applied at the eight-leaf stage is beneficial to improve the seed filling rates and grain yield of maize in semiarid regions.

Soil Inorganic Carbon Sequestration Following Afforestation Is Probably Induced by Pedogenic Carbonate Formation in Northwest China.

In arid and semiarid areas, the effects of afforestation on soil organic carbon (SOC) have received considerable attention. In these areas, in fact, soil inorganic carbon (SIC), rather than SOC, is the dominant form of carbon, with a reservoir approximately 2-10 times larger than that of SOC. A subtle fluctuation of SIC pool can strongly alter the regional carbon budget. However, few studies have focused on the variations in SIC, or have used stable soil carbon isotopes to analyze the reason for SIC variations following afforestation in degraded semiarid lands. In the Mu Us Desert, northwest China, we selected a shifting sand land (SL) and three nearby forestlands (Populus alba) with ages of 8 (P-8), 20 (P-20) and 30 (P-30) years, and measured SIC, SOC, soil organic and inorganic δ13C values (δ13C-SOC and δ13C-SIC) and other soil properties. The results showed that SIC stock at 0-100 cm in SL was 34.2 Mg ha-1, and it increased significantly to 42.5, 49.2, and 68.3 Mg ha-1 in P-8, P-20, and P-30 lands, respectively. Both δ13C-SIC and δ13C-SOC within the 0-100 cm soil layer in the three forestlands were more negative than those in SL, and gradually decreased with plantation age. Afforestation elevated soil fine particles only at a depth of 0-40 cm. The entire dataset (260 soil samples) exhibited a negative correlation between δ13C-SIC and SIC content (R2 = 0.71, P < 0.01), whereas it showed positive correlation between SOC content and SIC content (R2 = 0.52, P < 0.01) and between δ13C-SOC and δ13C-SIC (R2 = 0.63, P < 0.01). However, no correlation was observed between SIC content and soil fine particles. The results indicated that afforestation on shifting SL has a high potential to sequester SIC in degraded semiarid regions. The contribution of soil fine particle deposition by canopy to SIC sequestration is limited. The SIC sequestration following afforestation is very probably caused by pedogenic carbonate formation, which is closely related to SOC accumulation. Our findings suggest that SIC plays an important role in the carbon cycle in semiarid areas and that overlooking this carbon pool may substantially lead to underestimating carbon sequestration capacity following vegetation rehabilitation.