Plant root mechanisms and their effects on carbon and nutrient accumulation in desert ecosystems under changes in land use and climate

Deserts represent key carbon reservoirs, yet as these systems are threatened this has implications for biodiversity and climate change. This review focuses on how these changes affect desert ecosystems, particularly plant root systems and their impact on carbon and mineral nutrient stocks. Desert plants have diverse root architectures shaped by water acquisition strategies, affecting plant biomass and overall carbon and nutrient stocks. Climate change can disrupt desert plant communities, with droughts impacting both shallow and deep-rooted plants as groundwater levels fluctuate. Vegetation management practices, like grazing, significantly influence plant communities, soil composition, root microorganisms, biomass, and nutrient stocks. Shallow-rooted plants are particularly susceptible to climate change and human interference. To safeguard desert ecosystems, understanding root architecture and deep soil layers is crucial. Implementing strategic management practices such as reducing grazing pressure, maintaining moderate harvesting levels, and adopting moderate fertilization can help preserve plant-soil systems. Employing socio-ecological approaches for community restoration enhances carbon and nutrient retention, limits desert expansion, and reduces CO2 emissions. This review underscores the importance of investigating belowground plant processes and their role in shaping desert landscapes, emphasizing the urgent need for a comprehensive understanding of desert ecosystems.

Self-organization as a mechanism of resilience in dryland ecosystems

Self-organized spatial patterns are a common feature of complex systems, ranging from microbial communities to mussel beds and drylands. While the theoretical implications of these patterns for ecosystem-level processes, such as functioning and resilience, have been extensively studied, empirical evidence remains scarce. To address this gap, we analyzed global drylands along an aridity gradient using remote sensing, field data, and modeling. We found that the spatial structure of the vegetation strengthens as aridity increases, which is associated with the maintenance of a high level of soil multifunctionality, even as aridity levels rise up to a certain threshold. The combination of these results with those of two individual-based models indicate that self-organized vegetation patterns not only form in response to stressful environmental conditions but also provide drylands with the ability to adapt to changing conditions while maintaining their functioning, an adaptive capacity which is lost in degraded ecosystems. Self-organization thereby plays a vital role in enhancing the resilience of drylands. Overall, our findings contribute to a deeper understanding of the relationship between spatial vegetation patterns and dryland resilience. They also represent a significant step forward in the development of indicators for ecosystem resilience, which are critical tools for managing and preserving these valuable ecosystems in a warmer and more arid world.

[Plant community differentiation of desertification region in northwest Liaoning Province, China]

Understanding plant communities in desertification area is the scientific basis of evaluating the local eco-environmental quality and carrying out desertification control. According to longitude, we divided the desertification area in northwest Liaoning Province into three regions: the eastern region (122°50'37″ -123°49'40″ E), the middle region (121°16'41″-122°35'00″ E), and the western region (119°20'03″ -120°02'41″ E), and investigated the plant communities in each region. The results showed that the proportion of forest and canopy density of tree layer increased from the west to the east. Ass. Pinus sylvestris var. mongolica and Ass. Populus sp. in the eastern, Ass. Pinus tabuliformis and Ass. Populus sp. in the middle, as well as Ass. P. tabuliformis and Ass. Prunus sibirica in the western were dominant communities, respectively. The proportion of brush community in the eastern, middle and western was 0, 22.2%, and 28.0%, respectively. Grasslands formed mainly by human disturbance in the eas-tern and middle regions. The total species numbers were 110 in the middle, 88 in the western and 75 in the eastern, respectively. Therophytes were dominant in the eastern and middle with proportions of 68.2% and 66.7%, respectively. Hemicryptophytes were the dominant type (36.3%) in the western region. The proportion of microphanerophyt, nanophanerophyte, chamaephyte, and geophyte increased from the eastern to the western. The species number, Shannon index, and Simpson diversity index of the middle were the highest among the three regions. Pielou evenness index increased gradually from the eastern to the western. Community similarity between the eastern and the western was the lowest, as shown by the β-biodiversity, and the similarity between the middle and the western was the highest. The community type, species number, characteristics of species composition and species biodiversity of the middle region had the characteristics of ecological transition zone. In general, vegetation status in the desertification area of northwest Liaoning Province was in good condition. There were still some problems including the monotonous vertical structure of forest and tree species as well as the serious human interference.

A High-Precision Remote Sensing Identification Method for Land Desertification Based on ENVINet5

Land desertification is one of the serious ecological and environmental problems facing mankind today, which threatens the survival and development of human society. China is one of the countries with the most serious land desertification problems in the world. Therefore, it is of great theoretical value and practical significance to carry out accurate identification and monitoring of land desertification and its influencing factors in ecologically fragile areas of China. This is conducive to curbing land desertification and ensuring regional ecological security. Minqin County, Gansu Province, located in northwestern China, is one of the most serious areas of land desertification, which is also one of the four sandstorm sources in China. Based on ENVINet5, this paper constructs a high-precision land desertification identification method with an accuracy of 93.71%, which analyzes the trend and reasons of land desertification in this area, provides suggestions for disaster prevention in Minqin County. and provides a reference for other similar areas to make corresponding desertification control policies.

Plant and Soil Microbial Diversity Co-Regulate Ecosystem Multifunctionality during Desertification in a Temperate Grassland

Biodiversity plays a crucial role in driving multiple ecosystem functions in temperate grasslands. However, our understanding of how biodiversity regulates the impacts of desertification processes on ecosystem multifunctionality (EMF) remains limited. In this study, we investigate plant diversity, soil microbial diversity (fungal, bacterial, archaeal, and arbuscular mycorrhizal fungal (AMF) diversity), soil properties (soil water content, pH, and soil clay content), and multiple ecosystem functions (soil N mineralization, soil phosphatase activity, AMF infection rate, microbial biomass, plant biomass, and soil C and nutrients (N, P, K, Ca, Fe, Na, Cu, Mg, and Mn)) at six different grassland desertification intensities. The random forest model was conducted to assess the importance of soil properties, plant diversity, and soil microbial diversity in driving EMF. Furthermore, a structural equation model (SEM) was employed to analyze the indirect and direct impacts of these predictors on EMF. Our study showed that plant, soil bacterial, fungal, and archaeal diversity gradually decreased with increasing desertification intensity. However, only AMF diversity was found to be less sensitive to desertification. Similarly, EMF also showed a significant decline with increasing desertification. Importantly, both plant and soil microbial diversity were positively associated with EMF during desertification processes. The random forest model and SEM revealed that both plant and soil microbial diversity were identified as important and direct predictors of EMF during desertification processes. This highlights the primary influence of above- and below-ground biodiversity in co-regulating the response of EMF to grassland desertification. These findings have important implications for planned ecosystem restoration and sustainable grassland management.

Study of Changes in the Ulan Buh Desert under the Dual Impacts of Desert Farmland Development and Climate Change

Desert farmland provides food for desert areas, but water is the main limiting factor of this region, thus desert farmland has an extremely fragile ecological environment. This study investigated the temporal and spatial variations of vegetation NDVI (Normalized Difference Vegetation Index) in the Ulan Buh Desert, China, from 1990 to 2022, using long-term Landsat satellite data obtained from the Google Earth Engine platform and local statistical data. The results showed that from 1990 to 2022, the NDVI exhibited relatively small fluctuations and a steady increase. Furthermore, the study analyzed the impact of climate factors, namely precipitation and temperature, on NDVI, and collected the groundwater lever changes under irrigation and farmland development. The results demonstrated a positive correlation between NDVI and both precipitation and temperature from 1990 to 2006. The study area experienced an overall trend of increasing humidity. Specifically, from 1990 to 2006, significant positive correlations with precipitation and temperature were observed in 4.4% and 5.5% of the region, respectively. From 2007 to 2022, significant positive correlations were observed in 5.4% and 72.8% of the region for precipitation and temperature, respectively. These findings suggest that temperature has become increasingly influential on vegetation NDVI, while the impact of precipitation remains relatively stable. Moreover, the study assessed the impact of human activities on vegetation NDVI. The results revealed that from 1990 to 2006, human activities contributed to 43.1% of the promotion of local vegetation NDVI, which increased to 90.9% from 2007 to 2022. This study provides valuable insights into the dynamics of vegetation in the Ulan Buh Desert and its response to climatic changes and human activities. The findings highlight the significance of climate conditions and human interventions in shaping the vegetation dynamics in the region, offering essential information for ecological restoration and conservation efforts.

Effects of fine substance content in soil substrate on the formation of artificial cyanobacteria crusts

The use of artificial cyanobacteria crusts is one of the effective methods to prevention and control of desertification. Soil fine substance is one of the important factors limiting the colonization and growth of artificial cyanobacteria crusts. We compared the growth of artificial cyanobacterial crusts with different fine substance contents by setting the volume ratios of fine substance to quicksand as 0:1, 1:1, 2:1, 4:1 and 1:0. The results showed that the cover of artificial cyanobacteria crusts increased gradually with the increases of fine substance contents, while the contents of chlorophyll a and extracellular polysaccharide firstly increased and then decreased slightly. The optimum growth of artificial cyanobacterial crusts was achieved under the treatment of 4:1 ratio. Under such treatment after 60 days of incubation, artificial cyanobacteria crusts cover was 70%, and the contents of chlorophyll a, loosely bound exopolysaccharide (LB-EPS), tightly bound exopolysaccharide (TB-EPS), and glycocalyx exopolysaccharide (G-EPS) were 17.5, 70.0, 175.0, and 200.0 μg·cm-2, respectively. Increasing the amount of cyanobacteria under the condition of low fine substance content could promote the formation and growth of artificial cyanobacterial crusts (0.5 g of cyanobacteria per petri dish was the optimal). It could provide a new idea for the large-scale culture of artificial cyanobacterial crusts inoculum.

Adapting to Climate Change with Opuntia

Adapting our food production chain and increasing the flora and fauna's livelihood in climate change-affected areas using Opuntia is not only theoretical but already exists in practice in many places. This cactus grows in unsuitable soil for most species as it is adapted to arid and semi-arid soils and hot weather. In these regions, Opuntia protects from erosion and contributes to soil health. The usage of this plant as fodder is also discussed, with immense potential in substituting a part of livestock's diet and even increasing the quality of the animal's by-products and decreasing water consumption. This would result in a feed that is low-cost and has a lower environmental impact. It is to be noted that Opuntia has a high potential as an invasive species, with caution always being recommended when dealing with this specie. The high content of specific compounds, such as proline, indicaxanthin, and betanin, found in Opuntia ficus-indica, influence the plant's adaptation to unfavourable conditions. This collective evidence depicts Opuntia as a crop that can battle climate change and ensure food security.

Analysis of Growing Season Normalized Difference Vegetation Index Variation and Its Influencing Factors on the Mongolian Plateau Based on Google Earth Engine

Frequent dust storms on the Mongolian Plateau have adversely affected the ecological environmental quality of East Asia. Studying the dynamic changes in vegetation coverage is one of the important means of evaluating ecological environmental quality in the region. In this study, we used Landsat remote sensing images from 2000 to 2019 on the Mongolian Plateau to extract yearly Normalized Difference Vegetation Index (NDVI) data during the growing season. We used partial correlation analysis and the Hurst index to analyze the spatiotemporal characteristics of the NDVI before and after the establishment of nature reserves and their influencing factors on the GEE cloud platform. The results showed that (1) the proportion of the region with an upwards trend of NDVI increased from 52.21% during 2000-2009 to 67.93% during 2010-2019, indicating a clear improvement in vegetation due to increased precipitation; (2) the increase in precipitation and positive human activities drove the increase in the NDVI in the study region from 2000 to 2019; and (3) the overall trend of the NDVI in the future is expected to be stable with a slight decrease, and restoration potential is greater for water bodies and grasslands. Therefore, it is imperative to strengthen positive human activities to safeguard vegetation. These findings furnish scientific evidence for environmental management and the development of ecological engineering initiatives on the Mongolian Plateau.

The role of invasive plant species in drought resilience in agriculture: the case of sweet briar (Rosa rubiginosa L.)

Sweet briar (Rosa rubiginosa) belongs to the group of wild roses. Under natural conditions it grows throughout Europe, and was introduced also into the southern hemisphere, where it has efficiently adapted to dry lands. This review focuses on the high adaptation potential of sweet briar to soil drought in the context of global climatic changes, especially considering steppe formation and desertification of agricultural, orchard, and horticultural areas. We provide a comprehensive overview of current knowledge on sweet briar traits associated with drought tolerance and particularly water use efficiency, sugar accumulation, accumulation of CO2 in intercellular spaces, stomatal conductance, gibberellin level, effective electron transport between photosystem II and photosystem I, and protein content. We discuss the genetics and potential applications in plant breeding and suggest future directions of study concerning invasive populations of R. rubiginosa. Finally, we point out that sweet briar can provide new genes for breeding in the context of depleting gene pools of the crop plants.

South American Dry Chaco rangelands: Positive effects of cattle trampling and transit on ecohydrological functioning

Livestock production in drylands requires consideration of the ecological applications of ecohydrological redistribution of water. Intensive cattle trampling and the associated increase of surface runoff are common concerns for rangeland productivity and sustainability. Here, we highlight a regional livestock production system in which cattle trails and trampling surrounding an artificial impoundment are purposely managed to enhance redistribution and availability of water for cattle drinking. Based on literature synthesis and field measurements, we first describe cattle production systems and surface water redistribution in the Dry Chaco rangelands of South America, and then develop a conceptual framework to synthesize the ecohydrological impacts of livestock production on these ecosystems. Critical to this framework is the pioshere-a degraded overgrazed and overtrampled area where vegetation has difficulties growing, usually close to the water points. The Dry Chaco rangelands have three key distinctive characteristics associated with the flat sedimentary environment lacking fresh groundwater and the very extensive ranching conditions: (1) cattle drinking water is provided by artificial impoundments filled by runoff, (2) heavy trampling around the impoundment and its adjacent areas generates a piosphere that favors runoff toward the impoundment, and (3) the impoundment, piosphere, and extensive forage areas are hydrologically connected with a network of cattle trails. We propose an ecohydrological framework where cattle transit and trampling alter the natural water circulation of these ecosystems, affecting small fractions of the landscape through increased runoff (compaction in piosphere and trails), surface connectivity (convergence of trails to piosphere to impoundment), and ponding (compaction of the impoundment floor) that operate together making water harvesting and storage possible. These effects have likely generated a positive water feedback on the expansion of livestock in the region with a relatively low impact on forage production. We highlight the role of livestock transit as a geomorphological agent capable of reshaping the hydrology of flat sedimentary rangelands in ways that can be managed positively for sustainable ranching systems. We suggest that the Dry Chaco offers an alternative paradigm for rangelands in which cattle trampling may contribute to sustainable seminatural production systems with implications for other dry and flat rangelands of the world.

Monitoring Land Degradation Dynamics to Support Landscape Restoration Actions in Remote Areas of the Mediterranean Basin (Murcia Region, Spain)

This study aims to develop a workflow methodology for collecting substantial amounts of Earth Observation data to investigate the effectiveness of landscape restoration actions and support the implementation of the Above Ground Carbon Capture indicator of the Ecosystem Restoration Camps (ERC) Soil Framework. To achieve this objective, the study will utilize the Google Earth Engine API within R (rGEE) to monitor the Normalized Difference Vegetation Index (NDVI). The results of this study will provide a common scalable reference for ERC camps globally, with a specific focus on Camp Altiplano, the first European ERC located in Murcia, Southern Spain. The coding workflow has effectively acquired almost 12 TB of data for analyzing MODIS/006/MOD13Q1 NDVI over a 20-year span. Additionally, the average retrieval of image collections has yielded 120 GB of data for the COPERNICUS/S2_SR 2017 vegetation growing season and 350 GB of data for the COPERNICUS/S2_SR 2022 vegetation winter season. Based on these results, it is reasonable to asseverate that cloud computing platforms like GEE will enable the monitoring and documentation of regenerative techniques to achieve unprecedented levels. The findings will be shared on a predictive platform called Restor, which will contribute to the development of a global ecosystem restoration model.

Effects of Vertically Heterogeneous Soil Salinity on Genetic Polymorphism and Productivity of the Widespread Halophyte Bassia prostrata

Salinity is one of the environmental factors that affects both productivity and genetic diversity in plant species. Within the soil profile, salinity is a dynamic indicator and significantly changes with depth. The present study examined the effects of the vertical heterogeneity of soil salinity chemistry on the plant height, fresh and dry biomass accumulation, water content, level of genetic polymorphism, and observed and expected heterozygosity in seven populations of halophyte Bassia prostrata in natural habitats. Soil salinity ranged from slight (S_salts = 0.11-0.25%) to extreme (S_salts = 1.35-2.57%). The main contributors to salinity were Na⁺, Ca²⁺, and Mg²⁺. Multivariate analysis revealed that biomass accumulation is positively affected by moderate/high salinity in 20-60 cm soil layers, which may be associated with the salt required for the optimal growth of the halophyte B. prostrata. The formation of seed genetic diversity is negatively affected by slight/moderate salinity in the 0-40 cm layers. An increase in divalent ion content can reduce genetic diversity and increase the local adaptation of B. prostrata to magnesium-calcium sulfate salinity. The effect of the in-depth distribution of soil salinity on productivity and genetic diversity may be related to seasonal variables during biomass accumulation (summer) and seed formation (autumn).

Facile Access to Gleditsia microphylla Galactomannan Hydrogel with Rapid Self-Repair Capacity and Multicyclic Water-Retaining Performance of Sandy Soil

Sandy soil has poor water-holding performance, making it difficult for plants to survive, which worsens the deterioration of the ecological environment. Therefore, borax cross-linked Gleditsia microphylla galactomannan hydrogel (GMGH) was prepared, and its practicability as a water-retaining agent was analyzed. GMGH exhibited fast self-healing performance (150 s, ≈100%) and a high swelling index (88.70 g/g in pH 9). The feasibility of improving the water absorption and retention properties of sandy soil was explored by mixing different proportions (0.1, 0.3, 0.5 wt % sandy soil) of GMGH and sandy soil. The results showed that sandy soil had a more porous structure after adding 0.5 wt % GMGH, and its water absorption index increased from 15.68 to 38.12%. In an artificial climate box, the water-holding time of the sandy soil was extended from 3 to 23.5 days, and the cycles of water absorption and retention were more than 10 times. Therefore, GMGH has broad application prospects as a potential water-retaining agent for desertification control.

Biological invasions and climate change amplify each other's effects on dryland degradation

Climate models predict that, in the coming decades, many arid regions will experience increasingly hot conditions and will be affected more frequently by drought. These regions are also experiencing rapid vegetation change, notably invasion by exotic grasses. Invasive grasses spread rapidly into native desert ecosystems due, in particular, to interannual variability in precipitation and periodic fires. The resultant destruction of non-fire-adapted native shrub and grass communities and of the inherent soil resource heterogeneity can yield invader-dominated grasslands. Moreover, recurrent droughts are expected to cause widespread physiological stress and mortality of both invasive and native plants, as well as the loss of soil resources. However, the magnitude of these effects may differ between invasive and native grasses, especially under warmer conditions, rendering the trajectory of vegetated communities uncertain. Using the Biosphere 2 facility in the Sonoran Desert, we evaluated the viability of these hypothesized relationships by simulating combinations of drought and elevated temperature (+5°C) and assessing the ecophysiological and mortality responses of both a dominant invasive grass (Pennisetum ciliare or buffelgrass) and a dominant native grass (Heteropogan contortus or tanglehead). While both grasses survived protracted drought at ambient temperatures by inducing dormancy, drought under warmed conditions exceeded the tolerance limits of the native species, resulting in greater and more rapid mortality than exhibited by the invasive. Thus, two major drivers of global environmental change, biological invasion and climate change, can be expected to synergistically accelerate ecosystem degradation unless large-scale interventions are enacted.

Effects of Irrigation and Fertilization on the Morphophysiological Traits of Populus sibirica Hort. Ex Tausch and Ulmus pumila L. in the Semiarid Steppe Region of Mongolia

Desertification is impeding the implementation of reforestation efforts in Mongolia. Many of these efforts have been unsuccessful due to a lack of technical knowledge on water and nutrient management strategies, limited financial support, and short-lived rainfall events. We investigated the effects of irrigation and fertilization on the morphophysiological traits of Populus sibirica Hort. Ex Tausch and Ulmus pumila L. and to suggest irrigation and fertilization strategies for reforestation. Different irrigation and fertilizer treatments were applied: no irrigation, 2 L h^-1, 4 L h^-1, and 8 L h^-1 of water; no fertilizer, 2 L h^-1 + NPK, 4 L h^-1 + NPK, and 8 L h^-1 + NPK; and no compost, 2 L h^-1 + compost, 4 L h^-1 + compost, and 8 L h^-1 + compost. The leaf area (LA) and specific leaf area (SLA) of both species responded positively to 4 and 8 L h^-1. Results also showed that the addition of either NPK or compost to 4 or 8 L h^-1 irrigation resulted in a higher LA, SLA, and leaf biomass (LB). Total chlorophyll content decreased with irrigation in both species. The same pattern was detected when a higher amount of irrigation was combined with fertilizers. Lastly, we found that both diurnal and seasonal leaf water potential of plants grown in 4 or 8 L h^-1 were significantly higher than those of plants grown in control plots. Therefore, 4 or 8 L h^-1 with either NPK or compost has shown to be the optimal irrigation and fertilization strategy for the species in an arid and semiarid region of Mongolia. Results should provide us with a better understanding of tree responses to varying amounts of irrigation with or without fertilizer in pursuit of sustainable forest management in arid and semiarid ecosystems.

Effects of Climate Change on Vegetation Cover in the Oued Lahdar Watershed. Northeastern Morocco

Episodes of drought that Morocco experienced in the years 1984–1986, 1993–1995, and 1997–2000 had repercussions that were felt many years later and continue to pose serious problems for environmentalists, as some of the affected lands have become practically deserted. These problems acted on the socio-economic conditions and created severe constraints for the development of the country. This work was conducted to study and identify changes that occurred in vegetation cover in the Oued Lahdar watershed (Rif, Morocco) between 1984 and 2017 using Land Surface Temperature (LST), Normalized Difference Vegetation Index (NDVI), Landsat TM 5, and Landsat OLI 8. The LST had significantly increased overall from 1984 to 2017, where it moved from a mean value of 29.4 °C in 1984 to 40.4 °C in 2007 and then reduced slightly to 37.9 °C in 2017. The vegetation cover index for the study area indicates that in 1984, fully vegetated areas represented 94.3% before deteriorating to 35.4% in 2007 and recovering in 2017 to 54.3%. While bare soil, which previously constituted 5.7%, reached a very high value of 64.6% in 2007 and then decreased to 47.7%. This study contributes towards society as it provides interesting data about the consequences of climate change in the area studied as well as potential protective strategies to protect vegetation cover.

[Dynamics of desertification in the lower reaches of Shiyang River Basin, Northwest China during 1995-2018]

We collected remote sensing images of lower reaches of the Shiyang River Basin in 1995, 2000, 2005, 2010, 2015, and 2018. We analyzed the dynamics of desertification in Minqin County by constructing desertification difference index, using RS and GIS theories and methods. We established the Albedo-NDVI feature space based on the normalized vegetation index (NDVI) and surface albedo (Albedo). The results showed that the desertification area in the lower reaches of Shi-yang River Basin accounted for more than 90% of the total area of the Minqin. Oasis scattered in large areas of desertified land. Moderate desertification accounted for more than 70% of the total area of the county. The area of desertification in Minqin showed an decreasing trend from 1995 to 2018, with an average annual reduction area of 22.06 km² and an average annual reduction rate of 0.1%. During the study period, various types of desertification area contracted and expanded simultaneously, and the relative changes of severe, moderate, mild, and slight desertification areas were -1.5%, 0.2%, -0.9%, and 3.8% respectively. Those results indicated that the severity of desertification was reduced. The desertification area was generally at a stable state. There was no large-scale desertification process and no obvious trends of desertification. Desertification control had achieved phased results. In the study area, the area where the desertification decreased in a fluctuation way accounted for 15.2%, while the area with increased desertification only accounted for 3.9%. The areas with irregular fluctuations of desertification were mainly distributed in the transitional area of desert oasis and the edge area of oasis, with an area of 17.7% of the total land area. The desertification change was more active in the ecotone of oasis and desert area, which was the key control and repair region in the future.

Investigating the Drought and Salinity Effect on the Redox Components of Sulla Coronaria (L.) Medik

For the Mediterranean region, climate models predict an acceleration of desertification processes, thus threatening agriculture. The present work aimed to investigate the effect of drought and salinity on Sulla coronaria (L.) Medik., a Mediterranean forage legume, for understanding plant defence systems activated by these stressors. In detail, we focused our attention on the variations on the plant redox status. Plants were subjected to suboptimal watering and irrigation with sodium chloride (NaCl) solutions. The same salt treatment was applied for in vitro tests on seedlings. Water content did not change after treatments. Salt negatively influenced seed germination and seedling development, but it did not affect photosynthesis parameters, contrary to what was observed in adult plants. Proline concentration increased in all samples, while abscisic acid level increased exclusively in seedlings. NaCl caused accumulation of superoxide anion in plants and seedlings and hydrogen peroxide only in seedlings; nevertheless, lipid peroxidation was not detected. Total phenolics, glutathione, expression level, and activity of antioxidant enzymes were assayed, revealing a complex antiradical molecular response, depending on the type of stress and development stage. Our results confirm Sulla as a drought- and salt-tolerant species and highlight its ability to counteract oxidative stress. This evidence suggests a key role for the redox components, as signal transduction messengers, in Sulla acclimation to desertification. Finally, plants and seedlings showed different acclimation capacity to salinity, revealing a greater genomic plasticity for seedlings.

When Land Is Under Pressure Health Is Under Stress

The land provides vital resources to support life on Earth. Land ecosystems services have social, cultural, and spiritual benefits and promote human health and well-being. However, human activities, particularly ongoing unsustainable land practices, are negatively impacting ecosystems through desertification, land degradation and drought (DLDD). This article highlights the pressures and impacts of DLDD on human health through exposure pathways, including water security and safety; sanitation and hygiene; food security and safety; air quality; and soil quality. We describe the impacts on 19 health outcomes in three groups: non-communicable diseases; injuries; and infections, parasitic and nutritional diseases. The magnitude of these health impacts is mediated by social, economic, and health system-related factors. We propose actions for the health sector to respond to the DLDD challenges.

Effects of Nitrogen Addition and Reproductive Effort on Nutrient Resorption of a Sand-Fixing Shrub

Caragana microphylla is a sand-fixing leguminous shrub with strong resistance to drought, cold, and low soil fertility. As a result, it plays an essential role in combating desertification in northern China, but little is known about its nutrient budget. Nutrient resorption is a key process in plant nutrient conservation and has marked ecological implications for plant fitness and ecosystem nutrient cycling. We studied the effects of both nitrogen (N) addition and reproductive effort on leaf N resorption of C. microphylla in a temperate semi-arid sandy land in China. The results showed that sprouting of the early leaves from over-wintered buds employs a strategy for slow returns on nutrient investment with smaller specific leaf area (SLA) and higher N resorption efficiency, whereas the late leaves, which sprout from current-year buds, employ a strategy for quick returns on nutrient investment with higher SLA and lower N resorption efficiency. N addition significantly increased the N resorption efficiency from early leaves while exerting no impact on late leaves, suggesting that the increased N recovery from early leaves is done to sustain the high N demands of late leaves. Reproductive effort did not affect the N resorption from early or late leaves due to the temporal separation between fruit production and leaf senescence. Taken together, our results demonstrate that C. microphylla has evolved different investment strategies for leaf N in early and late leaves to conserve nutrients and facilitate its growth in desertified environments.

A lesson unlearned? Underestimating tree cover in drylands biases global restoration maps

Two recent global maps of tree restoration potential have identified vast regions where tree cover could be increased, ranging from 0.9 to 2.3 billion hectares. Both maps, however, emphasized dryland regions, with arid biomes making up 36%-42% of potential restoration area. Dryland biomes have repeatedly been recognized as inappropriate regions for expanding tree cover due to the risks of biodiversity loss, water overconsumption, and fire, so maps that highlight these regions for restoration must sustain careful scrutiny. Here, I show that both recent attempts to map restoration potential in arid regions have been hindered by underlying errors in the global tree cover maps they used. Systematic underestimates of existing sparse tree cover led directly to large overestimates of the potential for tree recovery in drylands. The Atlas of Forest Landscape Restoration Opportunities (Laestadius et al., Unasylva, 2011, 62, 47) overestimated tree restoration potential across a third of arid biomes by between 7% and 20% (55-166 million hectares [Mha]). Similarly, Bastin, Finegold, Garcia, Mollicone, et al. (Science, 2019, 365, 76) overestimated tree restoration potential across all arid biomes by 33%-45% (316-440 Mha). These inaccuracies limit the utility of this research for policy decisions in drylands and overstate the potential for tree planting to address climate change. Given this long-standing but underappreciated challenge in mapping global tree cover, I propose various ways forward that keep this lesson in mind. To better monitor and restore tree cover, I call for re-interpretation and correction of existing global maps, and for a new focus on quantifying sparse tree cover in drylands and other systems.

Theoretical Approaches and Practical Assessment of Socio-Economic Effects of Desertification in Mongolia

In this paper, we consider the effects of desertification in Mongolia, where the area of degraded land has increased significantly in the recent decade. Currently, almost the entire territory of the country is subject to varying degrees of degradation. The intensity of the desertification processes in different natural zones is influenced by both natural climatic and anthropogenic factors. The purpose of this study is to evaluate the impact of desertification on environmental and socio-economic living conditions, as well as on living standards of the local population. In this work, for the first time, the socio-economic aspects of desertification have been studied on a common methodological basis in different Mongolian aimags over a ten-year period. In order to carry out in-depth research, we used the submeridional and sublatitudinal principles for selecting the model study areas, as well as specific criteria and expert assessment. We used a sociological survey as the main method, based on a designed questionnaire, which was translated into Mongolian. The questionnaire includes questions regarding the influence of desertification on traditional nomadic farming, health of family members, water supply of households, water quality, living standards, etc. The results of the sociological surveys made it possible to draw conclusions on the impact of desertification on households, to identify the main problems of local people, and to describe the dynamics of the socio-economic status of the population living in the model areas. Our studies have demonstrated the intensification of the impact of desertification processes in different natural zones, administrative-territorial units and settlement systems in Mongolia.

Modifying connectivity to promote state change reversal: the importance of geomorphic context and plant-soil feedbacks

Alternative states maintained by feedbacks are notoriously difficult, if not impossible, to reverse. Although positive interactions that modify soil conditions may have the greatest potential to alter self-reinforcing feedbacks, the conditions leading to these state change reversals have not been resolved. In a 9-yr study, we modified horizontal connectivity of resources by wind or water on different geomorphic surfaces in an attempt to alter plant-soil feedbacks and shift woody-plant-dominated states back toward perennial grass dominance. Modifying connectivity resulted in an increase in litter cover regardless of the vector of transport (wind, water) followed by an increase in perennial grass cover 2 yr later. Modifying connectivity was most effective on sandy soils where wind is the dominant vector, and least effective on gravelly soils on stable surfaces with low sediment movement by water. We found that grass cover was related to precipitation in the first 5 yr of our study, and plant-soil feedbacks developed following 6 yr of modified connectivity to overwhelm effects of precipitation on sandy, wind-blown soils. These feedbacks persisted through time under variable annual rainfall. On alluvial soils, either plant-soil feedbacks developed after 7 yr that were not persistent (active soils) or did not develop (stable soils). This novel approach has application to drylands globally where desertified lands have suffered losses in ecosystem services, and to other ecosystems where connectivity-mediated feedbacks modified at fine scales can be expected to impact plant recovery and state change reversals at larger scales, in particular for wind-impacted sites.

Which practices co-deliver food security, climate change mitigation and adaptation, and combat land degradation and desertification?

There is a clear need for transformative change in the land management and food production sectors to address the global land challenges of climate change mitigation, climate change adaptation, combatting land degradation and desertification, and delivering food security (referred to hereafter as "land challenges"). We assess the potential for 40 practices to address these land challenges and find that: Nine options deliver medium to large benefits for all four land challenges. A further two options have no global estimates for adaptation, but have medium to large benefits for all other land challenges. Five options have large mitigation potential (>3 Gt CO2 eq/year) without adverse impacts on the other land challenges. Five options have moderate mitigation potential, with no adverse impacts on the other land challenges. Sixteen practices have large adaptation potential (>25 million people benefit), without adverse side effects on other land challenges. Most practices can be applied without competing for available land. However, seven options could result in competition for land. A large number of practices do not require dedicated land, including several land management options, all value chain options, and all risk management options. Four options could greatly increase competition for land if applied at a large scale, though the impact is scale and context specific, highlighting the need for safeguards to ensure that expansion of land for mitigation does not impact natural systems and food security. A number of practices, such as increased food productivity, dietary change and reduced food loss and waste, can reduce demand for land conversion, thereby potentially freeing-up land and creating opportunities for enhanced implementation of other practices, making them important components of portfolios of practices to address the combined land challenges.

The effect of climate change on the resilience of ecosystems with adaptive spatial pattern formation

In a rapidly changing world, quantifying ecosystem resilience is an important challenge. Historically, resilience has been defined via models that do not take spatial effects into account. These systems can only adapt via uniform adjustments. In reality, however, the response is not necessarily uniform, and can lead to the formation of (self-organised) spatial patterns - typically localised vegetation patches. Classical measures of resilience cannot capture the emerging dynamics in spatially self-organised systems, including transitions between patterned states that have limited impact on ecosystem structure and productivity. We present a framework of interlinked phase portraits that appropriately quantifies the resilience of patterned states, which depends on the number of patches, the distances between them and environmental conditions. We show how classical resilience concepts fail to distinguish between small and large pattern transitions, and find that the variance in interpatch distances provides a suitable indicator for the type of imminent transition. Subsequently, we describe the dependency of ecosystem degradation based on the rate of climatic change: slow change leads to sporadic, large transitions, whereas fast change causes a rapid sequence of smaller transitions. Finally, we discuss how pre-emptive removal of patches can minimise productivity losses during pattern transitions, constituting a viable conservation strategy.

Differential Impact of Salinity Stress on Seeds Minerals, Storage Proteins, Fatty Acids, and Squalene Composition of New Quinoa Genotype, Grown in Hyper-Arid Desert Environments

The effects of climate change and soil salinization on dryland ecosystems are already widespread, and ensuring food security is a crucial challenge. In this article, we demonstrate changes in growth performance and seed quality of a new high-yielding quinoa genotype (Q5) exposed to sodium chloride (NaCl), sodium sulfate (Na₂SO₄), and mixed salts (NaCl + Na₂SO₄). Differential responses to salt stress in growth performance, seed yield, and seed quality were identified. High salinity (mixed Na₂SO₄ + NaCl) reduces plant height by ∼30%, shoot and root dry weights by ∼29%, head panicle length and panicle weight by 36-43%, and seed yield by 37%, compared with control conditions. However, the 1,000-seed weight changes insignificantly under salinity. High content of essential minerals, such as Fe, Zn, and Ca in quinoa Q5 seeds produced under salinity, gives the Q5 genotype a remarkable advantage for human consumption. Biomarkers detected in our studies show that the content of most essential amino acids is unchanged under salinity. The content of amino acids Pro, Gly, and Ile positively correlates with Na⁺ concentration in soil and seeds, whereas the content of squalene and most fatty acids negatively correlates. Variation in squalene content under increasing salinity is most likely due to toxic effects of sodium and chlorine ions as a result of the decrease in membrane permeability for ion movement as a protective reaction to an increase in the sodium ion concentration. Low squalene accumulation might also occur to redirect the NADPH cofactor to enhance the biosynthesis of proline in response to salinity, as both syntheses (squalene and proline) require NADPH. This evidence can potentially be used by the food and pharmaceutical industries in the development of new food and health products.

Diversity of arbuscular mycorrhizal fungi associated with acacia trees in southwestern Saudi Arabia

Acacia species produce extensive, deep root systems with a capacity to develop mycorrhizal symbioses that facilitate plant nutrition via enhanced soil nutrient absorption. This study aimed to evaluate the mycorrhizal status and the diversity of arbuscular mycorrhizal fungi (AMF) associated with acacia trees in southwestern Saudi Arabia. The mycorrhizal status varied greatly between species. The highest values of AMF root colonization and spore density were observed in the roots and in the rhizospheric soil of Acacia negrii. DNA was extracted from plant roots and the AMF large subunit ribosomal DNA (LSU rDNA) was amplified by a nested polymerase chain reaction. A total of 274 LSU rDNA cloned fragments from roots of the three acacia trees were sequenced. Phylogenetic analysis revealed a high AMF diversity, especially in Acacia tortilis. On the basis of LSU rDNA sequences, AMF was grouped into five genera: Glomus, Claroideoglomus, Acaulospora, Gigaspora, and Scutellospora. The genus Glomus fungi were the dominant colonizers of all three acacia species, while the genus Scutellospora fungi were found only in A. tortilis roots. The high AMF-acacia diversity suggests that AMF plays an important role in the sustainability of acacia species in the arid environment.

[Response of soil microbial biomass and microbial entropy to desertification in desert grassland]

Using an approach of spatial sequence instead of temporal succession, we investigated the variation and driving factors of soil microbial biomass and microbial entropy in desert grasslands across four different desertification stages (grassland, fixed dune, semi-fixed dune and mobile dune) in Yanchi County, Ningxia, China. The results showed that soil microbial biomass carbon, nitrogen and phosphorus reduced by 46.1%, 80.8% and 30.0% from grassland to mobile dunes, respectively. The soil microbial entropy (qMBC, qMBN, and qMBP) decreased but soil-microbial stoichiometry imbalance (C:N_imb, C:P_imb and N:P_imb) generally increased with the development of desertification. There were significantly positive relationship between soil microbial biomass nitrogen and C:N_imb, soil microbial biomass phosphorus and C:P_imb, while negative relationship between soil microbial biomass nitrogen and N:P_imb. The RDA result showed that soil ecological stoichiometry (C:N, C:P) had the strongest negative effect on soil microbial entropy carbon (qMBC). Soil microbial biomass and microbial entropy were significantly affected by desertification in desert grassland.

Grazing and Cultivated Grasslands Cause Different Spatial Redistributions of Soil Particles

The distribution of soil particle sizes is closely related to soil health condition. In this study, grasslands under different grazing intensities and different cultivation ages grasslands were selected to evaluate the dynamics of soil particle size redistribution in different soil layers. When the grazing intensity increased, the percentage of 2000~150-μm soil particles in the 0–10-cm soil layer decreased; 150~53-μm soil particles remained relatively stable among the grazing intensities—approximately 28.52%~35.39%. However, the percentage of less than 53-μm soil particles increased. In cultivated grasslands, the larger sizes (>53 μm) of soil particles increased and the smaller sizes (<53 μm) decreased significantly (p < 0.05) in the 0–10 cm-soil layer with increasing cultivation ages. The increase in small soil particles (<53 μm) in topsoil associated with grazing intensity increased the potential risk of further degradation by wind erosion. The increase in big soil particles (>53 μm) in topsoil associated with cultivation ages decreased the soil capacity of holding water and nutrient. Therefore, to maintain the sustainability of grassland uses, grazing grasslands need to avoid heavy grazing, and cultivated grasslands need to change current cultivation practices.

Grazing Away the Resilience of Patterned Ecosystems

Ecosystems' responses to changing environmental conditions can be modulated by spatial self-organization. A prominent example of this can be found in drylands, where formation of vegetation patterns attenuates the magnitude of degradation events in response to decreasing rainfall. In model studies, the pattern wavelength responds to changing conditions, which is reflected by a rather gradual decline in biomass in response to decreasing rainfall. Although these models are spatially explicit, they have adopted a mean-field approach to grazing. By taking into account spatial variability when modeling grazing, we find that (over)grazing can lead to a dramatic shift in biomass, so that degradation occurs at rainfall rates that would otherwise still maintain a relatively productive ecosystem. Moreover, grazing increases the resilience of degraded ecosystem states. Consequently, restoration of degraded ecosystems could benefit from the introduction of temporary small-scale exclosures to escape from the basin of attraction of degraded states.

Productivity and Quality of Alpine Grassland Vary With Soil Water Availability Under Experimental Warming

The plant productivity of alpine meadow is predicted to generally increase under a warming climate, but it remains unclear whether the positive response rates will vary with soil water availability. Without consideration of the response of community composition and plant quality, livestock grazing under the current stocking rate might still lead to grassland degradation, even in meadows with high plant biomass. We have conducted a warming experiment from 2010 to 2017 to examine the interactive effects of warming and soil water availability on plant growth and forage quality at individual and functional group levels in an alpine meadow located in the permafrost region of the Qinghai-Tibetan Plateau. Warming-induced changes in community composition, biomass, and forage quality varied with soil water availability. Under dry conditions, experimental warming reduced the relative importance of grasses and the aboveground biomass by 32.37 g m-2 but increased the importance value of forbs. It also increased the crude fat by 0.68% and the crude protein by 3.19% at the end of summer but decreased the acid detergent fiber by 5.59% at the end of spring. The increase in crude fat and protein and the decrease in acid detergent fiber, but the decrease in aboveground biomass and increase the importance value of forbs, which may imply a deterioration of the grassland. Under wet conditions, warming increased aboveground biomass by 29.49 g m-2 at the end of spring and reduced acid detergent fiber by 8.09% at the end of summer. The importance value of grasses and forbs positively correlated with the acid detergent fiber and crude protein, respectively. Our results suggest that precipitation changes will determine whether climate warming will benefit rangelands on the Qinghai-Tibetan Plateau, with drier conditions suppressing grassland productivity, but wetter conditions increasing production while preserving forage quality.

[Fractal features of soil particle size in the process of desertification in desert grassland of Ningxia, China]

The variation of soil properties, the fractal dimension of soil particle size, and the relationships between fractal dimension of soil particle size and soil properties in the process of desertification in desert grassland of Ningxia were discussed. The results showed that the fractal dimension (D) at different desertification stages in desert grassland varied greatly, the value of D was between 1.69 and 2.62. Except for the 10-20 cm soil layer, the value of D gradually declined with increa sing desertification of desert grassland at 0-30 cm soil layer. In the process of desertification in de-sert grassland, the grassland had the highest values of D , the volume percentage of clay and silt, and the lowest values of the volume percentage of very fine sand and fine sand. However, the mobile dunes had the lowest value of D , the volume percentage of clay and silt, and the highest value of the volume percentage of very fine sand and fine sand. There was a significant positive correlation between the soil fractal dimension value and the volume percentage of soil particles <50 μm, and a significant negative correlation between the soil fractal dimension value and the volume percentage of soil particles >50 μm. The grain size of 50 μm was the critical value for deciding the relationship between the soil particle fractal dimension and the volume percentage. Soil organic matter (SOM) and total nitrogen (TN) decreased gradually with increasing desertification of desert grassland, but soil bulk density increased gradually. Qualitative change from fixed dunes to semi fixed dunes with the rapid decrease of the volume percentage of clay and silt, SOM, TN and the rapid increase of volume percentage of very fine sand and fine sand, soil bulk density. Fractal dimension was significantly correlated to SOM, TN and soil bulk density. Fractal dimension 2.58 was a critical value of fixed dunes and semi fixed dunes. So, the fractal dimension of 2.58 could be taken as the desertification indicator of desert grassland.

Significant Impacts of Increasing Aridity on the Arid Soil Microbiome

We identify key environmental and geochemical factors that shape the arid soil microbiome along aridity and vegetation gradients spanning over 300 km of the Atacama Desert, Chile. Decreasing average soil relative humidity and increasing temperature explain significant reductions in the diversity and connectivity of these desert soil microbial communities and lead to significant reductions in the abundance of key taxa typically associated with fertile soils. This finding is important because it suggests that predicted climate change-driven increases in aridity may compromise the capacity of the arid-soil microbiome to sustain necessary nutrient cycling and carbon sequestration functions as well as vegetative cover in desert ecosystems, which comprise one-third of the terrestrial biomes on Earth.

Global deserts occupy one-third of the Earth’s surface and contribute significantly to organic carbon storage, a process at risk in dryland ecosystems that are highly vulnerable to climate-driven ecosystem degradation. The forces controlling desert ecosystem degradation rates are poorly understood, particularly with respect to the relevance of the arid-soil microbiome. Here we document correlations between increasing aridity and soil bacterial and archaeal microbiome composition along arid to hyperarid transects traversing the Atacama Desert, Chile. A meta-analysis reveals that Atacama soil microbiomes exhibit a gradient in composition, are distinct from a broad cross-section of nondesert soils, and yet are similar to three deserts from different continents. Community richness and diversity were significantly positively correlated with soil relative humidity (SoilRH). Phylogenetic composition was strongly correlated with SoilRH, temperature, and electrical conductivity. The strongest and most significant correlations between SoilRH and phylum relative abundance were observed for Acidobacteria, Proteobacteria, Planctomycetes, Verrucomicrobia, and Euryarchaeota (Spearman’s rank correlation [r_s] = >0.81; false-discovery rate [q] = ≤0.005), characterized by 10- to 300-fold decreases in the relative abundance of each taxon. In addition, network analysis revealed a deterioration in the density of significant associations between taxa along the arid to hyperarid gradient, a pattern that may compromise the resilience of hyperarid communities because they lack properties associated with communities that are more integrated. In summary, results suggest that arid-soil microbiome stability is sensitive to aridity as demonstrated by decreased community connectivity associated with the transition from the arid class to the hyperarid class and the significant correlations observed between soilRH and both diversity and the relative abundances of key microbial phyla typically dominant in global soils.

IMPORTANCE We identify key environmental and geochemical factors that shape the arid soil microbiome along aridity and vegetation gradients spanning over 300 km of the Atacama Desert, Chile. Decreasing average soil relative humidity and increasing temperature explain significant reductions in the diversity and connectivity of these desert soil microbial communities and lead to significant reductions in the abundance of key taxa typically associated with fertile soils. This finding is important because it suggests that predicted climate change-driven increases in aridity may compromise the capacity of the arid-soil microbiome to sustain necessary nutrient cycling and carbon sequestration functions as well as vegetative cover in desert ecosystems, which comprise one-third of the terrestrial biomes on Earth.

Significant Impacts of Increasing Aridity on the Arid Soil Microbiome

Global deserts occupy one-third of the Earth's surface and contribute significantly to organic carbon storage, a process at risk in dryland ecosystems that are highly vulnerable to climate-driven ecosystem degradation. The forces controlling desert ecosystem degradation rates are poorly understood, particularly with respect to the relevance of the arid-soil microbiome. Here we document correlations between increasing aridity and soil bacterial and archaeal microbiome composition along arid to hyperarid transects traversing the Atacama Desert, Chile. A meta-analysis reveals that Atacama soil microbiomes exhibit a gradient in composition, are distinct from a broad cross-section of nondesert soils, and yet are similar to three deserts from different continents. Community richness and diversity were significantly positively correlated with soil relative humidity (SoilRH). Phylogenetic composition was strongly correlated with SoilRH, temperature, and electrical conductivity. The strongest and most significant correlations between SoilRH and phylum relative abundance were observed for Acidobacteria, Proteobacteria, Planctomycetes, Verrucomicrobia, and Euryarchaeota (Spearman's rank correlation [r_s] = >0.81; false-discovery rate [q] = ≤0.005), characterized by 10- to 300-fold decreases in the relative abundance of each taxon. In addition, network analysis revealed a deterioration in the density of significant associations between taxa along the arid to hyperarid gradient, a pattern that may compromise the resilience of hyperarid communities because they lack properties associated with communities that are more integrated. In summary, results suggest that arid-soil microbiome stability is sensitive to aridity as demonstrated by decreased community connectivity associated with the transition from the arid class to the hyperarid class and the significant correlations observed between soilRH and both diversity and the relative abundances of key microbial phyla typically dominant in global soils. IMPORTANCE We identify key environmental and geochemical factors that shape the arid soil microbiome along aridity and vegetation gradients spanning over 300 km of the Atacama Desert, Chile. Decreasing average soil relative humidity and increasing temperature explain significant reductions in the diversity and connectivity of these desert soil microbial communities and lead to significant reductions in the abundance of key taxa typically associated with fertile soils. This finding is important because it suggests that predicted climate change-driven increases in aridity may compromise the capacity of the arid-soil microbiome to sustain necessary nutrient cycling and carbon sequestration functions as well as vegetative cover in desert ecosystems, which comprise one-third of the terrestrial biomes on Earth.

Alternative Growth and Defensive Strategies Reveal Potential and Gender Specific Trade-Offs in Dioecious Plants Salix paraplesia to Nutrient Availability

Population sex ratios of many dioecious plants in nature are biased. This may be attributed to sexually different resource demands and adaptive capacity. In male-biasedPopulus, males often display stronger physiological adaptation than females. Interestingly, Populus and Salix, belonging to Salicaceae, display an opposite biased sex ratio, especially in nutrient-poor environmental conditions. Do female willows have a greater tolerance to nutrient deficiency than males? In this study, we investigated the growth and defensive strategies of Salix paraplesia cuttings, which were grown with high and low soil fertility for about 140 days over one growing season. Results suggest that different strategies for biomass allocation may result in sexually different defense capacities and trade-offs between growth and defense. Females are likely to adopt radical strategies, overdrawing on available resources to satisfy both growth and defense, which seems to be more like a gamble compared with males. It is also suggested that females may have an extra mechanism to compensate for the investment in growth under nutrient-poor conditions. In summary, the results may help focus restoration efforts on sex selection such that a moderate increase in female willow quantity could increase the resistance and resilience of willow populations to early sporadic desertification.

Assessing the robustness of spatial pattern sequences in a dryland vegetation model

A particular sequence of patterns, 'gaps→labyrinth→spots', occurs with decreasing precipitation in previously reported numerical simulations of partial differential equation dryland vegetation models. These observations have led to the suggestion that this sequence of patterns can serve as an early indicator of desertification in some ecosystems. Because parameter values in the vegetation models can take on a range of plausible values, it is important to investigate whether the pattern sequence prediction is robust to variation. For a particular model, we find that a quantity calculated via bifurcation-theoretic analysis appears to serve as a proxy for the pattern sequences that occur in numerical simulations across a range of parameter values. We find in further analysis that the quantity takes on values consistent with the standard sequence in an ecologically relevant limit of the model parameter values. This suggests that the standard sequence is a robust prediction of the model, and we conclude by proposing a methodology for assessing the robustness of the standard sequence in other models and formulations.

On regreening and degradation in Sahelian watersheds

Over many decades our understanding of the impacts of intermittent drought in water-limited environments like the West African Sahel has been influenced by a narrative of overgrazing and human-induced desertification. The desertification narrative has persisted in both scientific and popular conception, such that recent regional-scale recovery ("regreening") and local success stories (community-led conservation efforts) in the Sahel, following the severe droughts of the 1970s-1980s, are sometimes ignored. Here we report a study of watershed-scale vegetation dynamics in 260 watersheds, sampled in four regions of Senegal, Mali, and Niger from 1983-2012, using satellite-derived vegetation indices as a proxy for net primary production. In response to earlier controversy, we first examine the shape of the rainfall-net primary production relationship and how it impacts conclusions regarding greening or degradation. We conclude that the choice of functional relationship has little quantitative impact on our ability to infer greening or degradation trends. We then present an approach to analyze changes in long-term (decade-scale) average rain-use efficiency (an indicator of slowly responding vegetation structural changes) relative to changes in interannual-scale rainfall sensitivity (an indicator of landscape ability to respond rapidly to rainfall variability) to infer trends in greening/degradation of the watersheds in our sample regions. The predominance of increasing rain-use efficiency in our data supports earlier reports of a "greening" trend across the Sahel. However, there are strong regional differences in the extent and direction of change, and in the apparent role of changing woody and herbaceous components in driving those temporal trends.

Can we infer plant facilitation from remote sensing? a test across global drylands

Facilitation is a major force shaping the structure and diversity of plant communities in terrestrial ecosystems. Detecting positive plant-plant interactions relies on the combination of field experimentation and the demonstration of spatial association between neighboring plants. This has often restricted the study of facilitation to particular sites, limiting the development of systematic assessments of facilitation over regional and global scales. Here we explore whether the frequency of plant spatial associations detected from high-resolution remotely sensed images can be used to infer plant facilitation at the community level in drylands around the globe. We correlated the information from remotely sensed images freely available through Google Earth with detailed field assessments, and used a simple individual-based model to generate patch-size distributions using different assumptions about the type and strength of plant-plant interactions. Most of the patterns found from the remotely sensed images were more right skewed than the patterns from the null model simulating a random distribution. This suggests that the plants in the studied drylands show stronger spatial clustering than expected by chance. We found that positive plant co-occurrence, as measured in the field, was significantly related to the skewness of vegetation patch-size distribution measured using Google Earth images. Our findings suggest that the relative frequency of facilitation may be inferred from spatial pattern signals measured from remotely sensed images, since facilitation often determines positive co-occurrence among neighboring plants. They pave the road for a systematic global assessment of the role of facilitation in terrestrial ecosystems.

Ecosystem recharge by volcanic dust drives broad-scale variation in bird abundance

Across the globe, deserts and volcanic eruptions produce large volumes of atmospheric dust, and the amount of dust is predicted to increase with global warming. The effects of long-distance airborne dust inputs on ecosystem productivity are potentially far-reaching but have primarily been measured in soil and plants. Airborne dust could also drive distribution and abundance at higher trophic levels, but opportunities to explore these relationships are rare. Here we use Iceland's steep dust deposition gradients to assess the influence of dust on the distribution and abundance of internationally important ground-nesting bird populations. Surveys of the abundance of breeding birds at 729 locations throughout lowland Iceland were used to explore the influence of dust deposition on bird abundance in agricultural, dry, and wet habitats. Dust deposition had a strong positive effect on bird abundance across Iceland in dry and wet habitats, but not in agricultural land where nutrient levels are managed. The abundance of breeding waders, the dominant group of terrestrial birds in Iceland, tripled on average between the lowest and highest dust deposition classes in both wet and dry habitats. The deposition and redistribution of volcanic materials can have powerful impacts in terrestrial ecosystems and can be a major driver of the abundance of higher trophic-level organisms at broad spatial scales. The impacts of volcanic ash deposition during eruptions and subsequent redistribution of unstable volcanic materials are strong enough to override effects of underlying variation in organic matter and clay content on ecosystem fertility. Global rates of atmospheric dust deposition are likely to increase with increasing desertification and glacier retreat, and this study demonstrates that the effects on ecosystems are likely to be far-reaching, both in terms of spatial scales and ecosystem components.

Late Oligocene-early Miocene birth of the Taklimakan Desert

As the world's second largest sand sea and one of the most important dust sources to the global aerosol system, the formation of the Taklimakan Desert marks a major environmental event in central Asia during the Cenozoic. Determining when and how the desert formed holds the key to better understanding the tectonic-climatic linkage in this critical region. However, the age of the Taklimakan remains controversial, with the dominant view being from ∼ 3.4 Ma to ∼ 7 Ma based on magnetostratigraphy of sedimentary sequences within and along the margins of the desert. In this study, we applied radioisotopic methods to precisely date a volcanic tuff preserved in the stratigraphy. We constrained the initial desertification to be late Oligocene to early Miocene, between ∼ 26.7 Ma and 22.6 Ma. We suggest that the Taklimakan Desert was formed as a response to a combination of widespread regional aridification and increased erosion in the surrounding mountain fronts, both of which are closely linked to the tectonic uplift of the Tibetan-Pamir Plateau and Tian Shan, which had reached a climatically sensitive threshold at this time.

Heteroskedasticity as a leading indicator of desertification in spatially explicit data

Regime shifts are abrupt transitions between alternate ecosystem states including desertification in arid regions due to drought or overgrazing. Regime shifts may be preceded by statistical anomalies such as increased autocorrelation, indicating declining resilience and warning of an impending shift. Tests for conditional heteroskedasticity, a type of clustered variance, have proven powerful leading indicators for regime shifts in time series data, but an analogous indicator for spatial data has not been evaluated. A spatial analog for conditional heteroskedasticity might be especially useful in arid environments where spatial interactions are critical in structuring ecosystem pattern and process. We tested the efficacy of a test for spatial heteroskedasticity as a leading indicator of regime shifts with simulated data from spatially extended vegetation models with regular and scale-free patterning. These models simulate shifts from extensive vegetative cover to bare, desert-like conditions. The magnitude of spatial heteroskedasticity increased consistently as the modeled systems approached a regime shift from vegetated to desert state. Relative spatial autocorrelation, spatial heteroskedasticity increased earlier and more consistently. We conclude that tests for spatial heteroskedasticity can contribute to the growing toolbox of early warning indicators for regime shifts analyzed with spatially explicit data.

Fine-scale ecological and economic assessment of climate change on olive in the Mediterranean Basin reveals winners and losers

The Mediterranean Basin is a climate and biodiversity hot spot, and climate change threatens agro-ecosystems such as olive, an ancient drought-tolerant crop of considerable ecological and socioeconomic importance. Climate change will impact the interactions of olive and the obligate olive fruit fly (Bactrocera oleae), and alter the economics of olive culture across the Basin. We estimate the effects of climate change on the dynamics and interaction of olive and the fly using physiologically based demographic models in a geographic information system context as driven by daily climate change scenario weather. A regional climate model that includes fine-scale representation of the effects of topography and the influence of the Mediterranean Sea on regional climate was used to scale the global climate data. The system model for olive/olive fly was used as the production function in our economic analysis, replacing the commonly used production-damage control function. Climate warming will affect olive yield and fly infestation levels across the Basin, resulting in economic winners and losers at the local and regional scales. At the local scale, profitability of small olive farms in many marginal areas of Europe and elsewhere in the Basin will decrease, leading to increased abandonment. These marginal farms are critical to conserving soil, maintaining biodiversity, and reducing fire risk in these areas. Our fine-scale bioeconomic approach provides a realistic prototype for assessing climate change impacts in other Mediterranean agro-ecosystems facing extant and new invasive pests.

Colonization patterns of soil microbial communities in the Atacama Desert

BACKGROUND

The Atacama Desert is one of the driest deserts in the world and its soil, with extremely low moisture, organic carbon content, and oxidizing conditions, is considered to be at the dry limit for life.

RESULTS

Analyses of high throughput DNA sequence data revealed that bacterial communities from six geographic locations in the hyper-arid core and along a North-South moisture gradient were structurally and phylogenetically distinct (ANOVA test for observed operating taxonomic units at 97% similarity (OTU0.03), P <0.001) and that communities from locations in the hyper-arid zone displayed the lowest levels of diversity. We found bacterial taxa similar to those found in other arid soil communities with an abundance of Rubrobacterales, Actinomycetales, Acidimicrobiales, and a number of families from the Thermoleophilia. The extremely low abundance of Firmicutes indicated that most bacteria in the soil were in the form of vegetative cells. Integrating molecular data with climate and soil geochemistry, we found that air relative humidity (RH) and soil conductivity significantly correlated with microbial communities' diversity metrics (least squares linear regression for observed OTU0.03 and air RH and soil conductivity, P <0.001; UniFrac PCoA Spearman's correlation for air RH and soil conductivity, P <0.0001), indicating that water availability and salt content are key factors in shaping the Atacama soil microbiome. Mineralization studies showed communities actively metabolizing in all soil samples, with increased rates in soils from the southern locations.

CONCLUSIONS

Our results suggest that microorganisms in the driest soils of the Atacama Desert are in a state of stasis for most of the time, but can potentially metabolize if presented with liquid water for a sufficient duration. Over geological time, rare rain events and physicochemical factors potentially played a major role in selecting micro-organisms that are most adapted to extreme desiccating conditions.

Regime shifts in models of dryland vegetation

Drylands are pattern-forming systems showing self-organized vegetation patchiness, multiplicity of stable states and fronts separating domains of alternative stable states. Pattern dynamics, induced by droughts or disturbances, can result in desertification shifts from patterned vegetation to bare soil. Pattern formation theory suggests various scenarios for such dynamics: an abrupt global shift involving a fast collapse to bare soil, a gradual global shift involving the expansion and coalescence of bare-soil domains and an incipient shift to a hybrid state consisting of stationary bare-soil domains in an otherwise periodic pattern. Using models of dryland vegetation, we address the question of which of these scenarios can be realized. We found that the models can be split into two groups: models that exhibit multiplicity of periodic-pattern and bare-soil states, and models that exhibit, in addition, multiplicity of hybrid states. Furthermore, in all models, we could not identify parameter regimes in which bare-soil domains expand into vegetated domains. The significance of these findings is that, while models belonging to the first group can only exhibit abrupt shifts, models belonging to the second group can also exhibit gradual and incipient shifts. A discussion of open problems concludes the paper.

Quantification of the aridity process in South-Western Romania

The report released by the Intergovernmental Committee for Climate Change indicates that Romania ranks among the top seven countries in Europe that would be strongly impacted by aridity in the next few years, with climate changes consisting in a rise of average annual temperatures by as much as 5°C. The research work was conducted in the South of the Oltenia South-Western Development Region, where more than 700,000 hectares of farmland is impacted by aridification, more than 100,000 hectares among them impacted by aridity. Research methodology encompassed the analysis of average annual temperatures over the time span data was available for, at three weather stations, an analysis of average annual precipitations, an analysis of the piezometric data, the evolution of land use as a result of the expansion of the aridity process. The assessment of the aridity process also involved taking into consideration the state of the vegetation by means of the normalized difference vegetation index (NDVI), used to assess the quality of the vegetal stratum, an important element in the complex analysis of the territory. The aridity process is an effect of global warming, and, based on the results of this study, the post-1990 escalation of its effects was brought about by socio-economic factors. The destruction of the irrigation systems and protective forest belts because of the uncertain situation of land ownership are the main factors that contributed to amplification of the effects of aridity on the efficiency of agricultural systems that nowadays are exposed to very high risks.

Feeding and healing the world: through regenerative agriculture and permaculture

The study of soil is a mature science, whereas related practical methods of regenerative agriculture and permaculture are not. However, despite a paucity of detailed peer reviewed research published on these topics, there is overwhelming evidence both that the methods work and they may offer the means to address a number of prevailing environmental challenges, e.g. peak oil, climate change, carbon capture, unsustainable agriculture and food shortages, peak phosphorus (phosphate), water shortages, environmental pollution, desert reclamation, and soil degradation. What is lacking is a proper scientific study, made in hand with actual development projects. By elucidating the scientific basis of these remarkable phenomena, we may obtain the means for solving some of the otherwise insurmountable problems confronting humanity, simply by observing, and working with, the patterns and forces of nature. This article is intended as a call to arms to make serious investment in researching and actualising these methods on a global scale. Despite claims that peak oil is no longer a threat because vast resources of gas and shale oil (tight oil) can now be recovered by fracking (hydraulic fracturing) combined with horizontal drilling, the reality is that proven actual reserves are only adequate to delay the peak by a few years. Furthermore, because of the rapid depletion rates of flow from gas wells and oil wells that are accessed by fracking, it will be necessary to drill continuously and relentlessly to maintain output, and there are material limits of equipment, technology and trained personnel to do this. Moreover, to make any sensible difference to the liquid fuel crisis, which is the most immediate consequence of peak oil, it would be necessary to convert the worlds one billion vehicles to run on natural gas rather than liquid fuels refined from crude oil, and this would take some considerable time and effort. The loss of widespread personalised transportation is thus inevitable and imminent, meaning a loss of globalised civilisation and a mandatory return to living in smaller localised communities. Permaculture and regenerative agriculture offer potentially the means to provide food and materials on the small scale, and address the wider issues of carbon emissions, and resource shortages. Since over half the World's population lives in cities, it seems likely that strengthening the resilience of these environments, using urban permaculture, may be a crucial strategy in achieving a measured descent in our use of energy and other resources, rather than an abrupt collapse of civilization.

Damage caused to the environment by reforestation policies in arid and semi-arid areas of China

Traditional approaches to ecosystem restoration have considered afforestation to be an important tool. To alleviate land degradation in China, the Chinese government has therefore invested huge amounts of money in planting trees. However, the results of more than half a century of large-scale afforestation in arid and semi-arid China have shown that when the trees are not adapted to the local environment, the policy does not improve the environment, and may instead increase environmental degradation. When precipitation is lower than potential evaporation, surface soil moisture typically cannot sustain forest vegetation, and shrubs or steppe species replace the forest to form a sustainable natural ecosystem that exists in a stable equilibrium with the available water supply. The climate of much of northwestern China appears to be unsuitable for afforestation owing to the extremely low rainfall. Although some small-scale or short-term afforestation efforts have succeeded in this region, many of the resulting forests have died or degraded over longer periods, so policymakers must understand that these small-scale or short-term results do not support an inflexible policy of large-scale afforestation throughout arid and semi-arid northwestern China. Rather than focusing solely on afforestation, it would be more effective to attempt to recreate natural ecosystems that are better adapted to local environments and that thus provide a better chance of sustainable, long-term rehabilitation.

Effects of burial in sand and water supply regime on seedling emergence of six species

BACKGROUND AND AIMS

Air seeding has long been regarded as a quick and successful measure for vegetation rehabilitation in China. However, seedling emergence of often-used species including Agriophyllum squarrosum, Artemisia sphaerocephala, Artemisia ordosica, Hedysarum fruticosum, Caragana korshinskii and Medicago sativa is low. Experiments were conducted under controlled conditions to study the effects of sowing depth and water supply on seedling emergence, in order to understand the requirements for increasing seedling emergence.

METHODS

Seeds were exposed to different environments of burial and water supply regimes in PVC pots (7 cm in diameter and 11 cm in height) under the same light intensity and alternating temperature regimes in a growth chamber.

KEY RESULTS

Seedlings of three species (Agriophyllum squarrosum, Artemisia sphaerocephala, Artemisia ordosica) with relatively light seeds emerged well at a 0.5 cm sowing depth under a 7.5 and 10 mm water supply regime. However, few seedlings of these species emerged when the sowing depth was over 1 cm or when water supply was 5 mm. Seedlings of Caragana korshinskii, Hedysarum fruticosum and Medicago sativa emerged from sowing depths of 0.5-4 cm, 0.5-3 cm, and 0.5-4 cm, respectively, under both 7.5 and 10 mm water supply regimes. Under a 5 mm water supply regime, seedlings of these species also emerged at over 1 cm sowing depth. Seeds of all six species sown on the surface of sand did not germinate, and seedlings did not emerge when they were sown at depths greater than 6 cm.

CONCLUSIONS

Based on these experiments, a 0.5 cm sowing depth resulted in the highest seedling emergence and it is concluded that this is the optimal sowing depth for seedling emergence of all six species.