Semi-arid Ecosystems Research Articles

Wetting-warming climate increases ecosystem carbon use efficiency of Chinese arid and semi-arid ecosystem

Co-limited by environmental constraints, ecosystems in arid and semi-arid regions (ASARs) are extremely sensitive to climate change. A warmer and wetter climate trend has been observed extensively in ASARs of China, but whether and how the changing climate has influenced ecosystem carbon allocation and balance remains largely unclear. To bridge this knowledge gap, we conducted a comprehensive study integrating manipulative experiments, flux observations, and model simulations and our research findings reveal that the changing climate exerts a significant influence on ecosystem carbon use efficiency (CUEe) in ASARs. Specifically, the effect of increased precipitation has outweighed the warming effect, resulting in a widespread rise in CUEe across most parts of ASARs. In regions with alpine vegetation, the stimulated effects of increased temperature and precipitation play a dominant role in shaping the pattern of CUEe changes. However, with intensified warming, its stimulated effect on CUEe gradually diminishes or even reverses in ASARs. These findings can improve our understanding of ecosystem carbon sequestration regarding the response of resource-constrained ecosystems to climate change, thereby guiding ecosystem management.

Distinct response patterns of soil micro-eukaryotic communities to early-season and late-season precipitation in a semiarid grassland

Semiarid ecosystems are susceptible to changes in precipitation regimes. However, how soil micro-eukaryote communities in semi-arid ecosystems respond to variations in the seasonal distribution of precipitation remains elusive. A 5-year field experiment was performed to investigate the effect of changed precipitation distributions throughout the growing season on soil micro-eukaryotic communities in the temperate steppe. Early-season precipitation did not significantly affect the biomass of arbuscular mycorrhizal fungi (AMF) nor the composition and structure of AMF and protist communities. Late-season precipitation significantly increased the biomass of AMF while significantly altering the relative abundance of dominant genera in AMF and protist communities. There was a clear difference in the community structure of AMF and protists between the late-season precipitation and natural precipitation. In addition, late-season precipitation decreased the amount of consumer protists but enhanced the abundance of parasitic protists. These results indicate that the impact of precipitation limitations in the middle growing season can be weakened by increased precipitation in the early growing seasons, while an increase in precipitation later in the growing season does not improve the impact of a decrease in precipitation in the middle growing season. Our findings highlight the potential impact of intra-annual changes in precipitation in soil micro-eukaryotic communities in arid and semiarid regions.

Manure fertilizer divergently affects organic and inorganic carbon in a dryland agricultural soil

AbstractSoil carbon (C) is important to support sustainable agriculture, affect global C cycling, and influence the climate system. Manure fertilization is an important and widely used practice to increase agricultural productivity and soil organic carbon (SOC) pools, whereas its effect on soil inorganic carbon (SIC) and total C in deep soils is not reported. This knowledge gap restricts our ability to accurately evaluate C budget in agricultural soils because SIC in deep soils accounts for more than half of the global soil C pools, while current earth system models rarely take them into account. Herein, we examined changes of soil C along 0‐ to 3.0‐m depth after 35 years of application of manure in a dryland agricultural ecosystem. We also measured C concentrations in soil samples (0–0.2 m) from 1985 to 2019 to evaluate C dynamics in topsoils. The objective was to understand how SIC and SOC in deep soils respond to manure fertilization in semiarid ecosystem, where SIC accounts for a large fraction of total C. We showed a divergent effect of 35 years of manure application on SOC and SIC in 0–3.0 m soil from a dryland agricultural ecosystem. Either within or across the two cropping systems examined, manure increased SOC in top 0.8 m layer but decreased SIC in 0.8–3.0 m layer, which offset SOC increase and resulted in 63.8 Mg ha−1 decrease of total C in 0–3.0 m soil layer. Given the importance of soil C for sustainable agriculture and that drylands contain 80% of the global SIC and ∼50% of world cropland, immediate attention should be paid to such divergent effects in both mechanisms understanding and model prediction.

Nitrogen addition alleviates the adverse effects of drought on plant productivity in a temperate steppe.

Drought and nitrogen enrichment could profoundly affect the productivity of semiarid ecosystems. However, how ecosystem productivity will respond to different drought scenarios, especially with a concurrent increase in nitrogen availability, is still poorly understood. Using data from a 4-year field experiment conducted in a semiarid temperate steppe, we explored the responses of aboveground net primary productivity (ANPP) to different drought scenarios and nitrogen addition, and the underlying mechanisms linking soil properties, plant species richness, functional diversity (community-weighted means of plant traits, functional dispersion) and phylogenetic diversity (net relatedness index) to ANPP. Our results showed that completely excluding precipitation in June (1-month intense drought) and reducing half the precipitation amount from June to August (season-long chronic drought) both significantly reduced ANPP, with the latter having a more negative impact on ANPP. However, reducing half of the precipitation frequency from June to August (precipitation redistribution) had no significant effect on ANPP. Nitrogen addition increased ANPP irrespective of drought scenarios. ANPP was primarily determined by soil moisture and nitrogen availability by regulating the community-weighted means of plant height, rather than other aspects of plant diversity. Our findings suggest that precipitation amount is more important than precipitation redistribution in influencing the productivity of temperate steppe, and nitrogen supply could alleviate the adverse impacts of drought on grassland productivity. Our study advances the mechanistic understanding of how the temperate grassland responds to drought stress, and implies that management strategies to protect tall species in the community would be beneficial for maintaining the productivity and carbon sequestration of grassland ecosystems under climate drought.

Systematic design of habitat services network (HSsN) for updating conservation areas in iran's arid and Semi-Arid ecosystems

Threats caused by human activities have reduced the quantity and quality of wildlife habitats connectivity. This research seeks to protect habitat biodiversity by creating a network of high quality habitats that remained. Therefore, it is very necessary to know about the dynamic effects of changes in the landscape pattern on the quality of the habitat, because it helps to preserve biodiversity, guarantee ecological security, and environmental sustainability. In the present study, a systematic process was used to design a network of habitat services comprising hotspots and corridors in arid and semi-arid ecosystems of eastern Iran, South Khorasan Province. In this process, habitat quality was first modeled using the InVEST software, then data mining methods were used to identify habitat hotspots and their spatial distribution. In the next step, habitat corridors were extracted based on the circuit theory and using the Circuitscape software. In the ultimate step, using graph theory based on the concept of ecological security, the connectivity of the habitat network was evaluated. The results of habitat network construction showed that 8% and 6% of the total area of the study area included key habitat patches and corridors, respectively. On the other hand, the overlapping of habitat network components with the conserved areas of the study area showed that free or non-conservation areas make up a significant amount of network components (49.18% of the habitat patch and 80.02% of the habitat corridor). These results reveal the existence of habitat protection potential and can help in updating the new boundaries of conservation areas. Also, the composite indices of dPC and dIIC could determine the importance of each of the network's components in evaluating the connectivity of the habitat network, so that the application of the results can show the priority options to the land managers for protecting the habitat network. In general, the systematic process proposed in this research can be used in planning the sustainable conservation of habitat networks, identifying patterns of ecological security, evaluating and constructing habitat networks in lands with similar climates, and changing and wisely reviewing the conservation area boundaries.

Evaluation of PlanetScope-detected plant-specific phenology using infrared-enabled PhenoCam observations in semi-arid ecosystems

Phenology detection from remotely sensed data remains challenging in semi-arid ecosystems due to the unique spatial heterogeneity and irregular temporal growth in plants. PlanetScope imagery, with fine spatial and temporal resolutions, is revolutionizing the earth observation sector. It has demonstrated its effectiveness in monitoring phenology dynamics across various terrestrial ecosystems. However, the quality and accuracy of PlanetScope data for depicting plant growth development and detecting phenological metrics (phenometrics) in semi-arid environments have not been systematically examined. In this study, we evaluated the capability of PlanetScope for monitoring plant-specific phenology across the semi-arid western United States, by comparing phenometrics (onsets of greenup, maturity, senescence, and dormancy) retrieved from time series of two PlanetScope vegetation indices (VI), which are EVI2 (two-band Enhanced Vegetation Index) and NDVI (Normalized Difference Vegetation Index), with a set of PhenoCam observations at 15 sites. To conduct a comprehensive comparison, PhenoCam time series and phenometrics were extracted from infrared-enabled PhenoCam EVI2 and NDVI, as well as commonly used PhenoCam GCC (Green Chromatic Coordinate). Our results show that (1) time series of PlanetScope VI were consistent with PhenoCam GCC and VI time series during greenup phase but moderately comparable during senescence phase, with an average R2 of 0.67 and 0.57 for greenup and senescence phases, respectively; (2) phenometrics derived from PlanetScope VI exhibited better agreement with those from PhenoCam GCC and VI in greenup phase (greenup and maturity onsets) than in senescence phase (senescence and dormancy onsets), with an average R2 of 0.81, 0.84, 0.72, and 0.53 for greenup, maturity, senescence, and dormancy onsets, respectively; (3) PlanetScope-detected senescence onset and dormancy onset were systematically later than PhenoCam-based retrievals with a mean systematic bias of 12.6 days and 18.2 days, respectively; (4) phenometrics derived from PlanetScope VI were more comparable with PhenoCam VI retrievals than with PhenoCam GCC retrievals, which are reflected in better correlations and smaller bias between phenometrics, especially during senescence phase; and (5) PlanetScope and PhenoCam EVI2 time series produced the most comparable phenometrics, suggesting that EVI2 is an optimal index for vegetation phenology detections from different sensors. In summary, this study suggests PlanetScope has the ability to detect plant-specific phenology and to improve our understanding of phenology dynamics in heterogeneous semi-arid ecosystems at fine scales.

Response of Ecosystem Carbon–Water Fluxes to Extreme Drought in West Asia

Global warming has resulted in increases in the intensity, frequency, and duration of drought in most land areas at the regional and global scales. Nevertheless, comprehensive understanding of how water use efficiency (WUE), gross primary production (GPP), and actual evapotranspiration (AET)-induced water losses respond to exceptional drought and whether the responses are influenced by drought severity (DS) is still limited. Herein, we assess the fluctuation in the standardized precipitation evapotranspiration index (SPEI) over the Middle East from 1982 to 2017 to detect the drought events and further examine standardized anomalies of GPP, WUE, and AET responses to multiyear exceptional droughts, which are separated into five groups designed to characterize the severity of extreme drought. The intensification of the five drought events (based on its DS) increased the WUE, decreased the GPP and AET from D5 to D1, where both the positive and negative variance among the DS group was statistically significant. The results showed that the positive values of standardized WUE with the corresponding values of the negative GPP and AET were dominant (44.3% of the study area), where the AET values decreased more than the GPP, and the WUE fluctuation in this region is mostly controlled by physical processes, i.e., evaporation. Drought’s consequences on ecosystem carbon-water interactions ranged significantly among eco-system types due to the unique hydrothermal conditions of each biome. Our study indicates that forthcoming droughts, along with heightened climate variability, pose increased risks to semi-arid and sub-humid ecosystems, potentially leading to biome restructuring, starting with low-productivity, water-sensitive grasslands. Our assessment of WUE enhances understanding of water-carbon cycle linkages and aids in projecting ecosystem responses to climate change.

Urea fertilization increased CO2 and CH4 emissions by enhancing C-cycling genes in semi-arid grasslands

Global climate change is predicted to increase exogenous N input into terrestrial ecosystems, leading to significant changes in soil C-cycling. However, it remains largely unknown how these changes affect soil C-cycling, especially in semi-arid grasslands, which are one of the most vulnerable ecosystems. Here, based on a 3-year field study involving N additions (0, 25, 50, and 100 kg ha−1 yr−1 of urea) in a semi-arid grassland on the Loess Plateau, we investigated the impact of urea fertilization on plant characteristics, soil properties, CO2 and CH4 emissions, and microbial C cycling genes. The compositions of genes involved in C cycling, including C fixation, degradation, methanogenesis, and methane oxidation, were determined using metagenomics analysis. We found that N enrichment increased both above- and belowground biomasses and soil organic C content, but this positive effect was weakened when excessive N was input (N100). N enrichment also altered the C-cycling processes by modifying C-cycle-related genes, specifically stimulating the Calvin cycle C-fixation process, which led to an increase in the relative abundance of cbbS, prkB, and cbbL genes. However, it had no significant effect on the Reductive citrate cycle and 3-hydroxypropionate bi-cycle. N enrichment led to higher soil CO2 and CH4 emissions compared to treatments without added N. This increase showed significant correlations with C degradation genes (bglA, per, and lpo), methanogenesis genes (mch, ftr, and mcr), methane oxidation genes (pmoA, pmoB, and pmoC), and the abundance of microbial taxa harboring these genes. Microbial C-cycling genes were primarily influenced by N-induced changes in soil properties. Specifically, reduced soil pH largely explained the alterations in methane metabolism, while elevated available N levels were mainly responsible for the shift in C fixation and C degradation genes. Our results suggest that soil N enrichment enhances microbial C-cycling processes and soil CO2 and CH4 emissions in semi-arid ecosystems, which contributes to more accurate predictions of ecosystem C-cycling under future climate change.

Functional roles of biocrusts in enhancing soil quality in a semi-arid environment

Biocrusts play a wide range of ecological roles, especially in modifying surface soil properties and as a natural agent to combat soil degradation in fragile semi-arid and arid ecosystems globally. We examined the importance of biocrust on soil properties and quality in a semi-arid alluvial fan in northeastern Iran. The soil quality index (SQI) was used as the method for the quantitative evaluation of soil with or without biocrusts, using standard linear and nonlinear scoring methods. For this purpose, 17 biological, chemical, and physical soil properties were integrated into two indicator selection methods (total and minimum data set) and SQI has been calculated by the weighted additive method. The spatial patterns of SQI showed that overall the soil quality was (47%) increased in biocrust compared to non-biocrust soil. The increase of microbial biomass nitrogen, basal soil respiration, and microbial biomass carbon, and the decrease of available sodium and percentage sand were the most important indicators controlling the soil quality changes by biocrusts. In addition, biocrusts improved the soil structure by reducing bulk density and increasing the mean weight diameter of aggregates and available water capacity. Cyanobacteria communities of biocrusts were the initiators of soil quality improvement, while moss and cyanolichen communities played a major role from the moderate stages of biocrust occurrence. It is concluded that globally, in dry lands, biocrusts should be considered as signatures of enhanced soil quality.

Contribution of edible indigenous woody plants as a coping strategy during drought periods in the southeast lowveld of Zimbabwe: a review

Climatic change related extreme events such as droughts negatively affect local communities in the semi-arid savanna ecosystems. This study mainly records and analyses local knowledge on the use of edible indigenous woody plant species by local communities during drought periods, as a coping strategy, in southeast lowveld of Zimbabwe. Secondary data on utilization of edible indigenous woody plants were gathered from literature sources focusing mainly on the southeast lowveld parts of Zimbabwe and covering the period 2000–2019. Quantitative ethnobotanical data analysis involved computing the frequency of citation (FC), relative frequency of citation (RFC) and family importance value (FIV) to determine the local significance of indigenous woody plant species. A total of 23 species from 12 families were recorded as being used during drought periods with key species including baobab (Adansonia digitata), bird plum (Tamarindus indica), corky-monkey orange (Strychnos cocculoides) and black monkey orange (Strychnos madagascariensis). Major use categories were food, medicine, and livestock feed. The study findings points to the need for embracing indigenous woody plants as a buffer against drought in semi-arid parts of the savanna. Future projects should focus on developing innovative strategies such as value addition and promoting sustainable use and restoration of non-wood forest products as part of livelihood diversification under drought situations.

Effect of Mulches on Crop, Soil and Water Productivity: A Review

A mulch is a layer of material applied to the surface of an area of soil. Mulches are used for various reasons in agriculture but water conservation and erosion control are the most important objectives particularly in arid and semi-arid regions. Other reasons for use of mulching include soil temperature modification, weed control, soil conservation and after decomposition of organic mulch add plant nutrients, improvement in soil structure, increase crop quality and yield. Conservation of soil moisture by application of mulches becomes essential for profitable cultivation of the crop under rainfed condition of semi-arid ecosystem. In spite of no assured irrigation in these regions, the moisture conservation technique is not in practice. Mulches not only conserve soil moisture but also impart manifold beneficial effects, like suppression of extreme fluctuation of soil temperature and reduction of water loss through evaporation, resulting in more stored soil moisture, maintenance of soil fertility, suppression of weed growth, improvement in growth and yield. The requirement of water through mulch can further be reduced by using locally available organic materials as mulches which not only save irrigation water but also conserves soil moisture.

Understanding the rapid increase in drought stress and its connections with climate desertification since the early 1990s over the Brazilian semi-arid region

The aridity-related drought studies have been carried out extensively in Brazilian semi-arid ecosystems, although there is no report on relating aridity with different drought indices over the recent decades. Due to drought impact on agriculture and natural ecosystems, it has attracted extensive attention in the academic community. In this study, the Standardized Precipitation Evapotranspiration Index (SPEI), the Soil Moisture and Ocean Salinity-derived Soil Water Deficit Index (SWDI), the Meteosat Spinning Enhanced Visible and InfraRed Imager (SEVIRI) radiance-derived solar and infrared estimates, and the SEVIRI-derived Normalized Difference Vegetation Index (NDVI) datasets were employed to investigate the spatial and temporal characteristics of the drought episodes and the vegetation dynamic responses. An approach was implemented for identifying drought using a combination of mathematical and statistical features derived from the SPEI. The results showed that: (1) The frequency, duration, and intensity of drought severity identified by the SPEI and SWDI from 1990 to 2022 showed different characteristics in the Brazilian semi-arid region from 1990 to 2022. The frequency of moderate, severe, and extreme drought ranged from 5% to 92%, the duration was mostly concentrated in 5–6 dry months. (2) The whole Brazilian semi-arid region exhibited an overall drying tendency. (3) The NDVI-derived vegetation in the Brazilian semi-arid ecosystems exhibited an overall decreased trend during 2004–2022, indicating a degrading trend of the vegetation cover. The region where degrading trend of NDVI was negatively correlated with SPEI accounted for approximately 13% of the region. (4) The frequency, and average duration of the flash drought were 21% concentrated in 6 pentads, during the region growing season. (5) The spatial and temporal trends with the significance test of the rainfall, air temperature, and SEVIRI radiance-based estimations suited well with those of the SPEI data. These research results were significant for the region to respond to and prevent drought through human-induced land degradation.

Food resource competition between African wild dogs and larger carnivores in an ecosystem with artificial water provision.

Predators of similar size often compete over prey. In semi-arid ecosystems where water is a limiting resource, prey availability can be affected by water distribution, which further increases resource competition and exacerbate conflict among predators. This can have implications for carnivore dietary competition. Hence, we evaluated the dynamics of food resource competition between African wild dogs and four competing predators (cheetahs, leopards, lions and spotted hyaenas) in different seasons and across areas with different waterhole densities in Hwange National Park, Zimbabwe. We used the frequency of occurrence of prey items found in predators' scats to analyse diet composition, overlap and prey preference. For most predators, kudu was most frequently consumed and preferred. Low and medium water-dependent prey (medium and small-sized) were mostly consumed by wild dogs, leopards and cheetahs. Wild dog diet overlap was high with all predators, particularly with hyaenas and lions. There were no seasonal differences in the predators diet. The diet overlap of wild dogs with lions was highest in the low waterhole density area, and wild dog diet composition did not differ significantly from the diet of lions and hyaenas. In the low waterhole density area, wild dogs and hyaenas broadened their niche breadth, and predators diet had a higher proportion of low water-dependent prey. A low density of waterholes increased food resource competition. However, high density of waterholes, where there is more prey availability, can increase the aggregation and density of predators, and hence, increase the risks involved in interspecific competition on wild dogs. To reduce food resource competition on wild dogs, we propose to conserve larger-bodied prey that are less dependent on water (e.g. kudu, reedbuck, eland and gemsbok). As the use of water pumping is common practice, we propose maintaining water management heterogeneity where prey which is less dependent on water can also thrive.

Serological survey reveals enzootic circulation of St. Louis encephalitis and West Nile viruses in semiarid Monte ecosystem of Argentina

St. Louis encephalitis virus (SLEV) and West Nile virus (WNV) are arboviruses transmitted by Culex mosquitoes and amplified in avian hosts. The present study aimed to investigate the presence and seasonal circulation of SLEV and WNV in La Rioja province, within the semiarid ecoregion of the Monte, Argentina. Over a two-year period, avian sera were collected and tested for neutralizing antibodies against SLEV and WNV. Our results reveal the enzootic activity of both viruses in this challenging environment. SLEV seroprevalence was 4.5% (35/778), with higher activity in spring (2016) and autumn (2017). WNV seroprevalence was 3.5% (27/778), peaking during the summer 2016–2017. Greater seroprevalence for SLEV in 2016 was detected for the Lark-like Brushrunner (Coryphistera alaudina) and the Short-billed Canastero (Asthenes baeri) and in 2017 for the Black-crested Finch (Lophospingus pusillus) and Lark-like Brushrunner, whereas for WNV greater seroprevalence in 2016 was detected for the Picui Ground Dove (Columbina picui) and in 2017 for the Lark-like Brushrunner and Band-tailed Seedeater (Catamenia analis). Additionally, five avian individuals experienced seroconversion during the sampling period, namely the Lark-like Brushrunner and White-fronted Woodpecker (Melanerpes cactorum) for SLEV, and the Lark-like Brushrunner, Greater Wagtail Tyrant (Stigmatura budytoides) and Many-colored Chaco Finch (Saltatricula multicolor) for WNV. The study highlights the persistence and circulation of these viruses in a semiarid ecosystem, raising questions about overwintering mechanisms and transmission dynamics. This research contributes to understanding arbovirus ecology in diverse environments. Further investigations are needed to assess the specific mechanisms facilitating virus persistence in the Monte ecoregion.

Sorghum Response to Supplementary Irrigation at Different Growth Stage in Rain-Fed Agriculture for Increasing Yield and Water Productivity at Raya Valley

In arid and semi-arid ecosystems, the efficient use of water becomes increasingly important because water is a crucial limiting factor for increased food and fibre production to supply an ever-growing number of people. A field experiment was conducted in three consecutive seasons three year in Mekhoni Agricultural Research Centre, Raya valley, to investigate with the objective of to evaluate the influence of supplemental irrigation applied at different growth stages on the yield, to prevent sorghum failure caused by less rain water and to maximize the water productivity of the sorghum. The experiment was laid out in a random complete block design (RCBD) consisting of eleven supplemental irrigation treatments (one supplemental irrigation during initial stage, one supplemental during development stage, one supplemental during mid-stage, one supplemental during Late stage, one supplemental during initial and development stage, one supplemental during initial and mid stage, one supplemental during initial and late stage, one supplemental during development and late stage, one supplemental during development and late stage and rain-fed (with no SI) as a control treatment with three replications. The result was showed a significant difference on plant height, panicle length, grain, biomass yield and water productivity sorghum. The highest grain yield was obtained from the treatment supplement one SI at development and mid stage and followed by one SI at mid stage and at late stage. Whereas, the lowest grain yield of sorghum was observed from treatment with rainfed (non-supplementary). It is concluded that in the study area the rain fed amount were very inadequate and supplementary irrigation will help to increase crop productivity, minimize crop failure due to the low rainfed. The experiment showed that supplementary irrigation offers a great potential for improving crop production in Raya valley.

A Key Interaction Behind the Scenes: Dung Beetles in Livestock Production from Arid and Semi-Arid Rangelands.

Pastoralism is a dominant agricultural activity in arid and semi-arid ecosystems. The interaction between coprophagous insects and livestock is a key but an undervalued topic in rangeland management decisions. The objective was to identify similarities and differences in the composition of coprophagous insects and nesting strategies, associated with different climatic conditions within these regions. We performed a literature review of research articles available in the Scopus database which resulted in 17 articles. We examined the taxonomic diversity of dung beetles and their nesting strategies in relation to temperature and precipitation at the study sites. Results revealed a rich and varied interaction between dung beetles and livestock in arid and semi-arid environments, with 364 species from the Scarabaeoidea superfamily documented worldwide. The greatest diversity of dung beetles was reported in hot arid and semi-arid conditions with dry winters and in cold semi-arid ones with no marked annual precipitation cycle. These insects displayed diverse nesting strategies, with endocoprid strategies predominating in colder and drier settings, and paracoprid and telecoprid strategies in warmer, more humid environments. Domestic animal species are currently key components in promoting this interaction, which indicates that the ecological processes involving coprophagous fauna are occurring in production systems, which are under the influence of human decisions. We discuss the design and planning of livestock and rangeland management in arid and semi-arid environments, emphasizing in a more formalized manner the inclusion of this kind of interaction.

Seasonal dynamics of alfa fibers: Comprehensive characterization of chemical, elemental, and mechanical properties in a semi-arid ecosystem

This study comprehensively characterizes alfa fibers, focusing on their chemical and elemental compositions, granulometry, morphology, and mechanical properties, with a specific emphasis on their seasonal variation. The research site in Sbeïtla, Tunisia, is situated in a semi-arid bioclimatic stage with a unique ecosystem dominated by the alfa plant (Stipa tenacissima). Various parameters, including plant height, diameter, density, and vegetation cover, were assessed across different seasons. The mineral and biochemical analyses of alfa leaves, such as cellulose, ash, and protein content, were conducted, and the results revealed seasonal variations. Quality and mechanical parameters of alfa dough, used in papermaking, were also investigated, including dryness, weight, whiteness, breaking length, elongation, and ash content. Granulometry distribution of alfa fibers was analyzed to understand its impact on various industrial applications. The findings highlight the dynamic nature of alfa plants in response to seasonal changes and underscore the importance of seasonality in determining the quality and mechanical properties of alfa products, from paper to composite materials.

A novel linear spectral unmixing-based method for tree decline monitoring by fusing UAV-RGB and optical space-borne data

ABSTRACT Remote sensing-assisted monitoring of forest health entails methods that can provide up-to-date and accurate information on decline and mortality of individual trees, while maintaining time and cost efficiency. However, the trade-off of applying consumer-grade UAV-RGB data as the most affordable and accessible data source at the catchment level is constrained by its poor spectral information content. We developed a method based on the fusion of UAV-RGB data with space-borne Sentinel-2 Multispectral Instrument (MSI) at the level of tree crowns, with the specific target of supporting studies on semi-arid tree decline. We applied linear spectral unmixing (Spectral Unmixing-Based data Fusion method, LSUBF) by considering a limited number of endmembers and calculating the abundances (fractional covers) from the UAV data, and evaluated the results by high-resolution MSI space-borne data including SPOT-6 (1.5 m spatial resolution) and PlanetScope (3 m spatial resolution). This method suggested an increase in the coefficient of determination of the applied generalized additive model for decline severity estimation at tree crown level from 0.61 to 0.69, while it was improved from 0.70 to 0.91 when fitting a non-parametric random forest model. The results of sensitivity analysis demonstrated that the additional spectral information obtained from the proposed method results in higher accuracy in estimating decline severity. We suggest this method as a cost-effective alternative to monitor periodical tree decline, in particular across semi-arid ecosystems.

Biocrusts enhance soil organic carbon stability and regulate the fate of new-input carbon in semiarid desert ecosystems

Given their global prevalence, dryland (including hyperarid, arid, semiarid, and dry subhumid regions) ecosystems are critical for supporting soil organic carbon (SOC) stocks, with even small changes in such SOC pools affecting the global carbon (C) cycling. Biocrusts play an essential role in supporting C cycling in semiarid ecosystems. However, the influence of biocrusts and their successional stages on SOC and its fraction contents, as well as their role in regulating new input C into SOC fractions remain largely unknown. In this study, we collected continuous samples of bare soil (BS) and three successional stages of biocrust soils (cyanobacterial (CC), low-cover moss (LM), and high-cover moss (HM)) at 0–5 cm depth every month for one year in a semiarid desert ecosystem. We analyzed SOC changes among the samples and their fraction contents including: labile organic C (LOC) (composed of microbial biomass C (MBC), dissolved organic C (DOC), and easily oxidized organic C (EOC)) and recalcitrant organic C (ROC) fractions, soil nutrient content including: ammonium (NH4+-N), nitrate (NO3−-N), and available phosphorus (AP), and soil temperature and moisture. We also conducted a 13C pulse-labelling experiment in the field to accurately quantify the effects of biocrust successional stage on exogenous C allocation to SOC fractions. Our results showed that the three successional stages of biocrust (CC-LM-HM) increased SOC and ROC contents by an average of 5.3 ± 3.6 g kg−1 and 4.0 ± 3.0 g kg−1, respectively; and the MBC, DOC, and EOC contents increased by an average of 41.7 ± 24.8 mg kg−1, 28.7 ± 12.6 mg kg−1, and 1.2 ± 0.6 g kg−1, respectively, compared to that of BS. These increases were attributed to an increase in photosynthetic pigment content, higher nutrient levels, and more suitable microclimates (e.g., higher moisture and more moderate temperature) during biocrust succession. More importantly, SOC stability was greatly improved with biocrust succession from cyanobacteria to moss, as evidenced by the reduction in soil EOC:SOC and EOC:ROC ratios by an average of 50 ± 34 % and 99 ± 67 %, respectively, while the ROC:SOC ratio increased by 33 ± 16 % with biocrust succession compared to those of BS. The biocrust SOC, DOC, and MBC 13C contents at different stages were on average 0.096 ± 0.034 mg kg−1, 0.010 ± 0.005 mg kg−1, and 0.014 ± 0.005 mg kg−1 higher than those of BS. Similarly, the allocation of new-input C among the DOC and MBC at different biocrust stages (19 ± 10 %) was significantly higher than that of BS (9 ± 6 %). New-input C into the biocrusts was fixed by microbes (43 ± 18 %) within ∼10 days and converted into other forms of C (85 ± 5 %) after 80 days. Our study provides a new perspective on how biocrusts support C cycling in semiarid desert ecosystems by mediating new C inputs into diverse fractional contents, and highlights the significance of biocrust successional stages in maintaining soil C stocks and stability in the dryland soil system.

Agricultural land suitability classification and crop suggestion using machine learning and spatial multicriteria decision analysis in semi-arid ecosystem

Agricultural land suitability classification and crop suggestion using machine learning and spatial multicriteria decision analysis in semi-arid ecosystem