Xerophytic Shrubs Research Articles

Transcriptome analysis and codominant markers development in caper, a drought tolerant orphan crop with medicinal value

Caper (Capparis spinosa L.) is a xerophytic shrub cultivated for its flower buds and fruits, used as food and for their medicinal properties. Breeding programs and even proper taxonomic classification of the genus Capparis has been hampered so far by the lack of reliable genetic information and molecular markers. Here, we present the first genomic resource for C. spinosa, generated by transcriptomic approach and de novo assembly. The sequencing effort produced nearly 80 million clean reads assembled into 124,723 unitranscripts. Careful annotation and comparison with public databases revealed homologs to genes with a key role in important metabolic pathways linked to abiotic stress tolerance and bio-compounds production, such purine, thiamine and phenylpropanoid biosynthesis, α-linolenic acid and lipid metabolism. Additionally, a panel of genes involved in stomatal development/distribution and encoding for Stress Associated Proteins (SAPs) was also identified. We also used the transcriptomic data to uncover novel molecular markers for caper. Out of 50 SSRs tested, 14 proved polymorphic and represent the first set of SSR markers for the genus Capparis. This transcriptome will be an important contribution to future studies and breeding programs for this orphan crop, aiding to the development of improved varieties to sustain agriculture in arid conditions.

Analysis of Thermo chemical behaviour of Calotropis procera parts for their Potentiality

Calotropis procera (C.procera) is a xerophytic perennial shrub or small tree of flowering species belongs to the family Asclepiadaceae (Giant milkweed). It is native to tropical and subtropical Africa, South West Asia (India, Pakistan, Afghanistan, Iran, Arabia and Jordan) and common in the Middle East and its weed that grows profusely without management on road sides and waste lands. In this work, the stem, leaf, flower and the whole plant of C.procera were characterised to evaluate the suitability for use as renewable energy feedstock. The ultimate and proximate analyses were carried out to determine the elemental composition and volatile matter, ash and fixed carbon content respectively. Thermogravimetric analyses (TGA) were performed to study the pyrolysis and combustion characteristics. The chemical groups present in the plant parts were measured by FTIR spectroscopy analysis. The proximate and ultimate compositions of plant parts were similar to other lignocellulosic biomass. The whole plant exhibited a heating value of 21.85 MJ/kg whilst the mean higher heating value of the plant parts was 17.947 MJ/kg. The TGA profiles under nitrogen atmosphere presented significant mass loss of the plant parts. The pyrolysis of flower showed the highest reactivity with mass loss of 74%. The combustion profiles presented two distinct degradation stages each with a sharp peak indicating the oxidation of hemicellulose, cellulose, lignin and char. The average ignition and burnout temperatures estimated from the TG and DTG curves of plant parts was 240.25°C and 493.25°C respectively. The thermal behaviours under nitrogen and oxygen environment indicated that the plant parts are suitable for both pyrolysis and combustion processes. The FTIR analysis indicated the presence of aldehydes, ketones, organic acids, phenols and alcohols.

De novo transcriptome assembly and co-expression network analysis of Cynanchum thesioides: Identification of genes involved in resistance to drought stress

Cynanchum thesioides are upright, xerophytic shrubs that are widely distributed in arid and semi-arid areas of China, North Korea, Mongolia and Siberia. To date, little is known about the molecular mechanisms of drought resistance in C. thesioides. To better understand drought resistance, we used transcriptome analysis and Illumina sequencing technology on C. thesioides, to identify drought-responsive genes. Using de novo assembly 55,268 unigenes were identified from 207.58 Gb of clean data. Amongst these, 36,265 were annotated with gene descriptions, conserved domains, gene ontology terms and metabolic pathways. The sequencing results showed that genes that were differentially expressed (DEGs) under drought stress were enriched in pathways such as carbon metabolism, starch and sucrose metabolism, amino acid biosynthesis, phenylpropanoid biosynthesis and plant hormone signal transduction. Moreover, many functional genes were up-regulated under severe drought stress to enhance tolerance. Weighted gene co-expression network analysis showed that there were key hub genes related to drought stress. Hundreds of candidate genes were identified under severe drought stress, including transcriptional factors such as MYB, G2-like, ERF, C2H2, NAC, NF-X1, GRF, HD-ZIP, HB-other, HSF, C3H, GRAS, WRKY, bHLH and Trihelix. These data are a valuable resource for further investigation into the molecular mechanism for drought stress in C. thesioides and will facilitate exploration of drought resistance genes.

New microsatellites for the Atacama Desert endemic Balsamocarpon brevifolium (Fabaceae).

PremiseAlgarrobilla (Balsamocarpon brevifolium, Fabaceae) is an endemic xerophytic shrub restricted to the Atacama Desert in northern Chile. Extensive utilization of the region for coal production has endangered this species. Conservation efforts are underway, with genetic diversity analyses being key to the restoration of these populations.Methods and ResultsFifteen new microsatellite markers were developed for B. brevifolium and used to analyze three populations from the Atacama and Coquimbo regions in Chile. Microsatellites were highly polymorphic, with an average of 5.77 alleles per marker and an average level of expected heterozygosity of 0.72. These markers were evaluated and cross‐amplified on two related species (Senna cumingii and Caesalpinia angulata) with partial success.ConclusionsThe development of this set of markers permits an extensive study of B. brevifolium populations for conservation purposes.

Water Stress Patterns of Xerophytic Plants in an Urban Landscape

Efficient water use in urban landscapes is a common objective throughout the western United States. Vegetative species promoted for their drought tolerance characteristics are often included in landscapes designed for resource conservation. However, water requirements of most common landscape species have not been quantified. This is especially true for xerophytic species. This lack of landscape plant water requirement data is a significant constraint on the design of efficient irrigation systems and management practices affecting urban landscape water use. Current irrigation practices often fail to consider the unique physiology of xerophytic species, and irrigation scheduling models may not be appropriate for xeric landscapes using xerophytic vegetation as the primary method of reducing water use. This work describes the seasonal patterns of growth and xylem water status for four regionally native xeric shrub species planted in an unirrigated urban landscape in the semi-arid environment of central Oregon. The four species (Artemisia tridentata, Holodiscus microphyllus, Ericameria nauseosa, and Ribes cereum) exhibited substantial growth over the course of 18 months without irrigation in a heavily modified urban soil profile. Water potential of the four species was strongly correlated with surface (10 cm) soil moisture (r ≥ 0.90), less so with reference monthly evapotranspiration (r ≤ 0.55), and only weakly with water vapor deficit (r ≤ 0.22). In A. tridentata and H. microphyllus, xylem water potential became more negative during the growing season and tracked the seasonal decline in soil moisture. In contrast, the xylem water potential of E. nauseosa and R. cereum tracked soil moisture early in the season but became less responsive to soil moisture in the driest months, suggesting different drought adaptation strategies in these species. Three of the four species showed no visual signs of drought stress and maintained acceptable aesthetics even as soil moisture decreased to less than 10%. However, R. cereum exhibited a drought dormancy strategy that made it less aesthetically desirable. These results suggest that extreme xerophytic shrubs provide an opportunity for significant reductions in water use in urban landscapes.

NaCl stimulates growth and alleviates drought stress in the salt-secreting xerophyte Reaumuria soongorica

Reaumuria soongorica, a salt-secreting xerophytic shrub, is a dominant species in arid desert regions of northwest China. To investigate whether NaCl could stimulate the growth and alleviate drought stress in R. soongorica, the seedlings were treated with a range of different concentrations of 0–1.17 g kg−1 NaCl, and also were withheld water for drought stress under without or supplementary 0.59 g kg-1 NaCl. The results showed that 0.59 g kg-1 NaCl (moderate NaCl) significantly stimulated the growth of R. soongorica, and also effectively alleviated deleterious impacts of drought stress on its growth and leaf morphological structure. Further analysis showed that moderate NaCl significantly improved photosynthetic capacity and mitigated light suppression of drought stress on photosystem II in R. soongorica, concomitantly, decreased osmotic potential, enlarged turgor pressure as well as increased the relative water content in leaves under drought stress. Furthermore, moderate NaCl induced an obvious increase of Na+ accumulation in tissues of R. soongorica, which resulted in a significant increase of the contribution of Na+ to leaf osmotic potential from13 to 22% under drought stress. Additionally, moderate NaCl also promoted Na+ secretion via salt glands of leaf. These results suggest that the positive roles of NaCl on the growth and drought resistance of R. soongorica is due to the increase of Na+ accumulating in leaf tissues, facilitating plant to maintain higher photosynthetic activity and better water status in arid environment, simultaneously, salt secretion of salt glands protects plant from excess Na+ toxicity.

Coordinated changes in photosynthetic machinery performance and water relations of the xerophytic shrub Ziziphus lotus (L.) Lam. (Rhamnaceae) following soil drying

Aim of this study was to investigate the effect of water shortage in wild jujube plants, Ziziphus lotus (L.) Lam, and how it is related to its ecological success. All leaf anatomical traits were significantly affected following soil drying. Stressed plants displayed more negative stem water potential (ψw) and osmotic potential values of ca. -3.5 and -4.5 MPa, respectively, after 30 d. The relative water content declined although it still maintained high values (≥ 75%). The net photosynthetic rate, stomatal conductance, and transpiration rate were significantly inhibited as ψw decreased. However, the intrinsic water-use efficiency increased as water deficit was intensified; the difference became significant only after 30 d. As a consequence, the effective quantum yield of PSII photochemistry and the photochemical quenching coefficient significantly decreased although the maximal quantum yield of PSII photochemistry ratio remained statisticaly unchanged. Plants could maintain their water status sufficiently by increasing proline 1.7-fold and sucrose 1.8-fold in their leaves, respectively. The largest accumulation of both solutes may avoid photodamages at cellular level and play a critical role in maintaining osmotic adjustment.

Caragana korshinskii phenylalanine ammonialyase is up-regulated in the phenylpropanoid biosynthesis pathway in response to drought stress

Drought is one of the most severe abiotic stresses, the damage due to which, various plant species mitigate by activating mechanisms that are not yet well understood. Caragana korshinskii is a xerophytic shrub found in the semi-arid regions of northwest China with high tolerance to several abiotic stresses, including drought. Based on the de novo transcriptome data from C. korshinskii leaflets collected along a precipitation gradient on the Loess Plateau (China), most of the differentially expressed genes were explored using trend analysis along the precipitation gradient. Gene ontological analysis showed that “phenylpropanoid biosynthesis process → secondary metabolite biosynthetic process” terms were the most significant gene ontologies, whereas Kyoto Encyclopedia of Genes and Genomes-based analysis indicated that the biosynthesis of secondary metabolites was a significant metabolic pathway. Real-time polymerase chain reaction and enzyme activity analyses confirmed the increased transcription of the phenylalanine ammonialyase (PAL) gene in C. korshinskii under drought stress in field and laboratory conditions. These results suggested that C. korshinskii adjusts its secondary metabolism to water-deficit environments and activates PAL by drought stress. Therefore, further studies on the obtained data can expand the current understanding of the molecular and genetic mechanisms responsible for the drought endurance in C. korshinskii.

Two Thousand Years of Land-Use and Vegetation Evolution in the Andean Highlands of Northern Chile Inferred from Pollen and Charcoal Analyses

The European conquest of the New World produced major socio-environmental reorganization in the Americas, but for many specific regions and ecosystems, we still do not understand how these changes occurred within a broader temporal framework. In this paper, we reconstruct the long-term environmental and vegetation changes experienced by high-altitude wetlands of the southcentral Andes over the last two millennia. Pollen and charcoal analyses of a 5.5-m-long core recovered from the semi-arid puna of northern Chile indicate that while climatic drivers influenced vegetation turnaround, human land use and management strategies significantly affected long-term changes. Our results indicate that the puna vegetation mostly dominated by grasslands and some peatland taxa stabilized during the late Holocene, xerophytic shrubs expanded during extremely dry events, and peatland vegetation persisted in relation to landscape-scale management strategies by Andean pastoralist societies. Environmental changes produced during the post-conquest period included the introduction of exotic taxa, such as clovers, associated with the translocation of exotic herding animals (sheep, cattle, and donkeys) and a deterioration in the management of highland wetlands.

Effects of shrubs on soil nutrients and enzymatic activities over a 0–100 cm soil profile in the desert-loess transition zone

The creation of “fertile islands” beneath shrubs in dryland ecosystems has been widely reported worldwide and is the major factor influencing ecosystem structure and function. However, studies investigating whether and how shrubs affect soil biogeochemical cycles in deep soil layers are relatively limited. In this study, we examined the vertical distribution of the soil nutrient contents and enzymatic activities at the 0–100 cm soil profiles beneath three common xerophytic shrubs (Artemisia ordosica, Caragana korshinskii and Salix psammophila) and in interspace bare soils in a transition zone from desert to loess in the north of China. The soil metrics included the contents of organic carbon, total nitrogen, total phosphorus, nitrate and ammonium nitrogen, available phosphorus and potassium, and the activities of saccharase, urease, alkaline phosphatase and amylase. We found that the contents of organic carbon, total nitrogen and available potassium, and the activities of saccharase, urease and alkaline phosphatase were higher in the soils beneath shrubs than in the interspace bare areas, but these differences only occurred in the 0–10 cm soil profile but not in the soils below the depth of 10 cm. The soil quality index was consistently improved among the three shrub species in the topsoil. In addition, the soil nutrients were positively correlated with enzymatic activities, and the organic carbon content explained approximately 50% of the variations in the enzymatic activities. Collectively, our results demonstrated that the establishment of xerophytic shrubs improved the soil chemical and biological conditions in the desert-loess transition region, and the effect was restricted to the 0–10 cm soil layer.

Effects of mosaic-pattern shrub patches on runoff and sediment yield in a wind-water erosion crisscross region

Shrub patch fragmentation makes a substantial contribution to soil erosion in sandy regions. This study aimed to analyze the effects of mosaic-pattern shrub patch size on runoff and sedimentation in a wind-water erosion crisscross region. The influence of shrub patch size on runoff and sedimentation, and on several soil physical and vegetation factors was evaluated in a sandy Chinese landscape. Based upon the canopy diameter of Artemisia ordosica, a xerophytic shrub, three different patch sizes were set as the treatments, such as small (Ø < 60 cm), medium (60 < Ø < 160 cm) and large (Ø > 160 cm) shrub patches. Bare land served as control conditions. Three runoff plots were established for each shrub size, and runoff (Q) and sediment (SY) yields were monitored under natural rainfall conditions. The results indicated that rainfall distribution was uneven in the study area. Low-intensity (0–5 mm/h) and short-duration (0–5 h) rainfall events accounted for 82.6% and 71.7% of all events, respectively, during the 6-month test period, from May to October 2016. Linear regression indicated that Q and SY increased with increasing rainfall depth at the slope scale. The impact of rainfall erosion on bare land was the greatest. Compared with control plots, Q and SY reduction owing to the small, medium, and large shrub patches was 19.7% and 49.3%, 31.4% and 62.4%, and 35.9% and 94.9%, respectively. These results confirmed the different effects of shrub patches of different sizes on soil quality, runoff and sediment reduction. Besides, this study suggested that shrub patches could modify soil microhabitats on sandy soils, reducing the soil erosion rates and as well as favoring vegetation regeneration.

Sodium-Related Adaptations to Drought: New Insights From the Xerophyte Plant Zygophyllum xanthoxylum.

Understanding the unusual physiological mechanisms that enable drought tolerance in xerophytes will be of considerable benefit because of the potential to identify novel and key genetic elements for future crop improvements. These plants are interesting because they are well-adapted for life in arid zones; Zygophyllum xanthoxylum, for example, is a typical xerophytic shrub that inhabits central Asian deserts, accumulating substantial levels of sodium (Na+) in its succulent leaves while growing in soils that contain very low levels of this ion. The physiological importance of this unusual trait to drought adaptations remains poorly understood, however. Thus, 2-week-old Z. xanthoxylum plants were treated with 50 mM NaCl (Na) for 7 days in this study in order to investigate their drought tolerance, leaf osmotic potential (Ψs) related parameters, anatomical characteristics, and transpiration traits. The results demonstrated that NaCl treatment significantly enhanced both the survivability and durability of Z. xanthoxylum plants under extreme drought conditions. The bulk of the Na+ ions encapsulated in plants was overwhelmingly allocated to leaves rather than roots or stems under drought conditions; thus, compared to the control, significantly more Na+ compared to other solutes such as K+, Ca2+, Cl-, sugars, and proline accumulated in the leaves of NaCl-treated plants and led to a marked decrease (31%) in leaf Ψs. In addition, the accumulation of Na+ ions also resulted in mesophyll cell enlargement and leaf succulence, enabling the additional storage of water; Na+ ions also reduced the rate of water loss by decreasing stomatal density and down-regulating stomatal aperture size. The results of this study demonstrate that Z. xanthoxylum has evolved a notable ability to utilize Na+ ions to lower Ψs, swell its leaves, and decrease stomatal aperture sizes, in order to enable the additional uptake and storage of water and mitigate losses. These distinctive drought adaption characteristics mean that the xerophytic plant Z. xanthoxylum presents a fascinating case study for the potential identification of important and novel genetic elements that could improve crops. This report provides insights on the eco-physiological role of sodium accumulation in xerophytes adapted to extremely arid habitats.

Quantification of Retama raetam seed germination response to temperature and water potential using hydrothermal time concept

Retama raetam (Forssk Webb; Fabaceae) is a xerophytic shrub that is distributed from northern to southern Tunisia and which is of interest for medical use and for revegetation. To quantify seed germination responses of R. raetam to temperature (T) and water potential (ψ), and to determine cardinal Ts, a hydrothermal time model (HTT) was used. The experiment was conducted at six constant Ts (5, 10, 15, 20, 25, and 30 °C) at each of the following ψs (0, –0.3, –0.7 and −1 MPa; provided by PEG 6000). Results showed that germination rate (GR) and germination percentage (GP) were significantly influenced by ψ, T and their interactions (P < 0.01). Cardinal Ts for R. raetam was 4.2 °C for Tb (the base T), 17 °C for To (the optimum T) and 30 °C for Tc (the ceiling T) in the control condition (0 MPa). The Td (the T at which ψb(50) starts to change) was estimated to be 10 °C. By increasing T to To, hydrotime constant (θH) decreased nonlinearly and then stabilized to 30 MPa °C h at Ts ranging from 15 to 30 °C. The study showed that when the HTT model is applied, it can accurately describe the time course of germination across all Ts and ψs for this plant (R2 = 0.90). Moreover, estimated parameters using HTT model were 388.6 MPa °C h for the hydrothermal time constant (θHTT), –0.913 MPa for the base water potential (ψb(50)) and 0.047 MPa °C h for the kT (the slope of the relationship between ψb(50) and T ≥ Td). The parameters presented in this study can easily be used in R. raetam SG simulation models for characterizing the physiological status of R. raetam seed populations and also for predicting germination time courses of this plant under different environmental conditions.

NEW DATA ABOUT THE FAUNА OF ORIBATID MITES (ORIBATIDA) OF THE NORTH CAUCASUS

The purpose of this work is to publish new data on the species composition of oribatid mites in the North Caucasus, which will make possible to clarify the destribution of the oribatids of the world fauna region. The material was collected in 2003-2009, according to generally accepted methods, in 23 habitats in the territory of Adygea, Dagestan, Kabardino-Balkaria and the Krasnodar Territory in various altitudinal levels: in alpine and subalpine meadows, in mountain forests of various types (birch, pine, beech or mixed), mesophytic meadows in the forest zone, in xerophytic shrubs and mountain steppes, floodplain meadows and salt marshes of the semidesert biotopes of the lowland zone. Results. There were found 349 species of the oribatid mites from 158 genera and subgenera belonging to 62 families. Forest habitats are characterized by the greatest species diversity, there are found 232 species of oribatids. In the alpine and subalpine meadows 158 species are noted, 71 species are found in the mountain steppe zone, 47 species in the salt marshes of the semidesert zone, and 7 species in the floodplain meadows. For the first time in the Caucasian region one genus Novosuctobelba Hammer, 1977 and 29 species of the oribatid mites are registered, founded earlier only in Japan, China, Somalia and some countries of the Mediterranean. There are 14 new taxa for science: 12 species and 2 subspecies. Conclusion. In 23 biotopes of 18 geographical points of the Northern Caucasus 349 species of the oribatid mites from 158 genera and subgenus and 62 families were found. The number of species found in the biotopes of different altitude zones corresponds to the basic patterns of distribution of oribatids in mountain ecosystems: the biotopes of the forest zone are characterized by the greatest species diversity, the number of species in the soils of alpine and subalpine meadows and biotopes of the mountain-steppe zone is somewhat lower, the smallest number of species is found in the semidesert zone. For the first time in the Caucasian region one genus and 29 species of oribatid have been recorded, which allows to expand the areology of some species of the oribatid mites. There are 14 new taxa for science.

Morphoanatomical and histochemical characterization of Larrea species from Northwestern of Argentina

Larrea divaricata Cav., L. cuneifolia Cav. and L. nitida Cav., Zygophyllaceae, are evergreen xerophytic shrubs occurring in Northwestern Argentina used in traditional medicine. The aim of this work was to characterize the morphology, anatomy and histochemistry of the vegetative organs of three Larrea species by light and scanning electron microscopy in order to provide supporting data for their correct identification and to determine the site of synthesis and accumulation of its main active compounds. The shape, number and percentage of coalescence of leaflets, presence or absence of mucrones and rachis and the shape of the stipules represented the main botanical differences between the studied Larrea species. Anatomically three species presented amphystomatic leaves, with thick resinous slightly striated cuticle with resinous deposits, polygonal epidermal cells with straight anticlinal walls, ciclocytic, brachy-paracytic and paracytic stomatal types, non-glandular trichomes and isolateral mesophyll. The position and abundance of the sclerenchyma at the mid vein and petiole transection allows the differentiation of the three species, been more abundant in L. cuneifolia. Secondary phloem and parenchyma cells presented abundant calcium oxalate druses and solitary rhomboidal crystals. Epidermal cells and cuticle layer of leaflets and stipules of the three species presented amber resin deposits and content which stained positively for polysaccharides, phenolic compounds, flavonoids and tannins, while mesophyll palisade cells showed small refracting droplets stained positively for lipophilic substances.

Physicochemical composition and antioxidant activity of three Spanish caper (Capparis spinosa L.) fruit cultivars in three stages of development

Abstract Few studies have been performed on changes to physicochemical and functional properties during caper fruit development. In this work, a comparative study on the evolution of physical, chemical, and nutritive parameters and bioactive compounds of three Spanish caper cultivars was performed for the first time. These fruits were characterized by presenting the exocarp green in all stages of development, with very slight changes, which were not produced by an increase in the synthesis of carotenoids, but by partial degradation of chlorophylls a and b. There was a decrease in the protein content of the caper fruits. The H-TAA was approximately twice as much as the L-TAA. The amounts of total phenols (TPC), total flavonoids (TFC), and total flavonol compounds (TFoC) were very high in all stages of fruit development, as approximately 60% of the total phenols (TPC) were total flavonoids (TFC) and 60% of the TFC were TFoC. Given that the caper is a common perennial xerophytic shrub with a remarkable adaptability to harsh environments, and given the excellent properties of these fruits, it could be considered a species of great interest for its cultivation due to its resilience against climate change.

Evapotranspiration of xerophytic shrub Salsola passerina and Reaumuria soongorica in an arid desert ecosystem of NW China

AbstractUnderstanding the actual evapotranspiration (ET) variation of the sparsely distributed xerophytic shrubs is crucial to accurately upscale community ET to ecosystem scale. Here we quantified the actual ET of two dominant xerophytic shrubs of the Tengger Desert in northwestern China, i.e. Salsola passerina and Reaumuria soongorica, by using four large weighing lysimeters. The results showed that with the increase in precipitation from 140 to 171 mm in the year 2015/2016, the daily mean evaporation (E) of the bare area, and ET of the single shrub communities of S. passerina, R. soongorica, and the associated shrub community (S. passerina + R. soongorica) increased 50, 60, 44, and 47%, respectively; correspondingly, the total E and ET increased 49, 61, 44, and 47%, respectively. The variation of soil moisture within 0–40 cm depth plays a vital role in regulating the E and ET. The new shoot length, as one of important parameters of the xerophytic shrub, was significantly exponentially related to the cumulative ET. From the long- and short-term perspective, event-based precipitation and wind speed are the dominant driving factors behind changes in E and ET, respectively. Relative humidity is the main influencing factor for E and ET after a large rainfall event within 8 days.

Extrapolation of Leaf Measurements to Obtain the Whole-Canopy Transpiration of C3 and C4 Xerophytic Shrubs

Quantifying the water balance within areas with sparse vegetation requires frequent measurement of transpiration in water-limited, arid, desert ecosystems. Field experiments were conducted in Shapotou, northwestern China, to examine the feasibility of up-scaling the transpiration of C3 and C4 xerophytic shrubs (Reaumuria soongorica and Salsola passerina, respectively) from the leaf to the canopy level throughout the growing season in 2015. The large weighing lysimeter method and LI-6400XT portable photosynthesis system were used to make relatively long-term measurements of transpiration. The results indicated that meteorological factors coupled with stomatal conductance affected the transpiration rate of the two shrubs at the leaf level, and that the vapor pressure deficit other than net radiation and the air temperature affected the transpiration rate of S. passerina at the canopy level. Precipitation and vegetation characteristics determined the transpiration amount of the C3 and C4 xerophytic shrubs. The leaf gas exchange measurements were arithmetically scaled up to the canopy level based on the leaf area. The validity of the extrapolation was evaluated by comparing the upscale values of transpiration with the calculated values obtained from lysimeter measurement. The up-scaling approach accurately (±0.005 mm h−1, RMSE = 35%) obtained canopy transpiration from the leaf measurements. Our study suggests that the up-scaling method based on leaf area can be adopted to determine the canopy transpiration of C3 and C4 xerophytic shrubs in arid desert environments.

Afforestation with xerophytic shrubs accelerates soil net nitrogen nitrification and mineralization in the Tengger Desert, Northern China

Afforestation with xerophytic shrubs in drylands to curb desertification and land degradation has been increasingly implemented worldwide. However, the effects of this restoration practice on soil nitrogen mineralization and availability in desert areas remain poorly understood. We investigated the seasonal patterns of soil inorganic N pools and net N nitrification and mineralization in mobile sand dune and three shurblands (afforested in 1956, 1964 and 1981, respectively) in the Tengger Desert by using the in situ incubation method. Our results showed that afforestation significantly increased the soil inorganic N pools, and net nitrification and mineralization rates. Annual average values of NH4+-N, NO3−-N and total inorganic N were 2.64–4.06, 3.37–7.74 and 3.06–6.12 times greater in afforested sites that those in mobile sand dunes, with NO3−-N being predominated in all sites and its proportion being increased with stand age. In mobile sand dune, annual soil net N nitrification and mineralization rates were 1.25 and 1.87 mg N m−2 d−1, respectively, while those in afforested sites were 5.32–11.89 and 5.98–15.16 times higher, respectively, with nitrification predominated the N mineralization process. Marked seasonality in inorganic N pools, net N nitrification and mineralization were observed with the highest values in summer and the lowest in winter, which were closely linked to afforestation-induced changes in soil temperature and moisture as well as surface litter, content of clay and silt, C: N and OC of soil. The contrasting results for soil N transformations were observed during non-growing season, that was net N immobilization for the mobile sand dune without afforestation and the shrubland established in 1981, while net N mineralization for the shrublands established in 1964 and 1956, the latter two sites account for 2.65% and 9.68% of their total mineralization, respectively. These results suggested that afforestation with xerophytic shrubs has positive effects on soil nitrogen availability and cycling in desert region. It also implied that the afforestation-triggered recovery of biogeochemical cycling of N was a long-term process, and therefore soil habitat conservation is a vital issue in desert ecosystems.

Contrasting plant water‐use responses to groundwater depth in coastal dune ecosystems

AbstractGroundwater lowering can produce dramatic changes in the physiological performance and survival of plant species. The impact of decreasing water availability due to climate change and anthropogenic groundwater extraction on coastal dune ecosystems has become of increasing concern, with uncertainties about how vegetation will respond in both the short and long terms.We aimed to evaluate the water‐use responses of different plant functional types to increasing groundwater table depth and how this would affect their physiology in Mediterranean coastal dune systems differing in aridity.We modelled water‐table depth, quantified the contribution of different soil layers to plant water through Bayesian isotope mixing models and used a combination of spectral and isotope data to characterize plant ecophysiology. We found that increasing depth to groundwater triggered water uptake adjustments towards deeper soil layers only in the dry season. These adjustments in water source use were made by conifer trees (Pinus pinea,P. pinaster) and hygrophytic shrubs (Erica scoparia, Salix repens) but not by the xerophytic shrubCorema album. Moreover, we observed a greater use of groundwater under semi‐arid conditions. Accompanying the greater use of water from deep soil layers as a response to increasing groundwater depth, the semi‐arid dimorphic‐rooted conifer treeP. pineaand hygrophytic shrubE. scopariadeclined their water content (WI), without implications on photosynthetic parameters, such as chlorophyll content (CHL), photochemical index (PRI) and δ13C. Unexpectedly, under semi‐arid conditions, the shallow‐rooted xerophytic shrubC. album, associated with an absence of water source use adjustments, showed a decline inWI,CHLandPRIwith groundwater table lowering.We provide insight into how different species, belonging to different functional types, are acclimating to groundwater changes in a region experiencing climatic drought and a scarcity in groundwater due to anthropogenic exploitation. Greater depth to groundwater combined with limited precipitation can have a significant effect on plants’ water source use and ecophysiology in semi‐arid coastal dune ecosystems.Aplain language summaryis available for this article.