Arid Plant Research Articles

Seasonal Changes in Photosynthetic Energy Utilization in a Desert Shrub (Artemisia ordosica Krasch.) during Its Different Phenophases

Our understanding of the mechanisms of plant response to environment fluctuations during plants’ phenological phases (phenophases) remains incomplete. Continuous chlorophyll fluorescence (ChlF) measurements were acquired from the field to quantify the responses in a desert shrub species (i.e., Artemesia ordosica Krasch. (A. ordosica)) to environmental factors by assessing variation in several ChlF-linked parameters and to understand plant acclimation to environmental stresses. Maximal quantum yield of PSII photochemistry (Fv/Fm) was shown to be reduced by environmental stressors and to be positively correlated to air temperature (Ta) during the early and late plant-growing stages, indicating a low temperature-induced inhibition during the leaf expansion and coloration phases. Effective quantum yield of PSII photochemistry (ΦPSII) was negatively correlated to incident photosynthetically active radiation (PAR) irrespective of phenophase, suggesting excessive radiation-induced inhibition at all phenophases. The main mechanism for acclimating to environmental stress was the regulatory thermal dissipation (ΦNPQ) and the long-term regulation of relative changes in Chl a to Chl b. The relative changes in photosynthetic energy utilization and dissipation in energy partitioning meant A. ordosica could acclimatize dynamically to environmental changes. This mechanism may enable plants in arid and semi-arid environments to acclimatize to increasingly extreme environmental conditions under future projected climate change.

Establishing and validating a root water uptake model under the effects of superabsorbent polymers

AbstractIn‐depth understanding of the patterns of root water uptake (RWU) is the key to improving the water‐use efficiency of plants. Superabsorbent polymers (SAPs) can repeatedly absorb and then release water to plants when needed, which substantially increases the water‐use efficiency of plants in arid and semiarid farming. However, it also creates a challenge in modeling RWU due to unstable soil hydraulic parameters and the unclear response of root growth to SAP application. A controlled soil column experiment was conducted to investigate the response of two important root indexes, that is, root length density (RLD) and root nitrogen mass density (RND), to SAP application, as well as their relationships with RWU. The results showed that the use of the SAP caused a steady increase in RND, and it also substantially increased the RLD in the early stage, but the rate of increase gradually slowed over time. The effect of unstable soil hydraulic parameters on RWU was analyzed in a numerical experiment, which indicated that the time‐dependent effect of SAP on soil hydraulic parameters should be considered to avoid errors in calculating RWU. A specific method for calculating the RWU source/sink term in the Richards equation was proposed and ultimately used as the theoretical value of RWU to verify the RWU models based on RLD and RND to ensure the best one was selected. The results showed that RND was better able to be used for development of the RWU model to simulate the patterns of RWU under SAP application.

Plant community changes after land abandonment control CO2 balance in a dry environment

Human activities can dramatically alter natural plant communities which, after disturbance cessation, undergo secondary succession. In arid environments plant succession is quite slow, and its link to the carbon (C) cycle is not well known. We assessed changes in C balance on a semiarid plant community along a chronosequence spanning ca. 100 years after land abandonment in an arid environment in SE Spain to examine temporal changes in C following human disturbance. We selected 5 individuals of the dominant plant species along five plant community stages differing in the time since land abandonment occurred, and we used a closed-chamber infrared gas analyzer method to estimate the contribution of whole plants and bare soil to community C exchange. We estimated CO2 fluxes for each plant community stage and calculated temporal differences along the chronosequence. Plant community composition and plant cover changed throughout the chronosequence. Carbon balance was related to changes in plant photosynthesis and plant and soil respiration along the chronosequence. Overall, community C exchange shifted from source to sink as plant colonization progressed. It took 65 years for the system to recover the equivalent C sink capacity of the undisturbed site. Recovery of arid plant communities after land abandonment may enhance long-term C sequestration and significantly contribute to C balance at the global level.

Mind the gap among patches in arid plant communities: rapid root proliferation in response to N addition

In arid communities, it has been proposed that individual plants can extend their roots beyond their canopy exploring neighbouring bare ground areas. This becomes relevant in systems where the vegetation is distributed in patches surrounded by bare soil. However, whether roots of different species may be overlapping under bare ground areas is still controversial. The factors controlling root responses when no plants appear to be directly influencing the gap among patches are still unclear. The aim of our study was to detect perennial grasses responses to an N enrichment pulse. In a semi-arid steppe (Patagonia, Argentina), we buried root traps filled with sieved soil with and without N addition, under bare soil patches. Traps were harvested after 4 and 6 months. Trap neighbourhoods (30 cm in diameter) included at least three of the dominant tussock species. After harvests, we identified species in the traps by root traits and quantified diversity, biomass and specific relative growth rates. Bare ground areas show simultaneous root growth of different species. Diversity of perennial grass roots was higher with N addition than without it in the first harvest (4 months), but this difference disappeared in the second harvest (6 months). Root biomass was maximal after 6 months in N addition traps. Species preferred by herbivores (Bromus pictus and Poa ligularis) showed rapid growth and responses to N addition. Differences between harvests may be an indicative that N pulses interact with rising temperatures and soil water content as growing season progress.

Dew measurement and estimation of rain-fed jujube (Zizyphus jujube Mill) in a semi-arid loess hilly region of China

Dew is an important water source for plants in arid and semi-arid regions. However, information on dew is scarce in such regions. In this study, we explored dew formation, amount, and duration of rain-fed jujube (Zizyphus jujube Mill) trees in a semi-arid loess hilly region of China (i.e., Mizhi County). The data included dew intensity and duration, relative humidity, temperature, and wind speed measured from 26 July to 23 October, 2012 and from 24 June to 17 October, 2013 using a micro-climate system (including dielectric leaf wetness sensors, VP-3 Relative Humidity/Temperature Sensor, High Resolution Rain Gauge, and Davis Cup Anemometer). The results show that atmospheric conditions of relative humidity of >78% and dew point temperature of 1°C–3°C are significantly favorable to dew formation. Compared with the rainfall, dew was characterized by high frequency, strong stability, and long duration. Furthermore, heavy dew accounted for a large proportion of the total amount. The empirical models (i.e., relative humidity model (RH model) and dew point depression model (DPD model)) for daily dew duration estimation performed well at 15-min intervals, with low errors ranging between 1.29 and 1.60 h, respectively. But it should be noted that the models should be calibrated firstly by determining the optimal thresholds of relatively humidity for RH model and dew point depression for DPD model. For rain-fed jujube trees in the semi-arid loess hilly regions of China, the optimal threshold of relative humidity was 78%, and the optimal upper and lower thresholds of dew point depression were 1°C and 5°C, respectively. The study further demonstrates that dew is an important water resource that cannot be ignored for rain-fed jujube trees and may affect water balance at regional scales.

组织培养对沙柳器官形成与植株再生的影响研究

沙柳(Salix psammophila)是北方干旱和沙漠地区重要的生态经济植物之一。本研究以采自沙柳当年生健壮嫩枝茎段为研究对象，通过组织培养手段使其器官形成并分化，继而诱导继代形成再生植株，以探索其在不同组织培养条件下形成再生植株的关键技术。结果表明，沙柳在MS培养基上芽分化效果较好，适宜分化增殖培养基为MS + 0.5 mg/L 6-BA + 0.1 mg/L NAA；继代培养基为MS + 0.2 mg/L 6-BA + 0.2 mg/L KT + 0.1 mg/L NAA，并与激素稍高浓度的培养基MS + 1.0 mg/L 6-BA + 0.1 mg/L NAA交替培养达到效果更佳；生根培养基为1/2MS + 0.3 mg/L IBA + 0.05 mg/L NAA，可获得到沙柳再生体系的建立，该方法不仅为沙柳稳定性遗传转化研究提供材料来源，也为今后实现沙柳工厂化育苗提供理论与技术依据。 Salix psammophila is one of the important eco-economic plants in northern arid and desert region. In this experiment, on the basis of the strong tender stem segments, the key skills of how regene-rated plant forms in different Salix psammophila tissue culture conditions were explored, by means of tissue culture to get the organs formed and differentiated and to induce regeneration plants formed in succession. Research results show that Salix psammophila gets better bud differentiation effect in MS medium, the suitable differentiation and proliferation medium is MS + 0.5 mg/L 6-BA + 0.1 mg/L NAA; the subculture medium is MS + 0.2 mg/L 6-BA + 0.2mg/L KT + 0.1 mg/L NAA, with shifting the culture with the medium MS + 1.0 mg/L 6-BA + 0.1 mg/L NAA, a medium with little higher hormone, to achieve the best effect; the rooting medium is 1/2MS + 0.3 mg/L IBA + 0.05 mg/L NAA, all the results establish the regeneration system. This method not only provides the materials source for Salix psammophila stable genetic transformation studies, but also offers theoretical and technical support for Salix psammophila industrialized seeding production in the future.

Distribution changes of woody plants in Western Iran as monitored by remote sensing and geographical information system: a case study of Zagros forest

The status of woody plants in dry-land systems is a fundamental determinant of key ecosystem processes. Monitoring of this status plays an important role in understanding the dynamics of woody plants in arid and semi-arid ecosystems. The present study determined the dynamism of the Zagros forests in Iran using Remote Sensing and Geographic Information System techniques and statistical science. The results show that the density of trees varied from 10 to 53 % according to the physiographic and climatic conditions of semi-arid regions. The best and lowest correlation between vegetation indices and forest density were obtained for the global environmental monitoring index (GEMI; R 2 = 0.94) and soil adjust vegetation index (R 2 = 0.81), respectively. GEMI is used to monitor land use changes over a 10-year period. Results show that 2720 ha2 of forest have been destroyed by human interference and tillage on steep slopes during this period which also resulted in the loss of the fertile soil layer. GEMI determined the areas with a biomass of trees and could normally separate border regions with low biomass density of trees from regions without canopy cover. The results revealed that assessment of forest and vegetation cover in arid and semi-arid arduous forest regions using satellite digital numbers and ordinary sampling is subject to uncertainty. A stratified grouping procedure should be established to increase the accuracy of assessment.

Multi-scale object-based measurement of arid plant community structure

ABSTRACTThe measurement of plant community structure provides an extensive understanding of its function, succession and ecological process. The detection of plant community boundary is rather a challenge despite in situ work. Recent advances in object-based image analysis (OBIA) and machine learning algorithms offer new opportunities to address this challenge. This study presents a multi-scale segmentation approach to accurately identify the boundaries of each vegetation and plant community for mapping plant community structure. Initially, a very high resolution (VHR) Worldview-2 image of a desert area is hierarchically segmented from scale parameter 2 to 500. Afterward, the peak values of the standard deviation of brightness and normalized difference vegetation index (NDVI) across the segmentation scales are detected to determine the optimal segmentation scales of homogeneous single plant and plant community boundaries. A multi-scale classification of vegetation characterization with features of multiple bands, NDVI, grey-level co-occurrence matrix (GLCM) entropy and shape index is performed to identify dryland vegetation types. Finally, the four vegetation structural features on the type, diversity, object size and shape are calculated within the plant community boundaries and composed to plant community structure categories. Comparing the results with the object fitting index (FI) of the reference data, the validation indicates that the optimal segmentations of tree, shrub and plant communities are consistent with the identified peak values.

Native microhabitats better predict tolerance to warming than latitudinal macro‐climatic variables in arid‐zone plants

AbstractAimUnderstanding species ability to withstand heat stress is paramount for predicting their response to increasing temperatures and decreasing rainfall. Arid systems are subject to climatic extremes, where plants, being immobile, live on the frontline of climate change. Our aim was to investigate whether: (1) warming tolerance [WT = the difference between a species physiological thermal damage threshold (T50) and the maximum temperature within its distribution (Thab)] for desert plants is higher at high latitudes, as has been shown for terrestrial ectotherms, and (2) if T50 of desert plants better corresponds with broad climatic indicators or species native microhabitats.LocationThe Australian Arid Lands Botanic Garden, Port Augusta, South Australia.MethodsUsing chlorophyll fluorescence techniques, we measured T50 for 42 Australian arid plant species native to different microhabitats based on water availability. WT was calculated (T50−Thab) and each metric was compared against microhabitat and broad‐scale climatic variables for each species.ResultsT50 was unrelated to macro‐scale climate or latitude, whereas WT increased for species whose distributions extend into higher latitudes, a pattern hitherto not shown for terrestrial plants. We also found that species adapted to higher water availability in their native microhabitat had significantly lower T50 and WT than species from drier microhabitats.Main conclusions(1) Warming tolerance increased with latitude, but the strength of this relationship was related to the way WT was quantified, with Thab and latitude being linked. (2) T50 did not correlate with latitude, but both T50 and WT were strongly related to their microhabitats. Specifically, water availability is important, such that even within a desert biome, species associated with ‘wetter’ microhabitats, may be particularly vulnerable to heat stress. Thus, we show that local‐scale patterns better capture plant physiological responses to temperature than broad‐scale distributions.

Using polyaspartic acid hydro-gel as water retaining agent and its effect on plants under drought stress.

Polyaspartic acid (PASP) hydrogel is an important and widely applied water-retaining agent, thanks to its special space network structure which contains a carboxyl group attached on the side chain. In this study, the PASP hydrogel with high water absorption rate (300–350 g H2O/g hydrogel) was developed and adopted to transplant Xanthoceras sorbifolia seedlings in the ecological restoration project of Mount Daqing National Nature Reserve. Transplantation experiments showed that the survival rate and leaf water content index for X. sorbifolia seedlings were increased by 8–12% and 4–16%, respectively. Additionally, compared with the counterpart without PASP hydrogel, the value of chlorophyll fluorescence that was considered as one of the most important indicators of plant physiology, was significantly improved with the addition of PASP hydrogel. The PASP hydrogel displays a promising future for the applications of increasing the survival rate and simultaneously alleviating the drought stress effects on the pioneer plants in arid and semi-arid areas.

Root-associated fungal community response to drought-associated changes in vegetation community

Recent droughts in southwestern USA have led to large-scale mortality of piñon (Pinus edulis) in piñon-juniper woodlands. Piñon mortality alters soil moisture, nutrient and carbon availability, which could affect the root-associated fungal (RAF) communities and therefore the fitness of the remaining plants. We collected fine root samples at a piñon-juniper woodland and a juniper savannah site in central New Mexico. Roots were collected from piñon and juniper (Juniperus monosperma) trees whose nearest neighbors were live piñon, live juniper or dead piñon. RAF communities were analyzed by 454 pyrosequencing of the universal fungal ITS region. The most common taxa were Hypocreales and Chaetothyriales. More than 10% of ITS sequences could not be assigned taxonomy at the phylum level. Two of the unclassified OTUs significantly differed between savanna and woodland, had few like sequences in GenBank and formed new fungal clades with other unclassified RAF from arid plants, highlighting how little study has been done on the RAF of arid ecosystems. Plant host or neighbor did not affect RAF community composition. However, there was a significant difference between RAF communities from woodland vs. savanna, indicating that abiotic factors such as temperature and aridity might be more important in structuring these RAF communities than biotic factors such as plant host or neighbor identity. Ectomycorrhizal fungi (EM) were present in juniper as well as piñon in the woodland site, in contrast with previous research, but did not occur in juniper savanna, suggesting a potential shared EM network with juniper. RAF richness was lower in hosts that were neighbors of the opposite host. This may indicate competitive exclusion between fungi from different hosts. Characterizing these communities and their responses to environment and plant neighborhood is a step toward understanding the effects of drought on a biome that spans 19 000 000 ha of southwestern USA.

The effect of lichen-dominated biological soil crusts on growth and physiological characteristics of three plant species in a temperate desert of northwest China.

Biocrusts (biological soil crusts) cover open spaces between vascular plants in most arid and semi-arid areas. Information on effects of biocrusts on seedling growth is controversial, and there is little information on their effects on plant growth and physiology. We examined impacts of biocrusts on growth and physiological characteristics of three habitat-typical plants, Erodium oxyrhynchum, Alyssum linifolium and Hyalea pulchella, growing in the Gurbantunggut Desert, northwest China. The influence of biocrusts on plant biomass, leaf area, leaf relative water content, photosynthesis, maximum quantum efficiency of PSII (F(v)/F(m)), chlorophyll, osmotic solutes (soluble sugars, protein, proline) and antioxidant enzymes (superoxide dismutase, catalase, peroxidase) was investigated on sites with or without biocrust cover. Biomass, leaf area, leaf water content, photosynthesis, F(v)/F(m) and chlorophyll content in crusted soils were higher than in uncrusted soils during early growth and lower later in the growth period. Soluble sugars, proline and antioxidant enzyme activity were always higher in crusted than in uncrusted soils, while soluble protein content was always lower. These findings indicate that biocrusts have different effects on these three ephemeral species during growth in this desert, primarily via effects on soil moisture, and possibly on soil nutrients. The influence of biocrusts changes during plant development: in early plant growth, biocrusts had either positive or no effect on growth and physiological parameters. However, biocrusts tended to negatively influence plants during later growth. Our results provide insights to explain why previous studies have found different effects of biocrusts on vascular plant growth.

Molecular mechanisms of foliar water uptake in a desert tree

Water deficits severely affect growth, particularly for the plants in arid and semiarid regions of the world. In addition to precipitation, other subsidiary water, such as dew, fog, clouds and small rain showers, may also be absorbed by leaves in a process known as foliar water uptake. With the severe scarcity of water in desert regions, this process is increasingly becoming a necessity. Studies have reported on physical and physiological processes of foliar water uptake. However, the molecular mechanisms remain less understood. As major channels for water regulation and transport, aquaporins (AQPs) are involved in this process. However, due to the regulatory complexity and functional diversity of AQPs, their molecular mechanism for foliar water uptake remains unclear. In this study, Tamarix ramosissima, a tree species widely distributed in desert regions, was investigated for gene expression patterns of AQPs and for sap flow velocity. Our results suggest that the foliar water uptake of T. ramosissima occurs in natural fields at night when the humidity is over a threshold of 85 %. The diurnal gene expression pattern of AQPs suggests that most AQP gene expressions display a circadian rhythm, and this could affect both photosynthesis and transpiration. At night, the PIP2-1 gene is also upregulated with increased relative air humidity. This gene expression pattern may allow desert plants to regulate foliar water uptake to adapt to extreme drought. This study suggests a molecular basis of foliar water uptake in desert plants.

Hydrological niches in terrestrial plant communities: a review

Summary Despite the fundamental significance of water to plants and the persisting question of how competing species coexist, this is the first review of hydrological niches. We define hydrological niche segregation (HNS) as: (i) partitioning of space on fine‐scale soil‐moisture gradients, (ii) partitioning of water as a resource and/or (iii) partitioning of recruitment opportunities among years caused by species specializing on particular patterns of temporal variance of water supply (the storage effect). We propose that there are three types of constraint that lead to the trade‐offs that underlie HNS. (i) An edaphic constraint creates a trade‐off between the supply to roots of O2 on the one hand vs. water and nutrients on the other. (ii) A biophysical constraint governs gas exchange by leaves, leading to a trade‐off between CO2 acquisition vs. water loss. (iii) A structural constraint arising from the physics of water‐conducting tissues leads to a safety vs. efficiency trade‐off. Significant HNS was found in 43 of 48 field studies across vegetation types ranging from arid to wet, though its role in coexistence remains to be proven in most cases. Temporal partitioning promotes coexistence through the storage effect in arid plant communities, but has yet to be shown elsewhere. In only a few cases is it possible to unequivocally link HNS to a particular trade‐off. Synthesis. The field and experimental evidence make it clear that HNS is widespread, though it is less clear what its precise mechanisms or consequences are. HNS mechanisms should be revealed by further study of the constraints and trade‐offs that govern how plants obtain and use water, and HNS can be mechanistically linked to its consequences with appropriate community models. In a changing climate, such an integrated programme would pay dividends for global change research.

Effect of Drought Stress and its Interaction with Salicylic Acid on Fennel (Foeniculum vulgare Mill.) Germination and Early Seedling Growth

Environmental stress, particularly drought stress can play an important role in reducing plant growth especially during the germination stage in arid and semi-arid regions in Iran. For cultivation of medicinal plants in arid and semi-arid areas, the assessment of their tolerance is very important. In this research, in order to evaluate the effects of salicylic acid pretreatment on enhancement of seed germination and early seedling growth of Foeniculum vulgare Mill. under drought stress, a factorial experiment based on completely randomized design was employed. The factors were the combination of five levels of drought stress induced by poly ethylene glycol (0, -0.1, -0.2, -0.3 and -0.4 MPa) and five concentrations of salicylic acid (0, 0.25, 0.5, 0.75 and 1 mM) with three replicates. The results indicated that an increase in drought stress reduced germination components such as germination percentage and rate, total biomass, seed vigor index, root length, root fresh and dry weight, shoot length, shoot fresh and dry weight and relative water content and increased electrolyte leakage and proline content. Salicylic acid improved germination; therefore, the average time necessary for germination decreased under drought conditions. The seeds treated by salicylic acid, produced a higher root and shoot length, root and shoot fresh and dry weight, total biomass and seed vigor index. Salicylic acid ameliorated the negative effects of drought stress on fennel germination and seedling's growth. Higher concentrations of salicylic acid were more effective than the lower ones. It seems that salicylic acid can enhance the tolerant ability of the seeds to germination under drought stress.

How Fast Can Carbon Be Sequestered When Restoring Degraded Subtropical Thicket?

AbstractIs the maximum rate of carbon sequestration reported for the CAM‐C3 plant Portulacaria afra (spekboom), viz. 15.4 t CO2 ha−1 yr−1, unusual in comparison with other plants with similar physioliogies, or could such rates be expected routinely in restoration with P. afra? Private sector investors in thicket restoration need an answer to this question in order to assess the feasibility of using carbon finance as the main income stream from their investments. A literature review showed that 15.4 t CO2 ha−1 yr−1 is not an unusual rate of carbon sequestration for CAM plants in arid and semi‐arid environments, which suggests that investors in thicket restoration should not consider this an outlier value. The results also suggest that carbon finance could be used to fund restoration using other CAM plants in degraded xeric thickets in countries such as Argentina, Chile, Mexico, and Madagascar.

Differential Nitrogen Cycling in Semiarid Sub-Shrubs with Contrasting Leaf Habit

Nitrogen (N) is, after water, the most limiting resource in semiarid ecosystems. However, knowledge on the N cycling ability of semiarid woody plants is still very rudimentary. This study analyzed the seasonal change in the N concentrations and pools of the leaves and woody organs of two species of semiarid sub-shrubs with contrasting leaf habit. The ability of both species to uptake, remobilize and recycle N, plus the main storage organ for N during summer drought were evaluated. We combined an observational approach in the field with experimental 15N labelling of adult individuals grown in sand culture. Seasonal patterns of N concentrations were different between species and organs and foliar N concentrations of the summer deciduous Lepidium subulatum were almost double those of the evergreen Linum suffruticosum. L. subulatum up took ca. 60% more external N than the evergreen and it also had a higher N resorption efficiency and proficiency. Contrastingly, L. suffruticosum relied more on internal N remobilization for shoot growth. Differently to temperate species, the evergreen stored N preferentially in the main stem and old trunks, while the summer deciduous stored it in the foliage and young stems. The higher ability of L. subulatum to uptake external N can be related to its ability to perform opportunistic growth and exploit the sporadic pulses of N typical of semiarid ecosystems. Such ability may also explain its high foliar N concentrations and its preferential storage of N in leaves and young stems. Finally, L. suffruticosum had a lower ability to recycle N during leaf senescence. These strategies contrast with those of evergreen and deciduous species from temperate and boreal areas, highlighting the need of further studies on semiarid and arid plants.

Effects of Water Stress and Potassium on Quantity Traits of Two Varieties of Mung Bean (Vigna Radiata L.)

ABSTRACT Water stress is known as the major threat to reduced growth and yield of plants in arid and semi-arid regions. Potassium is one of the indicators of plant responses to water stress. To evaluate the impact of water stress and levels of potassium on yield and yield components of two varieties of mung bean (Vigna radiata) (promising lines VC6172 and Indian), an experiment in the form of split factorial, based on randomized complete block design with three replicates was conducted in 2011, at the research farm of Safi-Abad Dezfool, Iran (latitude 32°16’ N, longitude 48°26’ E and altitude 82.9 m above sea level) .Water stress in three levels: irrigation at 120 (no stress), 180 (moderate stress) and 240 (severe stress) mm evaporation from pan, were allocated to the main plots and potassium fertilizer at three levels (0, 90, 180 kg /ha) and two varieties of mung bean (promising line VC6172 and Indian) were allotted to the sub-plots. Results showed that water stress and potassium fertilizer significantly affect all traits. The highest grain yield (2093 kg /ha) was obtained from no stress treatment in the case of 180 kg /ha potassium. Total dry matter, number of pods and grain yield, were significantly different between the two varieties. The interaction between fertilizer and variety, on dry matter and grain yield and the interaction between irrigation and variety, on dry matter were significant. We conclude that use of potassium fertilizer can reduce the adverse effects of water stress.

Physiological and biochemical responses of Syntrichia caninervis at a snowfall event in different desert habitats

Aims Water is the most constraining factor to the growth of plants in arid and semiarid regions of China. Biological soil crusts(BSCs) develop well in Gurbantunggut Desert and Syntrichia caninervis is a dominant species in the moss crusts of this cold desert. Compared to other desert ecosystems, the Gurbantunggut desert is home to stable and abundant snow cover in winter. The moisturizing and warming effects of snow cover provide the desert mosses with optimal growth conditions. Our objective in this study was to determine how S. caninervis shoots utilize the special snow resources under different microhabitats in early winter. Methods The experiments were conducted from prior to the snowfall and until following the snow thawing at a long-term study site of the Gurbantunggut Desert. We measured the physiological and biochemical characteristics in S. caninervis in three habitats: the live shrub, the dead shrub, an exposed area. The shoot water content, chlorophyll fluorescence, proline content, soluble sugar content, soluble protein content, malonyldialdehyde(MDA) content, peroxidase(POD) and superoxide dismutase(SOD) activity were compared. Important findings The results showed that snowfall increased moss water content, the maximal photochemical efficiency of PSII(Fv/Fm), soluble sugar content, SOD and POD activity. The content of proline and MDA were reduced with snow melting. Microhabitats influenced the physiological characteristics in S. caninervis, with the effects varying with snowfall event. The water content and chlorophyll fluorescence activity were significantly higher in samples under the living shrub, while in the exposed area S. caninervis had lower water content and chlorophyll fluorescence activity regardless of the snowfall cover. These findings suggested that the S. caninervisplants under the loving shrub experienced the least stress and had the best physiological performance but weak resistance, and that those in exposed area were more stress tolerant and had poorer physiological performance. Following the snowfall, proline content, MDA content, POD and SOD activity all had significantly negative correlations with plant water content; whereas the soluble sugar and protein content displayed significantly positive correlations with plant water content. The results indicated that snowfall reduced the water stress in S. caninervis, and enhanced their physiological performance and photosynthesis, with the effects being facilitated by the low temperature of the early winter.

Evaluation of urban treated wastewater and irrigation method on growth indices of landscaping plants in arid and semi-arid regions

Today water scarcity in the agriculture has become a major problem. Sousing wastewater in the agricultural farms, gardens and landscapes has attracted much attention. In this research, the effects of irrigation with the urban treated wastewater were studied on the Laurus nobilis L. and the Buxus sempervirens L. plants. The irrigation treatments were: T1–Furrow irrigation with normal water, T2: DI system with treated wastewater (drip irrigation), T3–SDI system with treated wastewater (sub-surface drip irrigation) at depth of 15 cm, T4–SDI system with treated wastewater at 30 cm depth and T5: Furrow irrigation with treated wastewater. The experiment was conducted in the research field of Isfahan wastewater refinery with the three replications and five irrigation treatments during two years, 2010–2012. Results expressed that the irrigation with wastewater had the positive effects on the growth of both the plants. In the Laurus nobilis L., the greatest number of auxiliary shoots was observed in the surface drip irrigation with the treated wastewater. The height of main stem was increased in the furrow irrigation treatment with the treated wastewater. The analysis of B. sempervirens L. demonstrated that the SDI system with the treated wastewater at the depth of 15 cm had the highest number of branches and plant height. Accordingly the plant growth in the irrigation with wastewater was better than the normal water. In B. sempervirens L., T3 treatment had positive effects on the plant growth in both the stages. Therefore, using of sub-surface drip irrigation at the depth of 15 cm is recommended because of the reduction of the surface soil pollution.