Adaptive evolution of rbcL in Reaumuria soongarica (Tamaricaceae)

In the field of phylogenetic analyses, the rbcL gene encoded large subunit Ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco, EC4.1.1.39), which plays a crucial role in the process of photosynthesis for most terrestrial plants, has been considered to be conserved; however, recent controversy regarding rbcL conservation has appeared since it was proposed to be under natural selection within all principal lineages of land plants. In this study, by examining the variation of DNA and protein sequences among 17 species in the family Tamaricaceae, three nonsynonymous mutations were identified to be under positive selection. The favored sites were located in the alph-helix domains of Rubisco, with decreased hydrophobicity and increased entropy, which could facilitate CO₂ penetration into the active site of Rubisco. We also found that the expression level of rbcL in different genotypes of Reaumuria soongarica shifted in response to various stresses such as drought, temperature, salt, and light. This study not only sheds light on the functional/structural features of Rubisco in the evolution scenarios from C₃-like into C₄ in Tamaricaceae but also provides useful information on directing genetic performance to enhance photosynthesis efficiency of desert plants for sustaining fragile desert ecosystems; furthermore, it promotes the ability to cope with desert aridification and global warming.     

Microfungal community associated with rhizosphere soil of Zygophyllum qatarense in arid habitats of Bahrain

Population density and species diversity of microfungal communities were investigated in the rhizosphere soil of the halophytic plant Zygophyllum qatarense inhabiting saline and nonsaline habitats of the arid desert environment of Bahrain. Unlike the nonsaline habitat which is situated in the physiographic zone of multiple escarpment and backslopes, the saline site is located in the coastal lowlands and is featured by high chloride content, electrical conductivity, total soluble salts and low organic matter. Soils of both habitats are sandy, slightly alkaline, poor in nutrient sources, low in water-holding capacity and mainly dominated by a salt-tolerant flora. Quantification of data for the recovery of fungi were based on colony identification and counts by a series of ten-fold dilutions plate method, using various natural, synthetic and selective media. A total of 2780 isolates, fluctuating between 25 and 1109 per sample, were recovered during the present study among all habitats, seasons and plant sizes. Grouping of these isolates has resulted in a maximum of 28 fungal taxa varied between 5 and 15 species, of which 24 were hyphomycetes, 3 ascomycetes and one was an unknown species. All the recorded species in this study, excluding the genus Fusarium, are newly reported from the arid terrestrial habitats of Bahrain. Of the encountered fungi,Cladosporium sphaerospermum was the most dominant and frequent genus, among all plant sizes, followed by Penicillium citrinam and Aspergillus fumigatus, a finding with consistent documented data from similar arid Sahara ecosystems. Examination of data, supported by analysis of relative density values, percentage recovery rates, polar ordination and diversity indices revealed that the nonsaline habitat during the dry period yielded the highest isolate frequency, species abundance, and diversity when compared with the saline habitat. Moreover, a progressive increase in colony occurrence and species diversity was equivalently associated with increment in plant size in the nonsaline habitat. Apparently, the vast majority (moderate to low occurrence class) of the reported species are rhizosphere indigenous saprophytic cellulose-decomposers, whilst the sparse taxa (high occurrence class), e.g. C. sphaerospermum, are regarded as thermo-osmotolerant. Comparison of species richness among samples suggests that small plants inhabiting nonsaline habitats during the wet and dry season were richest in species composition. It is proposed that inter- and intra-specific variation in fungal community between the above habitats reflect not only the influence of plant age and season but also extends to critical multi-soil edaphic and biotic factors involving essentially soil moisture, salinity and root growth dynamic and exudates.     

Competition as a barrier to establishment of a native perennial grass (Elymus elymoides) in alien annual grass (Bromus tectorum) communities

The alien grass Bromus tectorum dominates stable annual-plant communities that have replaced native shrub-perennial grass communities over much of the semi-arid western United States. We conducted field competition experiments between B. tectorum and a native grass, Elymus elymoides, on two sites to determine the effects of B. tectorum competition on perennial grasses, and the role of B. tectorum competition in the stability of B. tectorum-dominated communities. B. tectorum competition acting on seedling-stage E. elymoides plants greatly reduced first-year relative growth rates and biomass which, in turn, reduced second-year survival, biomass, and flowering. However, B. tectorum competition acting on older E. elymoides plants had much less effect, which may help to explain why intact perennial-plant communities are resistant to B. tectorum invasion. At the drier site, direct effects of B. tectorum competition were less, but competition and drier habitat combined to produce greater E. elymoides mortality.     

高光谱指数法用于确定多枝柽柳(Tamarix ramosissima)蒸腾速率

蒸腾速率(Tr)是植物生理生态学研究中表征蒸腾耗水的常用指标,研究植物的蒸腾耗水有助于了解当地生态系统稳定性和水资源的可持续利用,但在遥感应用尤其在干旱区遥感应用中很少被使用。本文以古尔班通古特沙漠南缘的主要建群种多枝柽柳(Tamarix ramosissima)作为研究对象,应用高光谱指数法对其Tr日变化过程进行研究,寻找和确定最佳的Tr光谱指数。选择的6个光谱指数判定系数R2介于0.06~0.73,其中简单比值(SR)光谱指数有最高的判定系数(R2=0.73)、较低的均方根误差(RMSE=0.24)和较为简单的形式,光谱范围处于近红外波段(1 645~1 655nm)/(1 775~1 785nm)。SR作为Tr最佳光谱指数,对植被水分关系变化敏感,能够较好地记录和监测Tr日变化过程,有益于揭示光谱指数物理和生理机制。     

Growth response of the saltbush Atriplex nummularia L. to inoculation with the arbuscular mycorrhizal fungus Glomus intraradices

Plantlets of Atriplex nummularia were inoculated with the arbuscular mycorrhizal fungi Glomus intraradices in a pot experiment. Plants were grown in a low P soil. Highly significant growth response of a Chenopodiaceae was recorded for the first time. Mycorrhizal colonization of roots was well developed, internal hyphae and vesicles were observed, but not arbuscules. These observations suggest that arbuscules are not necessary to obtain significant growth stimulation from mycorrhizal inoculation. Atriplex nummularia is already used as forage crops, its high mycorrhizal dependency offers possibilities to develop this production and revegetation strategies.     

Water requirements for germination and early seedling establishment in four African savanna woody plant species

The aim of this study was to determine the water requirements for germination and early seedling establishment of four African savanna tree species, namelyAcacia karroo, A. nilotica, A. tortilisandMundulea sericea. The acacias are characteristic of nutrient-rich, andM. sericeaof nutrient-poor savannas. Imbibition times of scarified seeds ofA. karroo(4 h),M. sericea(6 h) andA. tortilis(8 h) were rapid relative toA. nilotica(28 h) and were inversely correlated with seed size. Imbibed water is lost in about 2 h after drying at 25°C for all species exceptA. nilotica(only 70% moisture loss). Seeds ofA. karrooandM. sericeakept at 40°C dried to below their original moisture contents within 2 h. Seeds ofA. niloticaandA. tortilisdried at 40°C lost viability relative to (undried) control seeds, while there was no significant loss of viability forA. karrooandM. sericea. For fully imbibed seeds to germinate in sandy savanna soils, all four species required at least the equivalent of 3 mm rainfall every 2 days under mild greenhouse conditions. However, most ungerminated seeds were still viable despite drying-out from a fully imbibed state. Maintenance of soil at 50% field capacity (FC), or watering to FC every 9th day is the maintenance requirements for 2-week-old seedlings ofA. niloticaandM. sericeato continue growth for a further 5 weeks under greenhouse conditions, althoughA. niloticamostly survived 25% FC with one seedling surviving 12·5% FC. Root penetration was rapid in sandy soils, withA. niloticaandM. sericeaattaining a depth of 40 cm within 15 days. Frequent, but not necessarily high, rainfall appears to be essential for germination and seedling survival over the first 7 weeks.     

种植于人工梭梭(Haloxylon ammodendron)林的肉苁蓉(Cistanche deserticola)个体质量特征

为掌握人工种植条件下肉苁蓉(Cistanche deserticola)个体质量特征,在塔克拉玛干沙漠腹地咸水滴灌人工梭梭林内,采用统一的开沟、撒种接种方式,对不同林龄、不同深度接种肉苁蓉以及造林当年接种连年采收肉苁蓉的质量进行了调查和分析。结果表明:(1)所有样地出土肉苁蓉个体间质量差异大,分布离散程度高。(2)接种时林龄越大,出土肉苁蓉个体平均质量、质量品质较好的比率以及质量分布离散程度都越高;不同林龄间肉苁蓉个体质量有极显著差异。造林当年接种、连年出土肉苁蓉个体质量的特征与不同林龄的相似,但质量品质较好的比率相对较低。(3)在40~120cm深度,随种植深度增加,出土2年生以上肉苁蓉个体的数量以及质量品质较好的比率总体呈现增加趋势,并可以分为3个层面:40cm、50~80cm、100~120cm。其中40cm深度质量指标明显较低,其他深度间没有表现出明显的差异和规律,100~120cm深度的肉苁蓉个体相对细长、品相差。     

The effect of radiation on seedling growth and physiology in four species of Prosopis L. (Mimosaceae)

Domestication of wild plants needs efforts focused particularly on the development of the theoretical basis of plant responses to environmental conditions. The objective of this study was to assess the effect of radiation on seedling growth and physiology of Prosopis alba, P. chilensis, P. flexuosa and P. glandulosa. Seedlings were grown in a greenhouse and randomly assigned to three light environments: full-sun, 52% sun, and 38% sun. No significant differences were found in the rate of leaf appearance and plant height 60 days after the light treatments began. Instantaneous CO₂uptake was not affected by the light environment during leaf development and did not differ among species. Variations in radiation availability resulted in significant differences in biomass accumulation, shoot/root ratio, protein and total non-structural carbohydrates contents. The practice of shading seedlings reduces the chances of survival ofProsopis due to an increase of the shoot/root ratio and a reduction of total biomass, stored carbohydrates, and the C:N balance.     

Salinity-induced growth and some metabolic changes in three Salsola species

Three Salsola species, Salsola dendroides Pall., S. richteri (Moq.) Karel ex Litw. and S. orientalis S.C. Gmel., were compared for their salt tolerance, inorganic ionic accumulation and their biomass production in saline conditions. Seeds were grown on sterilized quartz under five salinity levels in a factorial experimental design, with four replications, in greenhouse conditions.With salinity, Na⁺ accumulation increased while K⁺ accumulation decreased. All three species showed positive shoot growth for low levels of salinity. Root growth showed almost the same trend as shoot growth, with minor exceptions. At low levels of salinity, proline accumulated more in S. dendroides plant tissues than in the tissues of the other two species. These results suggest that the proline accumulation is a good index for salinity tolerance. Soluble sugars also increased as a result of salinity.     

Reproductive and recruitment traits as indicators of the invasive potential of Kalanchoe daigremontiana (Crassulaceae) and Stapelia gigantea (Apocynaceae) in a Neotropical arid zone

Populations of two ornamental exotic species, Kalanchoe daigremontiana and Stapelia gigantea, have been recently detected inside a protected area containing arid ecosystems in Venezuela. We indirectly tested their invasive potential by characterizing their reproductive biology and recruitment patterns and comparing our estimates against Baker's Law and reproductive profiles reported for invasive plants. K. daigremontiana is autogamous, produces >16,000 seeds per plant and also reproduces clonally. Despite low seed viability (17.9%) and germination rates (11.9%), seeds were present in the seed bank. Plantlets of asexual origin showed high survival (75–100%) compared to seedlings of sexual origin (10%). S. gigantea is self-incompatible, xenogamous and produces close to 1500 seeds per m² of plant tissue. Seed viability (77%) and germination rates (62%) were high, but this species is not represented in the seed bank. It has a vegetative growth. A combination of reproductive and recruitment attributes, which match those considered in Baker's Law and others reported for invasive plants, confer K. daigremontiana and S. gigantea the potential to invade Neotropical arid zones; the former mainly through selfing and production of numerous asexual plantlets, and the latter through an association with a locally abundant pollinator and production of wind dispersed seeds.     

Doing art and doing cultural geography: The fieldwork/field walking project1

With accompanying examples of initial visual experimentation from the fieldwork/field walking PhD project, the paper outlines some of the challenges of being an artist and using systems of understanding from science, the new ethnography, and cultural geography as a framework for making contemporary art. The PhD project is in its preliminary stages and is designed to explore the area of walking and fieldwork in art, and as art. Some of the challenges are the ambiguous role of the artist as scientist, ethnographer and researcher, the role of reflexivity in art practice; and the pitfalls of 'academic art'. While cultural geographers have used artworks as texts to explain places, this project endeavours to work with issues of place, landscapes, power, identity and representation in the art, to feed back into this dialogue. The bulk of the project will take place in the Kimberley region of Western Australia where the concepts of wilderness and wildness are most relevant. The research question posed by the fieldwork/field walking project is: within the discourse between art and science what is the connection between fieldwork and walking in the field?     

Tiller recruitment and mortality in the dryland bunchgrass Eragrostis curvula as affected by defoliation intensity

A greenhouse experiment was conducted to investigate the effects of moderate (14 cm) vs. severe (7 cm) defoliation on tiller recruitment and mortality within the interior and on the perimeter of weeping lovegrass (Eragrostis curvula) tussocks. Tiller number per marked shoot within the interior was significantly greater in plants defoliated at 14-cm stubble height than at 7-cm stubble height (2·37 vs. 0·43, p<0·05) 28 weeks after defoliation; likewise, tiller number per marked shoot was also greater on the perimeter of tussocks in the higher stubble than the lower stubble defoliation treatment (5·10 vs. 2·03, p<0·05). Tiller natality increased significantly 4 weeks after defoliation except for tillers cut to 7-cm stubble height within the interior of tussocks where tiller natality reached a peak at 4·5 weeks after defoliation. During the later stages of canopy development, tiller numbers per marked shoot gradually declined as tiller mortality increased. Tillers began senescing 13 weeks after defoliation, and the senescence rate was 52% greater in the 7-cm stubble height treatment than in the 14-cm stubble height treatment (2·33 vs. 1·53, p<0·0001). Within the interior of tussocks, number of the marked tillers more than doubled under the 14-cm stubble height treatment, whereas the plants lost 57% of the monitored tillers under the 7-cm stubble height treatment. We concluded that the central dieback process in weeping lovegrass is accelerated by severe defoliation.     

Phenology ofMedicago minimaandErodium cicutariumin semi-arid Argentina

The phenology ofMedicago minimavar.minimaandErodium cicutariumwas studied at two different field sites in the Calden District (approx. 10 million ha), a temperate semi-arid phytogeographical region in central Argentina. One site had been protected from wild and domestic herbivores for the 6 previous years. The other adjacent site had been exposed to continuous grazing by cattle for several decades. A phenological key was made for each species in 1988, and this key was improved during the 1989 growing season when phenological observations were made every 1–3 weeks.The growth cycle ofM. minimaandE. cicutariumwas similar at the two studied sites. Initiation of the cycle occurred in autumn and appeared to be associated with soil water availability. Phenological patterns were very dynamic at the reproductive stage in both species. This stage started earlier and was faster inE. cicutariumthan inM. minima. The end of the growing season occurred during late spring, concomitant with high maximum air temperatures. Our results suggest that these species hasten their development when air temperature increases and soil water availability decreases. This could be an important strategy in these species which allows them to persist as seeds, and produce a new generation under favourable environmental conditions.     

Studies on the effect of salinity, drought stress and soil type on nodule activities of Lablab purpureus (L.) sweet (Kashrangeeg)

Lablab purpureus(50 cultivars throughout the world) is a drought-tolerant legume widely grown as a high-protein grain food and forage legume within a wide range of neotropical regions with extensive production in India and similar climatic areas of Asia, Africa, Central and South America. The objective of this work was to study the nitrogen-fixing potentialities of L. purpureus under the effects of the extreme environmental conditions prevailing in the southern part of Egypt aiming at the recommendation of its propagation in areas of the National giant projects.L. purpureusinoculated with Rhizobium sp. Strain I₄ (21 days after planting) grown on Nile valley and Wadi Allaqi soils was relatively tolerant to mild levels of salinity, but the nodule number was reduced to about 35% of the control plants when subjected to a high salt level (120mM NaCl). Lablab plants were similarly affected by different rates of water deficits. This legume was tolerant to moderate levels of drought. The nodule number and weight at 50% of field capacity was about 70% of the control. These values were reduced to 45–55% at a field capacity of 16·5%.Absolute nitrogenase activity, leghaemoglobin content of nodules and protein content of bacteroids and cytosol were moderately affected by mild levels of NaCl and drought but significantly reduced to about 25–35% of the control treatments.The results also indicate that plants grown on the soil of Nile Valley exhibited slightly higher values (nitrogenase, protein, etc.) than those grown on Wadi Allaqi soil. This would encourage the possibility of propagating L. purpureus in the newly reclaimed areas of southern Egypt.     

Eco-physiological mechanisms of Caragana korshinskii Kom. adaptation to extreme drought stress: Leaf abscission and maintaining stem chloroplast integrity

In order to study the eco-physiological mechanisms of C. korshinskii adaptation to extreme drought stress, we investigated the variations of water content in soil, leaves, and stems, the chlorophyll a and b and the carotenoid content in leaves and stems, as well as changes of chloroplast ultrastructure in 2-year-old C. korshinskii specimens during a progressive soil drought process (by ceasing watering until all leaves were shed) and a subsequent rehydration process. During the dehydration process, the chlorophyll a and b and carotenoid contents in the leaves decreased, as did the carotenoid content in the stems. During the 4-day rehydration process, the chlorophyll a and b and carotenoid contents in the leaves and stems increased and gradually returned to normal levels. During ongoing drought stress, chloroplasts in the leaves broke away from cell walls and appeared in the center of cells. Under severe drought stress, the mesophyll ultrastructure and chloroplast configuration in leaves were irreversibly disturbed, as manifested by the inner and outer membranes being destroyed; the thylakoid system disintegrated, the starch grain disappeared, and parts of cell tissue were dismantled into debris. However, the mesophyll ultrastructure and chloroplast configuration in the stems remained complete. This indicates that C. korshinskii utilizes leaf abscission to reduce the surface area to avoid damage from extreme drought stress, and maintains chloroplast integrity and a considerable amount of chlorophyll to enable a rapid recovery of photosynthesis under the rehydration process.     

New Zealand chironomids as proxies for human-induced and natural environmental change: Transfer functions for temperature and lake production (chlorophyll a)

The analysis of chironomid taxa and environmental datasets from 46 New Zealand lakes identified temperature (February mean air temperature) and lake production (chlorophyll a (Chl a)) as the main drivers of chironomid distribution. Temperature was the strongest driver of chironomid distribution and consequently produced the most robust inference models. We present two possible temperature transfer functions from this dataset. The most robust model (weighted averaging-partial least squares (WA-PLS), n = 36) was based on a dataset with the most productive (Chl a > 10 μg l⁻¹) lakes removed. This model produced a coefficient of determination () of 0.77, and a root mean squared error of prediction (RMSEP_jack) of 1.31°C. The Chl a transfer function (partial least squares (PLS), n = 37) was far less reliable, with an of 0.49 and an RMSEP_jack of 0.46 Log₁₀μg l⁻¹. Both of these transfer functions could be improved by a revision of the taxonomy for the New Zealand chironomid taxa, particularly the genus Chironomus. The Chironomus morphotype was common in high altitude, cool, oligotrophic lakes and lowland, warm, eutrophic lakes. This could reflect the widespread distribution of one eurythermic species, or the collective distribution of a number of different Chironomus species with more limited tolerances. The Chl a transfer function could also be improved by inputting mean Chl a values into the inference model rather than the spot measurements that were available for this study.     

Directed dispersal of Opuntia species in the Karoo, South Africa: are crows the responsible agents?

The densities of self-established non-indigenous prickly pears (Opuntia ficus-indica) in rangelands of the Karoo recorded on 3434 km of road transects, were on average 800 times greater below telegraph and transmission poles than away from poles, and 200 times greater next to wire fences along roads than in open rangelands. We suggest that this uneven establishment pattern is mainly due to the dispersal of Opuntia ficus-indica seeds by crows and other vertebrates (chiefly primates). Cape (Corvus capensis) and pied crows (C. albus) feed on fruits of Opuntia ficus-indica in the Karoo, and regurgitate pellets containing viable seeds of these plants below nest sites, roosts and occasional perch sites. Crows use man-made structures such as wire fences, telegraph and transmission poles and windmills for perching, roosting and nesting. Crow pellets, containing regurgitated bones and viable seeds of Opuntia spp., and other alien and indigenous plants, are most common around such perch sites. Crows are frequently associated with roads in the Karoo because they scavenge on road kills in the Karoo as well as feeding on fruits, insects and reptiles in road verges. We suggest that dispersal of seeds by crows is important for range extension and establishment of new Opuntia populations.     

Effect of sand burial depth on seed germination and seedling emergence of Calligonum L. species

A greenhouse study was conducted to determine the effects of sand burial on seed germination and seedling emergence of ten Calligonum L. species. The results suggested that the deeper the seeds in sand, the lower and slower their germination and seedling emergence. Seedling emergence occurred from a maximum depth of 12 cm with most seedlings emerging from 2 and 4 cm depths. The percent seedling emergence, number of days of first emergence, percent seed germination and percent of dormant seeds were significantly affected by different species and burial depth. There was a significant positive correlation between the number of days to first emergence and burial depth. Both mean percent germination and percent seedling emergence were negatively correlated with depth significantly for each species.     

Effect of fire on growth of three perennial grasses from central semi-arid Argentina

The effect of fire on growth of Piptochaetium napostaense, Stipa tenuis, and Stipa gynerioides, three important native perennial grasses in the semi-arid region of central Argentina, was evaluated under different fire temperature regimes: 300–400°C (low temperature regime), 500–600°C (high temperature regime) and no fire (control). Fire treatments were applied with a portable propane plant burner in April and December 1994, May 1995, and January 1996. Overall results indicate that during the first months after fire occurrence, average total green length of S. tenuis, P. napostaense and S. gynerioides tillers was severely reduced (p<0.05) by fire. This effect was more pronounced in plants burned with the high temperature treatment. The observed patterns of response to fire for height of tillers were very similar to those already reported for total green length of tillers. Towards the end of each growth cycle, the number of green leaves per tiller of burned plants of P. napostaense, S. tenuis, and S. gynerioides were similar or greater (p<0.05) than the number of green leaves on tillers of control plants. Relative growth rates for total green length and for height in tillers of burned plants of S. tenuis, P. napostaense and S. gynerioides were greater than in tillers of control plants. Our results indicate that fire affected differentially the growth of the studied species; S. gynerioides was more affected by fire than P. napostaense and S. tenuis. The species most tolerant to fire was P. napostaense.     

Selection of plant species for rehabilitation of gypsum mine spoil in arid zone

Ten species were selected based on their economic value in order to study and compare their growth, nutrient uptake pattern, AM-fungal infection etc. in both mine spoil and normal cultivated soil in pot culture. In general, per cent root infection and number of viable AM fungal spores in the rhizosphere of the plant species grown in mine spoil were higher compared to those in normal cultivated soil. Mine spoil had supported significantly higher growth ofProsopis juliflora,Salvadora oleoidesandCenchrus ciliariscompared to normal soil. Concentrations of phosphorus, potassium and calcium in plants growing on gypsum mine spoil were higher than observed in normal soil. In general, micronutrient concentrations (namely Cu, Zn and Fe) were lower in all the plant species growing in normal soil.Salvadora oleoides,Colophospermum mopaneandPithecellobium dulcewere identified as calcium-loving plants. All the species tested can be employed for rehabilitation of gypsum mine spoil.