Casuarina Glauca Sieb Research Articles

Allelopathic effects of leachates of Casuarina glauca Sieb. ex Spreng. and Populus nigra L. on germination and seedling growth of Triticum durum Desf. under laboratory conditions

The decline in soil fertility and the poor distribution of precipitation during the growth and maturation of cereal crops are major constraints to improving yields in the Mediterranean zone in North Africa. The use of agroforestry species is one strategy for enhancing agronomic productivity and supporting a range of ecosystem services and environmental benefits. However, to our knowledge, the allelopathic effects of these agroforestry species on cereals are poorly documented under Mediterranean conditions. The effects of three aqueous extracts (leaves, roots and litter) from two agroforestry species (Casuarina glauca Sieb. Ex Spreng. and Populus nigra L.) have been evaluated for their allelopathic potential on seed germination and seedling growth of Triticum durum Desf. under laboratory conditions. These allelopathic effects were evaluated using several parameters including seed germination, total dry mass, root and shoot length, chlorophyll and protein concentrations in T. durum seedlings along with phenolic compounds in different parts (leaves, roots and litter) of the two allelopathic species. Exposure to the different extracts of C. glauca and P. nigra significantly reduced germination kinetics, dry mass production, root and shoot length, and chlorophyll and protein concentrations in T. durum seedlings. This reduction was significantly more pronounced for the different extracts from P. nigra. Our results showed a significant negative correlation between dry mass accumulation in T. durum seedling and polyphenol concentration. Overall, the findings of the present study support the introduction of C. glauca into the agroforestry system. However, field monitoring under natural conditions would be necessary to confirm in practice the results obtained with the bioassays.

Selection of arbuscular mycorrhizal fungal strains to improve Casuarina equisetifolia L. and Casuarina glauca Sieb. tolerance to salinity

Selection of the best salt-tolerant combination of Casuarina sp. and arbuscular mycorrhizal fungi (AMF) is one of the key criteria for successful setup of saline land rehabilitation program. Land salinization is a serious problem worldwide that mainly leads to soil degradation and reduces crop productivity. These degraded areas could be rehabilitated by planting salt-tolerant species like Casuarina glauca Sieb. and Casuarina equisetifolia L. These are pioneer plants, able to form symbiotic associations with arbuscular mycorrhizal fungi (AMF), ectomycorrhizal fungi (EMF), and nitrogen-fixing bacteria. The aim of this study was to select the highest salt-tolerant combination of Casuarina/AMF that can be used for the rehabilitation of lands degraded by salinity. C. equisetifolia and C. glauca were grown in sandy sterile soil in the greenhouse and inoculated separately with Rhizophagus fasciculatus (Thaxt.) C. Walker & A. Schusler, Rhizophagus aggregatus (N.C. Schenck & G.S. Sm.) C. Walker, and Rhizophagus intraradices (N.C. Schenck & G.S. Sm.) C. Walker & A. Schusler. After confirming the establishment of a symbiosis, the plants were watered with gradually increasing concentrations of saline solution. After harvest, size and biomass of the seedlings, root colonization by AMF, and AMF metabolic activities were evaluated. A larger growth was obtained in the two species when the individuals were inoculated with R. fasciculatus. Root colonization rates did not differ among fungal species, but fungal metabolic activities were higher in mycorrhizal roots of C. glauca plants inoculated with R. fasciculatus. Among the three mycorrhizal fungi, R. fasciculatus was more efficient in association with Casuarinaceae species under salt stress. Our results suggest that selection of appropriate fungal strains is crucial to improve plant performance in saline soils.

The impact of salinity on the symbiosis between Casuarina glauca Sieb. ex Spreng. and N2-fixing Frankia bacteria based on the analysis of Nitrogen and Carbon metabolism

Background and aims Casuarina glauca is an actinorhizal plant that establishes root-nodule symbiosis with N2-fixing bacteria of the genus Frankia. This plant is highly recalcitrant to extreme environmental conditions such as salinity and drought. The aim of this study was to evaluate the impact of salt stress on the symbiotic relationship between C. glauca and Frankia Thr, focusing on N and C metabolism.

Is salt stress tolerance in Casuarina glauca Sieb. ex Spreng. associated with its nitrogen-fixing root-nodule symbiosis? An analysis at the photosynthetic level

Casuarina glauca is an actinorhizal tree which establishes root-nodule symbiosis with N2-fixing Frankia bacteria. This plant is commonly found in saline zones and is widely used to remediate marginal soils and prevent desertification. The nature of its ability to survive in extreme environments and the extent of Frankia contribution to stress tolerance remain unknown. Thus, we evaluated the ability of C. glauca to cope with salt stress and the influence of the symbiosis on this trait. To this end, we analysed the impact of salt on plant growth, mineral contents, water relations, photosynthetic-related parameters and non-structural sugars in nodulated vs. non-nodulated plants. Although the effects on photosynthesis and stomatal conductance started to become measurable in the presence of 200 mM NaCl, photochemical (e.g., photosynthetic electron flow) and biochemical (e.g., activity of photosynthetic enzymes) parameters were only strongly impaired when NaCl levels reached 600 mM. These results indicate the maintenance of high tissue hydration under salt stress, probably associated with enhanced osmotic potential. Furthermore, the maintenance of photosynthetic assimilation potential (Amax), together with the increase in the quantum yield of down-regulated energy dissipation of PSII (YNPQ), suggested a down-regulation of photosynthesis instead of photo-damaging effects. A comparison of the impact of increasing NaCl levels on the activities of photosynthetic (RubisCO and ribulose-5 phosphate kinase) and respiratory (pyruvate kinase and NADH-dependent malate dehydrogenase) enzymes vs. photosynthetic electron flow and fluorescence parameters, revealed that biochemical impairments are more limiting than photochemical damage. Altogether, these results indicate that, under controlled conditions, C. glauca tolerates high NaCl levels and that this capacity is linked to photosynthetic adjustments.

Nitrogen sharing and water source partitioning co-occur in estuarine wetlands.

Plant-plant interactions are particularly complex in multi-resource limited environments. The aim of this study was to assess species interactions in estuarine wetlands where both N and fresh water are limited. We combined stable isotope methods and dissimilarity analyses to compare interspecific interactions in N source use and water source use. Both Melaleuca quinquenervia (Cav.) S. T Blake and Avicennia marina (Forssk.) Vierh. had a lower leaf δ15N when they were growing together with the N-fixer Casuarina glauca Sieb. ex Spreng. compared with those trees growing in monospecific stands, but their water isotopes, δ18O and δD, were different from C. glauca. Our results indicate that the N-fixer C. glauca shared their N with co-existing neighbours, either indirectly or directly, but that water sources were partitioned among them. Further analyses showed that M. quinquenervia and C. glauca had lower dissimilarity in N source use but higher dissimilarity in water source use than the C. glauca-A. marina pair, implying that the co-existence between M. quinquenervia and C. glauca is relatively stable. Our results suggest that facilitative interaction and resource partitioning can co-occur in estuarine wetlands, and which could be important in maintaining diversity across resource gradients.

Activation of the isoflavonoid pathway in actinorhizal symbioses.

We investigated the involvement of flavonoids in the actinorhizal nodulation process resulting from the interaction between the tropical tree Casuarina glauca Sieb. ex Spreng. and the actinomycete Frankia. Eight C. glauca genes involved in flavonoid biosynthesis: chalcone synthase (CHS), chalcone isomerase (CHI), isoflavone reductase (IFR), flavonoid-3-hydroxylase (F3H), flavonoid 3'-hydroxylase (F3'H), flavonoid 3',5' hydroxylase (F3'5'H), dihydroflavonol 4-reductase (DFR) and flavonol synthase (FLS), were identified from a unigene database and gene expression patterns were monitored by quantitative real-time PCR (qRT-PCR) during the nodulation time course. Results showed that FLS and F3'5'H transcripts accumulated in mature nodules whereas CHI and IFR transcripts accumulated preferentially early after inoculation with Frankia. Comparison of IFR and CHI expression in inoculated plants and in control plants cultivated with or without nitrogen confirmed that early expression of IFR is specifically linked to symbiosis. Taken together, these data suggest for the first time that isoflavonoids are implicated in actinorhizal nodulation.

Size‐Dependent Variation in Shoot Light‐Harvesting Efficiency in Shade‐Intolerant Conifers

Shoots and foliage elements of shade‐intolerant conifers strongly vary in size, but the effects of size on shoot light‐harvesting efficiency have not been quantified. We investigated shoot adaptation to seasonal average integrated quantum flux density in gymnosperms Pinus palustris Mill., P. patula Schlect. & Cham., and P. radiata D. Don. and angiosperm Casuarina glauca Sieb. ex Spreng. In addition, P. sylvestris L., sampled from infertile and fertile sites, and P. taeda L. were included to test for general correlations among shoot architecture and size. All studied species possess needle‐like photosynthetic elements. A shoot model was fitted to the data to separate the determinants of shoot light‐harvesting efficiency. The model estimated shoot light harvesting on the basis of angular distribution of foliage surface areas, degree of spatial clumping, foliage area density in shoot volume, and beam path length in shoot volume. Increases in irradiance primarily led to greater foliage aggregation, greater foliage area density in shoot volume, and to a minor degree, to changes in foliage area angular distribution. Greater foliage aggregation resulted in lower efficiency of light harvesting but greater investment of foliar biomass in high light where the photosynthetic returns are greater. The species behave similarly except that the light‐harvesting characteristics of P. patula, which has long, strongly bending needles, were independent of light. In all species, the shoots were larger in higher irradiance, and the fraction of biomass in shoot axis increased with increasing irradiance, indicating greater costs for light harvesting in high light. There were further significant species differences in light‐harvesting efficiency that were linked to differences in foliage and shoot size. Foliage element length varied between 1.1 and 31.4 cm and shoot axis length between 1.2 and 36.5 cm among the species, leading to 4 orders of magnitude variation in shoot cylinder volume and three orders of magnitude variation in foliage area density (ρ); ρ decreased with increasing foliage element length and shoot volume. The degree of foliage clumping scaled positively with ρ and negatively with foliage element length. Foliage clumping was positively associated with foliage dry mass to shoot silhouette area ratio, signifying a trade‐off between efficient light harvesting and large photosynthetic biomass accumulation. These data demonstrate a general increase of light‐harvesting efficiency with increasing length of foliage elements, but they also demonstrate that this increase is limited by enhanced bending of longer foliage elements and by augmented support costs.

Light-acclimation of cladode photosynthetic potentials in Casuarina glauca: trade-offs between physiological and structural investments.

Many arid and saline habitat species possess sparse canopies with cylindrical foliage that is considered relatively invariable along environmental gradients. However, even in sparse canopies strong gradients of light develop between the canopy top and bottom. We studied structural and photosynthetic acclimation to within-canopy light gradient in Casuarina glauca Sieb. ex Spreng., the photosynthetic organs of which are cylindrical cladodes. Seasonal average integrated quantum flux density (Qint) varied 25-fold between the canopy top and the canopy bottom. Cladode cross-sectional shape was unaffected by irradiance, but cladode dry mass per unit total area (MA) varied 2-fold within the canopy light gradient. This resulted primarily from light-dependent changes in cladode thickness (volume to total area ratio,V / AT) and to a lesser extent from changes in cladode density (D, MA = DV / AT). Nitrogen content, and the volume of mesophyll per unit surface area increased with increasing Qint and V / AT, resulting in positive scaling of foliage photosynthetic potential (capacity of photosynthetic electron transport and maximum Rubisco carboxylase activity per unit area) with light. However, nitrogen content per unit dry mass and the volume fraction of mesophyll decreased with increasing irradiance. This was explained by greater fractional investment in mechanical tissues in cladodes with greater volume to surface area ratio. This trade-off between photosynthetic and support investments reduced the cladode photosynthetic plasticity. Our study demonstrates a significant acclimation potential of species with cylindrical foliage that should be included in larger-scale carbon balance estimations of arid and saline communities.

Research note: The 35S promoter is not constitutively expressed in the transgenic tropical actinorhizal tree Casuarina glauca.

The tropical nitrogen-fixing tree, Casuarina glauca Sieb. ex Spreng. was genetically transformed using Agrobacterium tumefaciens C58C1(pGV2260; pBIN19GUSINT). We report on the expression pattern conferred by the cauliflower mosaic virus (CaMV) 35S promoter in transgenic C. glauca plants grown in vitro, and for one year in a greenhouse. Histochemical assays in shoots from in vitro plants revealed β-glucuronidase (GUS) staining in apical and axillary buds, and in nearly all tissues near the base of the stem. In roots, the CaMV 35S drove strong GUS expression in the apex and vascular tissue. In 1-year old plants grown in a greenhouse, the CaMV 35S promoter was highly active, except in peripheral suberized tissues. Transgenic C. glauca plants were nodulated by the actinomycete Frankia. Histochemical assays on vibratome sections of transgenic nodules demonstrated intense GUS activity in the vascular bundle, the phellogen, and in strands of uninfected cells filled with polyphenols. GUS expression was undetectable in Frankia-infected cells.

Cytometric determination of genome size and base composition of tree species of three genera of Casuarinaceae.

The genome size and base composition of diploid plant species from three genera of the Casuarinaceae family were determined by flow cytometry. Casuarina glauca Sieb. ex Spring. and Gymnostoma deplancheana (Miq.) L. Johnson showed a small genome with 2C = 0.70 pg, 58.6% AT, 40.5% GC for the first species and 2C = 0.75 pg, 58.7% AT, 40.5% GC for the second. Allocasuarina verticillata (Lam.) L. Johnson had a larger genome: 2C = 1.90 pg, 59.3% AT, 41.1% GC. One haploid genome of C. glauca is therefore about 340×106 base pairs. In leaves, roots or bark of these three species, polysomaty was virtually absent: a maximum frequency of 4C nuclei of only 0.08 was found in bark of C. glauca. The genome sizes of C. glauca and G. deplancheana are among the smallest described for higher plants. Small genome size, diploidy and the absence of polysomaty are advantageous traits for facilitating molecular approaches to improvement of these actinorhizal plants and developing the study of their symbiotic interactions with Frankia.

Temperature and water-use efficiency by lucerne (Medicago sativa) sheltered by a tree windbreak in Tunisia

Based on the assumption that with unrestricted water availability, temperature will determine the response of sheltered crops, the effects of a Casuarina glauca Sieb. windbreak on the microclimate, water use and biological production of a lucerne crop were investigated. Degree-days (dd) were used to compute an index for the efficiency of the thermal effects of the shelter on a well- watered lucerne, under favourable (10 to 30 °C) and unfavourable (above 30 °C) temperature conditions. Water use efficiency was considered for two contrasting water regimes, with no water stress or with a large water deficit. In June, under favourable temperature and water availability conditions, temperature efficiency of the windbreak was 39 g m−2 dd−1 at a distance of three times the height of the trees compared to an exposed situation, and water use efficiency increased by 7.1 g mm−1. However, the sheltered conditions induced a decrease in above ground biomass production and water use efficiency when a highly restrictive water regime was applied. In July, daytime temperatures were disadvantageous to the lucerne, and even with a high degree of water availability, there were no significant differences between sheltered and unsheltered conditions. This research may help decision makers to manage windbreak systems by designing an appropriate irrigated area according to the shelter and choosing crops that will best benefit from sheltered conditions.

Litterfall in Casuarina glauca Coastal Wetland Forests

Litterfall was measured over 3 years at two sites in coastal wetland forests dominated by Casuarina glauca Sieb. ex Spreng. in New South Wales. One site was in an incised river valley adjacent to the Hawkesbury River estuary, and the other site was in an open embayment adjacent to Botany Bay. Branchlets were the major litter component, followed by stems and infructescences. Significant year to year variation in branchlet fall correlated with storm events in one year. Overall, no significant differences in annual total litterfall were detected among sites and, averaged over all sites and years, the mean annual litterfall was 848 g m-2. This suggests that coastal wetland forests dominated by C. glauca have some of the highest recorded annual litterfall rates for Australian temperate and subtropical forests. A flood event in the river valley site removed about 75% of the standing litter accumulated on the forest floor prior to flooding (1244 g m-2). This suggests that accumulated organic matter and nutrients can be directly transported to estuarine ecosystems. Under non-flood conditions, however, these forests appear to act as organic matter and nutrient sinks.

Provenance trials ofCasuarina cunninghamiana, Casuarina glauca,andAllocasuarina verticillatain Israel

Summary Drought-resistant provenances of Casuarina cunninghamiana Mig, Casuarina glauca Sieb. ex Spreng. and Allocasuarina verticillata L. Johnson were established in 1984 on two sites, one (Duda'im) with low, mean annual rainfall of 204 mm, and the other (Tiberias) with infertile soil and mean annual rainfall of 431 mm. The seedlings of nearly all provenances were taller and had a larger DBH at Tiberias than at Duda'im, with a highly significant main effect of “site”. The analysis indicated that in the semi-arid environment of Israel, water, rather than soil, was the limiting factor for casuarina growth.