Acacia ampliceps

Overview

Acacia ampliceps occurs along salt-lake margins and saline grasslands in northern Australia. Seedling experiments show that growth and nodulation under salinity depend on the rhizobial strain. The experiments differ in seed source and exposure period. [S1, S2, S3, S4, S7]

Names and classification

Acacia ampliceps Maslin is documented as a wild shrub or small tree around salt lakes, springs, and saline grasslands in northern Australia. Salinity trials used seed supplied from Thailand or other experimental sources; those materials must not be conflated with the Australian field populations. [S1, S2, S8]

Morphology and identification

A shrub or small tree of northern Australia with narrow, often pendulous phyllodes. Its white to cream flower heads are spherical, and the pods are flattened. Identification should consider phyllode shape, flower-head colour, and pods together. Field records from saline habitats do not describe the full range of morphological variation. [S1, S2, S11]

Distribution, habitat and phenology

Surveys at Mandora Marsh/Walyarta in Western Australia recorded the species in inland salt-lake flats and spring-margin saline shrublands, alongside Tecticornia, Frankenia, and Sporobolus. A Ramsar information sheet for Eighty-mile Beach also records salt wattle at the edge of saline grassland. Separate studies concern planting at saline sites or experimentally stressed seedlings. [S1, S2, S8]

The available sources do not provide reliable flowering or fruiting dates that can be compared across regions; records from one locality or horticultural material do not establish species-wide phenology. [S8]

Salinity in natural habitats

Surveys at salt-lake margins, spring margins, and saline grasslands in Australia recorded A. ampliceps together with halophytic vegetation, providing field evidence for those regions. Seedling experiments using seed from elsewhere cannot be directly assigned to every field population. [S1, S2]

Salinity studies

Zou et al. (1995) inoculated Australian Tree Seed Centre provenance S15764 seedlings with salt-tolerant Rhizobium PMA63/1 or salt-sensitive Bradyrhizobium PMA37 and exposed them to 0, 100, and 200 mM NaCl in sterilized white silica sand. Salt treatment began in week 6 after sowing, rising by 25 mM d−1 to 100 mM and then by 50 mM d−1 to 200 mM. Experiment 1 harvested at weeks 4, 6, 8, 10, and 12 after sowing; Experiment 2 continued to week 14, with harvests at weeks 12 and 14. At 200 mM, PMA63/1-inoculated plants were less affected; new nodules were still observed after four and six weeks of exposure, and nodule number fell by 28%, compared with 74% for PMA37. The study also measured nodules, root and shoot dry mass, plant nitrogen, and nitrogenase activity; conclusions apply to this provenance–strain combination. [S4]

Seed-derived seedlings 25 ± 2 cm tall from Thailand were grown in greenhouse soil-filled bags and exposed to 0, 200, 400, or 600 mM NaCl in the soil solution for nine days. The study classified 200 mM as mild stress and 400–600 mM as high to extreme stress, and measured growth, ion and osmotic responses, and photosynthetic traits. The 600 mM result reflects acute severe stress and does not establish a sustained-growth duration. [S3]

The Australian salt-sensitivity database links two TSS equivalents to biomass reductions of 39% and 62%. Its 14-week endpoint may correspond to Experiment 2 in the full Zou et al. paper; that experiment continued through week 14 and harvested at weeks 12 and 14 after sowing, while the abstract summarizes observations only through week 12. The database row does not identify the specific treatment for its endpoint or give a conversion from TSS equivalents to the paper’s NaCl doses. [S6]

Three-week-old seedlings from the Peshawar Forest Institute/NIAB were grown in half-strength Hoagland solution. Salting began one week after transplanting and reached target levels over two days; shoot and root fresh mass, dry mass, and length were measured eight weeks after transplanting. Table 1 reports shoot/root dry mass of 0.63/0.28, 0.49/0.22, and 0.24/0.12 g plant⁻¹ at 100, 200, and 300 mM NaCl, respectively. Terminal dry mass remained nonzero at 200 mM, but initial dry mass was not measured. Exposure at the target concentration was about seven weeks by the schedule; 400 mM is mentioned only for survival, without displayed data. [S7]

Reported mechanisms and ecological adaptations

In a seedling experiment, responses differed between plants inoculated with salt-tolerant and salt-sensitive rhizobial strains. At 200 mM, growth, nodule number, and nitrogen status were less affected in the salt-tolerant strain treatment. This result applies to a particular seedling–symbiont combination, not all wild populations. [S1, S2, S4]

Conclusions and evidence gaps

In the full Zou et al. paper, Experiment 2 continued through week 14 and included harvests at weeks 12 and 14 after sowing; the abstract summarizes observations only through week 12. The Australian database’s 14-week endpoint may correspond to Experiment 2, but the row does not identify its specific treatment or provide a conversion from TSS to NaCl dose. Other salinity studies use different provenances, media and endpoints and cannot be combined into a single threshold. [S1, S2, S3, S4, S6, S7]