Oxygen availability determines aerenchyma formation of eucalyptus

Eucalyptus is an invasive species that was introduced to California in response to the 1850s Gold Rush population boom. Originally conceived as a fast-growing lumber source, eucalyptus wood soon proved to be too brittle and gnarled to work with. Eucalyptus trees have since taken over native vegetation and ecosystems to become one of the most prevalent trees within California's coastal fog belt. 

Free to expand without the constraint of natural predators such as the koala, eucalyptus both outcompetes native plant species and fundamentally changes its surrounding environment to be unsuitable for said species. This is how Eucalyptus Grove on the west side of campus bordering the Life Sciences Addition has become such a distinctive monoculture. It is now the largest, densest stand of eucalyptus in the world.

[Source: https://www.dailycal.org/2020/04/28/a-love-hate-relationship-with-eucalyptus/]


In order to evaluate the nutritional, physiological and morphological changes possibly involved in the differential tolerance of eucalyptus clones to ESBVRD, under hypoxia conditions and Mn excess, Fellip Januario Pinheiro Lacerda made a study on the gaseous exchanges and formation of Aerenchyma in Eucalyptus Clones and the study was published on the journal Probe - Soil Science.

In this study, two clones of eucalyptus, a sensitive (1213) and a tolerant (2719), were submitted to four O2 concentrations (1, 4, 6 and 8 mg/L), at the presence of 30 mg/L of Mn, a concentration considered excessive or toxic. The lengths of the root system and shoots were measured, as well as photosynthesis, stomatal conductance, transpiration and CO2 internal concentration. Also, roots samples were taken near the apex for anatomical analyzes. At the end of the experiment (21 days), the plants were harvested and separated into old and new leaves, stem and root.

Afterwards, the levels of Mn in the tissues were determined. The hypoxia condition limited the total dry matter, similar to both clones, although the root growth was the most sensitive indicator of stress condition caused by hypoxia, with more marked effect in the sensitive clone. The tolerant clone replied more clearly to the increase of O2 availability (lower hypoxia), with the increased metabolism due to the greater stomatal conductance, photosynthetic rate, transpiration and CO2 internal concentration, comparing to the sensitive clone. Hypoxia condition caused the most intense formation of aerenchyma in the sensitive clones root system, even though the arenchyma formation was also observed in the tolerant clone. Mn excess did not imply in great responses.

The study found that the hypoxia causes reduction in the growth of both clones, the sensitive and tolerant to ESBVRD, although the effect is more marked in the sensitive clone, being the root growth the best indicator of this fact; Mn does not change it. This condition (hypoxia) is more limiting to the stomatal opening of the tolerant clone than for the sensitive clone, consequently reducing the photosynthetic rate, respiration and the internal CO2 concentration. The mild hypoxia allows the aerenchyma formation in both clones.

Read the full paper at : http://probe.usp-pl.com/index.php/SS/article/view/1126