Seagrass meadows are among the most productive ecosystems on earth providing a range of key ecosystem services, enhancing marine biodiversity by providing feeding grounds and nursery areas for many important marine species such as sea turtles, dugongs, juvenile fish and crustaceans. Despite their high environmental and economic value, however, seagrass meadows are currently facing a global decline. In new research UTS Climate Change Cluster (C3) PhD candidate Kasper Elgetti Brodersen is using advanced microsensor and optode technology to examine how changing environmental conditions (such as light intensity, O2 availability, and temperature) affect the health and performance of seagrasses.
Together with colleague Dr. Klaus Koren - from C3 Distinguished Professor Michael Kühl’s team based at University of Copenhagen - Kasper developed a new technique where O2 and pH sensitive optical sensor nanoparticles are incorporated into transparent, artificial sediment. By applying this novel methodology the research team measured, for the first time, the O2 and pH micro-dynamics and heterogeneity in the seagrass rhizosphere on an entire rhizosphere level.
[Text overlay]: Putting sensor nanoparticles into the artificial sediment
[Student gently pours the artificial sediment around the roots]
[Student puts silicone on the chamber to ensure it will be sealed]
[Text overlay]: Keeping the leaves moist and clean
[Student squeezes water onto the seagrass from a pipette]
[Student closes the chamber after the artificial sediment has solidified]
[Text overlay]: When the chamber is sealed it can be turned and filled with seawater
[Student moves the chamber to the imaging setup]
[Student aligns the camera and LED]
[Text overlay]…and the setup is ready for measuring
Seagrasses are constantly challenged to transport O2 down to their below-ground tissues to maintain aerobic metabolism and to protect themselves against sediment-produced reduced phytotoxic compounds, such as hydrogen sulphide. By means of optical sensor nanoparticles the team discovered that seagrasses alter the rhizosphere pH microenvironment. They also found that the oxidation capacity of the below-ground tissues changes as a response to light stimulation of the leaf canopy, reduced water-column O2 levels during night-time, and elevated seawater temperatures. Very low water-column O2 levels during darkness strongly reduce the below-ground tissue oxidation capacity, thereby increasing the risk of phytotoxic hydrogen sulphide intrusion.
Ongoing climate changes are expected to lead to further seawater level rises, enhanced frequency of nutrient-driven algal blooms, and higher water-column temperatures, which reduces the light availability for underwater photosynthesis and the water column O2 levels during night-time owing to higher respiration rates. The results from this work may thus provide important information about how environmental changes affect processes in the seagrass rhizosphere and thus plant fitness. Such knowledge can ultimately help coastal managers to better manage and protect these vital marine ecosystems in future oceans e.g. by defining important thresholds for water column turbidity and other key hydrologic parameters affecting the microenvironmental controls of seagrass health.
For further information about Kasper Elgetti Brodersen’s research: elgetti.wordpress.com
Publication:
Brodersen KE, Koren K, Lichtenberg M, Kühl M (2016). Nanoparticle-based measurements of pH and O2 dynamics in the rhizosphere of Zostera marina L.: Effects of temperature elevation and light-dark transitions. Plant, Cell & Environment 205: 1264-1276.