Brief description
The influence of shading on the translocation of carbon (C) and nitrogen (N) in Posidonia sinuosa plants was investigated from December 2004 to January 2005 in Cockburn Sound by measuring 13C and 15N isotopes in leaf material to determine whether changes in resource distribution may be a mechanism sustaining its growth during a period of light reduction.Lineage
Maintenance and Update Frequency: notPlanned
Statement: Carbon (C) and nitrogen (N) translocation in P. sinuosa in control and shaded conditions were examined in Cockburn Sound near Perth, Western Australia. The study site was established at north-east Garden Island at a site 7 - 8 m deep, just short of the depth limit (32º 09' 39.0" S 115º 40' 45.7" E). This site has a summer water temperature range of 22 - 24ºC, salinity of 36 PSU and is oligotrophic with inorganic nitrogen concentrations ranging from 4 - 10 ug l-1 and total phosphorus from 11 - 40 ug l-1 and sediment pore water concentrations of 715 ug l-1 dissolved inorganic nitrogen (see Chapter 4 of thesis). The meadow consisted predominantly of P. sinuosa. At this depth, the spacing between shoots of P. sinuosa was variable with some tightly spaced semivertical axes (typical form in shallower depths) but generally the internodes on the horizontal axis were much longer.
Two in situ experiments were conducted (within-shoot and between-shoot). Both experiments compared the distribution of 13C carbon and 15N nitrogen following incubation with 13C-labelled H2CO3 and 15N labelled NH4+ under shaded and control conditions. Shade screens (n = 6) and control plots (n = 6) were established in early December 2004. The plots consisted of 6 × 2.4 m metal star pickets hammered at least 1 m into the sediment in each corner and, for the shaded plots, another picket placed in the centre of each side. A stainless steel wire was run through shackles attached to the top of the pickets, forming the frame of the screen. For shaded treatments, a 50% light reducing shade cloth was fastened to the wire. The final dimension of the screens was 4.5 m × 3 m. Shade and control plots were randomly mixed along the depth contour. Light availability in a control and shade plot was monitored from the first day of shading until the end of both experiments according the methods outlined in Chapter 4 of the thesis.
Statement: - Within-shoot translocation -
The within-shoot experiment was initiated after 10 days of shading in mid-December 2004. P. sinuosa shoots generally consist of one mature leaf, with or without a young emergent leaf. Shoots were selected for those with a single mature leaf (ML) and one emergent young leaf (YL) approximately 10 cm long (see thumbnail). An incubation chamber was formed from a plastic bag with an injection port, made from a two piece filter cassette pushed onto the bag with a tap (plastic luer stopcock) inserted into the cassette. The bag was pulled over the ML and fastened with a padded clip at the base of the leaf. Seawater was injected through the tap to a final volume of about 0.5 litres. A concentrated solution of NaH13CO3 and 15NH4Cl was later injected into the bag to produce a final concentration of about 300 uM NaH13CO3 and 40 uM 15NH4Cl (saturating; Pedersen et al., 1997) and the tap closed. After 2 h the bag was carefully removed from the leaf by sliding upwards while pinching the base, in order to contain as much of the solution as possible within the bag. The bag was taken at least 10 m away and washed free of all solution. Throughout bag removal, surrounding water was vigorously washed over the shoot to rapidly flush and dilute any solution that may have leaked during removal. In situ trials of the bag and tap system using injected natural dye P. sinuosa responses to light availability identified no leakage from the bag during simulated experiments. To test for leakage during the labelling experiments, shoots belonging to a different plant (i.e. not attached to the labelled shoot) were collected immediately adjacent (5 - 10 cm away) to the labelled shoot. Atom percent excess values in these shoots were on average 0.0008%, which was approximately 0.2% of enrichment in the labelled leaves, indicating some, but probably insignificant, leakage from the bags. After labelling, the shoots were marked at the base of the ligula using a needle for later determination of leaf production (Dennison, 1990).
For further methodology see section 6.2.1
Statement: - Between-shoot translocation -
The experiment to determine the translocation of C and N between shoots was initiated in early January, 2005 after 1 month of shading, coinciding with the 21 days within-shoot sampling. Within four of the control and shaded plots, four plants of P. sinuosa were selected for each of four sampling times. Plants were chosen for those where the rhizome could be sufficiently exposed and the number of shoots could be counted. The sand covering the rhizomes was gently washed away to expose the fourth or fifth shoot back from the rhizome apex. However, the number of shoots was not always clearly discernible and on two individuals, the third shoot was selected. The whole plant was marked with a peg and the incubated shoot was tagged for later identification.
For further methodology see section 6.2.2
Notes
CreditStrategic Research Fund for the Marine Environment (SRFME)
Purpose
To determine whether C and N translocation to growing tissues occurs in P. sinuosa; and to determine whether C and N translocation increases in response to shading
To determine whether C and N translocation to growing tissues occurs in P. sinuosa; and to determine whether C and N translocation increases in response to shading
Created: 29 08 2007
Data time period: 2004-12 to 2005-01
text: westlimit=115.6; southlimit=-32.4; eastlimit=115.75; northlimit=-32.05
text: uplimit=8; downlimit=7
Subjects
63 617003 |
Biogeochemical Cycles |
BIOSPHERE |
EARTH SCIENCE |
ECOLOGICAL DYNAMICS |
ECOSYSTEM FUNCTIONS |
Light Transmission |
Oceans | Marine Biology | Marine Plants |
Photosynthesis |
Posidonia sinuosa |
Stable Isotopes |
TERRESTRIAL HYDROSPHERE |
WATER QUALITY/WATER CHEMISTRY |
oceans |
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Other Information
(PhD Thesis)
global : 67c19c30-2444-11dc-95fb-00188b4c0af8
Identifiers
- global : c989aca0-55ef-11dc-8538-00188b4c0af8
