Something I neglected earlier is adding labels to individual points by selecting the rows you want labeled and going to Rows > Label/Unlabel. This should enable you to do what you want in this graph. I basically recreated your example (except without the error bars), but I had to journal the plots 1 at a time because I needed to change the labels for each panel.
Here's what the final result looks like:

I'm attaching the journal file, but there's a frustrating bug where the custom line settings get messed up after saving and re-opening the journal. You'll probably notice all the lines will be dashed when you open it.
Data table script (again, cannot attach data table directly):
New Table( "Multipanel Example with Tukey labels",
Add Rows( 4 ),
Set Header Height( 59 ),
New Script(
"Growth",
Graph Builder(
Size( 518, 446 ),
Show Control Panel( 0 ),
Show Legend( 0 ),
Variables(
X( :Treatment ),
Y( :Growth ),
Overlay( :Temperature Regime )
),
Elements(
Line( X, Y, Legend( 10 ) ),
Points( X, Y, Legend( 11 ), Jitter( "None" ) )
),
SendToReport(
Dispatch(
{},
"Growth",
ScaleBox,
{Format( "Fixed Dec", 12, 1 ), Min( 0.4 ), Max( 0.9 ),
Inc( 0.1 ), Minor Ticks( 0 )}
),
Dispatch(
{},
"400",
ScaleBox,
{Legend Model(
10,
Properties(
0,
{Line Color( 0 ), Line Style( "Dotted" ),
Fill Color( 0 )},
Item ID( "1", 1 )
),
Properties(
1,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "2", 1 )
)
), Legend Model(
11,
Properties(
0,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "1", 1 )
),
Properties(
1,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "2", 1 )
)
)}
),
Dispatch( {}, "graph title", TextEditBox, {Set Text( "" )} ),
Dispatch( {}, "X title", TextEditBox, {Set Text( "" )} )
)
)
),
New Script(
"chlorophyll",
Graph Builder(
Size( 518, 446 ),
Show Control Panel( 0 ),
Show Legend( 0 ),
Variables(
X( :Treatment ),
Y( :chlorophyll a ),
Overlay( :Temperature Regime )
),
Elements(
Points( X, Y, Legend( 6 ), Jitter( "None" ) ),
Line( X, Y, Legend( 7 ) )
),
SendToReport(
Dispatch(
{},
"chlorophyll a",
ScaleBox,
{Format( "Fixed Dec", Use thousands separator( 1 ), 12, 0 ),
Min( 0 ), Max( 8 ), Inc( 2 ), Minor Ticks( 0 )}
),
Dispatch(
{},
"400",
ScaleBox,
{Legend Model(
6,
Properties(
0,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "1", 1 )
),
Properties(
1,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "2", 1 )
)
), Legend Model(
7,
Properties(
0,
{Line Color( 0 ), Line Style( "Dotted" ),
Fill Color( 0 )},
Item ID( "1", 1 )
),
Properties(
1,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "2", 1 )
)
)}
),
Dispatch( {}, "graph title", TextEditBox, {Set Text( "" )} ),
Dispatch( {}, "X title", TextEditBox, {Set Text( "" )} ),
Dispatch(
{},
"Graph Builder",
FrameBox,
{DispatchSeg(
Marker Seg( "Marker (1)" ),
label offset( {0, -8, -13}, {1, -12, 26} )
), DispatchSeg(
Marker Seg( "Marker (2)" ),
label offset( {0, -5, 21}, {1, -14, -16} )
)}
)
)
)
),
New Script(
"Symbiodinium density",
Graph Builder(
Size( 518, 446 ),
Show Control Panel( 0 ),
Show Legend( 0 ),
Variables(
X( :Treatment ),
Y( :Symbiodinium density ),
Overlay( :Temperature Regime )
),
Elements(
Points( X, Y, Legend( 4 ), Jitter( "None" ) ),
Line( X, Y, Legend( 5 ) )
),
SendToReport(
Dispatch(
{},
"Symbiodinium density",
ScaleBox,
{Min( 1.5 ), Max( 4 ), Inc( 0.5 ), Minor Ticks( 0 )}
),
Dispatch(
{},
"400",
ScaleBox,
{Legend Model(
4,
Properties(
0,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "1", 1 )
),
Properties(
1,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "2", 1 )
)
), Legend Model(
5,
Properties(
0,
{Line Color( 0 ), Line Style( "Dotted" ),
Fill Color( 0 )},
Item ID( "1", 1 )
),
Properties(
1,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "2", 1 )
)
)}
),
Dispatch( {}, "graph title", TextEditBox, {Set Text( "" )} ),
Dispatch( {}, "X title", TextEditBox, {Set Text( "" )} ),
Dispatch(
{},
"Graph Builder",
FrameBox,
{DispatchSeg(
Marker Seg( "Marker (1)" ),
label offset( {0, 2, 24}, {1, -3, -16} )
), DispatchSeg(
Marker Seg( "Marker (2)" ),
label offset( {0, 3, -15}, {1, 1, 24} )
)}
)
)
)
),
New Script(
"max dark-adapted",
Graph Builder(
Size( 518, 446 ),
Show Control Panel( 0 ),
Show Legend( 0 ),
Variables(
X( :Treatment ),
Y( :Name( "max. dark-adapted quantum yield" ) ),
Overlay( :Temperature Regime )
),
Elements(
Points( X, Y, Legend( 3 ), Jitter( "None" ) ),
Line( X, Y, Legend( 4 ) )
),
SendToReport(
Dispatch(
{},
"max. dark-adapted quantum yield",
ScaleBox,
{Min( 0.72 ), Max( 0.77 ), Inc( 0.01 ), Minor Ticks( 1 )}
),
Dispatch(
{},
"400",
ScaleBox,
{Legend Model(
3,
Properties(
0,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "1", 1 )
),
Properties(
1,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "2", 1 )
)
), Legend Model(
4,
Properties(
0,
{Line Color( 0 ), Line Style( "Dotted" ),
Fill Color( 0 )},
Item ID( "1", 1 )
),
Properties(
1,
{Line Color( 0 ), Fill Color( 0 )},
Item ID( "2", 1 )
)
)}
),
Dispatch( {}, "graph title", TextEditBox, {Set Text( "" )} ),
Dispatch( {}, "X title", TextEditBox, {Set Text( "" )} ),
Dispatch(
{},
"Graph Builder",
FrameBox,
{DispatchSeg(
Marker Seg( "Marker (1)" ),
label offset( {0, -4, -17}, {1, -6, -18} )
), DispatchSeg(
Marker Seg( "Marker (2)" ),
label offset( {0, -7, -14}, {1, -4, -17} )
)}
)
)
)
),
New Column( "Treatment",
Character,
"Nominal",
Set Property( "Value Ordering", {"upwelling", "non-upwelling"} ),
Set Values( {"upwelling", "upwelling", "non-upwelling", "non-upwelling"} ),
Set Display Width( 132 )
),
New Column( "Temperature Regime",
Numeric,
"Nominal",
Format( "Best", 12 ),
Set Values( [1, 2, 1, 2] )
),
New Column( "Growth",
Numeric,
"Continuous",
Format( "Best", 12 ),
Set Values( [0.78, 0.75, 0.68, 0.82] )
),
New Column( "Symbiodinium density",
Numeric,
"Continuous",
Format( "Best", 12 ),
Set Values( [2.8, 3.05, 3.45, 3.38] )
),
New Column( "Tukey Symbiodinium",
Character,
"Nominal",
Set Values( {"B", "B", "A", "A"} )
),
New Column( "chlorophyll a",
Numeric,
"Continuous",
Format( "Best", 12 ),
Set Values( [7.2, 4.3, 5.5, 6.5] )
),
New Column( "Tukey chlorophyll",
Character,
"Nominal",
Set Values( {"A", "C", "BC", "AB"} )
),
New Column( "max. dark-adapted quantum yield",
Numeric,
"Continuous",
Format( "Best", 12 ),
Set Values( [0.76, 0.749, 0.753, 0.739] ),
Set Display Width( 148 )
),
New Column( "Tukey max",
Character,
"Nominal",
Set Values( {"A", "B", "B", "C"} )
),
Set Row States( [32776, 248, 32776, 248] ),
Set Label Columns( :Tukey max )
)I think this is possible without too much work and no scripting. The basic idea is to create a data table from your Tukey connecting letters report and join those letters to your original data matching the group name to the Levels column from the Tukey table. Then, combine the columns with the letter groups by selecting them > right-click on any of the highlighted columns > New Formula Column > Concatenate (with Space or with Comma). Next, select the resulting column and use it for labels (Cols > Label/Unlabel).
Finally, make your plot in Graph Builder. After I made a bar chart, I was able to add error bars and labels as you showed using the Control Panel controls for Bar.
**Community is not allowing me to post the table ("The contents of the attachment doesn't match its file type"). Here's the script to reproduce it:
New Table( "ExamplePlotTukeyLabels",
Add Rows( 17 ),
New Script(
"Source",
Data Table( "Untitled 4" ) << Join(
With( Data Table( "Untitled 6" ) ),
By Matching Columns( :Groups = :Level ),
Drop multiples( 0, 0 ),
Include Nonmatches( 0, 0 ),
Preserve main table order( 1 )
)
),
New Script(
"Make Into Data Table",
Names Default To Here( 1 );
platform = Current Data Table() << Oneway(
Y( :Y ),
X( :Groups ),
All Pairs( 1 )
);
Wait( 0 );
Report( platform )[Outline Box( "Oneway Analysis of Y By Groups" )][
Outline Box( "Means Comparisons" )][
Outline Box( "Comparisons for all pairs using Tukey-Kramer HSD" )][
Outline Box( "Connecting Letters Report" )][Table Box( 1 )] <<
Make Into Data Table;
Report( platform ) << Close Window;
),
New Script(
"Example with Tukey Levels",
Graph Builder(
Size( 518, 550 ),
Show Control Panel( 0 ),
Variables( X( :Groups ), Y( :Y ) ),
Elements(
Bar(
X,
Y,
Legend( 4 ),
Error Bars( "Standard Error" ),
Label( "Label by Row" )
)
)
)
),
New Column( "Groups",
Character,
"Nominal",
Set Values(
{"Group 1", "Group 1", "Group 1", "Group 1", "Group 1", "Group 2",
"Group 2", "Group 2", "Group 2", "Group 2", "Group 3", "Group 3",
"Group 3", "Group 3", "Group 3", "Group 4", "Group 4"}
)
),
New Column( "Y",
Numeric,
"Continuous",
Format( "Best", 12 ),
Formula(
Random Normal( 15, 3 ) + Col Mean( Random Normal( 0, 10 ), :Groups )
),
Suppress Eval
),
New Column( "Level",
Character,
"Nominal",
Set Values(
{"A", "A", "A", "A", "A", "B", "B", "B", "B", "B", "C", "C", "C", "C",
"C", "D", "D"}
)
),
New Column( "~Letter Column A",
Character,
"Nominal",
Set Values(
{"", "", "", "", "", "A", "A", "A", "A", "A", "", "", "", "", "", "A",
"A"}
)
),
New Column( "~Letter Column B",
Character,
"Nominal",
Set Values(
{"B", "B", "B", "B", "B", "", "", "", "", "", "B", "B", "B", "B", "B",
"B", "B"}
)
),
New Column( "Concatenate[~Le...etter Column B]",
Character,
"Nominal",
Formula( :Name( "~Letter Column A" ) || " " || :Name( "~Letter Column B" ) )
),
New Column( "Mean",
Numeric,
"Continuous",
Format( "Fixed Dec", 12, 6 ),
Set Values(
[12.8498772929854, 12.8498772929854, 12.8498772929854, 12.8498772929854,
12.8498772929854, 19.105279210907, 19.105279210907, 19.105279210907,
19.105279210907, 19.105279210907, 11.7021088825322, 11.7021088825322,
11.7021088825322, 11.7021088825322, 11.7021088825322, 16.4722902997683,
16.4722902997683]
)
),
Set Label Columns( :Name( "Concatenate[~Le...etter Column B]" ) )
)