Making tables with lots of footnotes and aligning the caption

I learnt Latex last month and am trying to write a large document with it. I have managed the text and figures, but not tables.
Although my table is centered, I would like my caption to begin along with the first cell of the table rather than the full left indent like a normal paragraph.

I also have many footnotes which pertain to the whole table rather than specific parts of the table. I tried using tablefootnote, but no text seems to appear. Also, I don’t want the numbers, just the text.

documentclass[a4paper, oneside]{book}
usepackage[left=35mm, right=15mm, top=20mm, bottom=15mm]{geometry}
usepackage{setspace}
usepackage{fixltx2e}
usepackage{graphicx}
usepackage{float}
usepackage{tabularx}
usepackage{amssymb}
usepackage{booktabs} % For toprule, midrule and bottomrule
usepackage{pgfplotstable} % Generates table from .csv
usepackage{longtable}    %Allows multi-page tables
usepackage{rotating}     %Allows for single page landscape using sidewaystable{}
usepackage{pdflscape}     %Allows for landscape
usepackage{multirow}      %Allows for merging across rows
usepackage{tablefootnote} 
usepackage{footnote}

begin{document}

begin{table}[h!]
begin{center}
caption{Proximate phenolic and carbohydrate content}
label{Table4}
 begin{tabular}{c c c c c c c} 
 toprule
 &multicolumn{2}{c}{textbf{Leaf}}& &multicolumn{2}{c}{textbf{Roots}}\
cline{2-3}cline{5-6} 
 textbf{Plant} & textbf{Colour} & textbf{Density} &  &textbf{Colour} & textbf{Density}\
 midrule
 Sample1&26.1$pm$0.7$^{c}$ &172.3$pm$9.0& & 25.5$pm$6.8$^{b}$&83.7$pm$4.5$^{a}$\
 Sample2&53.9$pm$2.0$^{d}$&129.5$pm$3.2& &29.4$pm$4.8$^{b}$&11.7$pm$1.8\
 Sample3&32.5$pm$3.2$^{c}$&163.3$pm$6.5& &96.8$pm$18.1&64.4$pm$1.3\
 Sample4&54.2$pm$2.3$^{d}$&82.6$pm$7.5& &28.9$pm$3.0$^{b}$&35.7$pm$1.2\
 Sample5&28.4$pm$3.9$^{c}$&172.1$pm$6.3& &26.9$pm$5.1$^{b}$&78.8$pm$2.8$^{a}$\
 Sample6&50.0$pm$2.0$^{d}$&112.3$pm$5.3& &54.1$pm$5.7&48.1$pm$7.1\
 bottomrule
end{tabular}
end{center}
footnotesize{Values expressed in %(mg.mg$^{-1}$)}\
footnotesize{Values with same superscript are statistically similar (OW-ANOVA,p textless 0.01)}\
footnotesize{NSP=Non-starch polysaccahride}
end{table}

end{document}

I tried to be clever, but didn’t work for the second caption:

begin{table}[h!]
begin{center}
caption{Proximate phenolic and carbohydrate content}
label{Table4}
 begin{tabular}{c c c c c c c} 
 toprule
 &multicolumn{2}{c}{textbf{Leaf}}& &multicolumn{2}{c}{textbf{Roots}}\
cline{2-3}cline{5-6} 
 textbf{Plant} & textbf{Colour} & textbf{Density} &  &textbf{Colour} & textbf{Density}\
 midrule
 Sample1&26.1$pm$0.7$^{c}$ &172.3$pm$9.0& & 25.5$pm$6.8$^{b}$&83.7$pm$4.5$^{a}$\
 Sample2&53.9$pm$2.0$^{d}$&129.5$pm$3.2& &29.4$pm$4.8$^{b}$&11.7$pm$1.8\
 Sample3&32.5$pm$3.2$^{c}$&163.3$pm$6.5& &96.8$pm$18.1&64.4$pm$1.3\
 Sample4&54.2$pm$2.3$^{d}$&82.6$pm$7.5& &28.9$pm$3.0$^{b}$&35.7$pm$1.2\
 Sample5&28.4$pm$3.9$^{c}$&172.1$pm$6.3& &26.9$pm$5.1$^{b}$&78.8$pm$2.8$^{a}$\
 Sample6&50.0$pm$2.0$^{d}$&112.3$pm$5.3& &54.1$pm$5.7&48.1$pm$7.1\
 bottomrule
end{tabular}
end{center}
begin{tabular}
footnotesize{Values expressed in %(mg.mg$^{-1}$)}\
footnotesize{Values with same superscript are statistically similar (OW-ANOVA,p textless 0.01)}\
footnotesize{NSP=Non-starch polysaccahride}
end{tabular}
end{table}

Would this solution work in landscape format? I have tables of that variety as well

documentclass[a4paper, oneside]{book}
usepackage[left=35mm, right=15mm, top=20mm, bottom=15mm]{geometry}
usepackage{setspace}
usepackage{fixltx2e}
usepackage{graphicx}
usepackage{float}
usepackage{tabularx}
usepackage{amssymb}
usepackage{booktabs} % For toprule, midrule and bottomrule
usepackage{pgfplotstable} % Generates table from .csv
usepackage{longtable}    %Allows multi-page tables
usepackage{rotating}     %Allows for single page landscape using sidewaystable{}
usepackage{pdflscape}     %Allows for landscape
usepackage{multirow}      %Allows for merging across rows
usepackage{tablefootnote} 
usepackage{footnote}

usepackage{threeparttable}
usepackage{caption}
captionsetup{singlelinecheck=false}
usepackage{siunitx}
sisetup{input-uncertainty-signs=pm, 
         separate-uncertainty=true}
        
begin{document}

begin{table}[h!]
centering
begin{threeparttable}
caption{Proximate phenolic and carbohydrate content}
label{Table4}
sisetup{table-format=2.1(3), 
         table-space-text-post=tnote{a}, 
         table-align-text-post=false}
 begin{tabular}{l S S S S} 
 toprule
 &multicolumn{2}{c}{textbf{Leaf}}& multicolumn{2}{c}{textbf{Roots}}\
cmidrule(r){2-3}cmidrule(l){4-5} 
 {textbf{Plant}} & {textbf{Colour}} & {textbf{Density}} & {textbf{Colour}} & {textbf{Density}}\
 midrule
 Sample1 & 26.1 pm 0.7tnote{c} & 172.3 pm 9.0 & 25.5 pm 6.8tnote{b} & 83.7 pm 4.5tnote{a} \
 Sample2 & 53.9 pm 2.0tnote{d} & 129.5 pm 3.2 & 29.4 pm 4.8tnote{b} & 11.7 pm 1.8          \
 Sample3 & 32.5 pm 3.2tnote{c} & 163.3 pm 6.5 & 96.8 pm 18.1         & 64.4 pm 1.3          \
 Sample4 & 54.2 pm 2.3tnote{d} & 82.6  pm 7.5 & 28.9 pm 3.0tnote{b} & 35.7 pm 1.2          \
 Sample5 & 28.4 pm 3.9tnote{c} & 172.1 pm 6.3 & 26.9 pm 5.1tnote{b} & 78.8 pm 2.8tnote{a} \
 Sample6 & 50.0 pm 2.0tnote{d} & 112.3 pm 5.3 & 54.1 pm 5.7          & 48.1 pm 7.1          \
 bottomrule
end{tabular}
footnotesize
Values expressed in %(mg.mg$^{-1}$)

Values with same superscript are statistically similar (OW-ANOVA,p textless 0.01)
 
NSP=Non-starch polysaccharide
end{threeparttable}
end{table}



end{document}