Dietary and taxonomic controls on incorporation of microbial carbon and phosphorus by detritivorous
caddisflies
Halvor M. Halvorson1*, Grant White1, J. Thad Scott2, and Michelle A. Evans-White1
1
University of Arkansas Department of Biological Sciences, Fayetteville, AR
2
University of Arkansas Department of Crop, Soil, and Environmental Sciences, Fayetteville, AR
*Corresponding author – Email: halvorso@gmail.com; Phone: 479 575 6342; Fax: 479 575 4010
Highlighted student research:
This study is an outstanding contribution because it employs novel methods to dually examine
factors controlling incorporation of microbial carbon (C) and phosphorus (P) by detritivorous animals.
Diet leaf type did not affect incorporation of microbial C or P; however, detritivorous caddisflies reduced
incorporation of microbial P on higher-P detritus and two taxa of lower body C:P incorporated microbial
C and P more efficiently than a higher C:P taxon. These data support ecological stoichiometry theory of
broad constraints on energy and nutrient flow from detritus through detrital food webs.
Author contributions: JTS and MAEW formulated the original idea, HMH and MAEW designed
experiments, and HMH and GW performed experiments and conducted statistical analysis. HMH and
MAEW wrote the manuscript and all authors provided editorial advice.
Supplemental 1. (a) Design of radiation chambers used in caddisfly radiolabel experiments. Potassium
hydroxide (KOH) served as a trap for CO2 entering and leaving the system to prevent release of 14C-CO2,
whereas air and water (H2O) chambers served as safety traps and buffer chambers respectively to
prevent transmittance of KOH to the insect chamber (fourth from left). Each series of tubes was
replicated to permit radiolabeling of 20 individuals from each genus. (b) Final constructed version of
chambers (1 rack containing tubes for 4 total labeling chambers) used in experiments.
Supplemental 2. Mean (±1 SE) elemental content (percent (%) carbon (C), nitrogen (N), and phosphorus
(P) as well as molar ratios of C:N, C:P, and N:P) of maple and oak litter after 3 d of leaching but prior to
microbial conditioning, as an indicator of initial detrital substrate stoichiometry.
Leaf
Maple
Oak
%C
46.7 (0.1)
48.9 (0.2)
%N
0.69 (0.12)
1.05 (0.03)
%P
0.031 (0.002)
0.031 (0.002)
C:N
79.2 (5.9)
55.7 (3.5)
C:P
3950 (340)
4170 (270)
N:P
49.9 (3.3)
75.4 (3.2)
Supplemental 3. Mean (±1 SE) elemental content (percent (%) carbon (C), nitrogen (N), and phosphorus
(P) as well as molar ratios of C:N, C:P, and N:P) of maple and oak litter conditioned for 77 d under 50 or
500 µg P L-1 prior to feeding to caddisflies.
Leaf
Maple
Oak
[P]
50
500
50
500
%C
49.6 (0.4)
49.0 (0.4)
48.2 (0.3)
47.3 (0.3)
%N
1.68 (0.07)
2.07 (0.16)
1.71 (0.06)
1.96 (0.05)
%P
0.050 (0.004)
0.117 (0.015)
0.042 (0.005)
0.098 (0.007)
C:N
35.0 (1.5)
29.0 (2.2)
33.3 (1.4)
28.3 (0.7)
C:P
2700 (210)
1360 (260)
3830 (930)
1330 (120)
N:P
76.4 (3.7)
54.6 (16.5)
119 (33)
46.8 (3.7)
Supplemental 4. Mean (± 1 SE) incorporation efficiencies of microbial carbon (IEC) and microbial
phosphorus (IEP) and relative use efficiencies of microbial C and P (C:P RUE) by caddisflies using 14C and
33
P as radiotracers. Caddisfly genera are arranged from top to bottom by order of increasing body P
content.
[P]a
IEC
IEP
C:P RUE
50 0.059 (0.009) 0.11 (0.08)
0.22 (0.08)
500 0.031 (0.004) 0.21 (0.11)
0.22 (0.10)
Ironoquia
50 0.133 (0.020) 0.46 (0.14)
0.34 (0.03)
500 0.102 (0.016) 0.23 (0.05)
0.49 (0.06)
Pycnopsyche
50 0.196 (0.042) 0.34 (0.07)
0.66 (0.17)
500 0.191 (0.037) 0.47 (0.13)
0.51 (0.07)
a
-1
Leaf litter incubation phosphorus concentration (µg L )
Genus
Lepidostoma