Supporting isotopic data for: Differential utilization of submerged leaf litter by microbial biofilms and macroinvertebrates in a large dryland river

In river food webs, the energetic coupling of nutrient-rich ‘fast’
autochthonous (algal) and recalcitrant ‘slow’ allochthonous (terrestrial)
resources may confer stability. Additionally, microbial biofilms may
enhance the nutritional quality of allochthonous resources for
macroinvertebrate consumers, potentially facilitating trophic linkages
within slow energy channels. We used 16S and 18S rRNA gene sequencing and
essential amino acid (AAESS) carbon isotope (δ13C) analysis to
characterize microbial biofilms and quantify proportional contributions of
AAESS derived from algae, terrestrial plants, and microbes (Archaea,
Bacteria, fungi) to macroinvertebrates across a series of mesocosm and in
situ leaf pack experiments in the middle Rio Grande of central
New Mexico, USA. In our 12-week mesocosm experiment, we found that leaves
of native Rio Grande Cottonwood trees (Populus deltoides wislizeni)
contributed greater mean estimated proportions of AAESS (0.41–0.81) to
Chironomidae larvae than those of nonnative Russian Olive trees (Elaeagnus
angustifolia; 0.18–0.50). Microbes were notable sources of AAESS to
macroinvertebrates inhabiting native C4 grass (Spike Dropseed; Sporobolus
contractus) leaf packs (0.08–0.26). Our field experiment demonstrated
river sediment was the main source of microbes colonizing submerged
Cottonwood leaves and that allochthonous resource use varied across
macroinvertebrate taxa, such that Chironomidae assimilated the highest
mean estimated proportions of AAESS from Cottonwood leaves (0.36–0.65)
while Ephemeroptera and Trichoptera assimilated the highest mean estimated
proportions of AAESS from algae (0.82–0.94). Our work indicates
terrestrial tree leaves are important sources of AAESS to Chironomidae,
while algae are the dominant source of AAESS to other macroinvertebrates
in the middle Rio Grande.