What could explain 13C signature of dryland biocrusts? Evaluating potential resource transfer between plants and biocrusts.

Dryland ecosystems are increasing in geographic extent and contribute
greatly to interannual variability in global carbon dynamics.
Disentangling interactions among dominant primary producers can help
partition their contributions to dryland C dynamics. We measured the
δ13C signatures of biological soil crusts and dominant plant species
(C3 and C4) across a regional scale in the southwestern USA to
determine if biocrust cyanobacteria were coupled to plant productivity
(using plant-derived C mixotrophically), or independent of plant
activity (and therefore purely autotrophic).