Common soil invertebrate (Collembola: Isotomiella minor) reduces weed biomass and alters weed communities

Soil microarthropods affect soil ecosystems in a manner that may contribute to balancing the goals of building soil health and controlling weeds in organic agricultural systems. While soil microarthropod feeding behavior can affect plant growth, their impacts on plant communities in agricultural systems are largely unknown. A greenhouse experiment was conducted to investigate the impacts of microarthropods on weed communities. A model weed seed bank was used in each mesocosm, which included yellow foxtail ( Setaria pumila (Poir.) Roem&Schult.), giant foxtail ( Setaria faberi Herrm.), Powell amaranth ( Amaranthus powellii S. Watson ), waterhemp ( Amaranthus tuberculatus (Moq.) Sauer), common lambsquarters ( Chenopodium album L.), and velvetleaf ( Abutilon theophrasti Medik.). The study included three treatments: Collembola ( Isotomiella minor , Schaffer 1896) abundance (none, low, high), soil microbial community (sterilized/non-sterilized), and fertilizer (presence/absence of compost). A lab experiment examining individual weed species interactions with I. minor was conducted to elucidate the mechanisms driving the greenhouse experiment findings. Twenty seeds of each weed species were placed on moistened germination paper in containers with varying I. minor abundance levels (none, low, high, very high). Seed germination was recorded after five and seven days. In the greenhouse, the presence of I. minor increased total weed emergence during the first two weeks, but this effect diminished after three weeks. Increasing I. minor abundances generally decreased weed biomass, though this effect was greater in the non-sterilized soil. In the non-sterilized soil, I. minor presence decreased total aboveground weed biomass production by up to 23 %. The Amaranthus species, Powell amaranth and waterhemp, drove this effect with a 55 % and 32 % reduction in biomass, respectively. In tandem, the Amaranthus species had reduced abundances in the presence of I. minor . I. minor increased yellow foxtail germination in the lab, while not affecting the other weed species. This suggests that their effects on the Amaranthus weeds in the greenhouse were likely not caused by direct effects on germination, but instead through nutrient cycling or root herbivory. The proposed mechanism underlying these interactions is that I. minor can initially stimulate germination by feeding on seed coats, but when the seed coats are minimal can damage the seedling. Our findings indicate I. minor could impact weed growth in a manner that affects management decisions and outcomes. • Isotomiella minor decreased total aboveground weed biomass production by up to 23 %. • Powell amaranth (55 %) and waterhemp (32 %) biomass were most decreased by I. minor . • I. minor directly increased yellow foxtail germination in lab study. • Seed coat composition may influence the outcomes of seed-Collembola interactions.