Collembola, commonly known as springtails, are soil microarthropods which play important roles in organic matter decomposition, nutrient cycling, and microbial interactions in agricultural systems. However, little research has assessed their direct interactions with plants. The few studies that have researched these direct interactions have found mixed effects of Collembola on germination and plant growth outcomes. This research aims to further investigate the role of Collembola in seed germination and early seedling development. Two complementary lab experiments were conducted using species in the Amaranthus family, spinach (crop) and waterhemp (weed), to explore the role of seed coat thickness in Collembola-seed interactions. We hypothesize that spinach, with its thick seed coat, would be stimulated by Collembola grazing without sustaining damage, whereas waterhemp, with its thin seed coat, would experience adverse effects, leading to physiological stress. The first experiment was conducted using deli cups lined with germination paper. The treatments included the two plant species and the Collembola Isotomiella minor at three abundance levels (none (0), low (15), and high (30)). Each treatment combination was replicated 5 times. For each plant species, ten seeds were randomly arranged in each deli cup and the Collembola treatments were added. Mesocosms were maintained in growth chambers at 24°C and deionized water was added as needed to maintain moisture. Germination was recorded after 5, 7, and 10 days. Both the spinach and waterhemp germination were not affected by the Collembola treatments. However, spinach had consistently high germination, whereas waterhemp had consistently low germination. The second experiment was conducted using transparent mesocosms filled with a transparent plant growing medium to simulate a 3-D soil structure. The treatments were the same as the experiment described previously. The sealed mesocosms were maintained in growth chambers at 24°C for four weeks. Germination was recorded 5, 7, 10, and 14 days after planting. Collembola interactions with the root systems were monitored using video and photographic recordings throughout the experiment. After four weeks, in mesocosms with true leaf development, plant leaves were measured for stomatal conductance, transpiration, photosystem II efficiency, and chlorophyll content. Each plant was then harvested, and aboveground and root biomass was collected, dried, and weighed. Overall, germination in the mesocosms was low for both spinach and waterhemp, and the Collembola treatments did not have any significant effects. Our initial findings suggest that seed coat thickness may not play a role in the outcomes of Collembola-seedling interactions.
