Crumb rubber microplastics alter soil water dynamics and plant biomass allocation in soybeans
Description
A controlled greenhouse experiment evaluated the responses of soybean (Glycine max) plants grown in soil containing increasing proportions of crumb rubber (CR). Germination, plant growth, chlorophyll content, soil respiration, biomass production, water loss, root allocation, and elemental composition of soils and plant tissues were measured over a 21-day growth period.
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A controlled greenhouse experiment evaluated the responses of soybean (Glycine max) plants grown in soil containing increasing proportions of crumb rubber (CR). Germination, plant growth, chlorophyll content, soil respiration, biomass production, water loss, root allocation, and elemental composition of soils and plant tissues were measured over a 21-day growth period. The soil-crumb rubber prep: 0.47 L glass jars Control (0% CR; 150 g soil and 0 g CR) Low (16.6% CR; 125 g soil and 25 g CR) Medium (33.3% CR; 100 g soil and 50 g CR) High (50% CR; 75 g soil and 75 g CR) Heirloom soybean seeds (Glycine max, variety KS 5120N) were obtained from Outsidepride.com. One soybean seed was planted in each jar at a depth of 3.8 cm below the soil surface. Jars maintained in a controlled growth chamber at 22 °C under a 12 h light:12 h dark photoperiod with fluorescent lighting and a light intensity of approximately 400 µmol m⁻² s⁻¹ measured at canopy height. After planting, each replicate jar was watered to 20% of the combined mass of the jar and soil relative to the pre-watering weight, and the resulting mass was recorded as the target weight for that jar. At each watering event, the volume of water required to return each jar to its predetermined target weight was recorded. These values were summed across watering events to calculate cumulative water loss for each experimental unit. Plants were maintained for 21 days, during which jars were weighed and watered twice weekly (six watering events spaced approximately 3–4 days apart). Germination and plant height were recorded at each watering event. Jars were left uncovered to allow plant growth and gas exchange and placed randomly positioned within the growth chamber. Plants were harvested when they reached the first trifoliate developmental stage, 21 days after initiation. Germination and Plant Height Germination and plant height recorded at each watering event and on the final day. Germination defined as visible emergence of the seedling above soil surface. Plant height was measured using a metric ruler placed at soil surface and recorded as the distance from the soil surface to the highest point of plant. Chlorophyll On final day 21 before harvest, leaf chlorophyll content was measured using an Apogee Instruments MC-100 Chlorophyll Concentration Meter on the uppermost fully developed leaf. Mesocosm Respiration On final day 21 and before harvest, combined respiration of the plant and soil was measured using a PPSystems EGM-5 Portable CO₂ Gas Analyzer. Wet and Dry Biomass were measured using a lab balance. After drying, each plant was separated into root and shoot components, and weighed individually to determine dry root biomass (g) and dry shoot biomass (g). Total dry plant biomass (g) calculated as the sum of the dry root and dry shoot masses. Root:Shoot ratios recorded as dry biomass of roots divided by dry biomass of shoots.
Institutions
- Stony Brook UniversityNew York, Stony Brook