In Situ Changes to Soil Microbial Community Structure and Function Following Degradation of Potentially Biodegradable Mulch Films, Poster Board #100

Mulch films that are biodegradable are desirable alternatives to black plastic polyethylene mulches in agriculture. Although degradation is generally initiated by abiotic factors such as UV radiation, wind, temperature, and moisture, biodegradation by soil microorganisms ultimately transforms biodegradable material into biomass, CO₂, and H₂O. Little is known about the soil microbial community involved in these transformations. This study determined soil microbial community structure using phospholipid fatty acid (PLFA) profiles and function via two enzyme activities involved in chitin and cellulose degradation as affected by different biodegradable mulches across contrasting climate and soil types during 1.5-year in situ incubation. Four replications of both high-tunnel (HT) and open-field (OF) sites were established in three eco-regions of the United States (Southeast TN; Northwestern WA; and Northwest TX). Mulch treatments used at each site included: no mulch (NM) control; experimental spunbond poly-lactic acid (SB), BioAgri and BioTelo (starch-based films; BA and BT); and WeedGuardPlus (cellulose-based mulch; WG). Following the 2010 tomato harvest, used mulches were removed and 161 cm² nylon mesh bags, each containing 103 cm² of each mulch and ~400 g of resident soil were reburied into each mulch’s corresponding plot. The Mesh bags were extracted at 6- and 12-months following burial, and an 18-month sampling is underway. A distance-based MANOVA (perMANOVA) was run to determine the effect of SITE (HT vs. OF), TREATMENT (mulch films), and interaction at each region for the 6-month samples. There were significant main effects but no significant interaction. In general, total PLFA content was higher under HT compared to OF at each region. In WA and TN, HT had greater relative abundance (mol%) of fungi compared to OF, whereas in TX, the  fungal mol% was greater in OF. The most consistent trend among mulches was that fungal mol% was greatest under WG. In TN, the average fungal mol% for WG was 10.4% compared to 8.9% for all other mulches. The fungal mol% of WG for TX and WA were similar (average 15%) and higher than all other mulches (average 11%). Trends among the bacterial markers were less consistent between regions; however, at all regions, the mol% of Actinomycete markers were lower and the fungal:bacteria ratio was highest under WG compared to all other mulches. There were no significant differences for enzyme activities due to mulch treatments. However, there was significantly greater chitin-degrading activity in HT compared to OF at each region. Twelve-month samples are now being processed.