Date of Award

Fall 12-1-2006

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Life Sciences

First Advisor

Mary Ann McLean

Second Advisor

Kathleen Dannelly

Third Advisor

Elaina Tuttle

Abstract

Increased temperature in urban areas compared to rural areas is known as the urban heat island (UHi) effect. The effects of UHI on ecosystem processes can indicate the potential effects of global warming on processes such as organic matter decomposition and nutrient cycling, etc. It was reported that the urban isolates of two fungal species ( Chrysosporium pannorum and Trichoderma koningii) appeared to have adapted to higher temperatures in urban oak forest compared to rural isolates. Since these fungi decompose chitin, releasing ammonium, the apparent adaptation of these fungi to higher temperatures is probably due to increased chitinolytic enzyme activity and abundance. Ammonium and ergosterol ( a measure of biomass) production of T. koningii and C. pannorum in chitin-amended soil were assessed over 6 weeks to determine the biomass and overall chitinolytic enzyme activity patterns of urban and rural isolates at different temperatures (15, 22 and 29°C). Furthermore, the activity of three key chitinolytic enzymes (N-acetylglucosimidase, chitobiosidase, and endochitinase) of urban and rural isolates of C. pannorum and T. koningii at different temperatures were investigated to determine whether differences in enzyme activity could account for the increased growth of urban isolates at higher temperature. Urban T. koningii biomass was greater at 29°C and less at 15°C than rural T. koningii (P<0.05). Since no significant differences in ammonium and ammonium per unit biomass production were observed between the urban and rural isolate of T. koningii, it is unlikely that alterations in chitinolytic enzyme activity can account for the observed increase in growth by the urban isolate at higher temperature. Chitobiosidase activity of the urban T. koningii was significantly lower than that of the rural isolate at 30°C (P<0.01). This may be due to the increased enzymatic activity at higher temperatures which can occur when fungi are acclimated to low temperatures. That at 30°C the activities of chitobiosidase and NAGase of T. koningii did not significantly correlate with ammonium production reflected a shift from the main chitin degrading pathway to the chitosanase pathway at higher temperatures. On the other hand, although biomass of urban C. pannorum did not differ from that of the rural isolate, ammonium and ammonium production per unit biomass by the urban isolate of C. pannorum were greater than those of the rural isolate at 22°C (both Ps< 0.01 ), indicating that the urban isolate produced more chitinolytic enzymes or more active enzymes. NAGase activity of the urban C. pannorum was significantly greater than that of the rural isolate only at 15°C (P<0.01). Furthermore, NAGase and endochitinase activities and overall ammonium production by the urban isolate tended to be higher than those by the rural isolate at 25°C. Since the correlation between ammonium production and chitobiosidase and NAGase activities was low, the faster growth of urban C. pannorum at higher temperatures was likely due to use of the chitosanase pathway. Above all, two fungal species using the same resource appeared to have responded to increased temperature in the urban site in different ways. That overall chitinolytic enzyme activity between these two fungal species was different and urban isolates of both of these common chitinolytic fungal species appeared to have altered their enzyme activities may have important implications for the dynamics of urban soil communities and the ecosystem processes mediated by these species. If the alteration of chitinolytic activity is the general response by soil fungi to the urban heat island, and these changes increase or decrease chitin decomposition, this may result in significant changes in C and N cycling in urban ecosystem.

Download

Share

COinS