PS 86-132 - Relationship of riparian tree species diversity and litter breakdown in a central Texas stream: The role of an introduced tree species

Friday, August 12, 2011
Exhibit Hall 3, Austin Convention Center
Trey Nobles1, Derek M. Wallace1 and Yixin Zhang2, (1)Department of Biology, Texas State University, San Marcos, TX, (2)Department of Biology, Texas State University at San Marcos, San Marcos, TX

In order to understand biodiversity-ecosystem functioning relationship, we examined effects of riparian vegetation diversity on leaf litter decomposition in a stream.  Because terrestrial leaf-litter is the dominant energy source to many streams, riparian vegetation diversity can have profound influence on streams ecosystems, which are impacted by human watershed disturbances, including species losses and non-native species introduction. If introduced tree species influences biodiversity-ecosystem functioning relationship in streams is largely unknown. The objective of this study is to assess the effects of tree species diversity (five native riparian species and one introduced species) on leaf litter breakdown in a stream. We conducted a field experiment over 56 days in Barton Creek (Central Texas) to examine temporal patterns of litter breakdown and to detect any non-additive effects of litter diversity on decomposition. The 12 treatments of leaf-bags were the six single species alone and six three-species combinations we created based on a priori assumption of leaf quality (high, medium, and low). We placed 4.5-gram leaf bags (5mm mesh) into four riffles, which were collected on days 1, 18, 35, and 56. Collected leaves were washed into a .5mm sieve, dried at 60 °C for 24 hours, and weighed.


Significant differences were found between several of the treatments. Japanese Privet, the non-native species, was the most labile, losing nearly 60 mg of dry mass per day. American Elm, the most labile native species used in the study, lost 45 mg/day. Pecan was intermediate, losing 33 mg/day; and Live Oak, Red Oak, and Sycamore were all similarly recalcitrant, losing 13, 14, and 15 mg/day respectively. The combination treatments showed intermediate decay rates between 26 and 44 mg/day. There was wide variation in decay rates among the six species of leaves in this study, which could result in both short-term and long-term resource availability to aquatic organisms. No significant differences were found between the predicted and actual decomposition rates in any of the combination treatments, suggesting only additive effects of mixed species. The high breakdown rate of introduced Japanese Privet could influence this natural subsidy processing regime, depending on which riparian species it is replacing. Our results did not detect a significant effect of introduced species on biodiversity-ecosystem functioning relationship in Barton Creek. This study shows that changing riparian tree diversity towards either more labile or more recalcitrant species could significantly alter the availability of resources to stream organisms.

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