Alteration of Microbial Communities Colonizing Leaf Litter in a Temperate Woodland Stream by Growth of Trees under Conditions of Elevated Atmospheric CO ₂

Abstract

Elevated atmospheric CO 2 can cause increased carbon fixation and altered foliar chemical composition in a variety of plants, which has the potential to impact forested headwater streams because they are detritusbased ecosystems that rely on leaf litter as their primary source of organic carbon. Fungi and bacteria play key roles in the entry of terrestrial carbon into aquatic food webs, as they decompose leaf litter and serve as a source of nutrition for invertebrate consumers. This study tested the hypothesis that changes in leaf chemistry caused by elevated atmospheric CO 2 would result in changes in the size and composition of microbial communities colonizing leaves in a woodland stream. Three tree species, Populus tremuloides, Salix alba, and Acer saccharum, were grown under ambient (360 ppm) or elevated (720 ppm) CO 2 , and their leaves were incubated in a woodland stream. Elevated-CO 2 treatment resulted in significant increases in the phenolic and tannin contents and C/N ratios of leaves. Microbial effects, which occurred only for P. tremuloides leaves, included decreased fungal biomass and decreased bacterial counts. Analysis of fungal and bacterial communities on P. tremuloides leaves via terminal restriction fragment length polymorphism (T-RFLP) and clone library sequencing revealed that fungal community composition was mostly unchanged by the elevated-CO 2 treatment, whereas bacterial communities showed a significant shift in composition and a significant increase in diversity. Specific changes in bacterial communities included increased numbers of alphaproteobacterial and cytophaga-flavobacter-bacteroides (CFB) group sequences and decreased numbers of betaproteobacterial and firmicutes sequences, as well as a pronounced decrease in overall Gram-positive bacterial sequences.

Decomposer communities in human‐impacted streams: species dominance rather than richness affects leaf decomposition

“…The most common fungal identity was the uncultured fungus clone AA45‐20 (33% of all OTUs), which has been reported in only a single study in a woodland stream in North America (Kelly et al . ) (these strains were 100% similar by the sequenced region). The proportional abundance of the uncultured fungus clone AA45‐20 correlated strongly with fungal evenness ( r = −0.…”

Future increase in temperature more than decrease in litter quality can affect microbial litter decomposition in streams

“…A recent study also found that fungal communities were not affected by litter quality changes induced by increased atmospheric CO 2 (Kelly et al 2010). However, when differences in litter quality are greater, for example, between litter species, aquatic hyphomycete community structure can be affected (Gulis 2001;Ferreira et al 2006).…”

“…Litter toughness has been shown to determine litter decomposition rates, sometimes even overcoming the importance of litter chemistry (Quinn et al 2000;Li et al 2009). The few studies addressing the effects of changes on litter quality induced by increases in atmospheric CO 2, on aquatic microbial communities and litter decomposition have shown that these effects are stronger at early stages of litter decomposition than at later stages, when secondary compounds have been leached; however, overall they remain weak and speciesdependent (Rier et al , 2005Tuchman et al 2003b;Kelly et al 2010). Evidence from terrestrial systems also indicates that the effects of elevated CO 2 on litter quality are species specific and not always translated into differences in litter decomposition rates (Gorissen and Cotrufo 2000;King et al 2001;Norby et al 2001).…”

“…A CO 2 -induced decrease in litter quality might therefore affect its use by aquatic decomposers and, thereby affect litter decomposition. However, to date, only a few studies have addressed this question (Tuchman et al , 2003bRier et al 2002Rier et al , 2005Kelly et al 2010), and in all of these studies CO 2 -induced changes in litter quality were considered irrespective of variations in temperature, despite the fact these two factors vary simultaneously.…”

Soil organic matter availability and climate drive latitudinal patterns in bacterial diversity from tropical to cold temperate forests

“…Bacterial phylotype richness increased with reduced community‐weighted means of leaf C/N (Table ; Table S4). Generally, leaves with higher C/N ratios are decomposed more slowly than those with a low C/N ratio, likely due to reduced nitrogen availability and, consequently, lower bacterial diversification (Kelly et al., ) or the promotion of resource partitioning among the component soil organisms (Wardle, ). In line with finding, leaf C/N was significantly positively correlated with the relative abundance of Acidobacteria , which can adapt to low nutrient availability (Table S6).…”