Litter Supply as a Driver of Microbial Activity and Community Structure on Decomposing Leaves: a Test in Experimental Streams

Abstract

e Succession of newly created landscapes induces profound changes in plant litter supplied to streams. Grasses dominate inputs into open-land streams, whereas tree litter is predominant in forested streams. We set out to elucidate whether the activity and structure of microbial communities on decomposing leaves are determined by litter quality (i.e., grass or tree leaves colonized) or whether changes during riparian succession affecting litter standing stocks on the stream bed play an overriding role. We used 15 outdoor experimental streams to simulate changes in litter supplies reflecting five stages of riparian succession: (i) a biofilm stage with no litter, (ii) an open-land stage characterized by grass litter inputs, (iii) a transitional stage with a mix of grass and tree litter, (iv) an early forested stage with tree litter, and (v) an advanced forested stage with 2.5 times the amount of tree litter. Microbial activities on tree (Betula pendula) and grass (Calamagrostis epigejos) litter were unaffected by either the quantity or type of litter supplied to the experimental streams (i.e., litter standing stock) but differed between the two litter types. This was in stark contrast with bacterial and fungal community structure, which markedly differed on grass and tree litter and, to a lesser extent, also among streams receiving different litter inputs. These patterns reveal distinct responses of microbial community structure and activity to the bulk litter available in streams but consistent responses to the litter type colonized.

Composition of riparian litter input regulates organic matter decomposition: Implications for headwater stream functioning in a managed forest landscape

“…Specifically, our results suggest that the input of high‐quality plant litter from the riparian zone may accelerate the decomposition of native litter species in boreal headwaters (cf. Frossard, Gerull, Mutz, & Gessner, 2013). Although we are not certain of the mechanisms involved, the composition (i.e., mixing) of the riparian plant community, together with in‐stream physicochemical variables, was clearly related to the variation in breakdown observed among sites.…”

“…However, microbial communities that should be adapted to low‐quality litter (i.e., spruce) seemed more able to utilize lodgepole pine as a resource (Figure 4d). Such communities are likely not as abundant in streams where high‐quality vegetation dominates the input (Frossard et al., 2013), and this could explain the low lodgepole pine litter decomposition rates in sites with high‐quality litter input, and conversely, the positive relationship between processing rate and coniferous litter inputs. Hence, we cannot rule out that the low decomposition rate of lodgepole pine is a consequence of few microbial groups found in Swedish boreal headwaters being adapted to its litter (sensu Gundale et al., 2014; Jackrel & Wootton, 2014), rather than it merely resulting from the low quality of this litter.…”

Leaf litter diversity and structure of microbial decomposer communities modulate litter decomposition in aquatic systems

“…Surprisingly, in aquatic ecosystems, the focus has often been on effects of leaf litter quality, climate or the structure of the decomposer community (e.g. Frainer et al., ; Frossard et al., ; García‐Palacios et al., ; Hines, Reyes, & Gessner, ) on decomposition rates, rather than on effects of litter diversity per se (but see, e.g., Gessner, Inchausti, Persson, Raffaelli, & Giller, ; Giller et al., ; Handa et al., ). Consequently, the specific effects of leaf litter diversity and identity and the decomposer community in aquatic systems are still not completely resolved and have been proposed to be to some degree system dependent (Cardinale et al., ; Hättenschwiler et al., ; Lecerf et al., ).…”

Soil organic carbon and soil structure are driving microbial abundance and community composition across the arid and semi-arid grasslands in northern China

“…In a number of studies it has been shown that the carbon source that had the most pervasive effects on the microbial community was the decomposing plant litter (e.g. Aneja et al, 2006;Frossard et al, 2013). A characteristic shift in microbial community structure is related to additions of root exudates that increase the relative abundance of Gram-negative bacteria, while decreasing the proportion of Gram-positive bacteria (Griffiths et al, 1998;Lu et al, 2007;McMahon et al, 2005;Brant et al, 2006;Williams et al, 2007).…”

“…Aneja et al, 2006;Frossard et al, 2013). Unsurprisingly soil carbon sources are routinely identified as key ecological drivers of microbial community dynamics (Johnson et al, 2003;el Zahar Haichar et al, 2008;Djukic et al, 2010;Vries et al, 2012).…”