Role of physical fragmentation and invertebrate activity in the breakdown rate of leaves

Abstract

We evaluated the relative importance of current velocity and invertebrate activities in the breakdown rate of alder [Alnus glutinosa (L.) Gaertner] leaves. Decomposition experiments were carried out in artificial channels, where current velocity and shredder presence were manipulated, and in a 4 th order stream, in both summer and autumn, where litter bags were incubated in several reaches differing in both depth and current velocity. Alder leaves incubated in artificial channels decomposed significantly faster in the presence of shredders than in their absence (k = 0.0368/d vs. k = 0.0210/d in low current and k = 0.0472/d vs. k = 0.0219/d in high current). However, current (up to 2.35 m/s) had no significant effect on decomposition rates. In channels without invertebrates, no significant differences in k values were found between coarse and fine mesh bags in high (0.20 m/s) and low (0.05 m/s) current. Leaves incubated in the stream during summer, in reaches with current velocity ranging from 0.003 to 1.185 m/s, did not differ in their decomposition rates (k = 0.0489/d to k = 0.0645/d). In autumn, leaves exposed to high current (1.228 m/s) had faster decomposition rate (k = 0.0417/d vs. k = 0.0136/d), which may be related to sediment transport during this time of the year or to the tendency for higher number of shredders in high current-shallow reaches.

The influence of flow and season upon leaf-litter breakdown in monsoonal Hong Kong streams

“…Our results show that flow plays an important direct role in litter breakdown during high-flow periods, but is overwhelmed by biological processes during the low-flow conditions (Ferreira et al, 2006). Although litter breakdown rates appear to offer a promising functional indicator of the impacts of water extraction during in the wet season in Hong Kong, our wet-season data merely reflected the physical effects of flow rather than underlying biological processes, and the lack of a response to flow reductions during the dry season, when conditions are likely to be more critical for the biota, was notable.…”

“…Litter breakdown process is also influenced by hydrological regime, especially current velocity and high-flow events (Bird & Kaushik, 1992;Lepori et al, 2005;Paul et al, 2006). While stream flow alone plays a minor role in determining breakdown directly, its effect seems more usually indirect by way of an influence on biological processes (Woodcock & Huryn, 2005;Ferreira et al, 2006;Hoover et al, 2006). For instance, breakdown rates of two leaf species in an Arizona stream decreased by *20% when flows were reduced by 95%, and this decrease was associated with cooler temperatures as well as lower fungal biomass and macroinvertebrate diversity on the leaves (Muehlbauer et al, 2009).…”

Effect of experimental and seasonal warming on litter decomposition in a temperate stream

“…Correlative studies have found a positive relationship between decomposition rates of litter incubated along elevation (Fabre and Chauvet 1998), latitudinal (Irons et al 1994;Boyero et al 2011b), or geothermal gradients (Friberg et al 2009). Studies under different seasonal thermal regimes have also reported faster litter decomposition in warmer seasons (Swan and Palmer 2004;Ferreira et al 2006). However, the relative sensitivity to temperature of microbial-driven and invertebrate-driven litter decomposition has rarely been discussed (but see Irons et al 1994;Friberg et al 2009;Boyero et al 2011b), despite the possibility that the two groups have distinct sensitivities to temperature (Boyero et al 2011b).…”

Seasonal patterns in decomposition and nutrient release from East African savanna grasses grown under contrasting nutrient conditions

“…Both abiotic and biotic processes regulate litter decomposition, including photodegradation, and microbial breakdown (Facelli and Pickett, 1991) and also physical fragmentation (leaching of soluble C) during rainfall events (Ferreira et al, 2006). Decomposition rates are controlled primarily by extrinsic drivers such as climate (Aerts, 2006;Austin and Vitousek, 2000;Gill and Burke, 2002) and soil properties (Gill and Burke, 2002).…”