Origin of the nitrogen assimilated by soil fauna living in decomposing beech litter

Abstract

We investigated the nitrogen source for main taxa of soil fauna in two beech forests of contrasted humus type using 15 N-labelled beech litter and 15 N analysis of soil fauna. 15 Nlabelled beech litter was deposited on the topsoil in December 2000 in four stands of different ages at Leinefelde (Germany) with mull humus and in one mature stand at Sorø (Denmark) with moder humus. The fate of the tracer isotope was measured in litter and soil, as well as in the soil fauna, and for each taxa, we calculated the proportion of N in the animal derived from the labelled substrate. Of the original N contained in the litter, 20% to 41% was lost after 9 months at Leinefelde, and only 10% at Sorø. This loss was counterbalanced by the incorporation of 24% to 31% external N at Leinefelde, and 31% at Sorø, partly originating from fungal colonisation of the added litter. The proportion of N assimilated from the labelled litter by the different soil animals varied in relation to their mobility and feeding preferences.Large and mobile soil animals, especially predators, derived on average less 15 N because they were also able to feed outside the labelled litter boxes. Detritivores assimilated at most 15% of their nitrogen content at Leinefelde and 11% at Sorø from the decomposing labelled litter.The most labelled taxa at Leinefelde were small fungivorous and coprophagous species, mainly isotomid Collembola such as Isotomiella and Folsomia. At Sorø, best labelled taxa were saprophagous species such as Enchytraeidae, Glomeridae and Phthiracaroidea. These low rates of 15 N assimilation indicate that fresh litter is not directly the main N source for soil animals. The results obtained suggest that soil fauna fed preferentially upon microorganisms colonising the litter at Leinefelde (mull) and from litter itself at Sorø (moder).

Modificações na fauna edáfica durante a decomposição da palhada de centeio e aveia preta, em sistema plantio direto

“…6/ AV = aveia; AV+N = aveia + adubação nitrogenada; CE = centeio; CE+N = centeio + adubação nitrogenada; DES = solo descoberto. L. C. Gatiboni et al Caner et al, 2004). Ainda, o efeito detectado pode ser devido à menor quantidade de palhada remanescente sobre o solo nos tratamentos sem adubação nitrogenada, principalmente na cultura da aveia preta.…”

Water, Rather than Temperature, Dominantly Impacts How Soil Fauna Affect Dissolved Carbon and Nitrogen Release from Fresh Litter during Early Litter Decomposition

“…Researchers found that oribatid mites are one of the most abundant soil meso-fauna in terrestrial ecosystems [54] and can increase microbial activity [55]. However, some fungivorous fauna in turn feed on fungi [56] because they cannot directly utilize resistant litter as a nutrient source [7]. On the other hand, studies have demonstrated that some oribatid mites can stimulate the release of dissolved carbon and nitrogen from fresh litter [55].…”

“…Versini et al also demonstrated that the low DOC and TDN concentrations derived from fresh litter can percolate deep into mineral soil [6]. These findings imply that dissolved carbon and nitrogen are important sources of carbon and nutrients for soil decomposers and may be quickly assimilated by soil organisms living on the litter surface [4,7] because of the low molecular weight of the litter leachates [8]. However, information regarding how soil fauna contribute to the release of dissolved carbon and nitrogen from plant litter is limited.…”

“…However, some researchers did not find significant differences in the decomposition rate between relatively high-and low-quality litter that were affected by soil fauna [13]. Isotopic labeling studies have suggested that most soil fauna settle upon the litter surface [18] and preferentially feed on available nutrients rather than the recalcitrant plant detritus itself [7,19]; thus, compared with the total litter materials, the dissolved parts (i.e., DOC and TDN) in newly shed litter may be affected by soil fauna, and such an effect may be greater for high-quality litter.…”

Mycorrhizal fungi supply nitrogen to host plants in Arctic tundra and boreal forests: 15N is the key signalThis article is one of a selection of papers in the Special Issue on Polar and Arctic Microbiology.

“…These labile C inputs are necessary to support the extraction of nutrients by mycorrhizal fungi from soil organic matter of low C quality. For example, fungi are quite important in moving N into decomposing litter from lower soil horizons (Frey et al 2003;Caner et al 2004).…”