Species-specific effects of live roots and shoot litter on soil decomposer abundances do not forecast plant litter-nitrogen uptake

Abstract

Plant species produce litter of varying quality and differ in the quality and quantity of compounds they release from live roots, which both can induce different decomposer growth in the soil. To test whether differences in decomposer growth can forecast the amount of N species acquire from plant litter, as suggested by theory, we grew individuals of three grassland plants-Holcus lanatus, Plantago lanceolata and Lotus corniculatus-in soils into which (15)N-labelled litter of either Holcus, Plantago or Lotus was added. We measured the effects of live roots and litter of each species on soil microbes and their protozoan and nematode feeders, and to link decomposer growth and plant nutrient uptake, we measured the amount of N taken up by plants from the added litter. We hypothesised that those species that induce the highest growth of microbes, and especially that of microbial feeders, will also take up the highest amount of N from the litter. We found, however, that although numbers of bacterial-feeding Protozoa and nematodes were on average lower after addition of Holcus than Plantago or Lotus litter, N uptake was higher from Holcus litter. Further, although the effects on Protozoa and bacterial- and fungal-feeding nematodes did not differ between the live plants, litter-N uptake differed, with Holcus being the most efficient compared to Plantago and Lotus. Hence, although microbes and their feeders unquestionably control N mineralization in the soil, and their growth differs among plant species, these differences cannot predict differences in litter-N uptake among plant species. A likely reason is that for nutrient uptake, other species-specific plant traits, such as litter chemistry, root proliferation ability and competitiveness for soil N, override in significance the species-specific ability of plants to induce decomposer growth.

Root trait–microbial relationships across tundra plant species

“…Harvested blocks were stored at 4°C in the dark for a maximum of 3 d and the harvesting order of individual pots within blocks was random. After carefully removing the plants from the pots by tapping the pot, plants were gently shaken (Saj et al ., 2009) over trays layered with aluminium foil to obtain the rhizosphere soil surrounding the plant roots (i.e. soil stuck to plant roots) (Smalla et al ., 2001; Carrillo et al ., 2017).…”

Effects of native and exotic range‐expanding plant species on taxonomic and functional composition of nematodes in the soil food web

“…Exotic plants have been shown to alter soil biological and chemical characteristics in the rhizosphere, which can influence the structure of the microbial community (Kourtev et al 2003). This could have an indirect effect on bacterivorous‐ and fungivorous nematode community and their predators, through altered resource quality and quantity (Saj et al 2009).…”

Terrestrial ecosystems buffer inputs through storage and recycling of elements

“…For example, the addition of 15 N-enriched plant litter and the subsequent recovery of 15 N in plants can be used to estimate the magnitude of recycling for plant N uptake. In contrast to the large contribution of recycling to plant N uptake reported above based on an indirect mass-balance approach, all studies tracing the fate of leaf-litter derived N based on isotopes report surprisingly small recoveries in aboveand below ground plant biomass irrespective of experimental duration (up to eleven years): \ 5% in forests (Zeller et al 2000(Zeller et al , 2001Stoelken et al 2010;Guo et al 2013b;Leppert et al 2017) and grasslands (Seeber et al 2008;Saj et al 2009). The small 15 N tracer recovery in plant biomass in direct approaches might be related to: (1) long-term storage of N-rich organic matter in soils (see ''Storage of elements in plants'' section); (2) methodological constraints, namely the non-homogeneous distribution of the 15 N label; and (3) the importance of root rather than leaf litter (Schmidt et al 2011;Guo et al 2013a;Ruppenthal et al 2015) for element recycling, which is not accounted for in studies adding 15 N-labeled leaf litter.…”