Quantifying the Contribution of Entire Free-Living Nematode Communities to Carbon Mineralization under Contrasting C and N Availability

Abstract

To understand the roles of nematodes in organic matter (OM) decomposition, experimental setups should include the entire nematode community, the native soil microflora, and their food sources. Yet, published studies are often based on either simplified experimental setups, using only a few selected species of nematode and their respective prey, despite the multitude of species present in natural soil, or on indirect estimation of the mineralization process using O2 consumption and the fresh weight of nematodes. We set up a six-month incubation experiment to quantify the contribution of the entire free living nematode community to carbon (C) mineralization under realistic conditions. The following treatments were compared with and without grass-clover amendment: defaunated soil reinoculated with the entire free living nematode communities (+Nem) and defaunated soil that was not reinoculated (-Nem). We also included untreated fresh soil as a control (CTR). Nematode abundances and diversity in +Nem was comparable to the CTR showing the success of the reinoculation. No significant differences in C mineralization were found between +Nem and -Nem treatments of the amended and unamended samples at the end of incubation. Other related parameters such as microbial biomass C and enzymatic activities did not show significant differences between +Nem and -Nem treatments in both amended and unamended samples. These findings show that the collective contribution of the entire nematode community to C mineralization is small. Previous reports in literature based on simplified experimental setups and indirect estimations are contrasting with the findings of the current study and further investigations are needed to elucidate the extent and the mechanisms of nematode involvement in C mineralization.

Nematode exclusion and recovery in experimental soil microcosms

“…Although the understanding of how nematodes interact within extremely complex soil food webs has rapidly grown (Ferris, 2010;Cesarz et al, 2015), there is an immediate need for further experiments studying their responses to global change, and possible consequences for soil and ecosystem function. The manipulation of nematode functional diversity in soil is key to answering such questions (Xiao et al, 2010;Gebremikael et al, 2015).…”

Nitrogen Limitations on Microbial Degradation of Plant Substrates Are Controlled by Soil Structure and Moisture Content

“…Gram-negative bacteria were represented by the sum of cyC17:0, cyC19:0, C16:1c9, and C18:1c11 ( Denef et al, 2009 ). The sum of 10MeC16:0 and 10MeC18:0 was used to indicate the actinobacteria ( Moeskops et al, 2010 ; Gebremikael et al, 2015 ). The sum of marker PLFAs for Gram-positive bacteria and Gram-negative bacteria and C17:0 designated the total bacterial community ( Ameloot et al, 2013 ; Gebremikael et al, 2015 ).…”

Influence of Nematode-Bacterial Interactions on N and P Mineralisation in Soil and on Decomposition of Crop Residues During Aerobic Composting

“…As is evident from Fig.8, the decline in C:N ratios in various substrates was not affected significantly by presence of bacterivorous nematodes in cabbage or soybean composting on any day of sampling. It has been found that, in nutrient rich conditions (amended soil), the presence of nematodes may not significantly enhance organic matter decomposion and the subsequent nutrient mineralization (Ingham et al, 1985;Bjornlund et al, 2012;Gebremikael et al, 2015). Gebremikael et al (2015) found that there is no significant contribution of entire free living nematode community to C mineralisation either in native soil organic matter or added organic matter (grass covered amendments).…”

“…It has been found that, in nutrient rich conditions (amended soil), the presence of nematodes may not significantly enhance organic matter decomposion and the subsequent nutrient mineralization (Ingham et al, 1985;Bjornlund et al, 2012;Gebremikael et al, 2015). Gebremikael et al (2015) found that there is no significant contribution of entire free living nematode community to C mineralisation either in native soil organic matter or added organic matter (grass covered amendments). However, this was attributed to lower nematode density in the experiment or significant decrease in nematode population density over the time.…”

“…However, in the present study contribution of single species of bacterivorous nematodes to nutrient mineralisation and organic matter decomposition was studied in the controlled environment but in realistic condition, decomposition process is regulated by several biotic and abiotic factors. Hence as suggested by Gebremikael et al (2015) studies are needed for realistic determination of contribution of entire free-living nematode communities including all feeding groups and indigenous microbial communities as occur in nature and management changes that are required for increasing the availability of nitrogen and other minerals especially in organic and low input farming systems.…”