Effects of detritivorous invertebrates on the decomposition of rice straw: evidence from a microcosm experiment

© 2017, The International Society of Paddy and Water Environment Engineering and Springer Japan KK, part of Springer Nature. Decomposition of crop residues is a key process in agricultural systems that influences nutrient cycling and productivity. To clarify the roles of different groups of invertebrates in decomposition in paddy fields, we conducted a microcosm experiment, testing the effects of soil eluate filtered through a 21 μm mesh (control treatment) against the effects of microfauna (< 0.1 mm) and small gastropods (juvenile golden apple snails (Pomacea canaliculata), ca. 2 mm shell diameter), both separately and in combination, on rice straw decomposition. Rice straw in litterbags was incubated at the soil surface and in the soil together with standardized amounts of the respective detritivores for 10 and 21 days. Compared to the control treatment, snails and microfauna enhanced the reduction in straw mass on the soil surface by 19 and 22%, respectively. Both groups combined increased the reduction in straw biomass by 30%. Below the soil surface, the contribution of detritivores to decomposition was smaller, reducing straw biomass by just 1% (snails), 11% (microfauna) and 14% (snails + microfauna) compared to the control. The effects of microfauna and snails on decomposition were not fully additive, a pattern that could be due to competition or trophic interactions. Model selection using Akaike’s information criterion on nested linear mixed effects models led to a model including the main effects (snails, microfauna, position and time), several two-way interactions and the three-way interaction snails * microfauna * litterbag_position as the most parsimonious description of the data. Keeping straw accessible to aquatic invertebrate detritivores should be a suitable management strategy to enhance decomposition in paddy fields, although trade-offs with other management issues such as pest control need to be considered

Endogenous rhythmic growth, a trait suitable for the study of interplays between multitrophic interactions and tree development

As long-lived organisms, trees use resources to support both growth and below- and aboveground trophic interactions. Resources fluctuate in relation to periods of growth cease that are regulated by internal and external factors, and these fluctuations feed backs to trophic partners. Some major forest trees display an endogenous growth rhythm, and related pulses of variation in allocation of resources have been detected. As this trait makes it possible to separate growth into defined phases, it offers an opportunity to disentangle the intermingled complex regulation of growth and multitrophic interactions in trees. We present “TrophinOak”, a platform using microcuttings of pedunculated oak, a tree that displays endogenous rhythmic growth characterized by alternating shoot and root growth flushes. We select seven beneficial or detrimental above- and belowground partners including animals (Lymantria dispar, Pratylenchus penetrans, Protaphorura armata), fungi (Piloderma croceum, Microsphaera alphitoides, Phytophthora quercina) and bacteria (Streptomyces sp.), to synthesize bi- and tripartite trophic interactions, including ectomycorrhizal symbioses, and monitor fluctuations of carbon and nitrogen allocation as well as plant gene expression at distinct phases of oak growth. We use this model to identify and resolve the experimental challenges inherent in synthesizing diverse types of associations in a common microcosm system, in labeling plants with stable N and C isotopes and in analyzing transcripts in a non-model plant, a process which requires generating a specific contig library. We develop hypotheses and experimental design to test them in order to identify core mechanisms that help trees to modulate their own development and their multitrophic interactions for optimizing their long term performance in their environment. First results constitute a proof of concept that the platform works and enables us to test the hypotheses