Conversion of rainforest to oil palm and rubber plantations alters energy channels in soil food webs

Abstract

In the last decades, lowland tropical rainforest has been converted in large into plantation systems. Despite the evident changes above ground, the effect of rainforest conversion on the channeling of energy in soil food webs was not studied. Here, we investigated community‐level neutral lipid fatty acid profiles in dominant soil fauna to track energy channels in rainforest, rubber, and oil palm plantations in Sumatra, Indonesia. Abundant macrofauna including Araneae, Chilopoda, and Diplopoda contained high amounts of plant and fungal biomarker fatty acids (FAs). Lumbricina had the lowest amount of plant, but the highest amount of animal‐synthesized C20 polyunsaturated FAs as compared to other soil taxa. Mesofauna detritivores (Collembola and Oribatida) contained high amounts of algal biomarker FAs. The differences in FA profiles between taxa were evident if data were analyzed across land‐use systems, suggesting that soil fauna of different size (macro‐ and mesofauna) are associated with different energy channels. Despite that, rainforest conversion changed the biomarker FA composition of soil fauna at the community level. Conversion of rainforest into oil palm plantations enhanced the plant energy channel in soil food webs and reduced the bacterial energy channel; conversion into rubber plantations reduced the AMF‐based energy channel. The changes in energy distribution within soil food webs may have significant implications for the functioning of tropical ecosystems and their response to environmental changes. At present, these responses are hard to predict considering the poor knowledge on structure and functioning of tropical soil food webs.

Trophic niche differentiation and utilisation of food resources in Collembola is altered by rainforest conversion to plantation systems

“…These findings are in line with the results of the study of Krause et al (2019) investigating oribatid mites at the same study sites and showing that the shift in trophic niches to be mainly due to changes in the use of basal resources rather than trophic levels. Similar to previous studies on centipedes, oribatid mites and other soil animal taxa ( Klarner et al, 2017 ; Susanti et al, 2019 ; Krause et al, 2019 ), we also found the conversion of rainforest into plantations to be associated in Collembola with a shift from detritivory towards herbivory (i.e., lower 13 C enrichment). In rainforest and jungle rubber, δ 13 C values of Collembola were 2.0–5.0‰ higher compared to leaf litter, which resembles the shift observed in temperate forest ecosystems ( Pollierer et al, 2009 ).…”

“…We attributed low δ 15 N values in epedaphic and atmobiotic Collembola to algae or lichen feeding, which is widespread in Collembola in temperate forests ( Potapov Korotkevich & Tiunov, 2018 ), but in our study only few species had δ 15 N values below those of litter. This contradicts results based on fatty acid analysis suggesting that Collembola feed more on algae in tropical than in temperate ecosystems ( Susanti et al, 2019 ). To clarify the contribution of algae in soil food webs in tropical and temperate ecosystems, more data on stable isotope composition of various food resources in tropical forests, or direct experimentation, are needed.…”

“…Uneven decline in energy flux across size classes and trophic levels was documented for meso- and macrofauna soil communities leading to strong alterations in soil food-web structure ( Potapov, Tiunov & Scheu, 2019 ). Different basal resources available in different land-use systems result in changes in trophic niches of decomposer and predatory soil invertebrates, and results in reduced abundance of primary decomposers and in soil animals shifting their feeding habits towards herbivory ( Klarner et al, 2017 ; Krause et al, 2019 ; Susanti et al, 2019 ). Land-use change may also result in reduced trophic niche differentiation among species in belowground communities ( Korotkevich et al, 2018 ), but this has not been investigated in tropical ecosystems.…”

“…Trophic positions and length of trophic chains can be assessed using δ 15 N values, whereas the range of δ 13 C values reflects variability in the use of basal resources ( Potapov, Tiunov & Scheu, 2019 ). Stable isotope composition of consumers follows that in food resources, thus allowing to reveal potential diet switching with land-use change ( Klarner et al, 2017 ; Krause et al, 2019 ; Susanti et al, 2019 ).…”

Stable isotopes of amino acids indicate that soil decomposer microarthropods predominantly feed on saprotrophic fungi

“…They are linked to energy channels originating directly from plants or from bacteria and fungi utilizing plant‐derived resources (Moore and Hunt 1988, Moore et al 2005). The relative importance of these different energy channels may shift with land‐use intensity (Moore 1994, Bardgett et al 1996, de Vries et al 2013, Susanti et al 2019), ecosystem type (e.g., forests vs. grasslands; Crotty et al 2014), forest type (Ferlian and Scheu 2014), or even tree species/leaf litter type (Wardle et al 2006, D’Annibale et al 2017). In addition, local abiotic factors also influence the relative importance of these energy channels for soil food webs (Ferlian et al 2012).…”