Biochar but not earthworms enhances rice growth through increased protein turnover D. Noguera a, b, c , S. Barot d, * , K.-R. Laossi e , J. Cardoso c , P. Lavelle a, c , M.H. Cruz de Carvalho b a UPMC e Bioemco (UMR CNRS 7618), 32 avenue Henri Varagnat, 93143 Bondy Cedex, France b Université Paris Est-Créteil e Bioemco (UMR CNRS 7618), 61 avenue du Général de Gaulle, 94010 Créteil Cedex, France c Centro Internacional de Agricultura Tropical (CIAT), AA 6713, Cali, Colombia d IRD e Bioemco (UMR CNRS 7618), Ecole Normale Supérieure, 46 rue d’Ulm, 75230 Paris cedex 05, France e Agronomy Department, Centre R&D Nestlé Abidjan, 01 BP 11356, Abidjan 01, Ivory Coast article info Article history: Received 3 December 2011 Received in revised form 26 March 2012 Accepted 5 April 2012 Available online 23 April 2012 Keywords: Earthworms terra preta Biochar Nitrogen Protein turnover Transcript accumulation Proteolytic activity Rice abstract The aim of this work was to compare the effects of biochar and earthworms on rice growth and to investigate the possible interactions between both. In addition to classic macroscopic variables we also monitored some leaf-level cellular processes involved in protein turnover. Both biochar and earthworms significantly increased shoot biomass production. However, biochar had a higher effect on the number of leaves (þ87%) and earthworms on leaf area (þ89%). Biochar also significantly increased the leaf turnover. At the cellular level, biochar but not earthworms enhanced protein catabolism by an increase in leaf proteolytic activities. This could be related to the increased expression of three of the six genes tested related to protein catabolism, one serine protease gene OsSP2 (þ24%), one aspartic acid protease gene, Oryzasin (þ162%) and one cysteine protease gene OsCatB (þ257%). Furthermore, biochar also enhanced the expression level of two genes linked to protein anabolism, coding for the small and large subunits of rubisco (þ33% and þ30%, for rbcS and rbcL, respectively), the most abundant protein in leaves. In conclusion, our data gives evidence that biochar increased rice biomass production through increased leaf protein turnover (both catabolism and anabolism) whereas earthworms also increased rice biomass production but not through changes in the rate of protein turnover. We hypothesize that earthworms increase nitrogen uptake at a low cost for the plant through a simultaneous increase in mineralization rate and root biomass, probably through the release in the soil of plant growth factors. This could allow plants to accumulate more biomass without an increase in nitrogen metabolism at the leaf level, and without having to support the consecutive energy cost that must bear plants in the biochar treatment. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Many soils of the lowland humid tropics are thought to be too infertile to support sustainable agriculture. One of the major problems is the rapid decomposition of organic matter (Zech et al., 1990) due to the high temperatures, intense precipitation, and the lack of stabilizing minerals. On soils with low nutrient retention capacity the strong tropical rains easily leach available and mobile mineral nutrients limiting the efficiency of conventional fertilizers. The reduction of soil content in organic matter (SOM) is causing soil degradation. The agriculture is often not sustainable without nutrient inputs beyond 3 years of cultivation (Tiessen et al., 1994). In tropical areas, the development of techniques improving soil fertility is thus a priority. The use of more stable organic matter could help to increase the sustainability of soil fertility. In this context, biochar addition to soils is a promising alternative to transfer of more easily decomposable organic matter (Zech et al., 1990; Fearnside et al., 2001). Indeed, the existence of anthropo- genic biochar-enriched dark soils (terra preta de indio) and the fact that they have kept a high fertility for hundreds of years supports this idea. Apart from high carbon contents, the most striking feature of biochar is its capacity to retain mineral nutrients (Glaser, 2007). The fertility of terra preta de indio is most likely linked to an anthropogenic accumulation of phosphorus (P), calcium (Ca), and fragmented biochar. Another sustainable way to increase tropical soil fertility is by maintaining high biomasses of earthworms (Lavelle et al., 2001). They are known to positively affect plant growth via five main mechanisms (Scheu, 2003; Brown et al., 2004): (1) an increased mineralization of soil organic matter (2) the production of plant * Corresponding author. E-mail address: sebastien.barot@ird.fr (S. Barot). Contents lists available at SciVerse ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2012.04.004 Soil Biology & Biochemistry 52 (2012) 13e20