The effects of fresh and stabilized pruning wastes on the biomass, structure and activity of the soil microbial community in a semiarid climate I.F. Torres *, F. Bastida, T. Hernández, C. García Department of Soil and Water Conservation, Group of Soil Enzymology and Bioremediation and Organic Wastes, CEBAS-CSIC, Campus Universitario de Espinardo, 30100 Espinardo, Murcia, Spain A R T I C L E I N F O Article history: Received 17 September 2014 Received in revised form 26 December 2014 Accepted 27 December 2014 Available online xxx Keywords: Semiarid Long-term Pruning waste Composting Biochemical and microbiological properties A B S T R A C T The incorporation of organic amendments from pruning waste into soil may help to mitigate soil degradation and to improve soil fertility in semiarid ecosystems. However, the effects of pruning wastes on the biomass, structure and activity of the soil microbial community are not fully known. In this study, we evaluate the response of the microbial community of a semiarid soil to fresh and composted vegetal wastes that were added as organic amendments at different doses (150 and 300 t ha 1 ) five years ago. The effects on the soil microbial community were evaluated through a suite of different chemical, microbiological and biochemical indicators, including enzyme activities, community-level physiological profiles (CLPPs) and phospholipid fatty acid analysis (PLFA). Our results evidenced a long-term legacy of the added materials in terms of soil microbial biomass and enzyme activity. For instance, cellulase activity reached 633 mg and 283 mg glucose g 1 h 1 in the soils amended with fresh and composted waste, respectively. Similarly, bacterial biomass reached 116 nmol g 1 in the soil treated with a high dose of fresh waste, while it reached just 66 nmol g 1 in the soil amended with a high dose of composted waste. Organic amendments produced a long-term increase in microbiological activity and a change in the structure of the microbial community, which was largely dependent on the stabilization level of the pruning waste but not on the applied dose. Ultimately, the addition of fresh pruning waste was more effective than the application of composted waste for improving the microbiological soil quality in semiarid soils. ã 2015 Elsevier B.V. All rights reserved. 1. Introduction Soil degradation is one of the main threats to arid and semiarid ecosystems and is characterized by loss of organic matter (OM) as a consequence of scarce vegetal growth (García et al., 1996). Yet organic matter plays a central role in maintaining key soil functions and global biochemical cycles. Furthermore, it is an essential determinant of soil fertility and resistance to erosion (Ros et al., 2006; Fonte et al., 2009). In scenarios of soil degradation, the application of organic wastes to the soil constitutes an environmen- tal and agricultural means to maintain soil organic matter, reclaim degraded soils and supply plant nutrients. The fresh organic matter present in organic wastes stimulates the development and activity of the soil microbial community (Yang et al., 2003; Bonilla et al., 2012) and can incorporate also exogenous microbes to the soil environment. Moreover, organic matter improves the physical structure of the soil and contributes to carbon sequestration (Foley and Cooperband, 2002; Ros et al., 2006). Nevertheless, the biostimulant capacity of organic amendments depends on their chemical composition (Ajwa and Tabatabai, 1994). Agricultural and gardening activities produce large quantities of vegetal residues and by-products. These residues cause serious environmental and visual pollution such as formation of pests that can move to new crops, gas emissions, toxic particle accumulation, and so on (Blázquez et al., 2011); particularly in agricultural areas like southeast Spain. A sustainable valorization of this vegetal waste is therefore need. It has been observed that the incorpo- ration of green wastes derived from pruning into soil may improve long term soil fertility and quality (Doran et al., 1988). Moreover, composting these vegetal wastes can also help to reduce waste production. Composting is one of the best known processes for the biological stabilization of solid organic wastes. It involves the accelerated degradation of organic matter by microorganisms under controlled conditions, in which the organic material * Corresponding author. Tel.: +34 968396397. E-mail address: iftorres@cebas.csic.es (I.F. Torres). http://dx.doi.org/10.1016/j.apsoil.2014.12.009 0929-1393/ ã 2015 Elsevier B.V. All rights reserved. Applied Soil Ecology 89 (2015) 1–9 Contents lists available at ScienceDirect Applied Soil Ecology journal homepage: www.elsevier.com/locate/apsoil