Introduction Directory UMM :Data Elmu:jurnal:S:Soil Biology And Chemistry:Vol32.Issue13.Nov2000:

Enzyme dynamics on decomposing leaf litter of Cistus incanus and Myrtus communis in a Mediterranean ecosystem A. Fioretto, S. Papa, E. Curcio, G. Sorrentino, A. Fuggi Dipartimento di Scienze della Vita, Seconda Universita` di Napoli. Via Vivaldi, 43. 81100 Caserta, Italy Accepted 5 April 2000 Abstract The decomposition of Cistus incanus leaf litter, a summer deciduous species, was compared to that of Myrtus communis, an evergreen species, during 15 months of incubation in a Mediterranean low shrubland. The litterbags were placed under randomly selected shrubs of Myrtus and Cistus, respectively. Owing to the different microclimatic conditions under deciduous and evergreen shrubs Cistus litter was also incubated under Myrtus shrubs. Microbial activity was evaluated by measuring litter respiration and enzyme activities cellulase, xylanase, a -amylase, b-amylase, laccase and peroxidase. During the first 8 months of incubation the decomposition rate of both litters was inde- pendent of litter quality and incubation conditions. The average decay constant k ranged between 0:29 0:03 and 0:33 0:03 yr 21 : Subsequently, it increased only for litters incubated under Myrtus shrubs …k ˆ 0:57 0:15 and 0:48 0:16 yr 21 for Cistus and Myrtus litters, respectively. The dry summer affected the decay rate of litters incubated under Myrtus but not under Cistus. Microbial respiration showed seasonal changes from 25 to 150 mmol CO 2 g 21 dry wt. 24 h 21 , with low levels in summer, mainly because of the low litter water content. After samples were placed in the field, a-amylase activity decreased rapidly, dropping to zero in Cistus litter, whereas it remained detectable in Myrtus litter .0.02 mmol glucose g 21 dry wt. h 21 . The b-amylase activity was low over the entire period. The activities of cellulase and xylanase ranged from 1 to 30 mmol glucose equivalents reducing sugar g 21 dry wt. h 21 . Both litters showed the lowest enzyme activities in summer, when litter respiration was also at the lowest level. Peroxidase activity was detected in the litter of Myrtusfrom 0 to 50 mmol o- tolidine oxidised g 21 dry wt. h 21 and had a seasonal pattern similar to cellulase and xylanase. It was undetectable in Cistus. In both litters laccase increased significantly going from 10 to 140 mmol o-tolidine oxidised g 21 dry wt. h 21 between eight and nine months when a large increase of fungal biomass occurred from 0.5 to 2.5 mg g 21 dry wt.. The analyses of these enzymes have shown qualitative and quantitative differences depending on the litter type and the microclimatic conditions, suggesting changes in the microbial succession. q 2000 Elsevier Science Ltd. All rights reserved. Keywords: Litter decomposition; Xylanase; Cellulase; Amylases; Laccase; Peroxidase; Cistus incanus, Myrtus communis

1. Introduction

Plant litter decomposition is a critical process in nutrient cycling within temperate forest ecosystems Swift et al., 1979. Over the past 30 years, many studies have been carried out on litter decomposition and the dynamics of nutrient release to analyse the effect of climate and litter quality Taylor et al., 1989; Arianoutsou, 1993; Virzo De Santo et al., 1993; Berg et al., 1995; Rutigliano et al., 1996; Fioretto et al., 1998 as well as of soil organisms Anderson and Ineson, 1984; Moore and Walter, 1988; Persson, 1989; Ponge, 1991; Dilly and Irmler, 1998. In recent years, atten- tion has turned to the degrading capacity of microorganisms by evaluating their enzyme activities. Microbial species and communities release enzymes into the environment in order to degrade macromolecular and insoluble organic matter prior to cell uptake and metabolism Burns, 1982. This important property may allow decomposition rates to be related to the enzymes that directly mediate the degradation of the major structural components of plant material and can provide functional information on specific aspects of the microbial community and succession Sinsabaugh et al., 1991. Moreover, both the enzymes involved in the degra- dation of main litter components, such as cellulose, hemi- cellulose and lignin, and those involved in the cycling of nitrogen, phosphorus and sulphur, are of primary interest in understanding the factors controlling plant litter decomposi- tion. Lignocellulolytic enzyme activities have been reported as good indicators of mass loss rates Sinsabaugh et al., 1994. The release of extracellular enzymes is species-dependent Soil Biology Biochemistry 32 2000 1847–1855 0038-071700 - see front matter q 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 8 - 0 7 1 7 0 0 0 0 1 5 8 - 9 www.elsevier.comlocatesoilbio Corresponding author. Tel.: 139-823-274550; fax: 139-823-274571. E-mail address: antonietta.fiorettounino2.it A. Fioretto. and is influenced by temperature, moisture, pH, and quality and quantity of available substrate Linkins et al., 1984; Sinsabaugh and Linkins, 1987. Studies on litter decomposition analysing enzyme activ- ities have been performed in aquatic and forest ecosystems Sinsabaugh et al., 1991; 1992, 1993; Joshi et al., 1993; Rosenbrock et al., 1995; Dilly and Munch, 1996 but no data are available for Mediterranean ecosystems. In this paper, we compare the pattern of microbial enzyme activities cellulase, xylanase, a-amylase, b- amylase, laccase and peroxidase and respiration during litter decomposition of two species in a Mediterranean low shrub land: Cistus incanus L., a summer deciduous species, and Myrtus communis L., an evergreen sclerophyll species. The aim of the work was to analyse the time of appearance and the activity of enzymes in qualitatively different litter in order to obtain functional information on microbial succession. The effect of microclimatic condi- tions on litter decomposition rate and enzyme activities was also evaluated.

2. Materials and methods