Decomposition and nutrient dynamics in mixed litter of Mediterranean species

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<ul><li><p>REGULAR ARTICLE</p><p>Decomposition and nutrient dynamics in mixed litterof Mediterranean species</p><p>Giuliano Bonanomi &amp; Guido Incerti &amp;Vincenzo Antignani &amp; Manuela Capodilupo &amp;Stefano Mazzoleni</p><p>Received: 6 July 2009 /Accepted: 17 December 2009 /Published online: 20 January 2010# Springer Science+Business Media B.V. 2010</p><p>Abstract In the last decade a great research effortaddressed the effects of litter diversity on ecosystemfunctions, reporting both synergistic and antagonisticeffects for decomposition dynamics. Four coexistingMediterranean species, representing a range of litterquality, were used to arrange litter mixtures at threediversity levels for a litterbag decomposition experi-ment. Species identity appeared as the major deter-minant for litter mass loss (Coronilla emerusHederahelix&gt;Festuca drymeia&gt;Quercus ilex) and nutrientrelease, with rates for all leaf litter types followingthe sequence K&gt;N&gt;MgCa&gt;&gt;Fe. Additive diversityeffects were prevalent pooling together all data butalso for nutrients separately. Antagonistic interactionswere more common than synergistic in the cases ofmass loss, N and Ca contents, but not for K, Mg andFe dynamics. The number of species in the litterbagsignificantly affected the outcome of non-additive</p><p>interactions, which were mostly antagonistic for two-species mixtures, and synergistic for the combined 4species. Litter quality appears to be the mostimportant factor affecting mass loss and nutrientdynamics, while litter diversity, influencing the ratesof these processes, plays an important role in reducingtheir variability, thus suggesting a greater stability ofecosystems properties in presence of mixed litter.</p><p>Keywords Species diversity . Ecosystem functions .</p><p>Litter-mix experiment .Quercus ilex forest . Litternutrients</p><p>Introduction</p><p>The study of relationships between species diversityand ecosystem processes has been receiving growingattention in recent years. It is now well recognized thatbiodiversity strongly affects some ecosystem functionssuch as productivity (Tilman et al. 2001), stability(McGrady-Steed et al. 1997) and invasibility (Jiangand Morin 2004), while the role of diversity on litterdecomposition is still questioned (Gartner and Cardon2004; Httenschwiler et al. 2005). Decomposition ratesand nutrients dynamics have been widely studied andrelated to environmental conditions (Gholz et al. 2000),litter chemical characteristics (Coteaux et al. 1995),and biotic factors (Httenschwiler and Gasser 2005).Despite the fact that litter layers in natural plantcommunities are generally made of more than one</p><p>Plant Soil (2010) 331:481496DOI 10.1007/s11104-009-0269-6</p><p>Responsible Editor: Alfonso Escudero.</p><p>G. Bonanomi (*) :V. Antignani :M. Capodilupo :S. MazzoleniDipartimento di Arboricoltura,Botanica e Patologia Vegetale,University of Naples Federico II,via Universit 100,Portici, NA 80055, Italye-mail: giuliano.bonanomi@unina.it</p><p>G. IncertiDipartimento di Scienze della Vita, University of Trieste,via Giorgieri 10,Trieste 34127, Italy</p></li><li><p>species, most studies reported so far on single speciesanalysis (Berg and McClaugherty 2003).</p><p>The effects of mixed plant litter have been firstaddressed more than 60 years ago (Gustafson 1943)and recently reconsidered (review in Gartner andCardon 2004; Httenschwiler et al. 2005). Both massloss and nutrient release are expected to be affectedby litter diversity because of three major mechanisms.First, passive diffusion or microbial active transport ofnutrients between different materials may enhance thedecay rate of nutrient poor litter (Chapman et al.1988; Wardle et al. 1997). Second, higher waterretention capacity by some litter types could bebeneficial to the decay of other plant residues (Wardleet al. 2003). Third, litter decay can be slowedcompared to monoculture because of the release,from some materials, of compounds with antimicro-bial activity e.g. tannins and polyphenols (Schimel etal. 1998). This has been observed in litter mixtureswith secondary metabolites by Empetrum hermaph-roditum (Nilsson et al. 1998) and Quercus nigra(McArthur et al. 1994). The former mechanismsshould generate synergistic interactions with mixedlitter decaying faster than what would be expectedbased on the monocultures; antagonistic interactionsshould be produced by the latter process withreductions of decomposition rates of fast decayinglitter when mixed to other inhibitory materials.</p><p>The literature evidence summarized by Gartner andCardon (2004) indicates, for mass loss, synergisticinteractions ranging from +1% to +65% compared topure litter, and variations of antagonistic interactionsbetween -1.5% and -22%. However, also additiveeffects were often reported, accounting for 30% ofthe experimental cases (Gartner and Cardon 2004).Concerning nitrogen release, the same authors reportedthat 76% of these interactions were non-additive,ranging from +25% nitrogen release to +100% nitrogenimmobilization (Gartner and Cardon 2004). Thesecontrasting results suggest that neither decompositionnor nutrients release patterns can be assessed on thebase of single species dynamics. Without taking intoaccount the litter diversity effects, data from single-species litterbag studies might as well have biased thatecosystem level carbon and nutrients fluxes estimates.</p><p>Most decomposition studies on mixed litter reportedon mass losses and nitrogen dynamics (Gartner andCardon 2004). Far less attention was given to therelease of other nutrients during decomposition pro-</p><p>cesses in spite of their importance for plant mineralnutrition (Marschner 1995). Gartner and Cardon (2004)reviewed a total of 162 experiments on litter mass loss,where 133 cases reported on nitrogen dynamics and 25cases, from three papers only, concerned other nutrients(P, Ca, K, Mg, Al, Fe and Mg). Most of these studieshave been carried out in temperate forests and only fewin tropical forests and grasslands (Httenschwiler et al.2005). Despite the high biodiversity of Mediterraneanevergreen forests (Blondel and Aronson 1999) nostudies, so far, reported on litter decomposition dynam-ics based on mixtures of Mediterranean species(Httenschwiler et al. 2005).</p><p>Finally, some studies explored the effects ofmixed-species litters on decomposition stability interms of mass loss, reporting a consistent reduction ofdecay rates variability, compared to monospecificlitters (Schdler and Brandl 2005; Lecerf et al. 2007;Keith et al. 2008). However, the stability-diversityhypothesis has not yet been addressed in the frame ofnutrient dynamics, despite its importance for plantnutrition in natural communities.</p><p>This work reports on the results of a litterbagexperiment on decomposition of leaf litter mixturesfrom four coexisting species selected from a Mediterra-nean evergreen forest. Litter decomposition in openfield mainly depends on organic matter quality, wateravailability and temperature (Berg and McClaugherty2003). To avoid the effect of the two latter relevantsources of variation, we worked under controlledcondition reproducing temperature and water availabil-ity in the sampled site, focusing only on the effects oflitter quality and diversity. The aims were to assess:</p><p>i. mass loss and nutrient dynamics of monospecificlitter;</p><p>ii. effect of litter diversity on mass loss;iii. effect of litter diversity on N, K, Ca, Mg and Fe</p><p>dynamics;iv. effect of litter diversity on the stability of the</p><p>decomposition process.</p><p>Materials and methods</p><p>Plant material collection</p><p>Four species of different functional groups wereselected from a natural old-growth holm oak forest</p><p>482 Plant Soil (2010) 331:481496</p></li><li><p>located on Vesuvius southern slope (Portici 40 4843 N 14 20 49 E, Southern Italy): Quercus ilex(the dominant evergreen oak tree), Coronilla emerus(a nitrogen fixing shrub), Hedera helix (an evergreenvine) and Festuca drymeia (a perennial grass). Thesenaturally coexisting species represent a wide range oflitter quality (Wardle et al. 2006; Lecerf et al. 2007).Freshly abscissed leaves were collected (n of plants&gt;20) when most of the litter fall occurs by means ofnets placed under the canopy, dried (40C untilconstant weight was reached) and stored afterwardsat room temperature.</p><p>The field site has aMediterranean climate with a highmean annual rainfall of 1,007 mm distributed in winter(324), spring (211) and fall (372) and a moderate drysummer (100). Mean monthly temperatures rangebetween 25C (August) and 8C (January). Mean dailyand night temperature of the spring season (April, Mayand June) are 23C and 13C, respectively.</p><p>Litter decomposition experiment</p><p>A decomposition experiment was carried out inmicrocosms placed in a greenhouse to simulate fielddecomposition conditions. The litterbag method (Bergand McClaugherty 2003; Bonanomi et al. 2006) wasused. Large (2020) terylene litterbags (mesh size2 mm) were filled with 6 g of dry leaf litter. Litterbagswere placed on the top of large trays (30 cm deep,100 cm for each side) filled with soil from the samestand (a Volcanic ash soil with the followingcharacteristics: sand 73.8%, silt 15.5%, clay 10.7%;pH 7.05; organic matter 5.4%; total N 0.33 g/kg; C/N9.6; electrical conductivity 91.3 S/cm). Soil blocks(sized 252520 cm) collected in the sampled sitewere placed in the microcosms, preserving the naturalsoil stratification. Microcosms were kept in controlledtemperature (142C night and 242C day) andwater conditions (daily watering to field capacity withdistilled water) simulating a typical spring and earlyfall conditions of the sampled site.</p><p>We prepared 15 types of bags, containing: i. litterof each single species (4 types), ii. all possible two-species mixtures (6 different combinations with aloading ratio 50:50), and, iii. five different fourspecies-mixtures, one of them with a constant loadingratio (25:25:25:25) for all the species, and four with a50:16.7:16.7:16.7 loading ratio characterized by adifferent dominant species. Consequently, the exper-</p><p>iment encompasses 15 treatments with three levels ofspecies richness: 1, 2 and 4 species.</p><p>A total of 135 litterbags (15 types 3 samplingdates 3 replicates) were used and harvested after 10,30 and 90 days of decomposition. All bags wereoven-dried in the laboratory (at 40C until constantweight was reached), and the litter was gently brushedto remove adhering soil debris and then weighed.Short-term experiments with similar duration havebeen previously done to assess the effect of litterdiversity on decomposition in other systems (Brionesand Ineson 1996; Hector et al. 2000). Our study wasspecifically designed to represent the decompositionprocess occurring in a single season (spring or fall)when water and temperature are not strong limitingfactors. Previous studies showed that long periodsbefore litter harvesting could mask differences occur-ring during the incubation time (McTiernan et al.1997; Gartner and Cardon 2004). This is why, toovercome this problem and to reveal details of thelitter nutrient dynamics, we opted for a multiple litterharvest design within a short time frame.</p><p>Litter chemical analyses</p><p>The litter nutrients were determined by standardmethods as follow: total C and N contents by flashcombustion of microsamples (5 mg of litter) in anElemental Analyser NA 1500 (Carlo Erba Strumenta-zione, Milan, Italy). K, Ca, Mg and Fe by atomicabsorption spectrometry (Perkin Elmer 3110) using aflame to atomize the samples, made of 250 mg ofpulverized dried litter solubilized in a mixture of 4 mlof nitric (65%) and 2 ml of fluoridric acid (50%).</p><p>Data analysis</p><p>Litter mass loss (%), changes of nutrients concen-trations (mg g-1), and total litter nutrient content (% ofthe initial amount) of monocultures were statisticallyevaluated by analysis of variance (ANOVA). Percent-age data were log-transformed to satisfy the assump-tion of normality. Regression analysis was used toassess the relationships between initial litter quality,i.e. nutrient content, litter mass loss and final nutrientcontent. Significance was evaluated in all cases at pMgCa&gt;&gt;Fe for all leaf litter types. This studyshowed that in the early stage of the decompositionprocess mineral nutrients are continuously released byboth the slow decomposing F. drymea (N and K) andQ. ilex (only K), and the fast decaying H. helix andC. emerus (N, K, Ca and Mg). Considered that nutrientrelease starts immediately after leaf shedding, theoccurrence of H. helix in woodlands might play apeculiar positive role at ecosystem level. This becausethe different phenology of this vine (leaf litter partiallyshed in spring), coupled with its rapid decompositionrate, can produce a consistent nutrient flux synchronizedwith the forest growth season (Badre et al. 1998). Thisresult can be relevant considering that litter is one of themost important sources for plant mineral nutrition.</p><p>This study, the first reporting on Mediterraneanspecies, contributes to the debate about whether plantspecies diversity affects the litter decay rate and therelated nutrient release (Gartner and Cardon 2004;Httenschwiler et al. 2005). The results provided</p><p>494 Plant Soil (2010) 331:481496</p></li><li><p>evidence that, at least at early stages of decay, litterquality is the most important factor affecting massloss and nutrient dynamics, but litter diversity wasalso shown to clearly affect the rate of these processesas well as reducing their variability. The mostinteresting point from this research was the positiverelationship between litter diversity and the release ofimportant nutrients (N, K, Ca and Fe). Future studiesshould improve the understanding of the role of litterdiversity on ecosystem functions. This should beachieved by focusing on the role of specific litterquality traits, and of composition and diversity of thedecomposer communities, in order to reveal themechanisms determining the apparent idiosyncraticeffects observed in litter mixtures.</p><p>Acknowledgements The work has been supported withgrants by MIUR (PRIN 2005-050197 and FISR MESCO-SAGR). We thank two anonymous reviewers whose commentshave been useful to improve early version of the manuscript.</p><p>References</p><p>Ayres E, Steltzer H, Simmons BL, Simpson RT, Steinweg JM,Wallenstein MD, Mellor N, Parton WJ, Moore JC, WallDH (2009) Home-field advantage accelerates leaf litterdecomposition in forests. Soil Biol Biochem 41:606610</p><p>Badre B, Nobelis P, Trmolires M (1998) Quantitative studyand modelling of the litter decomposition in a Europeanalluvial forest. Is there an influence of overstorey treespecies on the decomposition of ivy litter (Hedera helixL.)? Acta Oecol 19:491500</p><p>Ball BA, Hunter MD, Kominoski JS, Swan CM, Bradford MA(2008) Consequences of non-random species loss fordecomposition dynamics: experimental evidence for addi-tive and non-additive effects. J Ecol 96:303313</p><p>Bardgett RD, Freeman C, Ostle NJ (2008) Microbial contribu-tion to climate change through carbon cycle feedbacks.ISME J 2:805814</p><p>Berg B, Staaf H (1981) Leaching, accumulation, and release ofnitrogen in decomposing forest litter. Ecol Bull 33:163178</p><p>Berg B, McClaugherty C (2003)...</p></li></ul>

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