FARIAS, M.

FORSTER, B.

LUIZAO, R.

English

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Proceedings ....1998 PC - 1999 . OO0591111111111111111111111111111111111111114191-1Microbial respiration and biomass in tropical forest soil and litterBernhard Fõrster ', Maristela Farias! and Regina Luizão3lEMBRAPA Amazônia Ocidental, Manaus/AM, Brazil;2ECT Oekotoxikologie GmbH, Flõrsheim, Germany;3INPA, Manaus/ AM, BrazilABSTRACTMicroorganisms play a major role in the decomposition of organic matter and in the cyclingof nutrients. Microbial biomass and metabolic activity are ecologically relevant parametersfor the description of the structure and function of ecosystems. We measured the microbialsubstrate-induced respiration (SIR) and the basal respiration (BR) of the top soil and of thelitter layer of a primary forest, a secondary forest and of a plantation. Measurements weremade in a continuous flow-through system connected to an infra-red gas analyzer (IRGA).Microbial biomass was calculated on the basis of the SIR values. From the data of the firstthree sampling dates we conclude that microbial biomass of the three field sites does notdiffer significantly. There is a high natural spatial variability within each field site.RESUMOMicroorganismos têm um papel principal na decomposição de matéria orgánica e no ciclode nutrientes. Biomassa microbiana e atividade metabôlica são parámetros ecológicospertinentes para a descrição da estrutura e função de ecossistemas. Nos medimos a respiraçãomicrobiana induzida por substrato (SIR) e a respiração basal (BR) do solo de topo e dacamada de serrapilheira de uma floresta primária, uma floresta secundária e de uma plantação.As medidas foram feitas em um sistema de fluxo continuo conectado a um analisador de g.sinfra-vermelho (IRGA). Biomassa microbiana foi calculada em base dos valores de SIR. Dosdados das primeiras trés datas concluimos que a biomassa microbiana dos trés locais decampo não difere significativamente. Há uma variabilidade espacial natural alta dentro decada local de campo.ZUSAMMENF ASSUNGMikroorganismen spielen eine bedeutende Rolle in der Zersetzung organischer Substanzund in Nãhrstoffkreislaufen. Mikrobielle Biomasse und Stoffwechselaktivitat sind õkologischrelevante Parameter für die Beschreibung von Struktur und Funktion von Õkosystemen, WirmaBen die mikrobielle substratinduzierte Atmung (SIR) und die Basalatmung (BR) imOberboden und in der Streuschicht eines Primãrwaldes, eines Sekundãrwaldes und einerPlantage. Die Messungen wurden in einem "continuous-flow" - System durchgeführt, das miteinem Infrarot-Gas-Analysator verbunden war (IRGA). Die mikrobielle Biomasse wurde aufder Basis der SIR-Werte kalkuliert. Aus den Ergebnissen der ersten drei Probentermineschlieêen wir, daê sich die mikrobielle Biomasse der drei Untersuchungsflachen nichtsignifikant unterscheidet. Es gibt eine hohe natürliche rãurnliche Variabilitãt innerhalb jederUntersuchungsflãche,483INTRODUCTIOMicroorganisms are the most abundant organisms in soil and litter layers. The microbialbiomass is an important structural element of the soil compartment. ln the Northemhemisphere more than 80 % of the non-plant biomass of soil is provided by microorganisms.Moreover microorganisms play an important role in the decomposition of organic matter andin the cycIing of nutrients, thus fulfil essential ecosystem functions.There are only few data available on the microbial biomass and activity in tropical forestsoil and litter (Yang and lnsam 1991, Feigl et a\. 1995, Wood 1995).The aim of the study was to compare the microbial biomasses and the metabolic activitiesof soil and plant litter of different tropical forest types: a primary forest (FLO), a secondaryforest (SEC) and an abandoned plantation of rubber trees (Seringueira) which was used as apolyculture forestry research area since 1992 (POA/POC).MATERIAL AND METHODSThe study area belongs to the agricultural research station EMBRAPA - AmazôniaOcidental (altitude 44 m), which is located cIose to the city of Manaus, Amazonas, Brazil. ln1997, the mean annual temperature was 27.9 C and the precipitation was 2585 mm. Aliinvestigation plots were located within a distance of less than 200 m and share the same soilproperties (Table 1), but the vegetation cover differs greatly since especiaIIy POAIPOC hasbroad open spaces.Every three months, 20 soil samples (top soil 0-5 em and 5-15 em) were sampled on eachplot with a soil corer (6.5 em diameter). Soil samples were sieved and stored at 10°C untilused.The amount of microbial biomass in the soil and in the litter was estimated by applying thesubstrate-induced respiration (SIR) method (Anderson and Domsch 1978).Metabolic activity was assessed by measuring the basal respiration (BR) of the soil and ofthe litter. lf necessary, soil and litter were adjusted to the optimal moisture (ca. 40 % WHC)and pre-incubated before measuring respiration.All measurements were done in a continuos flow-through system connected with an Infra-red gas analyser (IRGA) under controlled temperature conditions.Table 1: Soil properties ofthe three investigation plots *Parameter FLO SEC POAIPOCPrimary forest Secondary forest PolycultureVegetationSoil TypepH (H20)diverse Secondary vegetation Secondary vegetationSandy cIay (60 % cIay, 25 % sand, 15 % silt)4.2 - 4.8Org. content ?4.7 - 5.02.4 - 5.34.2 - 6.02.4 - 6.8* see also Roembke et al., this volume, p. 488484RESULTS AND DISCUSSIONThe data of the first four samplings during July 97 and March 98 indicate that there seemsto be no statistically significant difference between the three forest soils with respect to theamount of microbial biomass and activity (Table 2). Compared to forest soils from thenorthem hemisphere the values for microbial biomass (Cmie) are low whilst the basalrespiration seems to be comparable thus resulting in a relatively high biomass-specificrespiration rate.First measurements of the leaf litter indicate an increased microbial respiration rate ascompared to the soil by a factor ofroughly 40 (data not shown).Table 2: Microbial basal respiration [111 CO2 h-I g-I soil], microbial biomass [ug Cmieg" soil]and specific respiration [111 CO2 mg" Cmieh-I] ofthe top soillayer (O - 5 cm)*Basal Biom. Spec Basal Biom. Spec Basal Biom. Spec Basal Biom. SpecJuly 97 FLO FLO FLO SEC SEC SEC POC POC POC POA POA POAMEAN 1.91 426.13 4.54 2.07 398.29 5.25 1.99 429.46 4.42 1.40 454.82 3.16SD 0.53 74.77 1.18 0.64 104.59 1.40 1.09 158.60 0.94 0.60 201.33 0.62Sep.97 FLO FLO FLO SEC SEC SEC POC POC POC POA POA POAMEAN 1.52 385.63 3.95 1.13 464.88 2.42 1.09 390.07 2.74 1.70 503.71 3.30SD 0.53 68.47 1.26 0.39 113.79 0.49 0.43 94.49 0.52 0.77 127.69 0.96Dec.97 FLO FLO FLO SEC SEC SEC POC POC POC POA POA POAMEAN 2.07 396.23 5.15 1.79 418.97 4.15 1.62 421.08 4.00 1.90 510.26 3.69SD 0.88 121.33 1.45 0.75 95.63 1.03 0.62 107.83 1.28 0.58 113.67 0.97Mar. 98 FLO FLO FLO SEC SEC SEC POC POC POC POA POA POAMEAN 1.75 378.80 4.58 1.48 411.47 3.60 1.40 393.37 3.47 1.48 370.30 3.98SD 0.56 52.23 1.21 0.41 46.40 0.99 0.82 72.55 1.67 0.53 62.67 1.20* Mean values and standard deviation (FLO, SEC, n = 20; POC, POA, n = 10)ACKNOWLEDGEMENTSWe thank the German Federal Ministry for Education and Research (BMBF) and theBrazilian Research Council (CNPq) for funding the studies reported here.REFERENCESAnderson, JPE, and Domsch, KH, 1978: A physiological method for the quantitativemeasurement of microbial biomass in soils. Soil Biology & Biochemistry 10,215-221.Feigl, BJ, Sparling, GP, Ross, DJ, and Cerri, CC, 1995: Soil microbial biomass in Amazoniansoils: evaluation ofmethods and estimates ofpool sizes. Soil Biol. Biochem. 27(11),1467-1472Wood, M, 1995: The role of bacteria and actinomycetes in litter decomposition in the tropics.ln: Reddy, MV (ed), Soil Organisms and Litter Decomposition in the Tropics, 15 - 56Yang, JC, and lnsam, H, 1991: Microbial biomass and reIative contributions of bacteria andfungi in soil beneath tropical rain forest, Hainan lsland, China. 1. Tropical Ecology 7, 385-393.485

Microbial respiration and biomass in tropical forest soil and litter.

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Microbial respiration and biomass in tropical forest soil and litter.

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