Influence of the El Niño and La Niña climate events and litter removal on inorganic nitrogen dynamics in pine forest soils on Central Java, Indonesia

Influence of the El Niño and La Niña climate events and litter removal on inorganic nitrogen dynamics in pine forest soils on Central Java, Indonesia

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  This article was srcinally published in a journal published byElsevier, and the attached copy is provided by Elsevier for theauthor’s benefit and for the benefit of the author’s institution, fornon-commercial research and educational use including withoutlimitation use in instruction at your institution, sending it to specificcolleagues that you know, and providing a copy to your institution’sadministrator.All other uses, reproduction and distribution, including withoutlimitation commercial reprints, selling or licensing copies or access,or posting on open internet sites, your personal or institution’swebsite or repository, are prohibited. For exceptions, permissionmay be sought for such use through Elsevier’s permissions site at:     A   u    t    h   o   r    '   s    p   e   r   s   o   n  a    l    c   o   p   y Original article Influence of the and climate eventsand litter removal on inorganic nitrogen dynamicsin pine forest soils on Central Java, Indonesia Agna S. Krave  a,c , Nico M. van Straalen  b , Henk W. van Verseveld  c ,Wilfred F.M. Ro¨ling  c, * a e bc Received 23 May 2005; accepted 27 March 2006Available online 30 August 2006This paper is dedicated to the kind memory of our friend and mentor Henk van Verseveld, who died 11 July 2003. Abstract To determine to what extent environmental factors and anthropogenic disturbances dictate N dynamics in tropical forest soils,changes of concentrations of inorganic N in soil were investigated during a period of extreme climatic conditions caused byand . This allowed the determination offactors driving the N-dynamics in tropical soils more clearly than during normalseasonal cycles. Three N-limited pine forests in Central Java, Indonesia, were studied monthly for over a year. N-NH 4 þ and N-NO 3  were abundant in the organic layers, and decreased with increasing depth. Regular litter removal from the forest floor and branch-cut-ting at two pine forest sites significantly reduced the N-NH 4 þ concentration in the organic and mineral layers, but had only a minorinfluence on N-NO 3  concentration. The N-NH 4 þ and N-NO 3  concentrations and pH showed a distinct seasonal variation with ex-tremely largeamplitudeinallstudied soillayers,this correspondedtovariation insoilmoisturecontent.Concentrations werelow dur-ingtheextremedryperiodof of1997,andsignificantlyincreasedduringthesubsequentlongwetperiodof .Thelargestchangesoccurredintheorganictoplayersandchangesweremorepronouncedthanduringnormalseasonalcycles.ItisconcludedthatN-dynamics in litter and fragmentation layers were most influenced by seasonal precipitation and to a lesser degree by litter removal.  2006 Elsevier Masson SAS. All rights reserved. ; ; Nitrogen conversion; Nitrification; Pine forest; Tropical soil 1. Introduction Primary rain forest on the heavily populated islandof Java, Indonesia, has nearly disappeared due toextensive deforestation. Pine forests now contribute * Corresponding author. Tel.:  þ 31 20 598 7192; fax:  þ 31 20 (W.F.M. Ro¨ling).1164-5563/$ - see front matter    2006 Elsevier Masson SAS. All rights reserved.doi:10.1016/j.ejsobi.2006.03.005European Journal of Soil Biology 43 (2007) 39 e 47     A   u    t    h   o   r    '   s    p   e   r   s   o   n  a    l    c   o   p   y approximately 50% of the total area offorests asa resultof an intensive reforestration program. Forests mainlyconsist of native and are located inhigh elevation areas on marginal or nutrient-limitedsoils that do not allow sustainable growth of crops [3].Nitrogen (N) is the growth-limiting nutrient in thesesystems [3]. A better understanding of the factors andprocesses that affect inorganic N concentrations insoil layers of tropical pine plantations will help toimprove management of these plantations, which areof environmental (e.g. erosion prevention) and econom-ical (e.g. logging) importance. Decomposition, N-mineralization and nitrificationrates in tropical forest ecosystems are substantiallyfaster than in temperate forest ecosystems [11,23,32,33], resulting in a larger amount of N being circulatedannually [30,33]. Litter turnover and nutrient mobiliza-tion in tropical pine forests are influenced by soil mois-ture content, which in turn is affected by the highlyvariable and seasonal precipitation. The seasons hardlydiffer in average air and soil temperature [4,9,10]. Thissuggests that the alternating dry and wet seasons ratherthan temperature will have the largest effect on the Ntransformations affecting concentrations of inor-ganic N. However, the inorganic N concentra-tions in tropical pine forest soils often do not clearlyshow a seasonal pattern (e.g. ref. [29]). The extremeclimatic conditions caused by and in1997 and 1998 offered the unique opportunity to testthe hypothesis that soil humidity determinesinorganic N concentrations. At the same time our studyprovided insight into how the forests might respond toglobal climate changes. Dynamics in inorganic Nconcentrations were investigated for three pine forestsin Central Java, subjected to different degrees of distur-bance, allowing us also to determine the effect of litterremoval. 2. Materials and methods The three pine plantation study sites are situatedon Central Java, Indonesia. Site 1 is situated on theSouthern slope of Mt. Ungaran near the village of Gintungan (1200 m above sea level), site 2 is situatedon the Southern slope of Mt. Telomoyo near thevillage of Jengkol (1300 m), and site 3 is situatedon the North-east slope of Mt. Merbabu near thevillage of Selodhuwur (1300 m). Site 1 is consideredto be a non-disturbed forest ecosystem. Intensivebranch cutting (the branches are used as fuel) takesplace at site 2, resulting in thin litter and fragmenta-tion layers. At site 3, local villagers regularly removelitter (for use as fuel, compost and cattle bedding) re-sulting in a thin litter layer and the absence of thefragmentation layer (Table 1).Reg. is the main understorey vegetation at site 1and 2 and covers the forest floor almost completely,especially during the wet season. Characteristics of the sites are shown in Table 1.Three rainfall collectors (15 cm diameter, 160 mmcapacity) were installed in open areas near eachresearch plot. Throughfall water was collected 1 mabove ground level; these collectors (15 cm diameter,3 per site) were randomly installed within the plots.The volume of collected water was determined two tothree times per month. N-deposition rates were calcu-lated by multiplying the collected volumes by theconcentrations of N-NH 4 þ , N-NO 2  and N-NO 3  mea-sured (for measurements: see Section 2.5). Table 1Characteristics of the three pine forests on Central Java, Indonesia, forwhich the N dynamics were studied in 1997 e 1998Characteristics Mt. Ungaran Mt. Telomoyo Mt. MerbabuYear of planting 1963 1964 1963Soil type BrownAndosolBrownAndosolBrownAndosolLitter 2 e 5 cm 2 e 3 cm  < 1 cmFragmentation/ Humus3 e 6 cm 2 e 3 cm AbsentLitter 95.6    1.6 92.5    2.2 88.9    3.4Fragmentation 92.2    2.4 76.7    5.8 AbsentMineral 0 e 5 cm 33.5    1.7 23.4    2.0 20.3    1.8Mineral 5 e 15 cm 29.1    2.5 21.1    1.6 18.6    1.6  Dry season 24.2    0.8 22.3    0.3 23.0    0.6Wet season 21.8    1.4 21.3    0.8 20.0    0.2Total N in rainfall 13.5    0.7 16.2    0.4 12.7    1.1Total N inthroughfall14.9    0.8 25.1    2.0 12.7    0.2Mt. Ungaran is an undisturbed pine forests, for Mt. Telemoyo branchcutting and removal is conducted, while at Mt. Merbabu litter isremoved.40  e     A   u    t    h   o   r    '   s    p   e   r   s   o   n  a    l    c   o   p   y A representative research plot of 30 m    40 m wasinstalled at each site in a relatively flat area. The plotwas divided into three sub-plots of 10 m    40 m andsampled monthly over the period September 1997  e December 1998. Soil samples of about 100 g were col-lectedfromtheorganiclayers(litterandfragmentation),and the mineral layer (at two depths; 0 e 5 cm and5 e 15 cm) using a soil corer (diameter: 13 cm). Ateach occasion, four random samples were taken fromeach sub-plot and each layer. The collected sampleswere placed in sterile polyethyleneglycol bottles andbrought to the laboratory within four hours for immedi-ate analysis. The four soil samples from the same sub-plot were mixed thoroughly, leaving three replicatesperlayerfor each site. Litter and fragmentation materialwere cut into small fragments with sterile scissors priorto KCl extraction. Five grams of litter or fragmentationand 10 g of mineral soil were extracted with 50 ml KCl(2 M) and shaken at 200 rpm for 1 h, followed bycentrifugation at 5000 rpm for 15 min. The clear super-natant was directly used in chemical analysis of pH,N-NH 4 þ , N-NO 2  and N-NO 3  (see Section 2.5).Soil leachate was collected from the pine forest onMt. Ungaran.Tocollect soilleachate,100 ml perforatedplastic bottles with funnels were carefully embeddedunder the litter and fragmentation layers, and in themineral layer at depths of 2 cm, 5 cm, 10 cm and15 cm. Triplicate leachate collectors were installed foreach soil layer and soil depth. Leachates were collectedtwice a month. Collectors were replaced monthly withnew sterile collectors. N-NH 4 þ , N-NO 3  and N-NO 2  concentrations and pH were determined (see Section2.5) immediately after the collected leachate had beenbrought to the laboratory (within four hours after sam-pling). The methodology and problems of soil leachatecollection have been reviewed by Liator [16].Samples of 10 g from each layer were dried at100   C for 72 h to determine the soil moisture content.Next, the dry matter was combusted at 600   C for 2 h ina furnace to determine the organic matter content. pHwas measured using a Consort P 907 pH meter.Concen-trations of N-NH 4 þ , N-NO 3  and N-NO 2  were deter-mined with spectrophotometric methods according toKeeney and Nelson [12].One-way analysis of variance (ANOVA) with LeastSignificant Difference as post-hoc test, was used tocompare means of the soil inorganic N concentrationsamong seasons and sites. Data met the criteria of nor-mality and homogeneity of variance. Correlation analy-sis was conducted to explore interrelationships amongthe variables. All statistical computations were under-taken with SPSS for Windows version 7.5. 3. Results Normally, the dry and wet seasons on Java last fromApril to October and from October to April, respec-tively. The extreme and events affectedthe seasonal rainfall pattern in 1997/1998; an extremelydry period extended until the end of November 1997,while 1998 was wetter than usual (Fig. 1). Only inAugust and September 1998 little rainfall occurred.As a result, during the entire year 1998 the soils werewet (moisture content above 50% for the litter and frag-mentation layers, and above 40% for the minerallayers).The soil concentrations of N-NH 4 þ and N-NO 3  at thethree study sites increased during the rainy season andfluctuated with a large amplitude over the periodSeptember 1997 e December 1998 in all soil layers.N-NO 2  was never found in appreciable amounts( > 1 mg kg  1 dry weight soil). Only the data forMt. Ungaranaregivenbyway ofexample(Fig.2). Con-centrations of N-NH 4 þ and N-NO 3  in collected soilleachate also increased during the rainy season, al-though the concentrations of mobile N-NO 3  were 01002003004005001995-19961997-1998    P  r  e  c   i  p   i   t  a   t   i  o  n   (  m  m   p  e  r  m  o  n   t   h   ) Month J F M A M J J A S O N D J F M A M J J A S O N D Fig. 1. Monthly precipitation over the extreme-climate influencedperiod of January 1997 e December 1998, and how it compares tonormal seasonal cycles (1995 e 1996).41 e     A   u    t    h   o   r    '   s    p   e   r   s   o   n  a    l    c   o   p   y higher than that of N-NH 4 þ (data not shown). Maximumconcentrations of N-NH 4 þ and N-NO 3  were 2.5 mg/land 11.4 mg/l, respectively. The concentrations of N-NH 4 þ and N-NO 3  were significantly higher in leachate(  < 0.05; Analysis of Variance (ANOVA)) than inthroughfall and rainfall water (max. concentrations of N-NH 4 þ and N-NO 3  were 0.6 and 0.2 mg/l, respec-tively). N-NH 4 þ and N-NO 3  concentrations in leachateshowed significant correlations with soil N-NH 4 þ andsoil N-NO 3  (  < 0.05).In order to statistically evaluate the effect of seasonon N-transformations, as well to visualize thedifferences between soil layers and between researchlocations, the data were clustered into two groups, onegroup representing the dry season, the other groupthe wet season. In 1998, only August and Septemberwere relatively dry (Fig. 1), but the low amount of rain-fall in these months did not severely reduce the soilmoisture contents in soil layers, the large reductionwas observed for the litter layers (reduction from anaverage of 78% in July 1998 to 66% in September1998). Therefore, all data in the period of December1997 to December 1998 were considered as belongingto the wet season, the dry season was taken fromSeptember to November 1998.For all soil layers and research locations a significantinfluence of season on moisture content, N-NH 4 þ and N-NO 3  concentrations and pH was observed (Fig. 3).Moisture content, N-NH 4 þ and N-NO 3  concentrationsand pH increased during the wet season. A clear soillayer stratification in N-NH 4 þ and N-NO 3  concentra-tions was observed both in the dry and wet season(Fig.3
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