Soil-plant dynamics of water, nitrogen and sulfur: A study on indigenous and exotic tree species in Munessa Forest, Ethiopia Dissertation zur Erlangung des Doktorgrades an der Fakultät Biologie/Chemie/Geowissenschaften der Universität Bayreuth vorgelegt von Florian Fritzsche (Diplom-Geoökologe, Universität Bayreuth) Erstgutachter: Prof. Dr. Wolfgang Zech Bayreuth, Juni 2005 Diese Arbeit wurde am Lehrstuhl für Bodenkunde und Bodengeografie der Universität Bayreuth bei Prof. Dr. Wolfgang Zech mit Fördermitteln der Deutschen Forschungsgemeinschaft (DFG, Gu 406/8) angefertigt. Vollständiger Abdruck der vom Fachbereich Biologie/Chemie/Geowissenschaften der Universität Bayreuth genehmigten Dissertation zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften. Arbeit eingereicht am 28. Juni 2005 Zulassung der Arbeit: 06. Juli 2005 Tag des wissenschaftlichen Kolloquiums: 08. Februar 2006 Prüfungsausschuss: Prof. Dr. Erwin Beck Prof. Dr. Georg Guggenberger Prof. Dr. Bernd Huwe (Vorsitz) Prof. Dr. Egbert Matzner (2. Gutachter) Prof. Dr. Wolfgang Zech (1. Gutachter) Dissertation als PDF-Datei verfügbar Dissertation available as PDF file Dedicated to Seyoum Kebede Miriam Contents LIST OF TABLES V LIST OF FIGURES VIII ACKNOWLEDGEMENTS XIII SUMMARY XV ZUSAMMENFASSUNG XVII EXTENDED SUMMARY XXI Research problem: sustainable forest management in the tropics XXI Nutrient cycling and ecosystem sustainability XXII Objectives XXIV The regional context (Study 1) XXIV Ecosystem dynamics: experimental approach XXVII Isotope labelling XXIX In-situ measurements and sampling XXXI Water-related parameters and roots XXXI Nutrient cycling XXXI Analytical methods XXXII Soil extraction XXXII Chemical analyses XXXII Isotope analyses XXXII Water dynamics (Study 3) XXXIV Plant effects on N cycling (Study 4) XXXVIII Recycling of S from litter (Study 5) XLI Synthesis on ecosystem dynamics of water, N and S XLIV Conclusions and outlook XLVI Methodological aspects XLVI Outlook on sustainable forest management XLVII Contributions to the included manuscripts XLVIII References LI Introduction -------------------------------------------------------------------------------------1 RESEARCH BACKGROUND 1 THE MUNESSA FOREST AS A STUDY AREA 2 RESEARCH OBJECTIVES AND EXPERIMENTAL APPROACH 3 II REFERENCES 6 Study 1: Soils of the Main Ethiopian Rift Valley escarpment: a catenary study -------------------------------------------------------------------11 ABSTRACT 13 INTRODUCTION 14 MATERIALS AND METHODS 15 Study area and sampling sites 15 Sampling and analyses 20 RESULTS AND DISCUSSION 20 General description and horizon classification 22 Soil water 22 Organic nutrients 23 Weathering and soil reaction 25 Exchange complex and metal cations 27 Soil minerals, geohistory and pedogenesis 29 CONCLUSIONS 31 ACKNOWLEDGEMENTS 32 REFERENCES 32 Study 2: Signal improvement in elemental analyzer-continuous flow isotope ratio mass spectrometry for samples with low sulfur contents by on-line concentration adjustment -----------------------------------------37 ABSTRACT 39 INTRODUCTION 40 MATERIALS AND METHODS 41 RESULTS AND DISCUSSION 43 CONCLUSIONS 46 ACKNOWLEDGEMENTS 46 REFERENCES 47 Study 3: Soil-plant hydrology of indigenous and exotic trees in an Ethiopian montane forest -------------------------------------------------------49 ABSTRACT 51 INTRODUCTION 52 MATERIALS AND METHODS 54 III Study area 54 Methodology 56 Climate 56 Soil water matric potential 56 Stable isotope signature of water 57 Root system 58 Transpiration 58 Statistical analysis 59 RESULTS 60 Climate 60 Soil water transport and availability by matric potential 61 Variability of soil matric potential 64 δ18O values 66 Root distribution 67 Transpiration by heat dissipation 69 DISCUSSION 70 CONCLUSIONS 75 ACKNOWLEDGEMENTS 76 REFERENCES 76 Study 4: Nitrogen dynamics in three forest types of the South-Ethiopian highlands ------------------------------------------------------ 83 ABSTRACT 85 INTRODUCTION 86 MATERIALS AND METHODS 88 Site description 88 Experimental setup, 15N labelling and sampling 89 Analyses and statistical treatment 90 RESULTS 91 Bulk C and N concentrations 91 N concentrations in soil extracts 93 δ15N values at natural abundance 95 Soil δ15N values after labelling 95 Plant uptake 96 Tracer recovery 98 IV DISCUSSION 98 Bulk nutrient concentrations 98 Extractable Nitrogen 100 Isotopic evidence 103 Plant N dynamics 105 CONCLUSIONS 106 ACKNOWLEDGEMENTS 107 REFERENCES 108 Study 5: Sulfur cycling in natural forest versus plantations: a 34S litter- labelling experiment in a South-Ethiopian montane forest----------- 115 ABSTRACT 117 INTRODUCTION 118 MATERIALS AND METHODS 120 Study area 120 Methodology 121 Statistical analysis 124 RESULTS 125 Bulk S content and extractable S 125 34 Plant labelling by K2 SO4 127 δ34S of bulk soil 128 δ34S of soil extracts 129 Tracer uptake by vegetation 131 DISCUSSION 133 CONCLUSIONS 138 ACKNOWLEDGEMENTS 139 REFERENCES 139 General conclusions ------------------------------------------------------------------------ 145 METHODOLOGICAL ASPECTS 145 ECOLOGICAL IMPLICATIONS 146 RESEARCH PERSPECTIVES 148 REFERENCES 149 DECLARATION 151 V List of Tables + - Table I: Contribution of Neo and Nei (= NH4 + NO3 ), respectively, to bulk N of two soil layers, including the ratio of these layers (SE in parenthesis, n = 112 for C. lusitanica, n = 110 for P. falcatus, n = 111 for E. globulus, total n = 333). XXXVIII Table 1-1: Basic analytical characteristics of six soil profiles: Profile code, horizon, lower horizon boundary (lhb), bulk density (BD), coarse sand (CSa, 2000 – 200 µm), fine sand (FSa, 200 – 20 µm), silt (20 – 2 µm), clay (< 2 µm), Munsell colour (moist), pH (KCl), concentrations of C, N, S, C/N ratio, potential CEC, base saturation, exchangeable basic cations, extractable Fe and Al. 21 Table 1-2: Multiple regression analysis for predicting CEC, separately for topsoils (1 model) and subsoils (two models): model, variable, standardized regression coefficients β, adjusted regression coefficients B, partial correlations r, multiple R² in stepwise model, probability of error. 28 Table 1-3: Mineralogical characteristics of the uppermost B horizon along the soil catena through Munessa Forest from powder XRD, and Feo/Fed ratios integrated for the whole profiles. 30 Table 2-1: Known isotope ratios (δ34S CDT) of standard substances, measured values, linearly corrected values, sample numbers and standard deviations. 41 Table 2-2: Sulfur content and replicate corrected measurements of isotope ratios (δ34S values) of sandstone samples from Germany and soil and plant samples from Ethiopia (individual replicates, means and standard deviations for measurements). 45 Table 3-1: Basic characteristics of the soils under the studied trees. 55 VI Table 3-2: Oxygen isotope ratios (δ18O VSMOW) after the main rainy season of 2003 by tree species: Xylem water (median, n = 6), soil water (median, n = 4) at 20, 50, 100, 200 cm depth, and vertical span (in italics). Values higher or equivalent to the xylem water are represented as bold numbers. 66 Table 3-3: Average daily transpiration values for several individuals of Cupressus lusitanica, Podocarpus falcatus and Eucalyptus globulus as measured in wet and dry period in Munessa-Shashemene Forest (ca. 20 cm diameter at breast height; n = 5, mean ± 1 SD). 69 Table 4-1: Sampling programme for soil and vegetation samples. The sampling on day 0 took place preceding the 15N labelling. 90 + Table 4-2: Contents of C, N, and the phosphate-extractable species NH4 , - NO3 , and extractable organic N in three forest types and two depth layers (SE in parenthesis; n = 8 for day 0, n = 12 for later dates; median values are displayed in bold font). 92 + - Table 4-3: Contribution of Neo and Nei (= NH4 + NO3 ), respectively, to bulk N of two soil layers, including the ratio of these layers (SE in parenthesis, n = 112 for C. lusitanica, n = 110 for P. falcatus, n = 111 for E. globulus, total N = 333). 93 Table 4-4: Correlation matrices (Rs) of bulk C, bulk N and extractable N species (ammonium, nitrate, total extractable N and extractable organic N) for two soil depth layers (0 – 30 cm and 30 – 60 cm) of three forest types. 102 Table 4-5: Correlations (Rs) of extractable N species between soil layers within three forest types: upper layer (0 - 30 cm) values with lower layer (30 - 60 cm). 103 Table 5-1: Mean S concentrations in bulk soil (Sb) and KH2PO4 extracts (Se), proportion of Se to Sb for the three forest types over the whole study period (Cl: Cupressus lusitanica; Pf: Podocarpus falcatus; Eg: Eucalyptus globulus). 125 VII Table 5-2: Properties of the label applied under the three tree species: 34 dry litter mass (Mspec), S content and S isotope enrichment, applied isotope tracer per area and correction factor (Facspec) for equalization of label for the 3 tree species. 127 Table 5-3: Plant uptake of mineralized S from label by trees and understorey plants by forest types: δ34S values normalized to the label of Podocarpus falcatus. 132 VIII List of Figures Fig. I: Geo-ecological transect through the study area with 6 soil profiles classified according to WRB and Soil Taxonomy. XRD spectra are included for two horizons of the lowermost, polygenetic profile (dominant clay minerals: B - smectite, 2B - kaolinite). XXV Fig. II: Permanent experimental plot in the C. lusitanica plantation, equipped with rain collectors, sap flow probes, litter collectors, litter lysimeters, 4 clusters of tensiometers and three clusters of suction cups, protected by fence. XXVIII Fig.