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Effects of Litter and Woody Debris Quality on Decomposition and Nutrient Release in Exotic Forests in New Zealand

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Effects of Litter and Woody Debris Quality on Decomposition and Nutrient Release in Exotic Forests in New Zealand Lincoln University Digital Thesis Copyright Statement The digital copy of this thesis is protected by the Copyright Act 1994 (New Zealand). This thesis may be consulted by you, provided you comply with the provisions of the Act and the following conditions of use: you will use the copy only for the purposes of research or private study you will recognise the author's right to be identified as the author of the thesis and due acknowledgement will be made to the author where appropriate you will obtain the author's permission before publishing any material from the thesis. EFFECTS OF LITTER AND WOODY DEBRIS QUALITY ON DECOMPOSITION AND NUTRIENT RELEASE IN EXOTIC FORESTS IN NEW ZEALAND A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University by G.K.Girisha Lincoln University 2001 This thesis is dedicated to my parents Keshavamurthy and Saraswathi and my wife Vani ii Abstract of a thesis submitted in partial fulfilment of the requirement for the Degree of Doctor of Philosophy EFFECTS OF LITTER AND WOODY DEBRIS QUALITY ON DECOMPOSITION AND NUTRIENT RELEASE IN EXOTIC FORESTS IN NEW ZEALAND Ganjegunte Keshavamurthy Girisha Short rotation plantation forestry based on exotic tree species (principally radiata pine (Pinus radiata)) is a major land use in New Zealand (1.7 million ha, 7% of total land area). The maintenance of primary production in such a plantation forest ecosystem depends upon a number of factors including replenishment of available nutrients removal in harvested biomass. Litterfall is a major pathway of nutrient return to the forest floor. In addition, understorey biomass and woody debris from thinning and pruning also contribute to nutrient and organic matter cycling in a managed forest. Needle litter, understorey litter and woody debris undergo decomposition to release nutrients and thereby maintain the integrity of the forest ecosystem. Substrate quality is an important factor that regulates the decomposition of litter and woody debris materials. Decomposition and associated nutrient release from selected above ground litter and woody debris components from radiata pine forests were investigated using a combination of controlled environment (microcosm) and field experiments. The principle objective of the study was to determine the influence of litkr and woody debris quality on decomposition and associated nutrient release. The impact of green needle litter on senescent needle litter decomposition and nutrient turnover in the forest floor was investigated under controlled conditions (microcosm) and in the field. The results obtained indicated that green needle addition did not significantly affect organic matter and nutrient turnover. However, addition of green needles did affect short-term nutrient availability. Green needles lost 69,87,75,72, and 79 % of the original nitrogen, phosphorus, calcium, magnesium, and potassium, respectively after 10 months, while the corresponding data for senescent needles was 22, 71,31,4, and 38 %, respectively. iii The effect of selected understorey litters on decomposition and nutrient release from senescent pine needles was investigated in a microcosm experiment. After 10 months the weight loss of senescent pine needles (64%) was significantly greater than bracken (Pteridium aquilinum-26%), gorse (Ulex europaeus-30%), broom (Cytisus scoparius-30%) and lotus (Lotus pedunculatus-40%) litter. Net release of all nutrients (nitrogen, phosphorus, calcium, magnesium and potassium) occurred from decomposing senescent pine needles, although net immobilization of potassium was observed for all understorey litters. Mixing pine and understorey litter significantly influenced decomposition rate and associated nutrient release. Pine needles mixed with understorey litter decomposed slower than needles alone, but mixed understorey litter (except bracken) decomposed faster than understorey alone. Nutrient availability (especially magnesium and potassium) was found to be as important as energy availability in determining the overall rate of decomposition. A laboratory study on the biodegradability of dissolved organic carbon from radiata pine litter indicated that this was influenced by its quality as determined by the stage of decomposition. The aqueous extract of the litter (L) layer decomposed faster (38%) than that of the fermentedlhumus (FH) layer (15%) during 3 months of incubation. The inhibitory effects of polyphenols on the biodegradability of dissolved organic carbon was confirmed in this study. The l3C NMR technique was used to describe the DOC degradation. The NMR results complemented the results obtained through the proximate analyses and it gave better insights in to the pathways of Land FH DOC breakdown. A chronosequence study of woody debris decomposition over 13 years showed that the overall half- life was 14 years and decomposition of different components was clearly related to quality. Thus, log wood contained greater concentrations of carbohydrates (soluble and holocelluose) and decomposed faster than log bark and side branches. l3C NMR technique was used to study the decomposition of wood, bark and sidebranches over 13 years. The NMR spectra confirmed the results obtained through proximate analysis and proved to be an useful technique in understanding the process of litter decomposition. The slower decomposition rate of log bark was attributed to the higher polyphenol concentration, while higher lignin concentration and an unfavorable microclimate were the main reasons for slow decomposition of side branches. The mass and volume of woody iv debris was much lower than that of natural conifer forests due to the young age of woody debris (thinning slash) and net mineralization of nutrients from the decomposing woody debris was apparent during decomposition. Even after 13 years, woody debris contained 1 1 considerable amounts of carbon (5.5 t ha- ) and nutrients (41, 2,41,8,3 kg ha- of nitrogen, phosphorus, calcium, magnesium and potassium, respectively). Therefore, management of woody debris (thinning residues) may be important for the long-tenn sustainability of forest soils. Keywords: Pinus radiata, litter quality, understorey, green needles, senescent needles, decomposition, leaching, microcosm, chronosequence, coarse woody debris, dissolved organic carbon, nutrients, soluble carbohydrates, polyphenols, holocellulose, lignin, l3e NMR. v ACKNOWLEDGEMENTS I sincerely thank Dr Leo Condron for his patient supervision, help, guidance and constant encouragement during the course of this study. His excellent editing has greatly improved the clarity of this thesis. I am grateful to Dr Peter Clinton for his keen interest, constant encouragement, expertise, valuable advice and guidance throughout this research project. Many thanks to Mr Murray Davis and Dr John Adams for their guidance and useful comments throughout this study. I wish to thank Dr Scott Chang for his guidance and useful suggestions in the earlier stages of this study. Dr Chris Frampton for help in statistical analysis of data. Dr Nathalie Mahieu (Queen Mary and Westfield College, London)for her help in 13C NMR analysis. Thanks to Mike Kwant of Carter Holt Harvey Limited for permitting me to carry out field experiments at Eyrewell forest. Many thanks to Roger Cresswell, Leanne Hasell, and Jason for the technical advice and assistance with sample analysis. Maureen McCloy for help in external check of sample analysis. Gina, Colin, and Hayley for thesis proof reading. Thanks to Roger McLenaghenfor giving me an opportunity to work with him. Thanks are due to New Zealand Vice Chancellors Committee for providing the commonwealth scholarship and Tata Energy Research Institute for providing the study leave to conduct this research. My special thanks to Kiri Manuera (scholarships officer, NZVCC) for her constant encouragement and support throughout my study period. I would also like to thank Ms Toni Tebbutt and Ms Pat Yadgren (Scholarship officers, Lincoln University) for their help in scholarship matters. My sincerely thanks Dr Pachauri, Director, Tata Energy Research Institute, without his timely help I would not have reached this stage. Special thanks to Dr Badrinath, Prof. Siddaramappa (University of Agricultural Sciences, Bangalore) and Dr Leena Srivastava (Dean, TERI) for supporting my candidature for the scholarship and Dr Sujata Gupta (Dean, TERI)for her constant encouragement and inspiration to pursue this research. I am grateful to Bhujang Rao for his friendship, guidance and useful discussions. vi I am thankful to Ramesh and Rajni for their encouragement, friendship and help during my stay here. My sincere thanks to Gurpal and Ramandeep for help I received during the course of this study and friendship. My dear friend Paramjit for the help with references. Special thanks to Dr Surinder Tandon and Archanafor their love, friendship and timely help, without which I could not completed my studies here. Raj and Sumana for their love and support. Peter, Graeme and Mary for love, friendship and enlightening me with their knowledge of yoga. Neil Smith for empowering me with Reiki. I would like to thank my friends Silva, Matt Early, Clinton, Shane, Corine, Sally, Zheng, Chen, Thomas, Kuldip, Jamuna, Mathew, Aziz, Suman, and Prasadfor the lively atmosphere around. My sincere thanks to my parents Keshavamurthy Saraswathi, my brother Ravi and my sister Geetha, Sajad and Iqbal for their encouragement. To my mother-in-law, Shanta, for taking care of my wife when
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