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Effects of slash-and-burn on soil chemistry and arbuscular mycorrhizal fungi abundance in soil and roots of Didierea Madagascariensis, in the dry tropical Spiny Forest of South-West Madagascar

Donnellan Barraclough, Alicia (2013) BION31 20131
Degree Projects in Biology
Abstract
Abstract

Deforestation and the use of fire to clear land have drastic effects on ecosystem functioning and compromise the continuity of many important ecosystem services. This is specially the case in tropical countries such as Madagascar, where people's reliance on forest exploitation and subsidence agriculture is driving severe forest decline. In this study we evaluated the effects of slash-and-burn practices on soil nutrients and Arbuscular Mycorrhizal (AM) fungi abundance in the dry Spiny Forest of south-western Madagascar. Nine sample pairs were established along the border of a private reserve within the PK-32 complex, where soil and seedling root samples of the endemic tree Didierea madagascariensis were taken. We analysed soil... (More)
Abstract

Deforestation and the use of fire to clear land have drastic effects on ecosystem functioning and compromise the continuity of many important ecosystem services. This is specially the case in tropical countries such as Madagascar, where people's reliance on forest exploitation and subsidence agriculture is driving severe forest decline. In this study we evaluated the effects of slash-and-burn practices on soil nutrients and Arbuscular Mycorrhizal (AM) fungi abundance in the dry Spiny Forest of south-western Madagascar. Nine sample pairs were established along the border of a private reserve within the PK-32 complex, where soil and seedling root samples of the endemic tree Didierea madagascariensis were taken. We analysed soil extractable nutrients (Bray-1 and NaFS orthophosphate, NH4+ and NO3-) as well as total soil carbon and nitrogen, expecting to see a surge in plant available nutrients and a decline in soil carbon. We also analysed AM fungal abundance in soil and roots, through fatty acid marker analysis (NLFA and PLFA 16:1ω5), spore extraction and Trypan Blue staining. We hypothesised that deforestation would cause a decline in fungal abundance. As expected, slash-and-burn practices caused increased pH and pyromineralization to double plant available nutrients quantities in soil (soil extractable phosphate (μg/g) went from 7.4 to 13.1, and soil nitrate (μg/g) went from 6.9 to 13.2). Deforestation did not affect levels of soil ammonium, probably due to volatilization and increased nitrification in deforested areas. Contrary to expectations, total C and total N increased in deforested soil (respectively, from 0.6% to 0.84% and from 0.06% to 0.08%), likely caused by incorporation of ash, burned and unburned residues to an otherwise poor mineral soil. Significant decline in AM fungi abundance in soil was only observed in NLFA 16:1ω5 (from 0.2 to 0.12 nmol/g). Hyphal network destruction and removal of plant hosts is hypothesised to be behind the observed reduction. AM fungi abundance in D. madagascariensis roots was also negatively affected, colonization levels decreased from 27.7% to 16.9% and NLFA 16:1ω5 decreased from 75.7 to 19 nmol/g of dried root. Together with hyphal network disruption, increased nutrient availability is proposed as an additional explanation behind AM symbiosis decline in D. madagascariensis. AM fungi spore density in soil was found to be unaffected. This is the first study to report such an event in Madagascar south-western ecosystems. We propose additional research to disentangle predominant factors driving observed trends and further study on the potential effects of secondary plant succession on deforested land.

Popular science summary:

Effects of slash-and-burn in a forest of South-West Madagascar

Deforestation and the use of fire to clear land have drastic effects on ecosystem functioning and endanger many important services that healthy ecosystems provide. This is especially the case in many tropical countries. In this study we evaluated the effects of slash-and-burn, a kind of forest clearing, in the dry Spiny Forest of south-western Madagascar. This is a forest of great biodiversity value, with 90% of its species existing nowhere else in the world. In particular, we looked at changes in soil nutrient levels, which are an important indicator of nutrient cycles. We also analysed arbuscular mycorrhizal (AM) fungi abundance, an important symbiont of land plants, which helps them with nutrient absorption and resistance to stress. Slash-and-burn caused plant available nutrients, phosphate and nitrate, to double their quantities in the soil. Contrary to expectations, carbon and total nitrogen increased in deforested soil, probably caused by incorporation of unburned residues and black carbon to the poor mineral soil. Significant decline in AM fungi abundance in soil was observed, probably due to destruction of the fungi network and removal of plant hosts. AM fungi spore density in soil didn’t change however. We also found that AM fungi abundance in the roots forest tree went down, likely due to hyphal network disruption and increased nutrient availability. As soil nutrients are more available, the plant may not find it so advantageous to exchange its own carbon for those nutrients provided by the AM fungi. This study is the first investigation into the effects of slash-and-burn practices on soil chemistry and arbuscular mycorrhizal fungi abundance in this ecosystem. Results show clear effects of the practices used by the inhabitants of this region on soil and AM fungi. Further studies are needed to asses the dynamics of nutrient stocks and arbuscular mycorrhizal fungi and their response to seasonality and vegetation cover changes across a larger time scale. Given the high originality of this endangered ecosystem such knowledge is essential in order to understand and predict the future direction of vegetation patterns and ecosystem resilience to human action.


Advisor: Pal Axel Olsson
Master´s Degree Project 45 credits in Plant Ecology 2013
Department of Biology, Lund University and Systematics (Less)
Please use this url to cite or link to this publication:
author
Donnellan Barraclough, Alicia
supervisor
organization
course
BION31 20131
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
3910181
date added to LUP
2013-06-26 10:40:09
date last changed
2013-06-26 10:40:09
@misc{3910181,
  abstract     = {Abstract

Deforestation and the use of fire to clear land have drastic effects on ecosystem functioning and compromise the continuity of many important ecosystem services. This is specially the case in tropical countries such as Madagascar, where people's reliance on forest exploitation and subsidence agriculture is driving severe forest decline. In this study we evaluated the effects of slash-and-burn practices on soil nutrients and Arbuscular Mycorrhizal (AM) fungi abundance in the dry Spiny Forest of south-western Madagascar. Nine sample pairs were established along the border of a private reserve within the PK-32 complex, where soil and seedling root samples of the endemic tree Didierea madagascariensis were taken. We analysed soil extractable nutrients (Bray-1 and NaFS orthophosphate, NH4+ and NO3-) as well as total soil carbon and nitrogen, expecting to see a surge in plant available nutrients and a decline in soil carbon. We also analysed AM fungal abundance in soil and roots, through fatty acid marker analysis (NLFA and PLFA 16:1ω5), spore extraction and Trypan Blue staining. We hypothesised that deforestation would cause a decline in fungal abundance. As expected, slash-and-burn practices caused increased pH and pyromineralization to double plant available nutrients quantities in soil (soil extractable phosphate (μg/g) went from 7.4 to 13.1, and soil nitrate (μg/g) went from 6.9 to 13.2). Deforestation did not affect levels of soil ammonium, probably due to volatilization and increased nitrification in deforested areas. Contrary to expectations, total C and total N increased in deforested soil (respectively, from 0.6% to 0.84% and from 0.06% to 0.08%), likely caused by incorporation of ash, burned and unburned residues to an otherwise poor mineral soil. Significant decline in AM fungi abundance in soil was only observed in NLFA 16:1ω5 (from 0.2 to 0.12 nmol/g). Hyphal network destruction and removal of plant hosts is hypothesised to be behind the observed reduction. AM fungi abundance in D. madagascariensis roots was also negatively affected, colonization levels decreased from 27.7% to 16.9% and NLFA 16:1ω5 decreased from 75.7 to 19 nmol/g of dried root. Together with hyphal network disruption, increased nutrient availability is proposed as an additional explanation behind AM symbiosis decline in D. madagascariensis. AM fungi spore density in soil was found to be unaffected. This is the first study to report such an event in Madagascar south-western ecosystems. We propose additional research to disentangle predominant factors driving observed trends and further study on the potential effects of secondary plant succession on deforested land.

Popular science summary:

Effects of slash-and-burn in a forest of South-West Madagascar

Deforestation and the use of fire to clear land have drastic effects on ecosystem functioning and endanger many important services that healthy ecosystems provide. This is especially the case in many tropical countries. In this study we evaluated the effects of slash-and-burn, a kind of forest clearing, in the dry Spiny Forest of south-western Madagascar. This is a forest of great biodiversity value, with 90% of its species existing nowhere else in the world. In particular, we looked at changes in soil nutrient levels, which are an important indicator of nutrient cycles. We also analysed arbuscular mycorrhizal (AM) fungi abundance, an important symbiont of land plants, which helps them with nutrient absorption and resistance to stress. Slash-and-burn caused plant available nutrients, phosphate and nitrate, to double their quantities in the soil. Contrary to expectations, carbon and total nitrogen increased in deforested soil, probably caused by incorporation of unburned residues and black carbon to the poor mineral soil. Significant decline in AM fungi abundance in soil was observed, probably due to destruction of the fungi network and removal of plant hosts. AM fungi spore density in soil didn’t change however. We also found that AM fungi abundance in the roots forest tree went down, likely due to hyphal network disruption and increased nutrient availability. As soil nutrients are more available, the plant may not find it so advantageous to exchange its own carbon for those nutrients provided by the AM fungi. This study is the first investigation into the effects of slash-and-burn practices on soil chemistry and arbuscular mycorrhizal fungi abundance in this ecosystem. Results show clear effects of the practices used by the inhabitants of this region on soil and AM fungi. Further studies are needed to asses the dynamics of nutrient stocks and arbuscular mycorrhizal fungi and their response to seasonality and vegetation cover changes across a larger time scale. Given the high originality of this endangered ecosystem such knowledge is essential in order to understand and predict the future direction of vegetation patterns and ecosystem resilience to human action.


Advisor: Pal Axel Olsson
Master´s Degree Project 45 credits in Plant Ecology 2013
Department of Biology, Lund University and Systematics},
  author       = {Donnellan Barraclough, Alicia},
  language     = {eng},
  note         = {Student Paper},
  title        = {Effects of slash-and-burn on soil chemistry and arbuscular mycorrhizal fungi abundance in soil and roots of Didierea Madagascariensis, in the dry tropical Spiny Forest of South-West Madagascar},
  year         = {2013},
}