19The interest in using Jatropha curcas L. (JCL) as a feed stock for the production of 20 bio-diesel is rapidly growing. The properties of the crop and its oil have persuaded 21 investors, policy makers and Clean Development Mechanism (CDM) project developers to 22 consider JCL as a substitute for fossil fuels to reduce greenhouse gas emissions. However, 23 JCL is still a wild plant of which basic agronomic properties are not thoroughly understood 24 and the environmental effects have not been investigated yet. Gray literature reports are 25 very optimistic on simultaneous wasteland reclamation capability and oil yields, further 26 fueling the Jatropha bio-diesel hype. In this paper, we give an overview of the currently 27 available information on the different process steps of the production process of bio-diesel 28 from JCL, being cultivation and production of seeds, extraction of the oil, conversion to 29 and the use of the bio-diesel and the by-products. Based on this collection of data and 30 information the best available practice, the shortcomings and the potential environmental 31 risks and benefits are discussed for each production step. The review concludes with a call 32 for general precaution and for science to be applied. 33 34 Keywords 35Jatropha curcas; physic nut; cultivation; bio-energy; energy conversion, bio-fuel; 36 environmental impact; greenhouse gas balance; land use impact; human health 37 2

(250 words) 21Jatropha curcas is a multipurpose, drought resistant, bio-fuel tree originating from Central 22and South America, but now growing pantropic. The tree produces seeds containing 27-23 40% inedible oil, which is easily convertible into bio-diesel. Although even some basic 24 agronomic characteristics of J. curcas are not yet fully understood, the plant enjoys a 25 booming interest, which may hold the risk of unsustainable practice. Our qualitative 26 sustainability assessment, focusing on environmental impacts and strengthened by some 27 socio-economic issues, is quite favorable as long as only wastelands or degraded grounds 28 are taken into J. curcas cultivation. Preliminary life cycle energy and GHG balances are 29 positive, but the GHG balance is expected to be much dependent on the type of land use 30 which is converted to J. curcas. Removing natural forest will have a severe impact on the 31 global warming potential of the Jatropha bio-diesel. The cultivation intensity and the 32 distance to markets is expected to have a significant impact on the GHG balance as well. 33 Similar reasoning applies for the impact on soil, water, vegetation structure and 34 biodiversity, although the latter will always depend on local circumstances. Next to bio-35 diesel production and wasteland reclamation, J. curcas also hosts socio-economic 36 development potential. The multipurpose character of the plant and the labour intensive 37 production chain are thought to be the main drivers for rural development, but are 38

In a greenhouse experiment we applied three levels of drought stress and monitored growth variables and biomass production of J. curcas seedlings propagated from three seed accessions. We determined biomass allocation, allometric relationships and plant traits. Well-watered J. curcas seedlings grew 0.81±0.15 cm day -1 in length and produced 1.49±0.31 g dry biomass day -1 . Under medium stress (40% plant available water) the plants maintained a similar stem shape, although they grew at lower rate (stem length: 0.28±0.11 cm day -1 ; dry biomass production: 0.64±0.18 g day -1 ). Seedlings under extreme drought stress (no irrigation) stopped growing, started shedding leaves and showed shrinking stem diameter from the 12 th day after the start of the drought treatment.The drought treatment did not influence the wood density (0.26 g cm -3 ). The root/shoot ratio of the wet treatment was 0.27, which is low compared to other tropical trees. Both 3

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