Tree or shrub: a functional branch analysis of Jatropha curcas L.

Abstract

Jatropha curcas is an oil-bearing semievergreen shrub or small tree with potential as a source of sustainable biofuel, yet information regarding vegetative and fruit biomass in relation to plant architecture is lacking. Research conducted in Indonesia used the tree based functional branch analysis (FBA) model as a non-destructive method to estimate above and belowground biomass, and plant architecture. The FBA utility for shrubs was unknown and required modification. This research used destructive measurements to validate modifications to the FBA model that included subcategorisation of the tapering coefficient for twig, branch, and wood diameter classes, and addition of a fruit load parameter in the distal link. The modified FBA model confirmed jatropha to be a shrub rather than a tree, producing variable estimates for aboveground biomass. This variation was due to morphological plasticity in the length-diameter relationship of the branches that diverged from fractal branching architecture. Fruit biomass variation between replicates was not well estimated and total proximal root diameter was a poor predictor of total root biomass, due to the proximal roots having enlarged water storage structures that do not follow fractal branching assumptions. Jatropha fruit was shown to predominate on twigs with a diameter between 0.9 and 1.4 cm. Understanding the correlation between fruit development and plant architecture will be necessary for fine-tuning the FBA model for future commercial breeding and selection. The high degree of morphological plasticity displayed by jatropha requires consideration when determining plant biomass.

Relationships among Jatropha curcas seed yield and vegetative plant components under different management and cropping systems in Indonesia

“…In a previous study [19] of unpruned jatropha (n ¼ 10) in four-year-old monoculture plantings, above-ground biomass allocation to different plant parts shows the partitioning to fruit is 1%, to leaf 8%, and to stem, branch and twig is 91%. It is therefore not surprising that pruning influences vegetative structures as opposed to generative and yield, as was shown in the second hedge experiment (Fig.…”

“…Average stem diameters at 10 cm and 15 cm above ground were used as independent variables in allometric equations to calculate total above-ground biomass, branch, twig, leaf and fruit biomass [19]. Canopy width and height were used to calculate canopy volume when the canopy was considered ellipsoid [31].…”

“…Wood has diameter !7 cm, branch a diameter ranging from 2 cm to 6.99 cm, and twig category a diameter 1.99 cm. We found that jatropha fruit develop on twigs that in the majority of cases have diameters ranging from 0.9 cm to 1.4 cm [19]. We named these twigs, fruit-bearing or productive twigs as opposed to nonproductive twigs.…”

“…In an earlier study of four-year-old jatropha at Gunungkidul in Indonesia, we determined above-ground and fruit biomass allocation relative to plant architecture using Functional Branch Analysis (FBA) [19]. Using the FBA model, we classified the plant into three categories, wood, branch, and twig according to diameter size.…”

“…Our previous findings were based on unpruned monocultures of jatropha [19] and have not been tested in different management or cropping systems. For these reasons, the aim of this study was to determine jatropha seed yield, and to identify the vegetative plant components that influence seed yield under different management and cropping systems.…”