Hortensia Sixto

Performance of hybrid poplar clones in short rotation coppice in Mediterranean environments: analysis of genotypic stability

Improving production in short rotation coppice (SRC) plantations requires, among other elements, a proper understanding of clonal performance. Genotypic stability over a range of environments is a factor of concern for breeding and recommendation purposes. Most common stability measures can be embedded in a mixed‐model framework accounting for interaction and heterocedasticity in genotype‐by‐environment tables. Data from nine hybrid poplars of different taxonomic background were tested in four Mediterranean sites under three agronomic practices (control, herbicide application, and supplementary fertilization) for total biomass (TB), stem biomass (SB), and branch biomass (BB) at the end of the first rotation. Stability models (stability variance, Finlay–Wilkinson and Eberhart–Russell) were compared, also allowing for the definition of groups of genotypes with distinct taxonomic backgrounds and a priori different variabilities. Results showed that genotype‐by‐environment (GE) interactions were associated with factors inherent to evaluation sites rather than to the agronomic practices tested. Depending on biomass fraction, regression models provided appropriate stability measures. Highly reactive clones to improving environmental conditions (e.g., ‘AF2’) tended to show the largest mean TB. However, this was not always the case, as clone ‘Monviso’ showed both intermediate reactivity (i.e., stable sensu Eberhart–Russell) and enhanced overall performance. The taxonomic group was relevant for explaining stability patterns for SB. The stability assessment for BB indicated different patterns in biomass allocation. Present findings point to the feasibility of either exploiting specific adaptation (in which case hybrid type may play a relevant role) or searching for broadly adapted, stable material exhibiting good performance in Mediterranean conditions.

Biomass production assessment from Populus spp. short‐rotation irrigated crops in Spain

The aim of this study was to evaluate the biomass production potential for the Spanish Iberian Peninsula using the Populus spp. ‘I‐214’ clone under several management regimes and land availability scenarios, and to determine its future contribution to Spanish energy demands.

On the site-level suitability of biomass models

Tree biomass estimates in environmental studies are based on allometric models, which are known to vary with species, site, and other forest characteristics. The UNFCCC published a guideline to evaluate the appropriateness of biomass models before application, but it misleads the concept of model suitability and does also allow the selection of models with systematic deviations in the predictions. Here we present an alternative approach based on non-parametric techniques. The approach was tested for pure stands, but this methodology is likewise applicable to mixed forests. The proposed tests perform well in rejecting a model if the predictions for the targeted population are systematically deviant. It is demonstrated that the suitability of an allometric model is a matter of accuracy. The proposed method also allows localizing the model. The presented approach can improve the transparency of global forest monitoring systems and can be implemented with relatively small effort. Biomass model suitability is often judged by the fitting statistics of the model.Characteristics of the local population are usually ignored in suitability checking.We propose statistical test to evaluate the suitability of biomass models.Biomass model suitability is a matter of accuracy and not precision.A new approach to evaluate model suitability based on statistical tests is presented.

Interpreting genotype‐by‐environment interaction for biomass production in hybrid poplars under short‐rotation coppice in Mediterranean environments

Understanding genotype × environment interaction (GEI) is crucial to optimize the deployment of clonal material to field conditions in short‐rotation coppice poplar plantations. Hybrid poplars are grown for biomass production under a wide range of climatic and edaphic conditions, but their adaptive performance in Mediterranean areas remains poorly characterized. In this work, site regression (SREG) and factorial regression mixed models are combined to gain insight into the nature and causes underlying GEI for biomass production of hybrid poplar clones. SREG addresses the issue of clonal recommendation in multi‐environment trials through a biplot representation that visually identifies superior genotypes. Factorial regression, alternatively, involves a description of clonal reaction to the environment in terms of physical variables that directly affect productivity. Initially, SREG aided in identifying cross‐over interactions that often involved hybrids of different taxonomic background. Factorial regression then selected latitude, mean temperature of the vegetative period (MTVP) and soil sand content as main site factors responsible for differential clonal adaptation. Genotypic responses depended strongly on taxonomic background: P. deltoides Bartr. ex Marsh. × P. nigra L. clones showed an overall positive sensitivity to increased MTVP and negative sensitivity to increased sand content, whereas the opposite occurred for P. trichocarpa Torr. & Gray × P. deltoides clones; the three‐cross hybrid [(P. deltoides × P. trichocarpa) × P. nigra] often displayed an intermediate performance. This information can contribute toward the identification and biological understanding of adaptive characteristics relevant for poplar breeding in Mediterranean conditions and facilitate clonal recommendation at eco‐regional level.

On the Genetic Affinity of Individual Tree Biomass Allometry in Poplar Short Rotation Coppice

Woody biomass is one of our main resources available to enhance the bio-economy, but its production varies considerably depending on the species, the environment and crop management. The variability associated with these crops complicates the estimation of biomass through prediction models. The specificity of environment or genotype level limits the application of many of the models, which are often developed for use at local geographical levels. Although generalizations involve some loss of accuracy, the inclusion of a wide range of data for a wide range of environments and genotypes can improve model applicability. A total of 11,265 data from short-rotation, high-density poplar plantations (from 22 sites in Spain, covering 29 genotypes belonging to 7 different taxonomic groups) were used to develop biomass prediction models under Mediterranean conditions and to test whether similarities in individual tree biomass allometry occur within the taxonomic group level. A general model and both taxonomic group- and genotype-level models were fitted using weighted nonlinear regression. The simplified model, in which only the basal diameter is included, presented the best model performance, explaining 87% of the variability. The allometric similarities among different genotypes were evaluated in order to explore the relationship between the most frequently used poplar genotypes in the Mediterranean area, and although certain groups were identified, it was not possible to relate these similarities among different genotypes to their taxonomic group affinity. This was also confirmed by comparing the performance of the general models with the taxonomic group-level models when predicting at the genotype level. Although estimates made using the general models are relatively precise, the use of genotype-level models is recommended for more accurate predictions.

Impact of RAV1-engineering on poplar biomass production: a short-rotation coppice field trial

BackgroundEarly branching or syllepsis has been positively correlated with high biomass yields in short-rotation coppice (SRC) poplar plantations, which could represent an important lignocellulosic feedstock for the production of second-generation bioenergy. In prior work, we generated hybrid poplars overexpressing the chestnut gene RELATED TO ABI3/VP1 1 (CsRAV1), which featured c. 80% more sylleptic branches than non-modified trees in growth chambers. Given the high plasticity of syllepsis, we established a field trial to monitor the performance of these trees under outdoor conditions and a SRC management.ResultsWe examined two CsRAV1-overexpression poplar events for their ability to maintain syllepsis and their potential to enhance biomass production. Two poplar events with reduced expression of the CsRAV1 homologous poplar genes PtaRAV1 and PtaRAV2 were also included in the trial. Under our culture conditions, CsRAV1-overexpression poplars continued developing syllepsis over two cultivation cycles. Biomass production increased on completion of the first cycle for one of the overexpression events, showing unaltered structural, chemical, or combustion wood properties. On completion of the second cycle, aerial growth and biomass yields of both overexpression events were reduced as compared to the control.ConclusionsThese findings support the potential application of CsRAV1-overexpression to increase syllepsis in commercial elite trees without changing their wood quality. However, the syllepsis triggered by the introduction of this genetic modification appeared not to be sufficient to sustain and enhance biomass production.

Control de malas hierbas en viveros de chopo mediante la aplicación de herbicidas

Se estudia la respuesta de cinco herbicidas de preemergencia (Oxadiazon, Isoxaben, Oxifluorfen, Tiazopir y Pendimetalina) sobre estaquillados de chopo sin brotar en condiciones de vivero. Para evaluar cuantitativamente la selectividad y la eficacia de los tratamientos herbicidas, se considero la altura de los arboles, asi como el peso seco de la hierba presente. Se identificaron las especies y se valoro su presencia en los tratamientos. El control de la flora adventicia fue satisfactorio en todos los viveros ensayados, con la excepcion de Stellaria media (L.) Vill, cuando se aplico Oxadiazon. No se apreciaron sintomas fitotoxicos significativos en las plantas de chopo para ninguno de los herbicidas ensayados.