ALBERT

Description: 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 (MET) 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 at 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 towards the identification and biological understanding of adaptive characteristics relevant for poplar breeding in Mediterranean conditions and facilitate clonal recommendation at eco-regional level. This article is protected by copyright. All rights reserved.

Description: [1]  Stable isotopes in tree rings provide climatic information with annual resolution dating back for centuries or even millennia. However, deriving spatially explicit climate models from isotope networks remains challenging. Here we propose a methodology to model regional precipitation from carbon isotope discrimination (Δ 13 C) in tree rings by (1) building regional spatial models of Δ 13 C ( isoscapes ), and (2) deriving precipitation maps from Δ 13 C-isoscapes, taking advantage of the response of Δ 13 C to precipitation in seasonally-dry climates. As a case study, we modeled the spatial distribution of mean annual precipitation (MAP) in the northeastern Iberian Peninsula, a region with complex topography and climate (MAP = 303–1086 mm). We compiled wood Δ 13 C data for two Mediterranean species that exhibit complementary responses to seasonal precipitation ( Pinus halepensis Mill., N = 38; Quercus ilex L.; N = 44; pooling period: 1975–2008). By combining multiple regression and geostatistical interpolation, we generated one Δ 13 C-isoscape for each species. A spatial model of MAP was then built as the sum of two complementary maps of seasonal precipitation, each one derived from the corresponding Δ 13 C-isoscape (September–November from Q. ilex ; December–August from P. halepensis ). Our approach showed a predictive power for MAP (RMSE = 84 mm) nearly identical to that obtained by interpolating data directly from a similarly dense network of meteorological stations (RMSE = 80–83 mm, N = 65), being only outperformed when using a much denser meteorological network (RMSE = 56–57 mm, N = 340). This method offers new avenues for modeling spatial variability of past precipitation, exploiting the large amount of information currently available from tree-ring networks.

Description: Vegetation in water-limited ecosystems relies strongly on access to deep water reserves to withstand dry periods. Most of these ecosystems have shallow soils over deep groundwater reserves. Understanding the functioning and functional plasticity of species-specific root systems and the patterns of or differences in the use of water sources under more frequent or intense droughts is therefore necessary to properly predict the responses of seasonally dry ecosystems to future climate. We used stable isotopes to investigate the seasonal patterns of water uptake by a sclerophyll forest on sloped terrain with shallow soils. We assessed the effect of a long-term experimental drought (12 years) and the added impact of an extreme natural drought that produced widespread tree mortality and crown defoliation. The dominant species, Quercus ilex , Arbutus unedo and Phillyrea latifolia , all have dimorphic root systems enabling them to access different water sources in space and time. The plants extracted water mainly from the soil in the cold and wet seasons but increased their use of groundwater during the summer drought. Interestingly, the plants subjected to the long-term experimental drought shifted water uptake toward deeper (10-35 cm) soil layers during the wet season and reduced groundwater uptake in summer, indicating plasticity in the functional distribution of fine roots that dampened the effect of our experimental drought over the long term. An extreme drought in 2011, however, further reduced the contribution of deep soil layers and groundwater to transpiration, which resulted in greater crown defoliation in the drought-affected plants. The present study suggests that extreme droughts aggravate moderate but persistent drier conditions (simulated by our manipulation) and may lead to the depletion of water from groundwater reservoirs and weathered bedrock, threatening the preservation of these Mediterranean ecosystems in their current structures and compositions. This article is protected by copyright. All rights reserved.

Description: Article The evolution of agronomic conditions after domestication in the Fertile Crescent remains poorly understood. Here, Araus et al . show that water availability and soil fertility for crops were higher in the past and that domesticated cereals showed a progressive increase in kernel size following domestication. Nature Communications doi: 10.1038/ncomms4953 Authors: José L. Araus, Juan P. Ferrio, Jordi Voltas, Mònica Aguilera, Ramón Buxó

Description: 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.

Description: Abstract Aim The aim was to decipher Europe‐wide spatio‐temporal patterns of forest growth dynamics and their associations with carbon isotope fractionation processes inferred from tree rings as modulated by climate warming. Location Europe and North Africa (30‒70° N, 10° W‒35° E). Time period 1901‒2003. Major taxa studied Temperate and Euro‐Siberian trees. Methods We characterize changes in the relationship between tree growth and carbon isotope fractionation over the 20th century using a European network consisting of 20 site chronologies. Using indexed tree‐ring widths (TRWi), we assess shifts in the temporal coherence of radial growth across sites (synchrony) for five forest ecosystems (Atlantic, boreal, cold continental, Mediterranean and temperate). We also examine whether TRWi shows variable coupling with leaf‐level gas exchange, inferred from indexed carbon isotope discrimination of tree‐ring cellulose (Δ13Ci). Results We find spatial autocorrelation for TRWi and Δ13Ci extending over a maximum of 1,000 km among forest stands. However, growth synchrony is not uniform across Europe, but increases along a latitudinal gradient concurrent with decreasing temperature and evapotranspiration. Latitudinal relationships between TRWi and Δ13Ci (changing from negative to positive southwards) point to drought impairing carbon uptake via stomatal regulation for water saving occurring at forests below 60° N in continental Europe. An increase in forest growth synchrony over the 20th century together with increasingly positive relationships between TRWi and Δ13Ci indicate intensifying impacts of drought on tree performance. These effects are noticeable in drought‐prone biomes (Mediterranean, temperate and cold continental). Main conclusions At the turn of this century, convergence in growth synchrony across European forest ecosystems is coupled with coordinated warming‐induced effects of drought on leaf physiology and tree growth spreading northwards. Such a tendency towards exacerbated moisture‐sensitive growth and physiology could override positive effects of enhanced leaf intercellular CO2 concentrations, possibly resulting in Europe‐wide declines of forest carbon gain in the coming decades.

Description: Forests, Vol. 8, Pages 490: Warming Effects on Pinus sylvestris in the Cold–Dry Siberian Forest–Steppe: Positive or Negative Balance of Trade? Forests doi: 10.3390/f8120490 Authors: Tatiana Shestakova Jordi Voltas Matthias Saurer Rolf Siegwolf Alexander Kirdyanov Understanding climate change impacts on drought-prone forests is a critical issue. We investigated ring-width and stable isotopes (Δ13C and δ18O) in two Pinus sylvestris stands of the cold–dry Siberian forest–steppe growing under contrasting climatic trends over the last 75 years. Despite regional warming, there was increasing precipitation during the growing period at the southern site (MIN) but increasing water deficit (WD) at the northern site (BER). Intrinsic water use efficiency (WUEi) increased similarly (ca. 22%) in response to warming and rising atmospheric CO2. However, the steady increase in WUEi was accompanied by divergent growth patterns since 1980: increasing basal area increment (BAI) in MIN (slope = 0.102 cm2 year−2) and decreasing BAI in BER (slope = −0.129 cm2 year−2). This suggests that increased precipitation, mediated by CO2 effects, promoted growth in MIN, whereas intensified drought stress led to decreased carbon gain and productivity in BER. When compared to warm–dry stands of eastern Spain, the WUEi dependence on WD was three-fold greater in Siberia. Conversely, BAI was more affected by the relative impact of water stress within each region. These results indicate contrasting future trajectories of P. sylvestris forests, which challenge forecasting growth and carbon sequestration in cold–dry areas.