Leaf, xylem and phloem areas drive the water and carbon fluxes within branches and trees, but their mutual coordination is poorly understood. We test the hypothesis that xylem and phloem areas ...increase relative to leaf area when species are selected for, or branches are exposed to, higher levels of light intensity. Trees of 10 temperate, broadleaved and deciduous, tree species were selected. Fifty‐centimetre‐long branches were collected from shaded and exposed conditions at a height of 3–4 m. We measured the total leaf area, xylem area, phloem area and leaf traits, as well as the area of the constituent cell types, for a stem section at the branch base. Xylem area : leaf area and phloem area : leaf area ratios did not differ consistently between sun and shade branches, but, as expected, they decreased with species' shade tolerance. Similar trends were observed for conductive cell areas in xylem and phloem. Trees of light‐demanding species maintain higher water loss and carbon gain rates per leaf area by producing more xylem area and phloem area than shade‐tolerant species. We call for more comparative branch studies as they provide an integrated biological perspective on functional traits and their role in the ecology of tree species.
Oak wood was highly appreciated and widely used for construction in past centuries. As population sizes expanded in some regions of Europe, local forests were depleted of high-quality timber. ...Therefore, regions of soaring economies were importing timber initially from the European market and eventually from other continents. Origin of archaeological or historical timber is usually identified by means of dendroprovenancing, i.e. statistical matching of tree-ring-width (TRW) series of timber of unknown origin with TRW reference datasets. However, this method has pitfalls and limitations and therefore alternative techniques are needed. Here, we used three different DNA analysis methods to investigate the potential of using ancient (a)DNA, extracted from oak timber derived from historical buildings and shipwrecks from a variety of countries. All the material had also been analysed dendrochronologically, so its dating and provenance is demonstrated. We included heartwood samples in this analysis, for which DNA extraction is especially challenging as it contains chemicals that inhibit DNA amplification. We succeeded in amplifying DNA for at least one marker from 56% of samples (including heartwood samples), yielding crucial information that allowed us to identify the potential source area of centuries old timber buildings in Latvia and Denmark and of 750-year-old shipwreck material from Germany. Our results prove the strong potential of DNA analyses for identifying timber origin to the regional scale, but by combining these with the dendrochronological results, we can control the exactitude of the aDNA approach and demonstrate a more nuanced examination of the timber sources for these historic structures.
Spring flooding in riparian forests can cause significant reductions in earlywood-vessel size in submerged stem parts of ring-porous tree species, leading to the presence of 'flood rings' that can be ...used as a proxy to reconstruct past flooding events, potentially over millennia. The mechanism of flood-ring formation and the relation with timing and duration of flooding are still to be elucidated. In this study, we experimentally flooded 4-year-old Quercus robur trees at three spring phenophases (late bud dormancy, budswell, and internode expansion) and over different flooding durations (2, 4, and 6 weeks) to a stem height of 50 cm. The effect of flooding on root and vessel development was assessed immediately after the flooding treatment and at the end of the growing season. Ring width and earlywood-vessel size and density were measured at 25- and 75-cm stem height and collapsed vessels were recorded. Stem flooding inhibited earlywood-vessel development in flooded stem parts. In addition, flooding upon budswell and internode expansion led to collapsed earlywood vessels below the water level. At the end of the growing season, mean earlywood-vessel size in the flooded stem parts (upon budswell and internode expansion) was always reduced by approximately 50% compared to non-flooded stem parts and 55% compared to control trees. This reduction was already present 2 weeks after flooding and occurred independent of flooding duration. Stem and root flooding were associated with significant root dieback after 4 and 6 weeks and mean radial growth was always reduced with increasing flooding duration. By comparing stem and root flooding, we conclude that flood rings only occur after stem flooding. As earlywood-vessel development was hampered during flooding, a considerable number of narrow earlywood vessels present later in the season, must have been formed after the actual flooding events. Our study indicates that root dieback, together with strongly reduced hydraulic conductivity due to anomalously narrow earlywood vessels in flooded stem parts, contribute to reduced radial growth after flooding events. Our findings support the value of flood rings to reconstruct spring flooding events that occurred prior to instrumental flood records.
Trees scale leaf (A
L) and xylem (A
X) areas to couple leaf transpiration and carbon gain with xylem water transport. Some species are known to acclimate in A
L : A
X balance in response to climate ...conditions, but whether trees of different species acclimate in A
L : A
X in similar ways over their entire (continental) distributions is unknown.
We analyzed the species and climate effects on the scaling of A
L vs A
X in branches of conifers (Pinus sylvestris, Picea abies) and broadleaved (Betula pendula, Populus tremula) sampled across a continental wide transect in Europe.
Along the branch axis, A
L and A
X change in equal proportion (isometric scaling: b ~ 1) as for trees. Branches of similar length converged in the scaling of A
L vs A
X with an exponent of b = 0.58 across European climates irrespective of species. Branches of slow-growing trees from Northern and Southern regions preferentially allocated into new leaf rather than xylem area, with older xylem rings contributing to maintaining total xylem conductivity.
In conclusion, trees in contrasting climates adjust their functional balance between water transport and leaf transpiration by maintaining biomass allocation to leaves, and adjusting their growth rate and xylem production to maintain xylem conductance.
Forests of the future need to cope with adverse climatic conditions, in particular drought, to ensure forest stability and productivity. Given the usually long rotation period of forests, forest ...managers need to select appropriate, i.e. productive and climate-change resilient tree species and/or provenances, to lower tree-mortality risks and sustain current wood production rates at the end of the 21st century. A frequent means of assessing which provenances of a given species are adapted to anticipated climate conditions is common garden experiments, where trees from different provenances are planted under similar climate conditions. However, in this context soil conditions also play an important role, since they govern how climate translates into plant-available water and hence plant’s ability to cope with extreme drought events. Here, we examine the effects of soil conditions on pedunculate oak (Quercus robur L.), by studying 10 different Dutch oak provenances that were planted in three provenance trials on different soil types in 1988 in the Netherlands. Using dendroecological methods, we quantified provenance-specific productivity and assessed provenance- and site-specific growth patterns. Our results indicated clear differences in productivity among provenances as well as soil-type specific growth patterns. Consequently, our study highlights the importance of incorporating soil characteristics when evaluating the growth performance of provenances within common garden experiments.
During winter dormancy, temperate trees are capable of only a restricted response to wounding. Depending on the ambient temperature during winter dormancy, wounded trees may start ...compartmentalization, e.g. by producing inhibitory compounds, but it is thought that processes involving cell proliferation, such as the formation of callus and wound xylem, are delayed until the next growing season. We investigated the effect of two contrasting temperature regimes on early reactions of Acer palmatum trees to wounding during winter bud dormancy. Stems of A. palmatum trees were wounded and stored under an ambient temperature of 4 or 15 °C for 3 weeks during winter bud dormancy. We then studied wound reactions in the living bark, cambial region and xylem. In the 4 °C treatment, wound reactions were virtually absent. In the 15 °C treatment, however, trees reacted to wounding by dieback of the cortex and phloem and by the formation of ligno-suberized layers. In the cambial zone, cambial dieback occurred and callus tissue and wound xylem were formed locally, close to the wound margins. In the xylem, compartmentalization took place by deposition of inhibitory compounds in fibre cells and vessel elements. We conclude that temperature is an important factor in wound reactions during winter dormancy, and may even induce proliferation of callus and wound xylem within a 3-week period. It therefore seems likely that trees that have been wounded during dormancy in areas with mild or warm winters might cope better with wounding, as unlike trees in cold environments, they may compartmentalize wounds even during winter dormancy.
Ash dieback caused by the invasive fungus Hymenoscyphus fraxineus leads to massive mortality among common ash (Fraxinus excelsior) in Europe. To select tolerant genotypes, inoculation experiments are ...frequently conducted with isolates of the fungus. The aim of this study was to improve the inoculation methodology for evaluating susceptibility of ash genotypes to ash dieback through (i) testing the virulence of different isolates of Hymenoscyphus fraxineus and (ii) investigating temporal lesion development using three widely applied cultivars: Altena, Atlas and Westhof's Glorie. First, an experiment was conducted with a repeated measure design in which virulence of five different isolates was tested. Second, a subset of two isolates that induced the longest downward lesion length in experiment one was used in combination with a slightly adjusted inoculum protocol. Significant differences were found between isolates for downward lesion length, but a significant interaction effect of isolates and cultivars was absent. Also, the inoculation position within the stem affected lesion length; the largest lesions were found on the highest inoculation position within the stem. Furthermore, we found that cryopreserved isolates can remain virulent over years. The timing of inoculation at the end of the growing season was effective as large lesions already occurred during winter dormancy. For future inoculation studies, we propose to use: (i) isolates that induce large lesions, as less virulent isolates induced not only shorter but also fewer lesions; (ii) a similar inoculation position to better compare inoculations within and between experiments; (iii) cryopreserved isolates for testing over years; (iv) mycelial suspensions for inoculum preparation to cover wood chips more evenly; (v) reference clone—like the studied cultivars—to standardize research outcomes between years and research groups.
In trees, stem diameter variations are related to changes in stem water content, because internally stored water is depleted and replenished over a day. To confirm this relationship, non-invasive ...magnetic resonance imaging (MRI) was combined with point dendrometer measurements in three actively transpiring oak (Quercus roburL.) trees. Two of these oak trees were girdled to study the stem increment above the girdling zone. MRI images and micrographs of stem cross-sections revealed a close link between the water distribution and the anatomical features of the stem. Stem tissues with the highest amount of water were physiologically the most active ones, being the youngest differentiating xylem cells, the cambium and the youngest differentiating and conductive phloem cells. Daily changes in stem diameter corresponded well with the simultaneously MRI-measured amount of water, confirming their strong interdependence. MRI images also revealed that the amount of water in the elastic bark tissues, excluding cambium and the youngest phloem, contributed most to the daily stem diameter changes. After bark removal, an additional increase in stem diameter was measured above the girdle. This increase was attributed not only to the cambial production of new cells, but also to swelling of existing bark cells. In conclusion, the comparison of MRI and dendrometer measurements confirmed previous interpretations and applications of dendrometers and illustrates the additional and complementary information MRI can reveal regarding water relations in plants.
Combatting illegal timber trade requires forensic tools that independently verify claimed geographic origin of timber. Chemical and genetic wood characteristics are potentially suitable tools, but ...their performance at small spatial scales is unknown. Here we test whether stable isotopes and microsatellites can differentiate Tali timber (Erythrophleum spp.) at the level of forest concessions. We collected 394 wood samples from 134 individuals in five concessions in Cameroon and Congo Republic. The nearest neighbour concessions were 14 km apart and the furthest pair 836 km apart. We constructed genetic profiles using eight nuclear microsatellite markers and measured concentrations of δ18O, δ15N and δ13C. We differentiated provenances using PCA (microsatellites), ANOVA and kernel discriminant analysis (isotopes). Next, we performed assignment tests using blind samples (n = 12, microsatellites) and leave one out cross validation (LOOCV, isotopes). Isotopic composition varied strongly within concessions and only δ13C differed significantly between two concessions. As a result, LOOCV performed only marginally better than random. Genetic differentiation among provenances was also relatively low, but private alleles were commonly found. Bayesian clustering analysis correctly assigned 92% of the blind samples, including those of nearby concessions. Thus, Tali timber can be successfully assigned to the concession of origin using genetic markers, but not using isotopic composition. Isotopic differentiation may be possible at larger spatial scales or with stronger climatic or topographic variation. Our study shows that genetic analyses can differentiate the geographic origin of tropical timber at the scale of forest concessions, demonstrating their potential as forensic tools to enforce timber trade legislation.
Groundwater-dependent ecosystems occur in arid and semi-arid areas worldwide and are sensitive to changes in groundwater availability. Prosopis tamarugo Phil, endemic to the Atacama Desert, is ...threatened by groundwater overexploitation due to mining and urban consumption. The effect of groundwater depletion on two representative sites (low -and high-depletion) was studied using a multi-scale approach, combining remote sensing based estimations of canopy growth and water condition, and tree-ring based analysis of stem growth. On the stand level two NDVI (Normalized Difference Vegetation Index) -derived parameters: NDVI in winter and the difference between NDVI in summer and winter showed significant negative trends in the high-depletion site, indicating drought stress. Radial stem growth of viable P. tamarugo trees was 48% lower in the high-depletion site. At the tree level, the Green Canopy Fraction (GCF) also indicated drought stress since a larger percentage of trees fell within lower GCF classes. Groundwater depletion of 3 m, reaching a groundwater depth of >10 m, increased drought stress, and led to reduced growth in viable trees. Viable trees may be able to adapt to the drop in groundwater levels by increasing root growth, whereas for non-viable trees, the effects might be detrimental.
•Analysis of groundwater depletion in the Atacama Desert; the effects on tree growth.•Remote sensing metrics indicated reduced crown viability and growth.•Groundwater depletion resulted in a decrease of 48% radial stem growth.
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