Abstract
Fluctuations in climatic conditions during the growing season are recorded in Mediterranean tree-rings and often result in intra-annual density fluctuations (IADFs). Dendroecology and quantitative wood anatomy analyses were used to characterize the relations between the variability of IADF traits and climatic drivers in Pinus pinaster Aiton and Quercus ilex L. growing at sites with different water availability on the Elba island in Central Italy. Our results showed that both species present high xylem plasticity resulting in the formation of L-type IADFs (L-IADFs), consisting of earlywood-like cells in latewood. The occurrence of such IADFs was linked to rain events following periods of summer drought. The formation of L-IADFs in both species increased the hydraulic conductivity late in the growing season, due to their larger lumen area in comparison to “true latewood”. The two species expressed greater similarity under arid conditions, as unfavorable climates constrained trait variation. Wood density, measured as the percentage of cell walls over total xylem area, IADF frequency, as well as conduit lumen area and vessel frequency, specifically in the hardwood species, proved to be efficient proxies to encode climate signals recorded in the xylem. The response of these anatomical traits to climatic variations was found to be species- and site-specific.
Highlights
Mediterranean ecosystems are characterized by remarkable seasonal fluctuations in water availability during the growing season, which often lead to pronounced drought stress in summer.Intra-seasonal climatic fluctuations are becoming more and more marked as a consequence of ongoing climate change (IPCC, 2018)
The lumen areas of tracheids in rings without intra-annual density fluctuations (IADFs) decreased from earlywood to latewood (Figure 4a,b blue line), while in the rings with IADFs it increased around the 70% of vessels along the tree-ring width (Figure 4a,b red line), where sometimes earlywood-like cells were present
In the Q. ilex growing at wet site, we found a positive correlation between the lumen area of latewood vessels and precipitation in the period from October to December of the previous year (Figure 8a, Region 4, r = 0.256, p < 0.05), and a positive correlation between vessel lumen area of IADF
Summary
Mediterranean ecosystems are characterized by remarkable seasonal fluctuations in water availability during the growing season, which often lead to pronounced drought stress in summer. Fluctuations in climatic conditions during the growing season are recorded in xylem and often result in wood anatomical “anomalies”, changing the aspect of the typical tree-rings formed in temperate regions [15]. Such anomalies, called intra-annual density fluctuations (IADFs), have recently been classified as functional wood traits, as they play a functional role in the tree hydraulic system [15,16]. The study of specific regions within tree-rings has been used to evaluate the influence of environmental conditions on vessel lumen area throughout the growing season [19,34,37,38].
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