Linking wood anatomy and xylogenesis allows pinpointing of climate and drought influences on growth of coexisting conifers in continental Mediterranean climate

Abstract

Forecasted warmer and drier conditions will probably lead to reduced growth rates and decreased carbon fixation in long-term woody pools in drought-prone areas. We therefore need a better understanding of how climate stressors such as drought constrain wood formation and drive changes in wood anatomy. Drying trends could lead to reduced growth if they are more intense in spring, when radial growth rates of conifers in continental Mediterranean climates peak. Since tree species from the aforementioned areas have to endure dry summers and also cold winters, we chose two coexisting species: Aleppo pine (Pinus halepensisMill., Pinaceae) and Spanish juniper (Juniperus thuriferaL., Cupressaceae) (10 randomly selected trees per species), to analyze how growth (tree-ring width) and wood-anatomical traits (lumen transversal area, cell-wall thickness, presence of intra-annual density fluctuations-IADFs-in the latewood) responded to climatic variables (minimum and maximum temperatures, precipitation, soil moisture deficit) calculated for different time intervals. Tree-ring width and mean lumen area showed similar year-to-year variability, which indicates that they encoded similar climatic signals. Wet and cool late-winter to early-spring conditions increased lumen area expansion, particularly in pine. In juniper, cell-wall thickness increased when early summer conditions became drier and the frequency of latewood IADFs increased in parallel with late-summer to early-autumn wet conditions. Thus, latewood IADFs of the juniper capture increased water availability during the late growing season, which is reflected in larger tracheid lumens. Soil water availability was one of the main drivers of wood formation and radial growth for the two species. These analyses allow long-term (several decades) growth and wood-anatomical responses to climate to be inferred at intra-annual scales, which agree with the growing patterns already described by xylogenesis approaches for the same species. A plastic bimodal growth behavior, driven by dry summer conditions, is coherent with the presented wood-anatomical data. The different wood-anatomical responses to drought stress are observed as IADFs with contrasting characteristics and responses to climate. These different responses suggest distinct capacities to access soil water between the two conifer species.

Wood Cellular Dendroclimatology: Testing New Proxies in Great Basin Bristlecone Pine

“…In our dataset, ar1 of most anatomical parameters was lower than for ring-width chronologies, as intra-annual tracheids are largely affected by environmental conditions at the time of their formation, in particular the tree hydration status (Steppe et al, 2015). Reduced ar1 in anatomical time series (i.e., tracheid and vessel size) compared to ring-width series has been in fact reported in conifers (Pritzkow et al, 2014; Pacheco et al, 2016) and in hardwoods (García-González and Eckstein, 2003; Fonti and García-González, 2008). The values of ar1 for the chronologies of DWT and LW can be explained considering the seasonal dynamics of wood formation.…”

“…The ecological meaning of climate-anatomy relationships can be better understood if integrated with information on xylem phenology (e.g., the timing of wood formation) and intra-annual dynamics of stem growth obtained by repeated microcoring and dendrometer records (Rossi et al, 2012; Cocozza et al, 2016; Pacheco et al, 2016). In a study recently conducted at the same site (Ziaco et al, 2016), production of new tracheids in bristlecone pine during two consecutive years (2013–2014) started at the beginning of June, immediately after snowmelt, peaked in late June, and wood formation ended in mid-September.…”

“…March precipitation at the study area is important to recharge soil water, providing trees with moisture needed in the first phases of xylogenesis for maintaining cellular turgor (Turcotte et al, 2009). Summer precipitation relieves water stress and increases the margins for hydraulic safety, leading to the formation of larger cellular elements (Martin-Benito et al, 2013; Ziaco et al, 2014; Pacheco et al, 2016). It should also be noted that at high elevation (i.e., near treeline), reduced lumen sizes can also be interpreted as an adaptation of bristlecone pine to reduce the risk of freezing-induced embolisms (Pittermann and Sperry, 2003).…”

Wood anatomy and carbon‐isotope discrimination support long‐term hydraulic deterioration as a major cause of drought‐induced dieback

“…This separation was preferred over the delineation based on the Mork index (Denne, 1988) for its higher efficiency in defining earlywood and latewood in conifers within the Mediterranean region (e.g. Pacheco et al, 2015). Variables measured included ring width, number of tracheids forming a ring, their mean lumen area and cell-wall thickness (henceforth CWT), computed as the average between the tangential and radial thicknesses.…”

Retrospective Analysis of Wood Anatomical Traits Reveals a Recent Extension in Tree Cambial Activity in Two High-Elevation Conifers

“…Since both the dendroanatomical and xylogenetic approaches operate at cellular level, relating dendroanatomy to key environmental factors might also allow inferences on cambial activity to be extended from a few years to decades. However, up to now, only a few empirical studies have explored long-term effects of climate variability on the corresponding year-to-year change in wood anatomical traits and the related consequences for conifer tree physiology and growth (Olano et al, 2012; Fonti et al, 2013; Pacheco et al, 2016; Pellizzari et al, 2016). Furthermore, most of these investigations usually adopted a classical dendroclimatological approach to define the associations between climate and wood-anatomical parameters (e.g., using monthly resolved weather records and averaging the anatomical properties of the whole rings), therefore remaining disconnected from the cambium dynamics studies in terms of temporal resolution.…”