Responses of sapwood ray parenchyma and non‐structural carbohydrates of Pinus sylvestris to drought and long‐term irrigation

Abstract

Summary Non‐structural carbohydrates (NSC) play a crucial role in tree resistance and resilience to drought. Stem sapwood parenchyma is among the largest storage tissue for NSC in mature trees. However, there is a limited mechanistic understanding of how NSC reserves, stem parenchyma abundance and growth rates are interrelated, and how they respond to changing water availability. We quantified NSC, ray parenchyma abundance and ring width along four successive 5‐year radial sapwood segments of the stem of 40 mature Pinus sylvestris trees from a 10‐year irrigation experiment conducted at a xeric site in Switzerland. Percentage of ray volume (PERPAR) varied from 3·75 to 8·94% among trees, but showed low intra‐individual variability. PERPAR responded positively to irrigation with a lag of several years, but was unrelated to %NSC. %NSC was lower in wider rings. However, wider rings still contained a larger NSC pool that was positively related to next year's ring growth. Our results suggest that stem ray parenchyma does not limit NSC storage capacity, but responds to long‐term environmental drivers with years of delay. The observed carbon allocation patterns indicate a prioritization of storage over growth independent of growth conditions, likely as a mechanism to ensure long‐term survival. Furthermore, NSC pool size proved to be a determinant for the inter‐annual autocorrelation in tree‐ring growth. Our study highlights the importance of long‐term multi‐parameter studies to better understand tree responses to environmental variability at different time‐scales. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12860/suppinfo is available for this article.

Axial xylem architecture ofLarix deciduaexposed to CO2enrichment and soil warming at the tree line

“…The variability along the stem axis was very large both between and within trees (ranging from 0.12% to 2.55%). This finding confirms previous observations that the ray proportion of conifers varies widely, both among individuals von Arx et al, 2017) and within the stem (Baker et al, 2000;DeSmidt, 1922;von Arx et al, 2015), with only a relatively weak influence of environmental conditions (Esteban, Martín, de Palacios, & Fernández, 2012;Olano et al, 2013) and/or functional needs such as storage space requirements .…”

“…While the cell wall reinforcement ((t/b) 2 ) decreased with tree age but increased with height (Domec et al, 2009). A constant ray area and a decline of ray volume with cambial age was found in previous studies (Baker, Spicer, & Gartner, 2000;Bannan, 1937) but only little information is available on the sensitivity of ray parenchyma tissue to environmental conditions (Olano, Arzac, García-Cervigón, von Arx, & Rozas, 2013;von Arx et al, 2017). Further, there is still a lack of knowledge about how these and other functional traits covary both within the tree (e.g.…”

Homeostatic levels of nonstructural carbohydrates after 13 yr of drought and irrigation inPinus sylvestris

“…Patterns of NSC concentration under long-term drought vs the release of such drought exposure under field conditions have not been extensively studied. We also lack information on the interrelationship between NSC, growth, tissue nutrient concentrations and crown conditions under such long-term drought vs non-drought exposed conditions (but see von Arx et al, 2017). Decreasing leaf area (in some literature, referred to as 'crown transparency', a surrogate for relative leaf area (Dobbertin, 2005;Gottardini et al, 2016)) is correlated with long-term growth decrease , and also with stem sapwood NSC after a drought event (Galiano et al, 2011;Camarero et al, 2015).…”

Rainforest trees respond to drought by modifying their hydraulic architecture

“…A number of quantitative wood anatomical traits useful for parameterizing hydraulic architecture have been proposed (Carlquist, 2001;Scholz, Klepsch, Karimi, & Jansen, 2013;von Arx et al, 2017). For example, vessel size and densities per given sapwood area define the amount of water that may be conducted through stems, but large vessels increase risk of vessel cavitation under drought events (Tyree & Zimmermann, 2002).…”