Effects of Intra-Seasonal Drought on Kinetics of Tracheid Differentiation and Seasonal Growth Dynamics of Norway Spruce along an Elevational Gradient

Abstract

Research Highlights: Our results provide novel perspectives on the effectiveness and collapse of compensatory mechanisms of tracheid development of Norway spruce during intra-seasonal drought and the environmental control of intra-annual density fluctuations. Background and Objectives: This study aimed to compare and integrate complementary methods for investigating intra-annual wood formation dynamics to gain a better understanding of the endogenous and environmental control of tree-ring development and the impact of anticipated climatic changes on forest growth and productivity. Materials and Methods: We performed an integrated analysis of xylogenesis observations, quantitative wood anatomy, and point-dendrometer measurements of Norway spruce (Picea abies (L.) Karst.) trees growing along an elevational gradient in South-western Germany during a growing season with an anomalous dry June followed by an extraordinary humid July. Results: Strong endogenous control of tree-ring formation was suggested at the highest elevation where the decreasing rates of tracheid enlargement and wall thickening during drought were effectively compensated by increased cell differentiation duration. A shift to environmental control of tree-ring formation during drought was indicated at the lowest elevation, where we detected absence of compensatory mechanisms, eventually stimulating the formation of an intra-annual density fluctuation. Transient drought stress in June also led to bimodal patterns and decreasing daily rates of stem radial displacement, radial xylem growth, and woody biomass production. Comparing xylogenesis data with dendrometer measurements showed ambivalent results and it appears that, with decreasing daily rates of radial xylem growth, the signal-to-noise ratio in dendrometer time series between growth and fluctuations of tree water status becomes increasingly detrimental. Conclusions: Our study provides new perspectives into the complex interplay between rates and durations of tracheid development during dry-wet cycles, and, thereby, contributes to an improved and mechanistic understanding of the environmental control of wood formation processes, leading to the formation of intra-annual density fluctuations in tree-rings of Norway spruce.

The 2018 hot drought pushed conifer wood formation to the limit of its plasticity: Consequences for woody biomass production and tree ring structure

“…During droughts, even small intermittent rain events can stop in the downward trend in the enlargement rate of Scots pine, and a second small increase in silver fir, in turn, leading to a flattened negative trend in cell size. This emphasizes the highly plastic responses of wood formation in conifers to extreme environmental conditions (Montwé et al 2014;Nabais et al 2014;Stangler et al 2021).…”

“…Xylem cells must guarantee water transport to the crown by having a wide lumen and thin cell walls but must also physically support the tree through cells with thick cell walls and narrow lumens (Hacke & Sperry 2001). However, there is recent evidence that, under intense drought stress situations, these compensatory mechanisms fail, wood production becomes limited, and wood anatomy, thus the hydraulic system and the carbon stock of the tree are affected by environmental changes (Vieira et al 2020;Stangler et al 2021). It is still not fully known under which environmental conditions and at which time during the vegetation period the compensatory mechanisms can no longer function.…”

Origin of Intra-annual Density Fluctuations in a Semi-arid Area of Northwestern China

“…Our results indicate that climate drivers are uniform for cell enlarging and wall thickening of IADF cells: large IADF cells with thick walls were mainly induced by summer drought. Stangler et al (2021) demonstrated that the transition from a dry June to a wet July initiated IADF formation in Norway spruce at lower elevations in Germany. Accordingly, we detected the specific IADF phenology under water deficit and showed evidence of the climate driver of enlargement and wall thickening during IADF formation.…”

Relationships Between Wood-Anatomical Features and Resistance Drilling Density in Norway Spruce and European Beech

“…Thus, it can change from diffuseporous in normal years to nearly semi-ring porous in years with extremely dry summers (Arnič et al, 2021). In coniferous spruce, wood structural changes mainly refer to tracheid features (wall thickness and lumen size; e.g., Gao et al, 2021;Stangler et al, 2021), the ratio of earlywood to latewood (Samusevich et al, 2020), and the occurrence of IADFs (Mayer et al, 2020). In beech, the changes refer to the ratio between different cell types (i.e., vessels, fibers, and parenchyma; Zheng et al, 2019) and vessel features (i.e., size, distribution, and grouping; Diaconu et al, 2016a).…”