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.
Highlights
Research efforts to investigate the seasonal dynamics of tree-ring development based on the repeated sampling of microcores have gained considerable momentum during the last two decades [1,2,3,4]
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
This study investigates the impact of weather and climate on the kinetics of tracheid development, tracheid morphology, and the seasonal dynamics of radial xylem growth and woody biomass production of Norway spruce (Picea abies (L.) Karst.) trees growing along an elevational gradient in the Southwestern Black Forest, Germany
Summary
Research efforts to investigate the seasonal dynamics of tree-ring development based on the repeated sampling of microcores have gained considerable momentum during the last two decades [1,2,3,4]. The acquired data increases our understanding of the endogenous and environmental control of tree-ring formation and the impact of anticipated climatic changes on forest growth and productivity [9,10]. The typical tree-ring structure of conifers growing in temperate climates is characterized by gradually decreasing cell radial diameters and cell lumen diameters and increasing wall thickness from earlywood to latewood cells and is assumed to be largely under endogenous control [13,14]. According to the morphogenetic-gradient hypothesis, endogenous control is executed by an auxin concentration profile, peaking at the cambial zone and decreasing in a centripetal stem direction while signaling positional information to the individual tracheids and, thereby, controlling their transition through the subsequent stages of cell differentiation as well as their final geometry and relative position within the developed tree-ring [13,15]. Recent studies demonstrated that model-based simulations need to implement the interaction of auxin with a second biochemical signal, such as cytokinin or a TDIF peptide to realistically predict radial growth rates and zonation of cell differentiation [10,16]
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