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Turgor loss point (πtlp) has been suggested to be a key trait for drought resistance in woody species. In herbaceous grassland species, the role of πtlp for species drought survival has not yet been tested, although grasslands are projected to experience more frequent and intense droughts with climate change.To gain insights into the role of πtlp for drought resistance of temperate perennial grassland species, we assessed πtlp of 41 species common in Germany (20 forbs, 21 grasses). We directly related them to the species' comparative whole‐plant drought survival and midday leaf water potentials under drought (ΨMD) assessed in a common garden drought experiment, and to species moisture association.Species drought survival increased with increasing πtlp across all species as well as within forbs or grasses separately. ΨMD was positively related to πtlp and drought survival. Our results imply that high πtlp promotes drought survival of common perennial European temperate mesic grassland species by enabling them to maintain high leaf water potentials under drought, that is, a desiccation avoidance strategy. However, πtlp was not related to species moisture association.The positive relationship between πtlp and drought survival in herbaceous grassland species was opposite to the negative relationship previously established in woody plants, implying that mechanisms of drought resistance differ between woody and herbaceous species. Our results highlight the necessity of directly testing the relationship of functional traits to whole‐plant drought survival in different plant life forms, before using trait assessments for predicting plant responses to drought. A free plain language summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

In recent years, Central European forests and trees have been severely suffered from drought events in the growing season. To examine the tree growth response to drought stress, measurements of annual shoot lengths (ASL) of various tree species with distinct ages and habitats were taken in southeast Germany. The index of relative ASL increase (RAI), which is a standardized ASL increase, was calculated to indicate the growth rate of various tree species between the non-drought (2015–2017) and the drought period (2018–2020). The results showed the ASLs of most early-young trees (< 10 years) significantly showed a decreasing tendency in the drought period, whereas the middle-young (11–15 years) and late-young trees (> 16 years) presented a relatively stable trend. The ring-porous species with anisohydric behavior were likely to have higher RAIs associated with higher drought tolerance than diffuse-porous species with isohydric behavior. However, tree growth rate did not correlate with drought tolerance (resistance) of tree species indicated by leaf turgor loss point (Ψ tlp , MPa). Therefore, this study suggested parameters, such as growth rate, age phases, and microhabitats, should be considered to predict tree species' drought tolerance other than Ψ tlp. Finally, we emphasized tree shoot growth responses to drought were affected by multiple internal and external factors, and strongly depended on species- and site-specific characteristics, such as age phases, xylem structure, hydraulic strategy, microhabitat, grafting effect, and competition. ASL measurement can be recommended to be an easy, fast, and effective method to detect tree growth rate and response to environmental stress. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]