@article{LuebbeLamarqueDelzonetal.2022,
  author    = {L{\"u}bbe, Torben and Lamarque, Laurent J. and Delzon, Sylvain and Torres Ruiz, Jos{\´e} M. and Burlett, R{\´e}gis and Leuschner, Christoph and Schuldt, Bernhard},
  title     = {High variation in hydraulic efficiency but not xylem safety between roots and branches in four temperate broad-leaved tree species},
  series = {Functional Ecology},
  volume    = {36},
  journal   = {Functional Ecology},
  number    = {3},
  issn      = {0269-8463},
  doi       = {10.1111/1365-2435.13975},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318587},
  pages     = {699 -- 712},
  year      = {2022},
  abstract  = {Xylem hydraulic safety and efficiency are key traits determining tree fitness in a warmer and drier world. While numerous plant hydraulic studies have focused on branches, our understanding of root hydraulic functioning remains limited, although roots control water uptake, influence stomatal regulation and have commonly been considered as the most vulnerable organ along the hydraulic pathway. We investigated 11 traits related to xylem safety and efficiency along the hydraulic pathway in four temperate broad-leaved tree species. Continuous vessel tapering from coarse roots to stems and branches caused considerable reduction in hydraulic efficiency. Wood density was always lowest in roots, but did not decline linearly along the flow path. In contrast, xylem embolism resistance (P50) did not differ significantly between roots and branches, except for one species. The limited variation in xylem safety between organs did not adequately reflect the corresponding reductions in vessel diameter (by ~70\%) and hydraulic efficiency (by ~85\%). Although we did not observe any trade-off between xylem safety and specific conductivity, vessel diameter, vessel lumen fraction and wood density were related to embolism resistance, both across and partly within organs. We conclude that coarse roots are not highly vulnerable to xylem embolism as commonly believed, indicating that hydraulic failure during soil drying might be restricted to fine roots.},
  language  = {en}
}
@article{KumarWaitePaligietal.2022,
  author    = {Kumar, Manish and Waite, Pierre-Andr{\´e} and Paligi, Sharath Shyamappa and Schuldt, Bernhard},
  title     = {Influence of juvenile growth on xylem safety and efficiency in three temperate tree species},
  series = {Forests},
  volume    = {13},
  journal   = {Forests},
  number    = {6},
  issn      = {1999-4907},
  doi       = {10.3390/f13060909},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-278889},
  year      = {2022},
  abstract  = {The evolution of the internal water transport system was a prerequisite for high plant productivity. In times of climate change, understanding the dependency of juvenile growth on xylem hydraulic physiology is therefore of high importance. Here, we explored various wood anatomical, hydraulic, and leaf morphological traits related to hydraulic safety and efficiency in three temperate broadleaved tree species (Acer pseudoplatanus, Betula pendula, and Sorbus aucuparia). We took advantage of a severe natural heat wave that resulted in different climatic growing conditions for even-aged plants from the same seed source growing inside a greenhouse and outside. Inside the greenhouse, the daily maximum vapour pressure deficit was on average 36\% higher than outside during the growing seasons. Because of the higher atmospheric moisture stress, the biomass production differed up to 5.6-fold between both groups. Except for one species, a high productivity was associated with a high hydraulic efficiency caused by large xylem vessels and a large, supported leaf area. Although no safety-efficiency trade-off was observed, productivity was significantly related to P\(_{50}\) in two of the tree species but without revealing any clear pattern. A considerable plasticity in given traits was observed between both groups, with safety-related traits being more static while efficiency-related traits revealed a higher intra-specific plasticity. This was associated with other wood anatomical and leaf morphological adjustments. We confirm that a high hydraulic efficiency seems to be a prerequisite for a high biomass production, while our controversial results on the growth-xylem safety relationship confirm that safety-efficiency traits are decoupled and that their relationship with juvenile growth and water regime is species-specific.},
  language  = {en}
}
@phdthesis{Kumar2024,
  author    = {Kumar, Manish},
  title     = {Structural and compositional effects on tree-water relation},
  doi       = {10.25972/OPUS-32624},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-326245},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2024},
  abstract  = {Forests are essential sources of tangible and intangible benefits, but global climate change associated with recurrent extreme drought episodes severely affects forest productivity due to extensive tree die-back. On that, it appeals to an urgency for large-scale reforestation efforts to mitigate the impact of climate change worldwide; however, there is a lack of understanding of drought-effect on sapling growth and survival mechanisms. It is also challenging to anticipate how long trees can survive and when they succumb to drought. Hence, to ensure success of reforestation programs and sustainable forest productivity, it is essential to identify drought-resistant saplings. For that, profound knowledge of hydraulic characteristics is needed. To achieve this, the study was split into two phases which seek to address (1) how the hydraulic and anatomical traits influence the sapling's growth rate under drought stress. (2) how plant water potential regulation and physiological traits are linked to species' water use strategies and their drought tolerance. The dissertation is assembled of two study campaigns carried out on saplings at the Chair of Botany II, University of W{\"u}rzburg, Germany. The first study involved three ecologically important temperate broadleaved tree species — saplings of 18-month (Acer pseudoplatanus, Betula pendula, and Sorbus aucuparia) — grown from seeds in contrasting conditions (inside a greenhouse and outside), with the latter being subjected to severe natural heat waves. In the second study, two additional temperate species (Fagus sylvatica and Tilia cordata) were added. The drying-out event was conducted using a randomised blocked design by monitoring plant water status in a climate-controlled chamber and a greenhouse. In campaign I, I present the result based on analysed data of 82 plants of temperate deciduous species and address the juvenile growth rate trade-off with xylem safety-efficiency. Our results indicate biomass production varies considerably due to the contrasted growing environment. High hydraulic efficiency is necessary for increased biomass production, while safety-efficiency traits are decoupled and species-specific. Furthermore, productivity was linked considerably to xylem safety without revealing a well-defined pattern among species. Moreover, plasticity in traits differed between stressed and non-stressed plants. For example, safety-related characteristics were more static than efficiency-related traits, which had higher intra-specific variation. Moreover, we recorded anatomical and leaf traits adjustments in response to a stress condition, but consistency among species is lacking. In campaign II, I combined different ways to estimate the degree of isohydry based on water potential regulation and connected the iso-anisohydric spectrum (i.e., hydroscape area, HSA) to hydraulic traits to elucidate actual plant performance during drought. We analysed plant water potential regulation (Ψpd and Ψmd) and stomatal conductance of 28-29 month saplings of five species. I used a linear mixed modelling approach that allowed to control individual variations to describe the water potential regulation and tested different conceptual definitions of isohydricity. The combined methods allowed us to estimate species' relative degree of isohydry. Further, we examined the traits coordination, including hydraulic safety margin, HSM; embolism resistance, P88; turgor loss, Ψtlp; stomata closure, Ps90; capacitance, C; cuticular conductance, gmin, to determine time to hydraulic failure (Thf). Thf is the cumulative effect of time to stomata closure (Tsc) and time after stomatal closure to catastrophic hydraulic failure (Tcrit). Our results show the species' HSA matches their stomatal stringency, which confirms the relationship between stomatal response and leaf water potential decline. Species that close stomata at lower water potential notably had a larger HSA. Isohydric behaviour was mostly associated with leaf hydraulic traits and poorly to xylem safety traits. Species' degree of isohydry was also unrelated to the species' time to death during drying-out experiments. This supports the notion that isohydry behaviours are linked to water use rather than drought survival strategies. Further, consistent with our assumptions, more isohydric species had larger internal water storage and lost their leaf turgor at less negative water potentials. Counter to our expectations, neither embolism resistance nor the associated hydraulic safety margins were related to metrics of isohydry. Instead, our results indicate traits associated with plant drought response to cluster along two largely independent axes of variation (i.e., stomatal stringency and xylem safety). Furthermore, on the temporal progression of plant drought responses, stomatal closure is critical in coordinating various traits to determine species' hydraulic strategies. Desiccation avoidance strategy was linked to Tsc and coordinated traits response of Ps90, Ψtlp, and HSA, whereas desiccation tolerance was related to Tcrit and traits such as lower P88 value, high HSM, and lower gmin. Notably, the shoot capacitance (C) is crucial in Thf and exhibits dichotomous behaviour linked to both Tsc and Tcrit. In conclusion, knowledge of growth rate trade-offs with xylem safety-efficiency combined with traits linked to species' hydraulic strategies along the isohydry could substantially enhance our ability to identify drought-resistant saplings to ensure the success of reforestation programs and predicting sensitivity to drought for achieving sustainable forest ecosystems.},
  subject      = {Wachstumsrate},
  language  = {en}
}