Strong Coupling of Shoot Assimilation and Soil Respiration during Drought and Recovery Periods in Beech As Indicated by Natural Abundance δ13C Measurements

Blessing, Carola H.; Barthel, Matti; Gentsch, Lydia; Buchmann, Nina

doi:10.3389/fpls.2016.01710

Cited by 26 publications

(22 citation statements)

References 49 publications

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“…When drought becomes more intense, carbohydrate transport in the phloem can be expected to decrease as typically both the source (photosynthesis) and at least part of the sink (growth and respiration) activity rates decrease (Blessing et al 2016;Hagedorn et al 2016). Since photosynthesis can be maintained when drought is intense enough for growth to stop (Pantin et al 2013;Klein et al 2014), a sink-limited slowdown of transport under drought is likely to occur (Lemoine et al 2013).…”

Section: How Does Drought Affect Phloem Transport?mentioning

confidence: 99%

Drought impacts on tree phloem: from cell-level responses to ecological significance

et al. 2019

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On-going climate change is increasing the risk of drought stress across large areas worldwide. Such drought events decrease ecosystem productivity and have been increasingly linked to tree mortality. Understanding how trees respond to water shortage is key to predicting the future of ecosystem functions. Phloem is at the core of the tree functions, moving resources such as non-structural carbohydrates, nutrients, and defence and information molecules across the whole plant. Phloem function and ability to transport resources is tightly controlled by the balance of carbon and water fluxes within the tree. As such, drought is expected to impact phloem function by decreasing the amount of available water and new photoassimilates. Yet, the effect of drought on the phloem has received surprisingly little attention in the last decades. Here we review existing knowledge on drought impacts on phloem transport from loading and unloading processes at cellular level to possible effects on long-distance transport and consequences to ecosystems via ecophysiological feedbacks. We also point to new research frontiers that need to be explored to improve our understanding of phloem function under drought. In particular, we show how phloem transport is affected differently by increasing drought intensity, from no response to a slowdown, and explore how severe drought might actually disrupt the phloem transport enough to threaten tree survival. Because transport of resources affects other organisms interacting with the tree, we also review the ecological consequences of phloem response to drought and especially predatory, mutualistic and competitive relations. Finally, as phloem is the main path for carbon from sources to sink, we show how drought can affect biogeochemical cycles through changes in phloem transport. Overall, existing knowledge is consistent with the hypotheses that phloem response to drought matters for understanding tree and ecosystem function. However, future research on a large range of species and ecosystems is urgently needed to gain a comprehensive understanding of the question.

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Section: How Does Drought Affect Phloem Transport?mentioning

confidence: 99%

Drought impacts on tree phloem: from cell-level responses to ecological significance

et al. 2019

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“…Tight coupling between below‐ground autotrophic respiration and the availability of recently assimilated carbon (C) has become a paradigm in the ecophysiological literature (Högberg et al ., , ; Högberg & Read, ; Kuzyakov & Gavrichkova, ; Epron et al ., ; Blessing et al ., ). Substantial evidence supporting this paradigm comes from studies that have interrupted the transport of recently assimilated carbohydrates to the root system via stem girdling, a technique that severs phloem.…”

Section: Introductionmentioning

confidence: 97%

Stored root carbohydrates can maintain root respiration for extended periods

Aubrey

Teskey

2017

New Phytologist

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Tight coupling between below-ground autotrophic respiration and the availability of recently assimilated carbon (C) has become a paradigm in the ecophysiological literature. Here, we show that stored carbohydrates can decouple respiration from assimilation for prolonged periods by mobilizing reserves from transport roots to absorptive roots. We permanently disrupted the below-ground transfer of recently assimilated C using stem girdling and root trenching and measured soil CO efflux for over 1 yr in longleaf pine (Pinus palustris), a species that has large reserves of stored carbohydrates in roots. Soil CO efflux was not influenced by girdling or trenching through the 14-month observation period. Stored carbohydrate concentrations in absorptive roots were not affected by the disrupted supply of current photosynthate for over 1 yr; however, carbohydrate concentrations in transport roots decreased. Our results indicate that root respiration can be decoupled from recent canopy assimilation and that stored carbohydrates can be mobilized from transport roots to absorptive roots to maintain respiration for over 1 yr. This refines the current paradigm that canopy assimilation and below-ground respiration are tightly coupled and provides evidence of the mechanism and dynamics responsible for decoupling the above- and below-ground processes.

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“…In contrast to the vast number of studies reporting instantaneous tree responses to drought, little is known about recovery from this environmental stress, even though this ability is an important factor determining the drought resistance of trees on a longer time scale. A few studies have considered the photosynthetic response of saplings exposed to cycles of drought and re-watering ( Tognetti et al, 1995 ; Gallé and Feller, 2007 ; Arend et al, 2013 , 2016b ; Blessing et al, 2016 ), while others have focused on the year-to-year variation in tree-ring growth in adult trees caused by annual fluctuations in precipitation ( Dittmar et al, 2003 ; Pretzsch and Dieler, 2011 ). Findings from these studies have demonstrated the ability of beech to resume physiological activity, particularly photosynthesis, and growth after severe drought, but the processes occurring after stress release remain poorly understood.…”

Section: Introductionmentioning

confidence: 99%

Resilient Leaf Physiological Response of European Beech (Fagus sylvatica L.) to Summer Drought and Drought Release

et al. 2018

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Drought is a major environmental constraint to trees, causing severe stress and thus adversely affecting their functional integrity. European beech (Fagus sylvatica L.) is a key species in mesic forests that is commonly expected to suffer in a future climate with more intense and frequent droughts. Here, we assessed the seasonal response of leaf physiological characteristics of beech saplings to drought and drought release to investigate their potential to recover from the imposed stress and overcome previous limitations. Saplings were transplanted to model ecosystems and exposed to a simulated summer drought. Pre-dawn water potentials (ψpd), stomatal conductance (gS), intercellular CO2 concentration (ci), net-photosynthesis (AN), PSII chlorophyll fluorescence (PItot), non-structural carbohydrate concentrations (NSC; soluble sugars, starch) and carbon isotope signatures were measured in leaves throughout the growing season. Pre-dawn water potentials (ψpd), gS, ci, AN, and PItot decreased as drought progressed, and the concentration of soluble sugars increased at the expense of starch. Carbon isotopes in soluble sugars (δ13CS) showed a distinct increase under drought, suggesting, together with decreased ci, stomatal limitation of AN. Drought effects on ψpd, ci, and NSC disappeared shortly after re-watering, while full recovery of gS, AN, and PItot was delayed by 1 week. The fast recovery of NSC was reflected by a rapid decay of the drought signal in δ13C values, indicating a rapid turnover of assimilates and a reactivation of carbon metabolism. After recovery, the previously drought-exposed saplings showed a stimulation of AN and a trend toward elevated starch concentrations, which counteracted the previous drought limitations. Overall, our results suggest that the internal water relations of beech saplings and the physiological activity of leaves are restored rapidly after drought release. In the case of AN, stimulation after drought may partially compensate for limitations on photosynthetic activity during drought. Our observations suggest high resilience of beech to drought, contradicting the general belief that beech is particularly sensitive to environmental stressors.

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Strong Coupling of Shoot Assimilation and Soil Respiration during Drought and Recovery Periods in Beech As Indicated by Natural Abundance δ13C Measurements

Cited by 26 publications

References 49 publications

Drought impacts on tree phloem: from cell-level responses to ecological significance

Drought impacts on tree phloem: from cell-level responses to ecological significance

Stored root carbohydrates can maintain root respiration for extended periods

Resilient Leaf Physiological Response of European Beech (Fagus sylvatica L.) to Summer Drought and Drought Release

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