Interaction of Flooding with Carbon Metabolism of Forest Trees

Abstract

Waterlogging and flooding cause oxygen deprivation in the root system of trees. Since oxygen is essentially for mitochondrial respiration, this process cannot be maintained under anoxic conditions and must be replaced by other pathways. For the roots it is therefore a matter of survival to switch from respiration to alcoholic fermentation. Due to the low efficiency of this process to yield energy equivalents (ATP), energy and carbon metabolism of trees are usually strongly affected by oxygen deprivation, even if a rapid switch from respiration to fermentation is achieved. The roots can compensate for the low energy yield of fermentation either (1) by decreasing the demand for energy by a reduction of energy-dependent processes such as root growth and/or nutrient uptake, or (2) by consuming more carbohydrates per unit time in order to generate sufficient energy equivalents. In the leaves of trees, flooding and waterlogging cause a decline in the rates of photosynthesis and transpiration, as well as in stomatal conductance. It is assumed that, due to reduced phloem transport, soluble sugars and starch accumulate in the leaves of flooded trees, thereby negatively affecting the sugar supply of the roots. Thus, root growth and survival is negatively affected by both changes in root internal carbon metabolism and impaired carbon allocation to the roots by phloem transport. In addition, accumulation of toxic products of fermentation in the roots, such as acetaldehyde, can further impair root metabolism. A main feature of tolerance against flooding and waterlogging of trees seems to be the steady supply of carbohydrates to the roots in order to maintain alcoholic fermentation; in addition, roots of tolerant trees seem to avoid accumulation of fermentation-derived ethanol and acetaldehyde. From studies with flooding tolerant and non-tolerant tree species, it is hypothesized that (1) the transport of ethanol produced in the roots under hypoxic conditions into the leaves via the transpiration stream, (2) its conversion into acetyl-CoA in the leaves, and (3) its use in the plant's general metabolism, are mechanisms of flooding tolerance of trees.

The effect of flooding on the exchange of the volatile C<sub>2</sub>-compounds ethanol, acetaldehyde and acetic acid between leaves of Amazonian floodplain tree species and the atmosphere

“…Moreover, Q. ilex, a typical Mediterranean tree species generally experiencing rather water limitations than flooding conditions, has been reported to exhibit extremely high ethanol and acetaldehyde emission rates when exposed to flooding (Holzinger et al, 2000). These rates (∼15 000 and 4000 nmol m −2 min −1 of acetaldehyde and ethanol, respectively) were larger than those observed for the flooding tolerant Amazonian trees species in the present study (3-200 nmol and 42-4220 nmol m −2 min −1 of acetaldehyde and ethanol, respectively) and much larger than those for flooding tolerant and intolerant European tree species (∼100-1000 nmol m −2 min −1 acetaldehyde) (Kreuzwieser et al, 2004). Hence, not the flooding tolerance itself, but different physiological mechanisms contributing to a flooding tolerance determine the emission rates of ethanol and its oxidation products and emissions rates alone can not be used as indicators a flooding tolerance.…”

“…Taking into account that L. corymbulosa is also an isoprene emitting species (unpublished data), the total C-loss through emissions of volatile organic compounds might be quite substantial. Kreuzwieser et al (2004) hypothesized from their observations on European tree species that an effective carbon recycling of root derived ethanol inside plant leaves can be regarded as an important mechanism of flooding tolerance. Within this context a high emission rate of acetaldehyde may indicate a high metabolic turnover of ethanol in the leaves and an increased flooding tolerance.…”

Physiological Responses to Hypoxia and Manganese in Eucalyptus Clones with Differential Tolerance to Vale do Rio Doce Shoot Dieback

“…Trees in tropical areas with seasonal floods have a similar response (Rengifo et al, 2005), with a reduction in photosynthetic rate and stomatal conductance, but an accumulation of starch in leaves. The accumulation of starch and sugars in leaves compromises photosynthetic efficiency due to feedback-inhibition (Kreuzwieser et al, 2004;Dalberto et al, 2017).…”

“…A limitation in the activation or action of Rubisco, imbalances in the Calvin cycle, or even feedback-inhibition due to sugar accumulation may have occurred, resulting in this decrease. Feedback-inhibition by the accumulation of photoassimilates is commonly observed in plants with roots under hypoxia (Kreuzwieser et al, 2004;Rengifo et al, 2005). Regardless of the form of photosynthetic inhibition, excess light energy must be adequately dissipated or it may cause cell damage (Carvalho and Amancio, 2002;AbdElgawad et al, 2016).…”

Ecophysiological and biochemical behavior in young plants of Parkia gigantocarpa Ducke subjected to waterlogging conditions

“…The stomatal closure contributes to the preservation of leaf water potential, and decreasing the reduction of hydraulic conductivity of roots (Kreuzwieser et al, 2004). Thus, the stomatal closure, the reducing evaporation, and the maintenance of leaf water potential are strategies developed by plants in waterlogged conditions to minimize water loss (Davanso et al, 2002).…”