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Abstract Detail


Salvi, Amanda [1], Smith, Duncan D [2], McCulloh, Kate [3], Givnish, Thomas [4].

Mesophyll photosynthetic sensitivity to leaf water potential increases in Eucalyptus species native to moister Australian climates: a new dimension of plant adaptation to drought.

A fundamental constraint on land-plant evolution is the sensitivity of photosynthetic capacity to decreased leaf water potential (Ψleaf). While declines in photosynthesis with water stress can be mainly attributed to stomatal closure, there is a general but overlooked tendency for leaf dehydration to cause physical changes in photosynthetic machinery that reduce intracellular photosyn­the­tic capac­ity independent of stomatal closure. Little is known about how this non-stomatal, mesophyll limitation varies among ecologically divergent plants. We compared mesophyll photosynthetic sensitivity among 10 Eucalyptus species native to different parts of a steep gradient in the ratio of precipitation to pan evaporation (P/Ep) in SE Australia, to test whether those from moister habitats show greater mesophyll photosynthetic sensitivity. Over a slow drying period of 1-2 weeks per individual, we conducted several C02 response curves, which provide measures of mesophyll photosyn­thetic capacity with the effect of stomatal conductance largely subtracted, across several Ψleaf values to assess how Ψleaf affects rates of photosynthesis (Amax), carboxylation (Vcmax), and electron transport (Jmax). We hypothesized that species from drier habitats should exhibit less mesophyll photosynthetic sensitivity to Ψleaf, given the adaptive value of maintaining photosynthetic capacity during water stress. Across 10 Eucalyptus species stratified by subgenus and native P/Ep, Amax, Vcmax, and Jmax decline with Ψleaf. As predicted, P50leaf of 50% decline from the maximum Amax, Vcmax, and Jmax each) occurs at more negative Ψleaf as native P/Ep decreases. The decline in P50 for Amax with native P/Ep is highly significant in ordinary (p < 0.007) and phylogenetically structured (p < 0.008) regressions. The comparable declines for Vcmax and Jmax are also significant for both kinds of regression. These results indicate that non-stomatal limitations on photosynthesis caused by cellular dehydration occur at different Ψleaf across closely related species. The association between climate and species' responses further suggest that reduced mesophyll photosynthetic sensitivity to Ψleaf is adaptive in drier habitats. These findings provide the first comparative data on differences in mesophyll photosynthetic sensitivity across a set of species adapted to differing levels of soil moisture, providing important insights into a previously unexplored dimension of plant adaptive evolution in response to relative moisture supply.

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1 - University Of Wisconsin-Madison, Department Of Botany, 322 Birge Hall 430 Lincoln Drive, Madison, WI, 53706, United States
2 - University of Wisconsin Madison, Birge Hall 430 Linden Drive, Madison, WI, 53703, United States
3 - Department Of Botany, 430 Lincoln Dr, Madison, WI, 53706, United States
4 - University Of Wisconsin-Madison, Department Of Botany, 430 Lincoln Drive, Madison, WI, 53706.0, United States

A-ci curve.

Presentation Type: Oral Paper
Session: ECOPH1, Ecophysiology I
Location: San Pedro 2/Starr Pass
Date: Tuesday, July 30th, 2019
Time: 11:30 AM
Number: ECOPH1011
Abstract ID:747
Candidate for Awards:Physiological Section Physiological Section Li-COR Prize,Physiological Section Best Paper Presentation

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