Abstract Detail

Ecophysiology

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 (Ψ_leaf). 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/E_p) 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 Ψ_leaf values to assess how Ψ_leaf affects rates of photosynthesis (A_max), carboxylation (V_cmax), and electron transport (J_max). We hypothesized that species from drier habitats should exhibit less mesophyll photosynthetic sensitivity to Ψ_leaf, given the adaptive value of maintaining photosynthetic capacity during water stress. Across 10 Eucalyptus species stratified by subgenus and native P/E_p, A_max, V_cmax, and J_max decline with Ψ_leaf. As predicted, P₅₀ (Ψ_leaf of 50% decline from the maximum A_max, V_cmax, and J_max each) occurs at more negative Ψ_leaf as native P/E_p decreases. The decline in P₅₀ for A_max with native P/E_p is highly significant in ordinary (p < 0.007) and phylogenetically structured (p < 0.008) regressions. The comparable declines for V_cmax and J_max are also significant for both kinds of regression. These results indicate that non-stomatal limitations on photosynthesis caused by cellular dehydration occur at different Ψ_leaf across closely related species. The association between climate and species' responses further suggest that reduced mesophyll photosynthetic sensitivity to Ψ_leaf 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.

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

Keywords:
drought
vulnerability
A-c_i 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