Abstract Detail

Physiology & Ecophysiology

Losada, Juan M [1], Holbrook, N. Michele [2].

Hydraulic conductivity of the phloem in a woody basal angiosperm lineage.

The ecological context in which angiosperms evolved has been hotly debated in the last decades. Recent ecophysiological work with living taxa compared with anatomical information of fossils supports the idea of tropical-like and shaded environments as a credible niche for the rise of angiosperms. While these studies emphasized the low xylem hydraulic capacity of basal angiosperms, information on the functional relationship between anatomy of the phloem and its transport capacities is lacking. To better understand the ecological distribution of early angiosperms, we compared the anatomical properties of the phloem in the aerial parts of seedlings and mature plants of Illicium parviflorum, a basal angiosperm shrub growing in the understory tropical areas of the American continent. Anatomical studies revealed a direct relationship between the area occupied by the xylem and the diameter of the stem, and an inverse relationship for the cortical tissue. However, the proportion of the cross-section occupied by phloem tissue was maintained independently of the diameter. The geometrical properties of sieve element length and radius, as well as area and number of the sieve plates showed a direct linear relationship with the diameter of the stems, whereas pore size of the sieve areas was remarkably small (and independent of diameter). Interestingly, while the number of sieve elements increased with the diameter of the stem, the ratio of conductive elements with respect to other phloem cells was conserved in all the stem diameters studied. In both seedlings and adult plants, the phloem elements of the leaves showed a decrease in length and width from the major vein towards the secondary veins and the petioles. Additionally, photosynthetic activity was similar in both plants, but sap velocity was faster in the leaves of seedlings, suggesting a more efficient transport of solutes for rapid growth. The low light and humid environments where Illicium and related basal angiosperm taxa develop match with a general low hydraulic conductance of the phloem. Yet, phloem conductance increased from the stems with primary growth towards those with secondary growth. The low photosynthetic activity in both seedlings and mature plants showed a conserved developmental strategy, but the velocity of the sap was doubled in the leaves of seedlings compared to that of adult plants. These results point to sap velocity as a modulator of growth during the early ontogeny of woody plants adapted to shade.

1 - Arnold Arboretum Of Harvard University, Organismic And Evolutionary Biology, 1300 Centre Street, Boston, MA, 02131, USA
2 - Harvard University, Organismal And Evolutionary Biology, 16 Divinity Avenue, Cambridge, MA, 02138, USA

Keywords:
Phloem
hydraulics
anatomy
basal angiosperms
Austrobaileyales
Illicium.

Presentation Type: Oral Paper
Session: 23, Physiology & Ecophysiology
Location: Fort Worth Ballroom 6/Omni Hotel
Date: Tuesday, June 27th, 2017
Time: 9:00 AM
Number: 23002
Abstract ID:335
Candidate for Awards:None