Streamside trees: responses of male, female and hybrid cottonwoods to flooding

Abstract

Cottonwoods, riparian poplars, are dioecious and prior studies have indicated that female poplars and willows can be more abundant than males in low-elevation zones, which are occasionally flooded. We investigated the response to flooding of clonal saplings of 12 male and 9 female narrowleaf cottonwoods (Populus angustifolia) grown for 15 weeks in a greenhouse, along with three females of a co-occurring native hybrid (Populus × jackii = Populus deltoides × Populus balsamifera). Three water-level treatments were provided, with substrate inundation as the flood treatment. In the non-flooded condition, the hybrids produced about four-fold more dry weight (DW) than the narrowleaf cottonwoods (P < 0.01). In both cottonwood taxa, flooding reduced stem height and DW, root and leaf area and weight, leaf chlorophyll and stomatal conductance (all P < 0.01). Inundation increased the foliar carbon-to-nitrogen ratio (+11%; P < 0.05) but did not significantly alter leaf water potential (mean -1.5 MPa), or foliar δ(13)C, which was lower in P. angustifolia (-32.8‰) than P. × jackii (-31.5‰; P < 0.05). Water level influenced the root distribution as roots were sparse in the saturated substrate and abundant in the capillary fringe above. The male and female P. angustifolia genotypes grew similarly with the favorable water levels, but the males tended to be more inhibited by flooding. Sapling DW of males was reduced by 56% compared with a 44% reduction for females (P = 0.1), and there were similar lower reductions for leaf, stem and root DW in females. These results demonstrate the inundation response of floodplain trees and suggest relative flood tolerance as: P. angustifolia female > P. angustifolia male > P. × jackii female. This indicates that narrowleaf cottonwoods are relatively flood tolerant and suggests that females are more flood tolerant than males. We propose the concept of 'strategic positioning', whereby the seed-producing females could be better adapted to naturally flooded, low-elevation streamside zones where seedling recruitment generally occurs.

Root architecture of riparian trees: river cut-banks provide natural hydraulic excavation, revealing that cottonwoods are facultative phreatophytes

“…A challenge to the phreatophytic root distribution follows from the seasonal variation in river stage and groundwater elevation. With high streams flows, much of the deep root system would be inundated and this would impose anoxia and physiological stress, reducing water uptake and growth (Pezeshki 2001;Nielsen et al 2010;Rood et al 2010). While cottonwoods are flood-dependent for reproduction (Scott et al 1996;Mahoney and Rood 1998), the established trees are inundation-intolerant.…”

“…We considered prospective differences across species and along rivers in regions differing in climate. Since cottonwoods are considered as phreatophytes (Busch et al 1992;Smith et al 1998), we anticipated that the roots would be prevalent in deeper zones, near the capillary fringe above the saturated ground-water table (McBride and Strahan 1984;Mahoney and Rood 1998;Nielsen et al 2010). In alluvial valleys, those with river channels, banks and floodplains consisting of sands, gravels, and cobbles, the floodplain water table represents a near-horizontal extension from the river, since river water readily infiltrates through the alluvial sediments (Rood et al 1995;Scott et al 1999;Shafroth et al 2000).…”

Sex-specific responses to winter flooding, spring waterlogging and post-flooding recovery in Populus deltoides

“…For example, Nielsen et al . 4 and Rood et al . 8 suggested that female P. angustifolia were more flood-tolerant than males, and that females could be more successful in lower, more flood-prone sites.…”

“…Previous studies have focused on the phenotypic plasticity and adaptive plasticity of poplars in response to summer flooding or waterlogging stresses during the plant growth stage of development 4–8 . Poplars are deciduous species.…”

Ecophysiological and morphological adaption to soil flooding of two poplar clones differing in flood-tolerance

“…Flooding stress of woody plants was mainly studied in some tree species living in flood-prone environment (Ferreira et al, 2009;Kolb and Joly, 2009;Mielke et al, 2005;Yamanoshita et al, 2005). As for poplar, most studies were performed to clarify responses of growth and nutrient metabolism to flooding (Herschbach et al, 2005;Kreuzwieser et al, 2002;Nielsen et al, 2010). In the present study, a flood-tolerant and a floodsusceptible poplar clone were compared for ecophysiological and morphological adaptions to hypoxia.…”