Habitat specialization and the role of trait lability in structuring diverse willow (genusSalix) communities

Abstract

Abstract. The co-occurrence of closely related species is challenging to explain because biotic filters are expected to limit the ecological similarity of species within communities. To investigate the mechanisms important in facilitating species' co-occurrence in diverse willow and poplar communities, we examined functional diversity and community phylogenetic structure along a hydrologic gradient. We focused on traits related to drought tolerance, leaf hydraulics, and recruitment, and examined species' phylogenetic relatedness and trait lability using a molecular phylogeny. Within habitats, species exhibited phenotypic clustering, and across the landscape, species distributions were correlated with their functional traits in a manner consistent with environmental filtering. With increasing water availability, communities changed from being phylogenetically even to being phylogenetically clustered. We suggest that this shift results from environmental filtering acting on conserved traits in wet habitats and labile traits in dry habitats. Taken together, these results suggest that environmental filtering is important to community assembly along the entire hydrologic gradient within this system. Although many of the traits important to habitat specialization in upland habitats are phylogenetically labile, species' habitat affinity is phylogenetically conserved overall, indicating that niche conservatism can occur as an emergent property despite trait lability. This study demonstrates the complementary nature of trait and community phylogenetic analyses and how these methods can be used to better understand the processes involved in community assembly along environmental gradients.

Phloem Transport Velocity Varies over Time and among Vascular Bundles during Early Cucumber Seedling Development

“…Seedling physiology is critical to plant establishment and has important implications for species' distributions in their natural environments (Kitajima, 2002;Savage and Cavender-Bares, 2012) and their success in agriculture (Pujol et al, 2005). In this study, we demonstrate that phloem transport responds dynamically to changes in sink and source development and that transport velocity within a single plant can be heterogeneous.…”

“…Seedlings present a relatively simple source-sink network for studying patterns of carbon allocation, and by examining their development over time, it is possible to gain insights into how the structure of the phloem network influences its transport. Early stages of plant growth, including the transition to autotrophy and the development of true leaves, are also critical to plant survival and establishment in nature (Lovell and Moore, 1971;Kitajima, 2002;Savage and Cavender-Bares, 2012). Although several methods exist for measuring phloem transport velocity (Minchin and Thorpe, 2003;Windt et al, 2006;Froelich et al, 2011), the spatial and time resolution required for this study necessitated the use of a new dye-tracing technique .…”

Contrasting effects of plant species traits and moisture on the decomposition of multiple litter fractions

“…Collection populations were selected using data from previous field studies of natural populations in which water availability in the species' natural habitats was characterized (Savage and Cavender-Bares 2012). We collected from populations at Cedar Creek, as well as nearby Carlos Avery State Wildlife Management Area (Forest Lake, MN, 45°19′N, 93°05′W), that were located in habitats representative of the species' water regime affinities.…”

“…Initial leaf litter chemistry of the ground subsample was analyzed for: concentrations of carbon (C) and N (COSTECH ESC 4010 Elemental Analyzer, Valencia, CA, USA), phosphorus (P) by digestion with 10 N sulfuric acid after ashing samples at 300 °C for 30 min followed by 500 °C for 2 h (DeMott et al 1998), C fractions (soluble cell contents, SCC; cellulose, CELL; hemicellulose plus bound proteins, HBP; and lignin plus other recalcitrant compounds, LR; Ankom Fiber Analyzer, Ankom Technology, Macedon, NY, USA), and condensed Table 1 Native habitat affinity, growth form, and initial leaf litter chemistry of the 12 species (willow family, Salicaceae) studied Species are ordered based on their distribution across a water availability gradient from wet to dry habitats. Growth form and habitat affinity classifications are from field studies of natural populations in Savage and Cavender-Bares (2012). All values are expressed as mg g −1 leaf litter and n = 3 (standard error in parentheses) SCC leaf litter initial soluble cell contents, HBP leaf litter initial hemicellulose plus bound proteins, CELL leaf litter initial cellulose, LR leaf litter initial lignin plus recalcitrants, N leaf litter initial nitrogen, P leaf litter initial phosphorus, CT leaf litter initial condensed tannins tannins (CT) by acid butanol assay with quebrancho extract standard (Porter et al 1986).…”

“…We used green leaf maximum photosynthetic capacity (A max ; μmol CO 2 m −2 s −1 ), green leaf specific leaf area (SLA; cm g −1 ), green leaf turgor loss point (TLP, the leaf water potential at which a species wilts; MPa), and plant wood density (WD; g cm −3 ) measurements from field studies (Savage 2010;Savage and Cavender-Bares 2012). TLP and WD were selected in particular because previous research showed those traits to be significant indictors of drought tolerance (Savage and Cavender-Bares 2012). Furthermore, we used total plant relative growth rate (RGR; g g −1 day −1 ) measurements from a greenhouse study where the species were grown under common conditions where water was non-limiting (Savage and Cavender-Bares 2012).…”