Variation in xylem structure from tropics to tundra: Evidence from vestured pits

Abstract

Bordered pits play an important role in permitting water flow among adjacent tracheary elements in flowering plants. Variation in the bordered pit structure is suggested to be adaptive in optimally balancing the conflict between hydraulic efficiency (conductivity) and safety from air entry at the pit membrane (air seeding). The possible function of vestured pits, which are bordered pits with protuberances from the secondary cell wall of the pit chamber, could be increased hydraulic resistance or minimized vulnerability to air seeding. These functional hypotheses have to be harmonized with the notion that the vestured or nonvestured nature of pits contains strong phylogenetic signals (i.e., often characterize large species-rich clades with broad ecological ranges). A literature survey of 11,843 species covering 6,428 genera from diverse climates indicates that the incidence of vestured pits considerably decreases from tropics to tundra. The highest frequencies of vestured pits occur in deserts and tropical seasonal woodlands. Moreover, a distinctly developed network of branched vestures is mainly restricted to warm habitats in both mesic and dry (sub)tropical lowlands, whereas vestures in woody plants from cold and boreal arctic environments are usually minute and simple. A similar survey of the frequency of exclusively scalariform perforation plates illustrates that the major ecological trend of this feature is opposite that of vestured pits. These findings provide previously undescribed insights suggesting that vessels with vestured pits and simple perforation plates function as an efficient hydraulic system in plants growing in warm environments with periodical or continuous drought stress.B otanists have long speculated on the mutual relationship between the structure and function of different wood anatomical features and how ecological conditions correlate with xylem features (1-4). The evolution of xylem vessels has been considered a key adaptation marking the pinnacle of hydraulic efficiency in flowering plants, because plants with vessels generally have higher hydraulic conductivities than plants that rely solely on tracheids for water transport (5). The traditional view is that evolutionary trends of vessel elements have been regarded as reliable tools in the study of angiosperm phylogeny, because vessel characters were considered conservative traits containing a wealth of potentially significant systematic information (2, 6, 7). Although parallel development of vessel characters is generally accepted, recent phylogenetic analyses of angiosperms suggest there have also been some reversals in the Baileyan transformation series (8, 9). Therefore, parallel evolution and reversibility in vessel characters imply a strong adaptive significance of xylem hydraulic architecture.The structure of bordered intervessel pits, which are small openings where the secondary cell wall was not deposited over the primary wall (Figs. 1 and 2 A), permits water flow between adjacent vessels, but pits are also a weak link in pro...

Wood Anatomy of Family Salvadoraceae from the Indian Subcontinent with Special Reference to the Ultrastructure of the Vessel Wall

“…Scanning electron microscopy showed these ingrowths to be vestures in the intervessel pits. The occurrence of vestured pits in Salvadora is consistent with the prevalence of pit vesturing in plants from tropical environments (Jansen et al 2004). The present study is the first to report vestures in genus Salvadora.…”

Anatomia e densidade básica da madeira de Caesalpinia pyramidalis Tul. (Fabaceae), espécie endêmica da caatinga do Nordeste do Brasil

“…A pontoação guarnecida é uma característica marcante entre as Leguminosas (Jansen et al 2004). Todos os gêneros das subfamílias Mimosoideae e Papilionoideae apresentam este tipo de pontoação.…”

“…Além da pontoação guarnecida ser um traço filogenético, ela pode também representar uma estratégia adaptativa de sucesso para a sobrevivência e competição de plantas sujeitas a contínuos ou sazonais períodos de seca em regiões de clima quente (Jansen et al 2004),. Assim, Caesalpinia pyramidalis, espécie endêmica da caatinga, apresentou este tipo de pontoação que caracteriza o traço filogenético do gênero e também contribui para a sobrevivência da espécie neste tipo de ecossistema, caracterizado por períodos de seca e com altas temperaturas.…”

“…Vasos com pontoações e perfurações destes tipos evitam a embolia em plantas crescendo em ambientes quentes com sazonalidade de estresses hídricos. Este tipo de sistema é mais eficiente quanto à demanda do intenso fluxo de água imposta pelas altas taxas de transpiração em plantas de regiões quentes e secas (Wheeler & Baas 1991;Jansen et al 2004).…”

ANATOMIA DO LENHO DE RAIZ, TRONCO E GALHO DE BARBATIMÃO (Stryphnodendron adstringens (Mart) Coville)

“…Segundo Carlquist (2001), Jansen et al (2004) Machado et al (1997) para Styrax camporum (Styracaceae), e Goulart (2012) em estudos comparados para lenho de raiz e caule de Aegiphila sellowiana (Verbenaceae), todas ocorrentes em áreas de cerrado. em relação ao diâmetro dos vasos, quando analisados todos os espécimes, não houve variação (Tabela 3), no entanto, houve muita variação entre os espécimes (Tabela 2).…”