Lianas and trees exhibit divergent intrinsic water‐use efficiency along elevational gradients in South American and African tropical forests

Abstract

Aim Elevational gradients provide excellent opportunities to explore long‐term morphological and physiological responses of plants to environmental change. We determined the difference in the elevational pattern of foliar carbon isotope composition (δ13C) between lianas and trees, and assessed whether this difference arises from changes in photosynthesis or stomatal conductance. We also explored the pattern of nutrient limitations with the elevation of these two growth forms. Location The study was conducted in two mountain forests situated in the Neotropics and Palaeotropics. Time period August–September 2015 and August–October 2016. Major taxa studied Lianas and trees. Methods We conducted inventories of lianas and trees using standardized techniques along elevational gradients in Ecuador and Rwanda. We determined the values of several foliar traits including δ13C and chemical traits in dominant liana and tree species. We set up Bayesian linear mixed‐effect models to quantify the effects of elevation and growth form on each of the foliar traits , and the difference of the effect of elevation between the two growth forms (lianas and trees). Results We found consistent growth form specific divergences in foliar δ13C and carbon to nitrogen ratio (C : N) responses to elevation. While we noted a meaningful increase in foliar δ13C and C : N with elevation for trees, lianas did not exhibit such a trend. Foliar δ13C and C : N remained relatively constant for lianas along the transects. Main conclusions Lianas operate at relatively constant intrinsic water‐ and nitrogen‐use efficiencies with elevation compared with trees. Altogether, the study suggests the existence of a functional divergence of water and nutrient use strategies between lianas and trees along tropical elevational transects.

Temperature, nutrient availability, and species traits interact to shape elevation responses of Australian tropical trees

“…We investigated trends in tree growth and leaf functional traits along an elevation gradient in the Australian Wet Tropics using a single, regionally important genus to gain insight into the responses of closely related species with differing elevational distributions. Observations in tropical rainforests on other continents have shown that tree growth rates and foliar δ 15 N typically decline with elevation (Bauters et al, 2017;Malhi et al, 2017), whereas LMA and foliar δ 13 C typically increase with elevation (Vitousek et al, 1990;Mumbanza et al, 2021). We confirmed from our field-based observations that similar trends also occur in Flindersia species in Australian tropical rainforests.…”

“…Foliar δ 13 C and δ 15 N have been used as indicators of intrinsic water-use efficiency (Cernusak et al, 2013), and ecosystem nitrogen cycling (Martinelli et al, 1999), respectively. However, although some of these trends with increasing elevation appear to be general in the literature (Vitousek et al, 1990;Bauters et al, 2017;Mumbanza et al, 2021), the mechanisms driving the observations are not fully resolved. Disentangling the direct and indirect role that temperature plays in determining these trends in plant functional traits is vital to understanding elevation gradients as proxies for predicting the response of forests to future climate scenarios.…”

Vegetative phenologies of lianas and trees in two Neotropical forests with contrasting rainfall regimes

“…The higher leaf water potentials in lianas suggest stronger stomatal control compared to trees, which allows lianas to reduce the variation in leaf water potentials by limiting transpiration (E) through reduced stomatal conductance (G s ) (Tyree & Sperry, 1988; Cochard et al ., 2002; Sperry et al ., 2002). Since such stronger stomatal control may lead to a higher water use efficiency (the ratio of biomass accumulation to water lost) (Sinclair et al ., 1984; Tardieu, 2013; Lawson & Blatt, 2014), this may allow the lianas under study here to maintain leaf productivity while preventing excessive dehydration under drier environmental conditions (Sinclair et al ., 1984; Mumbanza et al ., 2021). Such mechanisms may thus appear in the liana and tree communities under study here, as well as in liana communities in other forests (Andrade et al ., 2005; Chen et al ., 2015).…”

“…high water transport capacity) resulting from their wide and long xylem elements (Ewers et al ., 1991) may allow lianas to reduce water potential differences between soil and leaves, enabling high tissue water potentials and positive turgor potentials during drought. High water use efficiency resulting from strong stomatal control (Cai et al ., 2009; Chen et al ., 2015) may allow lianas to maximize gas exchange and growth while preventing excessive dehydration (see also Mumbanza et al ., 2021). Additionally, a high accumulation of nonstructural carbohydrates for osmoregulation and hydraulic function (O’Brien et al ., 2014; Martínez‐Vilalta et al ., 2016) and reductions in leaf area (Lambers & Oliveira, 2019) could also explain the maintenance of high water status and turgor potentials in lianas during seasonal drought.…”

Effects of Geographical and Climatic Factors on the Intrinsic Water Use Efficiency of Tropical Plants: Evidence from Leaf 13C

“…Zhang et al (2020) [ 24 ] found that wind speed affected the boundary layer of the air on the leaf surface, which decreased the resistance for gas exchange and the exchange of CO 2 and H 2 O between the leaf interior and ambient atmosphere, thereby influencing the leaf WUE. In addition, since climatic factors change with geographical factors, intrinsic WUE changes with geographical factors [ 25 , 26 ]. Although many previous works have focused on the relationships between plant WUE and climatic factors [ 15 ], most of these studies were concentrated mainly on arid and semiarid climate regions, or the research objects were mostly one or several plants [ 19 , 22 , 27 ]; in contrast, few studies have focused on tropical regions with high temperature and rainfall.…”