Search

Premise of research. Understanding the relationship between field-measured operating stomatal conductance (gop) and theoretical maximum stomatal conductance (gmax), calculated from stomatal density and geometry, provides an important framework that can be used to infer leaf-level gas exchange of historical, herbarium, and fossil plants. To date, however, investigation of the nature of the relationship between gop and theoretical gmax remains limited to a small number of experiments on relatively few taxa and is virtually undefined for plants in natural ecosystems.\ud \ud Methodology. We used the gop measurements of 74 species and 35 families across four biomes from a published contemporary data set of field-measured leaf-level stomatal conductance in woody angiosperms and calculated the theoretical gmax from the same leaves to investigate the relationship between gop and gmax across multiple species and biomes and determine whether such relationships are widely conserved.\ud \ud Pivotal results. We observed significant relationships between gop and gmax, with consistency in the gop ∶ gmax ratio across biomes, growth habits (shrubs and trees), and habitats (open canopy and understory subcanopy). An overall mean gop ∶ gmax ratio of 0.26 ± 0.11 (mean ± SD) was observed. The consistently observed gop ∶ gmax ratio in this study strongly agrees with previous hypotheses that an ideal gop ∶ gmax ratio exists.\ud \ud Conclusions. These results build substantially on previous studies by presenting a new reference for a consistent gop ∶ gmax ratio across many levels and offer great potential to enhance paleoclimate proxies and vegetation-climate models alike.

A rapid rise in CO2 has made evergreen trees more waterwise than deciduous trees, especially in cooler parts of the world., Intrinsic water use efficiency (iWUE), defined as the ratio of photosynthesis to stomatal conductance, is a key variable in plant physiology and ecology. Yet, how rising atmospheric CO2 concentration affects iWUE at broad species and ecosystem scales is poorly understood. In a field-based study of 244 woody angiosperm species across eight biomes over the past 25 years of increasing atmospheric CO2 (~45 ppm), we show that iWUE in evergreen species has increased more rapidly than in deciduous species. Specifically, the difference in iWUE gain between evergreen and deciduous taxa diverges along a mean annual temperature gradient from tropical to boreal forests and follows similar observed trends in leaf functional traits such as leaf mass per area. Synthesis of multiple lines of evidence supports our findings. This study provides timely insights into the impact of Anthropocene climate change on forest ecosystems and will aid the development of next-generation trait-based vegetation models.

Intrinsic water use efficiency (iWUE), defined as the ratio of photosynthesis to stomatal conductance, is a key variable in plant physiology and ecology. Yet, how rising atmospheric CO2 concentration affects iWUE at broad species and ecosystem scales is poorly understood. In a field-based study of 244 woody angiosperm species across eight biomes over the past 25 years of increasing atmospheric CO2 (~45 ppm), we show that iWUE in evergreen species has increased more rapidly than in deciduous species. Specifically, the difference in iWUE gain between evergreen and deciduous taxa diverges along a mean annual temperature gradient from tropical to boreal forests and follows similar observed trends in leaf functional traits such as leaf mass per area. Synthesis of multiple lines of evidence supports our findings. This study provides timely insights into the impact of Anthropocene climate change on forest ecosystems and will aid the development of next-generation trait-based vegetation models.

Stomatal conductance (gs) in terrestrial vegetation regulates the uptake of atmospheric carbon dioxide for photosynthesis and water loss through transpiration, closely linking the biosphere and atmosphere and influencing climate. Yet, the range and pattern of gs in plants from natural ecosystems across broad geographic, climatic, and taxonomic ranges remains poorly quantified. Furthermore, attempts to characterize gs on such scales have predominantly relied upon meta-analyses compiling data from many different studies. This approach may be inherently problematic as it combines data collected using unstandardized protocols, sometimes over decadal time spans, and from different habitat groups. Using a standardized protocol, we measured leaf-level gs using porometry in 218 C3 woody angiosperm species in natural ecosystems representing seven bioclimatic zones. The resulting dataset of 4273 gs measurements, which we call STraits (Stomatal Traits), was used to determine patterns in maximum gs (gsmax) across bioclimatic zones and whether there was similarity in the mean gsmax of C3 woody angiosperms across ecosystem types. We also tested for differential gsmax in two broadly defined habitat groups – open-canopy and understory-subcanopy – within and across bioclimatic zones. We found strong convergence in mean gsmax of C3 woody angiosperms in the understory-subcanopy habitats across six bioclimatic zones, but not in open-canopy habitats. Mean gsmax in open-canopy habitats (266 ± 100 mmol m-2 s-1) was significantly higher than in understory-subcanopy habitats (233 ± 86 mmol m-2 s-1). There was also a central tendency in the overall dataset to operate toward a gsmax of ∼250 mmol m-2 s-1. We suggest that the observed convergence in mean gsmax of C3 woody angiosperms in the understory-subcanopy is due to a buffering of gsmax against macroclimate effects which will lead to differential response of C3 woody angiosperm vegetation in these two habitats to future global change. Therefore, it will be important for future studies of gsmax to categorize vegetation according to habitat group.

Background and Aims: Studies have indicated that plant stomatal conductance (gs) decreases in response to elevated atmospheric CO2, a phenomenon of significance for the global hydrological cycle. However, gs increases across certain CO2 ranges have been predicted by optimisation models. The aim of this work was to demonstrate that under certain environmental condition, gs can increase in response to elevated CO2. Methods: When using (i) an extensive, up-to-date, synthesis of gs responses in FACE experiments, (ii) in situ measurements across four biomes showing dynamic gs responses to a CO2 rise of ~50ppm (characterising the change in this greenhouse gas over the past three decades) and (iii) a photosynthesis-stomatal conductance model, it is demonstrated that gs can in some cases increase in response to increasing atmospheric CO2. Key Results: Field observations are corroborated by an extensive synthesis of gs responses in FACE experiments showing that 11.8% of gs responses under experimentally elevated CO2 are positive. They are further supported by a strong data-model fit (r2=0.607) using a stomatal optimization model applied to the field gs dataset. A parameter space identified in the Farquhar-Ball-Berry photosynthesis-stomatal conductance model confirms field observations of increasing gs under elevated CO2 in hot dry conditions. It was shown that contrary to the general assumption, positive gs responses to elevated CO2, although relatively rare, are a feature of woody taxa adapted to warm, low-humidity conditions, and that this response is also demonstrated in global simulations using the Community Land Model (CLM4). Conclusions: The results contradict the over-simplistic notion that global vegetation always responds with decreasing gs to elevated CO2, a finding that has important implications for predicting future vegetation feedbacks on the hydrological cycle at the regional level. Irish Research Council Science Foundation Ireland

In the Supplementary Information file originally published, the caption for Supplementary Figure 3d-f was missing. This has now been corrected.

Climate change is likely to have altered the ecological functioning of past ecosystems, and is likely to alter functioning in the future; however, the magnitude and direction of such changes are difficult to predict. Here we use a deep-time case study to evaluate the impact of a well-constrained CO2-induced global warming event on the ecological functioning of dominant plant communities. We use leaf mass per area (LMA), a widely used trait in modern plant ecology, to infer the palaeoecological strategy of fossil plant taxa. We show that palaeo-LMA can be inferred from fossil leaf cuticles based on a tight relationship between LMA and cuticle thickness observed among extant gymnosperms. Application of this new palaeo-LMA proxy to fossil gymnosperms from East Greenland reveals significant shifts in the dominant ecological strategies of vegetation found across the Triassic–Jurassic transition. Late Triassic forests, dominated by low-LMA taxa with inferred high transpiration rates and short leaf lifespans, were replaced in the Early Jurassic by forests dominated by high-LMA taxa that were likely to have slower metabolic rates. We suggest that extreme CO2-induced global warming selected for taxa with high LMA associated with a stress-tolerant strategy and that adaptive plasticity in leaf functional traits such as LMA contributed to post-warming ecological success.

A new bicarpellate Buxus species, Buxus sirindhorniana W. K. Soh, M. von Sternburg, Hodk. & J. Parn., is described from northern Th ailand. Th is is the fi rst reported bicarpellate species of Buxus . Th e pollen morphology and the degree of pollen viability of the species are reported. DNA was extracted from herbarium samples and the internal transcribed spacer (ITS) region of nuclear ribosomal DNA sequenced. Th e palynological evidence and the phylogenetic reconstruction support the contention that this new species belongs to the genus Buxus . Th e morphological diversity of reproductive organs in the Buxaceae, in relation to this new species, is briefl y discussed.

Descriptions, illustrations, a distribution map and conservation assessments are provided for three new species of Syzygium from Indochina. Based on morphological characters, all three new species, Syzygium bokorense W. K. Soh & J. Parn., S. chantaranothaianum W. K. Soh & J. Parn. and S. cucphuongense W. K. Soh & J. Parn., belong to the subgenus Syzygium.

The leaf anatomy of 81 species of Syzygium was examined. General generic and subgeneric descriptions of Syzygium leaf anatomy are given. Four stomatal types (anisocytic, anomocytic, cyclo-staurocytic and paracytic) that occur exclusively or in combinations are recognised. Two major vascular systems are differentiated by the presence or absence of adaxial phloem partition. Phylogenetic inferences using maximum parsimony and Bayesian methods for separate and combined analyses of DNA (ETS and ITS) sequences and morphological (leaf anatomy and macromorphology) data were conducted. Results of the combined analyses gave slightly higher support value for clade than analyses based on DNA sequences. The subgenera Perikion, Sequestratum and Syzygium are strongly supported, but the subgenus Acmena is moderately supported in the Bayesian but not in the parsimony analysis of combined data sets. The relationships among subgenera are not fully resolved. All the leaf anatomical characters examined are homoplastic. We did not find any unique leaf anatomical characters allowing delimiting of the four subgenera in Syzygium. However, a combinations of non-unique leaf anatomical characters, including stomatal types, crystal types and frequency, and midrib vascular system (adaxial phloem partition) are diagnostic for subgeneric groups.

The genus Syzygium (Myrtaceae) is revised for Indochina (Cambodia, Laos and Vietnam). The species key, descriptions, typification, ecology, conservation status, phenology, vernacular names, usages, distribution maps, selected herbarium images and list of specimens examined are given. A total of fifty-six species are recognised in Indochina. Eight species including Syzygium bokorense W.K.Soh & J.Parn., S. chantaranothaianum W.K.Soh & J.Parn., S. crassiflorum Merr. & L.M.Perry, S. cucphuongense W.K.Soh & J.Parn., S. glomerulatum (Gagnep.) Merr. & L.M.Perry, S. harmandii (Gagnep.) Merr. & L.M.Perry, S. pierrei (Gagnep.) Merr. & L.M.Perry and S. tonkinense (Gagnep.) Merr. & L.M.Perry are confined to Indochina. 63 lectotypes were designated and 23 previously accepted species names are now synonyms under Syzygium. Vietnam harbours the largest number of species (49), followed by Laos (30) and Cambodia (27). Syzygium attopeuense (Gagnep.) Merr. & L.M.Perry and Syzygium corticosum (Lour.) Merr. & L.M.Perr...

Twenty-six species of Cinnamomum are recognised in Borneo. Seventeen species are endemic to Borneo. Fifteen species names are newly reduced to synonymy. The species nomenclature, description, distribution, ecology, vernacular names and uses are given.