Increases in drought‐induced tree mortality are being observed in tropical rain forests worldwide and are also likely to affect the geographical distribution of tropical vegetation. However, the ...mechanisms underlying the drought vulnerability and environmental distribution of tropical species have been little studied. We measured vulnerability to xylem embolism (P50) of 13 woody species endemic to New Caledonia and with different xylem conduit morphologies. We examined the relation between P50, along with other leaf and xylem functional traits, and a range of habitat variables. Selected species had P50 values ranging between −4.03 and −2.00 MPa with most species falling in a narrow range of resistance to embolism above −2.7 MPa. Embolism vulnerability was significantly correlated with elevation, mean annual temperature and percentage of species occurrences located in rain forest habitats. Xylem conduit type did not explain variation in P50. Commonly used functional traits such as wood density and leaf traits were not related to embolism vulnerability. Xylem embolism vulnerability stands out among other commonly used functional traits as a major driver of species environmental distribution. Drought‐induced xylem embolism vulnerability behaves as a physiological trait closely associated with the habitat occupation of rain forest woody species.
Increases in drought‐induced tree mortality are being observed in tropical rain forests worldwide and are also likely to affect the geographical distribution of tropical vegetation. However, the mechanisms underlying the drought vulnerability and environmental distribution of tropical species have been little studied. Trueba et al. measured vulnerability to xylem embolism, along with other easy‐to‐measure wood and leaf functional traits, of 13 species endemic to the tropical archipelago of New Caledonia. This study shows that xylem embolism vulnerability stands out among other functional traits as a major driver of species environmental distribution. Drought‐induced xylem embolism vulnerability behaves as a physiological trait closely associated with the habitat occupation of rain forest woody species.
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.
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.
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.
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.
Summary
The evolution of angiosperms was accompanied by the segregation and specialisation of their xylem tissues. This study aimed to determine whether the fraction and arrangement of parenchyma ...tissue influence the hydraulic efficiency–safety trade‐off in the basal angiosperms.
We examined xylem anatomical structure and hydraulic functioning of 28 woody species of Magnoliids in a tropical rainforest of Madagascar and reported, for the first time, quantitative measurements that support the relationship between vessel‐to‐xylem parenchyma connectivity and the hydraulic efficiency–safety trade‐off. We also introduced a new measurement – the distance of species from the trade‐off limit – to quantify the co‐optimisation of hydraulic efficiency and safety.
Although the basal angiosperms in this study had low hydraulic conductivity and safety, species with higher axial parenchyma fraction (APf) had significantly higher hydraulic conductivity. Hydraulic efficiency–safety optimisation was accompanied by higher APf and vessel‐to‐axial parenchyma connectivity. Conversely, species exhibiting high ray parenchyma fraction and high vessel‐to‐ray connectivity had lower Ks and were further away from the hydraulic trade‐off limit line.
Our results provide evidence that axial parenchyma fraction and paratracheal arrangement are associated with both enhanced hydraulic efficiency and safety.
Weeds are major threats to the integrity of agricultural and natural environments due to their invasive and competing potential. Bioherbicides are substances based on natural compounds that are ...biodegradable and often have low residual effects. Plant species able to produce and release phytotoxic compounds may represent effective bioherbicide sources. Leaves of Quillaja lancifolia D.Don (formerly Q. brasiliensis (A.St.-Hil. & Tul.) Mart.) produce water-soluble specialized metabolites of the saponin class that could be evaluated for phytotoxic activity and potential as natural herbicides. This study was conducted to examine the impacts of Q. lancifolia total saponins aqueous extract (AE) at 4 and 10% (w/v) and of two combined reverse-phase chromatography purified saponin fractions (QB) at 1 and 2% (w/v) on morpho-physiological parameters of Lactuca sativa (lettuce) and Echinochloa crus-galli (barnyardgrass) in pre- and post-emergence bioassays. QB was only tested in pre-emergence assays. In pre-emergence bioassays, the germination rate and germination kinetics were determined. Post-emergence evaluations included effects on seedling morphology, root and shoot length, dry mass, and chlorophyll content. Osmotic potential and pH analyses ruled out roles for these factors in the observed responses. AE had a high inhibitory impact on the germination of both lettuce and barnyardgrass. QB at 1% and 2% (w/v) significantly decreased the growth of lettuce seedlings germinated in its presence by more than 10-fold. Phytotoxic effects on the post-emergence growth of lettuce, especially at the highest concentration tested of AE (10% w/v), was also observed. The presence of quillaic acid-based triterpene saponins in AE and QB was confirmed using different analytical methods. Therefore, both saponin-enriched fraction and aqueous extracts of Q. lancifolia inhibited tested plant growth and development. The water solubility of saponins and the availability of a sustainable source of these molecules from the leaves of cultivated young Q. lancifolia plants make them attractive candidates for use as bioherbicides.
Severe droughts have the potential to reduce forest productivity and trigger tree mortality. Most trees face several drought events during their life and therefore resilience to dry conditions may be ...crucial to long-term survival. We assessed how growth resilience to severe droughts, including its components resistance and recovery, is related to the ability to survive future droughts by using a tree-ring database of surviving and now-dead trees from 118 sites (22 species, >3,500 trees). We found that, across the variety of regions and species sampled, trees that died during water shortages were less resilient to previous non-lethal droughts, relative to coexisting surviving trees of the same species. In angiosperms, drought-related mortality risk is associated with lower resistance (low capacity to reduce impact of the initial drought), while it is related to reduced recovery (low capacity to attain pre-drought growth rates) in gymnosperms. The different resilience strategies in these two taxonomic groups open new avenues to improve our understanding and prediction of drought-induced mortality.
Beetles (Coleoptera) are the most diverse and species-rich group of insects, and a robust, time-calibrated phylogeny is fundamental to understanding macroevolutionary processes that underlie their ...diversity. Here we infer the phylogeny and divergence times of all major lineages of Coleoptera by analyzing 95 protein-coding genes in 373 beetle species, including ~67% of the currently recognized families. The subordinal relationships are strongly supported as Polyphaga (Adephaga (Archostemata, Myxophaga)). The series and superfamilies of Polyphaga are mostly monophyletic. The species-poor Nosodendridae is robustly recovered in a novel position sister to Staphyliniformia, Bostrichiformia, and Cucujiformia. Our divergence time analyses suggest that the crown group of extant beetles occurred ~297 million years ago (Mya) and that ~64% of families originated in the Cretaceous. Most of the herbivorous families experienced a significant increase in diversification rate during the Cretaceous, thus suggesting that the rise of angiosperms in the Cretaceous may have been an 'evolutionary impetus' driving the hyperdiversity of herbivorous beetles.
The Indochinese Peninsula is a main center of speciation of Capparis, but the taxonomic treatment of the genus is still critical in this area. With regard to Vietnam, a discordant number of species ...was recorded by different authors during the last century, whereas various new species have been recently described. An updated checklist of the intrageneric taxa occurring in the country is here presented, including a new species from the island of Hon Tre, Khanh Hoa Province. The genus comprises in Vietnam 37 species, 9 subspecies and 3 varieties, all belonging to Capparis sect. Monostichocalyx. The study area, with 10 endemic species, is confirmed as one of the hotspots of the genus. Three lectotypes are also selected. The new species here described and illustrated, C. oxycarpa, is related to C. pranensis, differing in the few-flowered subumbels, narrower sepals, smaller petals, longer filaments and smaller, apiculate fruit; its affinities with related taxa and conservation status are discussed, and data on its ecology and phenology are given.
Chaetomium cupreum, a root endophyte in Miscanthus sinensis, enhances Al tolerance in M. sinensis by changing aluminum (Al) localization and the production of a siderophore, oosporein, which chelates ...Al for detoxification. Oosporein has various functions, including insecticidal activity, phytotoxicity, antifungal activity, and a siderophore. In our study, we focused on the detoxification effect of oosporein as a siderophore and on the growth of M. sinensis under Al exposure. In addition, the phytotoxicity of oosporein to M. sinensis was confirmed to compare with those in Lactuca sativa and Oryza sativa as control plants. Under Al stress, oosporein promoted plant growth in M. sinensis seedlings at 10 ppm, which was the same concentration as that detected in M. sinensis roots infected with C. cupreum in our previous study. Oosporein also showed low phytotoxicity to M. sinensis compared with L. sativa at even high concentrations of oosporein. These results suggest that the concentration of oosporein in M. sinensis roots would be maintained at the appropriate concentration to detoxify Al and would promote M. sinensis growth under Al stress, although oosporein would show low phytotoxicity to the natural host plant, M. sinensis, compared with the non-host plant, L. sativa.
Summary
Angiosperm dominance in terrestrial landscapes is partially attributable to high photosynthetic capacities. Angiosperms benefit from diverse anatomical and physiological adaptations, making ...it difficult to determine which factors may have been prerequisites for the evolution of enhanced photosynthetic rates in this group.
We employed a novel approach to this problem: comparisons between angiosperms and Marsileaceae, a family of semi‐aquatic ferns that are among the only land plants to match angiosperm photosynthetic rates.
We found that Marsileaceae have very high stomatal densities and, like angiosperms but unlike all other ferns previously studied, exhibit wrong‐way stomatal responses to excision.
These results suggest that stomatal density and a little‐studied angiosperm trait, the capacity for lateral displacement of guard cells into neighboring epidermal cells, are crucial for facilitating high rates of gas exchange. Our analysis also associates these adaptations in Marsileaceae with an increased risk of excessive water loss during drought. Our findings indicate that evolution in stomatal physiology was a prerequisite for high photosynthetic capacities in vascular plants and a key driver of the abrupt Cretaceous rise of the angiosperms.
Summary
Biodiversity today has the unusual property that 85% of plant and animal species live on land rather than in the sea, and half of these live in tropical rainforests. An explosive boost to ...terrestrial diversity occurred from c. 100–50 million years ago, the Late Cretaceous and early Palaeogene. During this interval, the Earth‐life system on land was reset, and the biosphere expanded to a new level of productivity, enhancing the capacity and species diversity of terrestrial environments. This boost in terrestrial biodiversity coincided with innovations in flowering plant biology and evolutionary ecology, including their flowers and efficiencies in reproduction; coevolution with animals, especially pollinators and herbivores; photosynthetic capacities; adaptability; and ability to modify habitats. The rise of angiosperms triggered a macroecological revolution on land and drove modern biodiversity in a secular, prolonged shift to new, high levels, a series of processes we name here the Angiosperm Terrestrial Revolution.
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