Lianas in tropical dry seasonal forests have a high hydraulic efficiency but not always a higher embolism resistance than lianas in rainforests.

BACKGROUND AND AIMS: Lianas have higher relative abundance and biomass in drier seasonal forests than in rainforests, but whether this difference is associated with their hydraulic strategies is unclear. Here, we investigate whether lianas of seasonally dry forests are safer and more efficient in water transport than rainforest lianas, explaining patterns of liana abundance. METHODS: We measured hydraulic traits on five pairs of congeneric lianas of the tribe Bignonieae in two contrasting forest sites: the wet 'Dense Ombrophilous Forest' in Central Amazonia (~2 dry months) and the drier 'Semideciduous Seasonal Forest' in the inland Atlantic Forest (~6 dry months). We also gathered a broader database, including 197 trees and 58 liana species from different tropical forests, to compare hydraulic safety between habits and forest types. KEY RESULTS: Bignonieae lianas from both forests had high and similar hydraulic efficiency but exhibited variability in resistance to embolism across forest types when phylogenetic relationships were taken into account. Three genera had higher hydraulic safety in the seasonal forest than in the rainforest, but species across both forests had similar positive hydraulic safety margins despite lower predawn water potential values of seasonal forest lianas. We did not find the safety-efficiency trade-off. Merging our results with previously published data revealed a high variability of resistance to embolism in both trees and lianas, independent of forest types. CONCLUSIONS: The high hydraulic efficiency of lianas detected here probably favours their rapid growth across tropical forests, but differences in hydraulic safety highlight that some species are highly vulnerable and may rely on other mechanisms to cope with drought. Future research on the lethal dehydration threshold and the connection between hydraulic resistance strategies and liana abundance could offer further insights into tropical forest dynamics under climatic threats.

How dehydration affects stem bending stiffness and leaf toughness after sampling of the liana Amphilophium crucigerum (L.) L.G.Lohmann (Bignoniaceae) / Como a desidratação afeta a flexibilidade do caule e a tenacidade das folhas pós-coleta na liana Amphilophium crucigerum (L.) L.G.Lohmann (Bignoniaceae)

Lianas are woody climbers and their stems and leaves deal with different environmental pressures such as resistance to mechanical damage and dehydration. The damage resistance of plants can be biomechanically evaluated by their stiffness, bending and toughness. Despite the well-known relationship between physical resistance and moisture of plant organs in woody plants, this relationship is uncertain and has not been previously evaluated in lianas. Thus, this study investigated experimentally the effect of stems and leaf dehydration on the structural Young's modulus in the stem and fracture toughness in leaves across time in the liana Amphilophium crucigerum (Bignoniaceae). Ten stem and leaf samples were collected and assigned to two distinct conditions: (i) samples kept moist and (ii) samples underwent gradual dehydration with natural moisture loss by air exposition. Successive measures of structural Young's modulus and fracture toughness were taken every 4 hours during a 48-hour period for both conditions. Stem and leaf samples which underwent gradual dehydration showed greater bending stiffness and fracture toughness, respectively, while the samples kept moist presented no changes in any studied biomechanical features during the entire experiment. We concluded that the moisture of both stem and leaf samples are critical factors to estimate the biomechanical properties of lianas stem and leaves.

Lianas são trepadeiras lenhosas e seus caules e folhas lidam com diferentes pressões ambientais, como a resistência aos danos mecânicos e de desidratação. A resistência ao dano das plantas pode ser biomecanicamente avaliada pelas propiedades de dureza, flexão e tenacidade. Apesar da conhecida relação entre resistência física e umidade dos órgãos das plantas em espécies lenhosas, essa relação não foi avaliada anteriormente e é incerta em lianas. Assim, este estudo investigou experimentalmente o efeito da desidratação de caules e folhas na estimativa do módulo estrutural de Young do caule e da tenacidade à fratura da folha ao longo do tempo, na liana Amphilophium crucigerum (Bignoniaceae). Dez amostras de caules e folhas foram coletadas e distribuídas em duas condições distintas: (i) amostras mantidas úmidas e (ii) amostras em processo de desidratação gradativa com perda natural de umidade quando expostas ao ar. Medidas sucessivas do módulo de Young e da resistência à fratura dos órgãos foram tomadas a cada 4 horas durante um período de 48 horas em ambas as condições. Amostras de caule e folhas que sofreram desidratação gradual apresentaram maior rigidez à flexão e tenacidade à fratura, respectivamente, enquanto as amostras mantidas úmidas não alteraram essas características durante o experimento. Concluímos que a umidade das amostras de caules e folhas em lianas também é um fator crítico para estimar as propriedades biomecânicas desses órgãos em seu ambiente natural.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Cucurbita ficifolia in Korea.

Cucurbita ficifolia Bouché, called fig-leaf gourd, is a cucurbitaceous climbing plant native to the Americas. During summer and autumn of 2020, almost all of fig-leaf gourds planted in an experimental plot in Jeonju (35°50'54″N, 127°07'46″E), Korea, were found to be infected by a powdery mildew with a 100% disease severity. Symptoms first appeared as white, small, irregular colonies, later coalesced into abundant hyphal growth on both sides of the leaves and young stems. Subsequently premature senescence and poor growth of affected leaves was observed. A voucher specimen was housed in the Korea University herbarium (KUS-F32173). For morphological characterization of the fungus, fresh materials were used for microscopy. Conidiophores (n = 30) were straight, 90 to 190 × 10 to 12 µm and produced three to six immature conidia in chains with a crenate outline. Conidia (n = 30) were ellipsoid-ovoid to barrel-shaped, measured 28 to 38 × 18 to 24 µm with a length/width ratio of 1.3 to 2.0, and contained distinct fibrosin bodies. No chasmothecia were found over the course of the season. The morphological feature of the fungus and the host genus were compatible with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012), a well-known cucurbitaceous powdery mildew. For further confirmation, DNA was extracted from mycelium taken from above mentioned specimen. Internal transcribed spacers (ITS1 and ITS2) and large subunit (LSU) gene of the rDNA were amplified using primer pairs ITS1F/PM6 and PM3/TW14, respectively (Takamatsu and Kano 2001). Newly obtained sequences were registered to the GenBank under the accession numbers OL677355 for ITS and OL677356 for LSU. Our sequences shared 99.54~99.77% identity for ITS (MW559231 and MT250855) and 99.58% for LSU with sequences of P. xanthii (MK357445 and MK357438) in BLAST'n search. Pathogenicity tests were performed twice by pressing method of mycelial patches of the infected leaf onto the young leaves of five healthy fig-leaf gourd plants. Five non-inoculated plants were used as controls. Inoculated leaves started to develop powdery mildew signs after 5 days treatment, whereas the control plants remained symptomless. The fungus on the inoculated plants was morphologically identical to that originally observed on diseased plants, fulfilling Koch's postulates. To date three powdery mildew species have been reported on C. ficifolia (Farr and Rossman 2021). Among these reports, Golovinomyces orontii sensu lato was known from Chile, Mexico, United Kingdom, and Germany, Leveillula taurica from Korea and Podosphaera fuliginea (currently P. xanthii) was recorded Australia and India. To our knowledge, this is the first report of P. xanthii on C. ficifolia in Korea. Since this plant is used as grafting rootstock for preventing soil-borne gummy stem blight of cucumber caused by Didymella bryoniae in Korea (Choi et al. 2009), economic importance of the powdery mildew occurring on leaves of this plant is currently limited. Nevertheless, presence of a powdery mildew could be informative to breeding program of Cucurbita spp. and safe production of C. ficifolia fruits globally.

Self-discrimination in vine tendrils of different plant families.

Previous study reported a novel type of self-discrimination in the tendrils of the vine Cayratia japonica (Vitaceae). However, whether self-discrimination in tendrils is common in vine plant species has not been elucidated. Here, we investigated whether tendrils of Momordica charantia var. pavel (Cucurbitaceae), Cucumis sativus (Cucurbitaceae) and Passiflora caerulea (Passifloraceae) can discriminate self and non-self plants. We also investigated whether the tendrils of M. charantia and C. sativus can discriminate differences in cultivars to determine the discrimination ability for genetic similarity. We found that tendrils of the M. charantia and P. caerulea were more likely to coil around non-self plant than self plants, but not in C. sativus. Our findings support the common occurrence of self-discrimination in tendrils in different plant taxa, although some species lacked it. Furthermore, tendrils of M. charantia more rapidly coil around different cultivars than around same cultivars. The tendrils of M. charantia may can discriminate differences in cultivars.

Facilitation of amphibious habit by physiological integration in the clonal, perennial, climbing herb Ipomoea aquatica.

Physiological integration of connected ramets of clonal plants can increase clonal performance when ramets grow in contrasting microenvironments within a habitat. In amphibious clonal species, integration of ramets in different habitats, terrestrial and aquatic, is possible. This may increase performance of amphibious clones, especially under eutrophic conditions. To test this, clonal fragments consisting of two ramets of the amphibious, perennial, climbing herb Ipomoea aquatica connected by a stem were placed such that the proximal ramet was rooted in a simulated riparian community of four other species, while the distal ramet extended into a simulated aquatic habitat with open water and sediment. The connection between ramets was either left intact or severed, and 0, 5, or 25mg N L-1 was added to the aquatic habitat to simulate different degrees of eutrophication. Without added N, fragments in which the original ramets were left connected accumulated two times more total mass than fragments in which the ramets were disconnected from one another. The positive effect of connection increased two-fold with increasing N. These results were consistent with the hypotheses that physiological integration between connected terrestrial and aquatic ramets can increase clonal performance in plants and that this effect can be greater when the aquatic ramet is richer in nutrients. Connection reduced root to shoot ratio in terrestrial ramets, but increased it in aquatic ones, suggesting that physiological integration induced a division of labor in which terrestrial ramets specialized for light acquisition and aquatic ramets specialized for acquisition of nutrients. This provides the first report of increase in clonal performance and induction of division of labor due to physiological integration between ramets in different habitats.

Vine tendrils use contact chemoreception to avoid conspecific leaves.

Movement and growth habit of climbing plants have attracted attention since the time of Charles Darwin; however, there are no reports on whether plants can choose suitable hosts or avoid unsuitable ones based on chemoreception. Here, I show that the tendrils of Cayratia japonica (Vitaceae) appear to avoid conspecific leaves using contact chemoreception for oxalates, which are highly concentrated in C. japonica leaves. The coiling experiments show that C. japonica has a flexible plastic response to avoid coiling around conspecific leaves. The coiling response is negatively correlated with the oxalate content in the contacted leaves. Experiments using laboratory chemicals indicate that the tendrils avoid oxalate-coated plastic sticks. These results indicate that the tendrils of C. japonica avoid coiling around a conspecific leaf based on contact chemoreception for oxalate compounds. The tendrils of climbing plants may function as a chemoreceptor system to detect the chemical cues of a contacted plant.