Vulnerability to cavitation is linked to home climate precipitation across eight eucalypt species

Vulnerability to cavitation in leaves is the result of highly adaptive anatomical and physiological traits that can be linked to water availability in a species' climate of origin. Despite similar gross leaf morphology, eucalypt species are often confined to specific climate envelopes across the variable rainfall environments of Australia. In this study, we investigate how the progression of cavitation differs among eucalypts and whether this is related to other hydraulic and physical leaf traits. We used the Optical Visualisation technique to capture cavitation progression across the leaves of eight eucalypt species (Angophora crassifolia, Corymbia tessellaris, Eucalyptus atrata, Eucalyptus grandis, Eucalyptus laevopinea, Eucalyptus longifolia, Eucalyptus macrandra, Eucalyptus tereticornis) from a wide range of climates and grown in a common garden setting. Vulnerability to cavitation, represented by the leaf water potential required for 50% cavitation of leaf vessels, varied significantly among species (-3.48 MPa to -8.25 MPa) and correlated linearly with home climate precipitation and leaf SLA (R2 of 0.64 and 0.75, respectively). P12-P88, the range of water potentials between which 12% to 88% of cavitation occurs, was decoupled from P50 but also correlated with leaf SLA (R2 of 0.72). We suggest the magnitude of P12-P88 may be representative of a species' drought strategy - a large P12-P88 signifying leaves that exhibit drought tolerance (retention of leaves under drought conditions) and a small P12-P88 signifying drought avoidance (leaf shedding after a threshold of drought is reached). Our results agree with other studies that highlight these cavitation metrics as genetically fixed traits. Turgor loss point, on the other hand, may be more plastic, as evidenced by the low variability of this trait across these eucalypt species grown in a common garden environment. Further study will help to establish the SLA-related anatomical traits that impart cavitation resistance and to extend these conclusions to a greater number of species and home climates.

Leaf Shedding and Non-Stomatal Limitations of Photosynthesis Mitigate Hydraulic Conductance Losses in Scots Pine Saplings During Severe Drought Stress

During drought, trees reduce water loss and hydraulic failure by closing their stomata, which also limits photosynthesis. Under severe drought stress, other acclimation mechanisms are trigged to further reduce transpiration to prevent irreversible conductance loss. Here, we investigate two of them: the reversible impacts on the photosynthetic apparatus, lumped as non-stomatal limitations (NSL) of photosynthesis, and the irreversible effect of premature leaf shedding. We integrate NSL and leaf shedding with a state-of-the-art tree hydraulic simulation model (SOX+) and parameterize them with example field measurements to demonstrate the stress-mitigating impact of these processes. We measured xylem vulnerability, transpiration, and leaf litter fall dynamics in Pinus sylvestris (L.) saplings grown for 54 days under severe dry-down. The observations showed that, once transpiration stopped, the rate of leaf shedding strongly increased until about 30% of leaf area was lost on average. We trained the SOX+ model with the observations and simulated changes in root-to-canopy conductance with and without including NSL and leaf shedding. Accounting for NSL improved model representation of transpiration, while model projections about root-to-canopy conductance loss were reduced by an overall 6%. Together, NSL and observed leaf shedding reduced projected losses in conductance by about 13%. In summary, the results highlight the importance of other than purely stomatal conductance-driven adjustments of drought resistance in Scots pine. Accounting for acclimation responses to drought, such as morphological (leaf shedding) and physiological (NSL) adjustments, has the potential to improve tree hydraulic simulation models, particularly when applied in predicting drought-induced tree mortality.

Litterfall seasonality and adaptive strategies of tropical and subtropical evergreen forests in China

Aims Tropical and subtropical evergreen broad-leaved forests (EBF) and needle-leaved forests (ENF) in China exhibit complex leaf shedding strategies in responses to soil water availability, vapor pressure deficits (VPD) and sunlight availability. However, the seasonal variations and triggers of litterfall differ significantly in tropical/subtropical forests, and there are still many uncertainties. Herein, we aim to explore the distinct climatic factors of seasonal litterfall in a climate-phenology correlation framework. Methods We collected seasonal litterfall data from 85 sites across tropical/subtropical China and used linear correlation coefficients between sunlight and rainfall to partition synchronous/asynchronous climates. Additional phase analysis and structural equation model analysis were conducted to model the climatic triggers of tropical phenology. Important Findings Results indicated two types of tropical litterfall phenology under two types of climates. In synchronous climates, where seasonal sunlight and rainfall are positively correlated, the litterfall peak of the unimodal phenology and the first litterfall peak of the bimodal phenology both happen at the end of dry season. The second litterfall peak of the bimodal phenology occurs at the end of rainy season due to water stress. In asynchronous climates, where seasonal sunlight and rainfall are negatively correlated, VPD shows consistent seasonal variations with incoming sunlight. The leaf senescence is accelerated at the end of dry season by higher VPD; while soil water deficit is in anti-phase with sunlight and mainly controls the second litterfall peak of the bimodal phenology in EBF. Our findings provide an important reference for modeling tropical phenology in Earth system models.

Novel sources of resistance to powdery mildew (Leveillula taurica (Lév.) Arnaud) in pepper

Peppers, a worldwide crop, are threatened by different pathogens. Powdery mildew, a biotroph fungal infection, can cause several damages directly on vegetative parts and indirectly on fruits. Despite some sources of resistance have been described, commercial genotypes only with partial resistance have been developed due to the complex nature of such resistance and variable genetic expression, which depends on the stage of the plants. In this paper 49 accessions from different Capsicum species and origins have been tested. Plants were grown in growth chambers inside of mini greenhouses. Repeated inoculations under pepper leaves were applied by spraying a suspension of 104 conidia ml-1. Readings were made at 30 and 60 days after inoculation (DAI). Total number of leaves (TL), total number of affected leaves (LA), and maximum area affected (MAA) in the most damaged leaf were scored. In addition, a composite infection index (CII) was calculated on the basis of the three mentioned traits. Inoculated plants showed more severe symptoms at 30 DAI than at 60 DAI. Different response patterns were observed: from accessions suffering high leaf shedding to some others with local hypersensitive response, indicating different gene action. The use of CII prevented species bias and disease response. In the present work, four highly tolerant accessions were identified, including two chiltepins, C. annuum wild relatives, Ag-01 and Ag-02, and two C. annuum A-06 and A-23.

Water balance of an Atlantic forest remnant under a prolonged drought period

ABSTRACT Since prolonged droughts have impacted Atlantic forests in Southeastern Brazil, further investigations to understand the effects of such stressful conditions in their hydrological behavior are required. This study aimed to assess the changes in the water balance of a semi-deciduous Atlantic forest remnant and how the forest responds to droughts. The Standardized Precipitation-Evapotranspiration Index was applied to identify droughts (from 1961 to 2019) and their severity in both the hydrological year and summer scales. Drought impacts on actual evapotranspiration, potential percolation, and soil water storage were assessed using Hydrus-1D, having net precipitation and potential evapotranspiration as inputs. Error analyses (< 10%) confirmed Hydrus-1D suitability for simulating soil moisture. Uncertainties regarding the soil saturated hydraulic conductivity are due to preferential flows, which are not accounted for in Richards’ equation. Drought intensification changed forest hydrology and triggered physiological responses to deal with it. Semi-deciduous Atlantic forests are adapted to dry conditions because of the existence of dry-affiliated species and the activation of physiological mechanisms. However, such adaptations responded differently regarding the drought scales. The intensification of summer droughts increased evapotranspiration and decreased the potential percolation. Leaf shedding changed the canopy structure in a two-year time lag as a response to the intensification of hydrological year droughts. Changes in forest hydrology are sudden and trigger physiological responses, such as leaf shedding, in a delayed process after droughts take place.

Rooting of Mini-Cuttings of guava cultivars (Psidium guajava L.) Treated with IBA under Misting Irrigation

Guava (Psidium guajava L.) is a plant whose fruit is very popular in Indonesia because it contains high vitamin C and its leaves can be used as herbal medicine. Orchard expansion of selected cultivars and fruit production of guava can be achieved vegetatively through propagation by using mini-cuttings with the use of Indole Butyric Acids (IBA). A study was conducted to compare rooting success of mini-cuttings of herbaceous stem of four guava cultivars with IBA treatment. Four guava cultivars tested were Bengkulu Round, Getas, Crystal, and Bangkok. Mini-cuttings were immersed in IBA solution at 0 ppm or 1000 ppm. Cultivar and IBA treatments were arranged factorially in a randomized complete block design with 3 replications, each consisting of 25 cuttings. Variables observed included percentage of original-leaf shedding, percentage of emerging shoots, percentage of sprouting cuttings, new leaf number, root number, root length, and percent of rooted cuttings. The results demonstrated that cultivars affected rooting percentage, sprouted percentage, percentage of original-leaf fall, and number of root. Getas had highest rooting and sprouting percentages, and showed lowest number of original-leaf shedding; whereas, Bangkok demostrated greatest number of root. IBA treatment increased the number of root and the number of original-leaf shedding, but reducing rooting percentage of mini-cutting. There was no interaction between cultivar and IBA teratment.

Reviewing the identity of the Maltese Polypodium (Polypodiaceae) – new evidence from morphology and flow cytometry

The first record of Polypodium from Gozo (Maltese Islands) was described as a new endemic taxon, Polypodium vulgare subsp. melitense, based on its unique set of morphological characters. It was treated as a novelty and designated as a subspecies of P. vulgare mainly due to the lack of paraphyses, the presence of 10–16 annular cells, and a mean spore length of 64 μm. The fern was reassessed by us employing a more rigid morphological analysis and the application of flow cytometry. The absence of paraphyses was confirmed, but the number of annular cells (5–11) and the spore length (70–79 μm) differed from the previous study. These and other morphological traits, the phenology (leaf-shedding in spring), the calcareous growth habitat, and the southern distribution implied that the fern is P. cambricum. Final confirmation was obtained from flow cytometry; the genome size of 17 pg corresponds perfectly with the range obtained for other accessions of this diploid species. The Polypodium reported from Malta does not merit taxonomic distinction despite being a rare form of P. cambricum, which lacks paraphyses.

Chemical Defoliant Promotes Leaf Abscission by Altering ROS Metabolism and Photosynthetic Efficiency in Gossypium hirsutum

Chemical defoliation is an important part of cotton mechanical harvesting, which can effectively reduce the impurity content. Thidiazuron (TDZ) is the most used chemical defoliant on cotton. To better clarify the mechanism of TDZ promoting cotton leaf abscission, a greenhouse experiment was conducted on two cotton cultivars (CRI 12 and CRI 49) by using 100 mg L−1 TDZ at the eight-true-leaf stage. Results showed that TDZ significantly promoted the formation of leaf abscission zone and leaf abscission. Although the antioxidant enzyme activities were improved, the reactive oxygen species and malondialdehyde (MDA) contents of TDZ increased significantly compared with CK (water). The photosynthesis system was destroyed as net photosynthesis (Pn), transpiration rate (Tr), and stomatal conductance (Gs) decreased dramatically by TDZ. Furthermore, comparative RNA-seq analysis of the leaves showed that all of the photosynthetic related genes were downregulated and the oxidation-reduction process participated in leaf shedding caused by TDZ. Consequently, a hypothesis involving possible cross-talk between ROS metabolism and photosynthesis jointly regulating cotton leaf abscission is proposed. Our findings not only provide important insights into leaf shedding-associated changes induced by TDZ in cotton, but also highlight the possibility that the ROS and photosynthesis may play a critical role in the organ shedding process in other crops.