Functional Changes and Threats to Hyperseasonal Neotropical Savannas After Australian Acacia Invasion

The hyperseasonal savanna experiences regular flooding and drought stresses and is a neotropical vegetation type threatened by global change including Acacia spp. invasion. To deepen the understanding of hyperseasonal savannas after Acacia invasion in a climate change scenario, we aimed to answer if: i) the plants of the studied hyperseasonal savanna are separated into C3, C4 or CAM species; ii) Acacia invasion can change the hyperseasonal savanna functioning for C3, C4 and CAM plants; iii) how invasive Acacia uptake water compared to native species in this hyperseasonal savanna. We detected both C3 and C4 metabolic groups of plants but two C3 species are possibly CAM facultative. The functioning of C3 plants as a group was not affected by the Acacia invasion, but this result does not exclude a species turnover between C3 herbs and C3 trees. The C4 plants of invaded Mussununga lost their response of increasing water use efficiency to the increasing Leaf N%. Plants of hyperseasonal savannas depend on the same water source as the soil water from recent rains. There are differences in d18O among species because some grow mostly during the rainy season with the 18O-enriched water meanwhile the invader Acacia mangium grows throughout the year whenever it rains. According to our results, the threat to C4 plants is high and they can be excluded from Mussunungas and from hyperseasonal savannas. However, hyperseasonal savannas are threatened as a vegetation. Therefore, hyperseasonal savannas should be considered critically endangered because of global change, especially bacause Acacia invasions. Initiatives for conservation of hyperseasonal savannas could save these remarkable ecosystems.

Effects of Light Condition on Growth and Physiological Characteristics of the Endangered Species Sedirea japonica under RCP 6.0 Climate Change Scenarios

This study was conducted to evaluate the physiological and growth responses of Sedirea japonica cultured in chambers under RCP 6.0 and different light conditions. S. japonica was grown in a soil–plant daylight system chamber under two treatments, a control (CO2 = 400 ppm) and a climate change treatment (CCT) (CO2 = 650 ppm, temperature = control + 3 °C), and three different shading treatments (60%, 90%, and no-shading). S. japonica showed the characteristics of typical Crassulacean acid metabolism (CAM) plants. As the shading rate increased, it increased chlorophyll content, leaf area, and leaf dry weight to efficiently absorb and use light. The CCT had a lower CO2 absorption rate, stomatal conductance, and growth rate and slightly higher water utilization efficiency than the control. This was because stomatal closure occurred in the CCT to reduce water loss due to a relatively higher temperature. As CO2 fixation decreased and consumption increased due to respiration, the overall growth was inhibited. The CCT without shading revealed a dynamic photoinhibition phenomenon showing a significant increase in ABS/RC, TRo/RC, ETo/RC, and DIo/RC and a decrease in PI ABS and DF ABS. In this group, leaf, root, and total dry weight, chlorophyll content, and carotenoid content were the worst growth indices.

Inference of Gene Regulatory Network Uncovers the Linkage between Circadian Clock and Crassulacean Acid Metabolism in Kalanchoë fedtschenkoi

The circadian clock drives time-specific gene expression, enabling biological processes to be temporally controlled. Plants that conduct crassulacean acid metabolism (CAM) photosynthesis represent an interesting case of circadian regulation of gene expression as stomatal movement is temporally inverted relative to stomatal movement in C3 plants. The mechanisms behind how the circadian clock enabled physiological differences at the molecular level is not well understood. Recently, the rescheduling of gene expression was reported as a mechanism to explain how CAM evolved from C3. Therefore, we investigated whether core circadian clock genes in CAM plants were re-phased during evolution, or whether networks of phase-specific genes were simply re-wired to different core clock genes. We identified candidate core clock genes based on gene expression features and then applied the Local Edge Machine (LEM) algorithm to infer regulatory relationships between this new set of core candidates and known core clock genes in Kalanchoë fedtschenkoi. We further inferred stomata-related gene targets for known and candidate core clock genes and constructed a gene regulatory network for core clock and stomata-related genes. Our results provide new insight into the mechanism of circadian control of CAM-related genes in K. fedtschenkoi, facilitating the engineering of CAM machinery into non-CAM plants for sustainable crop production in water-limited environments.

At the Edges of Photosynthetic Metabolic Plasticity—On the Rapidity and Extent of Changes Accompanying Salinity Stress-Induced CAM Photosynthesis Withdrawal

The common ice plant (Mesembryanthemum crystallinum L.) is a facultative crassulacean acid metabolism (CAM) plant, and its ability to recover from stress-induced CAM has been confirmed. We analysed the photosynthetic metabolism of this plant during the 72-h response period following salinity stress removal from three perspectives. In plants under salinity stress (CAM) we found a decline of the quantum efficiencies of PSII (Y(II)) and PSI (Y(I)) by 17% and 15%, respectively, and an increase in nonphotochemical quenching (NPQ) by almost 25% in comparison to untreated control. However, 48 h after salinity stress removal, the PSII and PSI efficiencies, specifically Y(II) and Y(I), elevated nonphotochemical quenching (NPQ) and donor side limitation of PSI (YND), were restored to the level observed in control (C3 plants). Swelling of the thylakoid membranes, as well as changes in starch grain quantity and size, have been found to be components of the salinity stress response in CAM plants. Salinity stress induced an over 3-fold increase in average starch area and over 50% decline of average seed number in comparison to untreated control. However, in plants withdrawn from salinity stress, during the first 24 h of recovery, we observed chloroplast ultrastructures closely resembling those found in intact (control) ice plants. Rapid changes in photosystem functionality and chloroplast ultrastructure were accompanied by the induction of the expression (within 24 h) of structural genes related to the PSI and PSII reaction centres, including PSAA, PSAB, PSBA (D1), PSBD (D2) and cp43. Our findings describe one of the most flexible photosynthetic metabolic pathways among facultative CAM plants and reveal the extent of the plasticity of the photosynthetic metabolism and related structures in the common ice plant.

EFICIÊNCIA FOTOQUÍMICA EM CLADÓDIOS DE PALMA FORRAGEIRA ‘GIGANTE’ CULTIVADA SOB DIFERENTES ESPAÇAMENTOS E ADUBAÇÃO MINERAL

A associação de fatores no sistema solo-água-planta-atmosfera, como adubação, espaçamento entre plantas e disponibilidade hídrica, pode influenciar a atividade fisiológica em palma forrageira nas condições adversas do semiárido. Assim, objetivou-se determinar a eficiência fotoquímica em cladódios de palma forrageira ‘Gigante’ cultivada sob diferentes espaçamentos e adubação mineral em região semiárida, no período seco e chuvoso. O experimento foi conduzido em blocos ao acaso em esquema fatorial 4 x 3 x 7, com três repetições. O primeiro fator foi constituído de quatro adubações (000-000-000; 000-150-000; 200-150-000 e 200-150-100 kg ha-1 de N-P2O5-K2O), o segundo, por três espaçamentos (1,0 x 0,5; 2,0 x 0,25 e 3,0 x 1,0 x 0,25 m) e o terceiro por sete horários de leitura (6; 8; 10; 12; 14; 16 e 18 h). Foram realizadas leituras de fluorescência da clorofila “a” em cladódios de palma forrageira nas épocas seca e chuvosa com auxílio de um fluorômetro de luz modulada. Verificou-se ajustes cúbicos para as variáveis de fluorescência da clorofila “a” ao longo dia com magnitude de respostas diferenciadas nos períodos seco e chuvoso. Os cladódios de palma forrageira ‘Gigante’ sofrem alterações no fotossistema II na época seca nas condições fisiográficas do semiárido baiano e na época de chuvas o rendimento fotossintético em cladódios de palma forrageira é considerado ideal com variações ao longo do dia. Palavras-chave: arranjo de plantas; Opuntia; plantas CAM. Photochemical efficiency in cladodes of ‘Gigante’ cactus pear cultivated under different spacing and mineral fertilization ABSTRACT: The association of factors in the soil-water-plant-atmosphere system, such as fertilization, spacing between plants and water availability, can influence the physiological activity in cactus pear in the adverse conditions of the semiarid. Thus, the objective was to determine the photochemical efficiency in cladodes of ‘Gigante’ cactus pear cultivated under different spacing and mineral fertilization in the semi-arid region, in the dry and rainy season. The experiment was conducted in a randomized block design in a 4 x 3 x 7 factorial scheme with three replicates. The first factor consisted of four fertilizations (000-000-000, 000-150-000, 200-150-000 and 200-150-100 kg ha-1 of N-P2O5-K2O), the second one, by three fertilizations (1.0 x 0.5, 2.0 x 0.25 and 3.0 x 1.0 x 0.25 m) and the third by seven reading times (6 a.m., 8 a.m., 10 a.m., 12 p.m., 2 p.m., 4 p.m. and 6 p.m). Fluorite readings of “a” chlorophyll were carried out in forage palm cladodes in the dry and rainy seasons with the help of a light modulated fluorometer. Cubic adjustments wereobserved for the fluorescence variables of “a” chlorophyll along day with magnitude of differentiated responses in dry and rainy periods. The cladodes of ‘Giant’ cactus pear alterations suffer in photosystem II in the dry season in the physiographic conditions of the Bahia semi-arid and in the rainy season the photosynthetic yield in cladodes of forage palm is considered ideal with variations along the day. Keywords: arrangement of plants; Opuntia; CAM plants.

The sensitivity of Neotoma to climate change and biodiversity loss over the late Quaternary

The late Quaternary in North America was marked by highly variable climate and considerable biodiversity loss including a megafaunal extinction event at the terminal Pleistocene. Here, we focus on changes in body size and diet in Neotoma (woodrats) in response to these ecological perturbations using the fossil record from the Edwards Plateau (Texas) across the past 20,000 years. Body mass was estimated using measurements of fossil teeth and diet was quantified using stable isotope analysis of carbon and nitrogen from fossil bone collagen. Prior to ca. 7000 cal yr BP, maximum mass was positively correlated to precipitation and negatively correlated to temperature. Independently, mass was negatively correlated to community composition, becoming more similar to modern over time. Neotoma diet in the Pleistocene was primarily sourced from C3 plants, but became progressively more reliant on C4 (and potentially CAM) plants through the Holocene. Decreasing population mass and higher C4/CAM consumption was associated with a transition from a mesic to xeric landscape. Our results suggest that Neotoma responded to climatic variability during the terminal Pleistocene through changes in body size, while changes in resource availability during the Holocene likely led to shifts in the relative abundance of different Neotoma species in the community.

Transcriptome and Degradome Profiling Reveals a Role of miR530 in the Circadian Regulation of Gene Expression in Kalanchoë marnieriana

Crassulacean acid metabolism (CAM) is an important photosynthetic pathway for plant adaptation to dry environments. CAM plants feature a coordinated interaction between mesophyll and epidermis functions that involves refined regulations of gene expression. Plant microRNAs (miRNAs) are crucial post-transcription regulators of gene expression, however, their roles underlying the CAM pathway remain poorly investigated. Here, we present a study characterizing the expression of miRNAs in an obligate CAM species Kalanchoë marnieriana. Through sequencing of transcriptome and degradome in mesophyll and epidermal tissues under the drought treatments, we identified differentially expressed miRNAs that were potentially involved in the regulation of CAM. In total, we obtained 84 miRNA genes, and eight of them were determined to be Kalanchoë-specific miRNAs. It is widely accepted that CAM pathway is regulated by circadian clock. We showed that miR530 was substantially downregulated in epidermal peels under drought conditions; miR530 targeted two tandem zinc knuckle/PLU3 domain encoding genes (TZPs) that were potentially involved in light signaling and circadian clock pathways. Our work suggests that the miR530-TZPs module might play a role of regulating CAM-related gene expression in Kalanchoë.

Overexpression of an Agave Phosphoenolpyruvate Carboxylase Improves Plant Growth and Stress Tolerance

It has been challenging to simultaneously improve photosynthesis and stress tolerance in plants. Crassulacean acid metabolism (CAM) is a CO2-concentrating mechanism that facilitates plant adaptation to water-limited environments. We hypothesized that the ectopic expression of a CAM-specific phosphoenolpyruvate carboxylase (PEPC), an enzyme that catalyzes primary CO2 fixation in CAM plants, would enhance both photosynthesis and abiotic stress tolerance. To test this hypothesis, we engineered a CAM-specific PEPC gene (named AaPEPC1) from Agave americana into tobacco. In comparison with wild-type and empty vector controls, transgenic tobacco plants constitutively expressing AaPEPC1 showed a higher photosynthetic rate and biomass production under normal conditions, along with significant carbon metabolism changes in malate accumulation, the carbon isotope ratio δ13C, and the expression of multiple orthologs of CAM-related genes. Furthermore, AaPEPC1 overexpression enhanced proline biosynthesis, and improved salt and drought tolerance in the transgenic plants. Under salt and drought stress conditions, the dry weight of transgenic tobacco plants overexpressing AaPEPC1 was increased by up to 81.8% and 37.2%, respectively, in comparison with wild-type plants. Our findings open a new door to the simultaneous improvement of photosynthesis and stress tolerance in plants.