Morphological plasticity and adaptation level of distylous Primula nivalis in a heterogeneous alpine environment

Alpine plant species converge towards adopting elevation-specific resource-acquisition strategy in response to experimental early snow-melting

Snow-melt is one of the important factors limiting growth and survival of alpine plants. Changes in snow-melt timing have profound effects on eco-physiological characteristics of alpine plant species through alterations in growing season length. Here, we conducted a field experiment and studied species response to experimentally induced early snow-melting (ES) (natural vs. early) at an alpine site (Rohtang) in the western Himalaya region. Eco-physiological response of eight snow-bed restricted alpine plant species from different elevations (lower: 3850 m and upper: 4150 m amsl) and belonging to contrasting resource acquisition strategies (conservative and acquisitive) were studied after 2-years (2019 & 2020) of initiating ES field experiment. We estimated the functional traits related to leaf economic spectrum and physiological performance and assessed their pattern of phenotypic plasticity. Analysis by linear mixed effect model showed that both the 'conservative' and 'acquisitive' species had responded to ES with significant effects on species specific leaf area, leaf dry matter content, leaf thickness, leaf water content and sugar content. Our results also revealed that ES treatment induced significant increase in leaf C/N ratio (10.57 % to 13.65 %) and protein content (15.85 % to 20.76 %) at both the elevations, irrespective of species groups. The phenotypic plasticity was found to be low and was essentially species-specific. However, for leaf protein content, the upper elevation species exhibited a higher phenotypic plasticity (0.43 ± 0.18) than the lower elevation species (0.31 ± 0.21). Interestingly, we found that irrespective of species unique functional strategy, species adapt to perform more conservative at lower elevation and more acquisitive at upper elevation, in response to ES. We conclude that plants occurring at contrasting elevations respond differentially to ES. However, species showed capacity for short-term acclimation to future environmental conditions, but may be vulnerable, if their niche is occupied by new species with greater phenotypic plasticity and a superior competitive ability.

Thermo-priming increases heat-stress tolerance in seedlings of the Mediterranean seagrass P. oceanica

Seawater warming and increased incidence of marine heatwaves (MHW) are threatening the integrity of coastal marine habitats including seagrasses, which are particularly vulnerable to climate changes. Novel stress tolerance-enhancing strategies, including thermo-priming, have been extensively applied in terrestrial plants for enhancing resilience capacity under the re-occurrence of a stress event. We applied, for the first time in seedlings of the Mediterranean seagrass Posidonia oceanica, a thermo-priming treatment through the exposure to a simulated warming event. We analyzed the photo-physiological and growth performance of primed and non-primed seedlings, and the gene expression responses of selected genes (i.e. stress-, photosynthesis- and epigenetic-related genes). Results revealed that during the re-occurring stress event, primed seedlings performed better than unprimed showing unaltered photo-physiology supported by high expression levels of genes related to stress response, photosynthesis, and epigenetic modifications. These findings offer new opportunities to improve conservation and restoration efforts in a future scenario of environmental changes.

Investigating the Phenotypic Plasticity of the Invasive Weed Trianthema portulacastrum L

Phenotypic plasticity is frequently highlighted as a key factor in plant invasiveness, as it enables invasive species to adapt to diverse, complicated habitats. Trianthema portulacastrum is one of the most common aggressive species that threaten different crops around the world. Phenotypic plasticity in T. portulacastrum was investigated by comparing variation in germination, vegetative macromorphology, photosynthetic pigments, stomatal complexes, and seed micromorphological traits of 35 samples collected from 35 different localities. One-way cluster analysis and principal component analysis (PCA) were used to classify samples into homogeneous groups based on the measured traits. Pairwise statistical comparisons were conducted between the three resulting groups. The phenotypic plasticity index (PI) was calculated and compared among different groups of characters. Results showed that photosynthetic pigments and macromorphological characteristics had the highest PI, followed by seed micromorphology, and then stomatal complex traits, while germination parameters showed the lowest PI. We propose that soil moisture, salinity, and temperature are the most determinative and explanative variables of the variation between the three classified groups. We strongly believe that the phenotypic plasticity of T. portulacastrum will support species abundance and spread even under expected changes in climatic conditions, in contrast to the vulnerable traditional crops.

Bridging the gap: linking morpho-functional traits' plasticity with hyperaccumulation

Plant species exhibiting heavy metal tolerance are instrumental in phytoremediation of metalliferous sites. Most of the time, variations in plant functional traits (PFTs) are overlooked while identifying hyperaccumulators. However, investigating morphological, physiological, and phenological variations can contribute to our knowledge about stress tolerance, and aid in identifying potential hyperaccumulators. In the present study, we investigated variation in morpho-functional traits in Solanum nigrum, a known hyperaccumulator, under lead (Pb) stress. Twenty-one PFTs including 9 above-ground (leaf count, leaf area, specific leaf area, leaf dry matter content, leaf thickness, leaf dry mass, shoot length, stem dry mass, stem diameter), 3 below-ground (root length, root dry mass, and root diameter), 4 reproductive (flower bud count, fruit count, flower count, and fruit dry mass), and 5 photosynthetic traits (total chlorophyll, total carotenoid, chlorophyll a, chlorophyll b, and photosynthetic efficiency) under varying Pb concentrations (500-2000 mg kg^-1) were assessed. Pillai's trace test (MANOVA) depicted significant variations in above-ground, below-ground, and photosynthetic traits, whereas reproductive traits did not vary significantly with progressive metal concentration. However, most of the studied traits except flower count, fruit dry mass, and chlorophyll b varied significantly under Pb stress. The study depicts that enhanced PFT's plasticity enables S. nigrum to grow in Pb-contaminated soil effectively without impacting plant fitness. Plasticity of morpho-functional traits, therefore, establishes itself as a resourceful approach in successful identification of phytoremediation capacity of a plant.

Elevation-related variation in the population characteristics of distylous Primula nivalis affects female fitness and inbreeding depression

The population characteristics of distylous species are highly sensitive to stochastic natural selection pressure. Therefore, populations growing under different environmental conditions may vary in floral morph ratios, potentially affecting female fitness and leading to inbreeding depression. However, the variation in offspring quality among populations as a result of inbreeding depression is poorly understood in distylous species. This study investigates variations in plant density, seed mass, seed viability, female fitness, and post-dispersal inbreeding depression in both sexual morphs (long-styled and short-styled plants) of the distylous Primula nivalis that were subjected to different pollination treatments along an elevational gradient from 1657 to 2704 m a.s.l. Population characteristics (morph plant density and ratio) and fruit set were significantly affected by sexual morph and elevation. Plant density and fruit set frequencies were lower for short-styled than for long-styled plants at 2704 m a.s.l. The seeds from the cross-pollinated flowers of both morphs were higher in quality than those of self-pollinated flowers. The female fitness of seeds from cross-pollinated flowers of both morphs was higher than that of seeds from open-pollinated and self-pollinated flowers. The female fitness of seeds from long-styled flowers was higher than that of seeds from short-styled flowers at all elevations. Inbreeding depression increased with elevation among plants with short-styled flowers but not among those with long-styled flowers. Variation in the elevation-dependent mating system might influence female fitness and affect inbreeding depression in both floral morphs. In conclusion, the low quality of seeds from short-styled flowers at high elevations might decrease short-styled flower frequency, affecting population characteristics.