Physiological, morphological and allocation plasticity of a semi-deciduous shrub

Thermal acclimation of tree species in a tropical Andean city: Exploring the role of species origin and thermal niche

PREMISE

The warmer and drier atmospheric conditions of urban environments challenge plant performance to different extents based on a species' ability to acclimate to the conditions. We evaluated the influence of species origin and thermal niche on the acclimation of leaf traits and shifts in the occupation of the functional trait space of 10 tree species growing in two environmentally contrasting sites in Bogotá, Colombia.

METHODS

We measured six leaf traits per species in both sites and used generalized linear models to evaluate the influence of origin and thermal niche on acclimation of leaf traits and t-tests to analyze shifts in the occupation of the functional trait space.

RESULTS

Species origin predicted thermal tolerance and morphological trait acclimation to warmer conditions. Although exotic species decreased thermal tolerance at the warmer site, species from both origins acclimated traits consistently. Shifts in the occupation of the functional trait space varied between origins; warmer conditions reduced the size of the functional trait space of exotics and increased the phenotypic similarity of natives. Thermal tolerance acclimation and changes in functional trait space varied across species. Finally, thermal niche metrics were uncoupled from species origin and failed to explain the acclimation capacity of the studied species.

CONCLUSIONS

Although species origin influenced acclimation to warmer conditions, the effect of origin was not related to species' thermal niches. Our results provide crucial information for decision-makers involved in designing urban and peri-urban green spaces that can withstand climate change.

Contrasting effects of experiencing temporally heterogeneous light availability versus homogenous shading on plant subsequent responses to light conditions

Temporally heterogeneous environments is hypothesized to correlate with greater plasticity of plants, which has rarely been supported by direct evidence. To address this issue, we subjected three species from different ranges of habitats to a first round of alternating full light and heavy shading (temporally heterogeneous light experience), constant moderate shading and full light conditions (temporally homogeneous light experiences, control) and a second round of light-gradient treatments. We measured plant performance in a series of morphological, biomass, physiological and biochemical traits at the end of each round. Compared to constant full light experience, temporally heterogeneous light conditions induced immediate active biochemical responses (in the first round) with improved late growth in biomass (during the second round); constant moderate shading experience increased photosynthetic physiological and biomass performances of plants in early response, and decreased their late growth in biomass. The karst endemic species of Kmeria septentrionalis showed greater improvement in late growth of biomass and lower decrease in biochemical performance, due to early heterogeneous experience, compared to the non-karst species of Lithocarpus glaber and the karst adaptable species of Celtis sinensis. Results suggested plants will prefer to produce morphological and physiological responses that are less reversible and more costly in the face of more reliable environmental cues at early stage in spite of decreased future growth potential, but to produce immediate biochemical responses for higher late growth potential when early environmental cues are less reliable, to avoid the loss of high costs and low profits. Typical karst species should be more able to benefit from early temporally heterogeneous experience, due to long-term adaptation to karst habitats of high environmental heterogeneity and low resource availability.

Trait value and phenotypic integration contribute to the response of exotic Rhus typhina to heterogeneous nitrogen deposition: A comparison with native Rhus chinensis

The temporal heterogeneity of nitrogen availability in soils is increasing due to agricultural deposition. We here compared the effects of gradually increasing nitrogen deposition rate and its increasing temporal heterogeneity patterns on the functional traits of seedlings of exotic species Rhus typhina and the native species Rhus chinensis. Nitrogen deposition rates of 0, 8, 20 g N m^-2 year^-1 and constant, single-peak, and double-peak nitrogen were added to simulate deposition rate and temporal heterogeneity. After 60 days of treatment, R. typhina seedlings had several advantageous growth trait values, such as higher total biomass production, but lower phenotypic plasticity than R. chinensis seedlings. R. typhina seedlings also had higher phenotypic integration, measured as the correlation among functional traits. The increased nitrogen deposition rate affected several traits of the two species differently. Thus, while R. chinensis seedlings allocated more biomass to leaves and less to roots with increasing N deposition, R. typhina seedlings had stable biomass allocation among all N treatments. Chlorophyll content, leaf phosphorus concentration, and water use efficiency increased, but the maximum net photosynthetic rate decreased, with N availability in R. chinensis, but not in R. typhina. Temporal heterogeneity had no significant effect on the total biomass of R. typhina and R. chinensis seedlings. Overall, the performance of R. typhina is better than that of R. chinensis seedlings under different nitrogen deposition treatments, which is due to the significantly advantageous trait values and greater phenotypic integration of R. typhina seedlings, whereas R. chinensis seedlings have higher phenotypic plasticity.

Two Dominant Herbaceous Species Have Different Plastic Responses to N Addition in a Desert Steppe

Nitrogen (N) deposition rates are increasing in the temperate steppe due to human activities. Understanding the plastic responses of plant dominant species to increased N deposition through the lens of multiple traits is crucial for species selection in the process of vegetation restoration. Here, we measured leaf morphological, physiological, and anatomical traits of two dominant species (Stipa glareosa and Peganum harmala) after 3-year N addition (0, 1, 3, and 6 g N m-2 year-1, designated N0, N1, N3, and N6, respectively) in desert steppe of Inner Mongolia. We separately calculated the phenotypic plasticity index (PI) of each trait under different N treatments and the mean phenotypic plasticity index (MPI) of per species. The results showed that N addition increased the leaf N content (LNC) in both species. N6 increased the contents of soluble protein and proline, and decreased the superoxide dismutase (SOD) and the peroxidase (POD) activities of S. glareosa, while increased POD and catalase (CAT) activities of P. harmala. N6 increased the palisade tissue thickness (PT), leaf thickness (LT), and palisade-spongy tissue ratio (PT/ST) and decreased the spongy tissue-leaf thickness ratio (ST/LT) of S. glareosa. Furthermore, we found higher physiological plasticity but lower morphological and anatomical plasticity in both species, with greater anatomical plasticity and MPI in S. glareosa than P. harmala. Overall, multi-traits comparison reveals that two dominant desert-steppe species differ in their plastic responses to N addition. The higher plasticity of S. glareosa provides some insight into why S. glareosa has a broad distribution in a desert steppe.

Halimium as an ectomycorrhizal symbiont: new records and an appreciation of known fungal diversity

Halimium is a genus of Cistaceae, containing a small group of shrub species found in open vegetation types and in degraded forest patches throughout the western and central Mediterranean region. We recently described the morpho-anatomical features of the ectomycorrhizae formed by Scleroderma meridionale on Halimium halimifolium, but the mycorrhizal biology of this host plant genus is still largely unexplored. Here, we report new data on the ectomycorrhizal fungal symbionts of Halimium, based on the collection of sporocarps and ectomycorrhizal root tips in pure stands occurring in Sardinia, Italy. To obtain a broader view of Halimium mycorrhizal and ecological potential, we compiled a comprehensive and up-to-date checklist of fungal species reported to establish ectomycorrhizae on Halimium spp. on the basis of field observations, molecular approaches, and mycorrhiza synthesis. Our list comprises 154 records, corresponding to 102 fungal species and 35 genera, revealing a significant diversity of the Halimium ectomycorrhizal mycobiota. Key ectomycorrhizal genera like Russula, Lactarius/Lactifluus, Amanita, Inocybe, and Cortinarius account for more than half of all mycobionts. A large proportion of Halimium fungal species are shared with other host plants in various ecological settings, suggesting a critical role of common mycorrhizal networks in the function played by this shrub in various Mediterranean ecosystems.

Summit evergreen shrubs living at a semi-arid treeline: photoprotection systems activation in an open vs an understory site

High-mountain-ecosystems in the Mediterranean-type climate are exceptional because of their outstanding biodiversity but also because of their characteristic drought stress in summer. Still, plant functioning in these habitats has been largely understudied. Here, morphological, photochemical, and biochemical traits were seasonally assessed in six shrubs characterized by contrasting morphological traits, in the Teide mountain in the Canary Islands. Two adjacent populations, the first located in an open site and the second in the understorey of Pinus canariensis treeline forest, were evaluated. We aimed at disentangling (1) the role of morphological and biochemical photoprotective strategies and of their seasonal plasticity to cope with changing environmental conditions in this semiarid ecosystem, (2) how the interspecific differences in biochemical photoprotection are related to leaf morphology and phenology and (3) how living in the understory of the treeline may affect those responses. Our results indicate that both morphological and biochemical traits (particularly leaf habit, morphology and carotenoids from the β-branch) play an intricate role in photoprotection, and that a high interspecific variability exists. According to the down-regulation of photochemical activity and the upregulation of photoprotective molecules, species could be grouped into three types: (1) those more responsive to summer stress (e.g. Descurainia bourgeauana); (2) those more responsive to winter stress (e.g. Pterocephalus lasiospermus, Scrophularia glabrata and Adenocarpus viscosus); and (3) those showing rather constant behavior across seasons (e.g. Spartocytisus supranubius and Erysimum scoparium). In all the species, plants in the open site showed a marked seasonal physiological response in most of the studied parameters. Pinus canariensis canopy buffers environmental abiotic constrains. On a global change scenario, and provided further functional studies are needed, our results pinpoints heterogeneity in the sensitivity of these species against for instance late-frost or summer-heat/drought events, which could easily shift current species distribution in the coming years.

Reproductive shoots of Berberis microphylla G. Forst. in relation with the floral bud development and the fruit set

The objective of this research was to study the reproductive shoots of Berberis microphylla G. Forst. in relation with the floral bud development and the fruit set among and within three populations of Tierra del Fuego during three consecutive years. Evolution of the different reproductive phenological phases of B. microphylla was in accordance with the climatic conditions of the sites and the years, in particular with the temperatures of the end of the winter and beginning of the spring. In fact, blooming period in US was advanced compared to FL and CI populations. Also, full bloom was shorter in US respect to FL and CI populations when the temperatures increased gradually as occurred in 2014 year. The development of reproductive shoots was significantly affected by the population, the shadow and the growing season. Mixed bud number/length was highest in US population; however fruit set was maximum in FL population. Shadow levels of 50% decreased total bud number, total bud number/node number, mixed bud number, mixed bud number/length and fruit number/length. Ultimately, mixed bud number, mixed bud number/length and aborted flowers were maxima in 2015–2016 growing season. The obtained results confirm the presence of phenotypic plasticity of the reproductive shoots of Berberis microphylla G. Forst. in relation with the floral bud development and the fruit set.

Nitrogen deposition does not affect the impact of shade on Quercus acutissima seedlings

Light and atmospheric nitrogen (N) deposition are among the important environmental factors influencing plant growth and forest regeneration. We used Quercus acutissima, a dominant broadleaf tree species native to the deciduous forests of Northern China, to study the combined effects of light exposure and N addition on leaf physiology and individual plant growth. In the greenhouse, we exposed Quercus acutissima seedlings to one of two light conditions (8% and 80% of full irradiation) and one of three N treatments (0, 6, and 12 g N m⁻² y⁻¹). After 87 d, we observed that nitrogen deposition had no significant effects on the seedlings regardless of light exposure. In addition, shade significantly reduced plant height, basal diameter, leaf number, total biomass, gas exchange capacity, and carbohydrate content. In contrast, however, shade significantly increased the amount of photosynthetic pigment, above-ground biomass allocation, and specific leaf area. There was also a hierarchical plasticity among the different seedling characteristics. Compared to traits of growth, biomass, biomass allocation and leaf morphology, the leaf physiology, including photosynthetic pigment, gas exchange, carbohydrate, and PUNE, is more sensitive to light conditions. Among the biomass allocation parameters, the leaf and root mass ratios had a relatively low phenotypic plasticity. The seedlings had high foliar physiological plasticity under various light conditions. Nevertheless, we recommend high irradiance to maintain vigorous seedling growth and, in turn, promote the restoration and reconstruction of vegetation.

To Produce or to Survive: How Plastic Is Your Crop Stress Physiology?

Abiotic stress causes major crop losses and is considered a greater challenge than biotic stress. Comparisons of the number of published articles and patents regarding these different types of stresses, and the number of commercially released crops designed to tolerate different types of stresses, revealed a huge gap in the bench-to-field transfer rate of abiotic stress-tolerant crops, as compared to crops designed to tolerate biotic stress. These differences underscore the complexity of abiotic stress-response mechanisms. Here, we suggest that breeding programs favoring yield-related quantitative physiological traits (QPTs; e.g., photosynthesis rate or stomatal conductance) have canalized those QPTs at their highest levels. This has affected the sensitivity of those QPTs to changing environmental conditions and those traits have become less plastic. We also suggest that breeding pressure has had an asymmetric impact on different QPTs, depending on their sensitivity to environmental conditions and their interactions with other QPTs. We demonstrate this asymmetric impact on the regulation of whole-plant water balance, showing how plastic membrane water content, stomatal conductance and leaf hydraulic conductance interact to canalize whole-organ water content. We suggest that a QPT's plasticity is itself an important trait and that understanding this plasticity may help us to develop yield-optimized crops.

Short-term physiological plasticity: Trade-off between drought and recovery responses in three Mediterranean Cistus species

Short-term physiological plasticity allows plants to thrive in highly variable environments such as the Mediterranean ecosystems. In such context, plants that maximize physiological performance under favorable conditions, such as Cistus spp., are generally reported to have a great cost in terms of plasticity (i.e., a high short-term physiological plasticity) due to the severe reduction of physiological performance when stress factors occur. However, Cistus spp. also show a noticeable resilience ability in response to stress factors. We hypothesized that in Cistus species the short-term physiological response to stress and that to subsequent recovery can show a positive trade-off to offset the costs of the photosynthetic decline under drought. Gas exchange, chlorophyll fluorescence, and water relations were measured in C. salvifolius, C. monspeliensis, and C. creticus subsp. eriocephalus during an imposed experimental drought and subsequent recovery. Plants were grown outdoor in common garden conditions from seeds of different provenances. The short-term physiological response to stress and that to recovery were quantified via phenotypic plasticity index (PIstress and PIrecovery, respectively). A linear regression analysis was used to identify the hypothesized trade-off PIstress-PIrecovery. Accordingly, we found a positive trade-off between PIstress and PIrecovery, which was consistent across species and provenances. This result contributes in explaining the profit, more than the cost, of a higher physiological plasticity in response to short-term stress imposition for Cistus spp because the costs of a higher PIstress are payed back by an as much higher PIrecovery. The absence of leaf shedding during short-term drought supports this view. The trade-off well described the relative variations of gas exchange and water relation parameters. Moreover, the results were in accordance with the ecology of this species and provide the first evidence of a consistent trade-off between the short-term physiological responses to drought and recovery phases in Mediterranean species.

Highlighting the differential role of leaf paraheliotropism in two Mediterranean Cistus species under drought stress and well-watered conditions

The differential degree by which paraheliotropism may counterbalance the deleterious impact of high irradiance between congeneric species in relation to different water availabilities has been poorly investigated. We followed the evolution of gas exchange, quenching analysis and OJIP parameters in restrained (R) and free (F) to move leaves of Cistus monspeliensis (CM) and Cistus salvifolius (CS) under drought stress (WS) and well-watered conditions (WW). Concerning gas exchange parameters, leaf restriction effect was overall not significant in CM except in apparent carboxylation efficiency (C_e) under WS, while CS showed a significant sensitivity of maximum net photosynthetic rate (A_max), stomatal conductance (gs) and C_e even under WW. The recovery analysis highlighted also a faster gs recovery in F leaves. Furthermore, in both the species, restriction affected photon allocation pathways especially in terms of light-regulated and light-independent constitutive non-photochemical energy dissipation under WW, ultimately affecting electron transport rate (ETR). Nevertheless, the OJIP analysis provided us evidences that CM was characterized by a down-regulation of ETR while an impairment occurs in CS. In CM this was due to its ability to modify a certain fraction of reaction centers thus resulting in a higher capability for dissipation of excess light energy under well-watered conditions, not affecting electron transport efficiency. This response was not observed in CS. Overall, we demonstrated that congeneric species, even mostly sharing the same physiological targets, differ in the degree by which leaf movements help to counterbalance the negative effect of the high irradiance in relation with the amount of water available.

Plant Phenotypic Plasticity in Response to Environmental Factors

Plants are exposed to heterogeneity in the environment where new stress factors (i.e., climate change, land use change, and invasiveness) are introduced, and where inter- and intraspecies differences may reflect resource limitation and/or environmental stress factors. Phenotypic plasticity is considered one of the major means by which plants can cope with environmental factor variability. Nevertheless, the extent to which phenotypic plasticity may facilitate survival under environmental condition changes still remains largely unknown because results are sometimes controversial. Thus, it is important to identify plant functional traits in which plasticity may play a determinant role in plant response to global change as well as on the ecological consequences at an ecosystem level for the competition between wild and invasive species, considering that species with a greater adaptive plasticity may be more likely to survive in novel environmental conditions. In the near future, it will be important to increase long-term studies on natural populations in order to understand plant response to environmental factor fluctuations including climate change. There is the necessity to analyze variations at phenotypic and genetic levels for the same species and, in particular, for endemic and rare species because these could have drastic effects at an ecosystem level.