In the 19th century it was proposed that ecophysiology was best studied in regions with extreme climatic conditions. In the present perspective, we argue that perhaps this is more timely than ever. The main reason is the need to improve crops to be simultaneously more productive-due to the increased population-and more stress tolerant-due to climate change. Climate change induces plants to face not just harsh but also 'unexpected' (unpredictable) climatic conditions. In this sense, we hypothesize that 'sherplants', namely plants living in the extremes of plant life (e.g. hot deserts, Arctic and Antarctica, or high elevations) can provide cues on how to break the trade-off between productivity and stress tolerance, as they need to be produced quickly due to the very short growing period while being stress tolerant due to the harsh and unpredictable climate endured during most of the year. We present glimpses of results from three consecutive projects developed over the last 10 years, in which hundreds of species from different regions of the world have been studied. In particular, we propose a pathway for developing 'shercrops' learning from 'sherplants', debate whether some of the already studied species may have really broken the aforementioned trade-off, and present a number of interesting unforeseen discoveries made when studying plants from extreme climates.

I performed my PhD in grapevine physiology under the supervision of Dr. H. Medrano, standing in the vineyards from pre-dawn to sunrise during many hot, wet and sunny days with my colleagues J.M.E. and J.B. I also spent many days and nights facing ticks year-round working in Mediterranean macchias with J.Gu. and M.M. Later I was able to supervise PhD students on grapevines – like A.P. and M.T. – and on Mediterranean vegetation – like J.Gal. With the incorporation to the group of M.R.-C. 'the puzzle' was completed and, combining the aforementioned studies, we could conclude (more than 20 years ago) things like: (1) stomatal conductance is the best proxy for 'water stress' in studies on photosynthesis; (2) steady-state chlorophyll fluorescence retrieves photosynthesis under saturating light; (3) photoinhibition is not a major photosynthetic limitation under water stress; (4) mesophyll conductance instead is; and (5) mesophyll conductance is a major driver of leaf water use efficiency. In view of these achievements which arose from the study of grapevines extended to other species, we realized that most current knowledge on plant ecophysiology is build on studies in temperate and Mediterranean species. Impelled especially by R.E.C. and in company of J.Gu., J.Gag., M-J.C-M., M.C., F.C and others we started studying plants in remote sites like Antarctica, Himalaya, Andes, etc … What we found there and why it may imply the 'and back' to agriculture is the object of this talk, which is intended as a homage to my supervisor and friend Hipólito Medrano on his retirement.

A trade-off between allocated resources for photosynthesis and stress tolerance is generally observed in nature. Thus, the search for outlier species breaking this trend is an interesting approach to identity new mechanisms for plant breeding purposes. Hypothetically, outlier extremophyte species present a distinctive arrangement of physiological functions that favor stress tolerance mechanisms without jeopardizing investment allocation into photosynthesis. We explored this trade-off, analyzing twenty-one plant species for desiccation tolerance, and photosynthetic capacity, under the extreme arid environments of the Atacama Desert and the Surire Salar in the Chilean Altiplano. Most of the studied species followed the trade-off tendency, however, we did find one outlier species, Prosopis tamarugo . To study the mechanisms involved in this atypical response, the Prosopis genus was analyzed more deeply. Our results suggest that the outlier response of P. tamarugo is multifactorial. This species presented a high photochemistry activity, associated with a higher synthesis of chlorophylls, photoprotective pigments, and complex antioxidant molecules. Moreover, the synthesis of no-nitrogen osmoprotectant molecules, such as ciceritol and mannitol in P. tamarugo , would allow the allocation of nitrogen to support its high photosynthetic capacity, without compromising its leaf desiccation stress tolerance.

Polylepis tarapacana is an exceptional species, forming the highest treeline in the world. In this work, we compared the climatic conditions of the main highest treelines around the world and highlight the unique conditions of the treelines of the Andes' Altiplano, the habitat of P. tarapacana. We review the current state of knowledge on the physiology of P. tarapacana and call for the urgent need of additional studies to assess the adaptive strategies of this species that allow it to withstand the harsh environments of high elevation climates.

Tree growth is generally considered to be temperature-limited at upper elevation treelines. Yet, climate factors controlling tree growth at semiarid treelines are poorly understood. We explored the influence of climate on stem growth and stable isotopes for Polyepis tarapacana, the world's highest elevation tree-species found only in the South American Altiplano. We developed tree-ring width index (RWI), oxygen (δ18O) and carbon (δ13C) chronologies for the last 60 years at four P. tarapacana stands located above 4,400 meters in elevation, along a 500-km latitude-aridity gradient. Total annual precipitation decreased from 300 to 200 mm from the northern to the southern sites. We used RWI as a proxy of wood formation (carbon sink) and isotopic tree-ring signatures as proxies of leaf-level gas exchange processes (carbon source). We found distinct climatic conditions regulating carbon-sink processes along the gradient. Current-growing season temperature regulated RWI at wetter-northern sites, while prior-growing season precipitation determined RWI at arid-southern sites. This suggests that the relative importance of temperature to precipitation in regulating tree growth is driven by site-water availability. In contrast, warm and dry growing-seasons resulted in enriched tree-ring δ13C and δ18O at all study sites, suggesting that similar climate conditions control carbon-source processes. Site-level δ13C and δ18O chronologies were significantly and positively related at all sites, with the strongest relationships among the southern-drier stands. This indicates an overall regulation of intercellular carbon dioxide via stomatal conductance for the entire P. tarapacana network, with greater stomatal control when aridity increases. The manuscript also highlights a coupling and decoupling of physiological processes at leaf level versus wood formation depending on their respectively uniform and distinct sensitivity to climate. This study contributes to better understand and predict the response of high-elevation Polylepis woodlands to rapid climate changes and projected drying in the Altiplano.

The mangrove Avicennia marina adjusts internal salt concentrations by foliar salt secretion. Deliquescence of accumulated salt causes leaf wetting that may provide a water source for salt-secreting plants in arid coastal wetlands where high nocturnal humidity can usually support deliquescence whereas rainfall events are rare. We tested the hypotheses that salt deliquescence on leaf surfaces can drive top-down rehydration, and that such absorption of moisture from unsaturated atmospheres makes a functional contribution to dry season shoot water balances. Sap flow and water relations were monitored to assess the uptake of atmospheric water by branches during shoot wetting events under natural and manipulated microclimatic conditions. Reverse sap flow rates increased with increasing relative humidity from 70% to 89%, consistent with function of salt deliquescence in harvesting moisture from unsaturated atmospheres. Top-down rehydration elevated branch water potentials above those possible from root water uptake, subsidising transpiration rates and reducing branch vulnerability to hydraulic failure in the subsequent photoperiod. Absorption of atmospheric moisture harvested through deliquescence of salt on leaf surfaces enhances water balances of Avicennia marina growing in hypersaline wetlands under arid climatic conditions. Top-down rehydration from these frequent, low intensity wetting events contributes to prevention of carbon starvation and hydraulic failure during drought.

Until recently, few data were available on photosynthesis and its underlying mechanistically limiting factors in plants, other than crops and model species. Currently, a new large pool of data from extant representatives of basal terrestrial plant groups is emerging, allowing exploration of how photosynthetic capacity (Amax) increases from minimum values in bryophytes to maximum in tracheophytes, which is associated to an optimization of the balance between its limiting factors. From predominant mesophyll conductance limitation (lm) in bryophytes and lycophytes (fern allies) to stomatal conductance (ls) and lm colimitation in pteridophytes (ferns) and gymnosperms, a balanced colimitation by the three limitations is finally reached in angiosperms. We discuss the implications of this new knowledge for future biotechnological attempts to improve crop photosynthesis.

Photosynthesis in bryophytes and lycophytes has received less attention than terrestrial plant groups. In particular, few studies have addressed the nonstomatal diffusion conductance to CO2 g(nsd) of these plant groups. Their lower photosynthetic rate per leaf mass area at any given nitrogen concentration compared with vascular plants suggested a stronger limitation by CO2 diffusion. We hypothesized that bryophyte and lycophyte photosynthesis is largely limited by low g(nsd). Here, we studied CO2 diffusion inside the photosynthetic tissues and its relationships with photosynthesis and anatomical parameters in bryophyte and lycophyte species in Antarctica, Australia, Estonia, Hawaii and Spain. On average, lycophytes and, specially, bryophytes had the lowest photosynthetic rates and nonstomatal diffusion conductance reported for terrestrial plants. These low values are related to their very thick cell walls and their low exposure of chloroplasts to cell perimeter. We conclude that the reason why bryophytes lie at the lower end of the leaf economics spectrum is their strong nonstomatal diffusion conductance limitation to photosynthesis, which is driven by their specific anatomical characteristics.

The central Chilean Andes are located in a Mediterranean-type climate zone, characterized by dry summers and high irradiance. This creates a contrasting elevational gradient because higher elevations get more solid precipitation and lower temperatures, resulting in higher soil humidity along the growing season compared with severe drought at lower elevations. Therefore, species with wide elevational distributions, such as Phacelia secunda, must have developed specific adaptations to cope with contrasting severity of drought stress-induced photoinhibition at different elevations. We hypothesize that P. secunda from lower elevation, is more tolerant to drought stress-induced photo-damage than plants from high elevation. This higher tolerance will be associated to a higher diversity of photoprotective strategies in plants that naturally suffers severe drought every growing season. To test this hypothesis, plants from 2700 and 3600 m in the central Chilean Andes were grown under the common garden and then subjected to water restriction. We measured stress indicators, photochemistry of PSII and PSI and estimate alternative electron sinks. Drought affected P. secunda photosynthetic performance differentially depending on the elevation of provenance. Plants from lower elevation exhibited higher drought tolerance than higher elevation ones. This was related to higher levels of heat dissipation and alternative electron sinks exhibited by plants from lower elevation under drought stress. We concluded that plants naturally subjected to recurrent drought are better adapted to respond to drought stress using additional photochemical photoprotective mechanisms and confirm the role of alternative electron sinks ameliorating photodamage.

In the present chapter, we review the current state-of-the-art of knowledge on mesophyll (internal) CO2 diffusion conductance of photosynthetic tissues (for simplification, g(m)). We show that, despite concerns regarding the methodological approaches currently used for its estimation, a large and consistent body of evidence has accumulated showing that g(m) is finite and significantly limiting for-photosynthesis, as well as being highly variable among photosynthetic organisms and in response to environmental changes. Part of this variation results from different anatomies of the photosynthetic tissues, with a particularly strong influence of chloroplast distribution and cell wall thickness. Besides these, it appears that a biochemical modulation of g(m) also occurs, likely involving aquaporins and, possibly, carbonic anhydrases and other metabolic components. Further efforts are needed in the near future to improve CO2 diffusion models, both for the estimation of g(m) and for the precise physiological understanding of the CO2 assimilation process in different plants, as well as to increase our knowledge of the mechanistic base for gm and its regulation.

Drier climatic conditions will be the future scenario in many regions worldwide, including southern South America. Few studies have characterized the ecophysiological vulnerability of the endemic tree species that inhabit this area, to climate change. In this study we assessed the hydraulic vulnerability of the longest-lived tree of the Southern Hemisphere, Fitzroya cupressoides, focusing on adult trees and saplings from two highly disturbed populations: the Coastal Range (AC) and Central Depression (FN) of southern Chile, which represent contrasting site conditions. This, as a basis for the design of conservation strategies to safeguard the persistence of these endangered forests in a drier future. We assessed water potentials (WP) throughout a growing season, their relationships with environmental conditions, as well as leaf and stem (branch) traits and hydraulic safety margins. Despite that the studied summer was the second driest in the last seven decades, minimum WP were not that negative (-1.3 to -1.5 MPa); which could be partly explained by a high leaf capacitance in this species. Adult trees and saplings from both sites did not significantly differ in their WP at turgor loss point, and their associated leaf safety margins, which were relatively low in all cases. However, they significantly differed in the xylem WP causing a 50% loss of stem conductivity (P-50): adults AC: -5.14, saplings AC: -2.53, adults FN: -3.71, and saplings FN: -3.87 MPa. These values led to a relatively large stem safety margin (SSM) in most cases, and their variation was not explained neither by wood density, nor by tracheid size changes. Moreover, there appears to be an ontogenic adjustment in the more restrictive site AC, which was not seen in FN. Within the continuum of species strategies to cope with water stress, Fitzroya has features of the two ends of the continuum: tissues with large SSM, and tissues that sustain milder operation pressures through capacitance. Although Fitzroya appears to be relatively resistant to water scarcity, saplings from AC, seem to be the most vulnerable to the acidification trend in southern Chile. Moreover, future drying could become a significant extra threat to the highly endangered Central Depression population. Conservation actions are urgently needed to secure the future of Fitzroya forests in southern Chile.

Many clonal plants produce vegetative recruits that remain connected to the parent plant. Such connections permit resource sharing among ramets, explaining the high survival rates of vegetative recruits during establishment under suboptimal conditions for sexual regeneration. We propose that differences in the regeneration niches of sexual and vegetative recruits reflect different physiological adjustments caused by parental supply of resources to the ramets. We conducted ecophysiological measurements in saplings and root suckers of Eucryphia cordifolia Cav., a tree species of the temperate rainforest of southern South America. We compared the following traits of saplings and suckers: gas exchange at the leaf level, crown architecture, daily crown carbon balance, biomass allocation to above-ground tissues (leaf-to-stem mass ratio, leaf mass area and leaf area ratio), xylem anatomy traits (lumen vessel fraction, vessel density and size) and stem ring width. We also correlated the growth rates of saplings and suckers with relevant environmental data (light and climate). Saplings showed morphological, architectural and physiological traits that enhance daily crown carbon balance and increase water-use efficiency, in order to supply their growth demands while minimizing water loss per unit of carbon gained. The radial growth of saplings diminished under dry conditions, which suggests a strong stomatal sensitivity to water availability. Suckers have low stomatal conductance, likely because the carbon supplied by the parent plant diminishes the necessity of high rates of photosynthesis. The low responsiveness of sucker growth to temporal changes in water availability also supports the existence of parental supply. The physiological differences between sexual and vegetative recruits satisfactorily explain the ecological niche of E. cordifolia, with saplings restricted to more closed and humid sites.

Water limitation is a major global constraint for plant productivity that is likely to be exacerbated by climate change. Hence, improving plant water use efficiency (WUE) has become a major goal for the near future. At the leaf level, WUE is the ratio between photosynthesis and transpiration. Maintaining high photosynthesis under water stress, while improving WUE requires either increasing mesophyll conductance (gm ) and/or improving the biochemical capacity for CO2 assimilation-in which Rubisco properties play a key role, especially in C3 plants at current atmospheric CO2 . The goals of the present analysis are: (1) to summarize the evidence that improving gm and/or Rubisco can result in increased WUE; (2) to review the degree of success of early attempts to genetically manipulate gm or Rubisco; (3) to analyse how gm , gsw and the Rubisco's maximum velocity (Vcmax ) co-vary across different plant species in well-watered and drought-stressed conditions; (4) to examine how these variations cause differences in WUE and what is the overall extent of variation in individual determinants of WUE; and finally, (5) to use simulation analysis to provide a theoretical framework for the possible control of WUE by gm and Rubisco catalytic constants vis-à-vis gsw under water limitations.

Ferns and fern allies have low photosynthetic rates compared with seed plants. Their photosynthesis is thought to be limited principally by physical CO2 diffusion from the atmosphere to chloroplasts. The aim of this study was to understand the reasons for low photosynthesis in species of ferns and fern allies (Lycopodiopsida and Polypodiopsida). We performed a comprehensive assessment of the foliar gas-exchange and mesophyll structural traits involved in photosynthetic function for 35 species of ferns and fern allies. Additionally, the leaf economics spectrum (the interrelationships between photosynthetic capacity and leaf/frond traits such as leaf dry mass per unit area or nitrogen content) was tested. Low mesophyll conductance to CO2 was the main cause for low photosynthesis in ferns and fern allies, which, in turn, was associated with thick cell walls and reduced chloroplast distribution towards intercellular mesophyll air spaces. Generally, the leaf economics spectrum in ferns follows a trend similar to that in seed plants. Nevertheless, ferns and allies had less nitrogen per unit DW than seed plants (i.e. the same slope but a different intercept) and lower photosynthesis rates per leaf mass area and per unit of nitrogen.

Premise of research.Heteroblastic species are those that show an abrupt change in shape and/or size among individual metamers during ontogeny. Gevuina avellana Mol. (Proteaceae) is a typical tree species in the temperate rain forests of Chile and Argentina. This tree shows drastic heteroblasty, changing from simple leaves at the seedling stage to pinnate leaves during development. It regenerates mostly in shady understories, but juveniles can be found growing under a wide range of light conditions (5%-50% canopy openness). Thus, considering that light has been proposed as a driver of the heteroblastic strategy, G. avellana is an interesting model to study the potential environmental modulation of its ontogenetically programmed heteroblasty. Therefore, the aim of this study was to determine the effect of light availability on G. avellana's heteroblastic trajectory. We postulated that G. avellana's ontogenetic changes in leaf complexity (i.e., heteroblasty) increase under high light availability.Methodology.Saplings along most of the light availability gradient were sampled. Plant height was used as a proxy for ontogeny. We measured several leaf traits (leaf area), shape (aspect ratio), pinnation (leaf dissection index), and complexity (fractal dimension index). First, we evaluated the change in each leaf trait with height by means of Pearson's correlation. Then we tested for differences in leaf traits along the ontogeny between two light environments (higher and lower than 10% canopy openness) by the line-fitting standardized major axis method.Pivotal results.We found positive correlations between each leaf trait and plant height (P < 0.001), while only leaf size and complexity showed higher ontogenetic increases under high light.Conclusions.Light environment has a small but significant effect on the heteroblastic trajectory of G. avellana. In particular, saplings inhabiting microsites with high light availability have larger and more complex leaves. While allometry would explain the ontogenetic trajectory of leaf size, the increased complexity could reflect functional advantages for large leaves in tall plants, especially under high light conditions.

The aim of the present study was to evaluate the applicability of maximal photochemical efficiency of photosystem II (Fv/Fm) as an early estimate of P. radiata micrografts viability coming from different position (basal vs. apical) in the ortets. We hypothesize that Fv/Fm variation is a good indicator of micrograft’s viability and phenological stage during micrograft development. The micrografts were established in QL medium supplemented whit 0.1 mg·L-1 IBA and 1 mg·L-1 BAP and cultured at 25°C ± 2°C and 80 μmol photons m-2s-1 of photosynthetic active radiation by 16 h per day. During the establishment and consolidation phase, we found significant differences in Fv/Fm with respect to time and buds positions provenience. During establishment, basal shoot tips have lower Fv/Fm than apical shoot tips, which agrees with the lowest viability (35%). However, during the consolidation phase, the trend changed and basal shoot tips presented higher Fv/Fm than apical shoot tips and showed an increase in ETR and NPQ, with respect to apical shoots and ortet. Although the measurement of fluorescence parameters implies the insertion of the fluorometer sonde in vitro, this implies aseptic considerations, but always conveies a contamination risk. We conclude that fluorescence (Fv/Fm, ETR, NPQ) can be indicators of the micrograft’s development according to the shoot tips position in the ortet and can be useful early-indicators of the scions’ physiological condition during micrograft transition from establishment to consolidation.

Plant growth at extremely high elevations is constrained by high daily thermal amplitude, strong solar radiation and water scarcity. These conditions are particularly harsh in the tropics, where the highest elevation treelines occur. In this environment, the maintenance of a positive carbon balance involves protecting the photosynthetic apparatus and taking advantage of any climatically favourable periods. To characterize photoprotective mechanisms at such high elevations, and particularly to address the question of whether these mechanisms are the same as those previously described in woody plants along extratropical treelines, we have studied photosynthetic responses in Polylepis tarapacana Philippi in the central Andes (18°S) along an elevational gradient from 4300 to 4900 m. For comparative purposes, this gradient has been complemented with a lower elevation site (3700 m) where another Polylepis species (P. rugulosa Bitter) occurs. During the daily cycle, two periods of photosynthetic activity were observed: one during the morning when, despite low temperatures, assimilation was high; and the second starting at noon when the stomata closed because of a rise in the vapour pressure deficit and thermal dissipation is prevalent over photosynthesis. From dawn to noon there was a decrease in the content of antenna pigments (chlorophyll b and neoxanthin), together with an increase in the content of xanthophyll cycle carotenoids. These results could be caused by a reduction in the antenna size along with an increase in photoprotection. Additionally, photoprotection was enhanced by a partial overnight retention of de-epoxized xanthophylls. The unique combination of all of these mechanisms made possible the efficient use of the favourable conditions during the morning while still providing enough protection for the rest of the day. This strategy differs completely from that of extratropical mountain trees, which uncouple light-harvesting and energy-use during long periods of unfavourable, winter conditions.

Adequate in vitro micro-environments are crucial to induce life compatible leaf development. Key morphological and physiological traits are needed to allow ex vitro survival. We study, how in vitro light and ventilation affect physiological performance and survival of ex vitro Castanea sativa plantlets. In vitro treatments consisted of two irradiances of 50 and 150 µmol m−2 s−1 in ventilated vessels (VL50 and VL150, respectively), compared to traditional cultures at 50 µmol m−2 s−1 in non-ventilated vessels (NVL50). After the exposure to each condition a photoinhibitory treatment (PhT) was also applied to study whether the above in vitro conditions exerted photoprotection and facilitated the recovery of C. sativa during sudden ex vitro transfer. During rooting, a decrease in net photosynthesis (Psat), electron transport rate (ETRII) and maximal efficiency of PSII (F v /F m ) were observed. Transpiration rates (E) decreased, concomitantly with a rise in water use efficiency (WUE), mainly in microplants originating from ventilated treatments (V). Throughout this stage, the PhT was lethal for all in vitro treatments. During acclimation, the number and leaf size increased principally in plantlets originating from V treatments. These microplants were also able to recover their ETR and F v /F m . Initially, the PhT produced a drastic drop in Fv/Fm of plantlets in all treatments however they did show a tendency to recover. Transferring plantlets to the greenhouse produced a decrease in the Psat in all treatments; however, over time Psat increased reaching values of 3.2 and 5.3 μmol CO2 m−2 s−1 in microplants originating from VL50 and VL150, respectively. Transpiration rate were similar in all treatments and remained at levels of about 0.9 mmol H2O m−2 s−1; thus, WUE increased significantly, reaching values of almost 3.8 µmol CO2/mmol H2O in microplants originating from VL150. After the PhT, all of the plantlet’s recovery capacity increased concomitantly with their dynamic heat dissipation and their de-epoxidation capacity. Our results suggest that managing in vitro conditions can improve plantlets photosynthetic performance in early stages after ex vitro transfer, playing a key role in the ameliorating the transfer stress.

Unmanned aerial vehicles (UAVs) present an exciting opportunity to monitor crop fields with high spatial and temporal resolution remote sensing capable of improving water stress management in agriculture. In this study, we reviewed the application of different types of UAVs using different remote sensors and compared their performance with ground-truth plant data. Several reflectance indices, such as NDVI, TCARI/OSAVI and PRInorm obtained from UAVs have shown positive correlations related to water stress indicators such as water potential (psi) and stomata] conductance (g(s)). Nevertheless, they have performed differently in diverse crops; thus, their uses and applications are also discussed in this study. Thermal imagery is also a common remote sensing technology used to assess water stress in plants, via thermal indices (calculated using artificial surfaces as references), estimates of the difference between canopy and air temperature, and even canopy conductance estimates derived from leaf energy balance models. These indices have shown a great potential to determine field stress heterogeneity using unmanned aerial platforms. It has also been proposed that chlorophyll fluorescence could be an even better indicator of plant photosynthesis and water use efficiency under water stress. Therefore, developing systems and methodologies to easily retrieve fluorescence from UAVs should be a priority for the near future. After a decade of work with UAVs, recently emerging technologies have developed more user-friendly aerial platforms, such as the multi-copters, which offer industry, science, and society new opportunities. Their use as high-throughput phenotyping platforms for real field conditions and also for water stress management increasing temporal and resolution scales could improve our capacity to determine important crop traits such as yield or stress tolerance for breeding purposes. (C) 2015 Elsevier B.V. All rights reserved.