Increase In Photosynthetic Capacity Research Articles

Shortcutting Photorespiration Protects Potato Photosynthesis and Tuber Yield Against Heatwave Stress.

Over two growing seasons, a chloroplast localized synthetic glycolate metabolic pathway expressed in potato, enhanced tuber biomass. We confirmed that this yield benefit did not come at the cost of tuber quality. In 2022, after two early season natural heatwaves, we observed enhanced daily carbon assimilation rates and increased photosynthetic capacity, with transformed plants having up to 23% higher Vcmax and 13% higher Jmax during tuber bulking stages, indicating that transformed plants were better able to withstand growing season heatwaves than untransformed controls. The increases in photosynthetic capacity and potato tuber mass after early season heatwaves were greater than in seasons without heatwaves and present the AP3 pathway as a promising avenue for yield increases in the face of forecast increased intensity and duration of heatwave events as a result of global warming.

The Multifunctional Anaphase Promoting Complex 7 (APC7) Gene Is Associated With Increased Plant Growth and Improved Resistance to DNA and RNA Viruses.

The anaphase promoting complex 7 (AtAPC7) is an APC/C subunit expressed in different organs of Arabidopsis thaliana and conserved among eukaryotes. A variant of the complete APC7 protein, containing its C-terminal region (named APC-CT), shows a high homology with a tobacco viral replication inhibitor (IVR-like) protein that reduces plant susceptibility to RNA viruses. Here, the role of the AtAPC7 gene was investigated by characterizing Arabidopsis plants overexpressing the full-length AtAPC7 (APC7OE) and the C-terminal portion (APC7-CTOE), by phenotypical, physiological and molecular approaches. APC7OE plants showed improved growth of vegetative organs, earlier flowering and increased photosynthetic efficiency, CO2 assimilation and productivity, compared with Col-0 control plants. Conversely, APC7-CTOE plants showed reduced susceptibility to both RNA and DNA viruses, along with an improvement in plant growth, although not surpassing APC7OE plants. Altogether, the data provide evidence for the role of the AtAPC7 in regulating cell division, expansion and differentiation, accompanied by an increase in photosynthetic capacity, resulting in enhanced plant biomass and seed yield. AtAPC7-CT might reduce growth-defence trade-offs, enabling plants to simultaneously defend themselves while promoting better growth. Our findings highlight the multifunctional role of AtAPC7, unveiling the potential of its orthologous genes as valuable biotechnological tools in important crops.

Leaf Photosynthetic and Photoprotective Acclimation in the Ultraviolet-A1 and Blue Light Regions Follow a Continuous, Shallow Gradient.

Although blue light is known to produce leaves with high photosynthetic capacity, the role of the blue-adjacent UV-A1 (350-400 nm) in driving leaf photosynthetic acclimation is less studied. Tomato plants were grown under hybrid red and blue (RB; 95/5 μmol m-2 s-1), as well as four treatments in which RB was supplemented with 50 μmol m-2 s-1 peaking at 365, 385, 410 and 450 nm, respectively. Acclimation to 365-450 nm led to a shallow gradient increase in trait values (i.e., photosynthetic capacity, pigmentation and dry mass content) as the peak wavelength increased. Furthermore, both UV-A1 and blue light grown leaves showed efficient photoprotection under high light intensity. When treated plants were transferred to fluctuating light for 5 days, leaves from all treatments showed increases in photosynthetic capacity, which were strongest in RB, followed by additional UV-A1 treatments; RB grown leaves showed reductions in maximum quantum yield of photosystem II, while UV-A1 grown leaves showed increases. We conclude that both UV-A1 and blue light effectively trigger photosynthetic and photoprotective acclimation, the extent of acclimation becoming stronger the longer the peak wavelength is. Acclimatory responses to UV-A1 and blue light are thus not distinct from one another, but follow a continuous gradient.

UV-A radiation increases biomass yield by enhancing energy flow and carbon assimilation in the edible cyanobacterium Nostoc sphaeroides.

Ultraviolet (UV) A radiation (315-400 nm) is the predominant component of solar UV radiation that reaches the Earth's surface. However, the underlying mechanisms of the positive effects of UV-A on photosynthetic organisms have not yet been elucidated. In this study, we investigated the effects of UV-A radiation on the growth, photosynthetic ability, and metabolome of the edible cyanobacterium Nostoc sphaeroides. Exposures to 5-15 W m-2 (15-46 µmol photons m-2 s-1) UV-A and 4.35 W m-2 (20 μmol photons m-2 s-1) visible light for 16 days significantly increased the growth rate and biomass production of N. sphaeroides cells by 18%-30% and 15%-56%, respectively, compared to the non-UV-A-acclimated cells. Additionally, the UV-A-acclimated cells exhibited a 1.8-fold increase in the cellular nicotinamide adenine dinucleotide phosphate (NADP) pool with an increase in photosynthetic capacity (58%), photosynthetic efficiency (24%), QA re-oxidation, photosystem I abundance, and cyclic electron flow (87%), which further led to an increase in light-induced NADPH generation (31%) and ATP content (83%). Moreover, the UV-A-acclimated cells showed a 2.3-fold increase in ribulose-1,5-bisphosphate carboxylase/oxygenase activity, indicating an increase in their carbon-fixing capacity. Gas chromatography-mass spectrometry-based metabolomics further revealed that UV-A radiation upregulated the energy-storing carbon metabolism, as evidenced by the enhanced accumulation of sugars, fatty acids, and citrate in the UV-A-acclimated cells. Therefore, our results demonstrate that UV-A radiation enhances energy flow and carbon assimilation in the cyanobacterium N. sphaeroides.IMPORTANCEUltraviolet (UV) radiation exerts harmful effects on photo-autotrophs; however, several studies demonstrated the positive effects of UV radiation, especially UV-A radiation (315-400 nm), on primary productivity. Therefore, understanding the underlying mechanisms associated with the promotive effects of UV-A radiation on primary productivity can facilitate the application of UV-A for CO2 sequestration and lead to the advancement of photobiological sciences. In this study, we used the cyanobacterium Nostoc sphaeroides, which has an over 1,700-year history of human use as food and medicine, to explore its photosynthetic acclimation response to UV-A radiation. As per our knowledge, this is the first study to demonstrate that UV-A radiation increases the biomass yield of N. sphaeroides by enhancing energy flow and carbon assimilation. Our findings provide novel insights into UV-A-mediated photosynthetic acclimation and provide a scientific basis for the application of UV-A radiation for optimizing light absorption capacity and enhancing CO2 sequestration in the frame of a future CO2 neutral, circular, and sustainable bioeconomy.

Applications of Xerophytophysiology and Signal Transduction in Plant Production—Flower Qualities in Eustoma grandiflorum Were Improved by Sub-Irrigation

Relatively mild xerophytic or hardening treatments can induce healthy development of plants. In the present study, as one of xerophytophysiological applications, sub-irrigation was applied to a flower plant of Eustoma grandiflorum to confirm whether the sub-irrigation improved flowering quality in addition to plant growth and physiology. As shown by the results, long-term sub-irrigation induced osmotic adjustment, with osmolyte concentration increasing 32.8 osmol m−3 (p ≤ 0.01), improved leaf photosynthetic activities, with more than 10% (p ≤ 0.05) increase in photosynthetic capacity, and promoted plant growth, with a shoot biomass increase by 27.5% (p ≤ 0.01) and a root increase by 50.5% (p ≤ 0.01). These improvements were attributed to turgor maintenance and cell water re-compartmentation into the symplasm, which were both the consequence of osmotic adjustment. The lower osmotic potential and lower relative leaf water potential at incipient plasmolysis suggested that plants in sub-irrigation plots might be more resistant to environmental stresses. Sub-irrigation also improved flower quality shown by increased anthocyanin concentration (16% up, p ≤ 0.01). Flower quality improvement might be attributed to up-regulation of the PAL gene, which could catalyze the synthesis of anthocyanins. PAL gene up-regulation might be associated with a concentration increase in salicylic acid (SA), which was suggested as a plant hormone for signaling. Sub-irrigation also affected the flower opening and closing oscillations with less changed opening size or oscillation amplitude. We adopted mathematical models and thoroughly analyzed dynamic changes in photosynthesis, plant growth, and flower opening oscillations. In conclusion, sub-irrigation was a feasible practice and could be used in E. grandiflorum culture to improve plant growth and flower opening quality.

Physiological and transcriptomic analyses provide insight into thermotolerance in desert plant Zygophyllum xanthoxylum

BackgroundHeat stress has adverse effects on the growth and reproduction of plants. Zygophyllum xanthoxylum, a typical xerophyte, is a dominant species in the desert where summer temperatures are around 40 °C. However, the mechanism underlying the thermotolerance of Z. xanthoxylum remained unclear.ResultsHere, we characterized the acclimation of Z. xanthoxylum to heat using a combination of physiological measurements and transcriptional profiles under treatments at 40 °C and 45 °C, respectively. Strikingly, moderate high temperature (40 °C) led to an increase in photosynthetic capacity and superior plant performance, whereas severe high temperature (45 °C) was accompanied by reduced photosynthetic capacity and inhibited growth. Transcriptome profiling indicated that the differentially expressed genes (DEGs) were related to transcription factor activity, protein folding and photosynthesis under heat conditions. Furthermore, numerous genes encoding heat transcription shock factors (HSFs) and heat shock proteins (HSPs) were significantly up-regulated under heat treatments, which were correlated with thermotolerance of Z. xanthoxylum. Interestingly, the up-regulation of PSI and PSII genes and the down-regulation of chlorophyll catabolism genes likely contribute to improving plant performance of Z. xanthoxylum under moderate high temperature.ConclusionsWe identified key genes associated with of thermotolerance and growth in Z. xanthoxylum, which provide significant insights into the regulatory mechanisms of thermotolerance and growth regulation in Z. xanthoxylum under high temperature conditions.

Daily changes on seasonal ecophysiological responses of the intertidal brown macroalga Lessonia spicata: Implications of climate change.

Global climate change is expected to have detrimental effects on coastal ecosystems, with impacts observable at the local and regional levels, depending on factors such as light, temperature, and nutrients. Shifts in dominance between primary producers that can capitalize on carbon availability for photosynthesis will have knock-on effects on marine ecosystems, affecting their ecophysiological responses and biological processes. Here, we study the ecophysiological vulnerability, photoacclimation capacity, and tolerance responses as ecophysiological responses of the intertidal kelp Lessonia spicata (Phaeophyceae, Laminariales) during a year through different seasons (autumn, winter, spring, and summer) in the Pacific Ocean (central Chile). Six different daily cycle experiments were carried out within each season. A battery of different biochemical assays associated with antioxidant responses and in-vivo chlorophyll a fluorescence parameter showed that during spring and summer, there was an increase in photosynthetic capacity in the macroalgae, although their responses varied depending on light and nutrient availability in the course of the year. Lessonia spicata showed maximal photosynthesis and a similar photoinhibition pattern in summer compared to the other seasons, and the contents of nitrate and phosphorous in seawater were less in winter. Thus, high irradiance during spring and summer displayed a higher maximal electron transport rate (ETRmax), irradiance of saturation (Ek), non-photochemical quenching (NPQmax), nitrogen and carbon contents, and photoprotector compound levels. Antioxidant activity increased also in summer, the seasonal period with the highest oxidative stress conditions, i.e., the highest level of hydrogen peroxide (H2O2). In contrast, under low irradiance, i.e., wintertime conditions, L. spicata demonstrated lower concentrations of the photosynthetic pigments such as chlorophyll a and carotenoids. Our study suggests that macroalgae that are subjected to increased irradiance and water temperature under lower nutrient availability mediated by seasonal changes (expected to worsen under climate change) respond with higher values of productivity, pigment contents, and photoprotective compounds. Thus, our findings strengthen the available evidence to predict that algae in the order Laminariales, specifically L. spicata (kelp), could better proliferate, with lower vulnerability and greater acclimation, than other marine species subject to future expected conditions associated with climate change.

Do larger plants produce more and better seeds and seedlings? Testing the hypothesis in a globose cactus, Wigginsia sessiliflora

In iteroparous plants, an increase in allocation to reproduction is expected with increasing plant size. The aim of this study was to analyze how plant diameter is related to total produced seed mass, seed number, mean seed mass, percentage and mean germination time (MGT), and seedling size and shape in Wigginsia sessiliflora (Hook.) D.M. Porter (Cactaceae), a slow-growing globose species from central Argentina. Plant diameter was measured in a population of 185 individuals, and fruits were collected. We counted all seeds to obtain seed number, and weighed them to get seed mass and total seed mass. Seeds were germinated and data of germination percentage and MGT were collected. We also measured the size (height and width) and shape of seedlings (height/width relationship). Fifty-four percent of the plants did not produce fruits. Plant diameter was unimodally related to fruit number, total seed mass, and seed number, i.e., intermediate-sized plants presented the highest values. Height and shape of seedlings were positively related to plant diameter. Surprisingly, plant diameter was related in a unimodal way to reproductive outputs. As plants grow, surface–volume ratio decreases, meaning that respiratory losses would be higher than the increase in photosynthetic capacity; therefore, fewer resources may be available for reproduction.

Seasonal Photoacclimation and Vulnerability Patterns in the Brown Macroalga Lessonia spicata (Ochrophyta)

Fluctuations in solar radiation are one of the key factors affecting productivity and survival in habitat forming coastal macroalgae, in this regard, photoacclimation has a direct impact on the vulnerability and the capacity of seaweed to withstand, for instance, radiation excess. Here, we study ecophysiological responses through photosynthetic activity measurements under time-dependent (one year) fluctuations in solar radiation in the brown macroalga L. spicata. The responses presented seasonal patterns, with an increase in photosynthetic capacity during summer, expressed in greater maximal electron transport rate (ETRmax) and diminished thermal dissipation (NPQmax). Moreover, we studied photoprotective compounds (phenolic compounds) and total antioxidant capacity, which demonstrated an increase during periods of high solar radiation. In addition, content of photosynthetic pigment (Chla, Chlc and Carotenoids) increased under greater solar irradiance. The L. spicata can accumulate as reservoir photoprotective and antioxidant substances to withstand periods of high solar irradiance. All ecophysiological and biochemical responses in L. spicata indicate high photoacclimation and low vulnerability in the species, especially during with greater levels of solar irradiance.

Photosynthetic characteristics and growth performance of lettuce (Lactuca sativa L.) under different light/dark cycles in mini plant factories

We investigated the photosynthesis and growth of lettuce (Lactuca sativa L.) grown under three light/dark cycles in a mini plant factory with artificial illumination. A relative longer light cycle [12/12 h (light/dark)] increased not only light-response curve parameters, such as light-saturated net photosynthetic rate, light-saturation point, light-compensation point, dark respiration rate, but also upregulated CO2-response curves parameters, such as CO2-saturated net photosynthetic rate, initial carboxylation efficiency, and photorespiration rate, compared to those of the shorter light cycles [6/6 h and 3/3 h (light/dark)]. A longer light cycle enhanced electron transfer potential, increased the chlorophyll amount, leaf area, and biomass and reduced the root/shoot ratio and the specific leaf area. Our results imply that the prolonged light cycle led to the increase in photosynthetic capacity and significantly enhanced the growth rate of lettuce.

Photosynthetic plasticity allows blueberry (Vaccinium corymbosum L.) plants to compensate for yield loss under conditions of high sink demand

In some growing environments blueberry (Vaccimium corymbosum L.) yields exhibit excessive annual variation associated with poor photosynthetic performance. The purpose of this study was to determine how photosynthesis may be affected by demand and to define the mechanisms underpinning photosynthetic plasticity. Manipulation of source-sink ratios revealed that yields were maintained following 50 % defoliation. This was associated with an adaptive increase in photosynthetic capacity mediated via changes in stomatal physiology, photosynthetic electron transport and CO2 assimilation. Transcripts encoding enzymes of the Calvin-Benson cycle including the Rubisco large subunit, Rubisco activase, phosphoribulokinase and plastid-localised glyceraldehyde phosphate dehydrogenase 3 were more abundant in leaves from partially defoliated plants relative to control plants. Short-term 13CO2 labelling experiments suggested that partial defoliation did not incur an assimilation penalty although the accumulation of sugars and starch in some organs was reduced. Metabolite profiles of leaves from partially defoliated plants exhibited some differences from those of control leaves, however, no changes in the diurnal content of leaf sugar and starch were observed between treatments. The data highlights the mechanisms by which blueberry leaves adapt to increased demand and demonstrate that photosynthetic plasticity can compensate for significant loss of the photosynthetic area.

Влияние органических удобрений и природного цеолита на содержание пигментов и урожайность растений рапса сорта Риф

Abstract. A comprehensive study of raw materials in the Lipetsk region as organic waste in conjunction with zeolite-containing rocks in crop production is necessary to obtain new fundamental knowledge. The purpose of the study was to study the influence of different norms of fertilizers on photosynthetic capacity and pigment of plant leaves and the yield of spring rapeseed under conditions of forest-steppe of Central Black Earth Region. Method of research. In the course of research, records and observations were made using the method of laying and conducting field experiments, which is generally accepted in agronomic science [3]. The number of chlorophylls a and b and the amount of caratinoids were determined using a spectrophotometric method. Results. Research conducted in the field experience on the basis of the Yelets State University named after I. A. Bunin allowed us to establish the influence of natural zeolite and organic fertilizers on changes in the pigment composition of leaves and productivity of spring rape plants in the rosette and flowering phases. Plants in the flowering phase had the highest photosynthetic potential. It was found that the application of organic fertilizers significantly contributed to the accumulation of chlorophyll a in plants and pigments in General at all the studied phases of development, and their joint use with zeolite led to an increase in crop yield. The maximum increase in yield was obtained in the variant with the introduction of chicken manure 10 t/ha and zeolite 3 t/ha, which was 16.8 c/ha compared to the control. The carried out researches allow to recommend the use of organic waste of poultry farms together with natural zeolite Terbunskiy field in the conditions of forest-steppe of Central Black Earth Region on leached Chernozem under spring rape. Scientific novelty. In the conditions of forest-steppe Central Black Earth Region first determined the optimal application rate of chicken manure and natural zeolite, which contribute to the increase in photosynthetic capacity and pigmentation of plant leaves that allows to obtain high yield and good seed quality.

Effectiveness of silicon sources for in vitro development of gerbera

Each species cultured in vitro has specific nutritional requirements on the culture medium. The use of silicon in culture can provide benefits to plants, such as increase of tolerance to water stress, increase of photosynthetic capacity and reduction in transpiration. These effects may be quite relevant for in vitro growth and development of plant and during acclimatization. However, the effectiveness of this nutrient may vary depending on the used sources. The aim of this study was to verify the ideal concentration of the MS culture medium and to evaluate the to evaluate the different sources as well as the function of silicon for in vitro development and acclimatization of gerbera plantlets. Shoots (4–6 cm) of gerbera (Gerbera jamesonii cv. Jaguar Cream) cultured in vitro were inoculated in MS medium with different concentrations of salts (MS ¼, MS ½, MS ¾, MS) supplemented with different silicon sources (potassium silicate, sodium silicate, calcium silicate and silicic acid) at concentrations of 0 (control), 0.25, 0.5, 0.75, and 1 mg L−1. The use of MS ¼ medium and the supplementation of 0.25 g L−1 calcium silicate provided better shoot development. The acclimatization rate was not affected by the origin of plants treated in vitro by different silicon sources, their concentrations, and the used culture medium. Thus, the use of silicon is beneficial for in vitro development of gerberas, however, the effectiveness depends on the used source. In vitro shoots of Gerbera jamesonii cv. Jaguar Cream regenerate better, shoots are taller and healthier, and root more effectively when are cultured on MS 1/4 supplemented with 0.25 mg L−1 calcium silicate.

Net carbon ecosystem exchange during 24 years in the Sorø Beech Forest – relations to phenology and climate

The carbon sequestration of plants through photosynthesis is responsible for removal of a substantial amount of the man-made CO2 emissions to the atmosphere. In recent years this so-called land-sink has removed about 30% of the man-made emissions to the atmosphere, with forests being the most important sinks. The land-sink is, however, vulnerable to changes in the environment, such as the atmospheric composition, climate change, and extreme events like storms and droughts. It is therefore important to study the effects of such change on terrestrial ecosystems to provide the basis for predicting the future of the sink. We here report the results of continuous CO2 flux measurements over a Danish beech forest during the years 1996–2019. Over the years the forest acted as a sink of CO2 with a net carbon sequestration ranging from about zero to 400 g C m–2 yr−1. We found significant trends in net ecosystem exchange (NEE) (increasing in absolute terms with 15 g C m–2 yr2), gross ecosystem exchange (GEE) (increasing with 25 g C m–2 yr–2), and ecosystem respiration (RE) (increasing with 10 g C m–2 yr–2). A prolonged growing season explained 73% of the increase in NEE. The increasing CO2 concentration in the atmosphere and a subsequent increase in photosynthetic capacity together with warming are the most likely main causes of the increased carbon uptake. The severe drought in the summer of 2018 resulted in a reduction of the annual NEE of 25%.

Boosting proso millet yield by altering canopy light distribution in proso millet/mung bean intercropping systems

To elucidate the mechanism by which intercropping proso millet (Panicum miliaceum L.) with mung bean (Vigna radiata L.) increases proso millet yield and to determine how this higher yield results from maximization of resources use efficiency, we designed and conducted four strip intercropping row arrangements, including two rows of proso millet alternating with two rows of mung bean (2P2M), four rows of proso millet alternating with two rows of mung bean (4P2M), four rows of proso millet alternating with four rows of mung bean (4P4M), two rows of proso millet alternating with four rows of mung bean (2P4M), sole proso millet (SP, control) and sole mung bean (SM, control) in Yulin, Shaanxi, China. Photosynthetically active radiation (PAR) in the canopy, radiation use efficiency (RUE), leaf photosynthetic characteristics, dry matter accumulation and allocation, and yield of proso millet were investigated. The results showed that the intercropping systems had higher PAR than the monoculture. Mean PAR intensities were increased by respectively 2.2%–23.4%, 19.8%–59.7%, and 61.2%–133.3% in the proso millet upper, middle and lower canopies compared with SP. The increase in PAR directly increased RUE, a result attributed mainly to the increase in photosynthetic capacity, including net photosynthetic rate and chlorophyll content. These responses resulted in increased dry matter allocation to plant organs. Yield of intercropped proso millet was 6.8%–37.3% higher than that under monoculture and the land equivalent ratios for the different intercropping patterns were all greater than unity (> 1). In general, yield followed a positive linear function of PAR in the intercropping system. The results indicated that intercropping can boost proso millet yield, evidently by altering light distribution within its canopy and consequently increasing RUE, thereby increasing leaf photosynthetic capacity, dry matter accumulation, and allocation to the grain. The optimum combination for improving the growth and yield of proso millet on the Loess Plateau of China was 2P4M.

Can Rose Bengal resilience be used as a marker for photosynthetic resilience of Nannochloropsis oceanica strains in excess light environments?

Singlet oxygen (1O2) is an interesting candidate for study due to the widely held opinion that it plays a key role in photoinhibition of photo system II (PSII). Many studies have been conducted to elucidate the exact role of singlet oxygen (1O2) in photo-damage/repair, photoprotection, oxidative protection, and signaling. However, few studies have addressed the potential role of singlet oxygen as a marker for resilience to excess light environments. In the present study, we focus on the question of whether singlet oxygen resilience correlates with a strain's robustness in excess light environments. In order to address this question, two Nannochloropsis oceanica mutant strains, RB2 and RB113, both selected for heightened resilience to Rose Bengal (RB), a singlet oxygen (1O2) photosensitizer, were characterized. This included the characterization of the photosynthetic apparatuses and specific growth rate in relation to photosynthetic photon flux density (PPFD) in the growth media.Both of the RB resistant mutants showed higher photosynthetic capabilities when grown in high PPFD environments relative to the wild type (WT) strain. This was evident by higher photosynthetic capacity (namely 27% higher in the RB113 mutant and 94% higher in the RB2 mutant) relative to the WT strain when grown in an optimal temperature and an excess light environment (25 °C and 500 photons μmol s−1 m−2). In addition to the increase in photosynthetic capacity in the excess light environment of 25 °C and 500 photons μmol s−1 m−2, mutant strains also showed higher specific growth rates reflected by a 38% and 48% increase in the RB113 and RB2 mutant strains respectively. These results lead us to propose that Rose Bengal resilience in Nannochloropsis may serve as a marker for selecting species or strains better suited for growth in high light environments.

Divergent growth responses to warming and drying climates between native and non-native tree species in Northeast China

Increased intrinsic water use efficiency enhances tree growth of native species, but not that of non-native species under warming and drying climates in Northeast China. Climate change significantly affects forest ecosystems. However, little is known about whether non-native and native tree species show similar responses to global warming. We found different trends in the basal area increment (BAI) and tree-ring stable carbon isotope ratio (δ13C) of two non-native (Pinus sylvestris var. mongolica and Populus × xiaozhuanica) and two native (Pinus tabuliformis and Ulmus pumila) tree species during the warming and drying periods from 1985 to 2014. The BAI of non-native tree species was stable, whereas that of the native tree species exhibited a significant increase. A significant increase in tree-ring δ13Ccorr (corrected for atmospheric changes in δ13C) for non-native tree species indicated increasing water stress. The intrinsic water use efficiency (iWUE, derived from tree-ring δ13C) of both non-native and native tree species increased significantly. However, the magnitude of the increase in iWUE was higher in non-native tree species than in native tree species, indicating that non-native tree species suffered stronger water stress. Increasing iWUE but no increase in BAI for non-native tree species suggested that water stress reduced stomatal conductance and, consequently, reduced carbon uptake. In contrast, increased iWUE accompanied by an enhanced BAI for native tree species indicated an increase in photosynthetic capacity induced by CO2 fertilization. These findings suggest that non-native tree species would experience greater mortality under extreme drought conditions once water stress passes a physiological threshold. However, native tree species would suffer only slightly due to benefiting from CO2 fertilization.

Water table fluctuations control CO2 exchange in wet and dry bogs through different mechanisms

High water tables (WT) stabilise peatland carbon (C) through regulation of biogeochemical processes. The impact of peatland WT on ecosystem function, including C exchange, alters over time, and the factors that cause some peatlands to display resilience and others to undergo degradation are poorly understood. Here we use CO2 flux measurements, measured by eddy covariance, to compare ecosystem function between two raised bogs; one drainage-affected, with a deep and fluctuating water table and the other near-natural, with a shallow and stable water table. The drainage-affected bog was found to be a moderate sink for CO2 (69 g C m−2 yr−1), which was 134 g C m−2 yr−1 less than the near-natural bog (203 g C m−2 yr−1). Greater ecosystem productivity has allowed the drainage-impacted bog to act as a CO2 sink despite higher ecosystem respiration; most likely due to an increase in photosynthetic capacity caused by expansion of ericaceous shrub cover. The tolerance of the vegetation community, particularly the main peat former Empodisma robustum (Restionaceae), to low and fluctuating WT appears to have been key in allowing the site to remain a sink. Despite the current resilience of the ecosystem CO2 sink, we found gross primary production to be limited under both high and low water tables, even in a year with typical rainfall. This is best explained by the limited physiological ability of ericaceous shrubs to tolerate a fluctuating WT. As such we hypothesise that if the WT continues to drop and become even more unstable, then without further vegetation change, a reduction in gross primary production is likely which may in turn cause the site to become a source for CO2.

Adjustment of photosynthetic carbon assimilation to higher growth irradiance in three-year-old seedlings of two Tunisian provenances of Cork Oak (Quercus suber L.)

Three-year-old seedlings of two Tunisian provenances of cork oak (Quercus suber L.) differing in climatic conditions at their geographical origin were subjected to increasing light intensities. Gaâfour was the provenance from the driest site and Feija from the wettest site. Low-light adapted seedlings from both provenances were exposed to two light treatments: full sunlight (HL) and low light (LL, 15% sunlight) for 40 days. The CO2-response curve of leaf net photosynthesis (An-Ci curve) established under saturated photon flux density was used to compare photosynthetic parameters between leaves subjected to continuous low light (LL leaves) and leaves transferred from low to high light (HL leaves). Transfer from low to high light significantly increased net photosynthesis (An) and dark respiration (Rd) in Gaâfour provenance but not in Feija. After transfer to high irradiance, specific leaf area (SLA) did not change in either provenance. This suggested that the increase in photosynthetic capacity on a leaf area basis in HL leaves of Gaâfour provenance was not due to increased leaf thickness. Only the seedlings from the Gaâfour provenance were able to acclimate to high light by increasing Vcmax and Jmax.

The increase of atmospheric CO2 affects growth potential and intrinsic water-use efficiency of Norway spruce forests: insights from a multi-stable isotope analysis in tree rings of two Alpine chronosequences

Relevant CO 2 increase affects iWUE and growth potential of Alpine Norway spruce forests due to triggering of photosynthetic capacity. Minor effect on iWUE of tree size/age ontogenetic factors. An increase in European forest productivity has been widely reported, but evidences on its causal relationship with climate change are still scarce, though they are crucial to understand the mitigation potential of forests and their future dynamics. In the present study, we first assessed the changes in forest productivity of two even-aged Norway spruce forests. Consequently, we investigated the role of several environmental drivers, such as atmospheric CO2 levels, temperature, and precipitation regimes on the intrinsic water-use efficiency (iWUE) temporal patterns of the above-mentioned forests. We applied a chronosequence approach, combining it with a multi-stable isotope analysis, including δ13C and δ18O, to infer tree responses to climate change over time in terms of iWUE changes. By this innovative methodology, we were able to separate environmental and age/size-related factors on iWUE changes. Results showed an increase in forest productivity in both sites, paralleled by a significant increase of iWUE, mainly triggered by a CO2-driven increase in photosynthetic capacity, rather than by a reduction of stomatal conductance. The paramount role of the increase in photosynthetic capacity was confirmed by a strong correlation between atmospheric CO2 concentration and iWUE temporal patterns. The effect of size/age of trees on iWUE temporal changes resulted to be less defining than that of climate change.