Key message: Restricted access of light for stems reduced carbon acquisition there and limited the biomass growth of the roots. Light access can affect the microatmosphere within stems, creating favourable conditions for photosynthesis. We tested the hypothesis that stem photosynthesis modifies carbon allocation within plants and also can affect root growth. To verify this hypothesis, parts ofClusia minorL.stems were covered with dark material for 8 months to block light access to stems, and then, we compared morphological traits, biomass increment, photosynthetic activity and carbon isotopic signature (δ¹³C) in plants with dark- and light-exposed stems.Clusia minorstems were characterized by chlorophyll presence from pith to cortex, active photosystem II and 79% re-assimilation of respired CO₂. We also revealed 24-h changes in the δ¹³C of carbohydrates exported from leaves. Keeping stems in darkness led to a significant lowering in root biomass and shoot-to-root weight index (I_w). Moreover, reductions in stem CO₂efflux and the δ¹³C in the roots and stems were also observed. Our results indicate that the lack of stem photosynthesis affects photosynthate flux to heterotrophic organs, such as roots, stems and probably expanding leaves.

The effects of ozone combined with other environmental factors remain an important topic of the research, both in connection with climate change and the possibility of using modern solutions in horticulture. In our experiment, we compared the influence of ozone (100 ppb) on photosynthesis and changes in the pigment composition of Chinese cabbage (Brassica rapa subsp. pekinensis) leaves depending on the spectral composition of light. We used white LED light (WL), a combination of red + green + blue (RGBL) with a dominant red component and white +blue (WBL) with a dominant blue component in comparison with the classic sodium lamp lighting (yellow light—YL). The values of the parameters describing the light-dependent phase of photosynthesis and the parameters of the gas exchange, as well as non-photosynthesis pigment contents, show that the spectral composition strongly differentiates the response of Chinese cabbage leaves to ozone. In general, the efficiency of photochemical reactions was the highest in YL, but after O₃ fumigation, it decreased. In plants growing in WL and WBL, the increase of O₃ concentration stimulated light photosynthesis reactions and led to the enhancement of transpiration, stomatal conductance and intracellular CO₂ concentration. Changes in photosynthetic activity were accompanied by an increase in the content of anthocyanins and flavonols.

Drought is a major stressor affecting tree physiology and is expected to intensify under climate extremes. Stems, partly due to their photosynthetic capacity, tend to be more drought-resilient than leaves. This study aimed to assess stem photosynthetic and its impact on carbon balance in leafless stems under drought conditions. Severe drought caused a marked decline in stem and root water potential (Ψ) and reduced stem water vapor conductance (g_tw) by about 40%. Despite this, stems retained the capacity for active gas exchange: though with reduced stem CO₂ efflux (ECO₂) and enhanced CO₂ refixation, which increased from about 40% under control conditions to ~55%–60% after drought, accompanied by a twofold increase in intrinsic water use efficiency (iWUE). Chlorophyll a fluorescence and pigment analyses indicated that the integrity of photosystem II (PSII) was preserved under drought, supporting sustained corticular photosynthesis. Concentrations of chloride, malate, and citrate in the xylem sap did not change significantly under drought, indicating a high capacity of stems to maintain homeostasis. Stable isotope analyses revealed drought-induced shifts in δ¹³C, consistent with altered carbon allocation following leaf abscission. These results confirm that stem photosynthesis and CO₂ reassimilation contribute significantly to stem metabolic resilience, mitigating drought-induced carbon losses and helping to preserve plant survival.

Background: Photosynthetic activity in plant stems, particularly in woody plants and shrubs, is well known and documented. Nevertheless, our knowledge about the role of photochemical processes occurring in the stems of cultivated plants and their contribution to plant growth and development, including the root system, still remains unclear. Therefore, this study aims to determine the role of cells equipped with chloroplasts and located in the stems of tomato ( Solanum lycopersicum L.) plants and whether changes in the activity of the photochemical processes affect the development of the plant’s root system and aboveground organs. Results: The described study was conducted on tomato plants with stems covered with a doubled agrotextile (DP) that absorb 99% of incident light and on plants growing without coverage (NDP). Stem darkening led to the changes in the intensity of photochemical processes in these organs - a decrease in both the maximum and actual photochemical efficiency [F _v /F _m and Y(II)], as well as an increase in energy dissipation, both controlled (NPQ – non-photochemical quenching) and uncontrolled [(Y(NO) - non-regulated energy dissipation in photosystem II] way. These changes correlate with alterations in the anatomy of the stem cross-section. Darkening led to an increase in stem surface conductance to water vapour but a decrease in stem CO ₂ efflux. The root length and dry mass of DP plants were significantly reduced compared to the roots of NDP plants. No significant differences were observed for the shoots (leaves + stems). The substantial changes in the structure of chloroplasts located in the stem cells of DP were also observed, with visible signs of ageing and disintegration of these organelles. In addition, the composition of the nitrogen forms in the soil where the plants were grown was different between DP and NDP. The soil from DP plants showed a higher total nitrogen content; however, unlike the ammonium and nitrate forms (NH ₄ ⁺ and NO ₃ ⁻), the nitrite form (NO ₂ ⁻) was present at a lower concentration in this substrate compared to that of the NDP plants. Darkening did not have a direct effect on the δ¹³C and δ¹⁵N composition between NDP and DP plants, nor on the carbon-to-nitrogen ratio in the leaves, roots, and stems. Nevertheless, based on the obtained results for δ¹³C, δ¹⁵N, and the nitrogen-to-carbon ratio, some general trends can be observed. Conclusions: The obtained results suggest that photochemical processes occurring in tomato stems have an important influence on the development of the tomato plant, especially on the root system. Limited light access to the stems restricts root system growth and development, but shows no visible negative effects on the above-ground parts of the tomato plants in this study. However, indirect effects on shoot growth and development cannot be excluded. Restricting light exposure to the stems likely reduces energy production in the form of energy carriers, such as ATP and NADPH, resulting in decreased efficiency of assimilate transport to the root. This disrupts the plant’s nitrogen uptake and balance, and in turn limits root system development. Moreover, it can be assumed that the chloroplasts present in tomato stems differ structurally and, as a consequence, functionally from those in leaves, which are specialised for efficient photosynthesis. Because a well-developed root system is an important factor affecting plant growth and yield, the obtained results may suggest the possibility of agronomic practices aimed at increasing the efficiency of photochemical processes and photosynthesis in the stems, and consequently improving yields.

Crassulacean acid metabolism (CAM) is an adaptation of certain plants to arid and water-stressed environments. The expression of the CAM cycle may be strongly modulated by developmental and environmental factors. Mesembryanthemum crystallinum is a well-known facultative halophyte that can shift its photosynthetic carbon fixation pathway from C₃ to CAM under salinity and other abiotic stress factors. However, until now, there has been no study about the volatile organic compounds (VOCs) that are emitted by M. crystallinum in its various life cycles, C₃ and CAM. Plants emit a part of the photosynthetically assimilated carbon into the atmosphere in the form of VOCs. Under normal conditions, isoprenoids (isoprene and monoterpenes) are the most abundant VOCs though methanol and acetaldehyde, and C-6 compounds are also emitted in great quantities. Under stress conditions, the emission of these compounds is generally altered. The study of how emissions change depending on stress conditions has become a useful “in vivo” indicator of plant vitality and of the plant response to abiotic stresses. Within this work, we aimed to analyze the VOCs emitted from C₃ or CAM-induced M. crystallinum in order to evaluate the possible role that VOCs may have in the C₃/CAM transition and consequently in the adaptation of this plant to salinity. Results showed that M. crystallinum emits different kinds of VOCs: aldehydes, hydrocarbons, ketones, alcohols, and terpenoids. VOC emissions were generally higher in plants representing C₃, with only few exceptions as butanone, octanal, and ethyl-hexanol that were similar in the III phase of CAM and C₃ plants. Regarding the emission of terpenoids, we could observe that whereas plants in the C₃ mode of photosynthesis emitted three types of monoterpenes: a-pinene, carene, and limonene, plants in the CAM state did not emit any terpenoid compound.