Summary: A minuscule fraction of the Earth's paleobiological diversity is preserved in the geological record as fossils. What plant remnants have withstood taphonomic filtering, fragmentation, and alteration in their journey to become part of the fossil record provide unique information on how plants functioned in paleo‐ecosystems through their traits. Plant traits are measurable morphological, anatomical, physiological, biochemical, or phenological characteristics that potentially affect their environment and fitness. Here, we review the rich literature of paleobotany, through the lens of contemporary trait‐based ecology, to evaluate which well‐established extant plant traits hold the greatest promise for application to fossils. In particular, we focus on fossil plant functional traits, those measurable properties of leaf, stem, reproductive, or whole plant fossils that offer insights into the functioning of the plant when alive. The limitations of a trait‐based approach in paleobotany are considerable. However, in our critical assessment of over 30 extant traits we present an initial, semi‐quantitative ranking of 26 paleo‐functional traits based on taphonomic and methodological criteria on the potential of those traits to impact Earth system processes, and for that impact to be quantifiable. We demonstrate how valuable inferences on paleo‐ecosystem processes (pollination biology, herbivory), past nutrient cycles, paleobiogeography, paleo‐demography (life history), and Earth system history can be derived through the application of paleo‐functional traits to fossil plants.

The photosynthetic differences between adult and juvenile Mediterranean plants were previously studied under field conditions, yet the corresponding differentiation of their photoprotective efficiency has not been sufficiently investigated. The present study aims to examine possible differences in the photoprotective potential between adults and juveniles of two native Mediterranean plants with distinct growth forms. Thus, the seasonal variations in individual carotenoids, electron transport rate (ETR), and non-photochemical quenching (NPQ) were monitored in fully exposed mature leaves from adults and juveniles of the winter deciduous tree Cercis siliquastrum L. and the evergreen sclerophyllous shrub Nerium oleander L. All plants were grown under apparently similar field conditions. In both species, juveniles displayed substantially lower ETR and increased NPQ values than adults in spring, with the differences intensifying during summer drought and diminishing in autumn. Concomitantly, juveniles showed significantly higher chlorophyll-based total carotenoids in spring and summer mainly due to the higher investment in xanthophyll cycle components (VAZ), in combination with an increased mid-day de-epoxidation state (DEPS) and partial retention of zeaxanthin in the dark. In N. oleander, although ETR was lower in juveniles during winter, NPQ was extremely low in both ages. In conclusion, juveniles exhibit enhanced photoprotection potential, especially in the summer, due to their reduced photochemical capacity. The photosynthetic superiority of adults during the favorable spring period may be attributed to the needs of the co-existing reproductive effort.

Societal Impact Statement: Botanic gardens play a crucial role in addressing global environmental challenges by providing a unique setting for long‐term plant studies and engaging the public in climate change awareness. Our review highlights the underuse of these gardens' living collections for monitoring climate impacts, revealing significant gaps in data and phylogenetic diversity. The Witness Tree Project at Trinity College Botanic Garden will enhance long‐term research and public engagement through open‐access data and protocols. This initiative not only advances scientific understanding but also fosters community involvement and education, promoting a collective effort towards mitigating climate change impacts.Summary: Botanic gardens are ideal settings for long‐term studies on plant responses to climate change, providing extensive outreach and visitor engagement opportunities. However, the use of living collections for multi‐year studies has not been thoroughly assessed. This paper first reviews environmental monitoring projects conducted in these institutions over three continuous years, revealing that fewer than 1% of botanic gardens and arboreta globally engage in long‐term research. There is also a notable lack of phylogenetic diversity, with only 3% of angiosperm and 35% of gymnosperm families represented. Monitoring efforts mainly focus on phenology and plant pathology, with limited attention to other subjects like plant traits. Moreover, no studies have linked climate change impacts on plants with urban green space research, despite the urban locations of many botanic gardens, and no structured guidelines exist for establishing long‐term monitoring programmes. In the second part of this paper, we introduce The Witness Tree Project (WTP) at Trinity College Botanic Garden (TCBG), a newly established long‐term (>30 years) annual monitoring programme. The WTP tracks the physiological performance of selected woody plants under climate change and the deposition of particulate pollution (PM 2.5 and PM10) on their leaves. The project leverages the potential of a university botanic garden to integrate multidisciplinary research, teaching and outreach activities, using open‐access protocols and data‐sharing practices. Finally, we outline a framework for designing long‐term monitoring programmes in botanic gardens and arboreta. This framework, informed by the establishment and pilot year of the WTP, encourages the use of living collections in advancing global change research.

Weathering, the breakdown of rock into its elements, is a carbon sequestering process and a significant component of the Earth’s long-term carbon cycle. As rock is weathered, atmospheric CO2 reacts with elements released, forming bicarbonates. These compounds are transported to the ocean where they are stored for thousands of years.The above mechanism has garnered much attention in recent years for its use as a potential negative emissions technology to advance efforts in climate change mitigation. Enhanced weathering (EW) aims to accelerate carbon sequestering reactions of rock weathering by applying crushed rock onto vegetated surfaces. It’s also believed this practice could provide secondary benefits of improving crop yields and soil conditions. A variety of rocks, such as basalt and olivine, have been applied to different crops all over the world in an attempt to test their potential as a CO2 removal technique and natural fertilizer.This study aims to build upon previous attempts by employing a novel material, crushed concrete. Concrete is abundant in fast-weathering minerals such as portlandite and amorphous calcium silicates, making it an ideal candidate for EW. By harnessing the same bicarbonate forming and carbon sequestering reactions but using a waste by-product of the construction industry, the sustainability and circularity of EW technology could be further increased.In this study, crushed concrete was applied to fields of oat (Avena sativa) and barley (Hordeum vulgare) in Co. Wexford, Ireland, during the spring growing season. Physiological (chlorophyll fluorescence and stomatal conductance) and morphological (dry mass and plant height) parameters were measured through multiple stages of the plant growth to assess the impact of concrete application on crop health and yield. Our results showed an increase in the dry mass (specifically seed dry mass) of barley, suggesting that barley may benefit from concrete application. No significant changes were observed in oat. Our results suggest that concrete does not negatively impact crop yields and could even improve yields in certain crop species.

In this study, we investigate the use of milled returned concrete as an enhanced weathering soil amendment, on two arable fields in County Wexford, Ireland. The applied concrete consists of portlandite (Ca(OH)2) cement with limestone (CaCO3) aggregate. The high cation concentration and rapid weathering kinetics of both components indicate good potential for carbonic acid neutralisation and atmospheric CO2 removal as soil-water dissolved bicarbonate (HCO3-). In spring 2023, prior to crop planting (oats and barley), both trial fields were divided into two sections. Milled returned concrete was applied to a ‘treatment’ section while no concrete was applied to a ‘control’ section. All other farming practices (ploughing, tilling, sowing and fertilisation) were equivalent across control and treatment. Twelve suction-cup lysimeters were installed in each field (6 control and 6 treatment) to collect soil-water samples across the growing season and the concentrations of bicarbonate, major cations and anions were measured to assess carbon removal. Preliminary results indicate that where nitrate (NO3-) levels are low in concrete amended sites, bicarbonate concentrations are elevated above control. However, where soil-nitrate levels are high, weathering liberated cations are balanced by nitrate, and bicarbonate production is suppressed. Our findings highlight the importance of fertiliser management for optimising CO2 removal outcomes of enhanced weathering.

Fruit photosynthesis occurs in an internal microenvironment seldom encountered by a leaf (hypoxic and extremely CO₂-enriched) due to its metabolic and anatomical features. In this study, the anatomical and photosynthetic traits of fully exposed green fruits of Quercus coccifera L. were assessed during the period of fruit production (summer) and compared to their leaf counterparts. Our results indicate that leaf photosynthesis, transpiration and stomatal conductance drastically reduced during the summer drought, while they recovered significantly after the autumnal rainfalls. In acorns, gas exchange with the surrounding atmosphere is hindered by the complete absence of stomata; hence, credible CO₂ uptake measurements could not be applied in the field. The linear electron transport rates (ETRs) in ambient air were similar in intact leaves and pericarps (i.e., when the physiological internal atmosphere of each tissue is maintained), while the leaf NPQ was significantly higher, indicating enhanced needs for harmless energy dissipation. The ETR measurements performed on leaf and pericarp discs at different CO₂/O₂ partial pressures in the supplied air mixture revealed that pericarps displayed significantly lower values at ambient gas levels, yet they increased by ~45% under high CO₂/O₂ ratios (i.e., at gas concentrations simulating the fruit’s interior). Concomitantly, NPQ declined gradually in both tissues as the CO₂/O₂ ratio increased, yet the decrease was more pronounced in pericarps. Furthermore, net CO₂ assimilation rates for both leaf and pericarp segments were low in ambient air and increased almost equally at high CO₂, while pericarps exhibited significantly higher respiration. It is suggested that during summer, when leaves suffer from photoinhibition, acorns could contribute to the overall carbon balance, through the re-assimilation of respiratory CO₂, thereby reducing the reproductive cost.