Is pollen size a robust proxy for moisture availability?

The development of well-constrained palaeo-proxies that enable the reconstruction of past climate change is becoming an ever more important field of scientific enquiry within the palaeobotanical community, with the potential to deliver broader impacts linked to understanding of future anthropogenic climate change. One of the major uncertainties in predicting climate change is how the hydrological cycle will respond to future warming. Griener and Warny (2015, Review of Palaeobotany and Palynology 221, 138-143) suggested that pollen size might be a useful proxy for tracking moisture availability, as pollen size appears to be negatively correlated with moisture. Given the long fossil record of pollen and spores such a proxy would have broad scope and the potential to deliver much needed information. Here we set out to fully evaluate and test the robustness of this proxy. We focus on a number of a key issues: controls on pollen size, data analysis, and finally proxy validation. Using this approach we find that there is little theoretical or empirical support for the original relationship proposed by Griener and Warny. Consequently it is currently premature to use pollen size as a moisture availability proxy in the fossil record. However, we recognise that the technique may have potential and conclude by offering a series of recommendations that would rigorously assess and test for a relationship between pollen size and moisture availability

Plant responses to simulated carbon capture and transport leakage: the effect of impurities in the CO2 gas stream

To deliver an effective transition from a carbon-based 24 to a carbon-free energy market, bridging technologies are required. One such possibility is the use of carbon capture and storage, (CCS). However, before such innovations can be rolled out a key requirement is to understand the environmental impact of these technologies. Recent experimental work has demonstrated that small scale CO2 leakage from CCS pipeline infrastructure has a localised and possibly transient impact. However, what remains unknown is the possibility of synergistic impact of impurities in the CO2 gas stream. Here we report the impact of two impurities SO2 (100 ppm SO2 in pure CO2) and H2S (80ppm H2S in pure CO2) on the growth and performance of two crop species (spring wheat, Triticum aestivum and beetroot, Beta vulgaris) in fully replicated experiments. Our data show that when compared to CO2-only gassed controls, the impact of these impurities are minimal as there are no statistically significant differences between performance parameters (photosynthesis, stomatal conductance and transpiration) or biomass. These results signify that from a plant health perspective it may not be necessary to completely remove these specific impurities prior to CO2 transportation

Ginkgo leaf cuticle chemistry across changing pCO2 regimes

Cuticles have been a key part of palaeobotanical research since the mid-19th Century. Recently, cuticular research has moved beyond morphological traits to incorporate the chemical signature of modern and fossil cuticles, with the aim of using this as a taxonomic and classification tool. For this approach to work, cuticle chemistry would have to maintain a strong taxonomic signal, with a limited input from the ambient environment in which the plant grew. Here, we use attenuated total reflectance Fourier Transform infrared (ATR-FTIR) spectroscopy to analyse leaf cuticles from Ginkgo biloba plants grown in experimentally enhanced CO2 conditions, to test for the impact of changing CO2 regimes on cuticle chemistry. We find limited evidence for an impact of CO2 on the chemical signature of Ginkgo cuticles, with more pronounced differences demonstrated between the abaxial (lower leaf surface) and adaxial (upper leaf surface) cuticles. These findings support the use of chemotaxonomy for plant cuticular remains across geological timescales, and the concomitant large-scale variations in CO2 concentrations

The impact of oxidation on spore and pollen chemistry

Sporomorphs (pollen and spores) have an outer wall composed of sporopollenin. Sporopollenin chemistry contains both a signature of ambient ultraviolet-B flux and taxonomic information, but it is currently unknown how sensitive this is to standard palynological processing techniques. Oxidation in particular is known to cause physical degradation to sporomorphs, and it is expected that this should have a concordant impact on sporopollenin chemistry. Here, we test this by experimentally oxidizing Lycopodium (clubmoss) spores using two common oxidation techniques: acetolysis and nitric acid. We also carry out acetolysis on eight angiosperm (flowering plant) taxa to test the generality of our results. Using Fourier Transform infrared (FTIR) spectroscopy, we find that acetolysis removes labile, non-fossilizable components of sporomorphs, but has a limited impact upon the chemistry of sporopollenin under normal processing durations. Nitric acid is more aggressive and does break down sporopollenin and reorganize its chemical structure, but when limited to short treatments (i.e. ≤10 min) at room temperature sporomorphs still contain most of the original chemical signal. These findings suggest that when used carefully oxidation does not adversely affect sporopollenin chemistry, and that palaeoclimatic and taxonomic signatures contained within the sporomorph wall are recoverable from standard palynological preparations

Palaeoproxies: botanical monitors and recorders of atmospheric change

The integration of plant and Earth sciences offers the opportunity to develop and test palaeobotanical monitors and recorders (palaeoproxies) of past atmospheric change that are understood from a mechanistic perspective, with the underpinning responses being identified and understood at the genetic level. This review highlights how this approach has been used to deliver two distinct palaeoproxies. The first is based on the negative relationship between stomata (breathing pores found on the leaf surface) and atmospheric CO2 concentration; the second is based on tracking chemical changes seen in the composition of pollen and spores to reconstruct changes in the flux of UV-B radiation on the Earth's surface and from this infer changes in stratospheric processes linked to the eruption and emplacement of Large Igneous Provinces. Here, we highlight the potential of integrating a new rapid, inexpensive chemical analysis technique with existing, robust palynological methods, opening the door to a deeper understanding of past environments via the palaeobiological record. A look to the future suggests a combined solar radiation–CO2 concentration approach could be readily applied across the geological record

Decomposition and nutrient mineralisation of leaf litter in smallholder cocoa agroforests: a comparison of organic and conventional farms in Ghana

© 2020, The Author(s). Purpose: Although litter decomposition and nutrient release patterns have been studied in cocoa agroforestry systems in general, studies focusing on organic and conventional cocoa systems are lacking which is critical as organic farms are particularly dependent on nutrient returns from decomposing litter. Materials and methods: Dynamics in leaf litter decomposition and the mineralisation of macro- and micro-nutrients in organic and conventional cocoa agroforestry systems were studied using the litterbag technique for 12months. Results: The average monthly mass loss was more than two times higher on organic farms (9.2–14.4gmonth−1) compared to conventional farms (4.2–7.3gmonth−1) in the first five months. The annual rate of decomposition (k) was higher on organic farms (1.9) compared to conventional systems (1.4). The time required for 50% (t50) and 99% (t99) decomposition of leaf litter was both lower on organic farms (t50 = 0.4years, t99 = 2.6years) than conventional farms (t50 = 0.5years, t99 = 3.5years). The estimated k values for macro- and micro-nutrients on organic cocoa systems ranged from 2.3 for calcium to 4.5 for potassium compared to 1.6 (Ca) to 2.8 (K) on conventional farms. The k values of all nutrients (except nitrogen and phosphorus) were significantly greater on organic farms than conventional systems. The estimated k values for both litter decomposition and nutrient mineralisation correlated with soil pH and moisture content, but not initial litter chemistry. Conclusions: Organic management of smallholder cocoa agroforestry systems enhanced leaf litter decomposition and nutrient mineralisation through improved soil conditions. Thus, organic management of cocoa agroforestry systems may contribute to sustainable cocoa production in smallholder systems through enhanced nutrient return from litter decomposition

Temporal changes in litterfall and potential nutrient return in cocoa agroforestry systems under organic and conventional management, Ghana

Litterfall is a critical link between vegetation and soils by which nutrients are returned to the soils, thus the amount and pattern of litterfall regulates nutrient cycling, soil fertility and primary productivity for most terrestrial ecosystems. We quantified, analyzed and compared macro and micro-nutrients return through litterfall in organic and conventional cocoa agroforestry systems in Suhum, Ghana. We further assessed the contribution of shade tree species to litterfall and nutrient dynamics. The annual pattern of litterfall was affected by seasonality, with a major peak in the dry season and minor peaks during the rainy season. In terms of annual fractional litterfall, mean leaf litter from shade tree species was significantly higher (50 %) in organic systems (5.0 ± 0.5 Mg ha-1 yr-1) compared to conventional systems (3.3 ± 0.6 Mg ha-1 yr-1). Whereas cocoa leaves (45.0 %) were the predominant fraction of annual litterfall from conventional farms, both shade leaves (40.0 %) and cocoa leaves (39.4 %) dominated litterfall from organic farms. The return of primary macro-nutrients (P and K), secondary macro-nutrients (Ca, Mg and S) and micro-nutrients (Mn, B, Cu, Zn and Mo) via litterfall varied significantly with season, and annual return of nutrients were similar in organic and conventional cocoa systems. Shade tree leaf litter accounted for 30–47 % of annual macro and micro-nutrient return (except Ni and Zn) in organic cocoa systems versus 20–35 % in conventional cocoa systems. The results emphasize the complementary role of the different shade tree species which compose organic and conventional cocoa systems in nutrient recycling. We conclude that organic management of cocoa agroforestry systems ensure nutrients return similar to those receiving synthetic fertilizer inputs, highlighting its potential to support cocoa productio

Quality not quantity: organic matter composition controls of CO₂and CH₄fluxes in neotropical peat profiles

Tropical peatlands represent an important source of carbon dioxide (CO₂) and methane (CH₄) to the atmosphere. However, we do not know where in the peat profile these gases are produced and how controlling factors, such as substrate quality, which can vary substantially with peat age, and anoxic-oxic conditions, interact to determine production rates. To address this knowledge gap, this study investigated if substrate limitation of CO₂ and CH₄ production differs under anoxic-oxic peat conditions using entire peat profiles, from tropical peatlands in Panama. We determined the variation in peat organic chemistry through stratigraphic profiles using tetramethylammonium-pyrolysis-gas chromatography-mass spectrometry (TMAH-Py-GC/MS). To explore how variation in peat organic chemistry through the depth profile impacted on CO₂ and CH₄ production rates under anoxic-oxic conditions we carried out a series of incubation experiments. The TMAH-Py-GC/MS analysis showed high concentrations of long chain fatty acids (>C₂₀) in surface peat, and variation in the distribution of the lignin monomers through the peat profile. Both anoxic CH₄ and CO₂ production was greatest from the surface of the peat profile with surface peat accounting for 92 ± 1.7 and 54 ± 2.9% of the cumulative CH₄ and CO₂ production, respectively. The high CO₂ and CH₄ production rate under anoxic conditions, in surface peat, was strongly related to greater concentrations of lignin, but also long chain fatty acids and polysaccharides, in this section of the peat profile. As expected, CH₄ production decreased, and became decoupled from peat organic chemistry, following peat aeration. In contrast, aeration dramatically increased CO₂ emissions throughout the entire peat profile. This demonstrates that the recalcitrance of buried peat does not protect C stocks in tropical peatlands, if their water tables are lowered in response to drainage or prolonged drought. In conclusion, our work highlight that information on both labile substrate availability and water table fluctuation are needed to predict CO₂ and CH₄ fluxes from tropical peatlands

Chemotaxonomy as a tool for interpreting the cryptic diversity of Poaceae pollen

The uniform morphology of different species of Poaceae (grass) pollen means that identification to below family level using light microscopy is extremely challenging. Poor taxonomic resolution reduces recoverable information from the grass pollen record, for example, species diversity and environmental preferences cannot be extracted. Recent research suggests Fourier Transform Infra-red Spectroscopy (FTIR) can be used to identify pollen grains based on their chemical composition. Here, we present a study of twelve species from eight subfamilies of Poaceae, selected from across the phylogeny but from a relatively constrained geographical area (tropical West Africa) to assess the feasibility of using this chemical method for identification within the Poaceae family. We assess several spectral processing methods and use K-nearest neighbour (k-nn) analyses, with a leave-one-out cross-validation, to generate identification success rates at different taxonomic levels. We demonstrate we can identify grass pollen grains to subfamily level with an 80% success rate. Our success in identifying Poaceae to subfamily level using FTIR provides an opportunity to generate high taxonomic resolution datasets in research areas such as palaeoecology, forensics, and melissopalynology quickly and at a relatively low cost