Victoria Martine Temperton

Non-invasive approaches for phenotyping of enhanced performance traits in bean

Plant phenotyping is an emerging discipline in plant biology. Quantitative measurements of functional and structural traits help to better understand gene-environment interactions and support breeding for improved resource use efficiency of important crops such as bean (Phaseolus vulgaris L.). Here we provide an overview of state-of-the-art phenotyping approaches addressing three aspects of resource use efficiency in plants: belowground roots, aboveground shoots and transport/allocation processes. We demonstrate the capacity of high-precision methods to measure plant function or structural traits non-invasively, stating examples wherever possible. Ideally, high-precision methods are complemented by fast and high-throughput technologies. High-throughput phenotyping can be applied in the laboratory using automated data acquisition, as well as in the field, where imaging spectroscopy opens a new path to understand plant function non-invasively. For example, we demonstrate how magnetic resonance imaging (MRI) can resolve root structure and separate root systems under resource competition, how automated fluorescence imaging (PAM fluorometry) in combination with automated shape detection allows for high-throughput screening of photosynthetic traits and how imaging spectrometers can be used to quantify pigment concentration, sun-induced fluorescence and potentially photosynthetic quantum yield. We propose that these phenotyping techniques, combined with mechanistic knowledge on plant structure-function relationships, will open new research directions in whole-plant ecophysiology and may assist breeding for varieties with enhanced resource use efficiency varieties.

The Importance of Being First: Exploring Priority and Diversity Effects in a Grassland Field Experiment

Diversity of species and order of arrival can have strong effects on ecosystem functioning and community composition, but these two have rarely been explicitly combined in experimental setups. We measured the effects of both species diversity and order of arrival on ecosystem function and community composition in a grassland field experiment, thus combining biodiversity and assembly approaches. We studied the effect of order of arrival of three plant functional groups (PFGs: grasses, legumes, and non-leguminous forbs) and of sowing low and high diversity seed mixtures (9 or 21 species) on species composition and aboveground biomass. The experiment was set up in two different soil types. Differences in PFG order of arrival affected the biomass, the number of species and community composition. As expected, we found higher aboveground biomass when sowing legumes before the other PFGs, but this effect was not continuous over time. We did not find a positive effect of sown diversity on aboveground biomass (even if it influenced species richness as expected). No interaction were found between the two studied factors. We found that sowing legumes first may be a good method for increasing productivity whilst maintaining diversity of central European grasslands, although the potential for long-lasting effects needs further study. In addition, the mechanisms behind the non-continuous priority effects we found need to be further researched, taking weather and plant-soil feedbacks into account.

Effects of Four Different Restoration Treatments on the Natural Abundance of 15N Stable Isotopes in Plants

δ15N signals in plant and soil material integrate over a number of biogeochemical processes related to nitrogen (N) and therefore provide information on net effects of multiple processes on N dynamics. In general little is known in many grassland restoration projects on soil–plant N dynamics in relation to the restoration treatments. In particular, δ15N signals may be a useful tool to assess whether abiotic restoration treatments have produced the desired result. In this study we used the range of abiotic and biotic conditions provided by a restoration experiment to assess to whether the restoration treatments and/or plant functional identity and legume neighborhood affected plant δ15N signals. The restoration treatments consisted of hay transfer and topsoil removal, thus representing increasing restoration effort, from no restoration measures, through biotic manipulation to major abiotic manipulation. We measured δ15N and %N in six different plant species (two non-legumes and four legumes) across the restoration treatments. We found that restoration treatments were clearly reflected in δ15N of the non-legume species, with very depleted δ15N associated with low soil N, and our results suggest this may be linked to uptake of ammonium (rather than nitrate). The two non-legume species differed considerably in their δ15N signals, which may be related to the two species forming different kinds of mycorrhizal symbioses. Plant δ15N signals could clearly separate legumes from non-legumes, but our results did not allow for an assessment of legume neighborhood effects on non-legume δ15N signals. We discuss our results in the light of what the δ15N signals may be telling us about plant–soil N dynamics and their potential value as an indicator for N dynamics in restoration.

Assembly Theory for Restoring Ecosystem Structure and Functioning: Timing is Everything?

The field of ecology focuses on interactions between organisms and between organisms and their environment. This includes an explicit focus on a large variety of different ways that species interact with one another. Such interactions form the basis of a key question in ecology, namely, what is found where and why? Species can have positive, neutral or negative effects on each other. The most famous ecological interactions are those of predation and competition. In plant ecology, we often invoke competition as the key driver of interactions between species that require the same essential resources.

Legacy effects of land-use modulate tree growth responses to climate extremes

Climate change can impact forest ecosystem processes via individual tree and community responses. While the importance of land-use legacies in modulating these processes have been increasingly recognised, evidence of former land-use mediated climate-growth relationships remain rare. We analysed how differences in former land-use (i.e. forest continuity) affect the growth response of European beech to climate extremes. Here, using dendrochronological and fine root data, we show that ancient forests (forests with a long forest continuity) and recent forests (forests afforested on former farmland) clearly differ with regard to climate–growth relationships. We found that sensitivity to climatic extremes was lower for trees growing in ancient forests, as reflected by significantly lower growth reductions during adverse climatic conditions. Fine root morphology also differed significantly between the former land-use types: on average, trees with high specific root length (SRL) and specific root area (SRA) and low root tissue density (RTD) were associated with recent forests, whereas the opposite traits were characteristic of ancient forests. Moreover, we found that trees of ancient forests hold a larger fine root system than trees of recent forests. Our results demonstrate that land-use legacy-mediated modifications in the size and morphology of the fine root system act as a mechanism in regulating drought resistance of beech, emphasising the need to consider the ‘ecological memory’ of forests when assessing or predicting the sensitivity of forest ecosystems to global environmental change.

Methane yield of biomass from extensive grassland is affected by compositional changes induced by order of arrival

Low‐input grassland biomass from marginal and other slightly more fertile sites can be used for energy production without competing with food or fodder production. The effect of grassland diversity on methane yield has received some attention, but we do not know how community assembly may affect methane yield from grassland biomass. However, methane yields determine the potential economic value of a bioenergy substrate. Hence, a better understanding of how plant community assembly affects methane yield would be important. We measured biomass production and methane yield in the second year of a grassland field experiment which manipulated the order of arrival of different plant functional groups (forbs, grasses or legumes sown first and all sown simultaneously) and sown diversity (9 vs. 21 species). The order of arrival of the plant functional groups significantly determined the relative dominance of each group which in turn mainly explained the variance in aboveground biomass production. Differences in area‐specific methane yields were driven by differences in biomass production and which plant functional groups dominated a plot. When grasses were sown first, legumes and grasses codominated a plot and the highest area‐specific methane yield was obtained. Overall, the results indicate that altering the order of arrival affected the community functional and species composition (and hence methane yields) much more than sown diversity. Our study shows that a combined use of positive biodiversity effects and guided plant community assembly may be able to optimize methane yields under field conditions. This may allow a guided, sustainable, and lucrative use of grassland biomass for biogas production in the future.

Plant density modifies root system architecture in spring barley (Hordeum vulgare L.) through a change in nodal root number

AimPreviously, we showed that sowing density influences root length density (RLD), specific root length (SRL) especially in the topsoil, and shallowness of fine roots of field grown spring barley (Hordeum vulagre L.). Here, we ask which trait components may explain these observed changes.MethodWe grew two spring barley cultivars at contrasting sowing densities in both field trials and rhizotrons, and excavated root crowns and imaged root growth.ResultsIn the field, tiller and nodal root numbers per plant decreased with increasing sowing density, however, nodal roots per tiller, seminal roots per plant, and lateral branching frequencies were not affected. Branching angle did not or only slightly declined with increasing sowing density. In rhizotrons, aboveground only tiller number was affected by sowing density. Root growth rates and counts were not (or only slightly) affected.ConclusionGreater RLD at high sowing densities is largely explained by greater main root number per area. The altered seminal to nodal root ratio might explain observed increases in SRL. We conclude that sowing density is a modifier of root system architecture with probable functional consequences, and thereby an important factor to be considered in root studies or the development of root ideotypes for agriculture.

Legume intercropping with the bioenergy crop sida hermaphrodita on marginal soil

The cultivation of perennial biomass plants on marginal soils can serve as a sustainable alternative to conventional biomass production via annual cultures on fertile soils. Sida hermaphrodita is a promising species to be cultivated in an extensive cropping system on marginal soils in combination with organic fertilization using biogas digestates. In order to enrich this cropping system with nitrogen (N) and to increase overall soil fertility of the production system, we tested the potential of intercropping with leguminous species. In a 3-year outdoor mesocosm study, we intercropped established S. hermaphrodita plants with the perennial legume species Trifolium pratense, T. repens, Melilotus albus, and Medicago sativa individually to study their effects on plant biomass yields, soil N, and above ground biomass N. As a control for intercropping, we used a commercial grass mixture without N2-fixing species as well as a no-intercropping treatment. Results indicate that intercropping in all intercropping treatments increased the total biomass yield, however, grass species competed with S. hermaphrodita for N more strongly than legumes. Legumes enriched the cropping system with fixed atmospheric nitrogen (N2) and legume facilitation effects varied between the legume species. T. pratense increased the biomass yield of S. hermaphrodita and increased the total biomass yield per mesocosm by 300%. Further, the total above ground biomass of S. hermaphrodita and T. pratense contained seven times more N compared to the mono-cropped S. hermaphrodita. T. repens also contributed highly to N facilitation. We conclude that intercropping of legumes, especially T. pratense and T. repens can stimulate the yield of S. hermaphrodita on marginal soils for sustainable plant biomass production.

Coming late for dinner: Localized digestate depot fertilization for extensive cultivation of marginal soil with Sida hermaphrodita

Improving fertility of marginal soils for the sustainable production of biomass is a strategy for reducing land use conflicts between food and energy crops. Digestates can be used as fertilizer and for soil amelioration. In order to promote plant growth and reduce potential adverse effects on roots because of broadcast digestate fertilization, we propose to apply local digestate depots placed into the rhizosphere. We grew Sida hermaphrodita in large mesocosms outdoors for three growing seasons and in rhizotrons in the greenhouse for 3 months both filled with marginal substrate, including multiple sampling dates. We compared digestate broadcast application with digestate depot fertilization and a mineral fertilizer control. We show that depot fertilization promotes a deep reaching root system of S. hermaphrodita seedlings followed by the formation of a dense root cluster around the depot-fertilized zone, resulting in a fivefold increased biomass yield. Temporal adverse effects on root growth were linked to high initial concentrations of ammonium and nitrite in the rhizosphere in either fertilizer application, followed by a high biomass increase after its microbial conversion to nitrate. We conclude that digestate depot fertilization can contribute to an improved cultivation of perennial energy-crops on marginal soils.