Linkages between traits and decomposition of weed communities along a soil management and pedoclimate gradient in Mediterranean vineyards.

BACKGROUND AND AIMS: Decomposition is a major ecosystem process which improves soil quality. Despite that, only a few studies have analysed decomposition in an agricultural context, while most agrosystems (e.g. vineyards) are facing decreasing soil quality. The objective of this study is to understand the impacts of both pedoclimate and weed management on the mass loss of vineyard weed communities during the early stages of the decomposition process through their functional properties. METHODS: In 16 Mediterranean vineyards representing both a pedoclimate and a soil management gradient, we measured the mass loss of green above-ground biomass of 50 weed communities during decomposition in standard conditions and key leaf traits of dominant species [e.g. leaf dry matter content (LDMC) and leaf lignin to nitrogen ratio (lignin:N)]. Both the mean [i.e. community-weighted mean (CWM)] and diversity (i.e. Rao index) were computed at the community level. Path analysis was used to quantify the effects of agro-environmental filters on the mass loss of weed communities through their functional properties. KEY RESULTS: Tillage and mowing filtered more decomposable communities than chemical weeding (16 and 8 % of higher mass loss after 2 months of decomposition). Path analysis selected weed management practice type as the main factor determining mass loss through its effect on functional properties, while soil and climate had minor and no effects, respectively. Chemical weeding favoured communities with higher investment in resistant leaves (e.g. 38 % higher lignin:N, 22 % lower leaf nitrogen content) which resulted in lower mass loss compared with tilled and mowed communities. Mowing favoured communities with 47 % higher biomass and with 46 % higher nitrogen content. CONCLUSIONS: Weed management significantly influenced weed mass loss, while the pedoclimate had little effect. Our results suggest that mowing is a promising alternative to herbicide use, favouring higher biomass, nitrogen content and decomposability potential of weeds.

Secondary metabolites have more influence than morphophysiological traits on litter decomposability across genotypes of Arabidopsis thaliana.

Although interspecific variation in plant phenotype is recognised to impact afterlife processes such as litter decomposability, it is still unclear which traits and selection pressures explain these relationships. Examining intraspecific variation is crucial to identify and compare trait effects on decomposability, and investigate the potential role of natural selection. We studied the genetic variability and relationships between decomposability, plant traits typically related to decomposability at species level (morphophysiological traits), and leaf metabolites among a set of genotypes of Arabidopsis thaliana grown under controlled conditions. We also investigated correlations between decomposability and environmental variables at genotypes collection site. We investigated the genetic architecture of decomposability with genome-wide association studies (GWAS). There was large genetic variability in decomposability that was correlated with precipitation. Morphophysiological traits had a minor effect, while secondary metabolites, especially glucosinolates, were correlated with decomposability. Consistently, GWAS suggested that genes and metabolites related to the composition of cell membranes and envelopes control the variation of decomposability across genotypes. Our study suggests that decomposability varies within species as a result of metabolic adaptation to climate. Our findings highlight that subtle variations of defence-related metabolites like glucosinolates may strongly influence after-life processes such as decomposability.

Climate as a driver of adaptive variations in ecological strategies in Arabidopsis thaliana.

Background and aims: The CSR classification categorizes plants as stress tolerators (S), ruderals (R) and competitors (C). Initially proposed as a general framework to describe ecological strategies across species, this scheme has recently been used to investigate the variation of strategies within species. For instance, ample variation along the S-R axis was found in Arabidopsis thaliana, with stress-tolerator accessions predominating in hot and dry regions, which was interpreted as a sign of functional adaptation to climate within the species. Methods: In this study the range of CSR strategies within A. thaliana was evaluated across 426 accessions originating from North Africa to Scandinavia. A position in the CSR strategy space was allocated for every accession based on three functional traits: leaf area, leaf dry matter content (LDMC) and specific leaf area (SLA). Results were related to climate at origin and compared with a previous study performed on the same species. Furthermore, the role of natural selection in phenotypic differentiation between lineages was investigated with QST-FST comparisons, using the large amount of genetic information available for this species. Key Results: Substantial variation in ecological strategies along the S-R axis was found in A. thaliana. By contrast with previous findings, stress-tolerator accessions predominated in cold climates, notably Scandinavia, where late flowering was associated with traits related to resource conservation, such as high LDMC and low SLA. Because of trait plasticity, variations in CSR classification in relation to growth conditions were also observed for the same genotypes. Conclusions: There is a latitudinal gradient of ecological strategies in A. thaliana as a result of within-species adaptation to climate. Our study also underlines the importance of growth conditions and of the methodology used for trait measurement, notably age versus stage measurement, to infer the strength and direction of trait-environment relationships. This highlights the potential and limitations of the CSR classification in explaining functional adaptation to the environment.

Traits determining the digestibility-decomposability relationships in species from Mediterranean rangelands.

Background and Aims: Forage quality for herbivores and litter quality for decomposers are two key plant properties affecting ecosystem carbon and nutrient cycling. Although there is a positive relationship between palatability and decomposition, very few studies have focused on larger vertebrate herbivores while considering links between the digestibility of living leaves and stems and the decomposability of litter and associated traits. The hypothesis tested is that some defences of living organs would reduce their digestibility and, as a consequence, their litter decomposability, through 'afterlife' effects. Additionally in high-fertility conditions the presence of intense herbivory would select for communities dominated by fast-growing plants, which are able to compensate for tissue loss by herbivory, producing both highly digestible organs and easily decomposable litter. Methods: Relationships between dry matter digestibility and decomposability were quantified in 16 dominant species from Mediterranean rangelands, which are subject to management regimes that differ in grazing intensity and fertilization. The digestibility and decomposability of leaves and stems were estimated at peak standing biomass, in plots that were either fertilized and intensively grazed or unfertilized and moderately grazed. Several traits were measured on living and senesced organs: fibre content, dry matter content and nitrogen, phosphorus and tannin concentrations. Key results: Digestibility was positively related to decomposability, both properties being influenced in the same direction by management regime, organ and growth forms. Digestibility of leaves and stems was negatively related to their fibre concentrations, and positively related to their nitrogen concentration. Decomposability was more strongly related to traits measured on living organs than on litter. Digestibility and decomposition were governed by similar structural traits, in particular fibre concentration, affecting both herbivores and micro-organisms through the afterlife effects. Conclusions: This study contributes to a better understanding of the interspecific relationships between forage quality and litter decomposition in leaves and stems and demonstrates the key role these traits play in the link between plant and soil via herbivory and decomposition. Fibre concentration and dry matter content can be considered as good predictors of both digestibility and decomposability.

Is it worth hyperaccumulating Ni on non-serpentine soils? Decomposition dynamics of mixed-species litters containing hyperaccumulated Ni across serpentine and non-serpentine environments.

BACKGROUND AND AIMS: Nickel (Ni)-hyperaccumulating species produce high-Ni litters and may potentially influence important ecosystem processes such as decomposition. Although litters resembling the natural community conditions are essential in order to predict decomposition dynamics, decomposition of mixed-species litters containing hyperaccumulated Ni has never been studied. This study aims to test the effect of different litter mixtures containing hyperaccumulated Ni on decomposition and Ni release across serpentine and non-serpentine soils. METHODS: Three different litter mixtures were prepared based on the relative abundance of the dominant species in three serpentine soils in the island of Lesbos, Greece where the Ni-hyperaccumulator Alyssum lesbiacum is present. Each litter mixture decomposed on its original serpentine habitat and on an adjacent non-serpentine habitat, in order to investigate whether the decomposition rates differ across the contrasted soils. In order to make comparisons across litter mixtures and to investigate whether additive or non-additive patterns of mass loss occur, a control non-serpentine site was used. Mass loss and Ni release were measured after 90, 180 and 270 d of field exposure. KEY RESULTS: The decomposition rates and Ni release had higher values on serpentine soils after all periods of field exposure. The recorded rapid release of hyperaccumulated Ni is positively related to the initial litter Ni concentration. No differences were found in the decomposition of the three different litter mixtures at the control non-serpentine site, while their patterns of mass loss were additive. CONCLUSIONS: Our results: (1) demonstrate the rapid decomposition of litters containing hyperaccumulated Ni on serpentine soils, indicating the presence of metal-tolerant decomposers; and (2) imply the selective decomposition of low-Ni parts of litters by the decomposers on non-serpentine soils. This study provides support for the elemental allelopathy hypothesis of hyperaccumulation, presenting the potential selective advantages acquired by metal-hyperaccumulating plants through litter decomposition on serpentine soils.

Domestication provides durum wheat with protection from locust herbivory.

Lower plant resistance to herbivores following domestication has been suggested as the main cause for higher feeding damage in crops than in wild progenitors. While herbivore compensatory feeding has also been proposed as a possible mechanism for raised damage in crops with low nutritional quality, predictions regarding the effects of plant domestication on nutritional quality for herbivores remain unclear. In particular, data on primary metabolites, even major macronutrients, measured in the organs consumed by herbivores, are scarce. In this study, we used a collection of 10 accessions of wild ancestors and 10 accessions of modern progenies of Triticum turgidum to examine whether feeding damage and selectivity by nymphs of Locusta migratoria primarily depended on five leaf traits related to structural resistance or nutrient profiles. Our results unexpectedly showed that locusts favored wild ancestors over domesticated accessions and that leaf toughness and nitrogen and soluble protein contents increased with the domestication process. Furthermore, the quantitative relationship between soluble protein and digestible carbohydrates was found to poorly meet the specific requirements of the herbivore, in all wheat accessions, both wild and modern. The increase in leaf structural resistance to herbivores in domesticated tetraploid wheat accessions suggested that resource allocation trade-offs between growth and herbivory resistance may have been disrupted by domestication in the vegetative organs of this species. Since domestication did not result in a loss of nutritional quality in the leaves of the tetraploid wheat, our results rather provides evidence for a role of the content of plants in nonnutritive nitrogenous secondary compounds, possibly deterrent or toxic, at least for grasshopper herbivores.

Plant traits and decomposition: are the relationships for roots comparable to those for leaves?

BACKGROUND AND AIMS: Fine root decomposition is an important determinant of nutrient and carbon cycling in grasslands; however, little is known about the factors controlling root decomposition among species. Our aim was to investigate whether interspecific variation in the potential decomposition rate of fine roots could be accounted for by root chemical and morphological traits, life history and taxonomic affiliation. We also investigated the co-ordinated variation in root and leaf traits and potential decomposition rates. METHODS: We analysed potential decomposition rates and the chemical and morphological traits of fine roots on 18 Mediterranean herbaceous species grown in controlled conditions. The results were compared with those obtained for leaves in a previous study conducted on similar species. KEY RESULTS: Differences in the potential decomposition rates of fine roots between species were accounted for by root chemical composition, but not by morphological traits. The root potential decomposition rate varied with taxonomy, but not with life history. Poaceae, with high cellulose concentration and low concentrations of soluble compounds and phosphorus, decomposed more slowly than Asteraceae and Fabaceae. Patterns of root traits, including decomposition rate, mirrored those of leaf traits, resulting in a similar species clustering. CONCLUSIONS: The highly co-ordinated variation of roots and leaves in terms of traits and potential decomposition rate suggests that changes in the functional composition of communities in response to anthropogenic changes will strongly affect biogeochemical cycles at the ecosystem level.

A Perspective on Plant Phenomics: Coupling Deep Learning and Near-Infrared Spectroscopy.

The trait-based approach in plant ecology aims at understanding and classifying the diversity of ecological strategies by comparing plant morphology and physiology across organisms. The major drawback of the approach is that the time and financial cost of measuring the traits on many individuals and environments can be prohibitive. We show that combining near-infrared spectroscopy (NIRS) with deep learning resolves this limitation by quickly, non-destructively, and accurately measuring a suite of traits, including plant morphology, chemistry, and metabolism. Such an approach also allows to position plants within the well-known CSR triangle that depicts the diversity of plant ecological strategies. The processing of NIRS through deep learning identifies the effect of growth conditions on trait values, an issue that plagues traditional statistical approaches. Together, the coupling of NIRS and deep learning is a promising high-throughput approach to capture a range of ecological information on plant diversity and functioning and can accelerate the creation of extensive trait databases.

Does seed mass drive interspecies variation in the effect of management practices on weed demography?

Optimizing the effect of management practices on weed population dynamics is challenging due to the difficulties in inferring demographic parameters in seed banks and their response to disturbance. Here, we used a long-term plant survey between 2006 and 2012 in 46 French vineyards and quantified the effects of management practices (tillage, mowing, and herbicide) on colonization, germination, and seed survival of 30 weed species in relation to their seed mass. To do so, we used a recent statistical approach to reliably estimate demographic parameters for plant populations with a seed bank using time series of presence-absence data, which we extended to account for interspecies variation in the effects of management practices on demographic parameters. Our main finding was that when the level of disturbance increased (i.e., in plots with a higher number of herbicides, tillage, or mowing treatments), colonization success and survival in large-seeded species increased faster than in small-seeded species. High disturbance through tillage increased survival in the seed bank of species with high seed mass. The application of herbicides increased germination, survival, and colonization probabilities of species with high seed mass. Mowing, representing habitats more competitive for light, increased the survival of species with high seed mass. Overall, the strong relationships between the effects of management practices and seed mass provide an indicator for predicting the dynamics of weed communities under disturbance.

The importance of insects on land and in water: a tropical view.

Tropical insects are astonishingly diverse and abundant yet receive only marginal scientific attention. In natural tropical settings, insects are involved in regulating and supporting ecosystem services including seed dispersal, pollination, organic matter decomposition, nutrient cycling, herbivory, food webs and water quality, which in turn help fulfill UN Sustainable Development Goals (SDGs). Current and future global changes that affect insect diversity and distribution could disrupt key ecosystem services and impose important threats on ecosystems and human well-being. A significant increase in our knowledge of tropical insect roles in ecosystem processes is thus vital to ensure sustainable development on a rapidly changing planet.

Leaf traits capture the effects of land use changes and climate on litter decomposability of grasslands across Europe.

Land use and climate changes induce shifts in plant functional diversity and community structure, thereby modifying ecosystem processes. This is particularly true for litter decomposition, an essential process in the biogeochemical cycles of carbon and nutrients. In this study, we asked whether changes in functional traits of living leaves in response to changes in land use and climate were related to rates of litter potential decomposition, hereafter denoted litter decomposability, across a range of 10 contrasting sites. To disentangle the different control factors on litter decomposition, we conducted a microcosm experiment to determine the decomposability under standard conditions of litters collected in herbaceous communities from Europe and Israel. We tested how environmental factors (disturbance and climate) affected functional traits of living leaves and how these traits then modified litter quality and subsequent litter decomposability. Litter decomposability appeared proximately linked to initial litter quality, with particularly clear negative correlations with lignin-dependent indices (litter lignin concentr tion, lignin:nitrogen ratio, and fiber component). Litter quality was directly related to community-weighted mean traits. Lignin-dependent indices of litter quality were positively correlated with community-weighted mean leaf dry matter content (LDMC), and negatively correlated with community-weighted mean leaf nitrogen concentration (LNC). Consequently, litter decomposability was correlated negatively with community-weighted mean LDMC, and positively with community-weighted mean LNC. Environmental factors (disturbance and climate) influenced community-weighted mean traits. Plant communities experiencing less frequent or less intense disturbance exhibited higher community-weighted mean LDMC, and therefore higher litter lignin content and slower litter decomposability. LDMC therefore appears as a powerful marker of both changes in land use and of the pace of nutrient cycling across 10 contrasting sites.

Litter quality and decomposability of species from a Mediterranean succession depend on leaf traits but not on nitrogen supply.

BACKGROUND AND AIMS: The rate of plant decomposition depends on both the decomposition environment and the functional traits of the individual species (e.g. leaf and litter quality), but their relative importance in determining interspecific differences in litter decomposition remains unclear. The aims of this study were to: (a) determine if species from different successional stages grown on soils with low and high nitrogen levels produce leaf and litter traits that decompose differently under identical conditions; and (b) assess which trait of living leaves best relates to litter quality and litter decomposability METHODS: The study was conducted on 17 herbaceous species representative of three stages of a Mediterranean successional sere of Southern France. Plants were grown in monocultures in a common garden under two nitrogen levels. To elucidate how different leaf traits affected litter decomposition a microcosm experiment was conducted to determine decomposability under standard conditions. Tests were also carried out to determine how successional stage and nitrogen supply affected functional traits of living leaves and how these traits then modified litter quality and subsequent litter decomposability. KEY RESULTS: The results demonstrated that leaf traits and litter decomposability varied according to species and successional stage. It was also demonstrated that while nitrogen addition affected leaf and litter traits, it had no effect on decomposition rates. Finally, leaf dry matter content stood out as the leaf trait best related to litter quality and litter decomposability CONCLUSIONS: In this study, species litter decomposability was affected by some leaf and litter traits but not by soil nitrogen supply. The results demonstrated the strength of a trait-based approach to predict changes in ecosystem processes as a result of species shifts in ecosystems.

Leaf economics and slow-fast adaptation across the geographic range of Arabidopsis thaliana.

Life history strategies of most organisms are constrained by resource allocation patterns that follow a 'slow-fast continuum'. It opposes slow growing and long-lived organisms with late investment in reproduction to those that grow faster, have earlier and larger reproductive effort and a short longevity. In plants, the Leaf Economics Spectrum (LES) depicts a leaf-level trade-off between the rate of carbon assimilation and leaf lifespan, as stressed in functional ecology from interspecific comparative studies. However, it is still unclear how the LES is connected to the slow-fast syndrome. Interspecific comparisons also impede a deep exploration of the linkage between LES variation and adaptation to climate. Here, we measured growth, morpho-physiological and life-history traits, at both the leaf and whole-plant levels, in 378 natural accessions of Arabidopsis thaliana. We found that the LES is tightly linked to variation in whole-plant functioning, and aligns with the slow-fast continuum. A genetic analysis further suggested that phenotypic differentiation results from the selection of different slow-fast strategies in contrasted climates. Slow growing and long-lived plants were preferentially found in cold and arid habitats while fast growing and short-lived ones in more favorable habitats. Our findings shed light on the role of the slow-fast continuum for plant adaptation to climate. More broadly, they encourage future studies to bridge functional ecology, genetics and evolutionary biology to improve our understanding of plant adaptation to environmental changes.

Plant species traits are the predominant control on litter decomposition rates within biomes worldwide.

Worldwide decomposition rates depend both on climate and the legacy of plant functional traits as litter quality. To quantify the degree to which functional differentiation among species affects their litter decomposition rates, we brought together leaf trait and litter mass loss data for 818 species from 66 decomposition experiments on six continents. We show that: (i) the magnitude of species-driven differences is much larger than previously thought and greater than climate-driven variation; (ii) the decomposability of a species' litter is consistently correlated with that species' ecological strategy within different ecosystems globally, representing a new connection between whole plant carbon strategy and biogeochemical cycling. This connection between plant strategies and decomposability is crucial for both understanding vegetation-soil feedbacks, and for improving forecasts of the global carbon cycle.

Contribution of leaf life span and nutrient resorption to mean residence time: elasticity analysis.

We tested the relative contribution of leaf life span (LLS) and nutrient resorption efficiency (RE) to nutrient mean residence time (MRT) in plants. To do so, we introduced the use of elasticity analysis, which aims to measure the impact on MRT of a small change in one component, relative to the impact of equal changes in the other element. We also quantified the joint effect of LLS and RE on MRT, which required the calculation of the second derivatives of MRT with respect to LLS and RE. The estimation of the first derivatives showed that, although MRT increases linearly with LLS for a given value of RE, the relative effect of RE on MRT elasticity varies according to RE values; when RE > 0.5, the MRT's elasticity increases exponentially. The calculation of the second derivatives confirmed the importance of RE on MRT's variation. We used the results of the elasticity analysis to analyze how MRT responded to variation in LLS and nitrogen RE on MRT at the intra- and interspecific levels. For this, we used 18 plant species from three stages of a Mediterranean old-field succession, grown in a common garden experiment at two levels of nitrogen supply.

Influence of management regime and harvest date on the forage quality of rangelands plants: the importance of dry matter content.

In spite of their recognized ecological value, relatively little is known about the nutritional value of species-rich rangelands for herbivores. We investigated the sources of variation in dry matter digestibility (DMD), neutral detergent fibre content (NDF) and nitrogen concentration (NC) in plants from species-rich Mediterranean rangelands in southern France, and tested whether the dry matter content (DMC) was a good predictor of the forage quality of different plant parts. Sixteen plant species with contrasting growth forms (rosette, tussock, extensive and stemmed-herb) were studied, representative of two management regimes imposed in these rangelands: (i) fertilization and intensive grazing and (ii) non-fertilization and moderate grazing. Among the 16 plant species, four species were found in both treatments, allowing us to assess the intraspecific variability in forage quality and DMC across the treatments. The components of nutritional value (DMD, NDF and NC) as well as the DMC of leaves, stems and reproductive plant parts, were assessed at the beginning of the growing season and at peak standing biomass. All components of nutritional value and DMC were affected by species growth form: rosettes had higher DMD and NC than tussocks; the reverse being found for NDF and DMC. As the season progressed, DMD and NC of the different plant parts decreased while NDF and DMC increased for all species. DMC was negatively related to DMD and NC and positively to NDF, regardless of the source of variation (species, harvest date, management regime or plant part). Path analysis indicated that NDF was the main determinant of DMD. Better assessment of forage quality in species-rich systems requires consideration of their growth form composition. DMC of all plant parts, which is closely related to NDF, emerged as a good predictor and easily measured trait to estimate DMD in these species-rich systems.

Species adaptive strategies and leaf economic relationships across serpentine and non-serpentine habitats on Lesbos, eastern Mediterranean.

Shifts in species' traits across contrasting environments have the potential to influence ecosystem functioning. Plant communities on unusually harsh soils may have unique responses to environmental change, through the mediating role of functional plant traits. We conducted a field study comparing eight functional leaf traits of seventeen common species located on both serpentine and non-serpentine environments on Lesbos Island, in the eastern Mediterranean. We focused on species' adaptive strategies across the two contrasting environments and investigated the effect of trait variation on the robustness of core 'leaf economic' relationships across local environmental variability. Our results showed that the same species followed a conservative strategy on serpentine substrates and an exploitative strategy on non-serpentine ones, consistent with the leaf economic spectrum predictions. Although considerable species-specific trait variability emerged, the single-trait responses across contrasting environments were generally consistent. However, multivariate-trait responses were diverse. Finally, we found that the strength of relationships between core 'leaf economic' traits altered across local environmental variability. Our results highlight the divergent trait evolution on serpentine and non-serpentine communities and reinforce other findings presenting species-specific responses to environmental variation.

Assessing the effects of land-use change on plant traits, communities and ecosystem functioning in grasslands: a standardized methodology and lessons from an application to 11 European sites.

BACKGROUND AND AIMS: A standardized methodology to assess the impacts of land-use changes on vegetation and ecosystem functioning is presented. It assumes that species traits are central to these impacts, and is designed to be applicable in different historical, climatic contexts and local settings. Preliminary results are presented to show its applicability. METHODS: Eleven sites, representative of various types of land-use changes occurring in marginal agro-ecosystems across Europe and Israel, were selected. Climatic data were obtained at the site level; soil data, disturbance and nutrition indices were described at the plot level within sites. Sixteen traits describing plant stature, leaf characteristics and reproductive phase were recorded on the most abundant species of each treatment. These data were combined with species abundance to calculate trait values weighed by the abundance of species in the communities. The ecosystem properties selected were components of above-ground net primary productivity and decomposition of litter. KEY RESULTS: The wide variety of land-use systems that characterize marginal landscapes across Europe was reflected by the different disturbance indices, and were also reflected in soil and/or nutrient availability gradients. The trait toolkit allowed us to describe adequately the functional response of vegetation to land-use changes, but we suggest that some traits (vegetative plant height, stem dry matter content) should be omitted in studies involving mainly herbaceous species. Using the example of the relationship between leaf dry matter content and above-ground dead material, we demonstrate how the data collected may be used to analyse direct effects of climate and land use on ecosystem properties vs. indirect effects via changes in plant traits. CONCLUSIONS: This work shows the applicability of a set of protocols that can be widely applied to assess the impacts of global change drivers on species, communities and ecosystems.