Functionally and phylogenetically diverse plant communities key to soil biota

Recent studies assessing the role of biological diversity for ecosystem functioning indicate that the diversity of functional traits and the evolutionary history of species in a community, not the number of taxonomic units, ultimately drives the biodiversity-ecosystem-function relationship. Here, we simultaneously assessed the importance of plant functional trait and phylogenetic diversity as predictors of major trophic groups of soil biota (abundance and diversity), six years from the onset of a grassland biodiversity experiment. Plant functional and phylogenetic diversity were generally better predictors of soil biota than the traditionally used species or functional group richness. Functional diversity was a reliable predictor for most biota, with the exception of soil microorganisms, which were better predicted by phylogenetic diversity. These results provide empirical support for the idea that the diversity of plant functional traits and the diversity of evolutionary lineages in a community are important for maintaining higher abundances and diversity of soil communities.

Rarity types among plant species with high conservation priority in Switzerland

We investigated the ecogeographic characteristics of 118 Swiss plant species listed as those deserving highest conservation priority in a national conservation guide and classified them into the seven Rabinowitz' rarity types, taking geographic distribution, habitat rarity and local population size into account. Our analysis revealed that species with high conservation priority in Switzerland mostly have a very restricted geographic distribution in Switzerland and generally occur in rare habitats, but do not necessarily constitute small populations and are generally not endemics on a global scale. Moreover, species that are geographically very restricted on a regional scale are not generally restricted on a global scale. By analysing relationships between rarity and IUCN extinction risks for Switzerland, we demonstrated that species with the highest risk of extinction are those with the most restricted geographic distribution; whereas species with lower risk of extinction (but still high conservation priority) include many regional endemics. Habitat rarity and local population size appeared to be of minor importance for the assessment of extinction risk in Switzerland, but the total number of fulfilled rarity criteria still correlated positively with the severity of extinction risk. Our classification is the first preliminary assessment of the relative importance of each rarity type among endangered plant species of the Swiss flora and our results underline the need to distinguish between a regional and a global responsibility for the conservation of rare and endangered species.

Characterization of the soil fertility and root system of restinga forests

The Restinga vegetation consists of a mosaic of plant communities, which are defined by the characteristics of the substrates, resulting from the type and age of the depositional processes. This mosaic complex of vegetation types comprises restinga forest in advanced (high restinga) and medium regeneration stages (low restinga), each with particular differentiating vegetation characteristics. The climate along the coast is tropical (Köppen). Of all ecosystems of the Atlantic Forest, Restinga is the most fragile and susceptible to anthropic disturbances. Plants respond to soil characteristics with physiological and morphological modifications, resulting in changes in the architecture (spatial configuration) of the root system. The purpose of this study was to characterize the soil fertility of high and low restinga forests, by chemical and physical parameters, and its relation to the root system distribution in the soil profile. Four locations were studied: (1) Ilha Anchieta State Park, Ubatuba; (2) two Ecological Stations of Jureia-Itatins and of Chauás, in the municipality of Iguape; (3) Vila de Pedrinhas in the municipality of Ilha Comprida; and (4) Ilha do Cardoso State Park, Cananeia. The soil fertility (chemical and physical properties) was analyzed in the layers 0-5, 0-10, 0-20, 20-40 and 40-60 cm. In addition, the distribution of the root system in the soil profile was evaluated, using digital images and the Spring program. It was concluded that the root system of all vegetation types studied is restricted to the surface layers, 0-10 and 10-20 cm, but occupies mainly the 0-10 cm layer (70 %); that soil fertility is low in all environments studied, with base saturation values below 16 %, since most exchange sites are occupied by aluminum; and that restinga vegetation is edaphic.

Fertilization with filter cake and micronutrients in plant cane

The response of sugarcane to application of micronutrients is still not very well known. In view of the need for this information, the aim of this study was to evaluate the application of the micronutrients Zn, Cu, Mn, Fe, B, and Mo to plant cane in three soils, with and without application of filter cake. This study consisted of three experiments performed in the State of São Paulo, Brazil, (in Igaraçu do Tiete, on an Oxisol; in Santa Maria da Serra, on an Entisol, both in the 2008/2009 growing season; and in Mirassol, on an Ultisol, in the 2009/2010 growing season) in a randomized block design with four replications with a 8 x 2 factorial combination of micronutrients (1 - no application/control, 2 - addition of Zn, 3 - addition of Cu, 4 - addition of Mn 5 - addition of Fe, 6 - addition of B, 7 - addition of Mo, 8 - Addition of Zn, Cu, Mn, Fe, B, and Mo) and filter cake (0 and 30 t ha-1 of filter cake) in the furrow at planting. The application of filter cake was more efficient than of Borax in raising leaf B concentration to sufficiency levels for sugarcane in the Entisol, and it increased mean stalk yield in the Oxisol. In areas without filter cake application, leaf concentrations were not affected by the application of Zn, Cu, Mn, Fe, B, and Mo in the furrow at planting; however, Zn and B induced an increase in stalk and sugar yield in micronutrient-poor sandy soil.

Molecular players shaping the arbuscular mycorrhizal symbiosis of rice

SUMMARY : The arbuscular mycorrhizal (AM) symbiosis is an evolutionarily ancient association between most land plants and Glomeromycotan fungi that is based on the mutual exchange of nutrients between the two partners. Its structural and physiological establishment is a multi-step process involving a tightly regulated signal exchange leading to intracellular colonization of roots by the fungi. Most research on the molecular biology and genetics of symbiosis development has been performed in dicotyledonous model legumes. In these, a plant signaling pathway, the common SYM pathway, has been found to be required for accommodation of both root symbionts rhizobia and AM fungi. Rice, a monocotyledon model and the world's most important staple crop also forms AM symbioses, has been largely ignored for studies of the AM symbiosis. Therefore in this PhD work functional conservation of the common SYM pathway in rice was addressed and demonstrated. Mycorrhiza-specific marker genes were established that are expressed at different stages of AM development and therefore represent readouts for various AM-specific signaling events. These tools were successfully used to obtain evidence for a yet unknown signaling network comprising common SYM-dependent and -independent events. In legumes AM colonization induces common SYM signaling dependent changes in root system architecture. It was demonstrated that also in rice, root system architecture changes in response to AM colonization but these alterations occur independently of common SYM signaling. The rice root system is complex and contains three different root types. It was shown that root type identity influences the quantity of AM colonization, indicating root type specific symbiotic properties. Interestingly, the root types differed in their transcriptional responses to AM colonization and the less colonized root type responded more dramatically than the more strongly colonized root type. Finally, in an independent project a novel mutant, inhospitable (iho), was discovered. It is perturbed at the most early step of AM colonization, namely differentiation of the AM fungal hyphae into a hyphopodium at the root surface. As plant factors required for this early step are not known, identification of the IHO gene will greatly contribute to the advance of mycorrhiza RÉSUMÉ : La symbiose mycorhizienne arbusculaire (AM) est une association évolutionnairement ancienne entre la majorité des plantes terrestres et les champignons du type Glomeromycota, basée sur l'échange mutuel d'éléments nutritifs entre les deux partenaires. Son établissement structural et physiologique est un processus en plusieurs étapes, impliquant des échanges de signaux étroitement contrôlés, aboutissant à la colonisation intracellulaire des racines par le champignon. La plupart des recherches sur la biologie moléculaire et la génétique du développement de la symbiose ont été effectuées sur des légumineuses dicotylédones modèles. Dans ces dernières, une voie de signalisation, la voie SYM, s'est avérée nécessaire pour permettre la mise en place de la symbiose mycorhizienne. Chez les plantes monocotylédones, comme le riz, une des céréales les plus importantes, nourrissant la moitié de la population mondiale, peu de recherches ont été effectuées sur les bases de la cette symbiose. Dans ce travail de thèse, la conservation fonctionnelle de la voie commune SYM chez le riz a été étudiée et démontrée. De plus, des gènes marqueurs spécifiques des différentes étapes du développement de l'AM ont été identifiés, permettant ainsi d'avoir des traceurs de la colonisation. Ces outils ont été utilisés avec succès pour démontrer l'existence d'un nouveau réseau de signalisation, comprenant des éléments SYM dépendant et indépendant. Chez les légumineuses, la colonisation par les AM induit des changements dans l'architecture du système racinaire, via la signalisation SYM dépendantes. Cependant chez le riz, il a été démontré que l'architecture de système racinaire changeait suite à la colonisation de l'AM, mais ceux, de façon SYM indépendante. Le système racinaire du riz est complexe et contient trois types différents de racines. Il a été démontré que le type de racine pouvait influencer l'efficacité de la colonisation par l'AM, indiquant que les racines ont des propriétés symbiotiques spécifiques différentes. De façon surprenante, les divers types de racines répondent de différemment suite à colonisation par l'AM avec des changements de la expression des gènes. Le type de racine le moins colonisé, répondant le plus fortement a la colonisation, et inversement. En parallèle, dans un projet indépendant, un nouveau mutant, inhospitable (iho), a été identifié. Ce mutant est perturbé lors de l'étape la plus précoce de la colonisation par l'AM, à savoir la différentiation des hyphes fongiques de l'AM en hyphopodium, à la surface des racines. Les facteurs d'origine végétale requis pour cette étape étant encore inconnus, l'identification du gène IHO contribuera considérablement a accroître nos connaissance sur les bases de la mise en place de cette symbiose.

Plant functional and phylogenetic turnover correlate with climate and land use in the Western Swiss Alps

Understanding the relative importance of historical and environmental processes in the structure and composition of communities is one of the longest quests in ecological research. Increasingly, researchers are relying on the functional and phylogenetic β-diversity of natural communities to provide concise explanations on the mechanistic basis of community assembly and the drivers of trait variation among species. The present study investigated how plant functional and phylogenetic β-diversity change along key environmental and spatial gradients in the Western Swiss Alps. Methods Using the quadratic diversity measure based on six functional traits: specific leaf area (SLA), leaf dry matter content (LDMC), plant height (H), leaf carbon content (C), leaf nitrogen content (N), and leaf carbon to nitrogen content (C/N) alongside a species-resolved phylogenetic tree, we relate variations in climate, spatial geographic, land use and soil gradients to plant functional and phylogenetic turnover in mountain communities of the Western Swiss Alps. Important findings Our study highlights two main points. First, climate and land use factors play an important role in mountain plant community turnover. Second, the overlap between plant functional and phylogenetic turnover along these gradients correlates with the low phylogenetic signal in traits, suggesting that in mountain landscapes, trait lability is likely an important factor in driving plant community assembly. Overall, we demonstrate the importance of climate and land use factors in plant functional and phylogenetic community turnover, and provide valuable complementary insights into understanding patterns of β-diversity along several ecological gradients.

Optical crop sensor for variable-rate nitrogen fertilization in corn: i - plant nutrition and dry matter production

Variable-rate nitrogen fertilization (VRF) based on optical spectrometry sensors of crops is a technological innovation capable of improving the nutrient use efficiency (NUE) and mitigate environmental impacts. However, studies addressing fertilization based on crop sensors are still scarce in Brazilian agriculture. This study aims to evaluate the efficiency of an optical crop sensor to assess the nutritional status of corn and compare VRF with the standard strategy of traditional single-rate N fertilization (TSF) used by farmers. With this purpose, three experiments were conducted at different locations in Southern Brazil, in the growing seasons 2008/09 and 2010/11. The following crop properties were evaluated: above-ground dry matter production, nitrogen (N) content, N uptake, relative chlorophyll content (SPAD) reading, and a vegetation index measured by the optical sensor N-Sensor® ALS. The plants were evaluated in the stages V4, V6, V8, V10, V12 and at corn flowering. The experiments had a completely randomized design at three different sites that were analyzed separately. The vegetation index was directly related to above-ground dry matter production (R² = 0.91; p<0.0001), total N uptake (R² = 0.87; p<0.0001) and SPAD reading (R² = 0.63; p<0.0001) and inversely related to plant N content (R² = 0.53; p<0.0001). The efficiency of VRF for plant nutrition was influenced by the specific climatic conditions of each site. Therefore, the efficiency of the VRF strategy was similar to that of the standard farmer fertilizer strategy at sites 1 and 2. However, at site 3 where the climatic conditions were favorable for corn growth, the use of optical sensors to determine VRF resulted in a 12 % increase in N plant uptake in relation to the standard fertilization, indicating the potential of this technology to improve NUE.

Yields, plant characteristics, total N and fibre composition of timothy cultivars grown at two latitudes

Selostus: Timoteilajikkeiden sadot, kasvuominaisuudet sekä typpi- ja kuitupitoisuus kahdella leveysasteella

Plant species distributions along environmental gradients: do belowground interactions with fungi matter?

The distribution of plants along environmental gradients is constrained by abiotic and biotic factors. Cumulative evidence attests of the impact of biotic factors on plant distributions, but only few studies discuss the role of belowground communities. Soil fungi, in particular, are thought to play an important role in how plant species assemble locally into communities. We first review existing evidence, and then test the effect of the number of soil fungal operational taxonomic units (OTUs) on plant species distributions using a recently collected dataset of plant and metagenomic information on soil fungi in the Western Swiss Alps. Using species distribution models (SDMs), we investigated whether the distribution of individual plant species is correlated to the number of OTUs of two important soil fungal classes known to interact with plants: the Glomeromycetes, that are obligatory symbionts of plants, and the Agaricomycetes, that may be facultative plant symbionts, pathogens, or wood decayers. We show that including the fungal richness information in the models of plant species distributions improves predictive accuracy. Number of fungal OTUs is especially correlated to the distribution of high elevation plant species. We suggest that high elevation soil show greater variation in fungal assemblages that may in turn impact plant turnover among communities. We finally discuss how to move beyond correlative analyses, through the design of field experiments manipulating plant and fungal communities along environmental gradients.

Plant adaptation to temperature and photoperiod

Selostus: Kasvien sopeutuminen lämpötilaan ja päivän pituuteen