Arbre | EPFL Graph Search

vignette|Les arbres sont notamment représentés par des espèces du groupe des plantes à fleurs comme ces jacarandas au Zimbabwe. vignette|Même les arbres les plus majestueux commencent leur existence sous forme de modestes plantules, comme celle-ci de hêtre (Fagus sylvatica). vignette|Les arbres contribuent significativement au bien-être et à la subsistance des sociétés humaines. De nombreuses espèces produisent des fruits comestibles, comme ici l'arbre à pain (Artocarpus altilis). vignette|Un tilleul, arbre commun d'Europe du Nord, planté en l'honneur de l'intronisation de Willem-Alexander des Pays-Bas. Un arbre (du latin arbor) est une plante ligneuse terrestre comportant un tronc sur lequel s'insèrent des branches ramifiées portant le feuillage dont l'ensemble forme le houppier, appelé aussi couronne. Les arbres sont des plantes pérennes qui vivent plusieurs années, plusieurs décennies, voire plusieurs siècles, et, dans de rares cas, plusieurs millénaires. Selon les estimations, la

Soil aggregation and associated nutrient content along a distance-from-tree gradient in a low input cropping system. Comparing the effect for two tree species: Mangifera indica (mango, Anacardiaceae) vs. Faidherbia albida (faidherbia, Fabaceae)

Pauline Chrobot

Trees can play a major role in improving soil quality and thus have the potential to enhance sustainability of agroecosystems. Although this has been well established, knowledge on the effect of individual trees on aggregate stability and associated-nutrient content remains scarce. This study aims to quantify the spatial extent and magnitude of influence of single-standing Mangifera indica (mango, Anacardiaceae) and Faidherbia albida (faidherbia, Fabaceae) trees on soil aggregate stability and aggregate-associated nutrient content (total carbon, nitrogen and phosphorus) in a lowinput maize cropping system. Mango and faidherbia differ fundamentally in their properties (e.g., phenology and N-fixing capacity) providing an interesting study system. We hypothesize that 1) the extent of tree influence on soil will be proportional to the tree crown, 2) soil aggregation and aggregate-associated nutrient content will decrease with distance from tree for both species due to greater organic matter inputs from leaves and roots closer to the tree, 3) the magnitude of tree influence will be greater for faidherbia relative to mango due to its N-fixing property. To test these hypotheses, soil samples, collected along four transects, laid out around each single tree and taken at four different distances (1, 4, 10 and 15 m) from the tree trunk, were fractionated and total carbon, nitrogen and phosphorus content within the different fractions was determined. Our results show that both species had an impact on soil fertility, but only the spatial influence of mango was proportional to its crown. We could identify no change in the measured indicators with distance around faidherbia suggesting the possibility that we were likely still in its impact zone. These results support the hypothesis that faidherbia has an extensive positive impact on the surrounding soil, and that mango crown also improves subcanopy soil fertility via a better aggregation and an increase in associated-nutrient content.

2017

Grammar-Based Tree Compression

Grammar-based compression means to find a small grammar that generates a given object. Such a grammar reveals the structure of the object (according to the grammar formalism used); the main advantage of this compression method is that the resulting grammar can often be used in further computations without prior decompression. A linear time bottom-up algorithm is presented which transforms a tree into a particular context-free tree grammar. For common XML documents the algorithm performs well, compressing the tree structure to about 5 per cent of the original size. The validation of an XML document against an XML type can be done without decompression, in linear time w.r.t. the size of the grammar (for a fixed type). While the involved grammars can be double exponentially smaller than the represented trees, testing them for equivalence can be done in polynomial space w.r.t. the sum of their sizes.

2004

Disentangling the impacts of rising temperature and evaporative demand on plants water status

Laura Mekarni

This study focuses on two of the impacts of global warming (increasing temperatures and increasing vapor pressure deficit - VPD) on plants water status. Three different tree species were selected and young three-years-old trees were placed in conditioned chambers. A total of 6 chambers each accommodated 6 plants of each species. This report presents the results of two measurement sessions: a first session (at time t0) before which all the chambers were configured under the same so-called "normal" conditions, then a second session, after 45 days during which each chamber represented a different combination of temperature and VPD. The experimental set-up therefore allowed to decorrelate these two environmental variables which in nature are always positively correlated, making it difficult to understand the specific impacts of each one. A workflow for in-vivo microCT living trees scanning has been defined and improved during this study, and the resulting images allowed to assess correctly the embolism inside the living trees. It has been shown that the three species had a different sensitivity to temperature and VPD increase, and statistical analyses showed a significant effect of temperature and VPD respectively, as well as a significant interaction between those two climatic parameters in certain cases.

2020

Pauline Chrobot

2017