SummaryAlthough fine roots are important components of the global carbon cycle, there is limited understanding of root structure-function relationships among species. We determined whether root respiration rate and decomposability, two key processes driving carbon cycling but always studied separately, varied with root morphological and chemical traits, in a coordinated way that would demonstrate the existence of a root economics spectrum (RES).Twelve traits were measured on fine roots (diameter ≤ 2 mm) of 74 species (31 graminoids and 43 herbaceous and dwarf shrub eudicots) collected in three biomes.The findings of this study support the existence of a RES representing an axis of trait variation in which root respiration was positively correlated to nitrogen concentration and specific root length and negatively correlated to the root dry matter content, lignin : nitrogen ratio and the remaining mass after decomposition. This pattern of traits was highly consistent within graminoids but less consistent within eudicots, as a result of an uncoupling between decomposability and morphology, and of heterogeneity of individual roots of eudicots within the fine-root pool.The positive relationship found between root respiration and decomposability is essential for a better understanding of vegetation-soil feedbacks and for improving terrestrial biosphere models predicting the consequences of plant community changes for carbon cycling.

Wood is the most important natural and endlessly renewable source of energy and therefore has a major future role as an environmentally cost-effective alternative to burning fossils fuels. The major role of wood is not only the provision of energy but also the provision of energy-sufficient material for our buildings and many other products. In addition, developing wood cells represent one of the most important sinks for excess atmospheric CO 2 , thereby reducing one of the major contributors to global warming. WOOD IS ALSO A RAW MATERIAL FOR A MAJOR GLOBAL INDUSTRY, AND ITS DEMAND IS INCREASING Wood is the fifth most important product of the world trade. Vast quantities of wood are logged by foresters to provide fuel, fibers (for pulp, paper products , and boards), and sawn timber (for house building and furniture) as commodities. The complex chemical makeup of wood (cellulose, hemicelluloses, lignin, and pectins) also makes it an ideal raw material for what could be a future "ligno-chemical" industry that could replace the petrochemical industry, in providing not only plastic and all kinds of chemical products, but also food and textile products. ENVIRONMENTAL BENEFITS OF TREES CONFLICT INCREASINGLY WITH INDUSTRIAL FORESTRY PRACTICES Resource analyses have led to the conclusion that wood and fiber needs over the next 40 years can only be met by logging 20% to 40% of the total present standing timber inventory in the natural forest (Food and Agriculture Organization). However, most agree that some of these forests should be either left completely alone or managed with only a minimum of wood extraction to preserve their environmental value. WHERE COULD THE WORLD FIND MORE WOOD IN THE NEW MILLENNIUM? The solution is to try to accomplish what agriculture has been doing for the last few centuries: grow wood as a crop in the same way that we grow wheat and maize. The future of the world's forests as well as the forest products industry will therefore depend to a huge extent on our ability to domesticate wild tree species and tailor them for maximum economic yield in the highly controlled environments typical of agriculture. The domestication of forest trees must be accomplished rationally, using the best available modern scientific methods, to develop high-yielding, intensively managed plantation forests, occupying a small percentage of existing forested land. In particular , the safe and careful application of biotechnology (marker-assisted breeding, genetic engineering, and in vitro propagation) to forestry practices, should help develop genetically superior trees in a time span of only a few decades. OUR UNDERSTANDING OF HOW WOOD DEVELOPS IS NOT COMPLETE Considering the important role that wood is foreseen to play in the near future, it is surprising to see that our understanding of how wood develops is far from complete. With a few exceptions, very little is known about the cellular, molecular, and developmental processes that underlie wood formation. Xy-logenesis represents an example of cell differentiation in...

The effects of plants on the biosphere, atmosphere, and geosphere are key determinants of terrestrial ecosystem functioning. However, despite substantial progress made regarding plant belowground components, we are still only beginning to explore the complex relationships between root traits and functions. Drawing on literature in plant physiology, ecophysiology, ecology, agronomy and soil science, we review 24 aspects of plant and ecosystem functioning and their relationships with a number of traits of root systems, including aspects of architecture, physiology, morphology, anatomy, chemistry, biomechanics and biotic interactions. Based on this assessment, we critically evaluate the current strengths and gaps in our knowledge, and identify future research challenges in the field of root ecology. Most importantly, we found that below-ground traits with widest importance in plant and ecosystem Accepted Article This article is protected by copyright. All rights reserved functioning are not those most commonly measured. Also, the fair estimation of trait relative importance for functioning requires us to consider a more comprehensive range of functionally-relevant traits from a diverse range of species, across environments and over time series. We also advocate that establishing causal hierarchical links among root traits will provide a hypothesis-based framework to identify the most parsimonious sets of traits with strongest influence on the functions, and to link genotypes to plant and ecosystem functioning.