Specific leaf area

Abstract: Although the structure and composition of plant communities is known to influence the functioning of ecosystems, there is as yet no agreement as to how these should be described from a functional perspective. We tested the biomass ratio hypothesis, which postulates that ecosystem properties should depend on species traits and on species contribution to the total biomass of the community, in a successional sere following vineyard abandonment in the Mediterranean region of France. Ecosystem-specific net primary productivity, litter decomposition rate, and total soil carbon and nitrogen varied significantly with field age, and correlated with community-aggregated (i.e., weighed according to the relative abundance of species) functional leaf traits. The three easily measurable traits tested, specific leaf area, leaf dry matter content, and nitrogen concentration, provide a simple means to scale up from organ to ecosystem functioning in complex plant communities. We propose that they be called ''functional markers,'' and be used to assess the impacts of community changes on ecosystem properties induced, in particular, by global change drivers.

Abstract: Variation in leaf life—span has long been considered of ecological significance.Despite this, quantitative evaluation of the relationships between leaf life—span and other plant and ecosystem characteristics has been rare. In this paper we ask whether leaf life—span is related to other leaf, plant, and stand traits of species from diverse ecosystems and biomes. We also examine the interaction between leaf, plant, and stand traits and their relation to productivity and ecological patterns. Among all species, both mass— (Amass) and area—based (Aarea) maximum net photosynthesis decreased with increasing leaf life—span, but the relationship was stronger on a mass (P .25, r2 = 0.01). Specific leaf area (SLA, leaf area/leaf dry mass) and leaf diffusive conductance also decreased with increasing leaf life—span. Decreasing Amass with increasing leaf life—span results from the impact of decreasing Nmass and SLA on Amass. Variation in leaf traits as a function of leaf life—span was similar for broad—leaved and needle—leaved subsets of the data. These leaf—scale data from several biomes were compared to a data set from a single biome, Amazonia. For several leaf traits (e.g., SLA, Nmass, and Amass) the quantitative relationship with leaf life—span was similar in the two independent data sets, suggesting that these are fundamental relations applicable to all species. Amass was a linear function of Nmass (P .001, r2 = 0.74) with a regression similar to previous analyses, while Aarea was not significantly related to Narea. These results suggest that the photosynthesis—leaf N relationship among species should be considered universal when expressed on a mass, but not on a leaf area, basis. Relative growth rates (RGR) and leaf area ratio (LAR, the whole—plant ratio of leaf area to total dry mass) of seedlings decreased with increasing leaf life—span (P < .001, r2 = 0.61 and 0.89, respectively). LAR was positively related to both RGR and Amass (r2 = 0.68 and 0.84, respectively), and Amass and RGR were also positively related (r2 = 0.55). Absolute height growth rates of young trees decreased with increasing leaf life—span (P < .001, r2 = 0.72) and increased with Amass (P < .001, r2 = 0.78). It appears that a suite of traits including short leaf life—span and high leaf Nmass, SLA, LAR, and Amass interactively contribute to high growth rates in open—grown individuals. These traits interact similarly at the stand level, but stands differ from individuals in one key trait. In closed—canopy forests, species with longer lived foliage (and low LAR as seedlings) have greater foliage mass per unit ground area (P < .001, r2 = 0.74) and a greater proportion of total mass in foliage. The aboveground production efficiency (ANPP/foliar biomass) of forest stands decreased markedly with increasing leaf life—span or total foliage mass (P < .001, r2 = 0.78 and 0.72, respectively), probably as a result of decreasing Amass, Nmass, and SLA, all of which were positively related with production efficiency and negatively related to total foliage mass. However, high foliage mass of species with extended leaf life—spans appears to compensate for low production per unit foliage, since aboveground net primary production (ANPP, in megagrams per hectare per year) of forest stands was not related to leaf life—span. Extended leaf life—span also appears to compensate for lower potential production per unit leaf N per unit time, with the result that stand—level N use efficiency is weakly positively related to leaf life—span. We hypothesize that co—variation among species in leaf life—span, SLA, leaf Nmass, Amass, and growth rate reflects a set of mutually supporting traits that interact to determine plant behavior and production, and provide a useful conceptual link between processes at short—term leaf scales and longer term whole plant and stand—level scales. Although this paper has focused on leaf life—span, this trait is so closely interrelated with several others that this cohort of leaf traits should be viewed as casually interrelated. Generality in the relationships between leaf life—span and other plant traits across diverse communities and ecosystems suggests that they are universal in nature and thus can provide a quantitative link and/or common currency for ecological comparisons among diverse systems.

Abstract: Publisher Summary This chapter discusses a search for physiological causes and ecological consequence in reference with the variation in growth rate between higher plants. When grown under optimum conditions, plant species from fertile, productive habitats tend to have inherently higher relative growth rates (RGR) than species from less favorable environments. Under these conditions, fast-growing species produce relatively more leaf area and less root mass, which greatly contributes to their larger carbon gain per unit plant weight. Fast-growing species also have higher respiration rates per unit organ weight, due to demands of a higher RGR and higher rate of nutrient uptake. Fast-growing species have a greater capacity to acquire nutrients, which is likely to be a consequence, rather than the cause, of their higher RGR. This chapter analyses variations in morphological, physiological, chemical, and allocation characteristics underlying variation in RGR, to arrive at an appraisal of its ecological significance. The lower specific leaf area (SLA) of slow-growing species is because of the relatively high concentration of cell-wall material and quantitative secondary compounds, which may protect against detrimental abiotic and biotic factors. This chapter concludes that it is likely that there are trade-offs between growth potential and performance under adverse conditions, however, the current ecophysiological information explaining variation in RGR is too limited to support this contention quantitatively.

Abstract: Convergence in interspecific leaf trait relationships across diverse taxonomic groups and biomes would have important evolutionary and ecological implications. Such convergence has been hypothesized to result from trade-offs that limit the combination of plant traits for any species. Here we address this issue by testing for biome differences in the slope and intercept of interspecific relationships among leaf traits: longevity, net pho- tosynthetic capacity (Amax), leaf diffusive conductance (Gs), specific leaf area (SLA), and nitrogen (N) status, for more than 100 species in six distinct biomes of the Americas. The six biomes were: alpine tundra-subalpine forest ecotone, cold temperate forest-prairie ecotone, montane cool temperate forest, desert shrubland, subtropical forest, and tropical rain forest. Despite large differences in climate and evolutionary history, in all biomes mass-based leaf N (Nmass), SLA, Gs, and Amax were positively related to one another and decreased with increasing leaf life span. The relationships between pairs of leaf traits exhibited similar slopes among biomes, suggesting a predictable set of scaling relationships among key leaf morphological, chemical, and metabolic traits that are replicated globally among terrestrial ecosystems regardless of biome or vegetation type. However, the intercept (i.e., the overall elevation of regression lines) of relationships between pairs of leaf traits usually differed among biomes. With increasing aridity across sites, species had greater Amax for a given level of Gs and lower SLA for any given leaf life span. Using principal components analysis, most variation among species was explained by an axis related to mass-based leaf traits (Amax, N, and SLA) while a second axis reflected climate, Gs, and other area-based leaf traits.