Browsing by Author "Ellsworth, D S"

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    Leaf life-span in relation to leaf, plant, and stand characteristics among diverse ecosystems
    (1992) Reich, Peter B; Walters, M B; Ellsworth, D S
    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 lifespan 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 < .001, r2 = 0.70) than an area (P < .05, r2 = 0.24) basis. Similarly, mass-based leaf nitrogen (leafNmass) decreased (P < .001, r2 = 0.52) with leaf life-span, but area-based leaf N (leaf Narea) did not (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 leaflife-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-leafN relationship among species should be considered universal when expressed on a mass, but not on a leaf arna, 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 leaflife-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 leafNmas"' 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 above ground 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• Nmam 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 above ground 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 leaflife-span, SLA, leafNmam 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 causally 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.
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    Photosynthesis and leaf nitrogen in five Amazonian tree species during early secondary succession
    (1996) Ellsworth, D S; Reich, Peter B
    Field measurements of maximum net photosynthesis (Pmax), leaf nitrogen (N) content (leaf N per area and percent N), and specific leaf area (SLA) were made for Amazonian tree species within and across early successional sites of known ages after abandonment from slash-and-burn agriculture. We examined five species across a successional sere near San Carlos de Rio Negro, Venezuela, to test whether plasticity was associated with successional status and to determine whether changes in foliar properties during secondary succession can be attributed to shifts in species composition, in resource availability, or both. Average leaf N concentration was high (nearly 3%) for a pioneer species (Cecropiaficifolia) early in succession (1-3 yr after abandonment) but was always lower for the other early and mid- to-late succession species, especially later in succession (1-2% at 5-10 yr after abandonment). Net photosynthetic capacity (P /area and P I mass) varied as much as sixfold, being higher in pioneer species such as Cecropia and Vismia on recently abandoned sites and lower in late successional species such as Miconia and Licania on 10-yr abandoned agricultural sites. Total daily light availability also varied widely (14-fold) from its peak 1 yr after farm abandonment to low levels 9 yr into succession. During the first 5 yr of secondary succession, there were significant (P < 0.05) differences in Pmax and leaf N concentration among species in any given year. In most species, Pmax values declined with increasing time since abandonment within any given site. There were important differences in photosynthetic plasticity among species: Pmax tended to be much greater in earlier than later successional species soon after abandonment. Also, the difference in Pmax among species narrowed (or reversed) over time since abandonment, largely because of decreasing Pmax in pioneer species. The results suggest that changes in both species composition and in resource availability combine to produce the common pattern of decreasing leaf N concentration and photosynthetic rates during early rain forest succession after agriculture. Early successional species showed strong (r2 - 0.57, P = 0.0001) mass-based photosynthesis-N relationships but weak (r2 = 0.40 or lower, P = 0.000 1) area-based relationships both across the secondary successional sere after agriculture and across sites varying in types of disturbance. Both mass- and area-based photosynthesis-N relationships were poorer or not significant (P > 0.05) for mid- to late-successional species. Higher instantaneous Pmax/N and greater slopes of the photosynthesis-N relationships in early than late successional species suggest that pioneer species may show greater carbon assimilation capacity with elevated leaf N concentration on early successional sites than co-occurring species. The data suggest that early and late successional species may differ in the mode and degree of leaf-level physiological plasticity across succession.