Photosynthetic capacities and leaf conductances of planted tree saplings and competing weeds in a tropical montane pasture confirm the general decline from pioneers to late successional species - studies with special emphasis on bracken (original) (raw)
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2006
Photosynthesis-nitrogen relationships in pioneer plants of disturbed tropical montane forest sites
1998
Tropical forest disturbances lead to the establishment of secondmy successional plant communities constituted by light demanding species with high relative growth rate that conduct to rapid canopy closure. Two main strategies for N nutrition are: (a) mineral N acquisition in the fmm of NH4 and N0 3 , and (b) symbiotic atrnospheric N2 fixation. Given the high N requirement for maximization of leaf area and radiant energy absorption, we hypothesize that contrasting strategies of N nutrition in these environments are reflected in leaf photosynthetic characteristics. We compared the N-photosynthesis relationships and carbon balance parameters per unit leaf area as they valY with age in two species with contrasting N acquisition strategies: a NTfixer Crola/aria anagyroides HBK (PapillOnoideae), and a mineral-N user Verhesina lurhacensls HBK (Asleraceae). N2 fixation capacity was associated to higher specific leaf area (SLA), higher photosynthetic capacity (P max ) per unit leaf area and leaf mass, and higher N content per unit leaf mass. The NT fixer species showed higher slope in the relationship 1'max-N per 1mit leaf mass and area when compared to the leaves of non-fixer species. Moreover, the intrinsic photosynthetic N use efficiency (1' maiN) was higher in the N2 fixer than in leaves of the non-fixer species. Changes in N due to leaf age resulted in larger changes in CO 2 flux density at the leaf level in the Nrfixer species. The higher photosynthetic capacity of the N 2 -fixer species was mechanistically related to higher stomatal conductance, internal CO 2 concentration (ei) values closer to atmospheric CO 2 concenh'ation Ce a ), and lower intrinsic water use efficiency than tire mineral N-user species. Despite their higher Fmax per unit leaf area, total non-stIuctural saccharides concentration was lower in mature leaves of the Nrfixer plant as compm'ed to the non-fixer counterpart. This might be caused by the presence of a larger root sink (symbionts) stimulating saccharides export and higher diurnal respiration rates.
Environmental and Experimental Botany, 2011
For a tree seedling to successfully establish in dense shrubbery, it must maintain function under heterogeneous resource availability. We evaluated leaf-level acclimation in photosynthetic capacity, seedling-level transpiration, and seedling morphology and growth to gain an understanding of the effects of above- and below-ground competition on Quercus robur seedlings. Experimental seedlings were established in a typical southern Swedish shrub community where they received 1 of 4 competition levels (above-ground, below-ground, above- and below-ground, or no competition), and leaf-level responses were examined between two growth flushes. Two years after establishment, first-flush leaves from seedlings receiving above-ground competition showed a maximum rate of photosynthesis (Amax) 40% lower than those of control seedlings. With the development of a second flush above the shrub canopy, Amax of these seedlings increased to levels equivalent to those of seedlings free of light competition. Shrubby competition reduced oak seedling transpiration such that seedlings exposed to above- and below-ground competition showed rates 43% lower than seedlings that were not exposed to competition. The impaired physiological function of oak seedlings growing amid competition ultimately led to a 60–74% reduction in leaf area, 29–36% reduction in basal diameter, and a 38–78% reduction in total biomass accumulation, but root to shoot ratio was not affected. Our findings also indicate that aboveground competition reduced Amax, transpiration and biomass accumulation more so than below-ground competition. Nevertheless, oak seedlings exhibited the ability to develop subsequent growth flushes with leaves that had an Amax acclimated to utilize increased light availability. Our findings highlight the importance of flush-level acclimation under conditions of heterogeneous resource availability, and the capacity of oak seedlings to initiate a positive response to moderate competition in a shrub community.
Tree Physiology, 2001
Monoculture and mixed stands of mahogany (Swietenia macrophylla King) and tonka bean (Dipteryx odorata Willd.) trees were established on degraded land in central Amazonia to compare leaf gas exchange parameters between plants grown in sunlight in an open field and in shade beneath a balsa wood (Ochroma pyramidale Cav.) canopy. Shading increased specific leaf area by about 50% in both species. Shading reduced height and diameter growth of S. macrophylla, whereas it increased these parameters for D. odorata. Lightsaturated photosynthesis (A max), stomatal conductance (g s) and transpiration (E) were higher in S. macrophylla than in D. odorata. In S. macrophylla, A max was higher in sun leaves (12.9 ± 0.9 µmol m-2 s-1) than in shade leaves (10.2 ± 1.0 µmol m-2 s-1), whereas light environment had no significant effect on A max of D. odorata. In both species, CO 2-saturated photosynthesis (A pot) was higher in sun leaves (22 ± 1.4 µmol m-2 s-1) than in shade leaves (17-20 ± 0.8 µmol m-2 s-1). Stomatal conductance and E increased in sun leaves of S. macrophylla by 45 and 38%, respectively, whereas light environment did not affect g s and E of D. odorata. Photorespiration rates (P r) varied from 28 to 36% of net photosynthesis (A) at ambient atmospheric CO 2 concentration (C a) but declined to around 7% of A at higher C a. Leaf dark respiration (R d) and the CO 2 compensation point (Γ) were lower in shade-grown plants than in open-grown plants. Compared with shade-grown plants, total nonstructural carbohydrate (TNC) concentrations increased by 56% in S. macrophylla and by 30% in D. odorata in the open field. Leaf nitrogen (N L) concentrations were higher in opengrown plants than in shade-grown plants of both species, and TNC and N L concentrations were negatively correlated (r =-0.77). High TNC accumulation in S. macrophylla in the open field suggests that photosynthesis is unlikely to be growth-limiting at this site. We conclude that photosynthetic parameters of D. odorata are less affected by light environment than those of S. macrophylla, indicating that D. odorata has lower physiological plasticity to light than S. macrophylla.
Phenology of fine roots and leaves in forest and grassland
Journal of Ecology, 2008
1. The phenology of temperate vegetation is advancing in association with climate warming. Most phenology data, however, comes from flowers and tree leaves. We tested the generality of results from shoot phenology by expanding data collection in two new directions. We related forest leaf phenology to root phenology, and to phenology in a second habitat, grassland. 2. We measured leaf and root phenology simultaneously in aspen forest and adjacent native grassland. Root growth accounts for 80-90% of productivity in these habitats. Seasonal variation in soil moisture and temperature were also measured. 3. Forest leaf production was greatest about 45 days before peak root production, resulting in a significant negative correlation between leaf and root production in forest. Grassland leaf production was greatest about 15 days before peak root production, and grassland leaf and root production were significantly positively correlated. The duration of root production was 40% greater than that of shoot production. 4. Forest leaf production increased significantly with increasing soil moisture, but not temperature. In contrast, the production of forest roots, grassland roots and grassland leaves increased significantly with soil temperature. 5. Synthesis. The most commonly measured aspect of phenology, forest leaves, is out of step with the majority of production in forest, as well as phenology in grassland. The invasion of grassland by woody vegetation is characterized by a decoupling of root and shoot phenology, a result that has not been reported previously. Given the global nature of woody plant encroachment, this decoupling may influence our general understanding of productivity and carbon sequestration in response to warming.
Photosynthesis-nitrogen relations in Amazonian tree species
Oecologia, 1994
Among species, photosynthetic capacity (Amax) is usually related to leaf nitrogen content (N), but variation in the species-specific relationship is not well understood. To address this issue, we studied Amax-N relationships in 23 species in adjacent Amazonian communities differentially limited by nitrogen (N), phosphorus (P), and/or other mineral nutrients. Five species were studied in each of three late successional forest types (Tierra Firme, Caatinga and Bana) and eight species were studied on disturbed sites (cultivated and early secondary successional Tierra Firme plots). Area x expressed on a mass basis (Amass) was correlated (p < 0.05) with N .... in 17 of 23 species, and Area x on an area basis (Aarea) was correlated (p<0.05) with N .... in 21 of 23 species. The slopes of Amax-N relationships were greater and intercepts lower for disturbance adapted early successional species than for late successional species. On a mass basis, the Amax-N slope averaged g 15 gmol CO2 [g N]-~ s-1 for 7 early secondary successional species and ~4 pmol CO2 [g N]-1 s-1 for 15 late successional species, respectively. Species from disturbed sites had shorter leaf lifespan and greater specific leaf area (SLA) than late successional species. Across all 23 species, the slope of the Amass-N .... relationship was related (p < 0.001) positively to SLA (r 2 = 0.70) and negatively to leaf lifespan (r 2= 0.78) and temporal niche during secondary succession (years since cutting-and-burning, r2= 0.90). Thus, disturbance adapted early successional species display a set of traits (short leaf lifespan , high SLA and Amax and a steep slope of Amax-N) conducive
Understanding the drivers of vegetation change, and interactions between them, is fundamental to understanding ecological systems. In this thesis I have measured the effects of competition and herbivory in driving change from heather (Calluna vulgaris) and grass (Molinia caerulea) dominated heath to birch (Betula pubescens) woodland. Invasion by birch marks the boundary of change between these two ecosystem states (heath and woodland), thus making this an interesting system for studying vegetation change. Furthermore, these two semi-natural vegetation types are both of local, national and global importance. Consequently, management often concentrates on encouraging change (for the purpose of woodland creation) or preventing change (for the purpose of conserving areas of heath). In this thesis I report on the results of three studies in which I investigated the role of competition and browsing by large herbivores in determining the fitness of birch saplings that are established in heath vegetation. Factors influencing sapling growth and/or morphology have the potential for impacting on both the probability of invasion and the temporal and spatial pattern of invasion. Browsing by deer has previously been identified as a major driver of vegetation change in this system. However, interactions with other plants also have the potential to impact on sapling fitness, and alter the response to browsing damage. In an observational field study I measured the morphological characteristics of B. pubescens saplings growing in C. vulgaris or M. caerulea under three different levels of herbivore densities. There was a strong effect of deer density on the growth of the saplings, indicating the importance of this driver. However, when deer densities (and therefore the amount of browsing damage) were low, sapling growth was influenced by the species of competing vegetation. Specifically, those growing with C. vulgaris were smaller than those growing with M. caerulea. This difference was absent when browsing pressure was higher. •In an ex-situ experiment I grew B. pubescens saplings in the presence of below- or above- and below-ground interactions from C. vulgaris or M. caerulea. Saplings were also subjected to simulated browsing by clipping (50% of current year's growth), either pre-senescence or at bud-burst. I measured the morphology and dry mass allocation response of the saplings over a period of two years. Additionally, by using 15N labeled fertilizer I was able to quantify N uptake, leaf-N withdrawal and remobilisation. Competition reduced sapling dry mass by approximately 50%, but C. vulgaris reduced dry mass to a greater extent than did M. caerulea. This concurs with the patterns in-situ. The total competition intensity of C. vulgaris was greater than that of M. caerulea, due to an apparent facilitative effect of M. caerulea shoots on birch growth. Saplings compensated for browsing damage, resulting in no difference in dry mass one year after damage. However, sapling morphological responses to browsing damage were dependent on the competing species. Competition reduced B. pubescens leaf-N withdrawal and remobilisation, with C. vulgaris having a greater effect than M. caerulea. However, simulated browsing had no significant effect on sapling N dynamics. The patterns of leaf-N withdrawal and remobilisation closely followed sapling dry mass. This indicates that the effect of competition on sapling mass reduces their N storage capacity. This reduces sink-strength for leaf-N withdrawal and the source-strength for remobilised N. The ability of saplings to compensate for browsing damage removed any potential effect of browsing on N dynamics. Finally, I examined the role of above-ground foraging in determining the ability of B. pubescens to utilise canopy gaps and therefore, effectively compete above-ground. I manipulated the light environment of B. pubescens seedlings, creating a spatially heterogeneous environment. Additionally, I induced nutrient limitation and simulated herbivory by removing seedling meristems. Seedlings foraged for light by placing leaf area in the light side of the pot. The degree of foraging was influenced by meristem removal and nutrient limitation, due to their effect on growth. This could, in part, explain the lack of above-ground competitive effect observed in the ex-situ study. This study highlights the importance of complexity in dynamic systems. Influences on the growth, and therefore, invasion success of birch were multifactorial. Additionally, the potential for interaction between factors further increases this complexity and contributes to the spatial and temporal heterogeneity that is characteristic of natural and semi-natural systems.
Leaf-level nitrogen-use efficiency of canopy and understorey species in a beech forest
Functional Ecology, 2002
In a forest stand, canopy and understorey species grow at completely different irradiances and consequently with different carbon and nitrogen availability ratios. We studied how the difference in growth irradiance influenced plant N use in a mature beech forest. 2. We defined leaf-level nitrogen-use efficiency (NUE L ) as the amount of the leaf dry mass produced per unit N taken up by leaves. NUE L was similar between the canopy species ( Fagus crenata ) and the understorey species ( Lindera umbellata and Magnolia salicifolia ). 3. NUE L was analysed further as the product of two components: leaf-level N productivity (NP L ) and mean residence time of leaf N (MRT L ). The canopy species had significantly larger NP L and significantly shorter MRT L than the understorey species. 4. As the photosynthetic capacity was similar among the species, different NP L between the species was attributable largely to the difference in light conditions to which their leaves were exposed. 5. The difference in MRT L was not attributable to potential efficiency of N resorption ( R EFF ) determined at leaf senescence, but to actual R EFF , which depended on the amount of green leaf lost before full senescence. The canopy species had significantly smaller actual R EFF because of strong wind actions in the canopy. 6. Although the canopy species realized higher NP L by virtue of high irradiance, it had shorter MRT L due to wind damage to pre-senescent leaves. On the other hand, the canopy species had shorter NP L under shady conditions, but had longer MRT L with little wind damage. Interplay of local environmental factors such as light and wind strongly influenced N use by plants in the beech forest.
Biomass distribution of two subalpine dwarf-shrubs in relation to soil moisture and nutrient content
Journal of Vegetation Science, 2004
Question: Do soil water content and/or soil nitrogen (N) content and/or soil phosphorus (P) content affect the biomass of Vaccinium myrtillus and V. vitis-idaea in a sub-alpine heath? Location: Dolomites, northern Italy, 1800 m a.s.l. Methods: We determined above-ground and below-ground biomass of the shrubs at three sites, each on a different substrate type. At each site, we determined soil N-and Pcontents. We also determined leaf water potential (ψ l ), N-and P-concentrations in plant tissues and litter, as well as δ 13 C and δ 15 N in mature leaves. Results: V. myrtillus biomass was highest at the silicate site, V. vitis-idaea biomass was highest at the carbonate site. Both shrubs had low biomass at the peat site, possibly due to a toxic effect of waterlogging in wet soils. For both species, pre-dawn ψ l indicated optimal hydration and midday ψ l did not show any sign of water stress. Water use efficiency (WUE) did not differ among sites for any species. Whole-plant nutrient concentrations showed that, with increasing biomass, N was diluted in V. myrtillus tissues while P was diluted in V. vitisidaea tissues. Foliar N-concentration was higher overall for V. myrtillus. Foliar P-concentration in V. myrtillus peaked at the silicate site. Foliar N : P ratios suggested that V. myrtillus was primarily P-limited and V. vitis-idaea primarily N-limited. Conclusions: Water content affected the distribution of the two shrubs in a similar way, higher P-availability in the soil enhanced V. myrtillus rather than V. vitis-idaea.
1 The facilitative and inhibitory effects of a nitrogen-fixing shrub, Carmichaelia odorata , during primary succession were studied using both field measurements in a New Zealand temperate montane valley, and manipulative glasshouse experiments on seedlings of the three dominant tree species, Griselinia littoralis , Metrosideros umbellata and Weinmannia racemosa . 2 During a stand development chronosequence of < 100 years in which Carmichaelia colonized, dominated and senesced, there was significant development of soil organic horizons and a large build-up of soil nitrogen, especially in the organic horizon. Soil organic matter and nitrogen levels across the sequence were strongly correlated with the main DCA axis of vascular plant species composition, along which there was change in dominance from herbaceous to woody species. Vegetation increased in height and light levels declined with stand development.