Seed mass and seed nutrient content as predictors of seed output variation between species

In patch-occupancy models for vegetation, propagule output per area occupied is a key species trait, influencing the potential to colonize vacant patches, and hence species dynamics and coexistence. We estimated seed output across a range of species and quantified its relationship to seed dry mass, seed N and P content, and accessory costs in fruiting structures. Fruiting and seed production data were obtained for 47 woody perennial species, spanning an almost 3000-fold range of seed mass, over a period of one year in Ku-ring-gai Chase National Park, New South Wales, Australia. Seed output was measured as numbers per m² canopy outline and per m² leaf area. Of cross-species variation in seed output per m² canopy outline per year, 72% could be predicted from seed mass alone, with a directly inverse relationship (log-log slope not significantly different from −1). Seed output per m² leaf area could be predicted somewhat more tightly (75%), indicating leaf area per canopy outline area accounted for some cross-species variation. Reproductive production per m² occupied per year varied much less than seed mass and accounted for the remaining variation in seed output. Although accessory costs were about equal in magnitude to seed mass as a component of aggregate investment per seed, they were strongly correlated with seed mass, and consequently did not add substantially to the predictive power. Total mass of N or P per seed were found to be slightly but significantly better predictors of seed output variation than dry seed mass (83% and 78%, respectively). This supports the idea that mineral nutrients are a more fundamental currency for seed production than dry mass. Seed mass, whether measured as dry mass or as N or P, appears to be the principal driver of variation in seed output per m² occupied, and consequently is among the most important dimensions of ecological variation across coexisting species.12 page(s

Does soil nitrogen influence growth, water transport and survival of snow gum (Eucalyptus pauciflora Sieber ex Sprengel.) under CO2 enrichment?

Eucalyptus pauciflora Sieber ex Sprengel. (snow gum) was grown under ambient (370 L-1) and elevated (700 L-1) atmospheric CO2 in open-top chambers (OTCs) in the field and temperature- controlled glasshouses. Nitrogen applications to the soil ranged from 0.1 to 2.75 g N per plant. Trees in the field at high N levels grew rapidly during summer, particularly in CO2-enriched atmosphere, but suffered high mortality during summer heatwaves. Generally, wider and more numerous secondary xylem vessels at the root-shoot junction in CO2-enriched trees conferred fourfold higher below-ground hydraulic conductance. Enhanced hydraulic capacity was typical of plants at elevated CO2 (in which root and shoot growth was accelerated), but did not result from high N supply. However, because high rates of N application consistently made trees prone to dehydration during heatwaves, glasshouse studies were required to identify the effect of N nutrition on root development and hydraulics. While the effects of elevated CO2 were again predominantly on hydraulic conductivity, N nutrition acted specifically by constraining deep root penetration into soil. Specifically, 15-40% shallower root systems supported marginally larger shoot canopies. Independent changes to hydraulics and root penetration have implications for survival of fertilized trees under elevated atmospheric CO 2, particularly during water stress

Does soil nitrogen influence growth, water transport and survival of snow gum (Eucalyptus pauciflora Sieber ex Sprengel.) under CO₂ enrichment?

Eucalyptus pauciflora Sieber ex Sprengel. (snow gum) was grown under ambient (370 µL L⁻¹) and elevated (700 µL L⁻¹) atmospheric [CO₂] in open-top chambers (OTCs) in the field and temperature-controlled glasshouses. Nitrogen applications to the soil ranged from 0.1 to 2.75 g N per plant. Trees in the field at high N levels grew rapidly during summer, particularly in CO₂-enriched atmosphere, but suffered high mortality during summer heatwaves. Generally, wider and more numerous secondary xylem vessels at the root–shoot junction in CO₂-enriched trees conferred fourfold higher below-ground hydraulic conductance. Enhanced hydraulic capacity was typical of plants at elevated [CO₂] (in which root and shoot growth was accelerated), but did not result from high N supply. However, because high rates of N application consistently made trees prone to dehydration during heatwaves, glasshouse studies were required to identify the effect of N nutrition on root development and hydraulics. While the effects of elevated [CO₂] were again predominantly on hydraulic conductivity, N nutrition acted specifically by constraining deep root penetration into soil. Specifically, 15–40% shallower root systems supported marginally larger shoot canopies. Independent changes to hydraulics and root penetration have implications for survival of fertilized trees under elevated atmospheric [CO₂], particularly during water stress.14 page(s

Evidence for a combination of pre-adapted traits and rapid adaptive change in the invasive plant Centaurea stoebe

1. Introduced plants have the potential to rapidly evolve traits of ecological importance that may add to their innate potential to become invasive. During invasions, selection may favour genotypes that are already pre-adapted to conditions in the new habitat and, over time, alter the characteristics of subsequent generations. 2. Spotted knapweed (Centaurea stoebe) occurs in two predominantly spatially separated cytotypes in its native range (Europe–Western Asia), but currently only the tetraploid form has been confirmed in the introduced range (North America), where it is invasive. We used several common garden experiments to examine, across multiple populations, whether tetraploids and diploids from the native range differ in life cycle, leaf traits and reproductive capacity and if such differences would explain the predominance of tetraploids and their advance into new habitats in the introduced range. We also compared the same traits in tetraploids from the native and introduced range to determine whether any rapid adaptive changes had occurred since introduction that may have enhanced invasive potential of the species in North America. 3. We found tetraploids had lower specific leaf area, less lamina dissection and fewer, narrower leaves than diploids. Diploids exhibited a monocarpic life cycle and produced few if any accessory rosettes. Diploids produced significantly more seeds per capitulum and had more capitula per plant than tetraploids. In contrast, the vast majority of European tetraploids continued to flower in both seasons by regenerating from multiple secondary rosettes, demonstrating a predominantly polycarpic life cycle. 4. During early growth tetraploids from North America achieved greater biomass than both tetraploids and diploids from the native range but this did not manifest as larger above-ground biomass at maturity. In North American tetraploids there was also evidence of a shift towards a more strictly polycarpic life cycle, less leaf dissection, greater carbon investment per leaf, and greater seed production per capitulum. 5.Synthesis: our results suggest that the characteristics of tetraploid C. stoebe pre-adapted them (compared to diploid conspecifics) for spread and persistence of the species into habitats in North America characterized by a more continental climate. After the species’ introduction, small but potentially important shifts in tetraploid biology have occurred that may have contributed significantly to successful invasion

Foliar chemistry of juvenile Eucalyptus grandis clones does not predict chemical defence in maturing ramets

a b s t r a c t The tendency for managers of eucalypt plantations to plant large, homogeneous (i.e. clonal) stands presents a new suite of problems. Perhaps foremost among them is the elevated risk of disease or predation. One way to counter this risk is to select material with high natal resistance, such as material with high concentrations of plant secondary metabolites. This would be much simpler if we could predict future defences from the chemistry of juvenile plants. The present study aimed to determine the relationship between the concentrations of formylated phloroglucinol compounds (FPCs) in the leaves of newly established Eucalyptus grandis (Hill ex Maiden) clones in the nursery and those in the same genetic material in experimental plantations. There was almost no relationship between the concentrations of defensive chemicals in the leaves of newly established E. grandis clones growing in pots in the nursery and of those in the same genetic material growing in plantations. This implies that age effects and probable gene × environment interactions prevent evaluating the defensive qualities of clones until they are several years old and even then the results are site-specific

Canopy development and hydraulic function in Eucalyptus tereticornis grown in drought in CO2-enriched atmospheres

We report on the relationship between growth, partitioning of shoot biomass and hydraulic development of Eucalyptus tereticornis Sm. grown in glasshouses for six months. Close coordination of stem vascular capacity and shoot architecture is vital for survival of eucalypts, especially as developing trees are increasingly subjected to spasmodic droughts and rising atmospheric CO 2 levels. Trees were exposed to constant soil moisture deficits in 45 L pots (30-50% below field capacity), while atmospheric CO2 was raised to 700 μL CO2 L-1 in matched glasshouses using a hierarchical, multi-factorial design. Enrichment with CO2 stimulated shoot growth rates for 12-15 weeks in well-watered trees but after six months of CO2 enrichment, shoot biomasses were not significantly heavier (30% stimulation) in ambient conditions. By contrast, constant drought arrested shoot growth after 20 weeks under ambient conditions, whereas elevated CO 2 sustained growth in drought and ultimately doubled the shoot biomass relative to ambient conditions. These growth responses were achieved through an enhancement of lateral branching up to 8-fold due to CO2 enrichment. In spite of larger transpiring canopies, CO2 enrichment also improved the daytime water status of leaves of droughted trees. Stem xylem development was highly regulated, with vessels per unit area and cross sectional area of xylem vessels in stems correlated inversely across all treatments. Furthermore, vessel numbers related to the numbers of leaves on lateral branches, broadly supporting predictions arising from Pipe Model Theory that the area of conducting tissue should correlate with leaf area. Diminished water use of trees in drought coincided with a population of narrower xylem vessels, constraining hydraulic capacity of stems. Commensurate with the positive effects of elevated CO2 on growth, development and leaf water relations of droughted trees, the capacity for long-distance water transport also increased

Canopy development and hydraulic function in Eucalyptus tereticornis grown in drought in CO₂-enriched atmospheres

We report on the relationship between growth, partitioning of shoot biomass and hydraulic development of Eucalyptus tereticornis Sm. grown in glasshouses for six months. Close coordination of stem vascular capacity and shoot architecture is vital for survival of eucalypts, especially as developing trees are increasingly subjected to spasmodic droughts and rising atmospheric CO₂ levels. Trees were exposed to constant soil moisture deficits in 45 L pots (30–50% below field capacity), while atmospheric CO₂ was raised to 700 μL CO₂ L–1 in matched glasshouses using a hierarchical, multi-factorial design. Enrichment with CO₂ stimulated shoot growth rates for 12–15 weeks in well-watered trees but after six months of CO₂ enrichment, shoot biomasses were not significantly heavier (30% stimulation) in ambient conditions. By contrast, constant drought arrested shoot growth after 20 weeks under ambient conditions, whereas elevated CO₂ sustained growth in drought and ultimately doubled the shoot biomass relative to ambient conditions. These growth responses were achieved through an enhancement of lateral branching up to 8-fold due to CO₂ enrichment. In spite of larger transpiring canopies, CO₂ enrichment also improved the daytime water status of leaves of droughted trees. Stem xylem development was highly regulated, with vessels per unit area and cross sectional area of xylem vessels in stems correlated inversely across all treatments. Furthermore, vessel numbers related to the numbers of leaves on lateral branches, broadly supporting predictions arising from Pipe Model Theory that the area of conducting tissue should correlate with leaf area. Diminished water use of trees in drought coincided with a population of narrower xylem vessels, constraining hydraulic capacity of stems. Commensurate with the positive effects of elevated CO₂ on growth, development and leaf water relations of droughted trees, the capacity for long-distance water transport also increased.13 page(s