Why are tropical conifers disadvantaged in fertile soils? Comparison of Podocarpus guatemalensis with an angiosperm pioneer, Ficus insipida

Conifers are, for the most part, competitively excluded from tropical rainforests by angiosperms. Where they do occur, conifers often occupy sites that are relatively infertile. To gain insight into the physiological mechanisms by which angiosperms outcompete conifers in more productive sites, we grew seedlings of a tropical conifer (Podocarpus guatemalensis Standley) and an angiosperm pioneer (Ficus insipida Willd.) with and without added nutrients, supplied in the form of a slow-release fertilizer. At the conclusion of the experiment, the dry mass of P. guatemalensis seedlings in fertilized soil was approximately twofold larger than that of seedlings in unfertilized soil; on the other hand, the dry mass of F. insipida seedlings in fertilized soil was ~20-fold larger than seedlings in unfertilized soil. The higher relative growth rate of F. insipida was associated with a larger leaf area ratio and a higher photosynthetic rate per unit leaf area. Higher overall photosynthetic rates in F. insipida were associated with an approximately fivefold larger stomatal conductance than in P. guatemalensis. We surmise that a higher whole-plant hydraulic conductance in the vessel bearing angiosperm F. insipida enabled higher leaf area ratio and higher stomatal conductance per unit leaf area than in the tracheid bearing P. guatemalensis, which enabled F. insipida to capitalize on increased photosynthetic capacity driven by higher nitrogen availability in fertilized soil.

Leaf growth in early development is key to biomass heterosis in Arabidopsis

Arabidopsis thaliana hybrids have similar properties to hybrid crops, with greater biomass relative to the parents. We asked whether the greater biomass was due to increased photosynthetic efficiency per unit leaf area or to overall increased leaf area and increased total photosynthate per plant. We found that photosynthetic parameters (electron transport rate, CO2 assimilation rate, chlorophyll content, and chloroplast number) were unchanged on a leaf unit area and unit fresh weight basis between parents and hybrids, indicating that heterosis is not a result of increased photosynthetic efficiency. To investigate the possibility of increased leaf area producing more photosynthate per plant, we studied C24×Landsberg erecta (Ler) hybrids in detail. These hybrids have earlier germination and leaf growth than the parents, leading to a larger leaf area at any point in development of the plant. The developing leaves of the hybrids are significantly larger than those of the parents, with consequent greater production of photosynthate and an increased contribution to heterosis. The set of leaves contributing to heterosis changes as the plant develops; the four most recently emerged leaves make the greatest contribution. As a leaf matures, its contribution to heterosis attenuates. While photosynthesis per unit leaf area is unchanged at any stage of development in the hybrid, leaf area is greater and the amount of photosynthate per plant is increased.

How functional traits influence plant growth and shade tolerance across the life cycle

Plant species differ in many functional traits that drive differences in rates of photosynthesis, biomass allocation, and tissue turnover. However, it remains unclear how—and even if—such traits influence whole-plant growth, with the simple linear relationships predicted by existing theory often lacking empirical support. Here, we present a theoretical framework for understanding the effect of diverse functional traits on plant growth and shade tolerance by extending a widely used model, linking growth rate in seedlings with a single leaf trait, to explicitly include influences of size, light environment, and five prominent traits: seed mass, height at maturation, leaf mass per unit leaf area, leaf nitrogen per unit leaf area, and wood density. Based on biomass growth and allocation, this framework explains why the influence of traits on growth rate and shade tolerance often varies with plant size and why the impact of size on growth varies among traits. Specifically, we demonstrate why for height growth the influence of: (i) leaf mass per unit leaf area is strong in small plants but weakens with size; (ii) leaf nitrogen per unit leaf area does not change with size; (iii) wood density is present across sizes; (iv) height at maturation strengthens with size; and (v) seed mass decreases with size. Moreover, we show how traits moderate plant responses to light environment and also determine shade tolerance, supporting diverse empirical results.

Divergent drivers of leaf trait variation within species, among species, and among functional groups

Understanding variation in leaf functional traits—including rates of photosynthesis and respiration and concentrations of nitrogen and phosphorus—is a fundamental challenge in plant ecophysiology. When expressed per unit leaf area, these traits typically increase with leaf mass per area (LMA) within species but are roughly independent of LMA across the global flora. LMA is determined by mass components with different biological functions, including photosynthetic mass that largely determines metabolic rates and contains most nitrogen and phosphorus, and structural mass that affects toughness and leaf lifespan (LL). A possible explanation for the contrasting trait relationships is that most LMA variation within species is associated with variation in photosynthetic mass, whereas most LMA variation across the global flora is associated with variation in structural mass. This hypothesis leads to the predictions that (i) gas exchange rates and nutrient concentrations per unit leaf area should increase strongly with LMA across species assemblages with low LL variance but should increase weakly with LMA across species assemblages with high LL variance and that (ii) controlling for LL variation should increase the strength of the above LMA relationships. We present analyses of intra- and interspecific trait variation from three tropical forest sites and interspecific analyses within functional groups in a global dataset that are consistent with the above predictions. Our analysis suggests that the qualitatively different trait relationships exhibited by different leaf assemblages can be understood by considering the degree to which photosynthetic and structural mass components contribute to LMA variation in a given assemblage.

Trajectories: how functional traits influence plant growth and shade tolerance across the life-cycle

Plant species differ in many functional traits that drive differences in rates of photosynthesis, biomass allocation, and tissue turnover. Yet, it remains unclear how – and even if – such traits influence whole-plant growth, with the simple linear relationships predicted by existing theory often lacking empirical support. Here we present a new theoretical framework for understanding the effect of diverse functional traits on plant growth and shade-tolerance, extending a widely-used theoretical model that links growth rate in seedlings with a single leaf trait to explicitly include influences of size, light environment, and five other prominent traits: seed mass, height at maturation, leaf mass per unit leaf area, leaf nitrogen per unit leaf area, and wood density. Based on biomass production and allocation, this framework explains why the influence of prominent traits on growth rate and shade tolerance often varies with plant size and why the impact of size on growth varies among traits. Considering growth rate in height, we find the influence of: i) leaf mass per unit leaf area is strong in small plants but weakens with size, ii) leaf nitrogen per unit leaf area does not change with size, iii) wood density is present across sizes but is strongest at intermediate sizes, iv) height at maturation strengthens with size, and v) seed mass decreases with size. Moreover, we show how traits moderate plant responses to light environment and also determine shade tolerance, supporting diverse empirical results. By disentangling the effects of plant size, light environment and traits on growth rates, our results provide a solid theoretical foundation for trait ecology and thus provide a platform for understanding growth across diverse species around the world.

Growth Analysis and Photosynthesis Measurements of Cucumber Seedlings Grown under Light with Different Red to Far-red Ratios

Light with a higher red to far-red ratio (R:FR) than sunlight reduces plant growth, but the cause has not been firmly established. In the present study, cucumber seedlings were grown under normal light (similar to sunlight; R:FR = 1.4) from metal-halide lamps or high-R:FR light (R:FR = 4.3) created by transmitting their light through FR-absorbing film, and then their growth parameters and photosynthesis were compared. The relative growth rate (RGR) at high R:FR was 92% of that under normal R:FR, although the net assimilation rate (NAR) did not differ between the treatments, indicating that changes in net photosynthesis per unit leaf area did not cause the growth inhibition at high R:FR. The CO2 exchange per unit leaf area did not differ between the treatments, which supports this hypothesis. The leaf area ratio (LAR) of total plant dry weight of high R:FR seedlings to that of normal R:FR seedlings was also 92%. This suggests that growth suppression in the high R:FR seedlings was caused mainly by decreased LAR. The specific leaf area (SLA) and leaf weight ratio (LWR), components of LAR, under high-R:FR light were 89% and 105%, respectively, of those under normal light, indicating that the smaller LAR at high R:FR mainly results from suppressed leaf enlargement per unit leaf dry matter.

Analysis of Carbon Sequestration and Oxygen Release Capabilities of 25 Afforestation Plants in Tianjin

CI-340 portable photosynthesis test system and JYM-B leaf area meter were employed to observe the physiological velocity and leaf area index of 25 widely used afforestation plants in Tianjin. The results indicate that the diurnal change curve of net photosynthesis rates of 25 experimental species has one or two peaks. The daily carbon sequestration and oxygen release per unit leaf area are respectively 3.98-13.01 g/( m2·d) and 2.9-9.46 g/( m2·d). Among arbors, the order of carbon sequestration and oxygen release capabilities per unit leaf area is Ulmus pumila >Fraxinus velutina>Sophora japonica>Salix matsudana f. pendula>Malus micromalus cv.‘American’>Koelreuteria paniculata>Acer truncatum>Ulmus pumila cv. ‘jinye’>Prunus davidiana>Malus micromalus>Cotinus coggygria > Rhus typhina> Platanus orientalis>Catalpa speciosa>Diospyros kaki> Morus alba cv. ‘Tortuosa’. Among shrubs, the order is Weigela florida>Euonymus japonicus>Cercis chinensis>Ligustrum vicaryi >Sorbaria sorbifolia> Syringa oblata > Lonicera maackii >Cornus alba>Lonicera japonica.

Effects of different bud loading levels on the yield, leaf and fruit characteristics of Hayward kiwifruit

The effects of different levels of bud loading on the yield and some leaf and fruit characteristics in Hayward cultivar (A. deliciosa) in the province of Ordu, Turkey were examined during two growing seasons in 2000–2001. Six years old kiwifruit vines were pruned to carry the loads of 120, 180, 240 or 300 buds/vine on the canes with 12 buds. The study determined probable total leaf area (PTLA), probable total leaf number (PTLN), probable total leaf weight (PTLW) and yield per vine. Mean fruit weight (MFW) and soluble solid contents (SSC, %) of fruits were expressed. In addition, unit leaf area/100 g fruit weight (ULA/FW) was calculated. Leaf characteristics were examined in 3 periods of the growing season. Correlations between yield, leaf and fruit characteristics and treatments were determined. The result of the experiment, namely mean leaf area (MLA), mean leaf weight (MLW), PTLA, PTLN, PTLW ranged between 185.51–194.17 cm², 7.98–8.67 g, 21.047–58.61 m²/vine, 1,129.6–3,035.3 number/vine, 9.04–25.68 kg/vine, respectively. The mean yields of vines loaded with 120 and 300 buds were 34.84 and 100.96 kg/vine (12.19 and 35.34 ton/ha), respectively. Mean leaf area and mean leaf weight increased with increasing levels of bud loading, whereas MFW and ULA/FW decreased. There was a negative relationship between MFW, SSC and yield, and a positive relationship between MLA, PTLA and yield. ULA/FW ratio was between 581.88–611.54 cm²according to the bud loading level. Fruit size diminished as a consequence of dense canopies in both levels of bud loading (120 and 300 buds/vine). Unit leaf area per fruit weight ranged between 581.88–611.54 cm²/100 g, with respect to the bud loading applications. Increasing levels of bud loading resulted in reduced ULA/FW ratio and affected yield and some leaf and fruit characteristics.