Abstract
Shoots and foliage elements of shade‐intolerant conifers strongly vary in size, but the effects of size on shoot light‐harvesting efficiency have not been quantified. We investigated shoot adaptation to seasonal average integrated quantum flux density in gymnosperms Pinus palustris Mill., P. patula Schlect. & Cham., and P. radiata D. Don. and angiosperm Casuarina glauca Sieb. ex Spreng. In addition, P. sylvestris L., sampled from infertile and fertile sites, and P. taeda L. were included to test for general correlations among shoot architecture and size. All studied species possess needle‐like photosynthetic elements. A shoot model was fitted to the data to separate the determinants of shoot light‐harvesting efficiency. The model estimated shoot light harvesting on the basis of angular distribution of foliage surface areas, degree of spatial clumping, foliage area density in shoot volume, and beam path length in shoot volume. Increases in irradiance primarily led to greater foliage aggregation, greater foliage area density in shoot volume, and to a minor degree, to changes in foliage area angular distribution. Greater foliage aggregation resulted in lower efficiency of light harvesting but greater investment of foliar biomass in high light where the photosynthetic returns are greater. The species behave similarly except that the light‐harvesting characteristics of P. patula, which has long, strongly bending needles, were independent of light. In all species, the shoots were larger in higher irradiance, and the fraction of biomass in shoot axis increased with increasing irradiance, indicating greater costs for light harvesting in high light. There were further significant species differences in light‐harvesting efficiency that were linked to differences in foliage and shoot size. Foliage element length varied between 1.1 and 31.4 cm and shoot axis length between 1.2 and 36.5 cm among the species, leading to 4 orders of magnitude variation in shoot cylinder volume and three orders of magnitude variation in foliage area density (ρ); ρ decreased with increasing foliage element length and shoot volume. The degree of foliage clumping scaled positively with ρ and negatively with foliage element length. Foliage clumping was positively associated with foliage dry mass to shoot silhouette area ratio, signifying a trade‐off between efficient light harvesting and large photosynthetic biomass accumulation. These data demonstrate a general increase of light‐harvesting efficiency with increasing length of foliage elements, but they also demonstrate that this increase is limited by enhanced bending of longer foliage elements and by augmented support costs.
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Claims 18
Claim · model-written summary
Higher irradiance increased foliage aggregation and area density.
Verbatim
e0“Increases in irradiance primarily led to greater foliage aggregation, greater foliage area density in shoot volume”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Higher irradiance altered foliage area angular distribution to a minor degree.
Not reportedDirection
Verbatim
e0“Increases in irradiance primarily led to greater foliage aggregation, greater foliage area density in shoot volume, and to a minor degree, to changes in foliage area angular distribution.”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Greater foliage aggregation lowered light harvesting efficiency.
Verbatim
e0“Greater foliage aggregation resulted in lower efficiency of light harvesting”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Greater aggregation accompanied greater foliar biomass investment in high light.
Verbatim
e0“greater investment of foliar biomass in high light where the photosynthetic returns are greater”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
P. patula light harvesting characteristics were independent of light.
- Taxon
- P. patula
Pinus patulae0 - Treatment
- lighte0
- Outcome
- light‐harvesting characteristicse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the light‐harvesting characteristics of P. patula, which has long, strongly bending needles, were independent of light.”
Claim · model-written summary
Shoots were larger at higher irradiance across species.
Verbatim
e0“In all species, the shoots were larger in higher irradiance”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Shoot axis biomass fraction increased with irradiance.
Verbatim
e0“the fraction of biomass in shoot axis increased with increasing irradiance”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Species differed significantly in light harvesting efficiency linked to foliage and shoot size.
Not reportedDirection
Verbatim
e0“There were further significant species differences in light‐harvesting efficiency that were linked to differences in foliage and shoot size.”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Foliage element length ranged from 1.1 to 31.4 cm.
Verbatim
e0“Foliage element length varied between 1.1 and 31.4 cm”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Shoot axis length ranged from 1.2 to 36.5 cm.
Verbatim
e0“shoot axis length between 1.2 and 36.5 cm”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Shoot cylinder volume varied four orders of magnitude.
Verbatim
e0“4 orders of magnitude variation in shoot cylinder volume”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Foliage area density varied three orders of magnitude.
Verbatim
e0“three orders of magnitude variation in foliage area density”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Foliage area density fell with foliage length and shoot volume.
Verbatim
e0“ρ decreased with increasing foliage element length and shoot volume.”
e1“foliage area density (ρ)”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Foliage clumping scaled positively with foliage area density.
Verbatim
e0“The degree of foliage clumping scaled positively with ρ”
e1“foliage area density (ρ)”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Foliage clumping scaled negatively with foliage element length.
Verbatim
e0“The degree of foliage clumping scaled positively with ρ and negatively with foliage element length.”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Foliage clumping was positively associated with foliage dry mass to silhouette area ratio.
Verbatim
e0“Foliage clumping was positively associated with foliage dry mass to shoot silhouette area ratio”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Light harvesting efficiency generally increased with foliage element length.
Verbatim
e0“a general increase of light‐harvesting efficiency with increasing length of foliage elements”
t0“Shade‐Intolerant Conifers”
Claim · model-written summary
Bending of longer foliage elements and support costs limited the efficiency gain.
Verbatim
e0“this increase is limited by enhanced bending of longer foliage elements and by augmented support costs.”
e1“light‐harvesting efficiency with increasing length of foliage elements”
t0“Shade‐Intolerant Conifers”