The hydraulic conductance of the leaf lamina ( K lamina ) substantially constrains whole-plant water transport, but little is known of its association with leaf structure and function. K lamina was measured for sun and shade leaves of six woody temperate species growing in moist soil, and tested for correlation with the prevailing leaf irradiance, and with 22 other leaf traits. K lamina varied from 7.40 ¥ ¥ ¥ ¥ 10-1 for Vitis labrusca sun leaves. Tree sun leaves had 15-67% higher K lamina than shade leaves. K lamina was co-ordinated with traits associated with high water flux, including leaf irradiance, petiole hydraulic conductance, guard cell length, and stomatal pore area per lamina area. K lamina was also co-ordinated with lamina thickness, water storage capacitance, 1/mesophyll water transfer resistance, and, in five of the six species, with lamina perimeter/area. However, for the six species, K lamina was independent of inter-related leaf traits including leaf dry mass per area, density, modulus of elasticity, osmotic potential, and cuticular conductance. K lamina was thus co-ordinated with structural and functional traits relating to liquid-phase water transport and to maximum rates of gas exchange, but independent of other traits relating to drought tolerance and to aspects of carbon economy.

Perennial wheat (Triticum aestivum L. × Thinopyrum spp.) and perennial rye (Secale cereale L. × S. montanum) are novel hybrid species under development as alternatives to annual cereal crops. We conducted a 2‐yr field study with a split plot design to evaluate agronomic performance, including yield, phenology, and biomass production, of perennial accessions of wheat and rye, along with annual analogs. This is one of the first studies to rigorously compare agronomic performance of 2‐yr‐old plants to 1‐yr‐old plants in perennial cereals. Perennial wheat produced 1.0 to 1.6 Mg ha−1 grain yield, 50% of annual wheat (2.7 Mg ha−1), while perennial rye produced 1.3 Mg ha−1, 73% of annual rye (1.8 Mg ha−1). Modest yields from perennials relative to annuals reflected lower harvest index, lower yield per tiller, and less kernel mass. One‐year‐old and 2‐yr‐old perennial plants had similar seed yields, yield components, and biomass production, indicating that plant age had little effect on these parameters and older plants maintained yield potential. In contrast, phenology did vary with plant age, and showed a shift toward earlier spring growth and later flowering dates in older perennial plants. This illustrates an expanded vegetative period for regrowing plants of these perennial cereals. There appears to be potential for producing an early season forage crop from these cereals, although biomass yields were not high at this site and regrowth was not always reliable. Overall, performance of perennial rye was consistent with a viable new cereal crop. On the other hand, perennial wheat requires further selection for allocation of biomass to grain and vigorous regrowth.

HighlightWe explore interactive effects of plant age and cold stress on photosynthetic rates and key photosynthetic enzymes in a herbaceous perennial in the field.

This study demonstrates that some perennial cereal species can maintain higher midseason A than their annual crop relatives. These changes are not fully explainable by increased access to soil water and may reflect trade-offs between allocation to reproduction and to resource acquisition. We also found evidence for age-related changes in photosynthetic physiology in a herbaceous perennial plant.

Newly developed perennial cereals have been developed as alternatives to annual food crops. These provide novel contexts in which to study source vs. sink limitations of plant productivity. This is one of the first investigations of source:sink effects on photosynthesis, seed size, and regrowth in perennial cereal crops as well as in the commercially important annual rye (Secale cereale L.). Through experimental manipulations of field‐grown plants, we studied the effect of manipulations of source:sink ratio (25% decreases and 100% increases) on photosynthetic rate in perennial wheat [Triticum aestivum L. × Thinopyrum elongatum (Host) D. R. Dewey], perennial rye [S. cereale × Secale strictum (C. Presl) C. Presl subsp. strictum (syn. Secale montanum Guss.)], annual wheat (Triticum aestivum L.), and annual rye. We measured carbohydrate pools, seed size, and regrowth as further indices of source vs. sink limitation. Perennial wheat showed sink limitation throughout. Annual and perennial rye appeared to be colimited. Low source:sink ratios in perennial wheat and rye were associated with up to 25% higher photosynthetic rates while high source:sink ratios led to up to 20% decreases. Seed size showed more stability under source:sink manipulation in perennials than in annuals while regrowth of perennials was not affected by source sink ratio, and all three species showed more stability of seed size in response to source:sink manipulation than annual wheat. Our results are consistent with perennial cereals operating below their maximum photosynthetic capacity, in contrast to annual wheat, and following a conservative reproductive strategy. By selecting for greater sink strength in perennial wheat, breeders may be able to achieve higher rates of photosynthesis and support higher yields in this new crop.

Previous studies have found that maximum quantum yield of CO2 assimilation (ΦCO2,max,app) declines in lower canopies of maize and Miscanthus, a maladaptive response to self-shading. These observations were limited to single genotypes, leaving it unclear that the maladaptive shade response is a general property of this C4 grass tribe, the Andropogoneae. We explored the generality of this maladaptation by testing the hypothesis that erect leaf forms (erectophiles), which allow more light into the lower canopy, suffer less of a decline in photosynthetic efficiency than drooping leaf (planophile) forms. On average, ΦCO2,max,app declined 27% in lower canopy leaves across 35 accessions, but the decline was over twice as great in planophiles than in erectophiles. The loss of photosynthetic efficiency involved a decoupling between electron transport and assimilation. This was not associated with increased bundle sheath leakage, based on 13C measurements. In both planophiles and erectophiles, shaded leaves had greater leaf absorptivity and lower activities of key C4 enzymes than sun leaves. The erectophile form is considered more productive because it allows a more effective distribution of light through the canopy to support photosynthesis. We show that in sorghum, it provides a second benefit, maintenance of higher ΦCO2,max,app to support efficient use of that light resource.

PREMISE Nucleic acid integrity can be compromised under many abiotic stresses. To date, however, few studies have considered whether nucleic acid damage and damage repair play a role in cold‐stress adaptation. A further insufficiently explored question concerns how age affects cold stress adaptation among mature perennials. As a plant ages, the optimal trade‐off between growth and stress tolerance may shift. METHODS Oxidative damage to RNA and expression of genes involved in DNA repair were compared in multiple mature cohorts of Thinopyrum intermedium (an emerging perennial cereal) and in wheat and barley under intermittent freezing stress and under nonfreezing conditions. Activity of glutathione peroxidase (GPX) and four other antioxidative enzymes was also measured under these conditions. DNA repair genes included photolyases involved in repairing ultraviolet‐induced damage and two genes involved in repairing oxidatively induced damage (ERCC1, RAD23). RESULTS Freezing stress was accompanied by large increases in photolyase expression and ERCC1 expression (in wheat and Thinopyrum) and in GPX and GR activity (particularly in Thinopyrum). This is the first report of DNA photolyases being overexpressed under freezing stress. Older Thinopyrum had lower photolyase expression and less freezing‐induced overexpression of ERCC1. Younger Thinopyrum plants sustained more oxidative damage to RNA. CONCLUSIONS Overexpression of DNA repair genes is an important aspect of cold acclimation. When comparing adult cohorts, aging was associated with changes in the freezing stress response, but not with overall increases or decreases in stress tolerance.

No abstract