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.