Lie-ins or early bedtimes : Do either affect how grasses perform in solar parks?

Owston, Nicole and Taylor, Samuel and Armstrong, Alona (2025) Lie-ins or early bedtimes : Do either affect how grasses perform in solar parks? Masters thesis, Lancaster University.

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Abstract

Agrivoltaics combines solar infrastructure with agriculture. Fixed bifacial, north–south oriented panel rows expose plants to temporally structured morning or afternoon shade. Whether plants benefit from a "lie-in" (morning shade) or an "early bedtime" (afternoon shade) is unknown, despite contrasting physiological demands. A trait-based approach using glasshouse and field experiments investigated whether forage species outcomes differ under temporally structured shade. Glasshouse experiments characterised photosynthetic induction, hydraulic, stomatal, and leaf structural traits of eight temperate forage species: Timothy (Phleum priatense); Cocksfoot (Dactylis glomerata); Meadow fescue (Festuca pratensis); Tall fescue (Festuca arundinacea); Perennial ryegrass (Lolium perenne); Italian ryegrass (Lolium multiflorum); Hybrid ryegrass (Lolium × hybridum), and white Clover (Trifolium repens). Stomatal opening time varied eightfold; stomatal limitation ninefold. Maximum contrasts were between Timothy (fast) and Clover (slow stomata). Principal component analysis explained 80.6% of variation and was dominated by contrasts between grasses and the sole dicot, Clover. When Clover was excluded, stomatal size and density, leaf mass per area (LMA), and leaf hydraulic conductance predicted dynamic performance among grasses. Field experiments examined four species (Timothy, Clover, Italian ryegrass and Perennial ryegrass) under morning and afternoon shade treatments reducing daily light integrals by c. 26%. Species explained 88% of multivariate trait variation, and treatment effects 4%. Timothy produced 69% more biomass under afternoon shade despite minimal plasticity in leaf traits. Clover showed no biomass gains but high plasticity in LMA. Jointly, experiments revealed kinetic speed alone did not predict biomass responses: Perennial ryegrass showed fast opening (6.3 min) but no biomass gain, whereas Italian ryegrass achieved +24% despite intermediate kinetics (11.5 min). This first trait-based framework for forage species selection in temperate agrivoltaic systems demonstrates that an 'early bedtime' benefits species whose stomatal kinetics, hydraulic traits, and leaf structure are coordinated for exploiting concentrated morning light, while a 'lie-in' offers no comparable advantage.