Physiological responses of four hazelnut hybrids to water availability in Nebraska

Responses of hazelnut hybrids (88BS, BOX1, G17, and GEL502) to water availability (watered and nonwatered) were examined in the field. The study site received 35% of long-term average precipitation between July and September. Photosynthesis (A), stomatal conductance (g_s), water potential (Ψ), and specific leaf area were generally lower in the nonwatered than in the watered treatment and exhibited significant seasonal decline, which was accompanied by an increase in water use efficiency (WUE) under both water treatments. Hybrids exhibited different strategies to cope with water availability. The hybrid 88BS was more water conserving, with the most decline in g_s, the least gradient in Ψ, and the lowest discrimination against ¹³C than in the remaining hybrids, indicating that 88BS responded to drought by increasing WUE and conserving water. BOX1 was more of a water spender, maintaining both higher g_s and A, low sensitivity of g_s to vapor pressure deficit (VPD) increase, largest gradient in Ψ, and the most negative carbon isotope ratio, indicating a higher capacity to absorb soil water and reach limited resources. GEL502 and G17 were more affected by water stress than were 88BS or BOX1. We conclude that relatively drought-resistant hazelnut hybrids suitable for the Great Plains can be identified for successful plantations.