Biochar and K‐fertigation modulate stomatal behaviour, ion homeostasis and water use efficiency in waxy maize seedlings under salt stress

ABSTRACT

K‐fertigation and soil amendment could ameliorate the adverse effects of saline stress on C ₄ crop physiology and performance, yet the underlying mechanisms remained largely elusive. This study investigated the interactive effects of two K‐fertigation regimes (full irrigation and deficit irrigation regime during K‐fertigation (FIK and DIK)) combined with two soil amendments (no (CK) and wheat straw biochar (WSB) amendment) on ABA signal, non‐stomatal limitation, gas exchange, water use efficiency (WUE) and ion homeostasis in C ₄ crops waxy maize seedlings under two salt stress levels (non‐salt stress, 0 mM NaCl and salt stress, 120 mM NaCl), totalling eight treatments, each with four biological replicates. The results indicated that salt stress and DIK conjointly reduced 48.19% gas exchange rates, 50.68% water relations and 94.34% leaf K/Na ratio, while increasing 6.37% leaf abscisic acid concentration ([ABA _l ]), 22.59% non‐stomatal limitation, 1.38% stomatal density and 16.54% carbon isotope discrimination. WSB notably increased 24.26% leaf photosynthetic capacity under salt stress and DIK, primarily by elevating 78.98% [ABA _l ] and thereby reducing 4.07% non‐stomatal limitation. Moreover, WSB improved 21.05% plant WUE and presented a synergistic effect when associated with the DIK regime, achieving a 7.96% higher plant WUE than either single factor. WSB reduced 30.41% leaf Na ⁺ accumulation and increased 59.70% leaf K/Na ratio to recover salt‐impaired ion homeostasis. These findings would provide some novel insights for efficient water use and ion homeostasis in C ₄ waxy maize seedlings under soil drying and salinity and support further field investigation.