Gersony Jess, Manandhar Anju, Hochberg Uri, Abdellaoui Nora, Llanos Paula, Dumais Jacques, Holbrook N Michele, Rockwell Fulton E
Department of Biological Sciences, Smith College, Northampton, MA 01060, USA.
Purdue University, Botany and Plant Pathology, West Lafayette, IN, USA.
Ann Bot. 2025 May 9;135(5):841-850. doi: 10.1093/aob/mcae221.
Nolana mollis is a dominant plant species in the hyper-arid Atacama Desert. A previous hypothesis states that N. mollis owes its success to the condensation of atmospheric water from undersaturated air onto its leaf surfaces by exuded salts, and absorption of this water by its leaves, or by shallow roots following drip onto the soil surface; living roots of N. mollis were suggested to only exist near the soil surface.
We conducted a field experiment with three treatments to establish the source of water for N. mollis: control, root cutting to block uptake of all soil moisture, and plastic skirting at the soil surface to block leaf drip of atmospheric water.
Xylem tensions monotonically increased after root cutting until the plants wilted irreversibly, diverging clearly from the skirted and control treatments showing diurnal patterns of increasing tension in the day followed by recovery overnight.
Hydration in N. mollis requires access to deep soil water, motivating an alternative hypothesis: imperfect salt exclusion at the root surface and salt exudation by the leaf results in less root fouling and lower xylem tensions, while during the day evaporation of the surface brine, condensed overnight, increases the water use efficiency of carbon gain.
软刺假茄是极度干旱的阿塔卡马沙漠中的优势植物物种。之前的一种假说认为，软刺假茄的成功归因于其通过分泌盐分将大气中的水分从不饱和空气中凝结到叶片表面，然后叶片或土壤表面滴落后的浅根吸收这些水分；有人认为软刺假茄的活根仅存在于土壤表层附近。
我们进行了一项田间试验，设置了三种处理方式来确定软刺假茄的水源：对照组、切断根系以阻断对所有土壤水分的吸收，以及在土壤表面设置塑料裙边以阻断叶片对大气水分的截留。
切断根系后，木质部张力单调增加，直至植株不可逆转地枯萎，这与设置裙边处理和对照处理明显不同，后两者呈现出白天张力增加、夜间恢复的昼夜模式。
软刺假茄的水分供应需要获取深层土壤水分，由此引出另一种假说：根系表面盐分排除不完全以及叶片盐分分泌导致根系污染减少和木质部张力降低，而在白天，夜间凝结的表层盐水蒸发，提高了碳同化的水分利用效率。
