Burkhardt J, Pariyar S
Plant Nutrition Group, Institute of Crop Science and Resource Conservation, University of Bonn, Bonn, Germany.
Plant Biol (Stuttg). 2016 Jan;18 Suppl 1:91-100. doi: 10.1111/plb.12402. Epub 2015 Oct 19.
Atmospheric vapour pressure deficit (VPD) is the driving force for plant transpiration. Plants have different strategies to respond to this 'atmospheric drought'. Deposited aerosols on leaf surfaces can interact with plant water relations and may influence VPD response. We studied transpiration and water use efficiency of pine, beech and sunflower by measuring sap flow, gas exchange and carbon isotopes, thereby addressing different time scales of plant/atmosphere interaction. Plants were grown (i) outdoors under rainfall exclusion (OD) and in ventilated greenhouses with (ii) ambient air (AA) or (iii) filtered air (FA), the latter containing <1% ambient aerosol concentrations. In addition, some AA plants were sprayed once with 25 mM salt solution of (NH4 )2 SO4 or NaNO3 . Carbon isotope values (δ(13) C) became more negative in the presence of more particles; more negative for AA compared to FA sunflower and more negative for OD Scots pine compared to other growth environments. FA beech had less negative δ(13) C than AA, OD and NaNO3 -treated beech. Anisohydric beech showed linearly increasing sap flow with increasing VPD. The slopes doubled for (NH4 )2 SO4 - and tripled for NaNO3 -sprayed beech compared to control seedlings, indicating decreased ability to resist atmospheric demand. In contrast, isohydric pine showed constant transpiration rates with increasing VPD, independent of growth environment and spray, likely caused by decreasing gs with increasing VPD. Generally, NaNO3 spray had stronger effects on water relations than (NH4 )2 SO4 spray. The results strongly support the role of leaf surface particles as an environmental factor affecting plant water use. Hygroscopic and chaotropic properties of leaf surface particles determine their ability to form wicks across stomata. Such wicks enhance unproductive water loss of anisohydric plant species and decrease CO2 uptake of isohydric plants. They become more relevant with increasing number of fine particles and increasing VPD and are thus related to air pollution and climate change. Wicks cause a deviation from the analogy between CO2 and water pathways through stomata, bringing some principal assumptions of gas exchange theory into question.
大气水汽压亏缺（VPD）是植物蒸腾作用的驱动力。植物有不同的策略来应对这种“大气干旱”。沉积在叶片表面的气溶胶可与植物水分关系相互作用，并可能影响对VPD的响应。我们通过测量液流、气体交换和碳同位素，研究了松树、山毛榉和向日葵的蒸腾作用和水分利用效率，从而探讨了植物/大气相互作用的不同时间尺度。植物在以下条件下生长：（i）在防雨的室外（OD），以及在通风的温室中，温室中有（ii）环境空气（AA）或（iii）过滤空气（FA），后者的气溶胶浓度低于环境浓度的1%。此外，一些AA植物用25 mM的（NH4）2SO4或NaNO3盐溶液喷洒一次。在存在更多颗粒的情况下，碳同位素值（δ(13)C）变得更负；与FA向日葵相比，AA向日葵的δ(13)C更负，与其他生长环境相比，OD苏格兰松树的δ(13)C更负。FA山毛榉的δ(13)C比AA、OD和用NaNO3处理的山毛榉的δ(13)C负性更小。变水的山毛榉随着VPD的增加液流呈线性增加。与对照幼苗相比，用（NH4）2SO4喷洒的山毛榉的斜率增加了一倍，用NaNO3喷洒的山毛榉的斜率增加了两倍，表明其抵抗大气需求的能力下降。相比之下，恒水的松树随着VPD的增加蒸腾速率保持恒定，与生长环境和喷洒无关，这可能是由于随着VPD增加气孔导度降低所致。一般来说，NaNO3喷洒对水分关系的影响比（NH4）2SO4喷洒更强。结果有力地支持了叶片表面颗粒作为影响植物水分利用的环境因素的作用。叶片表面颗粒的吸湿和离液性质决定了它们在气孔间形成“wick”的能力。这种wick增加了变水植物物种的非生产性水分损失，并降低了恒水植物的CO2吸收。随着细颗粒数量的增加和VPD的增加，它们变得更加重要，因此与空气污染和气候变化有关。wick导致通过气孔的CO2和水分途径之间的类比出现偏差，使气体交换理论的一些主要假设受到质疑。
