Wheat plants (Triticum aestivum) were grown for 43 days in a micro-porous tube nutrient delivery system. Roots were unable to penetrate the microporous tube, but grew on the surface and maintained capillary contact with the nutrient solution on the inside of the tube through the 5-μm pores of the porous tube. Water potential in the system was controlled at −0.4, −0.8, and −3.0 kPa by adjusting the applied pressure (hydrostatic head) to the nutrient solution flowing through the microporous tubes. A relatively small decrease in applied water potential from −0.4 to −3.0 kPa resulted in a 34% reduction of shoot growth but only a moderate reduction in the midday leaf water potential from −1.3 to −1.7 MPa. Carbon dioxide assimilation decreased and water use efficiency increased with the more negative applied water potentials, while intercellular CO2 concentration remained constant. This was associated with a decrease in stomatal conductance to water vapor from 1.90 to 0.98 mol m−2s−1 and a decrease in total apparent hydraulic conductance from 47 to 12 μmol s−1MPa−1. Although the applied water potentials were in the −0.4 to −3.0 kPa range, the actual water potential perceived by the plant roots appeared to be in the range of −0.26 to −0.38 MPa as estimated by the leaf water potential of bagged plants. The amount of K, Ca, Mg, Zn, Cu, and B accumulated with each unit of transpired water increased as the applied water potential became less negative. The increase in accumulation ranged from 1.4-fold for K to 2.2-fold for B. The physiological responses observed in this study in response to small constant differences in applied water potentials were much greater than expected from either the applied water potential or the observed plant water potential. Even though the micro-porous tube may not represent natural conditions and could possibly introduce morphological and physiological artifacts, it enables a high degree of control of water potential that facilitates the investigation of many aspects of water relations not practical with other experimental systems.

中文翻译：

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水的关系、气体交换和对长期持续缺水的营养反应

小麦植物 (Triticum aestivum) 在微孔管养分输送系统中生长 43 天。根不能穿透微孔管，但在表面生长并通过多孔管的 5-μm 孔与管内部的营养液保持毛细管接触。通过调节流经微孔管的营养液的压力（静水压头），将系统中的水势控制在 -0.4、-0.8 和 -3.0 kPa。应用水势从 -0.4 到 -3.0 kPa 的相对较小的下降导致芽生长减少 34%，但中午叶水势从 -1.3 到 -1.7 MPa 仅适度降低。二氧化碳同化减少，水利用效率随着施加的水势越负而增加，而细胞间二氧化碳浓度保持不变。这与气孔对水蒸汽的传导率从 1.90 降低到 0.98 mol m-2s-1 以及总表观水力传导率从 47 降低到 12 μmol s-1MPa-1 相关。尽管施加的水势在 -0.4 至 -3.0 kPa 范围内，但根据袋装植物的叶水势估计，植物根部感知的实际水势似乎在 -0.26 至 -0.38 MPa 的范围内。随着施加的水势变得不那么负，随着每单位蒸腾水积累的 K、Ca、Mg、Zn、Cu 和 B 的量增加。积累的增加范围从 K 的 1.4 倍到 B 的 2.2 倍。在这项研究中观察到的生理反应响应于施加的水势的微小恒定差异，远远大于从施加的水势或观察到的植物水势所预期的。尽管微孔管可能不代表自然条件，并且可能会引入形态和生理伪影，但它可以对水势进行高度控制，从而有助于研究其他实验系统不实用的水关系的许多方面。