Sorrell Brian K, Brix Hans, Orr Philip T
Murray-Darling Freshwater Research Centre, Albury NSW 2640, Australia.
Department of Plant Ecology, Institute of Biological Sciences, University of Aarhus, DK-8240 Risskov, Denmark.
New Phytol. 1997 Jul;136(3):433-442. doi: 10.1046/j.1469-8137.1997.00769.x.
The ability of diffusive gas transport and pressurized, convective flow to satisfy internal oxygen demands was examined for an aquatic sedge, Eleocharis sphacelata R. Br. Resistances to convection and diffusion through the plant were quantified from anatomical studies of the airspace dimensions, and these were used in mathematical models to calculate the fluxes required to satisfy oxygen demands measured in the tissue. The greatest resistance to diffusion in the underwater tissue was the submerged culm between the waterline and sediment surface (1560 Ms m per m culm length). Resistances of the nodal intercalary meristem (52 Ms m ) and rhizome internode (34 Ms m ) were minor. In contrast, resistances to convection were low in the culms (38 MPa s m per m culm length), and higher in the nodal meristems (93 MPa s m ). The rhizome internodes had large cortical canals with a low convective resistance (0.75 MPa s m ), and a parallel spongy pith with a very high resistance (518 MPa s m ) that is probably short-circuited by convection. The resistance of the submerged culm means that diffusion is inadequate to satisfy oxygen demands in plants growing in >10 cm of water, and that convection is therefore essential in the natural habitat of this species (water to c. 2 m depth). However, a convective oxygen influx as low as 28 × 10 mol s per culm (equivalent to a gas flow rate of 3 μl s per culm) could satisfy the entire oxygen demand of the underwater tissue; this value is well below actual rates. At this flow rate, the spongy pith in the rhizome would also remain aerobic: it has a low resistance to diffusion (73 Ms m ) and could receive sufficient oxygen by diffusion from the node. The data agree well with previous empirical measurements of convection in this species and show that diffusion and convection are both important processes for its aeration.
对一种水生莎草——黑穗荸荠（Eleocharis sphacelata R. Br.），研究了扩散性气体传输以及加压对流是否有能力满足其内部氧气需求。通过对气腔尺寸进行解剖学研究，量化了植物内部对流和扩散的阻力，并将这些阻力用于数学模型，以计算满足组织中测量到的氧气需求所需的通量。水下组织中对扩散的最大阻力存在于水线与沉积物表面之间的淹没茎（每米茎长度为1560 Ms m）。节间居间分生组织（52 Ms m）和根状茎节间（34 Ms m）的阻力较小。相比之下，茎中对流阻力较低（每米茎长度为38 MPa s m），而节间分生组织中的对流阻力较高（93 MPa s m）。根状茎节间有大型皮层通道，对流阻力较低（0.75 MPa s m），还有一个平行的海绵状髓，阻力非常高（518 MPa s m），可能会因对流而短路。淹没茎的阻力意味着扩散不足以满足生长在水深超过10厘米的植物的氧气需求，因此对流在该物种的自然栖息地（水深至约2米）中至关重要。然而，低至每茎28×10 mol s的对流氧气流入量（相当于每茎3 μl s的气体流速）就可以满足水下组织的全部氧气需求；这个值远低于实际速率。在这个流速下，根状茎中的海绵状髓也将保持有氧状态：它对扩散的阻力较低（73 Ms m），可以通过从节点扩散获得足够的氧气。这些数据与该物种先前对流的实证测量结果非常吻合，表明扩散和对流都是其通气的重要过程。
