水稻根系通气组织与根系泌氧及根际硝化作用的关系

通过根箱土培试验研究了不同产量籼稻品种中旱22(ZH,高产品种)及禾盛10号(HS,低产品种)苗期根系生长、通气组织发育、根系径向泌氧量(radial oxygen loss,ROL)以及根表和根际土壤硝化强度差异。结果表明,除水稻播种40 d时二者根数量和根干重无显著差异外,ZH根直径、根数量和根干重均显著高于HS,二者差异尤其表现在根系生物量差异。两个水稻品种在距根尖20 mm处均可见辐射状通气组织,ZH皮层薄壁细胞已经完全崩溃形成连接中柱和外皮层的纵向气腔,而HS皮层薄壁细胞未发生完全离解,但仍能观察到明显的连接中柱和外皮层的纵向气腔的形成。同时ZH外皮层厚壁细胞体积较小,排列紧密,细胞壁增厚程度大;而HS外皮层厚壁细胞体积相对较大,排列疏松,细胞壁增厚程度相对较小。表明高产品种通气组织发育比低产品种更加完善,表现为ZH根孔隙度(porosity of root,POR)显著高于HS,且高产品种对水稻根系ROL的屏蔽作用较低产品种更强,为根系提供更充足的氧气供应,促进根系生长。除了水稻播种后40 d时ZH和HS单根ROL无显著差异外(P<0.05),ZH单株、单位重量以及单根ROL均显著高于HS(P<0.01)。两个水稻品种硝化强度均表现为根际土壤显著高于根表土壤 (P<0.01),前者大约是后者的3-6倍。两个品种根表土壤硝化强度无显著差异,而ZH根际土壤硝化强度均显著高于HS。相关性分析结果表明水稻根际土壤硝化强度和整株水稻ROL呈极显著正相关关系(r=0.803,P<0.01),和水稻POR也呈现极显著正相关关系(r=0.808,P<0.01),同时和根系直径、数量和干重均呈极显著正相关关系(P<0.01)。而根表土壤硝化强度和以上指标均无相关关系。由于硝化作用是好氧过程,因此高产品种由于根系发达,通气组织发育好,相应ROL也较大,造成根际土壤氧气含量高,从而可能导致根际土壤硝化强度显著高于低产品种。

Relationship among rice root aerechyma, root radial oxygen loss and rhizosphere nitrification

A soil culture experiment with rhizobox was carried out to study the difference of rice root growth, aerenchyma development, root radial oxygen loss (ROL) and root surface and rhizosphere nitrification activities. Two Indica varieties with different yield potentials, Zhonghan 22 (ZH, high yield) and Hesheng 10 (HS, low yield) were used and the samples were collected at 40, 50 and 60 d after sowing. The results showed that root diameter, root number and root dry weight of ZH were always significantly greater than those of HS, expect for the root number and root dry weight at 40 d after sowing. The radial-arrangement aerenchyma tissues were examined at 20 mm behind root tips. The parenchyma cells of ZH entirely collapsed and the radial cell wall aggregated together to form a gas-filled space connected the stele and exodermis, while the parenchyma cells of HS partially collapsed and a gas-filled space connected the stele and exodermis was formed with the residual parenchyma cells and aggregated cell walls. The volume of porosity of root (POR) of ZH was significantly higher than that of HS, indicating better developed aerenchyma for ZH. The cortical prothenchyma cell (ROL barrier) size of ZH was relatively small and closely arranged, and the thickening effect for the cell wall was obvious, whereas that of HS was big and loosely arranged, suggesting that a strong ROL barrier effect is important to provide sufficient oxygen for rice root growth. Except for the difference of ROL per root between ZH and HS at 40 d after sowing, the ROL per plant, ROL per dry weight and ROL per root measured at 40, 50 and 60 d after sowing for ZH were always significantly higher than those for HS (P< 0.01). Rhizosphere nitrification activities of both varieties were 3 to 6 times higher than those measured in the root surface soil. Although there had no significant difference of root surface soil nitrification activities between these varieties, the rhizosphere nitrification activities for ZH were generally twice as high as those for HS, and appeared to be significantly correlated to rice ROL per plant, POR, root diameter, root number and root dry weight (r= 0.803, 0.808, 0.637, 0.646 and 0.696, respectively, P< 0.01). Because the nitrification prefers aerobic environment, the rice variety with well-developed root system and aerenchyma as well as correspondingly high ROL allows relatively high oxygen entering rhizosphere soil, which might improve rhizosphere nitrification activities.