红壤区不同产量籼稻品种苗期根表和根际土壤硝化特征

以不同产量籼稻品种中旱22(ZH,高产品种)和禾盛10号(HS,低产品种)为材料,采用根际培养箱(三室)--速冻切片技术研究了红壤水稻土种植条件下,水稻苗期生长、氮素积累和氮素利用率(NUE)、根孔隙度(POR)、根际土壤矿质态氮含量和硝化强度.结果表明,ZH苗期生长、氮素吸收及NUE均显著优于HS,且ZH单株不定根数量及根系通气组织发育程度(用POR表示)均显著高于HS.ZH根际和土体土壤中铵(NH+4)含量始终低于HS,而硝(NO-3)含量则始终高于HS,但二者根表土壤NH+4和NO-3含量均无显著差异.ZH和HS硝化强度最大发生部位均是在距根表2 mm的根际土壤,分别为:0.48 μmol kg-1h-1和0.31 μmol kg-1h-1.随着距根表越远,硝化强度就越弱,直至距根表10～20 mm处土壤硝化强度就接近于土体土壤.ZH根际土壤硝化强度始终显著高于HS,但二者根表和土体土壤硝化强度均无显著差异.与不种水稻的CK相比,根际土壤硝化强度提高了约2～3.5倍.尽管红壤水稻土硝化作用很弱,但红壤区水稻根际硝化作用与水稻苗期生长和氮素营养密切相关.

Research on characteristics of root surface and rhizosphere nitrification for Indica cultivars with different yield potential at the seedling stage in red soil regions

Two different Indica cultivars, Zhong Han 22 (ZH, high yield) and He Sheng 10 (HS, low yield) popularly planted in red paddy soil were used to study nitrogen (N) nutritional characteristics using a rhizobox with three compartments and a soil-slicing method. Rice plant biomass, N accumulation, N use efficiency (NUE), porosity of root (POR), rhizosphere mineral N concentration and nitrification activity were determined at 40, 50 and 60 d after sowing. The results obtained were showed as follows. The rice plant biomass, N accumulation, NUE and number of adventitious roots per plant for ZH were all superior to HS. Furthermore, aerenchyma development (expressed as POR) of ZH was also much better than that of HS. The ammonium (NH+4) concentrations in rhizosphere and bulk soil for ZH were much lower than those for HS, but the reverse was true for nitrate (NO-3). The mineral N (NH+4 and NO-3) concentrations in root surface soil were not significantly different between ZH and HS. Interestingly, the maximal nitrification activities were always found at the distance of 2 mm away from the root surface, and they were 0.48 and 0.31 μmol kg-1h-1 for ZH and HS, respectively. The nitrification activity decreased with the increasing distance from the root surface, and it was almost the same at the zone of 10-20 mm away from the root surface as the bulk soil. The rhizosphere nitrification activities for ZH were always much higher than HS, while there had no statistically significant difference of nitrification activity in root surface and bulk soil between both rice cultivars. Compared with the CK (rice plant free), the rhizosphere nitrification activities increased for 2-3.5 times. Although rhizosphere nitrification happened in red paddy soil was very weak, it might be important for rice growth and N nutrition at the seedling stage.