苗期干旱胁迫下施氮对玉米氮素吸收和土壤生物化学性质的影响

研究苗期干旱胁迫下施氮对东北春玉米氮素吸收利用和土壤生物化学性质的影响,为区域玉米养分管理与逆境调控提供依据。研究设置水、氮二因素盆栽试验,土壤水分包括3个水平:田间持水量的30%(W0),50%(W1)和70%(W2);施氮量包括2个水平:不施氮(N0)和施氮0.24 g/kg(N1),测定不同水氮条件下玉米苗期的植株干重和氮素吸收、根际和非根际土壤的化学性质、微生物量碳、氮(MBC、MBN)及土壤酶活性。结果表明:干旱胁迫显著降低玉米苗期植株干重和氮素吸收量,其中W0条件降幅最大(分别为51.1%,43.8%)。施氮促进各水分条件下植株生长,且与水分存在显著交互作用,W2条件下施氮后植株干重和氮素吸收量的增幅最高(分别为53.7%,83.2%)。干旱胁迫提高植株的水分利用效率,但降低氮肥利用效率。施氮显著提高W2条件植株的水分利用效率,但干旱条件下则无显著影响。水、氮及其交互作用对土壤性质的影响较为复杂。总体上,苗期干旱胁迫暂时提高了根际和非根际土壤pH,显著增加根际土壤的铵态氮和硝态氮含量。MBC、MBN对干旱胁迫的响应在根际与非根际土壤之间存在相反趋势,根际土壤随干旱程度增加而提高,非根际土壤则随之下降。土壤酶活性方面,干旱胁迫显著影响根际土壤的硝酸还原酶和亚硝酸还原酶活性。施氮增加所有水分条件下根际和非根际土壤的pH和铵态氮、硝态氮含量,其中根际土壤的增幅高于非根际土壤。施氮显著增加各水分条件下根际和非根际土壤的MBC、MBN、脲酶和硝酸还原酶活性,但显著降低根际和非根际土壤亚硝酸还原酶活性。水氮交互作用显著影响根际土壤的亚硝酸还原酶、非根际土壤的脲酶、亚硝酸还原酶和FDA水解酶活性。根际、非根际土壤各生物化学性质之间均存在显著的相关关系,而且根际土壤除土壤亚硝酸还原酶外的各指标均与植株氮素吸收和氮肥利用效率呈正相关。苗期干旱显著抑制玉米植株生长和氮素吸收,并对土壤生物、化学性质造成显著影响。施氮对植株和土壤性质的影响在不同水分条件下存在差异,而且植株表现与土壤生物、化学性质之间存在显著相关关系。

Effects of Nitrogen Application on Maize Nitrogen Uptake and Soil Biological and Chemical Properties Under Drought Stresses at Seedling Stage

The objective of this study was to explore the effects of nitrogen application on spring maize nitrogen uptake and soil biological and chemical properties under drought stresses at seedling stage in Northeast China. The results might provide a basis for regional maize nutrient management and adversity regulation. In this study, a pot experiment was conducted with two factors of water and nitrogen. The soil water level included 30%, 50% and 70% of field capacity (W0, W1 and W2), respectively, and nitrogen application included 0 and 0.24 g/kg soil (N0 and N1), respectively. The shoot dry matter and nitrogen uptake of maize at the seedling stage, soil chemical properties, microbial biomass carbon, nitrogen (MBC, MBN) and soil enzymes activities in the rhizosphere and bulk soil were measured in different water and nitrogen conditions. The results showed that drought stresses significantly reduced maize shoot dry matter and nitrogen uptake at seedling stage, and W0 condition decreased the most (51.1%, 43.8% respectively). Nitrogen application promoted plant growth under different water conditions and had significant interaction with water. The increase in shoot dry matter and nitrogen uptake was the highest (53.7%, 83.2% respectively) under W2 condition. Drought stresses increased water use efficiency (WUE), but decreased nitrogen use efficiency (NUE). Nitrogen application significantly increased WUE under W2 condition, but had no significant effect under drought conditions. The effects of water, nitrogen and their interaction on soil properties were complex. In general, drought stresses at seedling stage temporarily increased the pH value in rhizosphere and bulk soil, and significantly increased the contents of ammonium and nitrate nitrogen (NH₄⁺ and NO₃^-) inPJ] rhizosphere soil. The responses of MBC and MBN to drought stresses were opposite between rhizosphere and bulk soil. Rhizosphere soil increased with the increase of drought degree, while bulk soil decreased. In terms of soil enzyme activity, drought stresses significantly affected nitrate reductase (NR) and nitrite reductase (NiR) activities in rhizosphere soil. Nitrogen application increased the pH, NH₄⁺ and NO₃^- contents in rhizosphere and bulk soils under all water conditions, and the increase rate of rhizosphere soil was higher than that of bulk soil. Nitrogen application significantly increased MBC, MBN, urease (UR) and NR activities in rhizosphere and bulk soil under various water conditions, but significantly reduced NiR activity in rhizosphere and bulk soils. The interaction of water and nitrogen significantly affected NiR activity in rhizosphere soil, UR, NR and FDA activities in bulk soil. There was a significant correlation between the biological and chemical properties in rhizosphere and bulk soil, and the indexes of rhizosphere soil except NiR activity were positively correlated with plant nitrogen uptake and NUE. Drought at seedling stage significantly inhibited maize plant growth and nitrogen uptake, and significantly affected soil biological and chemical properties. The effects of nitrogen application on plant and soil properties were different under different water conditions, and there was a significant correlation between plant performance and soil biological and chemical properties.