旱地"垄覆沟播"冬小麦氮高效的根系形态和营养生理机制

Plant roots are the main organ for absorbing nutrients from soil. The morphological structure and biochemical characteristics of roots determine the ability of plants uptake and assimilation nutrients. This project focuses on the problem of low whinter wheat yield and nitrogen use effciency, and the fact that ridge mulching and furrow seeding practices could increase wheat yield and nitrogen use efficency compared to traditional cultivation practices. This research will combine the advanced research techniques (i.e., mini-rhizotrons and 14C tracer techniques) with traditional methods (i.e., soil core, and excavation and washing) to study the characteristics of winter wheat roots at the seedling, re-greening, elongation, flowering, and grain filling stages. The study objective is to compare the growth dynamics and morphological structure of wheat roots grown under ridge mulching and furrow seeding practices with those of wheat roots grown under traditional cultivation practices, to compare the effects of the two cultivation methods on the NO3- - N uptakes and deoxidization, to quantify the effects of the two cultivation methods on nitrogen accumulation across the growing season and on nitrogen translocation at the grain filling stage. This research aims to identify the roots morphological and physiological mechanism for improving winter wheat yield and nitrogen use efficiency under ridge mulching and furrow seeding practices. The results should provide a theoretical basis for high yield and benefits of whinter wheat in dryland areas of China.

根系是植物吸收养分的主要器官，其形态及生理生化特性决定了植物吸收和同化土壤养分的能力。本项目针对旱地小麦产量和氮肥利用率低的问题，以"垄覆沟播"栽培比农户常规栽培显著提高旱地小麦产量和氮肥效率为切入点，通过微根管法、14C同位素法，并结合挖掘冲洗法、根钻法等方法，在小麦冬前、返青、拔节、开花以及灌浆5个关键生育期，研究旱地 "垄覆沟播"小麦根系生长发育、形态和分布，根系硝态氮吸收与还原能力变化，以及根系氮素累积及运转。查明旱地"垄覆沟播"冬小麦肥料氮及土壤硝态氮高效利用的根系形态和营养生理机制，为旱地小麦高产高效栽培施肥提供理论依据。

研究发现，旱地冬小麦采用“垄覆沟播”（垄上覆盖塑料薄膜，沟内种植小麦）种植模式，相比农户常规不覆膜、平作模式，0-20 cm土壤耕层在小麦花期土壤水分增加28.3%，根系生物量增加31.7%，进而产量增加22.5%。进一步分析0-20 cm耕层根系生物量占0-100 cm土壤剖面比例，发现“垄覆沟播”模式0-20 cm根系生物量占0-100 cm土壤剖面的80.4%，而农户模式0-20 cm仅仅占60.5%。由此可见旱地小麦“垄覆沟播”通过减少蒸发提高了土壤表层水分，进而提高了表层根系生物量及其比例，提高了养分吸收利用，最终增加了产量。.根系活力大小与硝态氮吸收作用的强弱有直接关系。根系活力大则吸收能力强，反之则弱。我们在小麦花期测定根系活力，农户常规施肥栽培模式根系活力为15.0μg•g-1 FW•h-1，“垄覆沟播”模式为17.2μg•g-1 FW•h-1。“垄覆沟播”较农户常规施肥栽培模式根系活力提高14.7%。硝酸还原酶（NRA）是小麦根系硝态氮还原的关键性酶，影响小麦根系对硝态氮的吸收。温度的高低影响NRA活性，在合适的温度范围内，随着温度的升高，NRA活性提高。土壤水分也影响NRA活性，干旱情况下，小麦根系NRA合成受阻，分解加快，含量降低，NRA活性也随之降低。我们知道地膜覆盖有保墒增温作用，这种作用反过来可以促进小麦根系NRA活性发生改变。试验测得小麦花期农户常规施肥栽培模式根系NRA活性为4.5μg•g-1•h-1，“垄覆沟播”模式为5.0μg•g-1•h-1，“垄覆沟播”较农户常规施肥栽培模式NRA活性提高11.1%。.研究表明“垄覆沟播” 较农户常规施肥栽培模式不但提高了小麦表层根系生物量及其比例，而且具有较强的硝态氮吸收还原能力，所以4年定位试验收获期0-200cm土壤硝态氮残留“垄覆沟播”模式平均仅有76.5 kg.hm-2，农户常规施肥栽培模式为158.1 kg.hm-2，减少了51.6%，进而氮肥利用率平均由农户模式的63.4%提高到“垄覆沟播”模式的72.8%。