Abstract:

In order to explored the effects of planting density and nitrogen level on wheat photosynthesis， yield and soil nitrogen content， four treatments were set under field condition including conventional sowing rate+conventional nitrogen application rate （CBCF）， increasing sowing rate by 30%+conventional nitrogen application rate （ZBCF）， increased sowing by 30%+reduced nitrogen by 20% （ZBJF） and conventional seeding+20% nitrogen reduction （CBJF）， which conventional sowing rate was 232.5 kg·hm^-2， and conventional nitrogen application rate was 219 N kg·hm^-2. The photosynthetic indexes of wheat during main growth stage and different nitrogen forms in soil after harvest were measured and analyzed. The results were followed. ①The net photosynthetic rate and chlorophyll content increased first and then decreased with the growth period. The net photosynthetic rate at jointing stage under CBJF treatment was increased. In the filling stage， the net photosynthetic rate of ZBJF treatment reached the maximum of 20.53 μmol·m^-2·s^-1， which increased the chlorophyll content of wheat at jointing stage. ②The intercellular CO₂ concentration and stomatal conductance decreased with the growth period. And at jointing stage， the intercellular CO₂ concentration and stomatal conductance under the treatments with normal nitrogen application rate were significantly higher than that under the treatments with nitrogen reduction. The maximum intercellular CO₂ concentration and stomatal conductance were under ZBJF treatment with 270.87 μmol·mol^-1 and 0.33 μmol·m^-2·s^-1. ③The transpiration rate was firstly increased and then decreased during the growth stage. The maximum transpiration rate was 3.51 μmol·m^-2·s^-1 under ZBJF treatment at the filling stage. ④The number of grains per ear under ZBJF increased by 12% compared with that under CBJF treatment. The wheat yield under the treatments with nitrogen reduction was higher than that under the treatments with conventional nitrogen application. ⑤Compared with CBCF treatment， the contents of total nitrogen， alkali-hydrolyzed nitrogen， ammonium nitrogen， nitrate nitrogen， dissolved organic nitrogen and microbial biomass nitrogen in the soil layer of 10—20 cm were decreased under the treatments with nitrogen reduction. Under the experimental conditions， although the available nitrogen content in 10—30 cm soil layers was reduced under the treatments with nitrogen reduction， the partial productivity of nitrogen fertilizer was significantly increased compared with conventional nitrogen application treatment. Meanwhile， the wheat growth and yield did not be affected by the nitrogen reduction. Among them， under ZBJF treatment， the photosynthesis of wheat during filling stage and the chlorophyll content in the leaves before flowering stage were improved. Meanwhile， the grain number， thousand grain weight and yield were improved under ZBJF treatment.

Key words: wheat, seeding rate, nitrogen rate, photosynthetic characteristics, crop yield

摘要：

为揭示种植密度和施氮水平对土壤氮素形态及小麦光合作用、产量的影响，在大田条件下，分别设置常规小麦播量+常规施氮量（CBCF）、小麦播量增加30%+常规施氮量（ZBCF）、小麦播量增加30%+氮量减施20%（ZBJF）、常规小麦播量+氮量减施20%（CBJF）共4个处理，其中小麦常规播量为232.5 kg·hm^-2；常规施氮量为219 kg·hm^-2。分析不同处理下小麦主要生育期的光合参数指标、成熟期小麦产量及土壤不同形态氮素含量。结果表明，①净光合速率和叶绿素含量随生育时期呈现先上升后下降趋势，其中CBJF处理提高了拔节期净光合速率；ZBJF处理在灌浆期的净光合速率最大，为20.53 μmol·m^-2·s^-1，同时增加了小麦拔节期叶绿素含量。②胞间CO₂浓度和气孔导度均随生育时期呈现下降趋势，其中在拔节期常规施氮肥处理显著高于氮肥减施处理；灌浆期ZBJF处理胞间CO₂浓度和气孔导度显著高于其他处理，分别为270.87 μmol·mol^-1和0.33 μmol·m^-2·s^-1。③蒸腾速率随生育时期呈现先上升后下降趋势，在灌浆期ZBJF处理的蒸腾速率最高，为3.51 μmol·m^-2·s^-1。④ZBJF处理的穗粒数较CBJF处理增加12%，且减氮处理的小麦产量显著高于常规施氮处理。⑤相较于CBCF处理，氮肥减施处理降低了10—20 cm土层中全氮、碱解氮、铵态氮、硝态氮、可溶性有机氮和微生物量氮含量。本试验条件下，氮肥减施处理虽然减少了10—30 cm土壤有效态氮含量，但小麦生长和产量相较于常规施氮处理并未受到影响，从而提高了氮肥偏生产力，其中ZBJF处理提高了小麦灌浆期主要光合作用参数，并提高了小麦穗粒数、千粒重和产量。

关键词: 小麦, 种植密度, 施氮量, 光合特性, 产量