大气CO_2浓度增加与氮肥对棉花生物量、氮吸收量及土壤脲酶活性的影响

Effects of elevated atmospheric CO_2 and nitrogen application on cotton biomass,nitrogen utilization and soil urease activity

试验设置半开顶式CO2人工气候室,研究了不同CO2浓度处理（360、540μmol·mol^-1）与施氮（N）量（0、150、300和450 kg·hm^-2）对棉花干物质的积累与分配、氮素吸收量及土壤脲酶活性的影响.多样性指数和主成分分析表明：各施N水平下,CO2浓度增加下棉花蕾、茎、叶和整株的总干物质积累量显著增加;2个CO2浓度下,300 kg·hm^-2N（N300）处理棉花蕾、茎、叶、根及整株干物质量显著高于其他3个N肥处理,合理的氮肥施用可显著提高棉花干物质积累量.棉花蕾和茎的氮素吸收量受CO2浓度影响显著,与360μmol·mol^-1CO2浓度相比,CO2浓度为540μmol·mol^-1条件下蕾和茎的氮含量显著增加,其中N300处理下蕾的氮含量最高,N150和N300处理茎的氮含量高于N0和N450处理;叶的氮素吸收量受CO2和N的交互作用影响显著,在N0、N150、N300处理下,540μmol·mol^-1CO2浓度下叶的氮含量增加;棉花根的氮素吸收量受施N量的影响显著,540μmol·mol^-1CO2浓度下根的氮含量随着施N量的增加显著增加.总体上,540μmol·mol^-1CO2浓度下棉花的氮素吸收量高于360μmol·mol^-1CO2浓度,各CO2和N组合处理下,棉花各器官的氮素积累量蕾铃最高,叶片居中,其次是茎秆,根系最低.各施N水平下,两个土层的土壤脲酶活性随着CO2浓度升高而显著增加;不同CO2浓度处理下,0-20 cm土层土壤脲酶活性随着施N量的增加而增加,20-40 cm土层N300处理下的土壤脲酶活性高于其他N肥处理;CO2和N互作下,0-20 cm土层土壤脲酶活性的平均值显著高于20-40 cm土层.大气CO2浓度为540μmol·mol^-1、氮肥施用量为300 kg·hm^-2可显著提高棉花干物质积累量和氮素吸收量.

In this study,a semi-open-top artificial climate chamber was used to study the effect of CO2enrichment（ 360 and 540 μmol · mol^-1） and nitrogen addition（ 0,150,300 and 450kg·hm^-2） on cotton dry matter accumulation and distribution,nitrogen absorption and soil urease activity. The results showed that the dry matter accumulation of bud,stem,leaf and the whole plant increased significantly in the higher CO2 concentration treatment irrespective of nitrogen level. The dry matter of all the detected parts of plant with 300 kg·hm^-2nitrogen addition was significantly higher than those with the other nitrogen levels irrespective of CO2 concentration,indicating reasonable nitrogen fertilization could significantly improve cotton dry matter accumulation. Elevated CO2 concentration had significant impact on the nitrogen absorption contents of cotton bud and stem.Compared to those under CO2 concentration of 360 μmol·mol^-1,the nitrogen contents of bud and stem both increased significantly under CO2 concentration of 540 μmol·mol^-1. The nitrogen content of cotton bud in the treatment of 300 kg·hm^-2nitrogen was the highest among the four nitrogen fertilizer treatments. While the nitrogen contents of cotton stem in the treatments of 150 kg·hm^-2and300 kg · hm^-2nitrogen levels were higher than those in the treatment of 0 kg · hm^-2and 450kg·hm^-2nitrogen levels. The nitrogen content of cotton leaf was significantly influenced by the interaction of CO2 elevation and N addition as the nitrogen content of leaf increased in the treatments of 0,150 and 300 kg·hm^-2nitrogen levels under the CO2 concentration of 540 μmol·mol^-1. The nitrogen content in cotton root was significantly increased with the increase of nitrogen fertilizer level under elevated CO2（ 540 μmol·mol^-1） treatment. Overall,the cotton nitrogen absorption content under the elevated CO2（ 540 μmol·mol^-1） treatment was higher than that under the ambient CO2（ 360 μmol·mol^-1） treatment. The order of nitrogen accumulation content in organs was budleafstem root. Soil urease activity of both layers increased significantly with the elevation of CO2 concentration in all the nitrogen treatments. Under each CO2 concentration treatment,the soil urease activity in the upper layer（ 0- 20 cm） increased significantly with nitrogen application,while the urease activity under the application of 300 kg·hm^-2nitrogen was highest in the lower layer（ 20-40 cm）. The average soil urease activity in the upper layer（ 0- 20 cm） was significantly higher than that in the lower layer（ 20-40 cm）. This study suggested that the cotton dry matter accumulation and nitrogen absorption content were significantly increased in response to the elevated CO2concentration（ 540 μmol·mol^-1） and higher nitrogen addition（ 300 kg·hm^-2）.