陇东雨养农区紫花苜蓿叶片氮、磷、钾重吸收与生物固氮的偶联关系

叶片养分重吸收是植物提高养分利用效率、增强环境适应性的重要机制之一,易受多种因素影响。在豆科植物中,养分重吸收与生物固氮有何关联尚不可知。为揭示养分重吸收与生物固氮间的偶联关系,以陇东雨养农区已建植2、4、7、11和14年龄的陇东苜蓿草地为对象,测定了叶片N、P、K浓度及δ¹⁵N,分析了叶片N、P、K重吸收效率(NRE、PRE和KRE)、重吸收度(NRP、PRP和KRP)及其与生物固氮率的关系。随紫花苜蓿建植年龄增长,叶片NRE、PRE呈先增大后减小的趋势,NRE和PRE分别为36.5%(28.4%~43.4%)和52.6%(38.1%~68.2%),其中7年龄苜蓿的NRE和PRE最高;2、11和14年龄苜蓿KRE为17.8%(23.0%~27.5%),但4和7年龄为负值。随紫花苜蓿年龄变化,叶片NRP、PRP和KRP均无明显变化趋势。随紫花苜蓿年龄增长,生物固氮率先降低后升高,平均固氮率为51.0%,其中7年龄苜蓿的最低。紫花苜蓿生物固氮率与叶片NRE、PRE和KRP负相关,但与叶片KRE、NRP和PRP不相关。紫花苜蓿生物固氮与叶片的氮、磷、钾重吸收存在偶联关系,对氮、磷重吸收效率和钾重吸收度有显著影响。

Relationships between biological nitrogen fixation and leaf resorption of nitrogen,phosphorus, and potassium in the rain-fed region of eastern Gansu,China

Leaf nutrient resorption is influenced by many factors, and is one of the most important strategies to enhance nutrient use efficiency and adaptability in adverse environmental conditions. The aim of this study was to explore the relationship between biological nitrogen fixation (BNF) and leaf nutrient resorption. We analyzed lucerne (Medicago sativa cv. Longdong) stands of different ages (2, 4, 7, 11, and 14 years since establishment) in the rain-fed region of eastern Gansu, China. Plant samples were taken at the early flowering stage to measure the concentrations of nitrogen and δ¹⁵N, phosphorus, and potassium in green and senesced leaves. The resorption efficiencies of N and P (NRE and PRE, respectively) first increased and then decreased with stand age, while the changes in potassium resorption efficiency (KRE) showed a different pattern. The NRE ranged from 28.4% to 43.4% with an average of 36.5%, and PRE ranged from 38.1% to 68.2% and averaged 52.6%. The highest NRE and PRE were in the 7-year-old stand. The KRE values of 2-, 11-, and 14-year-old lucerne stands ranged from 23.0% to 27.5%, while they were less than zero in the 4- and 7-year-old stands. As the stands aged, the K, N, and P resorption proficiencies (KRP, NRP, and PRP, respectively) showed different patterns of change from those of resorption efficiencies. The percentage of N derived from the atmosphere (%Ndfa) tended to decrease first and then increase with stand age, and averaged 51.0%, with the minimum value in the 7-year-old stand. There were negative correlations between %Ndfa and NRE, PRE, and KRP, but few relationships between %Ndfa and KRE, NRP, and PRP. These results suggested that there is a close link between nutrient resorption and BNF in lucerne and that BNF affects NRE, PRE, and KRP.