苜蓿叶片氮、磷和钾养分重吸收与化学计量比的偶联关系

苜蓿作为一种优良的豆科牧草,具有较强的环境适应性。叶片养分重吸收是提高养分利用效率及增强环境适应性的重要机制之一,其直接影响了苜蓿的养分浓度,进而影响苜蓿元素的化学计量比。目前已有针对苜蓿养分重吸收及生态化学计量特征的研究,但关于苜蓿元素养分重吸收与生态化学计量比之间的偶联关系的研究还鲜有报道。为解释该偶联关系,以7个苜蓿品种作为研究对象,测定了成熟叶片和衰老叶片C、N、P、K元素浓度,分析了养分重吸收特征(包括养分重吸收率、养分重吸收度)及生态化学计量特征,进而分析了两者之间的偶联关系。结果表明,7个苜蓿品种的平均氮重吸收效率(NRE)、磷重吸收效率(PRE)和钾重吸收效率(KRE)分别为42.7%、42.4%和52.1%,分别低于全球陆生植物的NRE、PRE和KRE(分别为62.1%、64.9%和70.1%)。根据养分重吸收特征及生态化学计量比,判断苜蓿受土壤P含量影响最严重。叶片养分重吸收效率基本与衰老叶化学计量比呈正相关关系,而与成熟叶化学计量比呈负相关关系。由此可见,叶片养分重吸收与叶片生态化学计量比存在偶联关系,但受叶片成熟或衰老显著影响。

Relationships between alfalfa leaf nutrient resorption and stoichiometric ratios of nitrogen,phosphorus, and potassium

Alfalfa is an excellent legume with strong environmental adaptability. Leaf nutrient resorption is an important mechanism to improve nutrient use efficiency and enhance environmental adaptability. It directly affects the nutrient concentration, and consequently, the stoichiometric ratio of elements in alfalfa. Many studies have focused on the nutrient resorption and ecological stoichiometric characteristics of alfalfa, but few have focused on the relationship between nutrient resorption and stoichiometric ratios. To explore this relationship, we measured the concentrations of carbon, nitrogen, phosphorus, and potassium in the mature and senescent leaves of seven alfalfa cultivars. Then, the characters and the relationships between resorption (including resorption efficiency and resorption proficiency) and stoichiometry were analyzed. It was found that the average nitrogen, phosphorus, and potassium resorption efficiencies of alfalfa were 42.7%, 42.4%, and 52.1%, respectively, lower than those of global terrestrial plants (62.1%, 64.9%, and 70.1%, respectively). On the basis of the relationship between nutrient resorption and stoichiometric ratios, we concluded that the growth of alfalfa stands was limited by phosphorus in our study region. The leaf resorption efficiencies were positively correlated with the stoichiometric ratios in senescent leaves, but the opposite conditions were detected in the mature leaves. Thus, there is a close link between nutrient resorption and stoichiometric ratios, and this relationship is significantly affected by the growth status of the leaf (mature vs. senescent).