鲁东南地区不同年龄紫花苜蓿N、P生态化学计量特征研究

为了探索鲁东南地区不同年龄紫花苜蓿在不同茬次下化学计量特征存在怎样的差异,本试验通过测定与分析不同年龄(2、3、4、5龄)紫花苜蓿叶和茎的N、P含量及化学计量比,研究了年龄及茬次对紫花苜蓿化学计量特征的影响。结果表明,不同茬次内,苜蓿叶和茎的N、P含量随年龄的变化趋势不同,但总体上3龄苜蓿叶和茎的N、P含量高于其他年龄;每茬时,4龄苜蓿叶和茎N∶P均显著高于其他年龄(P0.05),3龄苜蓿叶和茎N∶P均低于其他年龄。4个年龄苜蓿叶和茎N、P含量随茬次呈先增加后减少的趋势,并在第3茬达到最大值(除3龄苜蓿茎的N含量);2龄和4龄苜蓿叶N∶P随茬次呈先降低后增加的趋势;苜蓿茎N∶P随茬次呈先降低再增加的变化趋势(除5龄),并均在第4茬时达到最低值;苜蓿年龄和茬次的变化均能显著影响苜蓿叶和茎的N、P含量及N∶P;苜蓿叶和茎的N含量与N∶P基本呈正相关,苜蓿叶和茎的P含量与N∶P基本呈负相关。随着年龄的增加,苜蓿由主要受N限制向主要受P限制转变。

Nitrogen and phosphorus ecological stoichiometry in different-aged alfalfa stands in southeast Shandong

The main aim of this study was to explore the stoichiometry of nitrogen (N) and phosphorus (P) in alfalfa stands of different ages and cutting frequencies in the southeast Shandong area.We analyzed N and P contents and their stoichiometric ratios in the leaf and stem of alfalfa plants in stands of different ages (2,3,4,and 5 years).The leaf and stem N and P contents of alfalfa differed significantly among different stand ages and cutting frequencies.The leaf and stem N and P contents were higher in the 3-year-old alfalfa stand than in alfalfa stands of other ages.The leaf and stem N ∶ P ratios were highest in the 4-year-old alfalfa stand and lowest in the 3-year-old alfalfa stand.The leaf and stem N and P contents of alfalfa first increased and then decreased with increased cutting frequency,reaching a maximum at the third cut (except the stem N content of 3-year-old alfalfa).The leaf N ∶ P ratio in 2-year-old and 4-year-old alfalfa stands first decreased and then increased with cutting,while the stem N ∶ P ratio first decreased and then increased with cutting (except in the 5-year-old stand),and showed the minimum value at the fourth cut.The N and P contents and the N ∶ P ratios in the leaf and stem were affected significantly by stand age and the cutting frequency.The N contents in the leaf and stem were positively correlated with the N ∶ P ratio.The P contents in the leaf and stem were negatively correlated with the N ∶ P ratio.These results show that the nutrient limiting alfalfa growth shifted from N to P as the stands aged.