不同施钾量对苜蓿碳水化合物含量及抗蓟马的影响

为了明确施钾是否能有效提高苜蓿对蓟马的抗性并研究相关生理变化,本试验以感蓟马苜蓿品种甘农3号和抗蓟马苜蓿品种甘农9号为材料,设0、6、9、12、15 (K₂O) g/m²等5个钾浓度水平,在大田蓟马为害高峰期,评价和测定了不同钾水平处理下苜蓿的受害指数、叶片钾含量、产量、碳水化合物含量;在苜蓿第二茬中,随着钾水平的升高,甘农3号和甘农9号老叶和心叶的钾含量、可溶性糖、淀粉和木质素含量升高,产量显著增加(P<0.05);受害指数均显著降低,且受害指数均在K₂水平下最低,分别较K₀水平降低了47.60%和46.11%;在第三茬中,甘农3号和甘农9号的受害指数、产量、钾含量、可溶性糖、淀粉和木质素含量的变化规律与第二茬相似,受害指数在K₂水平下分别较K₀水平降低了30.78%和23.27%。第二茬和第三茬中,在低于9 (K₂O) g/m²施钾水平下,苜蓿叶片钾含量与受害指数显著负相关(P<0.05);高于12 (K₂O) g/m²水平下,苜蓿叶片钾含量与受害指数无显著相关性(P>0.05)。钾元素可通过提高苜蓿碳水化合物的合成(尤其是可溶性糖和淀粉)及生长性能来提高苜蓿对蓟马的耐害性。施钾后甘农3号的受害指数均低于未施钾甘农9号的受害指数,因此,通过施钾管理来提高苜蓿对蓟马的耐害性是一种有效的措施。9 (K₂O) g/m²是本试验中最经济有效的施肥量。

Effects of potassium application rates on carbohydrate content and resistance to thrips (Thripidae)in alfalfa

The aim of this research was to investigate the effects of potassium on alfalfa growth and its resist-ance to thrips.Two alfalfa varieties were chosen for the study;Gannong No.9 (thrip-resistant)and Gannong No.3 (thrip-susceptible).Potassium (K2 O)was applied to field-grown plants at five different levels (0,6,9, 12,and 15 g/m2 )during the peak thrip damage period,and then the damage index,the potassium and carbo-hydrate contents in leaves,and yield were evaluated.The results showed that the yields of both alfalfa varieties increased significantly with increasing K2 O levels.The potassium,soluble sugars,starch,and lignin contents in old and heart leaves increased with increasing K2 O levels,and the thrip damage index decreased significant-ly.The lowest damage index values were in the 9 g/m2 K2 O treatment (decreased 47.60% and 46.11% for Gannong No.9 and Gannong No.3 with the control,respectively).The damage index,yield,and potassium, soluble sugars,starch,and lignin contents at the second cutting showed similar trends to those at the third cut-ting.The damage index at the third cutting was decreased 30.78% and 23.27% for Gannong No.9 and Gan-nong No.3 with the control,respectively.Correlation analyses indicated that the potassium content of plants at the second and third cuttings was significantly negatively correlated with the damage index when the K2 O appli-cation rate was lower than 9 g/m2 ,but not significantly correlated with the damage index when the K2 O appli-cation rate was higher than 12 g/m2 .The damage index was lower in Gannong No.3 treated with potassium than in Gannong No.9 without potassium application.These results indicate that potassium can enhance the re-sistance of alfalfa to thrips by promoting the synthesis of carbohydrates (especially soluble sugars and starch) and plant growth.Therefore,potassium management is an effective method to increase the tolerance of alfalfa to thrips in the field.The most economical fertilizer application rate was 9 g K2 O/m2 in this experiment.