长脐红豆幼苗生长对不同土壤氮磷添加的响应及其对土壤养分的反馈

Growth performance of Ormosia balansae seedlings and their feedbacks on the soil nutrient under varied soil nitrogen and phosphorus addition conditions

以热带豆科树种长脐红豆(OrmosiabalansaeDrake)幼苗为研究对象,开展苗期控制试验,共设置了5个添加氮(N, N1—N5)和2个添加磷(P, LP—HP)梯度,观察长脐红豆在不同土壤N、P添加条件下的生长表现及对土壤养分的反馈。测定的植物和土壤响应指标包括:植株地上和地下生长量、叶面积、叶和根的N、P含量、根际和非根际土壤N、P含量等。结果表明:(1)从苗高、总叶面积、地上生物量、地下生物量、总根长和根表面积这6个指标总体来看,在低磷(LP)条件下,中、高浓度的N添加(N4、N5)对长脐红豆生长有抑制作用;高磷(HP)条件下,高浓度的N添加(仅有N5)对长脐红豆生长有抑制作用;表明长脐红豆的最适生长N浓度会随P添加浓度增加而升高;(2)随着N添加浓度的增加,根和叶的全N含量呈先增加后减小的趋势,N4处理条件下达到最大;根和叶的全P含量却呈现相反趋势,符合元素稀释效应。叶的N:P>16,且P浓度<1.0 mg·g^(-1),表明长脐红豆生长受P限制;(3)基于氨态氮、硝态氮和有效P这3个肥力指标,长脐红豆苗期非根际土壤肥力>根际土壤肥力,表明豆科树种长脐红豆在其幼苗期共生根瘤尚未明显形成时期,需补充适量N、P养分供给。

By the greenhouse control experiment,the growth performance of Ormosia balansae seedlings and their feedbacks on the soil nutrients were observed under five nitrogen(N,N1-N5)gradients and two phosphorus(P,LP-HP)addition gradients.Aboveground and belowground growth indices,total leaf area,N and P concentration of leaves and roots,rhizosphere and non-rhizosphere soil N and P concentration were measured after seedlings were harvested.The results are as follows.(1)By considering shoot height,total leaf area,shoot biomass,root biomass,root length and root surface area together,under the low phosphorus addition(LP)condition,O.balansae seedlings were inhibited by the middle N addition concentration of N4 treatment and high N addition concentration of N5 treatment.Under the high phosphorus addition(HP)condition,O.balansae seedlings were only inhibited by the high N addition concentration of N5 treatment.Therefore,the optimal growth N concentration of O.balansae seedlings increased with the increase of P addition.(2)With the increase of N addition concentration,the total N concentration of roots and leaves increased firstly and then decreased,reaching the maximum at the N4 treatment.However,total P concentration showed the opposite trend,which was consistent with the dilution effect of nutrients.Moreover,leaf N:P ratio>16 and leaf P concentration was less than 1.0 mg·g^-1,which indicated that O.balansae seedlings were limited by the P.(3)In terms of three soil fertility indices including soil ammonium nitrogen,nitrate nitrogen and available P,non-rhizosphere soil fertility>rhizosphere soil fertility,it indicated that O.balansae did not significanlty change the soil fertility at the seedling stage and needed extra fertilization to facilitate their growth.