氮磷配施对高寒草甸植物根系特征的影响

Effects of combined nitrogen and phosphorus application on root characteristics of alpine meadow

植物根系是固定和支撑植物体的重要器官,是草地生态系统重要的碳库之一。分析植物不同直径大小根系在不同浓度氮磷配施下的形态特征和生理功能,有利于了解高寒草甸植物根系生长特征、碳分配格局和养分循环。本研究在川西北高寒草甸采用微根管技术原位监测4个氮(N)、磷(P)梯度(CK:0 g·m^(-2);NP10:N 5 g·m^(-2)+P 5 g·m^(-2);NP_(2)0:N 10 g·m^(-2)+P 10 g·m^(-2);NP_(30):N 15 g·m^(-2)+P 15 g·m^(-2))根系动态(现存量、生产量、死亡量和周转率)的变化特征及其与环境因子间的相互关系。结果表明:1)土层间根系总现存量差异显著,0~10 cm土层施肥(NP10、NP20、NP30)显著降低了直径≤0.3 mm根系现存量,且NP30显著降低了总根系和直径>0.3 mm根系现存量;10~20cm土层NP20总根系和直径>0.3 mm根系现存量显著高于其他处理(P<0.05)。2)土层间根系总生产量和死亡量差异显著,0~10 cm土层,直径≤0.3 mm根系生产量和死亡量在处理间无显著差异,直径>0.3 mm根系在NP30死亡量显著增加;10~20 cm土层,直径≤0.3 mm根系生产量和死亡量在施肥处理下显著低于CK,直径>0.3 mm根系生产量和死亡量均在NP20、NP30显著高于CK(P<0.05)。3)土层及处理间根系周转速率无显著差异,但整体上直径≤0.3 mm根系周转速率高于直径>0.3 mm根系。4)结构方程模型进一步表明:根系现存量和生产量受土壤养分[全碳(TC);全氮(TN)]和根系直径大小的直接影响,土壤养分对根系周转率有正效应。综上:氮磷配施梯度对地下总根系现存量和死亡量影响显著,低、中氮磷(NP10、NP20)配施会降低植物对直径≤0.3 mm根系生物量的分配,投入更多的资源促进直径>0.3 mm根系的生长;高施肥(NP30)会使植物减少各直径大小根系生物量的分配,增加其死亡量,从而降低根系碳的积累。

The root system is a vital organ for plants to fix and support plant body,and it is also an important carbon pool in grassland ecosystems.In order to better understand the growth characteristics,carbon allocation pattern and nutrient cycle of roots in alpine meadow,we analyzed the morphological characteristics and physiological functions of roots with different diameters under four levels of nitrogen(N)and phosphorus(P)application rates.The minirhizotron observation method was applied to monitor the dynamics of root standing crop,production,death and turnover under CK(0 g·m^(-2) fertilizer),NP_(10)(N 5 g·m^(−2)+P 5 g·m^(−2)),NP_(20)(N 10 g·m^(−2)+P 10 g·m^(−2))and NP_(30)(N 15 g·m^(−2)+P 15 g·m^(−2))treatments in northwest Sichuan,and the relationships between root characteristics and environmental properties were examined.The results showed that:1)The standing crop of the total roots differed significantly between soil horizons.In 0-10 cm,fertilization(NP10,NP20,NP30)reduced the standing crop of roots≤0.3 mm significantly,and NP30 reduced the standing crop of the total roots as well as the roots>0.3 mm significantly;In 10-20 cm,the standing crop of the total roots as well as the roots>0.3 mm in NP20 were significantly higher than that in other treatments(P<0.05).2)There were significant differences in total root production and mortality between soil layers.In 0-10 cm,the production and mortality of the roots≤0.3 mm varied slightly,while the mortality of the roots>0.3 mm increased significantly in NP30;In 10-20 cm,the production and mortality of the roots≤0.3 mm in fertilization treatments were significantly lower than that in CK,and the production and mortality of the roots>0.3 mm in NP20 and NP30 were significantly higher than that in CK(P<0.05).3)The root turnover varied insignificantly between soil horizons and fertilization treatments,but the turnover of the roots≤0.3 mm was higher than that of the roots>0.3 mm.4)The structural equation model suggested that the root standing crop and production were directly affected by the soil nutrients(total carbon and total nitrogen)and the root diameter,and the soil nutrients had a positive effect on root turnover.In summary,the combined N and P application had significant effects on the total root standing crop and mortality.Low and middle levels of NP(NP_(10) and NP_(20))application could reduce the biomass allocation of roots≤0.3 mm while invest more to enhance the biomass of roots>0.3 mm.High level of NP(NP30)application could reduce both coarse and fine root biomass and increase root mortality,thus reducing root carbon accumulation.