水分胁迫下不同氮素对多枝柽柳幼苗生长及生理的影响

摘要

多枝柽柳是塔里木河下游优势物种，下游生态恢复过程中多枝柽柳幼苗的成活及其生长受水分和养分双重胁迫。本试验设置4个水分梯度（土壤相对含水量分别为 D1－20％、D2－35％、D3－50％与 D4－75％）并选用两种氮素（N1-KNO3与 N2-NH4 Cl）来探究水分与氮素对多枝柽柳幼苗生长及生理的影响。实验结果表明，1）水分是影响多枝柽柳幼苗表观生长的主要因子，施氮对其株高有显著的促进作用，D1时铵态氮对其株高的促进作用显著，而 D4时硝态氮的促进作用更为显著。2）幼苗在 D1受到严重胁迫时，两种氮素对叶绿素 a 的含量均有显著的促进作用，铵态氮在土壤水分为 D2、D3时，对叶绿素 b 有显著的促进作用。3）施氮可以提高幼苗的光合效率（φPS（Ⅱ）和ETR），D1、D3时，铵态氮对其影响显著，D2时硝态氮对其影响显著。4）铵态氮更容易被幼苗根系吸收用于总生物量的积累，硝态氮只有在水分 D4时对其总生物量有显著的促进作用，土壤水分为 D2、D3时，施氮使其比根长显著减小，说明幼苗生物量的分配更趋向地上部分；当水分不足时，硝态氮显著增加其根冠比，氮素更多地被幼苗用于根系生长，只有水分适宜时（D3），铵态氮使其根冠比显著减小，用于地上冠面积的增长。因此，水分作为多枝柽柳幼苗早期生长的关键因子，幼苗吸收氮素后与其之间的耦合效应，有利于幼苗改变表观生长及光合生理来适应不良的环境。%Tamarix ramosissima is a dominant species in the lower reaches of the Tarim River,and plant sur-vival and growth is affected by a double stress of nutrient and seasonal water deficit in the sandy soils in this lo-cality.More detailed information on the stress responses of this species will assist the process of ecological res-toration in the Tarim River lower reaches.Four soil watering regimes (D1 -20%,D2 -35%,D3 -50% and D4 -75% of relative field capacity)and two forms of fertilizer N;KNO3 (N1 )and NH4 Cl (N2 )were provided in order to explore drought stress and nitrogen responses.Changes in plant growth and photosynthetic physio-logical traits were measured shortly before flowering.Key results were:1 )Water is the main limiting factor for growth of T.ramosissima seedlings,and an increase in plant height occurred with the enhancement of N supply.For D1 ,ammonium nitrogen significantly affected plant height,but nitrate nitrogen was more signifi-cant for D4 .2)When seedlings were subjected to water stress,the two forms of nitrogen affected chlorophyll content differently.At higher soil moisture content in D2 and D3 ,chlorophyll b was increased more by ammo-nium nitrogen supply than chlorophyll a.At D3 ,the nitrate nitrogen was only increased the contents of chloro-phyll a.3)With enhanced N supply,we found an increase in photosynthetic efficiency (φPS(Ⅱ)-quantum yield of PSⅡ and ETR-estimated electron transport rate).At D1 and D3 the effect of ammonium nitrogen was more sig-nificant,but at D2 the effect of nitrate was more significant.4)Ammonium nitrogen was more easily absorbed by the root to promote total biomass accumulation,and nitrate nitrogen significantly increased the total bio-mass of seedlings only in the D4 soil water regime.With enhancement of N supply,the specific root length de-creased significantly when the soil water content is D2 and D3 ,it indicated that aboveground biomass of plant occupied more assignments.Under reduced water supply,the root∶shoot ratio of nitrate nitrogen was signifi-cantly increased,and captured nitrogen appears to have been consumed by growing roots.With adequate water (D3 ),ammonium nitrogen effects root ∶shoot ratio was significantly decreased,and the N appears to have been used to increase crown diameter.Therefore,water is the key factor in management of T.ramosissima seedlings,and when seedlings absorb nitrogen,the combined effect of water and nitrogen can improve seedling photosynthesis and growth and allow the seedlings to grow successfully in these undesirable surroundings.