【摘要】 通过对 7年生田间和 2年生盆栽金矮生苹果 ( Maluspumila CV.goldspur)进行不同土壤水分和光照条件下叶片光合速率测定研究 ,结果表明 ,光合速率 ( Pn)与光照强度 ( PAR)和土壤水分 ( SWC)之间存在着密切的关系。当林木供水充足 ,即 SWC( >1 5 % )达到田间持水量 ( FC)的 75 %以上时 ,Pn的光响应曲线为直角双曲线 ,但 SWC低于这一水平时 ,Pn的光响应曲线则为二次抛物线 ,表现出不同程度的光抑制 ,水分胁迫越严重 ,出现光抑制越早。弱光下 ( PAR<5 0 0 μmol· s- 1· m- 2 ) ,光合速率最大值 Pmax出现在 SWC比较低的范围内 ( 70 %～ 75 % FC) ,如果 SWC继续增大时 ,Pn反而下降 ;随着光强的增大 ,Pmax出现的 SWC水平随之提高。金矮生苹果 Pn的日变化规律在不同 SWC下并不相同 ,水分胁迫存在时 ,Pn的日变化表现出“午休”现象 ,水分胁迫越严重 ,“午休”时间越长 ;水分供应充足时 ,Pn从 1 0∶ 0 0的最大值直线下降 ,下午不再回升。轻度水分胁迫时 ,Pn日平均值接近或达到最大值 ;随着 SWC的提高 Pn日平均值反而有下降趋势。在正常光照条件下 (日均值 80 0～ 1 0 0 0μmol· s- 1· m- 2 ) ,当林木处于严重水分胁迫 ,即 SWC低于 FC的 5 5 %时 ,Pn随土壤水分的增加直线上升 ;当土壤水分供应充足 ( SWC>75 % F更多还原

【Abstract】 Net photosynthetic rate (Pn) of seven-year-old field and two-year-old potted the Goldspur apple tree (Malus pumila CV.Goldspur) was determined through the use of controlling different soil moisture (SWC) and irradiation intensity (Photosynthetically Active Radiation,for short PAR).The experimental site was located in Tuqiaogou watersheds,Yukou town,Fangshan county,Shanxi Province,China,a part of gully-hilly area of loessial plateau in the middle reaches of Yellow River,37°36′58″N,110°02′55″E.The average annual precipitation here amounts 416 mm,and the precipitation from June to August is more than 70%.The vegetation type is forest bush steppe.The soil moisture was 15.01 percent (equal to 75 percent of field capacity,FC) on August 17,1996,when Pn was measured in the field.To avoid the measured error caused by too high soil temperature due to the straightly irradiating of the sunlight when the pots are put in the air,the pot was buried in the field soil so that the temperature of the pot soil could be the same as the field soil,and the soil moisture of the pots was artificially controlled.In the study on response of the net photosynthetic rate to light,all experimental pots were divided into six groups (three pots per group),and represented with letter from a to f.In the first five days out of ten days before the observation on June 22,1996,each pot was watered adequately every.Since the beginning of the sixth day,the watering of the six groups of the pots was stopped in turn from a to f.As a result,SWC was controlled by six levels such as a (6.04%),b(9.11%),c(11.34%),d(15.46%),e(18.78%) and f(22.56%).In the study on response of net photosynthetic rate to water,the soil moisture of twenty-one potted samples was controlled in the successive variable system range of 5%～23% in the same way before the observation day (August 17,1996).SWC was determined through the use of soil sample drying and weighing,and field capacity (FC) of soil,measured with ring knife,was 20.01%.PAR was controlled at six levels,that is PAR<50,50<PAR<100,100<PAR<500,500<PAR<1000,1000<PAR<1400,PAR>1400 μmol·s -1·m -2 by using differently thick plastic membrane layers and pledget layers.Pn under different SWC and PAR was measured with a portable photosynthetic system (L1-6200,LI-COR Co.USA).At the same time PAR was determined using the quantorecorder sensor on the leaf chamber of L1-6200 photosynthetic system.Predawn leaf water potential and soil moisture characteristic curve was determined respectively employing a pressure chamber (ZLZ-4,Lanzhou University,China) and the method of pressure membrane.;The results showed that Pn related closely to PAR and SWC.When enough water was provided to tree and no water stress existed,or SWC(>15%) was more than 75 percent of field capacity,the curve of Pn response to PAR was a right-angled hyperbola (including pots and field site),the maximum photosynthetic rate (P max) as 24.40 μmolCO-2·s -1·m -2 was recorded for pots sample.The photoinhibition stresses didn’t occur in the range of determinable PAR.The curve of Pn response to PAR was a quadratic parabola when SWC is below the level,which means the arising of photoinhibition stresses.Water stress was more serious,and the photoinhibition stresses arose earlier.When SWC was in the range of 11%~15%(accounted for 55%~75% of FC),P max retarding with SWC increasing was 12~18 μmolCO-2·s -1·m -2.Under the serious soil water stress (SWC was 6.04% equal to 30% of FC),and PAR reached 300 μmol·s -1·m -2,P max was only 1.0832 μmolCO-2·s -1·m -2.;Through the determination of Pn of seven-years-old field Goldspur apple tree,it showed the decrease pattern at noon (noon break pattern),which was the same as the daily change of Pn of most plants and the phenomenon of noon break was obvious when water stress didn’t occur.The daily change law of Pn of Goldspur apple tree differed from different SWC.The time for noon break was longer if the water stress was more serious,which was also when SWC was smaller than 11% (below 55% of FC更多还原