金矮生苹果叶片气体交换参数对土壤水分的响应

RESPONSES OF GAS EXCHANGE PARAMETERS OF GOLDSPUR APPLE TREE TO SOIL WATER VARIATION

在黄土高原半干旱地区 ,通过测定 10年生金矮生苹果 (Maluspumilacv .Goldspur)叶片气体交换参数与土壤水分的定量关系 ,探讨了土壤水分胁迫对光合作用的影响规律 ,以确定苹果园节水灌溉适宜的土壤水分调控标准。结果表明 :叶片的净光合速率 (Pn)、蒸腾速率 (Tr)、水分利用效率 (WUE)、气孔导度 (Gs)、细胞间隙CO2 浓度(Ci)和气孔限制值 (Ls)对土壤水分的变化具有明显不同的阈值反应。土壤含水量 (SWC)大约在田间持水量的6 0 %～ 86 %范围内 ,Pn 和Tr 均保持较高的水平 ,小于田间持水量的 6 0 %～ 86 %后 ,两者均随土壤湿度的减少而明显下降。维持较高叶片水分利用效率 (WUE)的SWC约在田间持水量的 5 0 %～ 71%左右。当SWC小于田间持水量的 4 8%以后 ,Gs 和Ls 明显降低 ,而Ci 急剧增加 ,水分胁迫条件开始直接作用于叶肉细胞 ,导致光合速率下降 ,由气孔限制因素转变为非气孔因素。据此我们认为 :在半干旱黄土高原地区 ,金矮生苹果园节水灌溉适宜的SWC范围大约在田间持水量的 5 0 %～ 71%左右 ,所允许的土壤水分亏缺程度为田间持水量的 4

Goldspur Apple (Malus pumila cv. Goldspur) is one of the main fruit trees planted on the Loess Plateau in a semi-arid region. Gas exchange parameters in leaves of ten-year-old trees were studied under different soil water conditions with a LI-6200 portable photosynthesis system and a LI-1600 portable steady state porometer, in order to explore the effects of soil water stress on the photosynthesis and the suitable soil water content (SWC) for water-saving irrigation of the apple orchard. The experimental site is located in Tuqiaogou watersheds, Yukou town, Fangshan county, Shanxi province, China, a part of a gully-hilly area of Loess Plateau in the middle reaches of the Yellow River. It lies at 37° 36′ 58″ N, 110° 02′ 55″ E, with an average altitude of about 1 200 m and a maximum altitude of 1 446 m. The average annual precipitation is 416.0 mm, with the precipitation in June, July, August and September being more than 70% of the total amount. Annual potential evaporation is 1 857.7 mm and the greatest evaporation occurs in April to June. The soil belongs to medium soil and lossal soil and the average soil bulk density is about 1.2 g·cm -3, and mean field capacity (FC) is approximately 21.0%. In the study on responses of gas exchange parameters to soil water, eighteen apple trees were selected as experimental samples and divided into six groups (three trees per group and signed by Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ and Ⅵ). The soil water gradient was obtained in six groups by providing different water supply. During soil water treatment, SWC measured with LNW-50A neutron probe on June 12, June 16 and June 20, 1999 were as follows: group Ⅰ (22.4%, 18.7% and 16.7%), Ⅱ (20.1%, 17.4% and 16.2%), Ⅲ (18.2%, 16.7% and 14.8%), Ⅳ ( 15.9%, 13.6% and 11.9%),Ⅴ (11.7%, 10.5% and 9.6%) and Ⅵ (6.2%, 5.6% and 5.0%). A LI-6200 portable photosynthesis system was used to measure the photosynthesis parameters including photosynthetic rate (P n), stomatal conductance (G s) and intercellular CO 2 concentration (C i), while at the same time transpiration rate (T r) was measured with a LI-1600 portable steady state porometer. The water use efficiency (WUE) and stomatal limiting value (L s) were calculated according to formula WUE=P n/T r and L s=1-C i/C a. These gas exchange parameters were measured on the same day that SWC was observed on June 12, June 16 and June 20, 1999, and the duration of observation was at 9∶00-11∶00 am each time. The results showed that when SWC was within a range about 60%-86% of field capacity (FC), P n and T r were maintained in a relative steady state and higher level, but below 60%-86% of FC, both P n and T r decreased obviously with decreasing soil moisture. The SWC range to support WUE at a relative steady state and higher level was about 50%-71% of FC. When SWC was less than 48% of FC, G s and L s declined with decreasing of soil moisture, while C i increased rapidly. Based on the analysis of stomatal limitation of photosynthesis using two criteria (C i and L s) suggested by Farquhar and Sharkey, it implied that the predominant cause of restricting P n had turn into non-stomatal limitation under severe water stress. According to the main intention of water-saving irrigation for enhancing water use efficiency, it is concluded that the suitable range of SWC was about 50%-71% of FC, as the most severe degree of soil water stress tolerated for photosynthesis was about 48% of FC.