黄瓜幼苗干物质积累、膨压及光合速率对铵态氮和硝态氮的响应

The response of dry matter accumulation,turgor pressure and photosynthetic rate in cucumber seedlings to nitrate and ammonium nitrogen

采用溶液培养方法,研究了氮素形态及水平对黄瓜干物质积累、膨压及光合速率的影响。结果表明,同一氮素水平时,NO3--N处理黄瓜干物质重量、叶片面积、叶片含水量、水势、膨压等均高于NH4+-N处理。低水平NH4+-N(5 mmol/L)对黄瓜光合速率影响不大,甚至高于同水平NO3--N处理,叶片面积稍有减小;高水平NH4+-N显著抑制黄瓜干物质的积累,叶片面积仅是同水平NO3--N处理的12.7%,净光合速率(Pn)为CO21.6μmol/(m2.s),仅为同水平NO3--N处理的10%左右。NH4+-N处理引起黄瓜叶片面积的减小与叶片膨压降低相关性较大,相关系数为0.98;膨压与叶片水势直接相关,而渗透势对此影响不大。高水平NO3--N对黄瓜产生了渗透胁迫,抑制黄瓜生长,表现在渗透调节物质的大量积累。不同黄瓜品种对氮素形态及水平响应差异较大,所有处理中新泰密刺长势均好于吉尼罗。低水平的NH4+-N对黄瓜干物质的积累影响不大,高水平则明显抑制其生长。说明高浓度铵态氮对植物产生了毒害,而高浓度的硝态氮则是渗透胁迫。

Nitrate（NN） and ammonium（AN） were primary nitrogen forms of root uptake in high plant. It has been found that nitrate promoted plant growth, while high-level AN restrained it. The effects of nitrogen form and level on dry matter accumulation, turgor pressure and photosynthesis of hydroponically cultivated cucumber （ Cucumis sativus ） seedlings were investigated. The results showed that nitrate treatment could increase the shoot dry matter, leaf area, leaf water content, water potential turgor pressure and photosynthetic rate of cucumber seedlings compared with AN treatment. Though lowlevel AN （5 mmol/L） supply may affect leaf development of cucumber seedlings, it had no negative effect on photosynthetic rate. Compared to the same level of NN, low-level AN had higher photosynthetic rate. While under high-level AN, the dry matter accumulation of cucumber seedlings was significantly restrained, minimum net photosynthetic rate Pn was CO2 1.6 μmol/（m^2·s）, and leaf area and Pn was only 12.7% and 10% of them at the same level of NN, respectively. AN supply may cause leaf area decrease, which was more dependent on the reducing of its leaf turgor pressure, and relative coefficient of them was 0.98 ; the fall of turgor pressure was mainly correlated with water potential, but osmotic potential. Under high-level NN, Cucumber seedlings suffered osmotic stress, their growth restrained and accumulated abundant osmotic substance in plants. The growth of Xintaimici （XTMC） was better than Jiniluo （JNL） at all treatments. Low AN supply had little negative effect on dry matter accumulation, while high-level AN significantly inhibited cucumber growth. So we can concluded that high-level AN itseff was toxic to plants, while high-level NN restrained plants growth by oswotis stress.