CO_2浓度升高和氮素供应对黄瓜叶片光合色素的影响

Effects of Elevated CO_2, N Concentration and N Forms on Photosynthetic Pigments Concentration and Composition

本文通过N供应浓度[2(低N),7(中N)和14(高N)mmol/L]和CO_2浓度[400(C1),625(C2),1 200(C4)μmol/mol]处理的水培试验一,以及硝铵比[14/0(N1),13/1(N2),11/3(N3)和8/6(N4)]和CO_2浓度[400(C1),800(C3),1 200(C4)μmol/mol]处理的水培试验二,共同研究黄瓜叶片光合色素对CO_2升高、N供应浓度和形态的响应。研究结果表明:苗期时,低、中和高N下,C4处理使得植物干物质都明显增加;而初果期干物质提高程度下降,植株生长速率降低。中等CO_2浓度(C3)显著增加植物在各硝铵比处理的干物质量,但最高CO_2浓度(C4)有提高N3处理的干物质量的趋势。苗期时,在低N和中N供应时C4处理显著降低叶片叶绿素a、叶绿素b和胡萝卜素含量;但高N时,C3处理提高总色素含量,C4处理提高叶绿素b含量;初果期时CO_2浓度处理对色素含量无显著影响;N2硝铵比处理,中等CO_2浓度(C3)下叶片的3种色素含量最高。因此当苗期N素供应浓度较低时,CO_2浓度升高会显著降低叶片3种色素的含量,这主要可能与苗期植物生长速率显著提高产生的稀释作用有关。当N浓度为14 mmol/L时,CO_2浓度适当提高显著促进色素合成,其合成速率大于植物生长速率,导致色素含量提高,提高光合能力;初果期时,CO_2浓度升高的促进作用降低缓和了色素浓度的下降。适当提高NH4+-N供应比例也能达到提高色素含量的效果,但CO_2浓度不宜过高。故而植物光合色素含量可能受到CO_2浓度升高导致的植物干物质增加速率和光合色素合成速率改变的双重调节。中N和高N供应时,叶绿素a/b在苗期随着CO_2浓度的升高而降低,在初果期仅在高N时有显著降低。而在硝铵比试验中,植株种植稀疏时,C4处理提高叶绿素a/b。因此,CO_2浓度升高下的植物捕光能力的提高,可通过适当降低叶片光照强度和提高N供应浓度来实现。从实际生产角度出发,使用中等浓度CO_2施肥,提高N肥供应浓度和NH4+-N比例,结合植株的适当密植更有利于光合色素含量提高,优化其组成,从而有利于黄瓜生物量的提高。

This study consisted of two experiments to study the leaf photosynthetic pigment concentrations of cucumber. The first one studied the effects of elevated CO2 and nitrate concentration under three nitrate concentrations [2（low N）, 7（moderate N） and 14（high N） mmol/L] and three CO2 concentrations [400 （C1）, 625 （C2） and 1 200 （C4）μmol/mol]. The second one studied the effects of elevated CO2 and N forms under three CO2 concentrations [400 （C1）, 800（C3） and 1200 （C4） μmol/mol] and four ratios of nitrate to ammonium concentrations [14/0（N1）, 13/1（N2）, 11/3 （N3） and 8/6（N4）]. The results showed that： at the seedling stage, C4 treatment enhanced the biomass of all the three N supplies and this effect decreased at the initial fruit stage. The biomass of C3 treatment increased and was the highest among the CO2 treatments. At the seedling stage, the chlorophyll a, b and carotenoids concentrations of the low and moderate N increased under C3 treatment, while high N increased the chlorophyll b and total pigment concentrations. Three pigment concentrations of N2 treatment were the highest under C3 treatment, while their concentrations in N3 treatment were the highest under C4 treatment among the CO2 treatments. Thus, at the seedling stage, elevated CO2 decreased three pigment concentrations of low N due to ＂dilution effect＂ caused by the high growth rate. But when N concentration was 14 mmol/L, elevated CO2 increased the pigment synthesis and this rate was higher than the growth rate, which resulted in higher pigment concentrations. This effect also existed with high ammonium supply. The pigment concentration was generally controlled by the growth rate and pigments synthesis rate simultaneously. Under moderate and high N, chlorophyll a/b at the seedling stage increased under high CO2, but only that of the high N decreased at the initial fruit stage. Moreover, C4 treatment enhanced chlorophyll a/b, which may be enhanced by high light density and low N concentration. Practically, the cucumber cultivation under elevated CO2 should combine with high N concentration, high ammonium supply rates and high plant density.