修枝截干对二球悬铃木叶片光合特性的影响

Effect of branch and stem pruning on photosynthetic characteristics of Platanus acerifolia L.

采用Li-6400便携式光合作用测定系统对修枝截干和自然生长的二球悬铃木中部当年向南枝顶的完全展开叶进行单叶光合特性测定。结果表明,修枝截干和自然生长的二球悬铃木叶片的净光合速率(Pn)日变化均呈双峰曲线,有明显的"午休"现象,最高峰发生在11:00,次高峰在15:00,光强最大时(13:00)Pn最低,即两种生长状态下都受到光抑制。修枝截干二球悬铃木P_n[μmol(CO_2)·m^(-2)·s^(-1)]的最高峰为12.16,次高峰为9.21,最低谷为6.47,分别比自然生长高27.06%、69.93%和159.84%,这暗示修枝截干可促进光合作用,减轻光抑制。修枝截干的Pn?光量子通量密度(PPFD)响应可拟合为Pn=12.30(1-1.1353e^(-0.0302PPFD/12.30))(R^2=0.9891^(**)),自然生长的为P_n=10.92(1-1.1307e^(-0.0305PPFD/10.92))(R^2=0.9849^(**)),修枝截干的最大光合速率(P_(max))、光补偿点、光饱和点及光合幅度的估算值分别为12.30μmol(CO_2)·m^(-2)·s^(-1)、51.67μmol·m^(-2)·s^(-1)、1927.32μmol·m^(-2)·s^(-1)和1875.65μmol·m^(-2)·s^(-1),分别比自然生长提高12.64%、17.33%、13.85%和13.76%,这意味着修枝截干可提高单叶对光能的利用。修枝截干的P_n-CO_2浓度(Ci)响应可拟合为P_n=11.96(1-1.4716e^(-0.0287Ci/11.96))(R^2=0.9824^(**)),自然生长的为P_n=10.70(1-1.4657e^(-0.0292Ci/10.70))(R^2=0.9810^(**)),修枝截干的P_(max)、CO_2补偿点、CO_2饱和点及CO_2幅度估算值分别为11.96μmol(CO_2)·m^(-2)·s^(-1)、67.54μmol·mol^(-1)、872.02μmol·mol^(-1)和804.48μmol·mol^(-1),分别比自然生长提高11.78%、-27.44%、0.39%和3.73%,说明修枝截干可增强叶片对低浓度CO_2的同化能力。

Photosynthetic characteristics of south-facing single full-leaf in one-year branch of Platanus acerifolia L. with branch and stem pruning （BSP） or under natural conditions （NG） were determined using Li-6400 portable photo-meter. The results show that diurnal variations in net photosynthetic rate （Pn） of P. acerifolia single full-leaf under BSP and NG follows a di-peak curve. The first peak appears at 11：00, the second at 15：00, while the minimum peak occurs at 13：00 （when light intensity is highest）. This indicates a remarkable midday depression. The leaves under both conditions suffer from photo-inhibition. Pn [μmol（CO2） · m^-2 · s^-1] of the first peak, second peak and the minimum peak of P. acerifolia leaf under BSP are 12.16, 9.21 and 6.47, which are respectively 27.06%, 69.93% and 159.84% higher than those under NG This implies that BSP improves photosynthesis, while at the same time reduces photo-inhibition. Best-fit response curves for P, to photosynthetic photon flux density （PPFD） in P. acerifolia leaf under BSP and NG are expressed as Pn = 12.30 （1-1.135 3 e-0.030 2PPFD/12.30） （R2=0.989 1＊＊） and Pn = 10.92 （1-1.130 7e-0.030 5PPFD/10.92） （R2=0.984 9＊＊） respectively. The values of max P, （Pmax）, light compensate point, light saturation point and PPFD range of P. acerifolia leaf under BSP are 12.30 μmol（CO2）· m^-2 ·s^-1, 51.67μmol · m^-2 · s^-1, 1 927.32 μmol · m^-2 · s^-1 and 1 875.65 μmol · m^-2 · s^-1 respectively; which are 12.64%, 17.33%, 13.85% and 13.76% higher than those under NG, respectively. This suggests that BSP treatment could increase utilization of light energy in P. acerifolia. The best-fit response curves for Pn to CO2 concentration （Ci） of P. acerifolia leaf under BSP and NG are expressed as P, = 11.96（1-1.471 6e-0.028 7C/11.96） （R2 = 0.982 4＊＊） and Pn = 10.70（1- 1.465 7e-0.029 2C/10.70） （R2 =0.981 0＊＊） respectively. Pmax, CO2 compensate point, CO2 saturation point and Ci range under BSP are respectively 11.96 μmol（CO2） · m^-2 · s^-1, 67.54 μmol · mol^-1, 872.02 μmol · mol^-1, and 804.48 μmol · mol^-1; which are 11.78%, -27.44%, 0.39% and 3.73% higher than those under NG, respectively. This indicates that BSP treatment increases CO2 assimilation ability of P. acerifolia under low CO2 concentration condition.