城市土壤压实对树木叶片叶绿素及光合生理特性的影响

由于机械碾压、人为践踏等原因,城市土壤压实严重。由于压实,土壤物理性状发生改变:土壤容重增大、孔隙度降低及结构性变差等。这些改变影响土壤性质的同时影响树木的生长。以乐昌含笑Michelia chapensis、深山含笑Michelia maudiae和大叶冬青Ilexlatifola为实验材料,参照南京市土壤压实现状模拟不同程度的土壤压实环境,研究了土壤压实下乐昌含笑、深山含笑和大叶冬青3种幼树叶片叶绿素含量、光合生理特性等的变化情况。采用乙醇萃取法测定树木叶片叶绿素含量,用美国Li-COR公司生产的Li-6400光合仪测定树木叶片光合生理特性,测定参数包括净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、胞间CO2摩尔分数(Ci)等。并分析树木叶绿素含量在不同土壤压实环境下变化差异性,及各光合生理参数之间相关性。结果表明,随着压实强度的增强,3种树种叶绿素含量逐渐降低;与对照相比,不同压实处理下,叶片叶绿素含量均不同程度下降,且在重度压实下各树种叶片叶绿素含量降低幅度均最大,分别达到41.87%、29.36%及27.66%;方差分析表明,各土壤压实处理下叶绿素含量与对照之间存在显著性差异;在压实环境下,光合生理特性参数值净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)与对照下各参数数值相比也呈下降趋势。皮尔森相关性分析发现,各光合生理特性参数之间相关性显著。但不同压实处理下,各树木胞间CO2浓度(Ci)变化趋势不一致。

The impact of soil compaction on chlorophyll and photosynthetic characteristics of trees

The soil in urban area is often compacted resulted from machinery and human trampling, in which the physical character-istics of soil change remarkably with the increasing in bulk density, reducing in soil porosity as well as the damage to soil structure, and the plant growth is restricted as a result. In this paper, two months after four levels of soil compaction were simulated based on the investigation of soil compaction status in Nanjing city, the photosynthetic attributes and the chlorophyll concentrations of three types of saplings (Michelia chapensis, Michelia maudiae and Ilex latifola) were measured to study the impact of soil compaction. The chlorophyll concentrations of sapling were determined by the ethanol extraction method, and the photosynthetic attributes, such as net photosynthetic rate, stomatal conductance, transpiration rate and intercellular CO_2 concentration, were measured by Li-6400 system produced by Gene Company of USA. The main results showed, for the all three plants, the more the soil compacted, the lower the chlorophyll concentrations and net photosynthetic rates, stomatal conductance and transpiration rates, and the chlorophyll concentrations for Michelia chapensis, Michelia raaudiae and llex latifola decreased 41.87%, 29.36% and 27.66% compared with the control respectively Besides, there were existed significantly positive Pearson correlation among these photosynthetic parameters, but not the intercellular CO_2 concentration.