半干旱区植物生长过程中叶片氧同位素组成的影响因素

Factors on oxygen isotopic composition of growing plant leaf material in semi-arid region

为识别半干旱区C_4植物(玉米)在生长过程中叶片有机质氧同位素的组成特征及影响因素,首先,我们对陕西西安郊区的玉米样品在不同生长季节内按不同生长部位采样,将整体叶片进行测试分析,结果表明:6月份采集样品,顶部叶片相对于底部叶片的δ^(18)O值要偏重,这一差异主要与顶部相对湿度较小有关;7月份采集样品,顶部叶片相对于底部叶片的δ^(18)O值要偏轻,这一差异主要与顶部有机质合成点叶片水的同位素组成偏负有关;7月份采样叶片的δ^(18)O值比6月份总体偏负,这一差异主要与7月份降水的δ^(18)O值相对6月份偏负有关。其次,我们对内蒙古准格尔皇甫川水土保持实验站的玉米样品随机采样,叶片按纵向和横向等间距剪切后进行氧同位素的测试分析,结果表明:叶片总有机质的δ^(18)O值主要受湿度控制,随着叶片的不断扩展,叶片总有机质的δ^(18)O值逐渐偏正,反映玉米生长后期环境中的湿度应高于生长初期。通过对实验结果的比较,我们认为C_4植被有机质的δ^(18)O值随取样部位和取样时间的变化而不同,其数值既与气候因素有关,也受植物生长过程的生物化学作用的影响。这是利用植物氧同位素组成解释环境气候变化时应该考虑的问题。

To identificate the change of oxygen isotopic composition of leave organic matter and major environmental parameters during different growing period of maize in semi-arid region. We firstly measure the maize leaves collected from Chang＇an in Shaanxi province. By contrasting top leaves to bellow leaves in the same individual corn,we find δ^18O values of top samples are heavy than those of bellow samples in June, while heavy in July. We attribute the difference to low relative humidity in top leaves and negative δ^18O values in top leave water, respectively. Comparing samples during different growing period, we find δ^18O values of leaves material in July is negative than those of leaves matter in June. We think the difference results from negative δ^18O values of meteoric precipitation in July comparing to those of June. Besides, we also measure the maize leaves collected in Inner Mongolia. The results suggest that there is an increasing process of δ^18O values in bulk organic material along a single maize leaf with expansion, the large range of δ^18O values is strongly relative to relative humidity during maize leaf development, decreasing δ^18O values of maize leaf material increases with relative humidity during expansion, we think δ^18O of leaves matter varies with different growing period and parts. We suggest biochemical fractionation effect may play a key role in affecting δ^18O values of leaves material, except for climate parameters. We should consider biochemical fractionation effect inferring environmental parameters from δ^18O values of plant leaves material.