应用电子探针对植物根际和根内营养元素微区分布的探讨

用电子探针可检测出玉米、大豆根际和根内含有Na,Mg,Al,Si,P,S,Cl,K,Ca,Ti,Fe,Cu和Zn 13种元素。这些元素在根际土壤、粘液层和根组织内的含量分布有一定的规律性。除Si,Al,Ca,Fe在根际土壤中峰值较高外,Ti仅在土壤中达到可检测量;S,Fe和Zn富集在粘液层,Mg,P,Cl只在根组织内才有较明显的峰。这些规律可作为区分根—土界面的参考指标。K含量在根内明显高于根际土壤,并由表皮层到中柱径向增加;Ca则与K不同,且受植物种类的影响。

Distribution of Nutrients in the Root and Rhizosphere by Electron Probe X-ray Microanalysis

In the present investigation, the distribu-tion of 13 minera1 elements, i. e., Na, Mg, Al,Si, P. S. Cl, K. Ca, Ti, Fe, Cu, and Zn in therhizosphere and root tissues of maize and soy-bean grown in various types of soils has beenmeasured by electron X-ray microanalysis. The distribution of these elements showsome regular patterns. The peaks of Si, Al,Ca, Fe are the highest in rhizosphere, while Tiis detected only in rhizosphere but not in roottissue. However, most part of the surface ofthe root is found to be covered with mucilagelayer, and X-ray microanalysis shows enrich-ment of S, Fe and Zn, and to a lesser extentof Si, Al, Ca. The peaks of Mg, P, Cl are alsolimited to root tissue. Thus, these differencesin distribution may be useful in delineating theroot-soil interface by measuring to concentra-tion of different mineral elements. The results also reveal that the height ofthe peak of K increases from epidermis to steleof the roots, but P, S and Cl do not accumulatelocally. Fe and Zn are concentrated in the epi-dermis rather than in the stele. The distri-bution of Ca in the root varies with plant spe-cies and soil type. In maize roots, a lot ofCa is found in epidermis and endodermis butlittle in stele, indicating that the mechanisms ofK and Ca movement are different, Ca is severe-ly blocked by the Casparian strip developedin the endodermis. The same trend is alsoobserved for Mg. Nevertheless, in soybean rootsgrown on calcareous sandy loam, large amountsof Ca and Mg are detected in stele as well asin other parts, suggesting that Ca can permeatemore easily in soybean root than in maize root.But no accumulation of Ca and Mg appears inthe stele of roots grown on acid sandy loamwhich is low in concentration of these twoelements.