Studies On Nodule Structure Of Actinorhizal Plants And Photosynthetic Characteristics Of Alnus Cremastogyme

Actinorhizal Plants are a kind of important natural nitrogen-fixing resources,and they have high value in reforestation as pioneer and accompanying species.This study focused on the structural diversity of nitrogen-fixing system from seven actinorhizal species in China, and the photosynthetic characteristics of Alnus cremastogyme introduced into Jiangsu province.The main conclusions are as follows:(1)The primary structure and secondary structure of seven actinorhizal plants have the basic root structure of woody dicotyledon. But in both periods, the cell layers forming various structural parts and their proportion in root structure are significantly different.(2)The nodules of actinorhizal plants showed diversity in morphology and structure. Myrica rubra's nodules developed into clusters at the base, and the nodule-valves divided once, while the other six nodules were coral-spherical sphericity. Nodulesroots were found in Myrica rubra and Casuarina equisetifolia, while no nodulesroots were investigated in the other five speices. The distribution patterns of infected cortex cells were remarkably variable, e.g. continuous in Myrica rubra and Coriaria nepalensis, discrete in Casuarina equisetifolia, Alnus cremastogyme and Alnus rubra, and semi-continuous in Elaeagnus pungens and Hippophae rhamnoides. The infected cortex cells of Coriaria nepalensis were asymmetricaly distributed on one-half side of the vascular bundle, while the other species symmetrically around the vascular bundle.Sometimes there are two vascular bundle in the nodule-valves of Casuarina equisetifolia.(3)Alnus cremastogyme gennerally had more origins while forming nodule primordium,the primary nodule and the young nodule from nodule-valves were similar in the external morphology. Nodule primordium were not infected in early stage,but with the growing of primordium the Frankia began to invade from one side. The infected cortex cells occurred continuously, no stratification phenomenon was found.(4)The daily change of mature leaf in net photosynthesis rate in the stand of introduced Alnus cremastogyme showed two distinct kinds of variation patterns, e.g. single-peak curve in spring and autumn , and double-peak curve in summer. The annual change pattern of net photosynthesis rate was characterized by a double-peak curve. The change trends of net photosynthesis rate in the stand are similar to those in the original locality of this species, however, the time of peak value and change range is different.The growth season in Nanjing were available from March to November at least according to the annual changes of net photosynthesis rate.