Studies Of The Effects Of Accumulated CaCO₃in Soil On The Phenotypic Plasticity Of Artemisia Ordosica In Arid And Semi-arid Areas And Their Mechanisms

Artemisia ordosica Krasch. is an important constructive species on sandy land in the northwest of China, which is widely distributed in the Kubuqi desert, Mu Us Sandy land, Tengger Desert, Ulan Buh Desert, and Hexi Corridor sandy land in Gansu Province. A. ordosica plays an important role in desert and sandy land revegetation. Therefore, the stability of A. ordosica community is not only a significant practical problem, but also an important scientific issue. Preliminary study from the laboratory of Ecology of Nankai University showed that, A. ordosica community would be replaced by Ceratoides arborescens or Artemisia. frigida community, and the accmumulaton of calcium carbonate could affect the density of A. ordosica community. Theoretical analysis showed that, if the accumulation of calcium carbonate can affect the density of A. ordosica community, it can also affect its size and biomass. In other words, calcium carbonate would affect the phenotypic plasticity of A. ordosica plants, which needs to be confirmed by experiments.In this study, the inhibitive effects of accumulated calcium carbonate on A. ordosica seedlings were investigated by performing potting experiments, the effects of N/P ratios on the raletive growth rates of seedlings were also examined; the effects of accumulated calcium carbonate on the RNA contents in A. ordosica were investigated by field sampling analysis. To comprehensively analyze the inhibitive effects of accumulated calcium carbonate on the phenotypic plasticity of A ordosica and their possible mechanisms, the calcium carbonate contents in arid and semi-arid areas and the features of calcium components in A. ordosica from different geographical regions, as well as the calcium component contents in A. ordosica plants from arid and semi-arid areas, were studied. The four main results of this research were summarized as follows:1. To examine the response of A. ordosica seedlings to different concentrations of soil calcium carbonate, potting experiments were performed in Greenhouse. The results showed that, with the soil calcium carbonate concentrations increased, the root length, and the increment of plant height and root reduced, and the growth of the roots were restrained. The results of determination of N and P contents in seedlings showed that, the contents of N and P of the seedlings without calcium carbonate addition were significantly higher than those with calcium carbonate addition. The N contents decreased with the calcium carbonate contents increased. The P contents exhibited the same trends as that of N contents. The regression analysis showed that, the root relative growth rates showed significant logarithmic negative correlation with the N/P ratios, while showed logarithmic positive correlation with P contents of the seedlings. This result indicated that, accumulated calcium carbonate in the soil affected the phenotypic plasticity to A. ordosica seedlings, and the N/P ratios of A. ordosica seedlings were the direct cause.2. Representative A. ordosica communities were selected from natural habitats, and the plant and soil samplings were colleted, which were analyzed in the laboratory. The soil calcium carbonate contents and RNA contents in the A. ordosica leaves were determined. The results showed that, the soil calcium carbonate contents increased as the sandy land was fixed. However, RNA contents in the leaves showed the opposite trend. The regression analysis showed the same results. This result confirmed the results of the potting experiments as mentioned above. P availability in soil is affected by the increase of calcium carbonate, which can also affect the RNA content in plants. Based on this theory, the inhibitive effects on the A. ordosica seedlings was caused by the restriction of soil P availability which was caused by soil calcium carbonate accumulation, and therefore the RNA contents were reduced, and the growth of seedlings was restrained. All above factors finally directely inhibited the phenotypic plasticity of A. ordosica seedlings.3. Plant samples of A. ordosica were collected from Hangjin county, Wushen country and Alashan zuoqi country in Inner Mongoilia autonomous region, Yanchi country in Ningxia Hui autonomous region and Yuyang district of Yulin city in Shaanxi province, and calcium components of these samples were determined. The results showed that, in different geographical regions, the plants containing more water soluble Ca were from the populations with greater rainfall, while more hydrochloric acid soluble Ca were from the populations with less rainfall. Moreover, water soluble Ca mainly existed in leaves, while the hydrochloric acid soluble Ca distributed in the roots. The increment of soil calcium carbonate resulted in the soil water fixation and hence reduced the soil water avilabitlity. Therefore, accumulated soil calcium carbonate reduced the content of water soluble Ca in plants, hence affected the growth of plant. From another perspective, the alteration of calcium components in plants was another indirect reason affecting the phenotypic plasticity of A. ordosica.4. Analysis of soil calcium carbonate contents and calcium components of A. ordosica communities from Alashan country in arid land and Yulin city in semi-arid land showed that, in the depth of0-40cm in the A. ordosica communities from Alashan, soil calcium carbonate contents were significantly higher than those from Yulin city. In the A. ordosica community from Alashan, old plants held more hydrochloric acid soluble Ca than that in the adult plants, while in Yulin city adult plants held more hydrochloric acid soluble Ca than that in the old plants. Most of the hydrochloric acid soluble Ca existed in the roots of the plant from Alashan country, but most of the hydrochloric acid soluble Ca existed in the leaves of the plant from Yulin city. The content of hydrochloric acid soluble Ca in root and shoot of plants from Alashan country were significantly higher than that in Yulin city. Microscopic observations showed that, there were many calcium oxalate crystals with different shapes (druse, raphide, and column crystals) in the root, shoot and leaf of plants, especially in the root and shoot.In conclusion, accumulated calcium carbonate in the soil inhibited the phenotypic plasticity of A. ordosica plants. The change of N/P ratios in A. ordosica plants was the direct reason for the inhibitive effects on the phenotypic plasticity of A. ordosica plants, and the different content of RNA and calcium components were another two indirect reasons.