Ecological Stoichiometry Characteristics Of Gahnia Tristis In Red Soil Erosion Area Of South China

Red soil erosion area in South China is a typical area of serious ecosystem degradation,which is the area with the largest soil and the most serious soil erosion area in South China.The degraded ecosystem has seriously restricted the development of local economy and society.Vegetation restoration is the premise of restoration and reconstruction of degraded ecosystem,so the first step of ecological restoration and reconstruction is vegetation restoration.In this study,Laiyoukeng(plot I,plot II)and Huangnikeng(plot III)in Changting County,Fujian Province were selected as research areas,and the native plant Gahnia tristis was taken as research object.Through the experimental research on ecological stoichiometry,phenotypic characteristics and plant stress resistance,the growth status,nutrient demand and physiological response mechanism of Gahnia tristis were analyzed.Combined with the changes of soil factors,the relationship between the indexes of Gahnia tristis and the soil physical and chemical properties was analyzed,and the environmental adaptation of Gahnia tristis in the red soil erosion area was discussed.The main results were as follows:(1)The functional traits and morphological characteristics of the leaf of Gahnia tristis were different in different plots and time,among which leaf width,leaf tissue density,leaf chlorosis SPAD value and leaf length were larger in summer than in winter;The specific leaf area in summer was smaller than that in winter,while the leaf thickness,leaf area,leaf dry matter content and leaf relative water content had no obvious change trend.Root tissue density was higher in summer than in winter,while specific root length and specific root area were lower in summer than in winter.In addition to the carbon content,the nitrogen,phosphorus and potassium content in the leaf of Gahnia tristis increased in the order of I,II and III plots.The contents of root nutrients were lower in summer than in winter,and the time difference of the plots was more significant.On the whole,the nutrient contents of leaf were higher than those of roots,and higher in December than in July.The difference of root nutrient contents was more significant than that of leaf.The ratio of N/P was much more than 16,the ratio of N/K was much less than 2.1 and the ratio of K/P was also more than 3.4.In the process of adapting to the environment,the Gahnia tristis adjusts its functional traits and morphological characteristics continuously,which results in a series of complex correlation among the functional traits and morphological characteristics.(2)The physiological indexes of the leaf can reflect the degree of environmental stress and the tolerance of the plant to some extent.The three indexes of antioxidant enzyme activity show different trends.The activity of CAT in summer was higher than that in winter but the difference is not obvious,the activity of SOD in summer was higher than that in winter obviously,the activity of POD in winter was significantly higher than that in summer and plot III was significantly different from the other two plots.The change of relative conductivity in summer was significantly higher than that in winter.The change of MDA content was more complex,only plot II had significant difference in time.The change of free proline content showed a trend that summer was significantly greater than winter.In general,there were some differences in the physiological and biochemical indexes among plots especially in time.The SOD activity and relative conductivity are the most important physiological indexes in the leaf of Gahnia tristis,they can be used as the first index to evaluate the environmental adaptability of the plant.The stress was the most serious in July and the plot III,and the mechanism of plant mobilization and ecological adaptation was more prominent.Therefore,the growth of the plant was more sensitive to high temperature stress.(3)The change of soil bulk density was not significant,the soil water content and p H value were different among the three plots and the soil water content varied greatly in time.Due to the different sampling areas,the total nutrient content of soil in the study area was significantly different from that in plot I and II,which showed that the content of carbon and nitrogen was significantly lower than that in plot I and II,while the content of phosphorus and potassium was significantly higher than that in plot I and II.The content of nitrogen,phosphorus and potassium in the three plots showed a trend that summer was less than winter.There were some differences in the time of soil available nutrients between the sample plots and the sample plots themselves,ammonium nitrogen was the most significant in the time,which shows that the content of ammonium nitrogen in July was significantly higher than that in December.There were some differences in the stoichiometric ratio of soil nutrients between plots and in time,but the difference between AN / AP and AN / AK in summer and winter was the most significant.(4)The functional traits and morphological characteristics of the leaf of Gahnia tristis in the study area were mainly affected by the content of soil ammonium nitrogen,soil water content,soil total phosphorus content,soil available phosphorus content,soil available potassium content and soil total nitrogen content.Besides root diameter,root phenotypic characters were mainly affected by total nitrogen,ammonium nitrogen and soil moisture content.The correlation between the root system and soil nutrients was stronger than that of the leaf.In general,the total amount of soil and the available nutrients have little effect on the Gahnia tristis.Ammonium nitrogen,water content,total phosphorus and available phosphorus were the main factors affecting the changes of leaf physiological indexes.