Morphological Foraging Behavior And Nitrogen Utilization Strategy Of Vetiveria Zizanioides L. In The Process Of Ecological Restoration Of Coal Spoil-heaps

To figure out the proactive adaptation mechanism of Vetiveria zizanioides L.in ecological restoration of tailings,V.zizanioides planted on coal spoil-heaps of Dahe Coal Mine in Liupanshui City of Guizhou Province for 4,5,8 and 15 years were used as research objects,using a combination of field sampling and indoor analysis,the allometric growth of V.zizanioides biomass,the above-ground morphology,the nitrogen allocation proportion in root,stem,leaf and nitrogen and phosphorus ratio,nitrogen utilization efficiency of roots,stems,and leaf were studied dynamically(5-10 months).And the morphological indexes of the root of V.zizanioides were measured in July(Such as total root length,total surface area,volume,etc.),the main results were as follows:(1)The biomass of above-ground and under-ground of V.zizanioides was the smallest the planting year of 15 years.The “peak value” of above-ground and under-ground biomass of the four planting years of V.zizanioides occurred in September and August respectively,and the longer the planting year,the longer the biomass of V.zizanioides to decrease.There is an allometric relationship between biomass,and the decisive factor between above-ground and under-ground biomass is relatively low,only 0.74 or more,while the decisive factor of above-ground biomass and under-ground biomass and total biomass is 0.96 and 0.85 or more,which is relatively high,the use of above-ground biomass to estimate total biomass is better than under-ground biomass.(2)The plant height,tiller number and leaf area of V.zizanioides increased with the increase of planting years for the four planting years,but the tillering distance and stem diameter reached the maximum when the planting year was 8 years,plant height and tiller distance showed a gradual increase with the increase of the month with thegrowth period,and the value was the largest in October,while the maximum number of tillers,stem diameter and leaf area appeared in August.When the planting period was 4 years,the plant height and tiller distance of variation from of V.zizanioides were the maximum values among the 4 planting years,and the coefficient of variation of the number of tillers in the year was the minimum of 4 planting years.The tiller number is the largest at the time of planting 8 years,but the coefficient of variation of plant height at 8 years of planting is the minimum between 4 planting years.When the planting year was 15 years,the coefficient of variation from stem diameter was the minimum of 4 planting years.(3)The different root morphology of V.zizanioides had inconsistent trends with planting years and root diameter;the length of first lateral roots was about 20-35 cm,the length of second lateral roots was 8-14 cm,and the length of third lateral roots was 6-12 cm;the density of second lateral roots was above 0.76 No./cm,while the density of third lateral roots was above 2.68 No./cm.The specific root length of V.zizanioides increased gradually with the increase of planting year and reached the maximum value at the planting time of 8 years.The root length of the root diameter D? 1 mm was greater than the root diameter D >1 mm.In the root system,when the root area of D ? 1 mm had the smallest specific root area at 15 years,which 51.17cm~2/g,D>1 mm,the root area was the smallest at the planting age of 4 years,which is31.01.cm~2/g.(4)The content of nutrient elements of V.zizanioides is potassium > nitrogen >phosphorus.Nitrogen is mainly concentrated in leaves,phosphorus and potassium are mainly concentrated in stems and leaves.Nitrogen,phosphorus,and potassium in the roots are all less.The distribution of nutrient in V.zizanioides is influenced by the planting years and the growth period,and the timely transfer and distribution between the roots,stems and leaves.From May to October,the N/P of V.zizanioides increased gradually with the increase of planting year,but it was almost always below 14,which belonged to nitrogen limitation.The minimum nitrogen use efficiency of roots,stems,and leaves for four planting years occurred when the planting period was 15 years,and the utilization efficiency of the leaves was the lowest.The nitrogen use efficiencyof roots was higher than in stems from May to June,the nitrogen use efficiency of stems was higher than in the roots from July to October,and the utilization efficiency of the leaf was the lowest from May to October.