| Fine roots are not only an important pathway for atmospheric carbon(C)from plants put into soil,but also the main organs for plants to absorb soil nutrients.Change of fine root morphological and dynamic characteristics may regulate ecosystem C dynamics.With the development of the economy,atmospheric nitrogen(N)deposition has been increasing since the 20 th century,and may have potential effects on fine roots.Despite previous studies,the effects of N deposition on the morphological and dynamic characteristics of fine roots have been reported,but the results of many studies are not entirely consistent.At the same time,our understanding of the mechanisms of N deposition affecting fine-root changes is still unclear.Based on the uncertainty of the effect of N deposition on fine root characteristics,an N addition experiment was established in Larix gmelinii of Daxinganling to the effect of simulated N deposition on the morphological and dynamic characteristics of fine roots.The experiment plots were built in July 2010,and the N addition was started in May 2011.Four levels of N addition treatments were included in this study,Control(CK,0g N m-2 yr-1),Low-N(2.5g N m-2 yr-1),Medium-N(5 g N m-2 yr-1),high-N(7.5 g N m-2 yr-1),each treatment including 3 repeats.The root morphological characteristics(fine root surface area,diameter and number)and dynamic characteristics(fine root production and turnover)were observed using minirhizotron technology under the N addition treatments.The changes of root anatomical structure were observed by paraffin section technique,and the anatomical structure was used to explain the variation of fine root diameter.At the same time,soil physical and chemical properties(total C,total N,etc.)and environmental parameters(temperature and humidity)were also determined.In the upper layer(0-20 cm),the addition of nitrogen significantly reduced the number of fine roots and the total surface area during the observation period,and the amount decreased with the increase of nitrogen addition.Nitrogen addition significantly increased the mean diameter of the live fine roots.Nitrogen addition significantly reduced root production rate and reduced root turnover rate which estimated using root production.In the lower layer(20-40 cm),the results of observation were different from that of the upper soil.Low-N addition(Low-N and Medium-N treatments)significantly increased the number of live roots and surface area during the observation period in the deep soil layers,while no significant change was observed under high N addition treatment.Nitrogen addition increased the root production rate in the deep soil layers,but did not significantly alter the root turnover rate.By observing root anatomical structures,it was also found that low level N addition could significantly increase root diameter,but high levels of N addition did not significantly alter root diameter.Root anatomical structure explained that the increase of diameters of low order roots(1,2,3 roots)at low level of nitrogen treatment may be mainly due to the increase of vascular bundle diameter.In addition,the effects of nitrogen addition,soil depth,year and their interaction on root morphology,dynamics and soil physical and chemical properties were also significantly.The results showed that the decrease of root number and surface area and the increase of root number in the deep soil layers suggested that the increase of atmospheric nitrogen deposition might change the nutrient uptake strategy and vertical distribution of root system.The change of root number also indicated the decrease of underground C allocation.The decrease of root turnover rate under nitrogen deposition may increase the residence time of root carbon in the soil,and through increasing soil root life cycle decrease soil C cycle.Soil depth and year on root morphological characteristics and dynamic characteristics,indicating that environmental factors may also significantly affect the root production and turnover,thereby affecting the dynamics of ecosystem C. |
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