Investigation The Variation Of Soil Respiration And Its Influencing Factors From Eroding And Depositional Sites

Soil respiration is an important component of global carbon cycle,the part of CO₂ from soil respiration is 70% of ecosystem's and then a small variation of soil respiration can prominently influence atmospheric CO₂ concentration.At present,there are many conclusions about soil respiration,but it is shortage about soil respiration variation and its factors from soil erosion and deposition.Globally,more than 60% of the land area are slopes with gradients > 8°,soil erosion and deposition is a process of material exchanging on land surface.It is crucial to investigate the mechanism of soil respiration across erosion site and deposition site for evaluating carbon cycle of terrestrial ecosystem.At the present study,a simulated experiment on soil erosion and deposition was conducted from April 2015 to November 2016 at Changwu State Key Agro-Ecological Station,Shaanxi,China.During the experiment,soil respiration was periodically measured using an automated CO₂ flux system Li-8100?LI-COR,Lincoln,NE,USA?and soil temperature and moisture were taken by series data collection system of soil temperature and soil moisture?EM50,DECAGON,USA?.The measurement frequency of soil respiration was once a week during 9 and 11 am.Soil temperature and soil moisture of 10 cm topsoil were measured continuously?at an interval of 30 minutes?.At the same time,runoff and sediment were collected as well each rain event,and then other indicators were measured including soil organic carbon?SOC?,dissolved organic carbon?DOC?and microbe biology carbon?MBC?.The results indicated that?1?Soil respiration at deposition sites was higher than at erosion sites?17.9%-57.7%?under different slopes.With slope increasing,soil respiration presented a decreasing tendency at erosion sites,it of 10 oand 20°had reduced 12.0% and26.1% comparing to the 5°,conversely it increased weakly at deposition sites.For the total soil respiration of erosion site and deposition site,it decreased gradually?5°: 3349.40 g.C.y-1>10°: 3089.44 g.C.y-1>20°: 2969.63 g.C.y-1?with slope growing.?2?Soil moisture had a remarkable variation between soil erosion sites and deposition sites across different slopes?P<0.05?.Soil moisture at deposition sites enhanced 8.7%-28.6%significantly than at erosion sites.There was a change e vidently with slope growing?P<0.05?both erosion sites and deposition sites.At erosion sites,soil moisture presented 5°>10°>20° and it trended as 5°<10°<20°at deposition sites.There was a small difference between erosion sites and deposition sites,and also it had no significant variation under differentslopes.?3?MBC of deposition sites was than erosion site's?P<0.05?that the amplification6.5%-49.8%.By slope growth,MBC of erosion site varied weakly,but it tended rising rapidly at deposition site(5°: 123.20 g.kg^-1>10°: 158.80 g.kg^-1>20°: 171.73 g.kg^-1).SOC and DOC of erosion site and deposition site varied similarly with MBC.Howe ver,SOC content in deposition site improved 7.2% than erosion site's on slope 5°and the difference of DOC between deposition site and erosion site was small.?4?In this experiment,soil moisture was a key factor affecting soil respiration which correlated with soil respiration showing an extremely significance quadratic relationship?P<0.0001?.Runoff related closely with soil moisture.The correlation between soil substrate and soil respiration was evidently.Soil respiration presented a rising tendency with SOC,MBC and DOC content increasing.And the spatial variation of soil substrate was caused by sediment transporting from erosion site to deposition site.Soil respiration under soil erosion and deposition had no relationship closely.It concluded that spatial variation of soil moisture and substrate was resulted from runoff and sediment redistribution on erosion site and deposition site.Soil erosion and deposition would contribute to reduce CO₂ flux of land surface.