Spatio-Temporal Character Of Soil Respiration And Its Influence Factors In Apple Orchard Of Weibei Dryland

The Loess Plateau is not only an area suffering serious soil erosion in China, but also asuitable area for quality apple growth. Returning farmland to fruit is not only an importantmeans for local residents to get rid of poverty and become better off, but also a promisingmeasure to control soil erosion. The region has been seeing rapid growth of the apple orchardsince1980, and the apple orchard area has reached over100million hectares in2009,contributing to an output value of20billion yuan. Land use change is one of the importantfactor affecting terrestrial carbon cycle, Changing farmland to orchard is very likely animportant factor affecting regional carbon cycle. Understanding of carbon stock changes andits influencing factors after the conversion from farmland to the orchard contributes to theevaluation of ecosystem conversion of regional terrestrial ecosystem in view of its carbonsources and sinks feature.Chang Wu National Field Station for farmland ecosystem research on the Loess Plateauecosystem was taken as the base of this study, the orchard and adjacent farmland of the stationarea were selected as the object. Through field investigation and laboratory analysis,aboveground vegetation biomass, underground root biomass and organic carbon and nitrogenreserves of the0-100cm soil layer and its affecting factors were investigated after20years'history of restoring fruit. On this basis, the use of the LI-8100soil carbon flux measurementsystem (Li-COR, Lincoln, NE, USA) was conducted from June2010to December2011,respiration of orchard soil, soil temperature and moisture were determined. Interrelationamong soil respiration and soil temperature, soil moisture and other environmental impactfactors was analyzed. The nearby farmland (shilipu Experiment Station long-termexperimental field) was control treatment. From the point of view of soil organic carbonstorage and soil respiration, the mechanisms of returning farmland to fruit on the soil organiccarbon cycle of terrestrial ecosystems were discussed. The main results are as follows:(1) The SOC storage in0-100cm soil in apple orchard was50.7MgC ha-1, which waslower than that in crop land. For topsoil (0-20cm), SOC storage in apple orchard increased by9.2%against cropland, and for subsoil (20-100cm), SOC storage in cropland was more thanapple orchard. Total N in0-100cm of apple orchard was lower than that in cropland (p>0.05). Carbon and nitrogen storage in aboveground and root of apple tree were5.8and1.7times ascrop plant after20year conversion of cropland to apple orchard in the sloping cultivatedland.The apple tree trunk, branches and roots of new biomass is the main factor to lead to theaccumulation of carbon and nitrogen reserves of the orchard ecosystem.(2) In the two different land use patterns(Orchards and farmland), soil respiration has asimilar seasonal variation. Orchard soil respiration rate than the adjacent farmland30%(p <0.05), Cumulative soil respiration orchard in a year and a half increased by26%comparedwith farmland. In spring, orchards and farmland soil respiration rate of1.96μmol m^-2s^-1and2.21μmol m^-2s^-1, Orchard soil respiration rate was lower than11%of farmland (p>0.05).In summer and autumn, compared with farmland orchards average soil respiration rate, increased by41%and61%respectively.(p <0.05). In winter, the soil respiration is weak.Difference of Orchards and farmland soil temperature was significant, Orchards the averagesoil temperature lower than farmland1.8°C (p <0.05). Soil temperature and soil respirationshowed a significant exponential relationship (orchards: R2=0.6457,p <0.0001; farmland:R2=0.5650,p=0.0008),The temperature sensitivity of soil respiration (Q10) and orchards issimilar. Although soil temperature and moisture of the farmlands and orchards weredifferences, but can not explain the difference of the orchards and farmland soil respiration.(3) Different fruit tree crown (monoclonal), soil respiration spatial variability showed asimilar seasonal pattern, The average soil respiration rate were1.87μmol m^-2s^-1,1.91μmolm^-2s^-1s and2.06μmol m^-2s^-1.The average spatial coefficient of variation(CV) were25.1%,27.3%and22.3%.3,7,9month breathing space variation of the peak, other times thecoefficient of variation stabilized at around26.7percent. On a community scale, average soilrespiration rate of orchards is1.92μmol m^-2s^-1, average CV was11.7%, the amplitude ofvariation of less than farmland,The variation of the peak still appear in the3rd,7th,9thmonth.Level of spatial variability of the orchard soil respiration rate, soil temperature and itsvariability, soil moisture content and its variability were not significantly correlated. Theresult may be related to the heterogeneity the level of distribution of fruit tree roots (fine root).