The Respiration Study Of Soils With Moss Biocrusts In Karst Rocky Desertification Areas

In recent years,the CO₂ exchange between karst ecosystems and the atmosphere has received widespread attention under global climate change scenarios.As an important ground cover in karst rocky desertification areas,moss biocrusts can increase soil organic carbon content through photosynthetic carbon sequestration,affect soil respiration processes,and play an essential role in regional carbon cycling.In this study,respiration of soils with moss biocrusts was studied on both sides of Huajiang gorge,a typical karst plateau gorge with rocky desertification in Guizhou Province,China.By in situ monitoring experiments,we obtained the basic data of the dynamic changes of the photosynthetic rates of moss biocrusts and the respiration rates of soils with moss biocrusts,and revealed the effects of moss biocrusts on soil respiration in karst desertification areas.By measuring soil nutrient contents,enzyme activities,and microbial communities,we discussed the effects of moss biocrusts on soil respiration.The main results were as follows:(1)The photosynthetic rate of moss biocrusts peaked from 9:00 to 11:00,and the diurnal variation showed seasonal differences.The mean photosynthetic rate of moss biocrusts in spring,summer,autumn,and winter was 0.62,0.43,1.76,and 1.58?mol·m^-2·s^-1,respectively.The photosynthetic rate of moss biocrusts varied with month,with a maximum value of 2.64?mol·m^-2·s^-1 in January and a minimum value of 0.66?mol·m^-2·s^-1 in May.The photosynthetic rate of moss biocrusts was quadratically related to atmospheric temperature(Ta)and photosynthetically active radiation(PAR).When Ta<20°C or PAR<500?mol·m^-2·s^-1,the photosynthetic rate of moss biocrusts increased with increasing Ta or PAR.When Ta>20°C or PAR>500?mol·m^-2·s^-1,the photosynthetic rate of moss biocrusts decreased with increasing Ta or PAR.The photosynthetic rate of moss biocrusts showed a linear relationship with atmospheric relative humidity(RH),increasing with the increase of RH.(2)In spring and summer,the diurnal variation of net carbon flux in soils with moss biocrusts showed a single-peak curve,and soils with moss biocrusts showed carbon sources at each time of the day.In autumn and winter,the diurnal variation of net carbon flux of soils with moss biocrusts showed a"V"shape,and soils with moss biocrusts showed carbon sinks from 9:00 to 15:00.The diurnal variation of respiration rate of soils with moss biocrusts,soils without intact moss biocrusts,and bare soils showed a single-peak curve in spring and summer,peaking from 13:00 to 15:00.The diurnal variation of soil respiration rate of the three treatments was not obvious in fall and winter.The respiration rate of soils with moss biocrusts,soils without intact moss biocrusts,and bare soils varied with month.The mean value of soil respiration rate of the three treatments was as follows:soils with moss biocrusts(2.88?mol·m^-2·s^-1)>soils without intact moss biocrusts(2.33?mol·m^-2·s^-1)>bare soils(2.18?mol·m^-2·s^-1).The mean net carbon flux of soils with moss biocrusts was 1.62?mol·m^-2·s^-1,which was significantly lower than the mean respiration rate of soils without intact moss biocrusts and bare soils.The results indicated that moss biocrusts played an important role in carbon cycling by reducing carbon sources and increasing carbon sinks in karst rocky desertification areas.(3)The respiration rate of soils with moss biocrusts,soils without intact moss biocrusts,and bare soils were all significantly and exponentially correlated with soil temperature at 5 cm depth and soil volumetric water content at 0?5 cm,but soil temperature explained more of the variation in soil respiration rates(57.7%?65.3%)than soil volumetric water content(33.3%?40.0%)in all three treatments.The respiration rate of soils with moss biocrusts,soils without intact moss biocrusts,and bare soils increased exponentially with increasing soil temperature but decreased exponentially with increasing soil volumetric water content.There was significant difference in the temperature sensitivity of soil respiration among treatments.The mean temperature sensitivity of soil respiration(Q₁₀)of the three treatments was as follows:soils without intact moss biocrusts(4.60)>bare soils(3.43)>soils with moss biocrusts(2.34).The results implied that,compared with soils without intact moss biocrusts and bare soils,the cover of moss biocrusts will significantly reduce CO₂ emissions under global warming scenarios.(4)The removal of moss biocrusts significantly reduced soil nutrient contents and enzyme activities.Compared with soils with moss biocrusts,the removal of moss biocrusts reduced soil organic carbon,total nitrogen,total phosphorus,ammonium,and nitrate by 31.5%,38.9%,15.6%,51.4%,and 82.6%,respectively,and reduced soil sucrase,?-glucosidase,and urease by 57.0%,38.9%,and 47.0%,respectively.The removal of moss biocrusts significantly affected soil microbial communities.In comparison with soils with moss biocrusts,the removal of moss biocrusts significantly reduced soil bacterial 16S r RNA gene copy number and?-diversity(Shannon and Chao1 indices),as well as significantly altered soil bacterial community structure,functional profiles and co-occurrence network patterns.The results demonstrated that,in karst rocky desertification areas,moss biocrusts played an important role in maintaining soil fertility and microbial diversity,thus regulating soil respiration and its dynamic change.In summary,moss biocrusts play an important role in carbon cycling by reducing carbon sources and increasing carbon sinks by its photosynthesis and influence on soil respiration,and provide indispensable ecosystem functions and services by maintaining soil fertility and microbial diversity in karst rocky desertification areas.Therefore,this paper suggests that moss biocrusts could be involved as a supplementary method to improve the structure and function of the karst damaged ecosystem in combination with other ecological restoration methods,thereby promoting ecological restoration and reconstruction in karst rocky desertification areas.