| The characteristics of complexity and indirect observation of belowground ecosystem have influenced scientists’ in-depth investigation on its features and functions.Fine root(d<2 mm)is vital organ for transportation and absorption of water and nutrients,therefore its growth,turnover and decomposition play a significant role in carbon and nutrients cycling in terrestrial ecosystem,especially its contribution to organic carbon,nutrient elements(N,P,K),and biological circulation via plantation-soil-plantation.Qinghai is one of the most seriously injured provinces that suffers from severe desertification.Plant restoration and reconstruction of degraded ecosystem can be achieved by creating artificial forests for wind prevention and sand fixation,which further contributes to preventing the spread of desertification.As the most active part of roots in belowground ecosystem,influence mechanism of fine roots’ characteristics on material circulation and energy flow in desert ecosystem,as well as contribution rate of fine root dynamics towards carbon and nutrients cycling,stay unclear.Typical sand-fixation artificial forests on alpine sandy land in Qinghai Gonghe basin were research objects,including Salix cheilophila,Salix psammophila,Salix microstachya,Populus simonii,Salix cheilophila-Populus simonii mixed forest in dune slack,and Caragana intermedia,Caragana Korshinskii,Artemisia desertorum,Caragana intermedia-Artemisia desertorum mixed forest in fixed dune.Kinds of methods(Digging,soil core drilling,litter bag technique,traditional forest harvesting)were adopted to investigate the contribution rate of nine artificial forests’ fine roots biomass,production,decomposition,turnover and dynamics to plantation carbon and nutrient reserves.Results indicated that:(1)Typical sand-fixation artificial forests’ fine roots were mostly distributed in topsoil(0~40 cm).Salix cheilophila,Salix psammophila and Caragana intermedia possessed higher fine root biomass,productivity and environmental suitability than other plantations.Fine roots of two mixed forests had deeper distribution,better soil-fixation capability and higher deep-soil resource utilization rate than those of corresponding pure forests.Soil water content of Salix psammophila,Salix microstachya and Artemisia desertorum was markedly higher than other artificial forests,and mixed planting contributed to the ability of the soil to conserve water.Soil bulk density of pure Salix psammophila,Salix microstachya,Caragana intermedia and Caragana Korshinskii was relatively low,which benefited soil’s breathability and water permeability,and mixed planting could increase soil bulk density.Soil organic carbon content of Salix psammophila,Salix microstachya,Populus simonii,and Caragana intermedia was relatively high,and mixed planting led to the decrease of soil organic carbon content.Besides,typical sand-fixation artificial forests possessed relatively low soil total N and P contents.(2)Decomposition rate typical sand-fixation forests’ fine roots performed “fast-slow-relatively fast” trend during 489 days’ decomposition period.On the whole,fine roots experienced a quite slow decomposition since it took 12.57~39.21 years for 95% decomposition).Fine root decomposition rate was positively correlated to soil temperature,humidity and substrate P concentration significantly(P<0.05),while negatively correlated to substrate N concentration significantly(P<0.01).Fine root decomposition rate of pure Salix psammophila and Salix microstachya was markedly higher than that of pure Salix cheilophila and Populus simonii in dune slack,while the rate of pure Caragana intermedia,was significantly higher than that of pure Caragana Korshinskii and Artemisia desertorum in fixed dune.Besides,mixed planting could accelerate fine root decomposition rate.(3)Typical sand-fixation artificial forests’ fine roots turnover rate performed subshrub > shrub > arbor.Populus simonii and Caragana intermedia had longer fine root lifespan and lower fine root turnover rate than Salix psammophila and Artemisia desertorum.Salix psammophila and Artemisia desertorum accommodated themselves to arid environment and seasonal rainfall through updating fine roots persistently,while Populus simonii and Caragana intermedia reduced fine roots turnover rate to cut down water and nutrients consumption for their relatively long fine root lifespan.In addition,mixed planting could improve fine roots turnover rate for corresponding species.(4)Biomass was mainly distributed in stem for typical sand-fixation artificial forests in dune slack,while primarily in roots for the plantations in fixed dune(65.5%~93.9% root was distributed in 0~40 cm deep soil).Mixed plantation could improve N fixation capacity of forests.The ratio of fine roots’ annual carbon fixation amount to artificial forests’ total carbon fixation amount was 2.3%~15.5% in dune slack and 1.8%~16.8% in in fixed dune,respectively.Fine roots’ contribution to carbon fixation was higher for pure Salix psammophila,Salix microstachya,Caragana Korshinskii.For two kinds of mixed forests,Salix cheilophila and Caragana intermedia possessed higher fine roots’ carbon fixation contribution,respectively.(5)For typical sand-fixation artificial forests,59%~92% nutrients(N,P,K)were stored in vegetation stratum.Nutrients were mainly stored in leaves and branches for sand-fixation plantations in dune slack,while primarily in roots and branches for those in fixed dune.In nutrient storage,nutrient P achieved the least amount.The ratio of remaining amount of nutrient N,P,K in roots to total remaining amount was 1.7%~42.5%,1.0%~28.3% and 1.3%~29.2%,respectively,with a general trend that the value of mixed forest of Artemisia desertorum,Artemisia desertorum,Caragana korshinskii,Salix microstachya,mixed forest of Salix cheilophila,Salix psammophila was higher than that of Caragana intermedia and Populus simonii.The artificial forests in this study possessed relatively strong nutrient storage capacity,low soil nutrient utilization efficiency and nutrient cycling rate.The nutrient N was the relatively active nutrient element,no matter in dune slack or fixed dune.Fine root dynamic characteristics and its influence on carbon and nutrient circulation of nine typical sand-fixation artificial forests were investigated in this study.The contribution of fine roots growth,distribution,production,turnover and decomposition dynamics to plantation carbon and nutrient reserves was discussed,and fine roots’ contribution rate to carbon and nutrient storage was revealed.Results indicated that Salix psammophila,Salix microstachya,Salix cheilophila and Caragana Korshinskii were good sand-fixation species for vegetation restoration and reconstruction on alpine sandy land,while pure Salix psammophila,Salix cheilophila-Populus simonii mixed forest,Caragana intermedia-Artemisia desertorum mixed forest were more suitable as protection forest.Results obtained in this study could provide theoretical basis to ecological effect assessment for alpine sandy land or similar region,and offer reference to service function construction in degraded land ecosystem. |
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