Long-term variability of root production in bioenergy crops from ingrowth core measurements

用内生长法测定的生物能源作物根生产的长期变化

Aims Long-term determination of root biomass production upon land-use conversion to biofuel crops is rare.To assess land-use legacy influences on belowground biomass accumulation,we converted 22-year-old Conservation Reserve Program(CRP)grasslands and 50+-year-old agricultural(AGR)lands to corn(C),switchgrass(Sw)and restored prairie(Pr)biofuel crops.We maintained one CRP grassland as a reference(Ref).We hypothesized that land-use history and crop type have significant effects on root density,with perennial crops on CRP grasslands having a higher root biomass productivity,while corn grown on former agricultural lands produce the lowest root biomass.Methods The ingrowth core method was used to determine in situ ingrowth root biomass,alongside measurements of aboveground net primary productivity(ANPP).Ancillary measurements,including air temperature,growing season length and precipitation were used to examine their influences on root biomass production.Important Findings Root biomass productivity was the highest in unconverted CRP grassland(1716 g m?2 yr?1)and lowest in corn fields(526 g m?2 yr?1).All perennial sites converted from CRP and AGR lands had lower root biomass and ANPP in the first year of planting but peaked in 2011 for switchgrass and a year later for restored prairies.Ecosystem stability was higher in restored prairies(AGR-Pr:4.3±0.11;CRP-Pr:4.1±0.10),with all monocultures exhibiting a lower stability.Root biomass production was positively related to ANPP(R2=0.40).Overall,attention should be given to root biomass accumulation in large-scale biofuel production as it is a major source of carbon sequestration.

对于土地用途转为种植生物燃料作物后的根系产量,还很少进行过长期的测定。为了评价此前的土地用途对地下生物量积累的影响,我们在“美国休耕保护项目”(Conservation Reserve Program,CPR)下生长了22年的草地(CRP草地)和使用期超过50年的农业用地(AGR农地)转为种植生物燃料作物玉米(Zea mays,Corn,C)、柳枝稷(Panicum virgatum,Switchgrass,Sw)和恢复性草原植被(Prairie,Pr)。我们将一块CPR草地维持为对照。我们的假设是土地利用历史和作物类型对根系密度有显著的影响;其中,原CRP草地上种植的多年生作物具有较高的根系生产力,而在原农业用地上种植的玉米的根系生产力最低。通过内生长土芯法对内生长根系生物量进行了原位测定,同时对地上净初级生产力(ANPP)进行了测量。包括气温、生长季长度和降水量在内的辅助测量则被用来考查它们对根系生产量的影响。根系生产力在未转变的CRP草地最高(1716 g m?2 yr?1),而在玉米田中最低(526 g m?2 yr?1)。由CRP草地和AGR农田转变而来的多年生作物种植地在第一年都具有较低的根系生物量和ANPP,但柳枝稷在2011年达到峰值,恢复后的草原植被也在一年后达到峰值。恢复后的草原生态系统稳定性较高(AGR-Pr:4.3±0.11;CRP-Pr:4.1±0.10),而仅种植单一作物的生态系统稳定性都较低。根系生产量与ANPP呈正相关性(R2=0.40)。总体而言,对生物燃料作物大规模种植过程中的根系生物量积累应予以重视,因为这是固碳的一种主要来源。