Study on the allocation patterns of above-and below-ground biomass of Actinidia chinensis in northern area of Qinling

Abstract: 【Objective】Plant species have evolved specialized strategies to regulate their above-and un-der-ground biomass allocation. The allocation not only influences the growth of fruit individual plant,butalso influences fruit vegetation structures and functions,and consequently impacts soil carbon as well asorchard ecosystem carbon cycling. To study the allocation patterns of above-and under-ground biomassof Actinidia chinensis has profound guiding significance for cultivation and production of kiwifruits.【Methods】Five-year old‘Huayou'and‘Hort16A'varieties were selected to analyze the allocation patterns,and three plants as replicate were selected in each orchard. The above-ground biomass including leaves,stems and branches was measured by standing crop method. After harvest,all aboveground biomass wasdried at(70±5)℃ for 48 h to constant weight. The belowground biomass was measured using diggingmethod in 0-60 cm depths. In each replicate,the roots mainly distributed from 0 to 60 cm,and hence weanalyzed changes in belowground biomass in the 0-60 cm depth separately within three layers,0-20 cm,20-40 cm,and 40-60 cm. The horizontal distribution of these three layers were 0-40 cm from plant.Changes in below-ground biomass among each soil layer were tested using Student's t-test and analysisof variance. Significant differences of all statistical tests were estimated at a significance level of P<0.05.All statistical analyses were performed using SPSS 18.0.【Results】The average tree trunk and crownwidth for‘Huayou'were 4.53 cm and 1.73 m,respectively,and‘Hort16A'were 4.90 cm and 1.88 m.Significant differences were found in average tree trunk and crown width between‘Huayou'and‘Hort16A'. For both‘Huayou'and‘Hort16A'varieties,the above-and below-ground biomassshowed a significant difference. The total biomass of‘Huayou'variety is 7 210.65 g·plant-1,and 8 525.63g·plant-1for‘Hort 16A'. The significant differences were found between above and belowground biomassin both‘Huayou'and‘Hort16A'. The above-ground biomass was greater than the corresponding below-ground biomass,and above-ground biomass was generally 3-5 times of the below-ground biomass. Thevertical distribution of below-ground biomass was an inverted typical pyramid,indicating that the below-ground biomass decreased with the increase of soil depth,which could be simulated by the linear function. Compared with that of‘Hort16A',the allocation proportion of belowground biomass in‘Huayou'was higher in 0-20 cm soil layer,whereas it was lower in 20-40 cm and 40-60 cm soil layers. The below-ground biomass of two varieties was mainly distributed in 0-40 cm at the vertical level,and the allocationproportion of each layer showed difference. The belowground biomass of‘Huayou'was(180.75-626.92)g·plant^-1,and‘Hort16A'was(220.65-765.93)g·plant^-1. The variation coefficient of‘Hort16A'and‘Huayou'was 14.87%-60.14% and 22.37%-86.92% respectively,which showed medium variation. Forthe horizontal distribution of 0-80 cm from plant,the tap-root and fine-root of‘Huayou'variety mainlydistributed in 0-40 cm soil layer which account for 87.89% and 82.04% of total biomass respectively.However,the tap-root and fine-root of‘Hort16A'were distributed in 0-40 cm and 40-80 cm soil layerrespectively which account for 86.70% and 84.93% of total biomass. The fine-root biomass of‘Huayou'and‘Hort16A'accounts for 2.94% and 1.01% of total biomass,respectively. The ratios of belowgroundand aboveground biomass were 0.30 and 0.21 for‘Huayou'and‘Hort16A',respectively. The lower ratioof below-and above-ground biomass might be related with the management level of orchard.【Conclu-sion】The allocation patterns of above-and below-ground biomass play an important role in fruit individu-al growth,vegetation structure composition,biomass allocation,and carbon sequestration of ecosystem.Root water uptake was always most intensive in the surface 20 cm soil layer,and the water variability in0-40 cm was high. Based on the characteristics of fine root system,the following irrigation and fertiliza-tion strategies are recommended for five-year old‘Huayou'and‘Hort16A'varieties. The goal is to max-imize soil water and fertilizer resource use by taking advantage of the particular characteristics of kiwifruitfine root allocation patters and water uptake ability. The best irrigation and fertilization depth is 40 cm for‘Huayou'and‘Hort16A'varieties,and the best horizontal distance is 60 cm from tree trunk for‘Huay-ou'whereas 100 cm for‘Hort16A'. The small-volume and high-frequency irrigation could be used inwater and fertilization management. This is because more fine roots distribute in the surface 40 cm,andfine roots in 0-20 cm soil layer also play the main uptake. Irrigation water and fertilizer should be mainlysupplied to the soil zone within 60-100 cm distance from the tree trunk,where could guarantee highersoil water and fertilizer use efficiency. But the horizontal distance of water and fertilizer management in or-chard should be adjusted according to the tree age. The ratio of belowground biomass and abovegroundbiomass should be improved based on the variety characteristics and scientific soli management methods.However,only the fine root allocation patters of a 5-year-old kiwifruit were studied. The suggested waterand fertilizer management strategies will have some limitations. In future research,the interannual varia-tions at different age of different kiwifruit varieties should be investigated.