Nitrogen Uptake Preference Of Herbaceous Plants With Different Life Types In Gurbantunggut Desert

The nitrogen uptake strategy of plants may be synergistically influenced by multiple factors,thus changing the variation pattern of plant nitrogen uptake strategy obtained from the analysis of single factor limitation.In order to gain insight into the survival mode of desert plants and to better understand the effect of nitrogen on plant survival strategies,for this purpose four short-lived desert herbaceous plants were selected in the Gurbantunggut Desert:Erodium oxyrrhynchum,Hyalea pulchella,Nonea capsica and Lactuca undulata;Two one-year growth nutrient stage desert herbs Ceratocarpus arenarius and Suaeda glauca were studied,the effects of soil depth,growing season,life types and their mutual sitting on plant nitrogen uptake strategies were analyzed and explored,and a simple judgment was made for whether desert herbaceous plants can effectively uptake organic nitrogen.The main conclusions were obtained as follows:(1)Four short-lived desert herbs,Erodium oxyrrhynchum,Hyalea pulchella,Nonea capsica and Lactuca undulata,have different nitrogen uptake strategies in different growing seasons:the N uptake rates of all four species in May were higher than were those in April at different soil depths.As for the uptake rates of different forms of N,that of glycine was lower than that of both nitrate and ammonium N.The highest recovery of nitrate N was achieved by N.caspica in April,up to 52.3%.Meanwhile,the highest recovery of ammonium N was achieved by N.caspica in May,reaching 90.7%.The uptake of 15N by H.pulchella was lower than was that by the other three species.The four short-lived plants could efficiently utilize not only soil inorganic N but also soil organic N,and E.oxyrrhynchum and L.undulata displayed a significant preference for nitrate N uptake.The findings reveal that in the Gurbantunggut Desert ecosystem,short-lived plants have differential and diversified N uptake capacity and can all absorb soluble organic state N sources from the soil.(2)N uptake strategies of two annual-growth nutrient stage desert herbaceous plants differ in different months and soil depths for different forms of N--C.arenarius and Suaeda glauca:the nitrogen absorption rates of the two plants in shallow soil were higher in July than those in June.Comparing the absorption rates of different nitrogen forms,plants preferred inorganic nitrogen to organic nitrogen.C.arenarius preferred nitrate nitrogen,and the highest nitrogen absorption rate was3.81?g·h^–1 per gram dry root,while S.glauca preferred ammonium nitrogen,and the highest nitrogen absorption rate was 4.74?g·h^–1 per gram dry root.The contribution rates of nitrate nitrogen out of total nitrogen uptake ranged from 35.7%to 43.9%for C.arenarius;while the contribution rate of ammonium nitrogen out of total nitrogen uptake ranged from 40.0%to 48.3%for S.glauca.The two annual plants can not only utilize inorganic nitrogen,but also directly absorb organic nitrogen in soil.The findings showed that the nitrogen uptake capacity of annual plants in Gurbantunggut desert was different and diversified,and all of them could absorb the soluble organic nitrogen sources in the soil.(3)The nitrogen uptake rates during the maximum biomass period of the two living plants were higher than those during the fastest growth period in different soil depths;Comparing the uptake rates of different forms of nitrogen,inorganic nitrogen was higher than organic nitrogen,and short-lived plants preferred to absorb nitrate nitrogen,with the highest uptake rate reaching 5.74?g h-1,annual plants prefer to take up ammonium nitrogen at a maximum rate of 4.74?g h-1;In terms of the contribution of different forms of nitrogen to total nitrogen,nitrate nitrogen was the favored form of nitrogen uptake by short-lived plants,with a contribution ranging from 36.98%to 48.13%;Ammonium nitrogen was the favored form of nitrogen uptake by annual plants,contributing up to 48.3%and as low as 30.47%.Different nitrogen forms,months and soil depths had significant effects on the nitrogen uptake strategies of all four plants.The 6 plants of the 2 life types can utilize not only the inorganic nitrogen in the soil but also directly absorb and utilize soil organic nitrogen.In summary,short-lived plants with shorter life histories did not adjust their preference for nitrate nitrogen uptake throughout their growth cycle,and annual plants with longer life histories had ample time to adjust their nitrogen uptake to their own needs.Plant species,nitrogen morphology,soil depth and growing season and their interaction relationships all influenced the nitrogen uptake strategies of six plant species with different life types in the Xinjiang Gurbantunggut Desert,causing the six species to exhibit significant differences in nitrogen uptake during their respective growth cycles,which in turn changed the strategies of plant coexistence and survival.