| Nutrient resorption is the key nutrient conservation strategy for perennials,which has profound influences on the nutrient cycling and adaptation of plants to environment change.Most previous studies have been focused on forest and grassland ecosystems,but few studies concern the nutrient resorption of desert plants.Desert ecosystem cover 20% of the earth.Most of the plants living in desert ecosystem are able to adapt to drought,salinity and nutrient poor environments.Study the nutrient resorption characteristics of these plants will not only helps to understand plant nutrient use strategies under abiotic stresses but also provides scientific evidence for the protection and restoration of desert ecosystem.In this study,a field investigation was undertaken in Gansu Anxi Extra-arid Desert National Reserve to explore the resorption patterns of Nitrogen(N),Phosphorus(P),Potassium(K)and Sodium(Na)in leaves of desert plants with different functional groups and to test the influence of environmental factors.A pot experiment was performed to evaluate the response of nutrient resorption to different levels of nitrogen and salt supply.The key results are shown below:1)Although nutrient resorption is important nutrient conservation strategy for desert plants,plants in the study area generally present incomplete resorption of N,P and K,which may be attributed to the inhibition effects of drought and high salinity.Field investigation showed the average resorption efficiency of N,P,K were 51.8%,55.5%,47.9% respectively,lower than the the global averages.Additionally,compared with global averages,the resorption proficiency of N and P also belongs to incomplete range.2)There were significant differences in nutrient resorption characteristics across different functional groups.Euhalophytes(Eu)have the highest N resorption efficiency and scretohalophyte(Se)have the lowest K resorption efficiency.There were no significant differences in P resorption efficiency among the four functional groups.The seemingly strict resorption of Na in Se because they can exclude Na through salt glands.The accumulation of Na in the senesced leaves of Eu caused significant increase of leaf succulence.3)Phylogeny did affect nutrient reisorption,but its influence act upon resorption proficiency rather than resorption efficiency,which more closely related species having more similar resorption proficiency than distantly related species.There were significant negative correlations between specific leaf area and resorption proficiency of N,P,which indicate that the “slow-return” desert plants also trend to have higher nutrient resorption potential.4)The environmental factors all together accounted for 18%-67% variation of community level nutrient content and resorption characteristics.However,most of the environmental factors including soil salinity showed non-significant independent effect.In contrast,in pot experiments,low salt treatment improve the N,P resorption efficiency of Tamarix ramosissima and Atriplex canescens significantly,while high slat treatment result in significant inhibitory effect.5)The response of desert plants to N addition were species-specificity.Pot experiment indicate N addition increase N resorption efficiency of Atriplex canescens and improve the amount of reabsorbed N of Tamarix ramosissima under N limitation.Moreover,P resorption of Atriplex canescens and K resorption of Tamarix ramosissima were also based on the availability of soil N.In conclusion,although nutrient resorption is the crucial nutrient conservation strategy,the resorption process in desert plants is generally incomplete due to drought and salinity.The significant influence of phylogeny on resorption proficiency further indicated that the incomplete resorption may be a characteristic of desert plants to adapt to environment.The soil N availability directly affects the resorption of N,P and K in desert plants under N limitation environment,however,this influence is species specific. |
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