Soil available phosphorus and moisture drive nutrient resorption patterns in plantations on the Loess Plateau

Nutrient resorption by senesced leaves is an important mechanism for the preservation of plant nutrients. However, our understanding of nutrient resorption patterns and drivers of plantations in Loess Plateau is limited. In this study, four main tree species (Robinia pseudoacacia [RP], Pinus tabuliformis [PT], Armeniaca sibirica [AS], and Caragana korshinskii [CK]) were compared in plantations on the Loess Plateau. We explored the relationships among nitrogen resorption efficiency (NRE), phosphorus resorption efficiency (PRE), plant nutrients (green leaf total nitrogen [TNgr] and total phosphorus [TPgr]), stand ages, growth rates (height growth rate [HGR] and diameter growth rate [DGR]), soil nutrients (soil total nitrogen [STN] and total phosphorus [STP]), available nutrients (soil inorganic nitrogen [SIN] and available phosphorus [SAP]), soil water content (SWC), and stoichiometries. We found that significant differences in nutrient resorption efficiencies among different afforested tree species. And the increase of N:P ratios of leaves and soil, and the decrease of SAP enhanced P-limited. Furthermore, the resorption efficiencies of different species differed in response to nutrients, stoichiometries, and plant growth. PRE was significantly negatively correlated with the DGR of deciduous species; however, NRE of N-fixing plant was positively correlated with plant growth rates. And the contributions of SWC and SAP were greater for nutrient resorption compared to other variables. The STN:STP and SIN:SAP were significantly correlated with leaf N:P, NRE, PRE, and PRE: NRE. Overall, plant growth rates may be regulated by absorption strategies due to leaf lifespan and N-fixing capacity of tree species. Resorption efficiencies were significantly correlated with SWC and SAP showed that soil moisture and available phosphorus were the primary drivers of nutrient resorption strategies. The association of PRE: NRE with N:P ratios indicated that nutrient resorption was driven by the coupling effect of N and P in plants and soil.