Nutrient resorption and stoichiometric responses of poplar (Populus deltoids) plantations to N addition in a coastal region of eastern China

Aims Leaf nutrient resorption is sensitive to changes in soil nutrients. However, the effects of N deposition on nutrient resorption efficiency (NuRE) in plant macro-nutrients remain unclear. Poplar (Populus deltoids) is one of the most extensively cultivated hardwood species worldwide. We explored general patterns and dominant drivers of NuRE and stoichiometry of poplar plantations in response to N addition. Methods We conducted a 4-year N-addition experiment to explore NuRE and stoichiometric responses to N addition in two poplar (Populus deltoids) plantations (8- and 12-year-old stands) in a coastal region of eastern China. We measured soil and foliar (green and senesced leaves) concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) for a series of N addition treatments including N0 (0 kg N ha ‒1 yr ‒1), N1 (50 kg N ha ‒1 yr ‒1), N2 (100 kg N ha ‒1 yr ‒1), N3 (150 kg N ha ‒1 yr ‒1), and N4 (300 kg N ha ‒1 yr ‒1). Important Findings Consistent for (both) 8- and 12-year-old stands, N addition did not affect the NuRE and stoichiometry (with the exception of CaRE and CaRE:MgRE ratio). NRE-PRE scaling slopes were consistently less than 1.0 under N addition. These results suggest that NRE generally decouples from PRE within each N treatment. Moreover, these results point to robust control of green leaf nutritional status on nutrient resorption processes as indicated by the positive relationships between nutrient resorption efficiency and green leaf nutrient concentrations. Our findings provided a direct evidence that growth in 12-year-old poplar plantations was N-limited in a coastal region of eastern China.

Biomass allocation between leaf and stem regulates community-level plant nutrient resorption efficiency response to nitrogen and phosphorus additions in a temperate wetland of Northeast China

Aims Nutrient resorption is a crucial component of plant nutrient use strategy, yet the controls on the responses of community-level nutrient resorption to altered nutrient availability remain unclear. Here, we addressed two questions: Did leaf and stem nutrient resorption respond consistently to increased nutrient availability? Was community-level plant nutrient resorption response after nutrient enrichment driven by the intra-specific plasticity in plant nutrient resorption or by altered species composition? Methods We investigated the changes in aboveground biomass, and leaf and stem nutrient resorption of individual species after three-year nitrogen (N) and phosphorus (P) additions, and assessed community-level nutrient resorption response to three-year nutrient additions in a graminoid-dominated temperate wetland, Northeast China. Important findings For both leaves and stems, N and P additions did not affect nutrient resorption efficiency, but they decreased respective nutrient resorption proficiency. Similarly, community-level N and P resorption proficiency declined with respective nutrient addition. Community-level N and P resorption efficiency was reduced by N addition primarily due to altered community composition and declined leaf:stem ratio. These results suggest that leaf and stem nutrient resorption processes exhibit consistent responses to increasing nutrient availability in the temperate wetland. These findings highlight the importance of altered species composition and biomass allocation between leaf and stem in driving community-level nutrient resorption response to nutrient enrichment.

Mangrove species maintains constant nutrient resorption efficiency under eutrophic conditions

Mangrove species have developed nutrient conservation mechanisms to adapt to oligotrophic intertidal environments. However, nutrient enrichment occurs worldwide, particularly in estuarine and coastal regions. Mangrove species may change their adaptive strategies if nutrient availability increases substantially. To understand how nutrient resorption (a major nutrient conservation strategy) responds to nutrient enrichment, a common mangrove species in China, Aegiceras corniculatum (black mangrove), was selected, and saplings were cultivated in nutrient-enriched soils. After one year, neither N nor P resorption efficiency showed significant variations with nutrient availability and there was no difference between N and P resorption efficiency. Overall, nutrient resorption efficiency of A. corniculatum remained at ∼40%, lower than the global average levels of evergreen plants (∼50%), indicating incomplete resorption of nutrients. Incomplete resorption was also evidenced by the nutrient concentrations, resorption proficiency and N: P ratio of plant leaves. Collectively, these results indicate that black mangrove can maintain constant nutrient resorption efficiency under eutrophic conditions.