Resorption Efficiency Research Articles

Enhancement of ecosystem carbon uptake in a dry shrubland under moderate warming: The role of nitrogen-driven changes in plant morphology.

Net ecosystem CO2 exchange is the result of net carbon uptake by plant photosynthesis and carbon loss by soil and plant respiration. Temperature increases due to climate change can modify the equilibrium between these fluxes and trigger ecosystem‐climate feedbacks that can accelerate climate warming. As these dynamics have not been well studied in dry shrublands, we subjected a Mediterranean shrubland to a 10‐year night‐time temperature manipulation experiment that analyzed ecosystem carbon fluxes associated with dominant shrub species, together with several plant parameters related to leaf photosynthesis, leaf morphology, and canopy structure. Under moderate night‐time warming (+0.9°C minimum daily temperature, no significant reduction in soil moisture), Cistus monspeliensis formed shoots with more leaves that were relatively larger and denser canopies that supported higher plant‐level photosynthesis rates. Given that ecosystem respiration was not affected, this change in canopy morphology led to a significant enhancement in net ecosystem exchange (+47% at midday). The observed changes in shoot and canopy morphology were attributed to the improved nutritional state of the warmed plants, primarily due to changes in nitrogen cycling and higher nitrogen resorption efficiency in senescent leaves. Our results show that modifications in plant morphology triggered by moderate warming affected ecosystem CO2 fluxes, providing the first evidence for enhanced daytime carbon uptake in a dry shrubland ecosystem under experimental warming.

Linkages Between Nutrient Resorption and Ecological Stoichiometry and Homeostasis Along a Chronosequence of Mongolian Pine Plantations.

Nutrient resorption is an important strategy for nutrient conservation, particularly under conditions of nutrient limitation. However, changes in nutrient resorption efficiency with stand development and the associated correlations with ecological stoichiometry and homeostasis are poorly understood. In the study, the authors measured carbon (C), nitrogen (N), and phosphorus (P) concentrations in soil and in green and senesced needles along a chronosequence of Mongolian pine (Pinus sylvestris var. mongolica) plantations (12-, 22-, 31-, 42-, 52-, and 59-year-old) in Horqin Sandy Land of China, calculated N and P resorption efficiency (NRE and PRE, respectively), and homeostasis coefficient. The authors found that soil organic C and total N concentrations increased, but soil total P and available P concentrations decreased with stand age. Green needle N concentrations and N:P ratios as well as senesced needle C:N ratios, NRE, and PRE exhibited patterns of initial increase and subsequent decline with stand age, whereas green needle C:N ratios and senesced needle N concentrations, and N:P ratios exhibited the opposite pattern. NRE was positively correlated with N concentration and N:P ratio, but negatively correlated with C:N ratio in green needles, whereas the opposite pattern was observed in senesced needles. PRE was negatively correlated with senesced needle P concentration, soil-available N concentration, and available N:P ratio. The homeostatic coefficient of N:P was greater when including all stand ages than when including only those younger than 42 years. These findings indicate that tree growth may change from tending to be N limited to tending to be P limited along the Mongolian pine plantation chronosequence. Nutrient resorption was coupled strongly to tree growth and development, whereas it played a lesser role in maintaining stoichiometric homeostasis across the plantation chronosequence. Therefore, adaptive fertilization management strategies should be applied for the sustainable development of Mongolian pine plantations.

Response of multi-ecological component stoichiometry and tree nutrient resorption to medium-term whole-tree harvesting in secondary forests in the Qinling Mountains, China

Carbon (C):nitrogen (N):phosphorous (P) stoichiometry and nutrient resorption are important indicators of biogeochemical cycles and functioning in ecosystems. However, the response of multi-ecological component (plant, litter and soil) stoichiometry and tree nutrient resorption of multi-plant functional species to medium-term whole-tree harvesting (WTH) in secondary forests remains unclear. To reveal how WTH affects C:N:P stoichiometry and tree nutrient resorption, multi-plant organs, senesced leaves, litter and soil samples were collected from one secondary forest after 5 years of five different WTH treatments (CK: 0% (control), T1: 15%, T2: 30%, T3: 45%, T4: 60% of the stand volume removed) in the Qinling Mountains, China. Excluding shrub leaf C contents, WTH did not influence the C, N and P contents or stoichiometric ratios of multi-plant organs and litter (including senesced leaves) at the plot level. Soil C, N and P contents and C:P and N:P ratios significantly decreased following thinning measures, while the C:N ratio had no significant change. The tree N resorption efficiency (NRE) and P resorption efficiency (PRE) showed no significant differences at the plot level among the different thinning measures. Plant nutrient contents and stoichiometric ratios were tightly linkages with soil and stand attributes, while NRE was positively correlated with shrub Shannon-Wiener index. Redundancy and Pearson analyses indicated that the decreased soil nutrients resulted from decreased stand density, volume, litter biomass and available nutrients and increased understory diversity and biomass and soil pH. The N:P ratios of green leaves (trees and understory plants), senesced leaves and litters, as well as the NRE:PRE ratios, suggested that plant growth was limited by N in the study region. Overall, the undifferentiated plant and litter nutrient characteristics and tree nutrient resorption and declining soil nutrients demonstrate that although WTH significantly reduced soil fertility, the plants maintained nutrient homeostasis at the plot level. Furthermore, adaptive fertilization management strategies should be considered to shift the N-limitation status following WTH.

Species-Specific Nitrogen Resorption Efficiency in Quercus mongolica and Acer mono in Response to Elevated CO2 and Soil N Deficiency

To test the effects of elevated CO2 and soil N deficiency on N resorption efficiency (NRE) from senescing leaves in two non-N2-fixing deciduous broadleaved tree species, Japanese oak (Quercus mongolica var. grosseserrata Blume) and Painted maple (Acer mono Maxim. var. glabrum (Lév. Et Van’t.) Hara), potted seedlings were grown in a natural daylight phytotron with either ambient or elevated CO2 conditions (36 Pa and 72 Pa CO2) and with two levels of N (52.5 and 5.25 mg N pot−1 week−1 for high N and low N, respectively). We examined the N content (Nmass) of mature and senescent leaves, as well as photosynthesis and the growth of plants, and calculated both the mass-based NRE (NREmass) and leaf area-based NRE (NREarea). In both species, the Nmass of mature leaves decreased with high CO2 and low N, whereas the leaf mass per area (LMA) increased under elevated CO2, regardless of N treatments. In Q. mongolica, both the maximum rate of carboxylation (Vcmax) and the maximum electron transport rate (Jmax) were reduced by elevated CO2 and low N, but Vcmax exhibited an interactive effect of N and CO2 treatments. However, in A. mono, both the Vcmax and Jmax decreased under elevated CO2, regardless of N treatments. The partitioning of N for the photosynthetic function within leaves was also significantly decreased by elevated CO2 in both species and increased under low N in A. mono. The Nmass of senesced leaves decreased under low N in both species and exhibited an increase (Q. mongolica) or no effect (A. mono) by elevated CO2. The NREarea of Q. mongolica was affected by CO2 and N treatments, with a decrease under elevated CO2 compared to ambient CO2 and under low N compared to high N. The NREarea of A. mono was also affected by CO2 and N treatments and decreased under elevated CO2; however, unlike in the case of Q. mongolica, it increased under low N. We speculate that these interspecific differences in the responses of leaf N allocation, indicated by the photosynthetic (Vcmax and Jmax) and morphological (LMA) responses to elevated CO2, may have affected the NRE during defoliation under high CO2 and soil N-deficient conditions.

A test of the photoprotection hypothesis for the evolution of autumn colours: Chlorophyll resorption, not anthocyanin production, is correlated with nitrogen translocation.

A prominent hypothesis for the adaptive value of anthocyanin production in the autumn leaves of trees and shrubs is that anthocyanins protect leaves from photooxidative stress at low temperatures, allowing a better resorption of nutrients-in particular, nitrogen-before leaf fall. While there is evidence that anthocyanins enable photoprotection, it is not clear whether this translates to improved nitrogen translocation and how this can explain inter-specific variation in autumn colours. A recent comparative analysis showed no correlation between temperature and anthocyanin production across species but did not analyse nitrogen content and nitrogen resorption efficiency. Here, we provide this comparison by analysing the nitrogen content of mature and senescent leaves and their autumn colours in 55 species of trees. We find no correlation between the presence of anthocyanins and the efficiency of nitrogen resorption. We find, instead, that nitrogen resorption is more efficient in species with yellow autumn colours, pointing to chlorophyll resorption, rather than anthocyanin synthesis, as the main determinant of nitrogen translocation efficiency. Hence, our results do not corroborate the photoprotection hypothesis for the evolution of autumn colours.

Biochar Amendment Alters the Nutrient-Use Strategy of Moso Bamboo Under N Additions.

Nutrient resorption can affect plant growth, litter decomposition, and nutrient cycling. Although the effects of nitrogen (N) and biochar fertilizers on soil nutrient concentrations and plant nutrient uptake have been studied, an understanding of how combined applications of N and biochar affect plant nutrient resorption in plantations is lacking. In this study, we applied N (0, 30, 60, and 90 kg N ha−1 yr−1 defined as N0, N30, N60, and N90, respectively) and biochar (0, 20, and 40 t biochar ha−1 defined as BC0, BC20, and BC40, respectively) to the soil of a Moso bamboo plantation. We investigated the effects of these treatments on N and phosphorus (P) resorption by young and mature bamboo plants, as well as the relationships between nutrient resorption and leaf and soil nutrient concentrations. Young bamboo showed significantly greater foliar N resorption efficiency (NRE) and P resorption efficiency (PRE) than mature bamboo. N addition alone significantly increased the N resorption proficiency (NRP) and P resorption proficiency (PRP) but significantly decreased the NRE and PRE of both young and mature bamboo. In both the N-free and N-addition treatments, biochar amendments significantly reduced the foliar NRE and PRE of young bamboo but had the opposite effect on mature bamboo. Foliar NRE and PRE were significantly negatively correlated with fresh leaf N and P concentrations and soil total P concentration but significantly positively correlated with soil pH. Our findings suggest that N addition inhibits plant nutrient resorption and alters the nutrient-use strategy of young and mature bamboo from “conservative consumption” to “resource spending.” Furthermore, biochar amendment enhanced the negative effect of N addition on nutrient resorption in young bamboo but reduced the negative effect on that of mature bamboo under N-addition treatments. This study provides new insights into the combined effects of N and biochar on the nutrient resorption of Moso bamboo and may assist in improving fertilization strategies in Moso bamboo plantations.

Plant nitrogen concentration is more sensitive in response to degradation than phosphorus concentration in alpine meadow

Exploring the early warning signals of plant and soil characteristics in response to degradation is of great theoretical significance to illuminate the underlying driving mechanism of alpine meadow degradation. Here, in alpine meadow of Damxung County on the Tibetan Plateau, a field survey along degradation gradients was conducted to measure plant and soil properties: from non-degradation to severely degradation, simultaneous impairments in plant total biomass, plant coverage, plant N concentration, soil moisture, soil total C and N were detected, which significantly (P<0.05) decreased by 85.36%, 54.30%, 25.23%, 26.95%, 28.94% and 12.85% in sequence, while no significant change in plant P concentration was observed. As grassland degradation increased, a consistent decrease of plant N: P ratios (<14) not only demonstrated that N was a strong limiting factor for plants growth, but also supported our hypothesis that plant N concentration was more sensitive in response to degradation than plant P concentration. Path analyses further indicated that soil moisture and soil total nitrogen were the most critical factors that mediated the plant N: P in response to degradation. Although our findings suggested that N resorption efficiency was improved after grassland degradation, the increase in grassland degradation would enhance the N concentration decoupling from P concentration, which in turn might further exacerbate the N limitation and the degradation in alpine ecosystems. The early-warning signals of grassland degradation obtained here not only can improve the understanding of grassland degradation, but also can provide guidance for the restoration and management of degraded alpine meadow on the Tibetan Plateau.

Historic grazing enhances root-foraging plasticity rather than nitrogen absorbability in clonal offspring of Leymus chinensis

Aims Plants with a history of overgrazing show trait-mediated legacy effects. These legacy effects strongly influence the growth dynamics and stress tolerance of plants, thus affecting ecosystem functioning. Long-term overgrazing has dramatic effects on plant growth and carbon assimilation via asexual propagation. However, the link between nitrogen (N) absorbability and assimilation with grazing-induced plant legacy effects remains largely unknown. Methods We investigated the strength of legacy effects induced by long-term overgrazing on N uptake and metabolism in the clonal plant Leymus chinensis, and its associated changes at the physiological and molecular levels. These tests were conducted in both field and greenhouse experiments. Results The clonal offspring of overgrazed L. chinensis were significantly smaller than the control offspring, with lower individual N uptake and utilisation efficiency, indicating that the N dynamics were affected by plant legacy effects. The response ratios of root length and biomass to N patches in the clonal offspring of overgrazed L. chinensis were significantly higher than those of the control, indicating that root nutrient foraging plasticity increased in response to grazing-induced N heterogeneity. Moreover, the observed plant legacy effects decreased N acquirement but significantly increased N assimilation by increasing N resorption efficiency, with biotic stress memory activated at the enzymatic and transcriptional levels. Conclusions We propose that multigenerational exposure of perennial plants to herbivore foraging can produce a legacy effect on N uptake, which offers insights into the potential resilience of grasslands to overgrazing.

High foliar K and P resorption efficiencies in old-growth tropical forests growing on nutrient-poor soils.

Resorption is the active withdrawal of nutrients before leaf abscission. This mechanism represents an important strategy to maintain efficient nutrient cycling; however, resorption is poorly characterized in old‐growth tropical forests growing in nutrient‐poor soils. We investigated nutrient resorption from leaves in 39 tree species in two tropical forests on the Guiana Shield, French Guiana, to investigate whether resorption efficiencies varied with soil nutrient, seasonality, and species traits. The stocks of P in leaves, litter, and soil were low at both sites, indicating potential P limitation of the forests. Accordingly, mean resorption efficiencies were higher for P (35.9%) and potassium (K; 44.6%) than for nitrogen (N; 10.3%). K resorption was higher in the wet (70.2%) than in the dry (41.7%) season. P resorption increased slightly with decreasing total soil P; and N and P resorptions were positively related to their foliar concentrations. We conclude that nutrient resorption is a key plant nutrition strategy in these old‐growth tropical forests, that trees with high foliar nutrient concentration reabsorb more nutrient, and that nutrients resorption in leaves, except P, are quite decoupled from nutrients in the soil. Seasonality and biochemical limitation played a role in the resorption of nutrients in leaves, but species‐specific requirements obscured general tendencies at stand and ecosystem level.

Groundwater Depths Affect Phosphorus and Potassium Resorption but Not Their Utilization in a Desert Phreatophyte in Its Hyper-Arid Environment.

Nutrients are vital for plant subsistence and growth in nutrient-poor and arid ecosystems. The deep roots of phreatophytic plants are necessary to access groundwater, which is the major source of nutrients for phreatophytes in an arid desert ecosystem. However, the mechanisms through which changes in groundwater depth affect nutrient cycles of phreatophytic plants are still poorly understood. This study was performed to reveal the adaptive strategies involving the nutrient use efficiency (NUE) and nutrient resorption efficiency (NRE) of desert phreatophytes as affected by different groundwater depths. This work investigated the nitrogen (N), phosphorus (P), and potassium (K) concentrations in leaf, stem, and assimilating branch, as well as the NUE and NRE of the phreatophytic Alhagi sparsifolia. The plant was grown at groundwater depths of 2.5, 4.5, and 11.0 m during 2015 and 2016 in a desert-oasis transition ecotone at the southern rim of the Taklimakan Desert in northwestern China. Results show that the leaf, stem, and assimilating branch P concentrations of A. sparsifolia at 4.5 m groundwater depth were significantly lower than those at 2.5 and 11.0 m groundwater depths. The K concentrations in different tissues of A. sparsifolia at 4.5 m groundwater depth were significantly higher than those at 2.5 and 11.0 m groundwater depths. Conversely, the NRE of P in A. sparsifolia was the highest among the three groundwater depths, while that of K in A. sparsifolia was the lowest among the three groundwater depths in 2015 and 2016. The N concentration and NUE of N, P, and K in A. sparsifolia, however, were not influenced by groundwater depth. Further analyses using structural equation models showed that groundwater depth had significant effects on the P and K resorption of A. sparsifolia by changing soil P and senescent leaf K concentrations. Overall, our results suggest groundwater depths affect P and K concentrations and resorption but not their utilization in a desert phreatophyte in its hyper-arid environment. This study provides a new insight into the phreatophytic plant nutrient cycle strategy under a changing external environment in a hyper-arid ecosystem.

Global scaling the leaf nitrogen and phosphorus resorption of woody species: Revisiting some commonly held views

Leaf nutrient resorption is one of the important mechanisms for nutrient conservation in plants. Element stoichiometry is crucial to characterizing nutrient limitations and terrestrial ecosystem function. Here, we use nitrogen (N) and phosphorus (P) resorption efficiencies (NRE and PRE) and their stoichiometry to evaluate the response patterns of leaf nutrient resorption efficiency (NuRE) to plant functional groups, species traits, climate, and soil nutrients on the global scale. In light of the findings from the global data set of published literature on N and P resorption by woody plants, we revisit the commonly held views that: The strong N fixation ability of N-fixers weakened the NRE, which was consistent with the general views. The NuRE was linearly negatively correlated with plant growth rate. The higher NuRE of evergreen species than deciduous plants revealed how leaf life span constrains nutrient conservation. From the perspective of NRE, PRE and their ratios, woody plants were limited by P in the tropical zone and the limiting nutrient gradually transformed into N in the temperate zone (23.43–66.57°). The NuRE of woody plants in the frigid zone was the largest than that of others implied that low temperature may limit the nutrient absorption by plant roots, thereby enhancing the retranslocation of nutrients by senesced leaves. Furthermore, Akaike weights analysis found that mean annual precipitation (MAP) and temperature (MAT), N-fixers, soil nutrients, and leaf life span have significant effects on nutrient resorption patterns, sequentially. Overall, these results showed that the plasticity of plant nutrient resorption patterns was strongly sensitive to plant functional groups and soil nutrients, but the regularity of NuRE on a global scale was controlled by temperature and precipitation. And the resorption stoichiometry pattern better interprets plant nutrient limitation and the synergy effect of N and P in plant and soil on multiple scales.

Short-Term N-Fertilization Differently Affects the Leaf and Leaf Litter Chemistry of the Dominant Species in a Mediterranean Forest under Drought Conditions

Nitrogen (N) deposition is a key driver of global change with significant effects on carbon (C) cycling, species fitness, and diversity; however, its effects on Mediterranean ecosystems are unclear. Here, we simulated N deposition in an N-fertilization experiment with 15N-labeled fertilizer in a montane evergreen Mediterranean holm oak forest, in central Catalonia, to quantify short-term impacts on leaf, leaf litter elemental composition, and resorption efficiency in three dominant species (Quercus ilex, Phillyrea latifolia, and Arbutus unedo). We found that even under drought conditions, 15N isotope analysis of leaf and leaf litter showed a rapid uptake of the added N, suggesting an N deficient ecosystem. Species responses to N fertilization varied, where A. unedo was unaffected and the responses in P. latifolia and Q. ilex were similar, albeit with contrasting magnitude. P. latifolia benefited the most from N fertilization under drought conditions of the experimental year. These differences in species response could indicate impacts on species fitness, competition, and abundance under increased N loads in Mediterranean forest ecosystems. Further research is needed to disentangle interactions between long-term N deposition and the drought predicted under future climate scenarios in Mediterranean ecosystems.

Global resorption efficiencies of trace elements in leaves of terrestrial plants

Abstract Leaf nutrient resorption is a critical nutrient conservation strategy. Previous studies focus mainly on resorption patterns of macronutrients, but resorption patterns of trace elements remain poorly understood. A meta‐analysis was conducted to explore the general patterns of the leaf resorption of eight trace elements [i.e. copper (Cu), molybdenum (Mo), zinc (Zn), boron (B), manganese (Mn), sodium (Na), aluminium (Al) and iron (Fe)], and a macronutrient [i.e. sulphur (S)] using data collected from 53 published studies. Sulphur (49.6%) had the highest average resorption efficiency followed by Cu (30.3%), Mo (29.5%), Zn (19.5%) and B (17.6%). Two structural elements, Na and Mn, were not resorbed, whereas two potentially toxic elements, Al (−55.6%) and Fe (−25.4%), were accumulated in senesced leaves. Both climatic factors and growth types affected leaf nutrient resorption efficiency, but the magnitudes and directions of the effects differed greatly between S and the trace elements. The resorption efficiencies of S, Cu, Mo and Zn decreased as leaf nutrient concentrations increased, but the structural or potentially toxic elements (i.e. B, Mn, Na, Fe and Al) presented no response or opposite trends. Our results provide global mean resorption efficiencies of trace elements for the first time, and highlight that structural and potentially toxic elements have relatively lower or no leaf resorption, which should be fully considered in biogeochemical models. A free Plain Language Summary can be found within the Supporting Information of this article.

Comparison of C:N:P Stoichiometry in the Plant–Litter–Soil System Between Poplar and Elm Plantations in the Horqin Sandy Land, China

Afforestation is among the most effective means of preventing and controlling desertification. Silver poplar (Populus alba) is commonly planted tree species for afforestation of the Horqin Sandy Land of China. However, this species has exhibited some drawbacks such as top shoot dieback, premature senescence and mortality, and soil and ecosystems degradation. In contrast, Siberian elm (Ulmus pumila) rarely experiences these problems in the same regions. Ecological stoichiometry plays a vital role in exploring ecological processes and nutrient cycle relationships in plant–litter–soil systems. To explore the differences in the carbon (C), nitrogen (N), and phosphorus (P) balance, the stoichiometry characteristics and stoichiometric homeostasis in elm and poplar plantations in the Horqin Sandy Land, we measured C, N, and P concentrations in leaves, branches, roots, litter, and soils and analyzed N and P resorption efficiencies in the two plantations. The results showed that soil C and N concentrations, C:P, and N:P were greater in the elm plantation than in the poplar plantation. The leaf and root C:P and N:P during summer and litter N and P concentrations were greater, whereas N and P resorption efficiencies were lower, in the elm plantation than in the poplar plantation. Generally, elm exhibited greater N:P homeostasis than poplar. N and N:P homeostasis were greater in roots than in leaves and branches in the elm plantation, but they varied with soil N concentration and N:P in the poplar plantation. These findings indicate that poplar exhibited more developed internal nutrient conservation and allocation strategies but poor nutrient accumulation in soil, which may contribute to degradation of poplar plantation. In contrast, elm tended to return more nutrients to the soil, showing an improved nutrient cycle in the plant–litter–soil system and increased soil C and N accumulation in the elm plantation. Therefore, compared with poplar, elm may be a more suitable afforestation tree species for the Horqin Sandy Land, in terms of promoting the accumulation of soil nutrients and enhancing nutrient cycling in the plant–litter–soil system.

Nitrogen and phosphorus contents and resorption efficiency of thirty broadleaved woody plants in Yangjifeng, Jiangxi, China.

Nutrient resorption is an important strategy of nutrient conservation, which reflecting the ability of plants to conserve and utilize nutrients and adapt to environment. To explore the relationship between nutrient content and nutrient resorption of broadleaved woody species of different life forms (i.e., evergreen vs. deciduous), we sampled 30 broadleaved woody species in subtropical region of China located in Yangjifeng National Nature Reserve, Jiangxi Province. The nitrogen (N) and phosphorus (P) concentrations in green and senescent leaves of each species were measured to calculate nutrient resorption efficiency. Furthermore, we analyzed the relationship of leaf nutrient concentration and resorption efficiency for the different life forms. The results showed that N and P concentrations in green leaves were significantly higher in deciduous trees than those in evergreen trees. The P concentrations of senescent leaves in deciduous woody species was significantly higher than that in evergreen woody species. There was no significant difference of N concentration in senescent leaves between evergreen and deciduous species. Nitrogen resorption efficiency (NRE) and phosphorus resorption efficiency (PRE) of the 30 broadleaved woody species were 49.6% and 50.9%, respectively. There were no significant differences between the NRE and PRE of evergreen and deciduous species. NRE and PRE negatively correlated with N and P concentrations in senescent leaves, respectively. Additionally, evergreen and deciduous species showed similar relationships between nutrient resorption efficiency and nutrient concentration in senescent leaves. The sca-ling exponent of allometric relationship between NRE and PRE was 1.18 across all the species. The nutrient resorption efficiency of all the species were affected by the nutrient status of the senesced leaves. Plants examined in this study generally re-absorbed P from senescing leaves than N.

Nitrogen and phosphorus resorption and stoichiometric characteristics of different tree species in a mid-subtropical common-garden, China.

To understand the nutrient use strategies of 11 tree species in a subtropical common-garden, we measured the specific leaf area, nitrogen (N) and phosphorus (P) resorption and stoichiometric characteristics of leaves in August 2019. The results showed that the specific leaf area, N and P concentrations in mature and senescent leaves of evergreen broadleaved (Lindera communis, Cinnamomum camphora, Schima superba, Castanopsis carlesii, Michelia macclurei and Elaeocarpus decipiens) and coniferous species (Cunninghamia lanceolata and Pinus massoniana) were lower than those of deciduous broadleaved species (Liquidambar formosana, Sapindus mukorossi and Liriodendron chinense). In contrast, C:N and C:P in mature leaves of evergreen broadleaved and coniferous species were significantly higher than those of deciduous broadleaved species. Except for C. carlesii, the N:P of all the species were lower than 14. Compared with other tree species, N and P resorption efficiencies of S. mukorossi were higher than 50% based on both mass and leaf area. Although P resorption efficiency of P. massoniana, C. lanceolata and C. camphora were higher than 50%, N and P resorption efficiency of M. macclurei were the lowest with only 15%-30%. In addition, specific leaf area of mature leaves was significantly positively correlated with N and P concentrations, but negatively correlated with C:N and C:P. In the common-garden, evergreen broadleaved species such as C. carlesii and L. communis, and coniferous species such as P. massoniana might belong to the slow investment species with lower specific leaf area, N and P concentrations, displaying relatively efficient in N and P resorption and utilization in comparison with other species. In contrast, deciduous broadleaved species such as S. mukoraiensis might be the fast investment species with low N and P use efficiency. Interestingly, tree species being restricted by N availability did not exhibit higher N resorption efficiency in the common-garden. Similarly, C. carlesii, the only P-restricted species here, did not exhibit higher P resorption efficiency. Our results provided scientific support for afforestation practice in the mid-subtropics.

Nitrogen deposition and phosphorus addition alter mobility of trace elements in subtropical forests in China

Trace elements are important in sustaining the functioning of forest ecosystems. However, knowing how nitrogen (N) deposition and phosphorus (P) addition alter the mobility of trace elements, and how trees equilibrate root capture and leaf resorption of trace elements remains unclear. We measured concentrations of five elements in rhizospheric soils, fine roots, twigs, and leaves in Chinese fir plantations fertilized with P (5 g P m−2 a−1) and/or N (5 and 10 g N m−2 a−1) over 5 years in subtropical China and calculated these mobility factors of four trace elements and Mg from soils to roots and from roots to twigs and leaves. Results showed that N addition increased the capacity of roots to capture Mg and to twigs re-adsorb Fe. Phosphorus regulated the employment of a Mn acquisition strategy under N deposition. Nitrogen addition increased the capacity of roots to capture and the efficiency of leaves to re-adsorb Mn without P addition while only increased the Mn capturing capacity with P addition. The Mg, Fe, and Mn were more sensitive than Cu and Zn to N deposition and P addition. The capture-resorption tradeoff depended more on element types than N and P supplies. In addition, the tradeoff between capture and resorption could be reflected by the transport capacity since transport capacities of Mg, Fe, Mn, and Zn were positively correlated with their corresponding capture capacities or resorption efficiencies. Furthermore, structural equation modeling showed the element mobility tended to be dominated by P rather than N. These findings suggest subtropical forests would adapt to atmospheric N deposition and soil P limitation by adjusting the tradeoff between capture and resorption strategies. The establishment of trace element mobility and tradeoff patterns provides insights into trace element cycling under human-driven nutrient imbalance scenarios.

Leaf nitrogen and phosphorus resorption improves wheat grain yield in rotation with legume crops in south-eastern Australia

Nutrient resorption from senescing leaves to grain at physiological mature stage is critical to recover nutrients and improve grain production in semi-arid environment in south-eastern Australia. The aim of this study is to examine nitrogen (N) and phosphorus (P) resorption patterns and their effects on grain yield and quality of wheat in rotation with legume crops. A range of legume crops were grown in the field followed by one and two wheat crops in contrast with continuous wheat and canola crops with N fertiliser over 3 years. The soil N and P availability, flag leaf N and P nutrient status and resorption were measured in the first and second wheat crops after legume crops. Including legume crops in crop rotation increased soil available N concentration. Green leaf N concentration, and senesced leaf N and P concentrations increased as soil available N increased. However, N resorption efficiency (NRE) and P resorption efficiency (PRE) decreased as soil available N concentration increased. The NRE and PRE were positive correlated to grain yield and 1000-grain weight, but negative correlated to grain protein. The soil N benefit from legume crops can last more than one growing season. Under moisture stress conditions increased grain yield was associated with improved nutrient resorption efficiency via increased grain size regardless soil nutrient availability.

Long‐term nitrogen addition impact on agronomic traits, nitrogen uptake and nitrogen resorption efficiency of wheat in a rainfed region

AbstractNitrogen (N) fertilizer management is one of the most important issues in wheat (Triticum aestivum L.) production. To explore the mechanism of N uptake efficiency (NupE) and N resorption efficiency (NRE) in wheat, this study examined the effects of different N fertilizer application rates (0, 52.5, 105, 157.5, 157.5, and 210 kg N ha−1 yr−1) on crop growth parameters, NupE, NRE, and N use efficiency (NUE). The results of the 2‐yr (2018 and 2019) study showed that the growth of crops was enhanced in high‐N treatments, resulting in higher N concentration in wheat tissues. The 105 kg N ha−1 treatment (N105) was the best rate for improving spring wheat yield and NUE, ensuring the highest values of N uptake, evapotranspiration, and leaf NRE. Compared with the non‐N‐fertilized control, N105 increased grain yield and N uptake by 46.90 and 90.54%, respectively; thus, N105 had 16.40% higher NUE, 28.33% higher N utilization efficiency (NutE), and 0.58 kg kg−1 greater NupE. Therefore, N uptake and N resorption are of great importance for increasing NUE of wheat, and for improving the sustainability of wheat production in the semi‐arid Loess Plateau of China.

Response of root nutrient resorption strategies to rhizosphere soil microbial nutrient utilization along Robinia pseudoacacia plantation chronosequence

Understanding root nutrient resorption strategies and their drivers is essential to explore plant nutrient acquisition strategies in restored ecosystems. However, the interaction between root nutrient resorption and the nutrient utilization of rhizosphere soil microorganisms in restored ecosystems has yet to be determined. In this study, we investigated plant fine roots and rhizosphere soils in Robinia pseudoacacia plantations at four stages of forest succession (14, 20, 30, and 45 years of age) on the Loess Plateau in China. We studied the characteristics of root nitrogen and phosphorus resorption efficiencies (NRE and PRE) at different recovery stages and analyzed the relationships among nutrient resorption and rhizosphere soil variables (nutrients and microbial communities). We detected a tendency of an initial reduction and subsequent increase in root NRE and PRE with stand age (the lowest value at 30-y sites), whereas the nutrient contents of rhizosphere soil increased with stand age, and soil available nutrients initially increased and then declined. The diversity of rhizosphere soil microorganisms also showed an initial increase and subsequent decline. Proteobacteria were considered to be at an advantage during the nutrient-rich stage of restoration (30-y sites), whereas Acidobacteria were found to be dominant during the low-nutrient restoration stage (14-y sites). Furthermore, the microbial nutrient utilization ratios of soil microbial biomass carbon: soil organic carbon, microbial biomass nitrogen: soil total nitrogen, and microbial biomass phosphorus: soil total phosphorus also showed an initial increase and then decreased (with peaks at the 30-y sites). Redundancy analysis indicated that the nutrient contents of rhizosphere soil were significantly related to microbial communities and correlation analysis revealed that microbial nutrient-use efficiencies were significantly related to rhizosphere soil nutrient contents and the dominant microbial communities. We also detected a significant negative correlation between root nutrient resorption and microbial nutrient utilization. Partial least squares path modeling revealed that forest restoration influences the contents of nutrients in rhizosphere soil and the composition of microbial communities, whereas microbial biomass and nutrient utilization efficiency were shown to have a negative effect on root resorption efficiency. Based on our findings, we propose that the highly conservative nutrient utilization strategies of the rhizosphere soil microbial community may negatively drive root nutrient resorption strategies during the succession of R. pseudoacacia.