Resorption Efficiency Research Articles

N, P and K stoichiometry and resorption efficiency of nine dominant shrub species in the deserts of Xinjiang, China

AbstractPlant nutrient stoichiometry and resorption efficiency are important functional traits related to plant nutrient status and biogeochemical cycling. Such traits are not well documented for desert shrubs. We studied how the stoichiometry and resorption efficiency of nitrogen (N), phosphorus (P) and potassium (K) varied among nine dominant desert shrub species through systematically investigating their concentrations in green and senesced leaves (or assimilation branches) of desert plants at 24 sites across Xinjiang, China. We hypothesized that desert shrubs should have low leaf N and P but high leaf K concentrations; and have high leaf N and P but low K resorption efficiency, given the low N and P but high K availability in this arid region. These shrubs had a mean leaf N concentration of 18.9 mg g−1, and lower leaf P but higher leaf K concentration (1.2 and 17.0 mg g−1, respectively) than desert plants at national and global levels. The mean (± SE) resorption efficiencies of leaf N, P and K in the desert shrubs were 51.0 ± 2.4%, 54.9 ± 2.0% and 46.3 ± 3.5%, respectively, lower than in the woody plants globally. The higher green‐leaf N:P (17.2 ± 0.8) and K:P (15.3 ± 1.0) relative to the corresponding critical ratios, and the higher P resorption efficiency (54.9%) relative to N (51.0%) and K (46.3%) resorption efficiency, suggested that the dominant desert shrubs in Xinjiang generally suffer from P (or both P and N) deficiency. Additionally, our results showed little evidence of higher resorption relative to their counterparts in most other ecosystems.

A missing key to our understanding of forest carbon dynamics. A commentary on: 'High nitrogen resorption efficiency of forest mosses'.

A missing key to our understanding of forest carbon dynamics. A commentary on: 'High nitrogen resorption efficiency of forest mosses'.

The C:N:P Stoichiometry of Planted and Natural Larix principis-rupprechtii Stands along Altitudinal Gradients on the Loess Plateau, China

Carbon:nitrogen:phosphorus (C:N:P) stoichiometry plays a critical role in nutrient cycling, biodiversity, and ecosystem functionality. However, our understanding of the responses of C:N:P stoichiometry to elevation and forest management remains elusive. Here we sampled 18 Larix principis-rupprechtii sites along altitudinal gradients (1700-2300 m) on Guandishan Mountain in the Loess Plateau, China. We determined the leaf, litter, and soil C N P contents and C:N:P stoichiometric ratios, as well as nutrient resorption efficiency (NuRE), and diameter at breast height (DBH) increments in both planted and natural stands, and then tested the impacts of elevation and stand origin on these parameters’ management. We found different C:N:P stoichiometry between natural and planted forests. The results revealed that: soil C, N, and N:P ratios, litter C:P and N:P ratios, leaf C:N and N:P ratios increased significantly; however, soil C:N ratios, litter P, leaf N and P, nitrogen resorption efficiency (NRE), and DBH increments decreased significantly with elevation in the planted forests. Soil C,N and N:P ratios, litter C, as well as C:N and C:P ratios increased significantly with elevation in natural forests. The soil N, P and N:P ratios, litter C:P and N:P ratios, leaf C, C:P and N:P ratios, nitrogen resorption efficiency (NRE), phosphorus resorption efficiency (PRE), and DBH increments were, on average, higher in the planted, rather than natural forests. Our results indicated that there was an enhancing P-limitation in both the planted and natural forests, and the plantations were more restricted by P. Moreover, compared to natural forests, plantations converged toward a higher conservative N- and P-use strategy by enhancing resorption efficiencies of internal nutrient cycling and a higher annual growth rate.

Impacts of drought and nitrogen enrichment on leaf nutrient resorption and root nutrient allocation in four Tibetan plant species

Plant nutrient resorption, a process by which plant withdraws nutrients from senescing structures to developing tissues, can significantly affect plant growth, litter decomposition and nutrient cycling. Global change factors, such as nitrogen (N) deposition and altered precipitation, may mediate plant nutrient resorption and allocation. The ongoing global change is accompanied with increased N inputs and drought frequency in many regions. However, the interactive effects of increased N availability and drought on plant nutrient-responses remain largely unclear. In a pot experiment, we examined the impacts of N enrichment and drought on leaf N and phosphorous (P) resorption and root nutrient allocation in four species from the Qinghai-Tibet Plateau, including two graminoid species (Kobresia capillifolia and Elymus nutans) and two forb species (Delphinium kamaonense and Aster diplostephioides). Our results showed divergent resorption patterns within the two functional groups. E. nutans and D. kamaonense showed stronger N resorption than K. capillifolia and A. diplostephioides. N addition did not alter their N resorption efficiencies, but decreased the N resorption proficiencies of the former two species. In contrast, drought did not affect N or P resorption proficiencies, but decreased N resorption efficiency of K. capillifolia. Besides, N addition facilitated P resorption in K. capillifolia and D. kamaonense, and drought did the same in A. diplostephioides, suggesting that P resorption plays an important role in nutrient conservation in these species. Moreover, species with stronger N resorption allocated more biomass C or N to aboveground and enhanced their litter quality under N enrichment, while species with weaker resorption allocated more biomass C and/or N to belowground part under drought. Together, these results show that the responses of nutrient resorption and allocation to N enrichment and drought are highly species-specific. Future studies should take these differential responses into consideration to better predict litter decomposition and ecosystem nutrient cycling.

Nutrient resorption patterns of Phragmites australis leaves and its response to soil moisture in Yangguan wetland, Dunhuang, Northwest China

Nutrient resorption of leaves is an important nutrient conservation mechanism for plants in nutrient-poor habitats. Understanding the responses of leaf nutrient resorption to soil moisture is helpful to reveal the adaptation strategies of plants to the environment. In this study, the dominant plant in the Yangguang wetland of Dunhuang Phragmites australis was used as research material, to explore nitrogen and phosphorus resorption patterns of P. australis leaves and their responses to soil moisture under different moisture regimes, i.e. high (33.5%±1.9%), medium (26.4%±1.3%) and low (11.3%±1.5%). The results showed that: 1) With the decreases of soil moisture, soil N concentration decreased significantly, and N concentrations in mature and senescent leaves increased significantly, the P concentration in mature and senescent leaves as well as in soil did not change. 2) N resorption efficiency of leaves under high moisture condition was 76.1%, which was significantly higher than the medium (65.5%) and low (62.5%) moisture conditions. P resorption efficiency varied among different moisture conditions. 3) The N concentrations of mature and senescent leaves were negatively correlated with N resorption efficiency. There was no significant correlation between P concentration and P resorption efficiency in mature leaves, but the P concentration of senescent leaves was negatively correlated with P resorption efficiency of leaves. As a result, water scarcity is not conducive to leaf N resorption.

Patterns of nitrogen resorption efficiency among different functional groups of trees in a subtropical forest of Meghalaya

Patterns of nitrogen resorption efficiency among different functional groups of trees in a subtropical forest of Meghalaya

Local edaphic factors influence leaf nutrient resorption efficiency of evergreen and deciduous trees: a case study from montane subtropical old-growth and regenerating forests of Meghalaya

Local edaphic factors influence leaf nutrient resorption efficiency of evergreen and deciduous trees: a case study from montane subtropical old-growth and regenerating forests of Meghalaya

Nitrogen, Phosphorus, and Potassium Resorption Responses of Alfalfa to Increasing Soil Water and P Availability in a Semi-Arid Environment

In semi-arid areas, alfalfa (Medicago sativa L.) is widely grown, but its growth is often restricted due to limited rainfall and soil nutrients, particularly phosphorus (P). Nutrient resorption is an effective strategy for dealing with nutrient shortages. Alleviation of these limited resources using film mulch and P fertilization—which are common practices in semi-arid areas—can affect the internal recycling of such nutrients. Little is known about such effects in alfalfa and the relationship between resorption efficiency and forage yield. We conducted a two-year field experiment in the semi-arid Loess Plateau of China using film mulch and P fertilization to investigate the response to long-term increasing soil water and P availability on leaf nitrogen (N), P, and potassium (K) concentrations and nutrient resorption characteristics in alfalfa. In green leaves, mulching significantly increased P concentration by an average of 5.5% but it had no significant effect on N concentration over two years, and it decreased K concentration by 16.1% in 2017. P fertilization significantly increased N concentrations to a greater degree in 2018 (8.1%) than 2017 (1.6%). P fertilization also significantly increased P concentrations by an average of 34.1% over two years. In contrast, P fertilization significantly decreased K concentration in the mulched treatment by an average of 17.3% in 2017 and 21.8% in 2018, but it had no effect in the no-mulch treatment. In senescent leaves, mulching significantly increased N concentration by an average of 3.9% and P concentration by an average of 16.7%, but it had no significant effect on K concentration over two years, while P fertilization significantly decreased N and K concentrations over two years by an average of 7.5%, and 32.8%, respectively. P fertilization significantly increased senesced P concentration by an average of 11.9% in 2017 and 17.5% in 2018; and year × mulching × P fertilization had a significant interaction on senesced leaf P concentration. For resorption efficiency, mulching decreased P resorption efficiency by an average of 3.0%, but it had no impact on N or K resorption efficiency, while P fertilization increased the N, P, and K resorption efficiencies in alfalfa by an average of 6.8%, 6.2%, and 76.4% over two years, respectively. Interactive effects of mulching and P fertilization were found on P and K resorption efficiencies over time. In addition, N and K resorption efficiencies were significantly higher in 2018 than in 2017. The application of P fertilizer without mulching resulted in positive correlations between forage yield and N, P, and K resorption efficiencies, but no correlations were observed under film mulch. That is, mulching changed the relationship between forage yield and N, P, and K resorption efficiencies in alfalfa, suggesting that N, P, and K resorption efficiencies may not be related to high yield. Our results provide new insights into the role of nutrient resorption in alfalfa in response to increasing soil water and P availability and the relationship between resorption efficiency and forage yield, which will help us to improve alfalfa yield in semi-arid regions.

Thinning drives C:N:P stoichiometry and nutrient resorption in Larix principis-rupprechtii plantations in North China

Carbon (C):nitrogen (N):phosphorous (P) stoichiometry and nutrient resorption play an important role in terrestrial biogeochemical cycling and functioning. However, little information is available about the changes in C:N:P stoichiometry and nutrient resorption following thinning in plantation forests. Here, to reveal how thinning affects the C:N:P stoichiometry and nutrient resorption and their relationships, green leaves, senesced leaves and soil samples were collected from a pure Larix principis-rupprechtii plantation in North China after 9 years of four different thinning treatments, i.e., control (CK, 0% thinning), low thinning (LT, 14% thinning), moderate thinning (MT, 28% thinning) and high thinning (HT, 42% thinning). The results showed that excluding the green leaf C contents, thinning significantly increased the C, N, and P contents in green leaves, senesced leaves, and soil (p < 0.05). Thinning significantly decreased the C:N and C:P ratios in green leaves, C:P and N:P ratios in senesced leaves, and C:N, C:P, and N:P ratios in soil (p < 0.05), while thinning did not significantly affect green leaf N:P and senesced leaf C:N ratios (p > 0.05). The N resorption efficiency (NRE) showed no significant differences among different thinning treatments (p > 0.05), while thinning significantly decreased the P resorption efficiency (PRE, p < 0.05). There were different degrees of correlations between nutrient contents, stoichiometry ratios and nutrient resorption, and most of which were affected by soil properties (bulk density, soil water contents, available nitrogen and phosphorus, pH, electrical conductivity, soil microbial biomass C and N, and the activities of soil β-glucosidase, N-acetylglucosaminidase, and acid phosphatase). The N:P ratios of green leaves and senesced leaf litter and the nutrient resorption suggested that Larix principis-rupprechtii plantations in the study region were limited by N. Overall, the variations in nutrient contents, stoichiometry ratios, nutrient resorption, and soil properties demonstrate that thinning can significantly increase nutrient contents, promote nutrient cycling, and improve soil fertility. Among the four thinning treatments, in terms of nutrients, MT is recommended in Larix principis-rupprechtii plantations in North China. Furthermore, appropriate fertilization management strategies should be considered to improve N-limitation status.

Hydrogen sulfide and rhizobia synergistically regulate nitrogen (N) assimilation and remobilization during N deficiency-induced senescence in soybean.

Hydrogen sulfide (H2 S) is emerging as an important signalling molecule that regulates plant growth and abiotic stress responses. However, the roles of H2 S in symbiotic nitrogen (N) assimilation and remobilization have not been characterized. Therefore, we examined how H2 S influences the soybean (Glycine max)/rhizobia interaction in terms of symbiotic N fixation and mobilization during N deficiency-induced senescence. H2 S enhanced biomass accumulation and delayed leaf senescence through effects on nodule numbers, leaf chlorophyll contents, leaf N resorption efficiency, and the N contents in different tissues. Moreover, grain numbers and yield were regulated by H2 S and rhizobia, together with N accumulation in the organs, and N use efficiency. The synergistic effects of H2 S and rhizobia were also demonstrated by effects on the enzyme activities, protein abundances, and gene expressions associated with N metabolism, and senescence-associated genes (SAGs) expression in soybeans grown under conditions of N deficiency. Taken together, these results show that H2 S and rhizobia accelerate N assimilation and remobilization by regulation of the expression of SAGs during N deficiency-induced senescence. Thus, H2 S enhances the vegetative and reproductive growth of soybean, presumably through interactions with rhizobia under conditions of N deficiency.

Global patterns of terrestrial nitrogen and phosphorus limitation

Nitrogen (N) and phosphorus (P) limitation constrains the magnitude of terrestrial carbon uptake in response to elevated carbon dioxide and climate change. However, global maps of nutrient limitation are still lacking. Here we examined global N and P limitation using the ratio of site-averaged leaf N and P resorption efficiencies of the dominant species across 171 sites. We evaluated our predictions using a global database of N- and P-limitation experiments based on nutrient additions at 106 and 53 sites, respectively. Globally, we found a shift from relative P to N limitation for both higher latitudes and precipitation seasonality and lower mean annual temperature, temperature seasonality, mean annual precipitation and soil clay fraction. Excluding cropland, urban and glacial areas, we estimate that 18% of the natural terrestrial land area is significantly limited by N, whereas 43% is relatively P limited. The remaining 39% of the natural terrestrial land area could be co-limited by N and P or weakly limited by either nutrient alone. This work provides both a new framework for testing nutrient limitation and a benchmark of N and P limitation for models to constrain predictions of the terrestrial carbon sink. Spatial patterns in the phosphorus and nitrogen limitation in natural terrestrial ecosystems are reported from analysis of a global database of the resorption efficiency of nutrients by leaves.

Linking leaf nutrient resorption and litter decomposition to plant mycorrhizal associations in boreal peatlands

Mycorrhizal type has been proposed as an effective trait integrator capturing varying biogeochemical syndromes in terrestrial ecosystems. However, for boreal peatlands, it is still unclear whether mycorrhizal associations of vascular plants can indicate leaf nutrient resorption patterns and litter decomposition rates. We determined leaf nitrogen (N) and phosphorus (P) resorption efficiency and proficiency of 11 common vascular plants belonging to three mycorrhizal types (ectomycorrhizal, ECM; ericoid mycorrhizal, ERM; and non-mycorrhizal, NM) in boreal peatlands of Northeast China, and measured leaf litter mass loss and N remaining of these 11 species after one and 3 years of decomposition using the litterbag method. Leaf nutrient resorption and litter decomposition rates varied significantly among the three mycorrhizal types. Specifically, ECM plants had greater green leaf nutrient (N and P) concentrations and lower leaf nutrient resorption efficiency and proficiency than ERM and NM plants. Moreover, ECM plants had higher leaf litter mass loss and lower N remaining than ERM and NM plants after one and 3 years of decomposition, respetively. In addition, both leaf litter mass loss and N remaining significantly correlated with N and P resorption efficiency and proficiency, indicating that plant nutrient resorption and litter decomposition were coupled. These results suggest that leaf nutrient resorption and litter decomposition are tightly linked to the mycorrhizal associations of vascular plants, and highlight that mycorrhizal type can be applied to explain and predict the dynamics of plant-mediated carbon and nutrient cycles in boreal peatlands.

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.

Enhancement of nutrient resorption efficiency increases plant production and helps maintain soil nutrients under summer grazing in a semi-arid steppe

Grazing regime is the most important factor that alters nutrient cycling in grassland ecosystems. Grazing exclusion has been used for restoration of degraded natural grasslands in Northern China during past two decades, while we propose that 'summer grazing' could be a better management than grazing exclusion for this purpose. Summer grazing allows plants to resorb more nutrients in autumn, thus preventing grazing-induced grassland degradation while keeping grassland in production. However, our understanding of grazing effects on nutrient resorption remains limited. In the present study, we examined plant nitrogen (N) and phosphorous (P) resorption at plant species and community levels in a natural steppe grassland that had experienced contrasting 'summer grazing' versus no-grazing treatments over a 6-year period in central Inner Mongolia. Plant community nutrient resorption efficiency (RE) and resorption fluxes were estimated, along with nutrient return fluxes via animal excreta and litter deposition. We found that (1) Summer grazing at moderate intensity increased plant production, but did not alter soil quality indicators such as soil organic carbon, total nitrogen, and total and plant available phosphorous. (2) Summer grazing increased plant community nutrient RE as the post-grazing plant re-growth with elevated nutrient concentration compensated for the nutrient removal by defoliation. Summer grazing increased nitrogen RE in Leymus chinensis and Cleistogenes squarrosa, but not in Stipa krylovii; and increased phosphorous RE in L. chinensis, but decreased that in S. krylovii and C. squarrosa. (3) Summer grazing accelerated nutrient cycling via animal excreta and litter deposition, but did not reduce plant nutrient resorption fluxes in autumn, which is a major mechanism for plant production enhancement and soil nutrient maintenance under the grazing regime. Our findings provide the key evidence to support moderate-intensity summer grazing as a sustainable grassland management regime to improve plant production while maintaining soil nutrients.

Nitrogen economy of alpine plants on the north Tibetan Plateau: Nitrogen conservation by resorption rather than open sources through biological symbiotic fixation.

Nitrogen (N) is one of the most important factors limiting plant productivity, and N fixation by legume species is an important source of N input into ecosystems. Meanwhile, N resorption from senescent plant tissues conserves nutrients taken up in the current season, which may alleviate ecosystem N limitation. N fixation was assessed by the 15N dilution technique in four types of alpine grasslands along the precipitation and soil nutrient gradients. The N resorption efficiency (NRE) was also measured in these alpine grasslands. The aboveground biomass in the alpine meadow was 4–6 times higher than in the alpine meadow steppe, alpine steppe, and alpine desert steppe. However, the proportion of legume species to community biomass in the alpine steppe and the alpine desert steppe was significantly higher than the proportion in the alpine meadow. N fixation by the legume plants in the alpine meadow was 0.236 g N/m2, which was significantly higher than N fixation in other alpine grasslands (0.041 to 0.089 g N/m2). The NRE in the alpine meadows was lower than in the other three alpine grasslands. Both the aboveground biomass and N fixation of the legume plants showed decreasing trends with the decline of precipitation and soil N gradients from east to west, while the NRE of alpine plants showed increasing trends along the gradients, which indicates that alpine plants enhance the NRE to adapt to the increasing droughts and nutrient‐poor environments. The opposite trends of N fixation and NRE along the precipitation and soil nutrient gradients indicate that alpine plants adapt to precipitation and soil nutrient limitation by promoting NRE (conservative nutrient use by alpine plants) rather than biological N fixation (open sources by legume plants) on the north Tibetan Plateau.

Tree growth rate and soil nutrient status determine the shift in nutrient-use strategy of Chinese fir plantations along a chronosequence

Nutrient resorption is a key nutrient-use strategy exhibited by perennial plants to overcome nutrient limitations and meet their nutritional demands. However, the factors that drive nutrient resorption with stand development remain largely unknown. In this study, we examined how a nutrient source (soil) and sink (trees) affected the resorption efficiency (RE) of nitrogen (N) and phosphorus (P). Fresh leaves, leaf litterfall, and soil samples were collected from a chronosequence of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook., Taxodiaceae) plantations at the ages of 3, 8–11, 16, 20, 25, 29, and 32 years. The N and P concentrations in stems, branches, leaves, coarse roots, and fine roots, stocks of N and P in soils, and the relative growth rate (RGR) of trees were measured. Fresh leaf N and P concentrations and RE decreased with stand age, while the N:P ratio in fresh leaves as well as the N and P concentrations in leaf litterfall increased. The RGR of trees declined with stand age. Soil P stocks increased but soil N stocks slightly decreased with stand age. A variation partitioning analysis revealed that the combined effect of RGR and soil P stocks on the RE of P (PRE) was stronger than the individual effect of each factor, while the RE of N (NRE) was greatly affected by the individual effect of RGR. With increasing age, Chinese fir plantations shifted from N-limiting to P-limiting conditions, and the nutrient-use strategy changed from “conservative consumption” to “resource spending”. These patterns were co-regulated by the tree growth rate and soil nutrient status. Thus, supply-demand relationships reflected the nutrient cycling status and could provide valuable information for sustainable nutrient management practices in tree plantations.

The growth of Chinese fir is limited by nitrogen: Evidences from N:P ratio, N or P variability and NuRE based on a regional investigation

Plant growth and vegetation productivity were generally limited either by nitrogen (N) or phosphorus (P) worldwide. To date, our current understandings on plant nutrient limitation are primarily derived from site-specific studies. By taking account into more factors, studies on regional or larger scales might resolve the divergences effectively arisen from regional differences, which would help provide new insights for plant nutrient limitation. In this study, we made an attempt to evidence the particular element that limiting the growth of Cunninghamia lanceolata (Chinese fir) based on a regional investigation. Firstly, we found that leaf N:P ratio (11.49) was significantly lower than 14, which suggested and evidenced that the growth of Chinese fir was limited by N. Next, leaf N concentration was less affected by the environmental variables, showing low variability. Leaf P concentration and N:P ratio were significantly affected by soil P concentration (SP), mean annual temperature (MAT) and altitude (ALT), and both of them showed high variability. Hence under same regional environmental changes, the level of the variability in leaf N or P concentration might affect the N or P supply for plant growth. Thirdly, the P resorption efficiency (PRE) was significantly higher than N resorption efficiency (NRE). Leaf N:P ratio decreased with the increasing PRE and |NRE − PRE|. Overall, our findings suggested that in subtropical China, low leaf N:P ratios, low N variability under, and high PRE were three major pieces of evidence that induce N- limitation for the growth of Chinese fir.

Mangrove species maintains constant nutrient resorption efficiency under eutrophic conditions

AbstractMangrove 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.

Imbalanced stoichiometric patterns in foliar nutrient resorption response to N and P addition in grazing alpine grassland

Although the effect of nutrient availability on plant nutrient resorption has been extensively studied, the influence of nutrient addition on the coupled biogeochemical cycling of N and phosphorus (P) remains unclear. Studies on how increased nutrient addition affects the imbalance between N and P resorption are limited. We investigated the influence of a wide nutrient addition gradient on the foliar nutrient resorption of dominant grass, Stipa capillata, in grazing alpine grassland. We applied seven addition levels for N (0.5–24 g N ∙ m−2 yr−1) and P (0.05–3.2 g P ∙ m−2 yr−1), collected plant and soil samples, and calculated plant foliar nutrient resorption. Results showed that N and P resorption efficiencies decreased with increasing N addition and N:P resorption ratios. However, N and P resorption efficiencies significantly decreased but N:P resorption ratios increased with the P addition gradient. Moreover, the N:P resorption ratios were negatively correlated with senesced foliar N:P ratios. Our findings suggest that N and P responses to nutrient fertilization are tightly coupled at the intraspecific level. Hence, plants show different tendencies of resorbing nutrient with N and P addition, leading to imbalance between N and P. Plant stoichiometric patterns were regulated by the nutrient status of senesced foliar. This study reveals that nutrient additions accelerate ecosystem N and P cycling, N and P cycles are coupled, but their resorptions are imbalanced. The imbalanced stoichiometric patterns in foliar nutrient resorption response to nutrient enrichment provide insights into N and P cycling under human-driven nutrient imbalance scenarios.

High nitrogen resorption efficiency of forest mosses.

Nutrient resorption from senescing tissue is a key mechanism for plants to conserve nutrients, and can affect the nutrient dynamics of ecosystems. Yet, our limited knowledge of nitrogen (N) resorption and release from mosses hampers our understanding of the role of mosses as N sources and, thereby, N cycling in moss-dominated ecosystems. The aims of this study were to estimate N resorption efficiency (NRE) of two moss species, identify the pathways of N release from the mosses and to provide a better understanding of N cycling and budgeting strategies of mosses. The dynamics of N allocation along annual moss segments of two dominant moss species (Actinothuidium hookeri and Hylocomium splendens) were assessed in old-growth fir forests using an in situ15N tracer experiment. The NRE of A. hookeri and H. splendens was 61 and 52 %, respectively. While the mosses lost 23 and 33 % N from live tissues via leaching, 15 and 14 % of N remained in senesced tissues (>3 years old) in A. hookeri and H. splendens, respectively. Both mosses resorbed the majority of their tissue N, but a considerable amount of N was lost from live segments. Our results highlight the crucial role mosses play as N sinks in ecosystems, since N retention (resorbed and sequestered in senescent tissue) outweighed N loss via leaching. However, the sink strength depends on temperature and precipitation, which will change in a future climate. The values for NRE, leaching, etc. estimated here can help improve biogeochemical models aiming to complete N budgets for moss-abundant ecosystems.