Resorption Efficiency Research Articles

Alignment efficiency and three-dimensional assessment of root resorption after alignment with conventional and copper-nickel-titanium archwires: A randomized controlled trial.

To compare alignment efficiency and root resorption between nickel-titanium (NiTi) and copper-nickel-titanium (CuNiTi) archwires after complete alignment in mandibular anterior region. In this two-arm parallel single-blind randomized controlled trial, forty-four patients with Class I malocclusion with mandibular anterior crowding were recruited form orthodontic clinic of All India Institute of Medical Sciences (Jodhpur, India). Patients were randomly allocated into NiTi and CuNiTi groups, with a 1:1 allocation. Alignment was performed using 0.014-in, 0.016-in, 0.018-in, 0.019x0.025-in archwire sequence in the respective groups, which terminated in 0.019 x 0.025-in stainless-steel working archwire. The primary outcome was alignment efficiency, measured on study models from baseline (T0) to the first, second, third, fourth and fifth-month (T5). Secondary outcome was root resorption, measured from CBCT scans taken at T0 and T5. Mixed-factorial ANOVA was used to compare Little's Irregularity Index (LII). For assessing the proportion of patients with complete alignment at the end of each month, Kaplan-Meier survival curve was built and time to treatment completion was compared between groups using log rank test. Paired t-test was used to assess external apical root resorption (EARR) within groups, whereas independent t-test was used to evaluate LII and EARR between the groups. Twenty-two patients were recruited in each group. One patient was lost to follow-up in the CuNiTi group. No statistically significant differences were observed in alignment efficiency between the groups (p>0.05). Intergroup comparison revealed that the changes in root measurement in three-dimensions were not statistically significant (p>0.05), except for mandibular right central incisor, which showed increased resorption at root apex in NiTi group (p<0.01). The two alignment archwires showed similar rate of alignment at all time points. Root resorption measurement did not differ between the NiTi and CuNiTi groups, except for the mandibular right central incisor, which showed more resorption in NiTi group.

Variations of trace-elements resorption efficiency in leaves of different tree species as affected by life forms in a mid-subtropical common garden

Variations of trace-elements resorption efficiency in leaves of different tree species as affected by life forms in a mid-subtropical common garden

Soil nutrient distribution and plant nutrient status in a mangrove stand adjacent to an aquaculture farm.

The marine aquaculture industry has caused a suite of adverse environmental consequences, including offshore eutrophication. However, little is known about the extent to which aquaculture effluents affect nearby wetland ecosystems. We carried out a field experiment in a mangrove stand located between two effluent-receiving creeks to estimate the extent to which marine aquaculture affects the soil nutrient distribution and plant nutrient status of adjacent mangroves. Carbon (C), nitrogen (N), and phosphorus (P) contents and C isotopic signatures were determined seasonally in creeks, pore water, surface soils, and in the leaves of the dominant mangrove species Kandelia obovata. The creeks exhibited nutrient enrichment (2.44mgN L-1 and 0.09mg P L-1 on average). The soils had N (from 1.40 to 2.70gkg-1) and P (from 0.58 to 2.76gkg-1) much greater than those of pristine mangrove forests. Combined analyses of the N:P ratio, nutrient resorption efficiency, and proficiency indicated that soil P met plant demands, but plants in most plots showed N limitation, suggesting that soil nutrient accumulation did not fundamentally impact the plant nutrient status. Collectively, this case study showsthat marine aquaculture farms can affect adjacent mangrove stands even though their effluents are not directly discharged into the mangrove stands, but mangrove forests may have substantial buffering capabilities for long-term nutrient loading.

Different Environmental and Phylogenetic Controls over the Altitudinal Variation in Leaf N and P Resorption Traits between Woody and Herbaceous Plants

Leaf nutrient resorption traits are regarded as important indicators reflecting the strategy of plant nutrient conservation, yet the mechanism underlying the variation of resorption traits in different plant growth forms (PGFs) remains unclear. In order to untangle the phylogenetic and environmental influences on leaf nitrogen (N) and phosphorus (P) resorption traits between woody and herbaceous plants, we investigated N and P contents of green and senesced leaves in 53 species along an altitudinal gradient (1374–3649 m) in the Taibai Mountain of central China and estimated leaf N and P resorption efficiency and proficiency. Our results show that leaf N and P resorption efficiency (NRE and PRE) had significant positive trends with altitude in both woody and herbaceous plants (all p &lt; 0.05); however, their altitudinal patterns of N and P resorption proficiency (NRP and PRP) were different. For woody plants, leaf NRP and NRE:PRE first decreased and then increased with altitude (p &lt; 0.05), while NRP:PRP had the opposite trend (p &lt; 0.05). In herbaceous plants, leaf NRP and PRP decreased but NRP:PRP increased with altitude (p &lt; 0.05). Climatic factors exerted the major influences on the variation in leaf NRE and PRE (18.5–24.8% explained variation). However, phylogenetic taxonomy mainly affected the variation of leaf PRP and NRP:PRP (45.2% and 41.4% explained variation) in all species, NRP:PRP in woody plants (37.8% explained variation), and NRE:PRE in herbaceous plants (49.7% explained variation). In addition, leaf NRP:PRP showed a significant phylogenetic signal (Blomberg’s p &lt; 0.05). These results highlight the importance of taking PGFs and phylogenetic information into consideration when examining the interspecies variation in leaf resorption under environmental changes, which can advance our knowledge of plant nutrient utilization strategies in response to fluctuating environments and lay the groundwork for the development of complex element biogeochemical models.

Characteristics of Carbon, Nitrogen and Phosphorus Stoichiometry and Nutrient Reabsorption in Alfalfa Leaves with Different Fall-Dormancy Levels in Northern Xinjiang, China

Alfalfa productivity and cold resistance in different regions are influenced by the fall-dormancy level of alfalfa. However, it is unclear whether the stoichiometric characteristics and nutrient resorption efficiency in alfalfa leaves also vary with the fall-dormancy level. In order to further understand the differences in nutrient absorption and requirements of different fall-dormant alfalfa, we conducted field trials on 30 different fall-dormancy alfalfa cultivars for 2 consecutive years in 2020 and 2021. We investigated the concentrations of carbon, nitrogen, and phosphorus in mature and senescent alfalfa leaves; nutrient stoichiometry ratios; and the coupling relationship between nutrient reabsorption efficiency and dry matter yield. The differences in nutrient reabsorption, fall dormancy, and dry matter yield of different fall-dormant alfalfa, and the correlation between indicators were utilized to further analyze the regulatory mechanisms of nutrient reabsorption in different fall-dormancy alfalfa varieties. The results demonstrated that the nitrogen reabsorption efficiency (NRE) and phosphorus reabsorption efficiency (PRE) of leaves increased first and then decreased with the increase in fall dormancy, whereas the carbon reabsorption efficiency (CRE) showed the reverse tendency. Different fall-dormancy alfalfa varieties significantly affected the dry matter yield and nutrient absorption in the first cut, while the last cut had the lowest variable coefficient and impact. There was a significant decrease in the over-winter survival rate of alfalfa as the fall-dormancy level increased, whereas the over-summer survival rate was less affected by the fall-dormancy level. As the growth year increased, there was a significant decrease in the over-winter survival rate. Among mature leaves, the NRE and PRE showed a significant positive correlation with the C concentration, while they showed a significant negative association with the N and P concentrations. In the same cut, the dry matter yield decreased with the increase in CRE but increased with the increases in NRE and PRE, while there was no significant trend in dry matter yield and nutrient resorption efficiency (NuRE) between different cuts. Taken together, the alfalfa survival rate and dry matter yield were relatively better in the moderate fall-dormancy (fall-dormancy level, FD = 4, 5) types and fall-dormancy (FD = 3) type, with a corresponding increase in the reabsorption requirements for nitrogen and phosphorus.

Effect of shrub encroachment on leaf nutrient resorption in temperate wetlands in the Sanjiang Plain of Northeast China

BackgroundNutrient resorption is an important plant nutrient conservation strategy in wetlands. However, how shrub encroachment alters plant nutrient resorption processes is unclear in temperate wetlands. Here, we collected green and senesced leaves of common sedge, grass, and shrub species in wetlands with high (50–65%) and low (20–35%) shrub covers in the Sanjiang Plain of Northeast China, and assessed the impact of shrub encroachment on leaf nitrogen (N) and phosphorus (P) resorption efficiency and proficiency at both plant growth form and community levels.ResultsThe effects of shrub cover on leaf nutrient resorption efficiency and proficiency were identical among shrubs, grasses, and sedges. Irrespective of plant growth forms, increased shrub cover reduced leaf N resorption efficiency and proficiency, but did not alter leaf P resorption efficiency and proficiency. However, the effect of shrub cover on leaf nutrient resorption efficiency and proficiency differed between plant growth form and community levels. At the community level, leaf N and P resorption efficiency decreased with increasing shrub cover because of increased dominance of shrubs with lower leaf nutrient resorption efficiency over grasses and sedges. Accordingly, community-level senesced leaf N and P concentrations increased with elevating shrub cover, showing a decline in leaf N and P resorption proficiency. Moreover, the significant relationships between leaf nutrient resorption efficiency and proficiency indicate that shrub encroachment increased senesced leaf nutrient concentrations by decreasing nutrient resorption efficiency.ConclusionsThese observations suggest that shrub encroachment reduces community-level leaf nutrient resorption efficiency and proficiency and highlight that the effect of altered plant composition on leaf nutrient resorption should be assessed at the community level in temperate wetlands.

Foliar Resorption Efficiency Does Not Change Along an Elevational Gradient in Two Dominant Peatbog Plant Species

Plants adapted to nutrient-poor temperate peatlands exhibit relatively low foliar N and P contents and resorb N and P from ageing leaves very efficiently to minimize their nutrient losses through litter fall. Changes in nutrient resorption efficiency due to an expectable increase of temperature may affect nutrient cycling in peatlands. We used an elevational gradient as a proxy for the effect of ongoing climatic change and compared the foliar N and P resorption efficiencies (REN, REP) of two co-occurring typical plant dominants (Molinia caerulea and Vaccinium uliginosum) at four microsites of each of two acidic peatbogs in southern Bohemia, Czechia, at two elevations differing by ca 500 m. No significant difference in soil nutrient content was found between the two sites. Foliar N and P contents in mature leaves in both species did not depend on the elevational gradient and were mostly not correlated with the inorganic soil nutrients. The REN (70–78%) and REP values (61–70%) in Vaccinium were markedly lower than those in Molinia (84–85% and 92–94%, respectively). In line with literature data, the peatland dominants Molinia and Vaccinium possess different strategies of foliar N and P resorption from ageing leaves. High REN and REP in Molinia obviously underlie its strong dominance in unmanaged peatland habitats. No elevational difference in both REN and REP was found in either species, indicating that the resorption efficiencies of these species are not expected to change markedly under the projected scenario of increasing temperature and lengthening growing season.

Relationships between tree functional traits and leaf nitrogen and phosphorus resorption efficiencies in subtropical young plantations

We examined the relationship between tree functional traits and leaf nitrogen and phosphorus resorption efficiencies across 29 species in 3-year-old pure plantations in subtropical China. The results showed that the average nitrogen (NRE) and phosphorus (PRE) resorption efficiencies in 29 young plantations were 50.5% and 57.3%, respectively. The average NRE of 22 arbuscular mycorrhizal (AM) tree species was 52.7%, significantly higher than that of the seven ectomycorrhizal (EM) tree species (45.1%). NRE was positively correlated with fine root tissue density across the 29 tree species. PRE was positively correlated with root diameter in the seven EM tree species. Functional traits of 22 AM tree species were not associated with NRE and PRE. Among all of the 29 tree species, mycorrhizal type, specific leaf area, fine root tissue density, leaf thickness, and the interaction effects of mycorrhizal type with leaf thickness explained 27% variation in NRE. Specific root length, fine root carbon content, fine root carbon to nitrogen ratio, mycorrhizal type, leaf carbon content, and the interaction effects of mycorrhizal type with leaf carbon content explained 35% variation in PRE. Root functional trait of subtropical species could predict nitrogen and phosphorus resorption efficiencies. The model with multiple functional traits could better reveal the relative importance of different biological factors on nutrient resorption efficiency.

Distribution and Resorption Efficiency of Macroelements (N, P, K, Ca, and Mg) in Organs of Rumex alpinus L. in the Alps and the Giant (Krkonoše) Mountains

Distribution and Resorption Efficiency of Macroelements (N, P, K, Ca, and Mg) in Organs of Rumex alpinus L. in the Alps and the Giant (Krkonoše) Mountains

Foliar resorption of nitrogen and phosphorus in Alcea apterocarpa (Malvaceae) in different habitats types

The study goal is to reveal foliar resorption patterns of Alcea apterocarpa populations in different habitats (riverbank, meadow and forest clearing) in the Central Black Sea Region of Turkey. We determined foliar nitrogen and phosphorus resorption, considering proficiency and efficiency. The resorption efficiency was also calculated using the mass loss correction factor (MLCF). Some studies indicated that MLCF provides unbiased resorption values. Phosphorus resorption proficiencies (PRP) of species were intermediate level, while nitrogen resorption proficiencies (NRP) were complete level. Phosphorus resorption efficiencies (PRE) were intermediate level for all habitats considering MLCF, while in meadow habitat, PRE was complete level without MLCF. Nitrogen resorption efficiencies (NRE) were intermediate level for all habitats without MLCF, but NRE values of meadow and forest clearing were incomplete level as using MLCF. Green leaf N/P ratios of A. apterocarpa were higher in riverbank, while senescence leaf N/P ratios were higher in meadow habitat. Only, the regression relationship between PRP and green leaf N/P ratio was not significant.

Analysis of nutrient resorption efficiency and homeostasis of four tree species in Kanas natural forest, Xinjiang, China

To explore the differences in stoichiometric homeostasis and resorption efficiency of nitrogen (NRE) and phosphorus (PRE) of tree species in Kanas natural forest. We selected four primary tree species: Larix sibirica (LS), Picea obovata (PO), Pinus sibirica (PS), and Betula pendula (BP) and measured concentrations of carbon (C), nitrogen (N), and phosphorus (P) in fresh leaves, leaf litters, and soil. Our findings showed that compared to deciduous species (LS, BP), evergreen species (PO, PS) had higher fresh leaf C concentrations and C: N ratios. As opposed to evergreen plants, deciduous species have higher levels of fresh leaf N concentration, while the P concentration and C: P did not exhibit such a pattern. Mass-based NRE and PRE averaged 52.55 and 49.16%, respectively, with a significant difference among life forms in NRE but no varied in PRE. NRE increased with N concentration in fresh leaves of BP, PO, and LS, NRE decreased with N concentration in leaf litters of all species; PRE increased with P concentration in fresh leaves of all species, PRE decreased with P concentration in leaf litters of LS, PO, and PS. Only NRE of BP and PS and PRE of PS showed significant relationship with soil N and P concentrations, respectively. Neither NRE nor PRE was insignificantly related to mean annual temperature (MAT) for all species. The N concentration of all species showed strict homeostasis corresponding to their being limited by the N element. Only the P concentration of PS and PO and N: P ratio of PS varied with corresponding traits in soil. Overall, our results provide insight into the N and P nutrient use characteristics of tree species in the Kanas natural forest and can provide a scientific basis for regional ecological restoration.

Warming delays but grazing advances leaf senescence of five plant species in an alpine meadow

Leaf senescence is the final stage in the life cycle of leaves and is critical to plants' fitness as well as to ecosystem carbon and nutrient cycling. To date, most understanding about the responses of leaf senescence to environmental changes has derived from research in forests, but the topic has been relatively neglected, especially under grazing conditions, in natural grasslands. We conducted a 3-year manipulative asymmetric warming with moderate grazing experiment to explore the responses of leaf senescence of five main species in an alpine meadow on the Qinghai-Tibetan Plateau. We found that warming prolonged leaf longevity through earlier leaf-out and later leaf senescence, and grazing prolonged it through a greater advance in leaf-out than first leaf coloration for all plants. Warming did not affect leaf nitrogen (N) content or N resorption efficiency (NRE), but grazing increased N content in coloring leaves for P. anserine and P. nivea and decreased NRE for K. humilis, P. anserine under no-warming, and for P. nivea under warming. The interactive effects of warming and grazing on leaf phenology and leaf traits depended on species identity and year. There were positive relationships between leaf-out and leaf senescence mainly derived from grazing, and positive relationships between NRE from old leaves and leaf senescence for three out of five plant species. Therefore, our results indicated that earlier leaf-out could result in earlier leaf senescence only under grazing, but depending on plant species. Delayed leaf coloring increased NRE from old leaves for some plant species measured under warming and grazing. Our results suggested that alpine plants may develop strategies to adapt to warming and grazing to assimilate more carbon through prolonged leaf longevity rather than increased NRE through earlier leaf coloring in the alpine meadow.

Exposure to strong irradiance exacerbates photoinhibition and suppresses N resorption during leaf senescence in shade-grown seedlings of fullmoon maple (Acer japonicum).

Leaves of fullmoon maple (Acer japonicum) turn brilliant red with anthocyanins synthesis in autumn. Based on field observations, autumn coloring mainly occurs in outer-canopy leaves exposed to sun, whereas inner-canopy leaves remain green for a certain longer period before finally turn yellowish red with a smaller amount of anthocyanins. Here, we hypothesized that outer-canopy leaves protect themselves against photooxidative stress via anthocyanins while simultaneously shading inner canopy leaves and protecting them from strong light (holocanopy hypothesis). To test this hypothesis, we investigated photoinhibition and leaf N content during autumn senescence in leaves of pot-grown seedlings of fullmoon maple either raised under shade (L0, ≈13% relative irradiance to open) or transferred to full sunlight conditions on 5th (LH1), 12th (LH2), or 18th (LH3) Oct, 2021. Dry mass-based leaf N (Nmass) in green leaves in shade-grown seedlings was ≈ 30 mg N g-1 in summer. Nmass in shed leaves (25th Oct to 1st Nov) was 11.1, 12.0, 14.6, and 10.1 mg N g-1 in L0, LH1, LH2, and LH3 conditions, respectively. Higher Nmass was observed in shed leaves in LH2, compared to other experimental conditions, suggesting an incomplete N resorption in LH2. Fv/Fm after an overnight dark-adaptation, measured on 19th Oct when leaf N was actively resorbed, ranked L0: 0.72 > LH3: 0.56 > LH1: 0.45 > LH2: 0.25. As decreased Fv/Fm indicates photoinhibition, leaves in LH2 condition suffered the most severe photoinhibition. Leaf soluble sugar content decreased, but protein carbonylation increased with decreasing Fv/Fm across shade-grown seedlings (L0, LH1, LH2, and LH3) on 19th Oct, suggesting impaired photosynthetic carbon gain and possible membrane peroxidation induced by photooxidative stress, especially in LH2 condition with less N resorption efficiency. Although the impairment of N resorption seems to depend on the timing and intensity of strong light exposure, air temperature, and consequently the degree of photoinhibition, the photoprotective role of anthocyanins in outer-canopy leaves of fullmoon maple might also contribute to allow a safe N resorption in inner-canopy leaves by prolonged shading.

Trees in silvopastoral systems reduce legume proportion with no consequence for internal N resorption efficiency

AbstractIn legume-based grasslands, legumes supply the sward with nitrogen (N) from biological N2-fixation. Previous studies in silvopastoral systems have emphasized that legume proportions decline near trees which would cause spatial variation in the N supply and the concentration of N in the harvested herbage of grass swards between trees. In natural ecosystems, it was shown that the N resorption efficiency (NRE) was increased by nutrient limitation, hence, near trees where legumes are scarce. Therefore, we tested the hypothesis that the NRE is increased near trees and compensates for the loss of legumes with respect to N concentration in live herbage. Two vegetation compositions consisting of legume-based grass swards were analysed across positions between tree lines in an alley cropping system established 5 years prior to this study. Legume proportion declined up to 45% towards the tree line, and also N concentration in live and dead herbage but on average only declined by 15%. As a consequence of a reduced N concentration and also herbage mass close to trees, the N yield decreased by up to 50%. Despite the loss of legumes near trees, the NRE was unaffected by the tree line irrespective of vegetation composition. Further, the results indicate that internal N cycling of managed grass swards in silvopastoral grassland with short defoliation intervals between harvests is of lesser relevance than in unmanaged ecosystems. Legume proportions control the N concentrations of live and dead herbage irrespective of tree shading in silvopastoral systems.

Divergent leaf nutrient-use strategies of coexistent evergreen and deciduous trees in a subtropical forest

Abstract Evergreen and deciduous species coexist in the subtropical forests in southeastern China. It has been suggested that phosphorus (P) is the main limiting nutrient in subtropical forests, and that evergreen and deciduous species adopt different carbon capture strategies to deal with this limitation. However, these hypotheses have not been examined empirically to a sufficient degree. In order to fill this knowledge gap, we measured leaf photosynthetic and respiration rates, and nutrient traits related to P-, nitrogen (N)- and carbon (C)-use efficiencies and resorption using 75 woody species (44 evergreen and 31 deciduous species) sampled in a subtropical forest. The photosynthetic N-use efficiency (PNUE), respiration rate per unit N and P (Rd,N and Rd,P, respectively) of the deciduous species were all significantly higher than those of evergreen species, but not in the case of photosynthetic P-use efficiency. These results indicate that, for any given leaf P, evergreen species manifest higher carbon-use efficiency (CUE) than deciduous species, a speculation that is empirically confirmed. In addition, no significant differences were observed between deciduous and evergreen species for nitrogen resorption efficiency, phosphorus resorption efficiency or N:P ratios. These results indicate that evergreen species coexist with deciduous species and maintain dominance in P-limited subtropical forests by maintaining CUE. Our results also indicate that it is important to compare the PNUE of deciduous species with evergreen species in other biomes. These observations provide insights into modeling community dynamics in subtropical forests, particularly in light of future climate change.

Nutrient Resorption and C:N:P Stoichiometry Responses of a Pinus massoniana Plantation to Various Thinning Intensities in Southern China

Understanding the responses of C:N:P stoichiometry and nutrient resorption to thinning is essential to evaluate the effects of management practices on biogeochemical cycling in plantation forest ecosystems. However, nutrient resorption and C:N:P stoichiometry do not always respond in the same way to various thinning intensities, and the underlying mechanisms are not well understood. In this study, we aimed to examine the mechanisms underlying the impacts of thinning on C:N:P stoichiometry in a Pinus massoniana plantation, focusing on interactions among soils, plant tissues (leaves and litter), and soil properties. We conducted four different thinning treatments to determine the effects of thinning on the C:N:P stoichiometric ratios in leaves, litter, and soil in a Pinus massoniana plantation ecosystem. Thinning significantly increased the C, N, and P content of leaves, litter, and soil (p &lt; 0.05). The effects of thinning on C:N:P stoichiometry varied strongly with thinning intensity. Specifically, thinning significantly decreased all C:N:P stoichiometry except leaf N:P and litter C:N (p &lt; 0.05). The N resorption efficiency (NRE) showed no significant change, but thinning significantly decreased the P resorption efficiency (PRE, p &lt; 0.05). This suggests that thinning has inconsistent impacts on N and P cycling in Pinus massoniana plantations. In addition, these different responses suggest that soil physicochemical processes play a crucial role in regulating the effects of thinning. Thinning intensity regulates the biogeochemical cycles of C, N, and P in Pinus massoniana plantation ecosystems by affecting nutrient resorption and soil physicochemical processes. The inconsistent results obtained can be attributed to the complexities of stand environments and the redistribution of site resources following thinning. Therefore, incorporating the effects of thinning intensity into nutrient cycling models may improve predictions related to achieving long-term forest management strategies.

Monthly Dynamical Patterns of Nitrogen and Phosphorus Resorption Efficiencies and C:N:P Stoichiometric Ratios in Castanopsis carlesii (Hemsl.) Hayata and Cunninghamia lanceolata (Lamb.) Hook. Plantations

Trees can resorb nutrients to preserve and reuse them before leaves fall, which could efficiently adapt to environmental changes. However, the nutrient requirements of trees in different months with seasonal climate changes are often neglected. In this study, we selected plantations of an evergreen broadleaf tree (Castanopsis carlesii (Hemsl.) Hayata) and a coniferous tree (Cunninghamia lanceolate (Lamb.) Hook.) in the subtropics. The monthly dynamics of leaf nitrogen (N) and phosphorus (P) resorption efficiencies and C:N:P stoichiometric ratios were checked along a growing season from April to October 2021. Trees in both plantations exhibited efficient N and P resorption but with significant monthly variations. The N and P resorption efficiencies in the Cunninghamia lanceolata plantation ranged from 34.26% to 56.28% and 41.01% to 54.85%, respectively, and were highest in September. In contrast, N and P resorption efficiencies in the Castanopsis carlesii plantation ranged from 11.25% to 34.23% and 49.22% to 58.72%, respectively, and were highest in July. Compared with the Cunninghamia lanceolata, the C:N of the Castanopsis carlesii plantation was significantly lower, while its C:P was significantly higher in May and September. The Castanopsis carlesii plantation was strongly limited by P (the N:P ratios in mature leaves were higher than 20), whereas the Cunninghamia lanceolata plantation might be limited by both N and P (the N:P ratios in mature leaves were between 10 and 20). In addition, the statistical analyses revealed that temperature and precipitation were significantly associated with N and P resorption efficiencies, but the relationships were controlled by forest types. These findings highlight that efficient resorption of N and P may be beneficial in regulating nutrient limitation and balance in subtropical forest ecosystems. These results contribute to the understanding of N and P utilization strategies of trees and provide a theoretical basis for vegetation management in the subtropics.

Effects of increased precipitation on C, N and P stoichiometry at different growth stages of a cold desert annual

Plant C, N and P can reflect plant strategies of nutrient utilization and allocation. Precipitation is a key factor affecting plant nutrient uptake and utilization strategies especially in arid and semiarid regions, and it is predicted to increase in the cold deserts of Northwest China due to climate change. However, the balance of C, N and P stoichiometry in annual plants at different growth stages in response to increased precipitation is not known. Thus, we performed an experiment on the annual grass Eremopyrum distans in the Gurbantunggut Desert to determine the effect of increased precipitation on C, N and P utilization and allocation at different growth stages. In the control, organ C concentration was relatively stable during the life cycle, but leaf and root N and P concentration increased during the vegetative stage; culm N concentration decreased and P concentration increased and then decreased with plant growth. Increased precipitation significantly increased the leaf N and P concentration and decreased the C:N and C:P ratios at the vegetative growth stage, but leaf N:P was lower than 14 during the whole growth stage. Increased precipitation could improve the leaf N and P resorption efficiency to cope with the reproduction allocation, and the root nutrients are more sensitive to increased precipitation. These results indicate that increased precipitation could improve the nutrient absorption and utilization for vegetative and reproductive growth of E. distans , and the root system plays crucially important role to influence the stoichiometry under varied environment.

Seasonal grazing alters nutrient resorption and conservation, and affects spring growth ofStipa grandis

AbstractNutrient resorption in autumn is a key mechanism of perennial plants for nutrient conservation and efficient use in grassland. Grazing effects on plant nutrient resorption may alter root nutrient conservation and affect plant growth in the subsequent spring. There are many studies on nutrient resorption and conservation of plants in grazing grassland, but few studies have investigated the effect of grazing on plant growth in subsequent spring. Taking Stipa grandis, a dominant perennial grass in a semi-arid steppe as a model plant, we examined plant nitrogen (N) and phosphorous (P) resorption traits (resorption efficiency, proficiency and flux) and root nutrient conservation traits (root biomass and nutrient pool) in autumn, and plant growth traits (height, biomass and nutrient pool) in the subsequent spring, in an experimental grassland under four grazing season treatments (i.e. grazing in spring, summer or autumn or no grazing). We found that (i) 51%–66% of N and 58%–80% of P in S. grandis shoots were resorbed in autumn, and the resorption flux was the lowest under autumn grazing, and highest under spring grazing. (ii) Root nutrient conservation traits were significantly reduced by summer grazing, slightly decreased by spring grazing, but not affected by autumn grazing. (iii) Plant growth in next spring was the best under early spring grazing and the worst under autumn grazing, which was mainly affected by soil moisture rather than root nutrient storage. Our study provides insights into the process of plant nutrient cycling and a theoretical basis for establishing grazing system for grassland protection and rational utilization.

Different adaptive strategies of three mangrove species to nutrient enrichment

Mangrove species are undergoing environmental changes from nutrient-poor to enrichment due to the large nutrient input. The potential difference in adaptive strategies between the slow- and fast-growing species may lead to great changes in species interaction and ecosystem stability. This study aims to test whether the slow-growing species Aegiceras corniculatum (L.) Blanco and Kandelia obovata Sheue, Liu & Yong sp. nov. are distinctly different from a fast-growing species Laguncularia racemosa (L.) Gaertn. f. in response to soil nutrient enrichment. With the increase of soil nutrients, L. racemosa shifted from a more conservative to a more acquisitive strategy. The potential causes included the increases in specific leaf area, nutrient resorption efficiency, and photosynthetic capacity as indicated by the increase of leaf δ13C and unchanged leaf succulence, as well as the relocation of photosynthetic products as indicated by the shift toward fast-growing at the cost of constructive and defense compounds. In contrast, A. corniculatum and K. obovata maintained conservative strategies at any soil nutrient levels with only a slight increase in growth. These findings implied that L. racemosa will be more competitive over the slow-growing species in nutrient-rich soils through altering adaptive strategies.