C:N:P stoichiometry and leaf traits of halophytes in an arid saline environment, northwest China

Leaf carbon, nitrogen, and phosphorus ecological stoichiometry of grassland ecosystems along 2,600-m altitude gradients at the Northern slope of the Tianshan Mountains

Ecological stoichiometry of terrestrial ecosystems has been a hot issue in current research, with intense focus on the proportional relationships of nutritional elements within plants and between plants and their environment. To clarify these relationships along continuous environmental gradients is essential for a more comprehensive understanding how plants adapt to a changing environment. In arid regions, the varying plant and soil types along altitude gradients offer a unique opportunity to examine the vertical spectrum of plant and soil ecological stoichiometry. In this study, the northern slope of the Tianshan Mountains was selected as the study area to explore the carbon (C), nitrogen (N), and phosphorus (P) ecological stoichiometric characteristics of herbaceous plants along 900-m-3,500-m altitude gradients. We also investigated the variation of ecological stoichiometric characteristics among different grassland types. The results indicated that the mean C, N, and P in leaf of grassland were 342.95 g·kg-1-557.73 g·kg-1, 6.02 g·kg-1-20.97 g·kg-1, and 0.71 g·kg-1-3.14 g·kg-1, respectively. There was no significant change in leaf carbon content along the elevation gradient, and the highest and lowest leaf C concentrations were in the upland meadow and the semidesert grasslands. Both N and P concentrations obtained their highest value in the meadow steppe. The P concentration gradually increased in desert and semidesert grasslands and reached the highest value in the meadow steppe, and then decreased to the lowest value in the upland meadow and subsequently increased in the alpine meadow. The ranges of the C:N ratio, C:P ratio, and N:P ratio were 16.36-155.53, 109.36-786.52, and 2.58-17.34, respectively. Due to fluctuations in the P concentration, the C:P ratio and N:P ratio reached the lowest value in the meadow steppe and obtained their highest value in the upland meadow. Redundancy analysis showed that temperature was the dominant factor affecting the C, N, and P ecological stoichiometry of herbaceous plants, followed by soil organic carbon, mean annual precipitation, soil pH, and soil electrical conductivity. Corresponding results could enhance predictive models of nutrient cycling and ecosystem responses to climate change, particularly in arid and semiarid regions.

In the Qaidam Basin, Soil Nutrients Directly or Indirectly Affect Desert Ecosystem Stability under Drought Stress through Plant Nutrients

The low nutrient content of soil in desert ecosystems results in unique physiological and ecological characteristics of plants under long-term water and nutrient stress, which is the basis for the productivity and stability maintenance of the desert ecosystem. However, the relationship between the soil and the plant nutrient elements in the desert ecosystem and its mechanism for maintaining ecosystem stability is still unclear. In this study, 35 sampling sites were established in an area with typical desert vegetation in the Qaidam Basin, based on a drought gradient. A total of 90 soil samples and 100 plant samples were collected, and the soil's physico-chemical properties, as well as the nutrient elements in the plant leaves, were measured. Regression analysis, redundancy analysis (RDA), the Theil-Sen Median and Mann-Kendall methods, the structural equation model (SEM), and other methods were employed to analyze the distribution characteristics of the soil and plant nutrient elements along the drought gradient and the relationship between the soil and leaf nutrient elements and its impact on ecosystem stability. The results provided the following conclusions: Compared with the nutrient elements in plant leaves, the soil's nutrient elements had a more obvious regularity of distribution along the drought gradient. A strong correlation was observed between the soil and leaf nutrient elements, with soil organic carbon and alkali-hydrolyzed nitrogen identified as important factors influencing the leaf nutrient content. The SEM showed that the soil's organic carbon had a positive effect on ecosystem stability by influencing the leaf carbon, while the soil's available phosphorus and the mean annual temperature had a direct positive effect on stability, and the soil's total nitrogen had a negative effect on stability. In general, the soil nutrient content was high in areas with a low mean annual temperature and high precipitation, and the ecosystem stability in the area distribution of typical desert vegetation in the Qaidam Basin was low. These findings reveal that soil nutrients affect the stability of desert ecosystems directly or indirectly through plant nutrients in the Qaidam Basin, which is crucial for maintaining the stability of desert ecosystems with the background of climate change.

Response of leaf functional traits to soil nutrients in the wet and dry seasons in a subtropical forest on an island

Introduction

Island ecosystems often have a disproportionate number of endemic species and unique and fragile functional characteristics. However, few examples of this type of ecosystem have been reported.

Methods

We conducted a comprehensive field study on Neilingding Island, southern China. The leaf samples of 79 subtropical forest tree species were obtained and their functional traits were studied in the dry and wet seasons to explain the relationships between plant functional traits and soil nutrients.

Results

We found a greater availability of soil moisture content (SMC) and nutrients in the wet season than in the dry season. The values of wet season soil available phosphorus (5.97 mg·kg-1), SMC (17.67%), and soil available potassium (SAK, 266.96 mg·kg-1) were significantly higher than those of the dry season. The leaf dry matter content, specific leaf weight, leaf density, leaf total carbon, leaf total nitrogen, leaf total calcium, and the N/P and C/P ratios of leaves were all significantly higher in the dry season than in the wet season, being 18.06%, 12.90%, 12.00%, 0.17%, 3.41%, 9.02%, 26.80%, and 24.14% higher, respectively. In contrast, the leaf area (51.01 cm2), specific leaf area (152.76 cm2·g-1), leaf water content (0.59%), leaf total nitrogen (1.31%), leaf total phosphorus (0.14%), and leaf total magnesium (0.33%) were much lower in the dry season than in the wet one. There were significant pairwise correlations between leaf functional traits, but the number and strength of correlations were significantly different in the dry and wet seasons. The SAK, soil total phosphorus (STP), and pH impacted plant leaf functional traits in the dry season, whereas in the wet season, they were affected by SAK, STP, pH, and NO3- (nitrate).

Discussion

Both soil nutrients and water availability varied seasonally and could cause variation in a number of leaf traits.

Leaf nitrogen and phosphorus stoichiometry of the halophytes across China

Halophytes play a crucial role in the ecological restoration of saline and alkaline land and hold promising benefits to food security in China. Although a variety of aspects of halophytes have been extensively addressed, there is still a lack of overall understanding of the leaf nitrogen (N) and phosphorus (P) stoichiometric characteristics, especially at a national scale. We compiled a national dataset of 311 observations from 113 sampling sites across China to explore the changing trends and influencing factors on leaf N and P concentrations, and N:P ratio of halophytes. The results showed that leaf N concentration decreased significantly with increasing latitude (LAT), which was mainly driven by the mean annual temperature (MAT) and mean annual precipitation (MAP). The leaf P concentration increased remarkably with increasing longitude (LON), which was induced by the variation in soil total P (TP) content. The leaf N:P ratio increased as LAT increased and LON decreased, which was potentially regulated by the MAT, MAP, and soil TP content. The scaling exponents of the N-P relationship differed significantly among halophyte types and were 0.40, 0.87, and 1.39 for euhalophyte, pseudohalophyte, and recretohalophyte, respectively. The leaf N concentration exhibited significant differences among ecosystem types and halophyte types, whereas the leaf P concentration and N:P ratio remained relatively stable. In summary, the leaf N concentration and N-P scaling exponent might be the classification criteria for halophyte types from the perspective of plant nutrient resource allocation. Moreover, this study characterized the spatial distribution and allocation strategy of leaf N and P stoichiometry in halophytes by data integration analysis, providing the basic information for nutrient management in the processes of the future domestication and introduction of halophytes.

Effects of drought and salt stress on seed germination and seedling growth of Elymus nutans

Drought and soil salinization are global environmental issues, and Elymus nutans play an important role in vegetation restoration in arid and saline environments due to their excellent stress resistance. In the process of vegetation restoration, the stage from germination to seedling growth of forage is crucial. This experiment studied the effects of PEG-6000 simulated drought stress and NaCl simulated salinization stress on the germination of E. nutans seeds, and explored the growth of forage seedlings from sowing to 28 days under drought and salinization stress conditions. The results showed that under the same environmental water potential, there were significant differences in responses of seed germination, seedling growth, organic carbon, total nitrogen and total phosphorus of above-ground and underground parts of E. nutans to drought stress and salinization stress. Using the membership function method to comprehensively evaluate the seed germination and seedling indicators of E. nutans, it was found that under the same environmental water potential, E. nutans was more severely affected by drought stress during both the seed germination and seedling growth stages. E. nutans showed better salt tolerance than drought resistance.

Seasonal variations in carbon, nitrogen, and phosphorus of Pinus yunnanenis at different stand ages

The seasonal variations in carbon (C), nitrogen (N), and phosphorus (P) at the organ level of Pinus yunnanenis during different season are poorly understood. In this study, the C, N, P, and their stoichiometric ratios in various organs of P. yunnanensis during the four seasons are discussed. The middle and young aged P. yunnanensis forests in central Yunnan province, China were chosen, and the contents of C, N, and P in fine roots (<2 mm), stems, needles, and branches were analyzed. The results showed that the C, N, P contents and their ratios in P. yunnanensis were significantly influenced by season and organ, less affected by age. The C content of the middle-aged and young forests decreased continuously from spring to winter, whereas N and P first decreased and then increased. No significant allometric growth relationships were observed between P-C of the branches or stems in the young and middle-aged forests, whereas a significant allometric growth relationship existed for N-P of needles in the young stands, indicating that the P-C and N-P nutrient distribution patterns shows different trends in the organ level in different age stands. The pattern of P allocation between organs shows differences in stand age, with more allocation to needles in middle-aged stands and more allocation to fine roots in young stands. The N:P ratio in needles was less than 14, indicating that P. yunnanensis was mainly limited by N and increasing the application of N fertilizer would be beneficial for the productivity of this stand. The results will be helpful to nutrient management in P. yunnanensis plantation.

C:N:P stoichiometric variations of herbs and its relationships with soil properties and species relative abundance along the Xiaokai River irrigation in the Yellow River Delta, China

INTRODUCTION

Soil salinity is known to affect plant performance and nutrient stoichiometry by altering their ecophysiology, and thus playing a crucial role in determining plant distribution patterns and nutrient cycles in salinized ecosystems. However, there was little consensus on the effects of salinity stress on plant C, N, and P stoichiometries. Moreover, determining the relationships between species relative species abundance and plant C, N, and P stoichiometries can help to understand the different adaptive strategies between the common and rare species as well as the community assembly process.

METHODS

We determined the plant C, N, P stoichiometries at the community and species levels and the relative abundance of species as well as the corresponding soil properties from five sampling sites along a soil salinity gradient in the Yellow River Delta, China.

RESULTS AND DISCUSSION

We found that the C concentration of belowground part increased with soil salinity. Meanwhile, plant community N concentration and C:N ratio tended to decrease with soil salinity, whereas the P concentration, C:P, and N:P ratios exhibited the opposite trends. This indicated that N use efficiency increased, while P use efficiency decreased with soil salinity. Moreover, the decreased N:P ratio indicated that N limitation was gradually aggravated along the soil salinity gradient. The soil C:P ratio and P concentration were the major factors of plant C, N, and P stoichiometries in the early growth stage, whereas the soil pH and P concentration were the major factors of plant C, N, and P stoichiometries in the late growth stage. Compared with that of the rare species, the C:N:P stoichiometry of the most common species was medium. Moreover, the intraspecific variations in the aboveground part N:P ratio and belowground part C concentration showed a significant correlation with species' relative abundance, which indicated that higher intraspecific trait variation might facilitate greater fitness and survival opportunities in environments with high heterogeneity.

CONCLUSION

Our results revealed that the plant community C:N:P stoichiometry and its determining soil properties varied with plant tissues as well as sampling seasons, and emphasized the importance of intraspecific variation in determining the functional response of plant communities to salinity stress.

Distinct leaf functional traits of Tamarix chinensis at different habitats in the hinterland of the Taklimakan desert

Leaf functional traits reflect plant adaptive strategies towards environmental heterogeneity. However, which factor play the key role of plasticity of leaf functional traits among various variable environmental factors remains unclear in desert hinterland oasis area. Here, we analyzed variations in leaf water content (LWC), δ ¹³C values of leaves (δ ¹³C), specific leaf area (SLA), leaf organic carbon concentration (LOC), leaf total nitrogen concentration (LTN), leaf total phosphorus concentration (LTP), and leaf C: N: P stoichiometry in Tamarix chinensis growing in five habitats at the Daliyabuyi, a natural pristine oasis in northwestern China, that differ abiotically and biotically. The spatial heterogeneity of leaf functional traits was evident. Abiotic factors vitally influence leaf functional traits, of which groundwater depth (GWD) and soil C: N stoichiometry (SOC: STN) are crucial. GWD exhibited close relationships with LWC (P < 0.05) and LOC: LTP (P < 0.01), but not δ ¹³C. Soil water content (SWC) and SOC: STN were negatively related to SLA (P < 0.01; P < 0.05). While, SOC: STN showed positive relationships with LOC: LTN (P < 0.05). As for biological factors, we found T. chinensis in habitat with Sophora alopecuroidies had the highest LTN, possibly as a result of N fixation of leguminous plants (S. alopecuroidies) promotes the N concentration of T. chinensis. Close relationships also existed between leaf functional traits, LWC showed significantly negatively relatd to δ ¹³C, LOC: LTN and LOC: LTP (P < 0.05), whereas δ ¹³C had positively correlated with LOC: LTN (P < 0.01) but negatively correlated with LTN (P < 0.05). T. chinensis had relative higher LWC couple with lower δ ¹³C, and exhibiting lower C, N, P in leaves and their stoichiometric ratios, and also lower SLA which compared with other terrestrial plant. Such coordinations suggesting that T. chinensis develops a suite of trait combinations mainly tends to more conservative to response local habitats in Daliyabuyi, which is contribute to understand desert plant resource acquisition and utilization mechanisms in extremely arid and barren environments.

Aridity and High Salinity, Rather Than Soil Nutrients, Regulate Nitrogen and Phosphorus Stoichiometry in Desert Plants from the Individual to the Community Level

The stoichiometric characteristics of plant nitrogen (N) and phosphorus (P) and their correlations with soil properties are regarded as key for exploring plant physiological and ecological processes and predicting ecosystem functions. However, quantitative studies on the relative contributions of water–salt gradients and nutrient gradients to plant stoichiometry are limited. In addition, previous studies have been conducted at the plant species and individual levels, meaning that how community-scale stoichiometry responds to soil properties is still unclear. Therefore, we selected typical sample strips from 13 sampling sites in arid regions to assess the leaf N and P levels of 23 species of desert plants and measure the corresponding soil water content, total salt content, total nitrogen content, and total phosphorus content. The aim was to elucidate the main soil properties that influence the stoichiometric characteristics of desert plants and compare the individual and community responses to those soil properties. Our results indicated that the growth of desert plants is mainly limited by nitrogen, with individual plant leaf nitrogen and phosphorus concentrations ranging from 4.08 to 31.39 mg g−1 and 0.48 to 3.78 mg g−1, respectively. Community stoichiometry was significantly lower than that of individual plants. A significant correlation was observed between the mean N concentration, P concentration, and N:P ratio of plant leaves. At the individual plant scale, aridity significantly reduced leaf N and P concentrations, while high salt content significantly increased leaf N concentrations. At the community scale, aridity had no significant effects on leaf nitrogen or phosphorus stoichiometry, while high salinity significantly increased the leaf N:P ratio and there were no significant interactions between the aridity and salinity conditions. No significant effects of soil nutrient gradients were observed on plant N and P stoichiometric characteristics at the individual or community levels. These results suggest that individual desert plants have lower leaf N and P concentrations to adapt to extreme drought and only adapt to salt stress through higher leaf N concentrations. The N and P stoichiometric characteristics of desert plant communities are not sensitive to variations in aridity and salinity in this extreme habitat. The results of this study could enhance our perceptions of plant adaptation mechanisms to extreme habitats within terrestrial ecosystems.

Physiological Adaptation of Three Wild Halophytic Suaeda Species: Salt Tolerance Strategies and Metal Accumulation Capacity

Understanding salt tolerance mechanisms in halophytes is critical for improving the world's agriculture under climate change scenarios. Herein, the physiological and metabolic responses of Suaeda monoica, Suaeda vermiculata, and Suaeda schimperi against abiotic stress in their natural saline environment on the east coast of the Red Sea were investigated. The tested species are exposed to different levels of salinity along with elemental disorders, including deficiency in essential nutrients (N&P in particular) and/or elevated levels of potentially toxic elements. The tested species employed common and species-specific tolerance mechanisms that are driven by the level of salinity and the genetic constitution of Suaeda species. These mechanisms include: (i) utilization of inorganic elements as cheap osmotica (Na+ in particular), (ii) lowering C/N ratio (S. monoica and S. schimperi) that benefits growth priority, (iii) efficient utilization of low soil N (S. vermiculata) that ensures survival priority, (v) biosynthesis of betacyanin (S. schimperi and S. vermiculata) and (vi) downregulation of overall metabolism (S. vermiculata) to avoid oxidative stress. Based on their cellular metal accumulation, S. monoica is an efficient phytoextractor of Cr, Co, Cu, Ni, and Zn, whereas S. vermiculata is a hyper-accumulator of Hg and Pb. S. schimperi is an effective phytoextractor of Fe, Hg, and Cr. These results highlight the significance of Suaeda species as a promising model halophyte and as phytoremediators of their hostile environments.

Grazing exclusion had greater effects than nitrogen addition on soil and plant community in a desert steppe, Northwest of China

BACKGROUND

The impacts of increasing nitrogen (N) deposition and overgrazing on terrestrial ecosystems have been continuously hot issues. Grazing exclusion, aimed at restoration of grassland ecosystem function and service, has been extensively applied, and considered a rapid and effective vegetation restoration method. However, the synthetic effects of exclosure and N deposition on plant and community characteristics have rarely been studied. Here, a 4-year field experiment of N addition and exclusion treatment had been conducted in the desert steppe dominated by Alhagi sparsifolia and Lycium ruthenicum in northwest of China, and the responses of soil characteristics, plant nutrition and plant community to the treatments had been analyzed.

RESULTS

The grazing exclusion significantly increased total N concentration in the surface soil (0-20 cm), and increased plant height, coverage (P < 0.05) and aboveground biomass. Specifically, A. sparsifolia recovered faster both in individual and community levels than L. ruthenicum did after exclusion. There was no difference in response to N addition gradients between the two plants.

CONCLUSIONS

Our findings suggest that it is exclusion rather than N addition that has greater impacts on soil properties and plant community in desert steppe. Present N deposition level has no effect on plant community of desert steppe based on short-term experimental treatments.

Functional structure of plant communities along salinity gradients in Iranian salt marshes

Salt marshes are unique habitats between sea or saline lakes and land that need to be conserved from the effects of global change. Understanding the variation in functional structure of plant community along environmental gradients is critical to predict the response of plant communities to ongoing environmental changes. We evaluated the changes in the functional structure of halophytic communities along soil gradients including salinity, in Iranian salt marshes; Lake Urmia, Lake Meyghan, Musa estuary, and Nayband Bay (Iran). We established 48 plots from 16 sites in four salt marshes and sampled 10 leaves per species to measure leaf functional traits. Five soil samples were sampled from each plot and 30 variables were analyzed. We examined the changes in the functional structure of plant communities (i.e., functional diversity [FD] and community weighted mean [CWM]) along local soil gradients using linear mixed effect models. Our results showed that FD and CWM of leaf thickness tended to increase with salinity, while those indices related to leaf shape decreased following soil potassium content. Our results suggest that the variations in functional structure of plant communities along local soil gradients reveal the effect of different ecological processes (e.g., niche differentiation related to the habitat heterogeneity) that drive the assembly of halophytic plant communities in SW Asian salt marshes.

Distinct Responses of Leaf Traits to Environment and Phylogeny Between Herbaceous and Woody Angiosperm Species in China

Leaf traits play key roles in plant resource acquisition and ecosystem processes; however, whether the effects of environment and phylogeny on leaf traits differ between herbaceous and woody species remains unclear. To address this, in this study, we collected data for five key leaf traits from 1,819 angiosperm species across 530 sites in China. The leaf traits included specific leaf area, leaf dry matter content, leaf area, leaf N concentration, and leaf P concentration, all of which are closely related to trade-offs between resource uptake and leaf construction. We quantified the relative contributions of environment variables and phylogeny to leaf trait variation for all species, as well as for herbaceous and woody species separately. We found that environmental factors explained most of the variation (44.4-65.5%) in leaf traits (compared with 3.9-23.3% for phylogeny). Climate variability and seasonality variables, in particular, mean temperature of the warmest and coldest seasons of a year (MTWM/MTWQ and MTCM/MTCQ) and mean precipitation in the wettest and driest seasons of a year (MPWM/MPWQ and MPDM/MPDQ), were more important drivers of leaf trait variation than mean annual temperature (MAT) and mean annual precipitation (MAP). Furthermore, the responses of leaf traits to environment variables and phylogeny differed between herbaceous and woody species. Our study demonstrated the different effects of environment variables and phylogeny on leaf traits among different plant growth forms, which is expected to advance the understanding of plant adaptive strategies and trait evolution under different environmental conditions.

Transgenerational Effects of Maternal Water Condition on the Growth, C:N Stoichiometry and Seed Characteristics of the Desert Annual Atriplex aucheri

Water conditions directly affect plant growth and thus modify reproduction allocation. However, little is known about the transgenerational effects of water conditions on xerophytes. The desert annual Atriplex aucheri produces three types of seeds (A: dormant, ebracteate black seeds; B: dormant, bracteolate black seeds; C: non-dormant, bracteolate brown seeds) on a single plant. The aim of this study was to investigate the effects of low/high water treatment (thereafter progeny water treatment) on aboveground biomass, C:N stoichiometry, and offspring seed characteristics of A. aucheri grown from brown seeds whose mother plants were under low/high water treatment (thereafter maternal water treatment). Progeny water only affected shoot dry weight and seed allocation of type A. Under low progeny water treatment, plants from parents with low maternal water treatment had the lowest biomass. Maternal water did not significantly influence the C and N content, however high maternal water increased the C:N ratio. Maternal water treatment did not significantly affect seed number. However, plants under low maternal and progeny water treatments had the lowest weight for type B seeds. When progeny plants were under low water treatment, seed allocation of type A, type B, and total seed allocation of plants under high maternal water were significantly lower than those of plants under low maternal water. These results indicate that water conditions during the maternal generation can dramatically contribute to progeny seed variation, but the transgenerational effects depend on the water conditions of progeny plants.

Trade-Off Relationships of Leaf Functional Traits of Lycium ruthenicum in Response to Soil Properties in the Lower Reaches of Heihe River, Northwest China

Soil properties affect plant growth and cause variation in leaf functional traits. Lycium ruthenicum Murray is one of the desert dominant shrubs and halophytes in the lower reaches of Heihe River, Northwest China. We analyzed the trade-off relationships of 14 leaf functional traits of eight L. ruthenicum populations growing at varying distances from the river and discussed the effects that soil properties have on leaf functional traits. The results showed that: Lower leaf nitrogen (N) content indicated that L.ruthenicum was located at the slow investment–return axis of the species resource utilization graph. Compared with non-saline and very slightly saline habitats, populations of slightly saline habitats showed a higher carbon to nitrogen ratio (C:N). Redundancy analysis (RDA) revealed a relatively strong relationship between leaf functional traits and soil properties, the first RDA axis accounted for 70.99 and 71.09% of the variation in 0–40 and 40–80 cm of soil properties. Relative importance analysis found that in the 0–40 cm soil layer, leaf traits variations were mainly influenced by soil moisture (SWC), HCO3− and CO32− ions content, while leaf traits variations in the 40–80 cm soil layer were mainly influenced by HCO3− and SO42−. L.ruthenicum has a foliar resource acquisition method and a resource conservation trade-off with a flexible life history strategy in habitats with drought and salinity stress. In the shallow soil layers, water affects leaf traits variation greater than salt, and in both shallow and deep soil layers, HCO3− plays a dominant role on leaf traits. This study provides insights into the adversity adaptation strategies of desert plants and the conservation and restoration of arid-saline ecosystems.

Coupling Relationship of Leaf Economic and Hydraulic Traits of Alhagisparsifolia Shap. in a Hyper-Arid Desert Ecosystem

In this study, Alhagisparsifolia Shap. was used to test the hypothesis that leaf economic and hydraulic traits are coupled in plants in a hyper-arid region. Five economic traits and six hydraulic traits were examined to explore the relationship. Results showed that the stomatal density (SD) on both surfaces was coupled with maximum stomatal conductance to water vapor (g_wmax) and leaf tissue density (TD). SD on adaxial surface (SD_aba) was significantly positively related to vein density (VD) but negatively related to leaf thickness (LT) and stomatal length on adaxial surface (SL_ada). Nitrogen concentration based on mass (N_mass) was significantly negatively correlated with leaf mass per area (LMA), LT, and VD, whereas nitrogen concentration based on area (N_area) was significantly positively related to LMA and TD. Mean annual precipitation (MAP) contributed the most to the changes in LT and stomatal length (SL). Soil salt contributed the most to TD, SD, and g_wmax. Soli nutrients influenced the most of LMA and VD. Mean annual temperature contributed the most to N_mass and N_area. In conclusion, the economics of leaves coupled with their hydraulic traits provides an economical and efficient strategy to adapt to the harsh environment in hyper-arid regions.

Moisture, Temperature, and Salinity of a Typical Desert Plant (Haloxylon ammodendron) in an Arid Oasis of Northwest China

The physical and chemical characteristics of soil and water sources affect desert plants’ growth, which is essential for the ecological protection in arid areas. The typical patch patterns of Haloxylon ammodendron in the oasis-desert ecotone in the southern margin of the Manas River Basin consists of bare patches (BP) and vegetation patches (VP). The water sources of H. ammodendron were studied using stable isotope technology, and the soil physical and chemical properties were monitored and analyzed. The results showed that the soil moisture presented a reversed “S” type curve, and the total salt content of the soil presented an “S” type curve. A “wet island” and “cold island” were formed in the low salt area with H. ammodendron at the center. NaCl was most abundant in the BP soil, and the milligram equivalent of Cl− was 80–90%, while CaSO4 was most abundant in the VP soil, in which the milligram equivalent of SO42− was 80–100%. Before the rain, H. ammodendron mainly relied on the soil water from a deeper layer (≥60 cm) to maintain its growth. However, after the rain, H. ammodendron mainly relied on shallow soil water (<60 cm) to maintain its growth.

Response of Leaf Traits of Eastern Qinghai-Tibetan Broad-Leaved Woody Plants to Climatic Factors

Plant ecologists have long been interested in quantifying how leaf traits vary with climate factors, but there is a paucity of knowledge on these relationships given a large number of the relevant leaf traits and climate factors to be considered. We examined the responses of 11 leaf traits (including leaf morphology, stomatal structure and chemical properties) to eight common climate factors for 340 eastern Qinghai-Tibetan woody species. We showed temperature as the strongest predictor of leaf size and shape, stomatal size and form, and leaf nitrogen and phosphorus concentrations, implying the important role of local heat quantity in determining the variation in the cell- or organ-level leaf morphology and leaf biochemical properties. The effects of moisture-related climate factors (including precipitation and humidity) on leaf growth were mainly through variability in leaf traits (e.g., specific leaf area and stomatal density) related to plant water-use physiological processes. In contrast, sunshine hours affected mainly cell- and organ-level leaf size and shape, with plants developing small/narrow leaves and stomata to decrease leaf damage and water loss under prolonged solar radiation. Moreover, two sets of significant leaf trait-climate relationships, i.e., the leaf/stomata size traits co-varying with temperature, and the water use-related leaf traits co-varying with precipitation, were obtained when analyzing multi-trait relationships, suggesting these traits as good indicators of climate gradients. Our findings contributed evidence to enhance understanding of the regional patterns in leaf trait variation and its environmental determinants.

Effect of Environmental Stress on the Nutrient Stoichiometry of the Clonal Plant Phragmites australis in Inland Riparian Wetlands of Northwest China

Clonal plants play an important role in determining ecosystem properties such as community stability, species diversity and nutrient cycling. However, relatively little information is available about the stoichiometric characteristics of clonal plants and their drivers in inland riparian wetlands under strong environmental stress. In this manuscript, we studied the clonal plant Phragmites australis in an inland riparian wetland of Northwest China and compared its nutrient distribution and stoichiometry trade-offs as well as its responses to soil environmental factors in three different environments, namely, a wetland, a salt marsh, and a desert. We found that (1) P. australis could adapt to heterogeneous environments by changing its nutrient allocation strategies, as evidenced by the significant decrease in N and P concentrations, and significant increase in whole-plant C:P and N:P ratios from the wetland to the desert habitats. (2) P. australis adapted to stressful environments by changing its nutrient allocation patterns among different modules, showing a greater tendency to invest N and P in underground modules (rhizomes and roots) and an increase in the utilization efficiency of N and P in the leaves, and stems as environmental stress increased. (3) The C-N, C-P, and N:P-C in the whole plant and in each module showed significant anisotropic growth relationships in the three habitats (P < 0.05). (4) Soil water, pH and salt were the main factors limiting nutrient stoichiometry. The results of this study clarified the ecological adaptation mechanism of the clonal plant P. australis to heterogeneous environments and provided targeted protection strategies for inland riparian wetlands in Northwest China.

Is salinity the main ecological factor that influences foliar nutrient resorption of desert plants in a hyper-arid environment?

BACKGROUND

Soil salinity is a major abiotic constraint to plant growth and development in the arid and semi-arid regions of the world. However, the influence of soil salinity on the process of nutrient resorption is not well known. We measured the pools of both mature and senesced leaf nitrogen (N), phosphorus (P), potassium (K), and sodium (Na) of desert plants from two types of habitats with contrasting degrees of soil salinity in a hyper-arid environment of northwest China.

RESULTS

N, P, K revealed strict resorption, whereas Na accumulated in senesced leaves. The resorption efficiencies of N, P, and K were positively correlated with each other but not with Na accumulation. The degree of leaf succulence drives both intra-and interspecific variation in leaf Na concentration rather than soil salinity. Both community- and species-level leaf nutrient resorption efficiencies (N, P, K) did not differ between the different habitats, suggesting that soil salinity played a weak role in influencing foliar nutrients resorption.

CONCLUSIONS

Our results suggest that plants in hyper-arid saline environments exhibit strict salt ion regulation strategies to cope with drought and ion toxicity and meanwhile ensure the process of nutrient resorption is not affected by salinity.

Seasonal Dynamics of Leaf Stoichiometry of Phragmites australis: A Case Study From Yangguan Wetland, Dunhuang, China

Leaf stoichiometry can enhance our understanding of leaf elements' (C, N and P) concentrations and their corresponding ratios in an ecosystem with seasonal environment changes. This study quantified the seasonal dynamics of leaf stoichiometry of P. australis from Yangguan wetland, Dunhuang, China as a case study example. The leaf C concentration (LC) of P. australis changed between seasons and was 392.26 (g×kg-1), 417.35 (g×kg-1) and 392.58 (g×kg-1) in spring, summer and autumn, respectively. Leaf N and P concentrations (LN and LP) were 23.49 (g×kg-1), and 17.54 (g×kg-1) and 5.86 (g×kg-1), and 1.00 (g×kg-1), 0.75 (g×kg-1) and 0.16 (g×kg-1), respectively, in the three seasons. The maximum (77.68) and the minimum values (17.00) of LC:LN were observed in the autumn and spring, respectively. Seasonal variations in LC:LP also showed a similar trend, with the greatest value of 3015.91 in autumn and the lowest value of 429.39 in spring. However, the highest (45.67) and the lowest values (24.18) of LN:LP were observed in autumn and summer, respectively, indicating that the growth of P. australis was mainly affected by P. Based on these results, it can be concluded that P. australis adopted a competition strategy during the early growth stage but took on a defense life strategy at the late growth stage to cope with various environments.

High nutrient uptake efficiency and high water use efficiency facilitate the spread of Stellera chamaejasme L. in degraded grasslands

BACKGROUND

Stellera chamaejasme L. is a poisonous plant widely distributes in degraded grasslands in China. The mechanism underlying its spread remains unknown. In some degraded grasslands, S. chamaejasme has gradually replaced previous dominant species, such as Leymus chinensis, Stipa krylovii, Artemisia eriopoda on typical steppes. Apart from its unpalatability by livestock, we hypothesized that the survival strategy (nutrient uptake and water use efficiency) of S. chamaejasme in degraded grasslands could be distinct from other coexisting species in the community. Recently, ecological stoichiometry has been suggested as a new approach for studying the demand for natural resources of plants in a changing world, and the leaf carbon isotopic composition (δ13C leaf) as a rapid and effective high throughput phenotyping method for water use efficiency (WUE), both of which can reveal the survival and adaptive strategies of plants. Therefore, in this study we aimed to fill the knowledge gap concerning ecological stoichiometry in the leaf, stem, and root of S. chamaejasme and its surrounding soil on grasslands with different degrees of degradation, and comparing the leaf nutrient content and δ13C of S. chamaejasme with the coexisting species (L. chinensis, S. krylovii, A. eriopoda) in the communities. Toward this goal, we conducted a field survey in which plants and soils were sampled from four different degraded grasslands on typical steppes in China.

RESULTS

Our results showed that there is no significant difference of carbon content (C%) and nitrogen content (N%) in leaves of S. chamaejasme in different degraded grasslands, and all element contents and element ratios in stems did not differ significantly. Meanwhile, ecological stoichiometry of S. chamaejasme is distinct from the coexisting species, with low C%, high N% and phosphorus content (P%) in the leaf, indicating high nutrient uptake efficiency of S. chamaejasme in nutrient-poor environments like degraded grasslands. Additionally, S. chamaejasme showed significant higher WUE than other species.

CONCLUSIONS

Our results indicated that high nutrient uptake efficiency and high WUE of S. chamaejasme might together contribute to the spread of S. chamaejasme in degraded grasslands.

The Latitudinal Patterns of Leaf and Soil C:N:P Stoichiometry in the Loess Plateau of China

Understanding the spatial patterns and the driving factors of plant leaf and soil stoichiometry are critical for improving the parameterization of future ecological models and to predict the responses of ecosystems to environmental changes. This study aimed to determine how the latitudinal patterns of leaf and soil C:N:P stoichiometry are affected by climate and vegetation types in the dryland ecosystems. The concentrations of leaf C, N, and P in herb community as well as soil nutrient concentrations along a 500-km-long latitudinal gradient in Northern Shaanxi of the Loess Plateau, were measured. The results showed that the soil C, N, P and C:N:P ratios at all three depths (0-10, 10-20, and 20-40 cm) showed significant latitudinal trends (except for soil C:N ratios) (P < 0.01). In general, the soil C, N and C:N:P ratios decreased exponentially while soil P increased first and then decreased with the latitude. The soil C, N, C:P, and N:P ratios at all three depths (0-10, 10-20 and 20-40 cm) were positively correlated with MAT and MAP (P < 0.05), while soil P and C:N ratios at all three depths were weakly correlated with MAT and MAP (P > 0.05). In addition, leaf C:N:P stoichiometry was significantly correlated with the latitude, MAT, and MAP (except for N:P ratios) (P < 0.01), such that, leaf C, C:N, and C:P ratios decreased as the latitude increased and MAT and MAP decreased, and leaf N, P concentrations increased as the latitude increased and MAT and MAP decreased, while leaf N:P ratios were weakly correlated with the latitude, MAT, and MAP (P > 0.05). Furthermore, the leaf C:N:P stoichiometry of herbaceous communities was related to the soil properties (except for soil P), and we found that the C:P ratios between the soil and leaves were strongly correlated. Compared with the global scale, the relatively high N:P ratios indicated that the vegetation growth of the herb community in the dryland of the Loess Plateau was more susceptible to P limitation.

Spatial variation in leaf nutrient traits of dominant desert riparian plant species in an arid inland river basin of China

Understanding how patterns of leaf nutrient traits respond to groundwater depth is crucial for modeling the nutrient cycling of desert riparian ecosystems and forecasting the responses of ecosystems to global changes. In this study, we measured leaf nutrients along a transect across a groundwater depth gradient in the downstream Heihe River to explore the response of leaf nutrient traits to groundwater depth and soil properties. We found that leaf nutrient traits of dominant species showed different responses to groundwater depth gradient. Leaf C, leaf N, leaf P, and leaf K decreased significantly with groundwater depth, whereas patterns of leaf C/N and leaf N/P followed quadratic relationships with groundwater depth. Meanwhile, leaf C/P did not vary significantly along the groundwater depth gradient. Variations in leaf nutrient traits were associated with soil properties (e.g., soil bulk density, soil pH). Groundwater depth and soil pH jointly regulated the variation of leaf nutrient traits; however, groundwater depth explained the variation of leaf nutrient traits better than did soil pH. At the local scale in the typical desert riparian ecosystem, the dominant species was characterized by low leaf C, leaf N, and leaf P, but high leaf N/P and leaf C/P, indicating that desert riparian plants might be more limited by P than N in the growing season. Our observations will help to reveal specific adaptation patterns in relation to the groundwater depth gradient for dominant desert riparian species, provide insights into adaptive trends of leaf nutrient traits, and add information relevant to understanding the adaptive strategies of desert riparian forest vegetation to moisture gradients.

Effect of Gap Sizes on Specific Leaf Area and Chlorophyll Contents at the Castanopsis kawakamii Natural Reserve Forest, China

The two hemispherical photographs (THP) method was used to calculate gap area. The areas of nine forest gaps were measured. Meanwhile, non-gap areas were selected as control groups with areas of 225 m2. Plots with areas of 25 m2 in five different directions within gap and non-gap areas were conducted for collecting leaf samples. To determine the effect of gap size on leaf traits the selected traits were leaf area (LA), leaf dry mass (LDM), specific leaf area (SLA), Chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (TChl), and carotenoid (CAR). Leaves were collected from the regeneration layer (<2 cm DBH, height 2–5 m) to measure the leaf traits in winter and summer seasons. Results confirmed significant positive correlations between LA and LDM in the small, medium, large gap sizes, and non-gap areas (r2 = 0.913, 0.827, 0.897, and 0.939, p < 0.01, respectively). On the contrary, relationships between LDM and SLA in the small, medium, large gap sizes, and non-gap areas have significant negative correlations (r2 = −0.269, −0.259, −0.417, and −0.505, p < 0.05, respectively). The effect of gap size on the average Chl a, Chl b, TChl, and CAR varies by the season. During the summer season, the highest chlorophyll contents were recorded in the small gap size and the lowest in the non-gap area, while during the winter season, the highest values of these chlorophyll contents appeared in the medium gap size. Moreover, the directions within the gap in the medium gap size of the summer season had an effect on the Chl a and TChl.

Separate and Combined Response to UV-B Radiation and Jasmonic Acid on Photosynthesis and Growth Characteristics of Scutellaria baicalensis

The negative effects of enhanced ultraviolet-B (UV-B) on plant growth and development have been reported with many species. Considering the ability of jasmonic acid (JA) to improve plant stress tolerance, the hypothesis that JA pretreatment could alleviate the adverse effects of UV-B on S. baicalensis was tested in this study with photosynthesis and growth characteristics. The results showed that UV-B or JA alone both induced photosynthesis inhibition and decreased biomass in stems and leaves. However, the photosynthetic reduction caused by increased UV-B was mainly related to the effect of nonstomatal-limitation, while that of JA was a stomatal-limitation effect. JA pretreatment prior to UV-B could remit the photosynthetic inhibition via the recovery of chlorophyll content, stomatal conductance; and intercellular CO₂ concentration (especially the maximum electron transport rate increase). Furthermore, the coaction of JA and enhanced UV-B alleviated some disadvantageous effects on the leaf and did not aggravate the growth damage induced by their separate actions.

Community Characteristics and Leaf Stoichiometric Traits of Desert Ecosystems Regulated by Precipitation and Soil in an Arid Area of China

Precipitation is a key environmental factor determining plant community structure and function. Knowledge of how community characteristics and leaf stoichiometric traits respond to variation in precipitation is crucial for assessing the effects of global changes on terrestrial ecosystems. In this study, we measured community characteristics, leaf stoichiometric traits, and soil properties along a precipitation gradient (35-209 mm) in a desert ecosystem of Northwest China to explore the drivers of these factors. With increasing precipitation, species richness, aboveground biomass, community coverage, foliage projective cover (FPC), and leaf area index (LAI) all significantly increased, while community height decreased. The hyperarid desert plants were characterized by lower leaf carbon (C) and nitrogen/phosphorus (N/P) levels, and stable N and P, and these parameters did not change significantly with precipitation. The growth of desert plants was limited more by N than P. Soil properties, rather than precipitation, were the main drivers of desert plant leaf stoichiometric traits, whereas precipitation made the biggest contribution to vegetation structure and function. These results test the importance of precipitation in regulating plant community structure and composition together with soil properties, and provide further insights into the adaptive strategy of communities at regional scale in response to global climate change.

A Destructive Leaf Spot and Blight Caused by Alternaria kareliniae sp. nov. on a Sand-Stabilizing Plant, Caspian Sea Karelinia

Leaf spots and stem lesions causing widespread mortality of Caspian Sea karelinia (Karelinia caspia) were observed in desert regions of Xinjiang Uyghur Autonomous Region, China. Fifteen samples were collected from five widely distributed counties of Tarim and Junggar Basins in 2016. The pathogen was identified using morphological observations and phylogenetic analyses based on combined partial sequences from seven genes (Alt a 1, ATPase, calmodulin, glyceraldehyde 3-phosphate dehydrogenase, internal transcribed spacer, RNA polymerase II, and translation elongation factor 1), and placed as a new species: Alternaria kareliniae sp. nov. in section Dianthicola. The fungus has a small conidium (24.3 to) 29.1 to 64.8 (to 75.8) by (9.3 to) 12.4 to 16.5 (to 21.7) μm with a long beak (130 to) 183.9 to 350.4 (to 378.2) μm, as well as four to eight transverse septa, which differs significantly from other species of Alternaria section Dianthicola. On potato carrot agar, it grew significantly more slowly than others of this section. Pathogenicity tests showed that the fungus could infect leaves and stems of K. caspia and cause the same symptoms as those observed in the field. The fungus was reisolated from inoculated leaves and stems of the host. The disease in desert regions appears to be increasing, and it may have future negative implications for desert ecology in these areas. Future research should concentrate on elucidating the disease cycle and disease management alternatives.

Nutrient resorption or accumulation of desert plants with contrasting sodium regulation strategies

Desert plants are thought to rely more heavily on nutrient resorption due to the infertile soil. However, little is known regarding the phylogenetic effects on this traits, specifically for halophytes. Here we determined contents of nitrogen (N), phosphorus (P), potassium (K), sodium (Na), calcium (Ca) and magnesium (Mg) in 36 desert plants in a hyper-arid environment. The patterns of resorption or accumulation of the six elements were compared among plant groups with diverse leaf Na regulation strategies: i.e., euhalophytes (Eu), secretohalophytes (Se), pseudohalophytes (Ps) and glycophytes (Gl). Overall, N, P, K presented strict resorption across all groups, but no more efficient than global estimations. Ca and Mg tended to be resorbed less or accumulated during leaf senescence. Significant phylogenetic signal of both leaf Na content and plant group implies the pivotal role of Na regulation in the adaptation of plants to desert environment. Resorption proficiency, rather than resorption efficiency, is more phylogenetically conservative and more relevant to leaf functional traits.

Crabbe MJ, Xu F, Wang W, Ma L, Niu R, Gao X, Li X, Zhang P, Ma X, Chen H. Seasonal variations in carbon, nitrogen and phosphorus concentrations and C:N:P stoichiometry in different organs of a Larix principis-rupprechtii Mayr. plantation in the Qinling Mountains, China

Understanding how concentrations of elements and their stoichiometry change with plant growth and age is critical for predicting plant community responses to environmental change. We used long-term field experiments to explore how the leaf, stem and root carbon (C), nitrogen (N) and phosphorous (P) concentrations and their stoichiometry changed with growth and stand age in a L. principis-rupprechtii Mayr. plantation from 2012-2015 in the Qinling Mountains, China. Our results showed that the C, N and P concentrations and stoichiometric ratios in different tissues of larch stands were affected by stand age, organ type and sampling month and displayed multiple correlations with increased stand age in different growing seasons. Generally, leaf C and N concentrations were greatest in the fast-growing season, but leaf P concentrations were greatest in the early growing season. However, no clear seasonal tendencies in the stem and root C, N and P concentrations were observed with growth. In contrast to N and P, few differences were found in organ-specific C concentrations. Leaf N:P was greatest in the fast-growing season, while C:N and C:P were greatest in the late-growing season. No clear variations were observed in stem and root C:N, C:P and N:P throughout the entire growing season, but leaf N:P was less than 14, suggesting that the growth of larch stands was limited by N in our study region. Compared to global plant element concentrations and stoichiometry, the leaves of larch stands had higher C, P, C:N and C:P but lower N and N:P, and the roots had greater P and C:N but lower N, C:P and N:P. Our study provides baseline information for describing the changes in nutritional elements with plant growth, which will facilitates plantation forest management and restoration, and makes a valuable contribution to the global data pool on leaf nutrition and stoichiometry.

Influence of aridity and salinity on plant nutrients scales up from species to community level in a desert ecosystem

Soil moisture and salt play key roles in regulating desert plant nutrient cycles on a local scale. However, information on the response of plant nutrient stoichiometric patterns to soil water and salt gradients is limited. Here, we assessed leaf N and P levels of 18 species of desert plants and measured the corresponding soil nutrient, water and salt concentrations, at four dry sites, five humid-saline sites and four humid-non-saline sites (reference sites) along a transect in a temperate desert in Xinjiang Province, northwest China. Our results indicated that the desert plants had lower N and P concentrations and higher N:P mass ratios in dry and humid-saline sites than in the humid-non-saline sites. Unlike the single-factor effect of salinity driving the plasticity of species N concentration, aridity and salinity interacted in their impact on the plasticity of plant P and the N:P ratio. Moreover, the plant community N and P concentrations and N:P ratio exhibited significant positive linear and nonlinear correlations with soil moisture in shallow and deep soil, respectively. Aridity reduced the N plasticity and increased P plasticity of the plant community. The results strongly supported the hypothesis that soil moisture and salt concentration were the dominant drivers of leaf N and P concentrations and their plasticity across species and community scales.

Stoichiometric variation of halophytes in response to changes in soil salinity

Variation in soil salt may change the stoichiometry of a halophyte by altering plant ecophysiology, and exert different influences on various plant organs, which has potentially important consequences for the nutrition of consumers as well as nutrient cycling in a saline ecosystem. Using a greenhouse pot experiment, we investigated the effect of salinity variability on the growth and stoichiometry of different organs of Suaeda glauca and Salicornia europaea - two dominant species of important ecological and economic value in the saline ecosystem. Our results showed that appropriate salt stimulated the growth of both species during the vigorous growth period, while high salt suppressed growth. Na significantly increased with increased salt in the culture, whereas concentrations of other measured elements and K:Na ratio for both species significantly decreased at low salt treatments, and became more gradual under higher salt conditions. Furthermore, with the change of salt in culture, variations in leaf (degenerated leaf for S. europaea, considered as young stem) stoichiometry, except N:P ratio, were large and less in stems (old stems for S. europaea) than in roots, reflecting physiological and biochemical reactions in the leaf in response to salt stress, supported by sharp changes in trends. These results suggest that appropriate saline conditions can enhance biological C fixation of halophytes; however, increasing salt could affect consumer health and decrease cycling of other nutrients in saline ecosystems.

Leaf N and P stoichiometry in relation to leaf shape and plant size for Quercus acutissima provenances across China

Plant stoichiometry in relation to the structure and function of biological systems has been investigated at multiple scales. However, few studies have focused on the roles of stoichiometry for a given species. In this study, we determined leaf N and P stoichiometry, leaf shape and plant size in three Quercus acutissima common gardens with different climatic and site conditions. In the three common gardens, leaf N and P stoichiometry was significantly correlated with leaf shape and plant size, suggesting that leaf N and P stoichiometry affects the morphological performance of the leaves and stem. The scaling slopes of the relationships between leaf N and P stoichiometry and leaf shape ranged from |0.12| to |1.00|, while the slopes of the relationships between leaf N and P stoichiometry and plant size ranged from |0.95| to |2.66|. These results suggest that non-functional tissues (stem) are more susceptible to leaf nutrition than functional tissues (leaves), and leaf stoichiometry is more important in the construction of non-functional tissues (stem). Between the northernmost and southernmost common gardens, leaf N and leaf width (W), N:P and stem height (H), and N:P and stem diameter (D) showed significant covariations, which indicates that leaf N and W, N:P and plant size exhibit similar plastic responses to environmental change.