To compare current methods of pretreatment/determination for plant foliar pH, we proposed a method for long-period sample preservation with little interference with the stability of foliar pH. Four hundred leaf samples from 20 species were collected and four methods of pH determination were used: refrigerated (stored at 4 °C for 4 days), frozen (stored at −16 °C for 4 days), oven-dried and fresh green-leaf pH (control). To explore the effects of different leaf:water mixing ratio on the pH determination results, we measured oven-dried green-leaf pH by leaf:water volume ratio of 1:8 and mass ratio of 1:10, and measured frozen senesced-leaf pH by mass ratio of 1:10 and 1:15. The standard major axis regression was used to analyze the relationship and the conversion equation between the measured pH with different methods. Foliar pH of refrigerated and frozen green leaves did not significantly differ from that of fresh green-leaf, but drying always overrated fresh green-leaf pH. During the field sampling, cryopreservation with a portable refrigerator was an advisable choice to get a precise pH. For long-duration field sampling, freezing was the optimal choice, and refrigeration is the best choice for the short-time preservation. The different leaf:water mixing ratio significantly influenced the measured foliar pH. High dilution reduced the proton concentration and increased the measured pH. Our findings provide the conversion relationships between the existing pretreatment and measurement methods, and establish a connection among pH determined by different methods. Our study can facilitate foliar pH measurement, thus contributing to understanding of this interesting plant functional trait.

Many mosses and lichens thrive in high-elevation subalpine forests and even become dominant species on the forest floor. Although they play an irreplaceable ecological role in the forest, less is known about their eco-physiological status, and how their photosynthesis-related functional traits differ from those of co-occurring vascular plants. We determined the carbon, nitrogen and phosphorus concentrations and stoichiometric ratios, tissue mass per area, chlorophyll concentrations and photosynthetic light–response curves of three lichens, three mosses and four vascular plants in a subalpine forest in the eastern Tibetan Plateau of China. Trait values were compared among and within each group. The lichens possessed a higher nitrogen concentration than that of mosses. In addition, the two poikilohydric groups exhibited lower concentrations of nitrogen, phosphorus and chlorophyll, light-saturated assimilation rates and photosynthetic nutrient use efficiencies, and higher light compensation points than those of vascular plant leaves. Furthermore, variations in photosynthesis-related traits for lichen species reflect their different adaptation strategies to their corresponding environments. In contrast, the differences were weak among the three forest-floor mosses and the three herb species. These results demonstrate that the high abundance of understory lichens and mosses in the high-elevation subalpine forest cannot be explained by the photosynthesis-related traits.

The leaf economic spectrum (LES) quantifies correlations between key leaf traits across vascular plants and distills much of the variation in these traits to a single axis. The LES, remarkable in its near universality, has been extensively researched across a variety of contexts. However, parasitic plants relationship to the LES framework remains relatively unexplored. Because the LES is, in part, driven by physiological tradeoffs in the acquisition of carbon (C), in theory heterotrophy in parasitic plants, which supplants some of the essential functions of leaves, could lead to departures from the LES. Using global leaf trait data from the TRY database, this work assessed the overall representation of parasitic plants in the TRY database, then compared the LES suite of leaf traits in parasitic plants to their non-parasitic counterparts. Despite their unique physiology, parasitic plants did not deviate dramatically from the LES, although there were examples of differences in position on the LES and relationships among traits. Perhaps more importantly, parasitic plants are not well represented in the TRY database, making any conclusions here premature.

Senesced-leaf nutrient concentrations vary significantly among coexisting plant species reflecting different leaf nutrient use strategies. However, interspecific variation in senesced-leaf nutrients and its driving factors are not well understood. Here, we aimed to determine interspecific variation and its driving factors in senesced-leaf nutrients. We explored interspecific variation in carbon (C), nitrogen (N) and phosphorus (P) concentrations in newly fallen leaves of 46 coexisting temperate deciduous woody species across the Maoershan Forest Ecosystem Research Station, Northeast China. The relative importance of 10 biotic factors (i.e. mycorrhiza type, N-fixing type, growth form, shade tolerance, laminar texture, coloring degree, coloring type, peak leaf-coloration date, peak leaf-fall date and end leaf-fall date) was quantified with the random forest model. N and P concentrations varied 4- and 9-fold among species, respectively. The high mean N (15.38 mg g⁻¹) and P (1.24 mg g⁻¹) concentrations suggested a weak N and P limitation in the studied forest. Functional groups had only significant effects on specific nutrients and their ratios. P concentration and N:P were negatively correlated with peak and end leaf-fall dates for the ectomycorrhiza species group. Brighter-colored leaves (red > brown > yellow > yellow-green > green) tended to have lower N and P concentrations and higher C:N and C:P than darker-colored leaves. The random forest model showed that autumn coloration and leaf-fall phenology contributed 80% to the total explanation of nutrient variability among species. The results increase our understanding of the variability in senesced-leaf nutrients as a strategy of woody plant nutrition in temperate forests.

Precipitation (PPT) is the primary climatic determinant of plant growth and aboveground net primary productivity (ANPP) for many of the world’s major terrestrial ecosystems. Thus, relationships between PPT and productivity can provide insight into how changes in climate may alter ecosystem functions globally. Spatial PPT–ANPP relationships for grasslands are found remarkably similar around the world, but whether and how they change during periods of extended climatic anomalies remain unknown. Here, we quantified how regional-scale PPT-ANPP relationships vary between an extended wet and a dry period by taking advantage of a 35-year record of PPT and NDVI (as a surrogate for ANPP) at 1700 sites in the temperate grasslands of northern China. We found a sharp decrease in the strength of the spatial PPT–ANPP relationship during an 11-year period of below average PPT. We attributed the collapse of this relationship to asynchrony in the responses of different grassland types to this decadal period of increased aridity. Our results challenge the robustness of regional PPT–productivity if aridity in grasslands is increased globally by climate change.

Soil microbial biomass is critical for biogeochemical cycling and serves as precursor for carbon (C) sequestration. The anthropogenic nitrogen (N) input has profoundly changed the pool of soil microbial biomass. However, traditional N deposition simulation experiments have been exclusively conducted through infrequent N addition, which may have caused biased effects on soil microbial biomass compared with those under the natural and continuous N deposition. Convincing data are still scarce about how the different N addition frequencies affect soil microbial biomass. By independently manipulating the frequencies (2 times vs. 12 times N addition yr^–1) and the rates (0–50 g N m⁻² yr⁻¹) of N addition, our study aimed to examine the response of soil microbial biomass C (MBC) to different N addition frequencies with increasing N addition rates. Soil MBC gradually decreased with increasing N addition rates under both N addition frequencies, while the soil MBC decreased more at low frequency of N addition, suggesting that traditional studies have possibly overestimated the effects of N deposition on soil microbial biomass. The greater soil microbial biomass loss with low N frequency resulted from the intensified soil acidification, higher soil inorganic N, stronger soil C and N imbalance, less net primary production allocated to belowground and lower fungi to bacteria ratio. To reliably predict the effects of atmospheric N deposition on soil microbial functioning and C cycling of grassland ecosystems in future studies, it is necessary to employ both the dosage and the frequency of N addition.

climate change| carbon sequestration| carbon–nitrogen interactions| grasslands| nitrogen limitation| stoichiometry

Sulfur is an essential functional element in leaves, and it plays important roles in regulating plant growth, development and abiotic stress resistance in natural communities. However, there has been limited information on the spatial variation in leaf sulfur content (LSC) and adaptive characters on a large community scale. Sulfur in leaves of 2207 plant species from 80 widespread ecosystems (31 forests, 38 grasslands and 11 deserts) in China was measured. One-way analysis of variance with Duncan’s multiple-range tests were used to evaluate the differences in LSC among different plant growth forms and ecosystems. We fitted the relationships of LSC to spatial and climate factors using regression. Structural equation modeling analysis and phylogenetic analysis helped us further explore the main factors of LSC variation. LSC ranged from 0.15 to 48.64 g kg^–1, with an average of 2.13 ± 0.04 g kg^–1 at the community scale in China. We observed significant spatial variation in LSC among different ecosystems and taxa. Overall, LSC was higher in arid areas and herbs. Furthermore, higher LSC was observed under environments of drought, low temperatures and intense ultraviolet radiation. Temperature, precipitation, radiation, soil sulfur content and aridity jointly regulated LSC, explaining 79% of the spatial variation. However, LSC was not significantly related to phylogeny. Our results demonstrate that LSC plays an important role in plant adaptations to extreme environments and further extend our understanding of the biological function of sulfur from the organ to the community level. These findings highlight the importance of sulfur metabolism for our understanding of the impact of global climate change on plants.

Resource sharing among connected ramets (i.e. clonal integration) is one of the distinct traits of clonal plants. Clonal integration confers Moso bamboo (Phyllostachys pubescens) a strong adaptability to different environmental conditions. But the mechanisms of how clonal integration makes Moso bamboo has better performance are still poorly understood. In this study, acropetal and basipetal translocation of photosynthates between Moso bamboo ramets were analyzed separately to investigate how clonal fragments obtain higher benefits under heterogeneous N conditions. Clonal fragments of Moso bamboo consisting of two interconnected mother–daughter ramets were used, each of the ramets was subjected to either with or without N addition. The acropetal and basipetal translocation of ¹³C-photosynthates was separated via single-ramet ¹³CO₂-labeling. Mother ramets translocated more ¹³C-photosynthates to daughter ramets with N addition, and the translocation of ¹³C-photosynthates to mother ramets was more pronounced when daughter ramets were treated with N addition. The ¹³C-photosynthates that were translocated from mother ramets without and with N addition were mainly invested in the leaves and roots of daughter ramets with N addition, from daughter ramets with N addition were mainly invested in the leaves and roots of mother ramets with and without N addition, respectively. These results suggest that mother ramets preferentially invest more resources in nutrient-rich daughter ramets, and that daughter ramets serve as efficient resource acquisition sites to specialize in acquiring abundant resources based on the resource conditions of mother ramets. Clonal plants can improve their resource acquisition efficiency and maximize the overall performance in this way.

Litter decomposition impacts carbon (C) and nutrient cycling. Nitrogen (N) and phosphorus (P) addition as well as litter age impact litter decomposition. Effects of nutrient addition and litter age on litter decomposition may impact emissions of soil nitrous oxide (N₂O), which is an important greenhouse gas. However, no study has examined the effects of interactions between litter age and nutrient addition on soil N₂O emissions, and explored the underlining mechanisms simultaneously, thus limiting our evaluation of litter decomposition effects on N₂O emissions. Litter with different age was collected from Cunninghamia lanceolata plantations experienced N and P addition treatments to examine the effects of nutrient addition and litter age on N₂O emissions by incubation study. Litter age generally increased N₂O emissions via a decrease in litter C:N ratio. While P addition decreased N₂O emissions, N addition increased them mainly by positive effects on soil enzymes as indicated by microbial functional genes associated with N₂O production and negative effects on litter C:N ratio. Litter age and nutrient addition interacted to impact soil N₂O emissions. In future forest management, both nutrient addition and litter age should be considered in evaluation of management effects on N₂O emissions, especially thinning or selectively cutting involving litter input with different age.

Changes in soil chemistry after invasion by bracken (Pteridium aquilinum) have been studied in heathlands, but comparable studies in meadows are lacking. We investigated if bracken invasion into P-deficient meadows alters the soil nutrient-resource pool, as well as the mechanisms behind it linked to soil processes and bracken nutrition. Furthermore, we investigated how community composition responds to differences in soil chemistry before and after the invasion. Soil and plant material sampling, along with vegetation survey, were performed during bracken peak biomass. Data analyses included analysis of variance and canonical correspondence analysis (CCA). Bracken invasion increased soil P availability, soil organic C concentration, as well as C:N, C:S and N:S ratios, while decreasing Fe and Co concentrations. Bracken pinnae were rich in P, and its rhizomes were rich in K, whereas N:P of pinnae and rhizomes was low. CCA showed contrasting abundance patterns of frequent meadow species related to P and K availability. Holcus lanatus exhibited competitive advantage under extremely low P availability. Increase in P availability under bracken may have occurred through promoting the leaching of Fe and Al. By increasing P availability for its growth and increasing N limitation for other species, bracken can gain a competitive advantage from the soil resource-niche perspective. Its ability to increase soil P availability, along with the physiological mechanisms behind its high P acquisition efficiency, seem to differentiate bracken from other species of competitive ecological strategy, which are mainly confined to nutrient-rich environments. This enabled bracken to invade P-deficient meadows.

Phenotypic plasticity enables plants to buffer against environmental stresses and match their phenotypes to local conditions. However, consistent conclusive evidence for adaptive plasticity has only been obtained for a few traits. More studies on a wider variety of plant functional traits and environmental factors are still needed to further understand the adaptive significance of plasticity. We grew 21 genotypes of the stoloniferous clonal plant Duchesnea indica under different light and nutrient conditions, and used selection gradient analyses to test the adaptive value (benefits) of morphological and physiological plasticity responding to variation in light and nutrient availability. Plants grown in shade exhibited lower values for fitness measures (fruit number, ramet number and biomass), shortened thinner internode length and decreased adult leaf chlorophyll content, but higher petiole length, specific leaf area and old leaf chlorophyll content, than plants grown without shade. Plants grown in the low nutrient condition had shorter petiole length, thicker and smaller leaf area, lower chlorophyll content, but higher fruit number and root:shoot ratio than plants grown under the high nutrient condition. Selection gradient analyses revealed that plasticity of petiole length and old leaf chlorophyll content in response to light variation was adaptive, and plasticity of old and adult leaf chlorophyll content in response to nutrient variation was adaptive. Therefore, the adaptive value of plasticity in different traits depends on the specific ecological context. Our findings contribute to understanding the adaptive significance of phenotypic plasticity of clonal plants in response to environmental variation.

Grasslands in the Qinghai–Tibet Plateau play an important role in preserving ecological security and high biodiversity in this region. However, the distribution of the composition and structure of plant community and the mechanism by which it maintains itself in this region are still poorly understood. Here, we designed 195 grassland plots in 39 grassland sites along an approximately 1700 m elevation gradient on the Northeastern Qinghai–Tibet Plateau. We found that the grassland community height decreased significantly with increasing elevation, whereas community coverage did not significantly change. With increasing elevation, plant species richness (α diversity) increased significantly, but the community variability (β diversity) decreased significantly. The constrained clustering analysis suggested that the α- and β-diversity in the grasslands transformed gradually with elevation, and that three discontinuous points (based on community structure) were observed at elevation of 3640, 4252 and 4333 m. Structural equation modeling (SEM) indicated that the increase in precipitation and the decrease in temperature significantly positively influenced α diversity, which was negatively correlated with β diversity. These results demonstrate a quantitative-to-qualitative change in the community composition and structure along this elevational gradient on the Qinghai–Tibet Plateau.

Previous studies indicated that grazing can cause significant changes in abiotic and biotic environment in grassland. However, how these changes impact germination trait selection in grassland has not been well studied. Thus, we aimed to explore whether grazing can significantly change germination trait diversity and composition of grasslands community. We measured the germination traits of species in the laboratory, and compared their performance in grazed and nongrazed grasslands. Then, we compared the community-weighted means of germination traits and functional diversity of grazed and nongrazed grasslands based on these germination traits to know whether grazed and nongrazed grasslands differed in their germination trait structures. At the species level, we found that the changes of abundance in grazed and nongrazed grasslands were not related to species’ germination traits. However, at the community level, compared with nongrazed grasslands, species in the grazed grasslands generally exhibited a higher seed germination percentage. Moreover, seed germination response in grazed grasslands was more positively related to alternating temperature than in nongrazed grasslands, and breadth of the germination temperature niche was narrower in grazed than in nongrazed grasslands. Compared with nongrazed grasslands, seed germination trait diversity was increased and germination trait evenness decreased in grazed grasslands. Grazing can change microhabitat conditions, thereby changing germination trait selection by environmental filtering, resulting in a significant difference in germinate trait composition at the community level.

Caryota obtusa of Arecaceae is a fascinating palm tree native to southwestern China, India, Myanmar, Thailand, Laos and Vietnam. It is an economically important and threatened species and appears as a canopy dominant in some karst areas in Yunnan. We aim to clarify the forest structure, species diversity, population status and regeneration dynamics of C. obtusa in the karst forest ecosystem of Yunnan, China. We established 56 vegetation plots dominated by C. obtusa in 10 counties of southern Yunnan. Based on the plot data, we analyzed the community stratification, floristic composition and C. obtusa’s population structure. We used questionnaires to interview local people and recorded the human activity history in C. obtusa-dominated forests. Caryota obtusa palm forests were distributed on limestone mountain slopes and gullies. There were seven forest community types. The stratification of each community included arborous layer, shrub layer and understory. The communities had rich species composition. For all the plots as a whole of each community type, Shannon–Wiener diversity index of either woody or herbaceous species ranged from 2.1 to 3.8. The diameter at breast height (DBH)-class frequency distribution of C. obtusa was a multimodal type. The regeneration was sporadic and dependent on intermediate natural disturbances. In the current population structure, a number of C. obtusa trees with small DBHs consisted mainly of the forest communities with no or a slight degree of human disturbances. Intensive human activities terribly hindered recruitment of C. obtuse, followed by the medium intensity of human activities.

Mikania micrantha (Asteraceae) is an invasive vine found in tropical and southern subtropical Asian and the Pacific Islands. The current methods used to control this vine are inadequate, which warrants the development of ecologically sustainable methods. Therefore, we investigated the ability of four grass species to prevent the invasion of M. micrantha, with an ultimate goal of developing ecologically sustainable control methods for widespread application. The clumps of native grass species from China (Panicum incomtum, Pennisetum purpureum, Saccharum arundinaceum and Microstegium vagans) were established. We sowed M. micrantha seeds and transplanted the seedlings into the grass clumps to examine whether the clumps could eliminate the new M. micrantha plants. In addition, we transplanted M. micrantha into existing grass clumps to examine whether the grass clumps could prevent the re-invasion of M. micrantha. Furthermore, we grew M. micrantha with P. incomtum and P. purpureum in the field to examine whether the grasses could outcompete M. micrantha. Mikania micrantha seeds germinated hardly in the grass clumps, and all seedlings died within 3 months. It was difficult for the vine to survive in the grass clumps. Our field experiments showed that the coverage of M. micrantha was significantly lower than that of the grass species in the first year, and that the vine was outcompeted after 2 years. To the best of our knowledge, this study is the first to reveal that tall grasses, particularly P. incomtum and P. purpureum, have potential to serve as bio-control agents for M. micrantha.

Soil biotic communities can strongly impact plant performance. In this paper, we ask the question: how long-lasting the effect of the soil microbial community on plant growth is. We examined the plant growth rates at three stages: early, mid and late growth. We performed two growth experiments with Jacobaea vulgaris, which lasted 49 and 63 days in sterilized soil or live soil. In a third experiment, we examined the effect of the timing of soil inoculation prior to planting on the relative growth rate of J. vulgaris with four different timing treatments. In all experiments, differences in biomass of plants grown in sterilized soil and live soil increased throughout the experiment. Also, the relative growth rate of plants in the sterilized soil was only significantly higher than that of plants in the live soil in the first two to three weeks. In the third experiment, plant biomass decreased with increasing time between inoculation and planting. Overall, our results showed that plants of J. vulgaris grew less well in live soil than in sterilized soil. The negative effects of soil inoculation on plant mass appeared to extend over the whole growth period but arise from the negative effects on relative growth rates that occurred in the first weeks.

Invasive alien plants threaten biodiversity across the world. Erigeron canadensis (horseweed) is one of the most problematic agricultural weeds and represents a classic example of intercontinental invasion. Here, we studied the genetic diversity and population structure of invasive alien populations from the Jiangsu and Zhejiang Provinces in China and native populations from Alabama, in the USA. We used 10 polymorphic SSR loci to genotype 312 individuals from 5 native and 5 invasive populations to estimate the genetic diversity and structure. Invasive populations from Jiangsu and Zhejiang Provinces showed, on average, similar genetic diversity to native populations from Alabama, indicating no severe genetic bottlenecks during the invasion. STRUCTURE revealed that low population differentiation occurred, and that only two genetic groupings were detected in both native and invaded ranges. The high diversity observed in the invasive populations suggested multiple introductions and/or the introduction of genetically diverse propagules during initial colonization. Our study provides new insights toward understanding the invasion dynamics of this globally noxious weed in Eastern China. Preventing gene flow via seed dispersal between invasive and native populations should be examined to prevent the introduction and dispersal of herbicide-resistant individuals and inform management practices.