Owing to the high carbon capture and storage capacity, salt marshes are considered an effective blue carbon sink for mitigating global warming. In addition, salt marshes are likely to increase their carbon sink capacity in the future in response to climate warming and sea level rise. Therefore, the blue carbon sink function of salt marshes has received increasing attention from the international research community. This study reviewed the five aspects comprising the key processes of blue carbon formation, photosynthetic carbon allocation, burial fluxes and sources of sedimentary organic carbon, stability of soil carbon pools and the associated microbial mechanisms, and the simulation and assessment of blue carbon sequestration potentials in salt marshes. On this basis, concerning the main knowledge gaps, this paper proposes further research on the effect of vegetation distribution pattern along the land-to-sea hydrologic gradient on photosynthetic carbon fixation and allocation, the response of soil organic carbon deposition and burial to global change, the stability of soil carbon pools and its lateral exchange, blue carbon simulation and assessment of blue carbon sink potential in the context of climate change and sea level rise, and technologies and approaches of blue carbon sequestration in salt marshes. Prioritizing these research topics may elucidate the formation processes and mechanisms of blue carbon, predict the changing trend of blue carbon sequestration potential under global changes, and offer new insights into achieving the goal of “carbon peak and carbon neutrality”.

Aims Parameterization of reference temperature has always been the key and difficult part in calculating evapotranspiration and its evaporation and transpiration components by using three-temperature model. In this paper, the best value of reference temperature was determined by quantifying and comparing the influence of different reference temperature values on the accuracy of transpiration estimation by three-temperature model.

Methods Based on the Bowen ratio and thermal infrared observation data of a typical urban lawn, sensitivity analysis and error analysis were carried out on the input variables involved in the sub-model of the three-temperature model to determine the most critical variables for the accuracy of transpiration estimation. Then the influence of input variables parameterization on the calculation of transpiration was quantified and compared to determine the best value of reference temperature.

Important findings When using the three-temperature model, the best estimation is to select the maximum temperature of the whole piece of paper as the reference leaf temperature (R² = 0.91, root mean square error (RMSE) = 0.078 mm·h^-1). When the maximum value of the vegetation canopy temperature was used as the reference temperature, it is directly assumed that the transpiration at the maximum temperature of the vegetation is zero (there is a certain transpiration rate in fact). Therefore, it is easy to underestimate the actual transpiration, resulting in that the estimation accuracy of the three-temperature model was slightly lower than the accuracy of using the maximum value of the reference leaf temperature, but the estimation effect is still good (R² = 0.87, RMSE = 0.080 mm·h^-1). Therefore, considering the limitations of the reference leaf settings, if the reference leaf temperature cannot be measured in practical applications, the maximum temperature of the vegetation canopy as the reference temperature can be used to achieve good estimate results.

Aims Grazing, as one of the important biological driving factors, plays a key role in the spatial heterogeneity of grassland plant community. Large herbivores can affect the spatial heterogeneity of grassland plant community by foraging, trampling and excreting dung. At the same time, plant community height is a key parameter to describe the structure of grassland. However, little attention has been paid to exploring the spatial heterogeneity of plant community height under different herbivore assemblages. Aim to this issue, this work examined the response of the spatial heterogeneity of plant community height to different herbivore assemblages in Horqin sandy grassland, which is helpful to better understand the importance of grazing in maintaining spatial heterogeneity of grassland plant community and promote grassland animal biodiversity.

Methods An experiment was conducted with four grazing treatments, including no grazing (NG), cattle grazing (CG), sheep grazing (SG) and mixed grazing (MG) of cattle and sheep. We established two perpendicular 15 m transects crossing at the centre point of each plot to reduce the variation caused by environmental gradient. Along the two transects, samples were taken from 0.25 m × 0.25 m quadrates with 0.5 m space interval, and totally 244 sampling points were measured. We used traditional and geostatistical methods to analyze the data from different grazing treatments.

Important findings Results showed that the mean of plant community height in our study plots satisfied the following ranking: SG (38.86 cm) > NG (21.01 cm) > MG (17.29 cm) > CG (13.36 cm). The coefficient of variation of all treatments had moderate level, and the variation range was 37.82%-66.97%, followed by NG > MG > CG > SG. According to the optimal model fitting by the parameters of semi-variance function, NG, MG, CG and SG corresponded to spherical model, exponential model, linear model and linear model respectively, and the structural proportion satisfied MG (82.7%) > NG (80.3%) > SG (40.2%) > CG (39.1%). Furthermore, Kriging interpolation and fractal dimension were used to analyze the spatial pattern of plant community height. It clearly showed NG had a patchy spatial distribution of plant height, MG could maintain the patchy spatial pattern, and CG and SG homogenized the spatial pattern. The fractal dimension value (D₀)of each grazing treatment was close to 2, which indicated the spatial structure of four treatments was good with simple spatial pattern. Thus, mixed grazing of cattle and sheep could maintain plant community structural heterogeneity, while the single grazing of cattle or sheep would reduce the spatial heterogeneity. Our findings shed novel light into management of mixed grazing of cattle and sheep, which should be adopted to maintain the spatial heterogeneity of grassland plant community in Horqin sandy grassland.

Aims Epiphytic vascular plants are characteristically important components of tropical forests. Studying the selectivity of epiphytic vascular plants for host trees is key to understanding the underlying mechanisms of biodiversity conservation and ecosystem functioning.

Methods All trees and shrubs with a diameter at breast height (DBH) >1 cm were recorded for the number, species identity, DBH, plant height and possession of substrate types in 21 fixed 20 m × 20 m plots, and the epiphytic vascular plants growing on them were measured for their number and types, in the Bawangling range of the Hainan Tropical Rainforest National Park. The relationships of epiphyte distribution with host species identity, DBH, plant height, and substrate types (bare bark, bryophytes, litter and soil) were analyzed with the methods of mixed linear model, one-way analysis of variance and selectivity index.

Important findings In all the sample plots with a total area of 8 400 m², a total number of 2 650 epiphytic vascular plants were recorded, belonging to 51 species. Epiphytic orchids and epiphytic ferns were found to be the dominant taxa, occurring on 10.6% of individual trees. Pyrrosia eberhardtii, Coelogyne fimbriata, Davallia repens, and Psychotria serpens showed some selectivity for host trees, with significant preferences for host trees from one to four species. The epiphytic vascular plants also showed a significant habitat preference for light substrate types (bryophytes), with more than 70% of the epiphytes occurring on mossy substrate.

Aims Pollen source influences the reproductive success of plants and the genetic structure of their populations, and maternal effects facilitate the adaptation of offspring to the environmental conditions that their parental generation were exposed to. However, the effect of pollen source combined with maternal effects on reproductive success of plants remains unknown under climate warming.

Methods In this study, Impatiens oxyanthera, a facultative outcrossing plant endemic to China, was taken as the research object. This study was designed using a randomized block design with two factors (warmed at 0 and 2 °C in parental generation, warmed at 0, 2 and 4 °C in offspring generation). From these two factors, six treatment combinations were obtained, aiming to better understand the effects of warming treatments in offspring generation on pollen source limitation of I. oxyanthera under different warming treatments in parental generation.

Important findings The seed setting rate and seeds of allogamous treatments were all higher than the corresponding values of autogamous, and two values showed different degrees of decrease with the increase of offspring temperature, in particular, seed set rate and seed number of selfing decreased significantly with warming treatments in offspring generation, while warming treatments in parental generation moderated the decreasing effect of reproductive success caused by autogamouy. This results suggested that the reproductive success of allogamy was greater than that of autogamy. Warming treatments in the offspring generation significantly reduced the fitness of self-fertilization, but warming treatments in the parental generation could mitigate this adverse effects, thus showed adaptive transgenerational plasticity in responses to warming.

Aims Early spring rainfall event is an important factor affecting the growth of desert ephemeral plants. This study aims to understand the effects of the first rainfall timing and amount on the photosynthesis and growth of desert ephemeral plants in early spring.

Methods Two dominant ephemeral species, Erodium oxyrhinchum and Centaurea pulchella were selected in the Gurbantünggüt Desert, and treatments of three times of the first rainfall (10, 20 and 30 days after the snow melted completely) and three amounts of rainfall (5, 10 and 15 mm) were conducted. The plant morphology, biomass and chlorophyll fluorescence of the two plants were determined.

Important findings When the rainfall occurred on the 10th day after the snow melted completely, the leaf area and total biomass of the E. oxyrhinchum increased significantly with the rainfall amount, while the maximum photochemical efficiency decreased. If the rainfall was applied on the 20th and 30th day after the snow melted completely, the leaf area of the E. oxyrhinchum and C. pulchellaincreased significantly with the rainfall amount. On the other hand, if the treatments were applied with the addition of 5 mm rainfall, the maximum photochemical efficiency of the E. oxyrhinchum and C. pulchella decreased firstly and then increased significantly with the delay of the first rainfall timing. If the treatments were applied with the addition of 10 mm rainfall, the shoot to root ratio (S/R), root length and total biomass of the E. oxyrhinchum increased firstly and then decreased significantly with the delay of the first rainfall timing, but the root length of the C. pulchella increased significantly. If the treatments were applied with the addition of 15 mm rainfall, the leaf area, S/R and maximum photochemical efficiency of the E. oxyrhinchum increased with the delay of the first rainfall timing. For the C. pulchella, total biomass increased significantly, maximum photochemical efficiency and S/R decreased significantly with the delay of the first rainfall timing. The root length of the E. oxyrhinchum and C. pulchella were significantly positively correlated with soil moisture content of 0-5 cm and 5-10 cm, respectively. In general, the effects of the first rainfall amount on plant growth are much larger than effects of the first rainfall timing in early spring. However, different ephemeral species showed different trends with the changes in rainfall pattern. The variation in early spring rainfall caused by climate change can affect the morphological characteristics of desert ephemeral plants in desert, and then may affect the stability of desert ecosystem in early spring.

Aims Habitat difference is one of the important factors affecting plant growth and development. Plant xylem hydraulic system is the main pathway of soil-plant-atmosphere continuum, which directly affects the basic behavior and function of plants and reflects the adaptability of plants to environmental changes. In the current study, the differences of xylem hydraulic function, mechanical and anatomical structure traits of three gymnosperm species in Tianmu Mountain, Zhejiang Province in different habitats (field habitat and garden habitat) were compared to reveal the adaptive mechanism of gymnosperm to different habitats.

Methods We measured and compared hydraulic safety trait (water potential at 50% loss of conductivity), hydraulic efficiency (specific hydraulic conductivity) and xylem anatomy, between field and garden plants of Pseudolarix amabilis, Cunninghamia lanceolata and Cedrus deodara.

Important findings 1) For all tree species, their hydraulic efficiency in garden habitats are lower than that of field habitats, but the embolism resistances are stronger, owing to the complexity of species adaptation strategies. 2) No matter in field or garden habitats, there was efficiency-safety trade-off in the xylem water diversion system in Cedrus deodara, but there is no efficiency-safety trade-off in hydraulic system of P. amabilis and Cunninghamia lanceolata. 3) There is a trade-off between hydraulic efficiency and mechanical strength in the xylem of P. amabilisand Cedrus deodara in garden habitat. Compared with garden habitats, in field habitats with low soil moisture availability, plants increased pit membrane diameter to improve hydraulic efficiency. In addition, in field habitat, the threat of embolism to plants could be avoided by increased wood density and expanding tracheid diameter.

Aims Myriophyllum aquaticum has high tolerance to high concentration of ammonium (NH₄⁺) and thus becomes the preferred species for swine wastewater treatment. It is of great significance to explore the effects of exogenous NH₄⁺ on the photosynthetic pigment composition and the stoichiometric characteristics of nitrogen (N) and phosphorus (P) of the M. aquaticum for improving the purifying efficiency of artificial wetlands system of M. aquaticum.

Methods Six NH₄⁺ concentration levels (0, 0.1, 1, 5, 15, 30 mmol·L^-1) were set up in this study. After 21 days of indoor cultivation, the contents of chlorophyll, N and P of M. aquaticum were measured to analyze their characteristics of changes.

Important findings The results showed that the relative stem height and biomass increased initially and then decreased, which were well fitted by a curve equation. Moreover, the peak of them appeared at 16.22 and 12.58 mmol·L^-1 exogenous NH₄⁺, respectively, via fitting non-linear Gaussian equation. With the increase of exogenous NH₄⁺ concentrations, the chlorophyll content in the leaves decreased significantly, but increased in the stems. In addition, there was a wide variation of chlorophyll a than chlorophyll b. The chlorophyll a/b did not change significantly among different NH₄⁺ treatments, except the value in the stems of 5 mmol·L^-1 NH₄⁺ treatment, which was significantly decreased. With the increase of exogenous NH₄⁺ concentrations, the N contents in the leaves and stems were significantly increased by 85%-235% and 127%-373%, respectively, and the P content in the leaves was increased by 49%-51% in comparison to the control (CK). When the concentrations of exogenous NH₄⁺ was no more than 15 mmol·L^-1, the N content and N:P ratio of the leaves and stems increased rapidly, so were relative stem height and relative biomass. Correlation analysis showed that the contents of N and P, and N:P ratio were negatively correlated with total chlorophyll content in the leaves, but positively correlated with total chlorophyll content in the stems. In conclusion, M. aquaticum grew well with larger biomass and higher absorption of N and P, when the concentrations of exogenous NH₄⁺ were in the range of 12-16 mmol·L^-1. Therefore, the constructed wetlands system planted with M. aquaticum can effectively remove N and P from polluted wastewater and achieve the purpose of efficient water purification.

Aims Grassland is an important component of the terrestrial ecosystems in China, and plays a vital role in ecosystem productivity and functioning. During the past decades, 90% of natural grasslands have been degraded as a result of climate change and anthropogenic activities. Grassland degradation altered soil nutrient balance, exerting substantial impacts on ecosystem structure and functions. Our objective was to explore the responses of soil and microbial carbon (C), nitrogen (N) and phosphorus (P) stoichiometry to grassland degradation across the Qingzang Plateau alpine grasslands.

Methods We collected soil samples (0-10 cm) along the degradation sequence (i.e., non-degradation, moderate degradation and heavy degradation) from five sites across the “Three-River Source” region. By determination of soil and microbial C, N and P, we examined the changes in their contents and stoichiometric ratios with grassland degradation. We further synthesized data from the whole Qingzang Plateau alpine grasslands to validate the measured results using a meta-analytical approach.

Important findings Grassland degradation significantly reduced soil organic C, total N and total P contents and their stoichiometric ratios. Although microbial C and N content declined with degradation, change in microbial P content was limited along the degradation gradient. The microbial C:N:P ratios showed minimal responses to degradation. No obvious relationships were observed among soil and microbial C:N:P ratios. The above results indicate that soil microbes have the ability to maintain a given elemental composition despite variation in soil elemental composition following grassland degradation. From a long-term perspective, the nutrient-balance based soil quality promotion technology is able to effectively enhance grassland restoration and improve ecosystem service.

Aims Long-term nitrogen (N) deposition induces soil nutrient imbalance and profoundly affects nutrient cycling processes, ecological functions and the sustainable development of forest ecosystems. Although previous studies have found that N deposition increased phosphorus (P) limitation of forest trees in southwest mountainous areas, China, whether soil microorganisms showed synergistic response with plants remains unclear.

Methods In this study, we measured soil available nutrients, soil microbial biomass carbon (C), N, P and extracellular enzyme activities in a typical subalpine coniferous plantation (Pinus armandii) with chronic N addition treatments in southwest China. Furthermore, three models of ecoenzymatic stoichiometry, i.e., enzymatic ratio model, vector analysis model and threshold element ratio model were used to evaluate changes of microbial nutrient limitation under N addition.

Important findings The results showed that: 1) N addition significantly increased the P-acquiring enzyme activities by 52.5% and 53.2% in rhizosphere soil and bulk soil respectively, leading to a decrease of enzymatic N:P ratio by 7.8% and 4.8% compared to the control in rhizosphere soil and bulk soil respectively. 2) Vector model analysis found that vector angles of two soil compartments under N addition exceeded 45°, and the vector angles of rhizosphere soil and bulk soil were 52.2° and 49.0°, respectively. 3) The C:P threshold ratios (TER_C:P) of microbes in two soil compartments were significantly reduced by N addition. Consequently, the ratio of TER_C:P to available C:P (Av_C:P) was much less than 1, and the response of rhizosphere microbes was more significant. Collectively, all three models of ecoenzymatic stoichiometry indicated that N deposition aggravated P-limitation of microbial metabolism, and the extent of P limitation was more intense in the rhizosphere soil, which was closely related to nutrient contents and stoichiometric ratios of soil and microbes. The findings of this study provide an important scientific basis for adaptive management of forest ecosystems under global climate change.

Climate diagram can be used to reflect visually observation data of temperature and precipitation as well as information of weather stations. It is an effective tool for studying the relationship between vegetation and climate. This paper aims to provide the atlas of climate diagrams of the Qingzang Plateau, based on the 30-year averaged observational records of national surface weather stations during 1951-1980 and 1981-2010, respectively, in order to understand the plateau climate feature of every vegetation region and to further explore the vegetation- climate relationships on the plateau. The atlas of climate diagrams of 205 weather stations on the Qingzang Plateau for both the two 30-year periods were produced according to the standard of climate diagrams in Vegetation of China. Results showed that the temperature and precipitation of the Qingzang Plateau were overall low in the whole year but relatively higher in summer, and differed obviously among different vegetation regions. The mean annual temperature and annual precipitation showed an increasing trend from the first 30-year period of 1951-1980 to the later one of 1981-2010. Although the number of weather stations in the western plateau is very sparse, this climate diagram dataset covers every vegetation regions of the plateau surface. This atlas can be used effectively to study the relationships between vegetation and climate, and conveniently to display the climate environment of the plateau.