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  • Volume 15 Issue 5
    The harvest season, presenting a magnificent landscape and the harmonious coexistence between man and nature in the agro-pastoral ecotone of northern China. However, the grassland in this area is extremely sensitive to global climate changes and anthropocentric disturbances. It is of great significance to study the carbon flux of grassland in agro-pastoral ecotone for accurate assessment of the carbon sink of grassland. Photo taken by Huiling Wang. See Diao et al. in this issue.
    Zhongmin Hu, Shiping Chen and Yanbin Hao
    2022, 15 (5): 879-881 .
    Abstract ( 83 )   PDF(pc) (319KB) ( 63 )   Save

    Carbon and water fluxes are the core ecosystem processes, which is linked to diverse ecosystem services (Lian et al. 2021). Therefore, clarifying the variations and controls of ecosystem carbon and water fluxes is an effective approach to clarifying how ecosystem respond to global change in EVAs (Baldocchi 2020). As the only technique can directly measure the carbon, water and energy fluxes between vegetation and atmosphere, eddy covariance technique has been considered as a standard method for flux observations (Chen et al. 2020). By integrating long-term, eddy covariance measurements over time and space, researches are able to assess ecosystem metabolism at different time scales (hours to decades) (Forzieri et al. 2020; Han et al. 2020; Jung et al. 2017). Eddy covariance measurements also produce information on how ecosystem respond to the changes in climate, which is useful for assessing ecosystem carbon sequestration (Hu et al. 2018), water and energy balance (Forzieri et al. 2020), resource use efficiency (Liu et al. 2019) and ecosystem feedback to climate change (Huang et al. 2019; Piao et al. 2020; Yue et al. 2020). Long-term flux measurements are also vital for detecting the responses of ecosystem functions to extreme events, optimizing and validating models on regional and global scales (Baldocchi 2020). Combining with remote sensing and ecosystem modeling techniques, scientists can upscale and evaluate the functional relations between carbon and water fluxes with environmental variables at high resolution and across diverse spatial/temporal scales (Niu et al. 2017; Xia et al. 2020).

    With the continual efforts from scientists in the past two decades, diverse observations facilities, especially eddy flux towers have been established to monitor ecosystem functioning in EVAs in China (Yu et al., 2006). With the data accumulated based on these observations, enhancing our knowledge of carbon and water fluxes in ecologically vulnerable areas in China become feasible. The authors of this special issue share their findings and insights on how ecosystem carbon and water fluxes at different spatial and temporal scales in EVAs in China. For example, on ecosystem carbon flux, in the water-limited grasslands in Inner Mongolia, You et al. (2022) found that leaf area index directly and soil water content indirectly affected photosynthetic parameters at the canopy scale. In a Tibetan alpine meadow ecosystem, Xu et al. (2022a) revealed that biotic factors, rather than climatic factors, dominated the interannual variations in carbon fluxes. In saline–alkaline grassland, Diao et al. (2022) found that nitrogen deposition simulated soil respiration and the effect was nitrogen compounds dependent from a 3-year field experiment. In the Bayinbuluk alpine wetland, Yao et al. (2022) used an automatic chamber system d reported that the seasonal variations of ecosystem respiration were controlled by soil temperature and water content. On ecosystem water flux, Xu et al. (2022b) reported that variations of ecosystem evapotranspiration (ET) were dominated by net radiation and air temperature and behaved energy limited in wet peak season. However, variations of ET were regulated by canopy stomatal conductance and leaf area index and were water limited in dry seasons. In a desert steppe, Du et al. (2022) found that gross primary production responded more quickly to the plant water stress than ET, which decreased water use efficiency. The large-scale afforestation should fully consider the cost of water consumption. On extreme climate, Zhang et al. (2022) conducted the Fisher discriminant model, involving soil water content and saturated vapor pressure deficit, and successfully detect drought occurrence. The publications of this special issue will largely enrich our understanding the functioning of ecosystems in vulnerable areas in China.

    We are grateful to the editorial team of Journal of Plant Ecology, particularly to Wen-Hao Zhang, Bernhard Schmid and Li-Juan Liu, for giving us the opportunity to organize this special issue. The publication of this special issue would not have been possible without their support. We sincerely hope that this special issue will advance our mechanistic understanding of carbon and water functions in vulnerable ecosystems in China.

    Research Articles
    Mingjie Xu, Yi Sun, Tao Zhang, Yangjian Zhang, Juntao Zhu, Yongtao He, Liwei Wang and Guirui Yu
    2022, 15 (5): 882-896 .
    Abstract ( 89 )   PDF(pc) (2413KB) ( 91 )   Save

    The alpine meadow ecosystem in Tibet is fragile and sensitive, and its carbon sink function with respect to climate change has become a matter of widespread concern. Therefore, this study aims to clarify the inter-annual variations (IAVs) in the carbon fluxes in an alpine meadow and to further quantify the contributions of the driving factors to the IAVs. Based on 7 years of flux data (2012–2018) and the corresponding climatic and biotic data, a set of look-up tables was used to separate and quantify the IAV sources. Furthermore, linear perturbation analyses were employed to quantify the contributions of each key factor. During 2012–2018, the net ecosystem productivity (NEP), gross primary productivity (GPP) and ecosystem respiration (Re) of this alpine meadow were 3.31 ± 26.90, 210.18 ± 48.35 and 206.88 ± 28.45 g C m−2 y−1, respectively, which indicated relatively large IAVs. When the contributions of climatic and biotic effects were distinguished and quantified, the dominant effects of biotic factors emerged. Additionally, negative interactions between climatic and biotic effects were detected. Among the climatic factors, only soil water content contributed relatively more to the IAVs and played a role in regulating the interactions between climatic and biotic effects. These results suggest that biotic effects must be carefully considered to reduce the uncertainties associated with future carbon flux estimates.

    Huajie Diao, Xiaopeng Chen, Ge Wang, Qiushi Ning, Shuya Hu, Wei Sun, Kuanhu Dong and Changhui Wang
    2022, 15 (5): 897-910 .
    Abstract ( 126 )   PDF(pc) (4162KB) ( 161 )   Save

    The increase in atmospheric nitrogen (N) deposition has profound effects on soil respiration (SR). However, the responses of SR to the addition of different N compounds, particularly in saline–alkaline grasslands remain unclear. A 3-year controlled field experiment was conducted to investigate the responses of SR to different N compounds (NH4NO3, (NH4)2SO4 and NH4HCO3) during the growing seasons in a saline–alkaline grassland located in the agro-pastoral ecotone of northern China. Our results demonstrated that SR showed a bimodal pattern and a significant interannual difference that was regulated by air or soil temperature and precipitation. Nitrogen addition had a significant effect on SR, and the effect of N addition on SR varied yearly, which was related to seasonal precipitation. The mean SR across 3 years (2017–2019) was increased by 19.9%, 13.0% and 16.6% with the addition of NH4NO3, (NH4)2SO4 and NH4HCO3, respectively. The highest effect of NH4NO3 addition on SR across 3 years was ascribed to the highest aboveground net primary production, belowground net primary production (BNPP) and soil NO3 concentrations. SR (C loss) was significantly increased while plant productivity (C input) did not significantly change under NH4HCO3 addition, indicating a decrease in C sequestration. In addition, BNPP was the main direct factor influencing SR in this saline–alkaline grassland, and soil salinization (e.g. soil base cations and pH) indirectly affected SR through soil microorganisms. Notably, NH4NO3 addition overestimated the response of SR to N addition, and different N compounds should be considered, especially in saline–alkaline grassland.

    Tao Zhang, Ximeng Ji, Yuanyuan Tang, Mingjie Xu, Yangjian Zhang, Guang Zhao, Ning Chen, Juntao Zhu and Yongtao He
    2022, 15 (5): 911-920 .
    Abstract ( 95 )   PDF(pc) (4194KB) ( 77 )   Save

    Fisher discriminant analysis can comprehensively take multiple factors into consideration and effectively conduct separations between two classes. If it can be used to detect the occurrences of drought, drought can be detected more effectively and accurately. Based on 9-year carbon flux and corresponding meteorological data, soil water content (SWC) and vapor pressure deficit (VPD) were selected as the discriminant factors. Drought occurrences were detected by applying the Fisher discriminant analysis method in an alpine ecosystem in Tibet. Fisher discriminant analysis was successfully applied to detect drought occurrence in an alpine meadow ecosystem. The soil water deficit and atmospheric water deficit were comprehensively taken into consideration. Consequently, this method could detect the onset and end date of droughts more accurately and reasonably. Based on the characteristics of drought and non-drought samples, the discriminant equation was constructed as y = 24.46SWC − 4.60VPD. When y > 1, the days were distributed above the critical line. In addition, when y was greater than one for more than 10 days, it was labeled as one drought event. If the interval between two drought processes was less than 2 days, it was considered one drought event. With increasing the study period and continued accumulation of observation data, the discriminant equation could be further optimized in the future, resulting in more accurate drought detection.

    Mingjie Xu, Tingting An, Zhoutao Zheng, Tao Zhang, Yangjian Zhang and Guirui Yu
    2022, 15 (5): 921-932 .
    Abstract ( 86 )   PDF(pc) (2078KB) ( 89 )   Save

    The Tibetan Plateau is generally referred to as the Chinese water tower, and evapotranspiration (ET) affects the water budget and stability of alpine meadows on the Tibetan Plateau. However, its variability and controlling mechanisms have not been well documented under the drier conditions induced by global warming. Therefore, this study aimed to clarify whether meteorological or biological factors primarily affected the variability in ET under contrasting water conditions in the alpine meadow ecosystem on the Tibetan Plateau. Based on 6-year (2013–2018) eddy covariance observations and the corresponding meteorological and biological data, linear perturbation analyses were employed to isolate the contributions of meteorological and biological factors to the variability in evapotranspiration (δET). The results showed that δET was mainly driven by meteorological factors in wet peak seasons (July and August), and was dominated by net radiation (Rn) and air temperature (Ta), indicating that the inadequate available energy is the factor limiting ET. However, the dominant factors affecting δET shifted from meteorological to biological in dry peak seasons when the canopy stomatal conductance (gs) and leaf area index were dominant. At this point, the ecosystem was limited by the water conditions. These results provide empirical insights into how meteorological and biological factors regulate variability in ET under contrasting water conditions. These findings can further improve our understanding of water cycle processes and can help effectively manage water resources in alpine meadow ecosystems under future climate change conditions.

    Hu Yao, Haijun Peng, Bing Hong, Hanwei Ding, Yetang Hong, Yongxuan Zhu, Jie Wang and Cheng Cai
    2022, 15 (5): 933-946 .
    Abstract ( 92 )   PDF(pc) (3180KB) ( 77 )   Save

    Wetlands store large amounts of carbon stocks and are essential in both global carbon cycling and regional ecosystem services. Understanding the dynamics of wetland carbon exchange is crucial for assessing carbon budgets and predicting their future evolution. Although many studies have been conducted on the effects of climate change on the ecosystem carbon cycle, little is known regarding carbon emissions from the alpine wetlands in arid northwest China. In this study, we used an automatic chamber system (LI-8100A) to measure ecosystem respiration (ER) in the Bayinbuluk alpine wetland in northwest China. The ER showed a significant bimodal diurnal variation, with peak values appearing at 16:30 and 23:30 (Beijing time, UTC + 8). A clear seasonal pattern in ER was observed, with the highest value (19.38 µmol m−2 s−1) occurring in August and the lowest value (0.11 µmol m−2 s−1) occurring in late December. The annual ER in 2018 was 678 g C m−2 and respiration during the non-growing season accounted for 13% of the annual sum. Nonlinear regression revealed that soil temperature at 5 cm depth and soil water content (SWC) were the main factors controlling the seasonal variation in ER. The diurnal variation in ER was mainly controlled by air temperature and solar radiation. Higher temperature sensitivity (Q10) occurred under conditions of lower soil temperatures and medium SWC (25% ≤ SWC ≤ 40%). The present study deepens our understanding of CO2 emissions in alpine wetland ecosystems and helps evaluate the carbon budget in alpine wetlands in arid regions.

    Ling-Tong Du, Long-Long Ma, Hai-Zhu Pan, Cheng-Long Qiao, Chen Meng, Hong-Yue Wu, Jing Tian and Hong-Yi Yuan
    2022, 15 (5): 947-960 .
    Abstract ( 90 )   PDF(pc) (3778KB) ( 119 )   Save

    The carbon and water cycle, an important biophysical process of terrestrial ecosystems, is changed by anthropogenic revegetation in arid and semiarid areas. However, there is still a lack of understanding of the mechanisms of carbon and water coupling in intrinsic ecosystems in the context of human activities. Based on the CO2 and H2O flux measurements of the desert steppe with the planted shrub Caragana liouana, this study explored the carbon and water flux coupling of the ecosystem by analyzing the variations in gross primary productivity (GPP), evapotranspiration (ET) and water use efficiency (WUE) and discussing the driving mechanisms of biological factors. The seasonal variation in climate factors induced a periodic variation pattern of biophysical traits and carbon and water fluxes. The GPP and ET fluctuated in seasons, but the WUE was relatively stable in the growing season. The GPP, ET and WUE were significantly driven by global radiation (Rg), temperature (Ta and Ts), water vapor pressure deficit, leaf area index and plant water stress index (PWSI). However, Rg, temperature and PWSI were the most important factors regulating WUE. Rg and temperature directly affected WUE with a positive effect but indirectly inhibited WUE by rising PWSI. Plant water stress inhibited photosynthesis and transpiration of the planted shrub community in the desert steppe. When the plant water stress exceeded a threshold (PWSI >0.54), the WUE would decrease since the GPP responded more quickly to the plant water stress than ET. Our findings suggest that policies related to large-scale carbon sequestration initiatives under afforestation must first fully consider the status of water consumption and WUE.

    Cuihai You, Yanbing Wang, Xingru Tan, Bingwei Zhang, Tingting Ren, Boyu Chen, Mengzhen Xu and Shiping Chen
    2022, 15 (5): 961-976 .
    Abstract ( 115 )   PDF(pc) (4131KB) ( 103 )   Save

    The ecosystem apparent quantum yield (α), maximum rate of gross CO2 assimilation (Pmax) and daytime ecosystem respiration rate (Rd), reflecting the physiological functioning of ecosystem, are vital photosynthetic parameters for the estimation of ecosystem carbon budget. Climatic drivers may affect photosynthetic parameters both directly and indirectly by altering the response of vegetation. However, the relative contribution and regulation pathway of environmental and physiological controls remain unclear, especially in semi-arid grasslands. We analyzed seasonal and interannual variations of photosynthetic parameters derived from eddy-covariance observation in a typical semi-arid grassland in Inner Mongolia, Northern China, over 12 years from 2006 to 2017. Regression analyses and a structural equation model (SEM) were adopted to separate the contributions of environmental and physiological effects. The photosynthetic parameters showed unimodal seasonal patterns and significantly interannual variations. Variations of air temperature (Ta) and soil water content (SWC) drove the seasonal patterns of photosynthetic parameters, while SWC predominated their interannual variations. Moreover, contrasting with the predominant roles of Ta on α and Rd, SWC explained more variance of Pmax than Ta. Results of SEM revealed that environmental factors impacted photosynthetic parameters both directly and indirectly through regulating physiological responses reflected by stomatal conductance at the canopy level. Moreover, leaf area index (LAI) directly affected α, Pmax and Rd and dominated the variation of Pmax. On the other hand, SWC influenced photosynthetic parameters indirectly through LAI and canopy surface conductance (gc). Our findings highlight the importance of physiological regulation on the photosynthetic parameters and carbon assimilation capacity, especially in water-limited grassland ecosystems.

    Bowen Li, Wangwang Lv, Jianping Sun, Lirong Zhang, Lili Jiang, Yang Zhou, Peipei Liu, Huan Hong, Qi Wang, Wang A, Suren Zhang, Lu Xia, Zongsong Wang, Tsechoe Dorji, Ailing Su, Caiyun Luo, Zhenhua Zhang and Shiping Wang
    2022, 15 (5): 977-990 .
    Abstract ( 114 )   PDF(pc) (1060KB) ( 62 )   Save

    Warming and grazing, and litter quality jointly determine litter decomposition and nutrient releases in grazing ecosystems. However, their effects have previously been studied in isolation. We conducted a two factorial experiment with asymmetric warming using infrared heaters and moderate grazing in an alpine meadow. Litter samples were collected from all plots in each treatment, among which some subsamples were placed in their original plots and other samples were translocated to other treatment plots to test the relative effects of each treatment on litter decomposition and nutrient releases. We found that warming rather than grazing alone significantly increased total losses of litter mass, total organic carbon, total nitrogen (TN) and total phosphorus (TP) per unit area due to increases in both mass loss rates and litter biomass. However, grazing with warming did not affect their total mass losses because increased mass loss was offset by decreased litter biomass compared with the control. Seasonal mean soil temperature better predicted litter decomposition than litter lignin content or carbon to nitrogen ratio. There were interactions between warming and grazing, but there were no interactions between them and litter quality on litter decomposition. The temperature sensitivity of TN loss was higher than that of TP loss per unit area. Our results suggest that increased temperature has a greater effect on litter decomposition and nutrient release than change in litter quality, and that more N release from litter could result in greater P deficiency in the alpine meadow.

    Bingqian Su and Zhouping Shangguan
    2022, 15 (5): 991-1006 .
    Abstract ( 105 )   PDF(pc) (2229KB) ( 107 )   Save

    All organisms need elements in fixed proportions for carrying out normal metabolic processes and how flexible they are depends on how effective they are utilizing these resources from external sources. It is important to understand the interactions among plant, soil and microbial biomass carbon (C), nitrogen (N) and phosphorus (P) stoichiometry under different conditions of resource supply. We conducted a pot experiment on 1-year-old Robinia pseudoacacia seedlings for nearly 5 months under different water, nitrogen and phosphorus supplies, and we determined plant, soil and microbial biomass C, N and P stoichiometry. We found that plant, soil and microbial nutrients and stoichiometry exhibited a certain degree of plasticity in response to the changes in water and nutrient conditions in their environments. Variation partitioning analysis showed that root stoichiometry accounted for a large part of the variance in microbial stoichiometry. Structural equation modeling further revealed that root stoichiometry and leaf stoichiometry were two direct factors affecting microbial biomass C:N and C:P, and that root stoichiometry had the greatest direct effect. In addition, the degree of homeostasis for microbial biomass C and C:P was more sensitive to changes in soil nutrients than changes in other factors, and other elements and elemental ratios displayed strict homeostasis. These results highlight the importance of studying microbial stoichiometry in improving our understanding of nutrient cycling of the plant–soil system under different water and nutrient supply.

    Qiang Guo, Ruo-Hui Zhang, Xue-Li Li, Xiao-Wei Liu, Ya-Nan Li and Fu Xing
    2022, 15 (5): 1007-1020 .
    Abstract ( 88 )   PDF   Save
    Rapid spread and growth of plants that are poisonous to animals produce large amounts of plant litter in degraded grasslands. Nitrogen (N) input may promote the growth of these poisonous plants and alter the rhizosphere microbes and arbuscular mycorrhizal fungi (AMF) in particular. However, it is unclear how poisonous plant litter affects the growth of palatable plants and their associated AMF in the rhizosphere and whether and how N deposition may mediate these effects. A greenhouse experiment was performed to test the combined effects of litter addition of a poisonous plant, Stellera chamaejasme, and N addition on the growth of a dominant grass, Leymus chinensis, AMF characteristics and soil properties. Litter addition significantly increased the ramet number and aboveground biomass of L. chinensis and soil available phosphorus (AP) concentration and decreased the spore density of AMF. However, the interaction of both treatments had no significant effects on traits of L. chinensis and AMF properties. Stellera chamaejasme litter positively affected L. chinensis by increasing AP and negatively affected AMF by combining balanced changes in soil nutrients and litter-induced allelopathic compositions. High N addition may alleviate soil N limitation and inhibit litter decomposition, thus overriding the litter’s effects on L. chinensis and AMF. These findings imply that it is necessary to objectively and comprehensively evaluate the ecological functions of poisonous plants beyond their harmful effects on livestock. Simultaneously, N deposition should be an indispensable factor in predicting the relationships between poisonous plants and edible plants in degraded grasslands.
    Peng Zhang, Xiao-Tao Lü, Mai-He Li, Tonggui Wu and Guangze Jin
    2022, 15 (5): 1021-1035 .
    Abstract ( 116 )   PDF   Save

    Forest productivity and carbon (C) sequestration largely depend on soil N and P availability. To date, however, the temporal variation of nutrient limitation along forest succession is still under debate. Leaf stoichiometry and nutrient resorption are important indicators for predicting nutrient limitation of plant growth. Here, we measured nitrogen (N) and phosphorus (P) concentrations in green leaves and leaf litter for all woody species at four stages of temperate forest succession, and analyzed how abiotic and biotic factors affect leaf stoichiometry and nutrient resorption along forest succession. At the individual scale, leaf N and P concentrations had a significant increase at the end of the succession, while no change in leaf N:P ratio was detected. Nitrogen resorption efficiency (NRE) increased significantly with succession, but P resorption efficiency (PRE) first increased and then decreased. Significant increases in NRE:PRE ratios only occurred at the end of the succession. Moreover, plant N cycling was less responsive to soil nutrient than P cycling. At the community scale, we found that leaf N and P concentrations first decreased and then increased along forest succession, which were mainly affected by Shannon–Wiener index and species richness. Leaf N:P ratio significantly varied with succession and was mainly determined by community-weighted mean diameter at breast height (DBH). NRE increased and was significantly influenced by species richness and DBH, while PRE was relatively stable along forest succession. Thus, the NRE:PRE ratios significantly increased, indicating that N limitation is exacerbated with the temperate forest succession. These results might reflect the intense interspecific competition for limiting resource in a higher biodiversity community. In conclusion, our findings highlight the importance of biotic factors in driving forest ecosystem nutrient cycling and provide valuable information for sustainable fertilizer management practices in China’s temperate and boreal forests.

    Yanhong Wang, Changliang Shao, Yajing Qiu, Shuquan Yu, Lina Xia, Xiaobin He, Aiping Wu and Naili Zhang
    2022, 15 (5): 1036-1048 .
    Abstract ( 100 )   PDF   Save

    Acid rain (AR), which occurs frequently in southern China, negatively affects the growth of subtropical tree species. Arbuscular mycorrhizal fungi (AMF) mitigate the detrimental effects induced by AR. However, the mechanisms by which AMF protect Zelkova serrata, an economically important tree species in southern China, from AR stress remain unclear. We conducted a greenhouse experiment in which Z. serrata plants were inoculated with AMF species Rhizophagus intraradices and Diversispora versiformis, either alone or as a mixed culture, or with a sterilized inoculum (negative control). The plants were subjected to three levels of simulated sulfuric AR and nitric AR (pH 2.5, 4.0 and 5.6) to examine any interactive effects on growth, photosynthetic capabilities, antioxidant enzymes, osmotic adjustment and soil enzymes. AR significantly decreased dry weight, chlorophyll content, net photosynthetic rate and soluble protein (SP) of non-mycorrhizal plants. Mycorrhizal inoculation, especially a combination of R. intraradices and D. versiformis, notably improved dry weight, photosynthetic capabilities, catalase, peroxidase, superoxide dismutase, SP and root acid phosphatase activity of Z. serrata under harsh AR stress. Moreover, the benefits from AMF symbionts depended on the identity of AM fungal species and the gradient of AR stress. Our results indicate that AM fungi protect Z. serrata against AR stress by synchronously activating photosynthetic ability, antioxidant enzymes and osmolyte accumulation. These findings suggest that a combination of R. intraradices and D. versiformis may be a preferable choice for culturing Z. serrata in southern China.

    Amara Sidiki Traoré, Kouadio Ignace Kouassi, Moussa Koné, Jacques Gignoux and Sébastien Barot
    2022, 15 (5): 1049-1064 .
    Abstract ( 70 )   PDF   Save

    Sofa J. van Moorsel
    2022, 15 (5): 1065-1079 .
    Abstract ( 98 )   PDF   Save

    The pollution of freshwater ecosystems is threatening freshwater plant species diversity worldwide. Freshwater plants, such as the common duckweed (Lemna minor), are potentially sensitive to novel stressful environments. To test if ecotype diversity could increase resistance to stressful environments, I used seven L. minor populations and measured their growth rates with and without moderate salt stress across an ecotype diversity gradient. The L. minor populations were grown over 5 months in 92 experimental mesocosms, either in ecotype monocultures or in polyculture with either one or three conspecific ecotypes (23 unique compositions). After growing the duckweed in unperturbed conditions (phase 1), the cultures were subjected to moderate salt stress (50 mmol/L NaCl) for several weeks (phase 2). The experiment was conducted in the presence of the natural epimicrobial community associated with the different ecotypes. In phase 2, a subset of these algae added an unintentional second stressor to the experiment. The ecotypes differed in their growth rates, the fastest growing at twice the rate of others. The diversity context further shaped the ecotype growth rates. Ecotype polycultures showed higher abundances towards the end of the experiment, thus over time, as the environment deteriorated, ecotype diversity gained in importance. These findings show that within-species variation in growth rates can translate to a positive effect of ecotype diversity on population abundance. Exposure of L. minor to moderate salt levels did not significantly impact growth rates, although the effect may have been masked by reduced algal stress in the saline environments.

    Xiaowen Ma, Yang Li, Weicheng Yu, Junnan Wang and Chunhua Liu
    2022, 15 (5): 1080-1090 .
    Abstract ( 71 )   PDF   Save

    Clonal integration benefits clonal plants by buffering environmental stress and increasing resource extraction efficiency. However, the number of connected ramet generations that benefit from clonal integration in a clonal system has received relatively little attention. A pot experiment was conducted to evaluate the extent of physiological integration within the clonal system of Vallisneria natans consisting of a mother ramet and three sequentially connected offspring ramets. Mother ramets were grown in full sunlight, and offspring ramets were heavily shaded with limited light availability. Stolons between mother ramets and offspring ramets were severed or connected, but connection among the three offspring ramets remained. The photosynthetic ability of unshaded mother ramets of V. natans was significantly enhanced, but their biomass accumulation was greatly reduced when connected to shaded offspring ramets. Clonal integration significantly increased biomass accumulation, C and N availabilities, extracellular enzyme activities and microbial biomass of the first ramet generation (adjacent ramet), but not later ramet generations. Our results indicate that support from the mother ramet of V. natans may be limited to the adjacent offspring ramet in a clonal system under severe light stress, implying an effect of ramet generation. Our results contribute to a better understanding of the hierarchy and segmentation of clonal plants. These findings suggest that the extent of clonal integration plays a vital role in ecological interactions of the ramet population.

    Ting Ma, Thomas Parker, Ned Fetcher, Steven L. Unger, Jon Gewirtzman, Michael L. Moody and Jianwu Tang
    2022, 15 (5): 1091-1105 .
    Abstract ( 64 )   PDF   Save

    The response of plant leaf and root phenology and biomass in the Arctic to global change remains unclear due to the lack of synchronous measurements of above- and belowground parts. Our objective was to determine the phenological dynamics of the above- and belowground parts of Eriophorum vaginatum in the Arctic and its response to warming. We established a common garden located at Toolik Lake Field Station; tussocks of E. vaginatum from three locations, Coldfoot, Toolik Lake and Sagwon, were transplanted into the common garden. Control and warming treatments for E. vaginatum were set up at the Toolik Lake during the growing seasons of 2016 and 2017. Digital cameras, a handheld sensor and minirhizotrons were used to simultaneously observe leaf greenness, normalized difference vegetation index and root length dynamics, respectively. Leaf and root growth rates of E. vaginatum were asynchronous such that the timing of maximal leaf growth (mid-July) was about 28 days earlier than that of root growth. Warming of air temperature by 1 °C delayed the timing of leaf senescence and thus prolonged the growing season, but the temperature increase had no significant effect on root phenology. The seasonal dynamics of leaf biomass were affected by air temperature, whereas root biomass was correlated with soil thaw depth. Therefore, we suggest that leaf and root components should be considered comprehensively when using carbon and nutrient cycle models, as above- and belowground productivity and functional traits may have a different response to climate warming.

IF: 2.7
5-year IF: 2.6
Yuanhe Yang
Bernhard Schmid
CN 10-1172/Q
ISSN 1752-9921(print)
ISSN 1752-993X(online)