Generalized linear mixed models (GLMMs) have been widely used in contemporary ecology studies. However, determination of the relative importance of collinear predictors (i.e. fixed effects) to response variables is one of the challenges in GLMMs. Here, we developed a novel R package, glmm.hp, to decompose marginal R² explained by fixed effects in GLMMs. The algorithm of glmm.hp is based on the recently proposed approach ‘average shared variance’ i.e. used for multivariate analysis. We explained the principle and demonstrated the use of this package by simulated dataset. The output of glmm.hp shows individual marginal R²s that can be used to evaluate the relative importance of predictors, which sums up to the overall marginal R². Overall, we believe the glmm.hp package will be helpful in the interpretation of GLMM outcomes.

Drought can affect the growth and soil enzyme activities of invasive alien plants (IAPs). It is imperative to evaluate the competitive advantage of IAPs compared with that of the native species and the activities of soil enzymes under drought. This study aimed to evaluate the competitive advantage of the IAP Amaranthus spinosus that originated from tropical America compared with the native Chinese species A. tricolor and the activities of soil enzymes under drought. A competitive co-culture of A. spinosus and A. tricolor was established using a planting basin experiment. The two species were treated with different levels of drought, i.e. (i) the control; (ii) a light level of drought and (iii) a heavy level of drought. The functional traits, osmotic adjustment and the activities of antioxidant enzymes of the two species, as well as soil pH and electrical conductivity, contents of soil microbial biomass carbon and the activities of soil enzymes were determined. The relative competition intensity and relative dominance of A. spinosus were greater than those of A. tricolor under drought. Drought may provide an advantage to the competitive advantage of A. spinosus. Soil water-soluble salt content and sucrose hydrolytic power of A. spinosus were greater than those of A. tricolor under drought. The ability of A. spinosus to grow in soil with higher levels of water-soluble salt contents and sucrose hydrolytic power under drought may aid in its acquisition and utilization of nutrients.

Precipitation (PPT) changes affect both aboveground vegetation dynamics and belowground carbon cycling processes, particularly in arid and semiarid regions. However, it remains unclear how extreme PPT variation can affect soil carbon sequestration potential. A 3-year PPT manipulation experiment with five levels (±40%, ±20% and ambient PPT) was conducted in a desert grassland of western Loess Plateau. Aboveground net primary productivity (ANPP) and soil respiration (Rs) were measured to examine whether the responses of ANPP and Rs to PPT changes displayed a double asymmetry model. The ANPP was more sensitive to extreme drought than extreme wet treatments in wet and dry years, which displayed a negative asymmetric model. The change in ANPP was mainly due to the direct effect of PPT change, and plant density variation also exerted some influence in the dry year. In contrast, Rs displayed a positive asymmetry response to PPT change in dry year. This may be ascribed to enhanced autotrophic respiration due to the enhanced positive responses of plant growth and ANPP to wet treatments as well as stronger birch effect of rainfall events on heterotrophic respiration. The saturating response of Rs to extreme drought (−40% PPT treatment) was also found in the dry year. Nevertheless, the response of Rs to PPT change displayed a negative asymmetry model in wet years. The contrasting models for ANPP and Rs in response to altered PPT regime suggest that extreme wet or dry treatments may increase soil C pools effluxes toward debt in this desert grassland.

Climatic warming affects plant growth and physiology, yet how warming alters chemistry in invasive plants and indirectly affects herbivorous insects remains largely unknown. Here, we explored warming-induced changes in leaf chemistry of the invasive plant Alternanthera philoxeroides and its native congener Alternanthera sessilis, and further examined how these changes affected the performance of the herbivores, Cassida piperata and Spodoptera litura. We conducted a simulated warming experiment to address its effects on 13 leaf chemical traits of A. philoxeroides and A. sessilis. We measured growth and development time of two herbivores reared on plants from warming or ambient controls. Warming significantly affected leaf chemistry composition for both the invasive and native Alternanthera. Warming decreased nitrogen concentration in A. philoxeroides and increased total flavonoid and total phenol concentration in A. sessilis. The effects of warming on nutrients (i.e. fructose, sucrose, total soluble sugar and starch) varied with individual chemicals and plant species. Weight of C. piperata pupal and S. litura larval reared on warming-treated A. sessilis significantly decreased compared with non-warmed control, and a similar pattern was observed for weight of S. litura larval feeding on warming-treated A. philoxeroides. In addition, warming-treated A. sessilis significantly prolonged larval development time of S. litura. These results indicate that warming can directly affect the leaf chemistry in both invasive plant and its native congener, but these effects vary by species. Such differences in warming-induced changes in plant chemistry could indirectly affect herbivorous insects associated with the invasive and native plants.

Plant invasions can affect soil properties in the invaded habitat by altering the biotic and abiotic nature of soils through positive or negative plant–soil feedback. Litter decomposition from many invasive species enhanced soil nutrients, thereby decreasing native plant diversity and leading to further plant invasions. Here, we examined the impact of litter decomposition from an invasive plant (Sphagneticola trilobata) in a range of soils at varying depths on growth and physiology of its native congener (Sphagneticola calendulacea). We added litter from S. trilobata to each soil type at different depths (0, 2, 4 and 6 cm). Plants of S. calendulacea were grown in each treatment, and morphological and physiological parameters were measured at the end of the growing period. All soils treated with litter displayed increases in soil nutrients at depths of 2 and 4 cm; while most growth traits, leaf chlorophyll and leaf nitrogen of S. calendulacea decreased at the same soil depths. Therefore, litter decomposition from invasive S. trilobata resulted in a positive plant–soil feedback for soil nutrients, and a negative plant–soil feedback for growth in native S. calendulacea. Our findings also suggest that the effects of litter decomposition from an invasive plant on soils and native species can vary significantly depending on the soil depth at which the litter is deposited. Future studies should focus on plant–soil feedback for more native and invasive species in invaded habitats, and the effects of invasive litter in more soil types and at greater soil depths.

Arbuscular mycorrhizal fungi (AMF) can increase host plant nutrient uptake via their mycelium, thus promoting plant growth. AMF have always been associated with successful invasion of most exotic plant species. However, knowledge regarding how AMF affect the success of plant invasion remains limited. Exotic Ambrosia artemisiifolia is an invasive and mycorrhizal plant species. A long-term field experiment was conducted to examine the differences in AMF diversity and composition in the roots of A. artemisiifolia and Setaria viridis subjected to interspecific competition during growth. A greenhouse experiment was also performed to test the effect of Funneliformis mosseae on the growth of these two species. Ambrosia artemisiifolia invasion caused AMF diversity to change in native S. viridis roots. Meanwhile, the relative abundance of F. mosseae was significantly higher in the roots of A. artemisiifolia than in those of S. viridis. The higher AMF colonization rate in the exotic species (A. artemisiifolia) than in the native species (S. viridis) was found in both the field and greenhouse experiments. The greenhouse experiment possibly provided that AMF advantaged to the growth of A. artemisiifolia, by influencing its photosynthetic capacity as well as its phosphorus and potassium absorption. These observations highlight the important relationship of AMF with the successful invasion of A. artemisiifolia.

Global changes have altered the distribution pattern of the plant communities, including invasive species. Anthropogenic contamination may reduce native plant resistance to the invasive species. Thus, the focus of the current review is on the contaminant biogeochemical behavior among native plants, invasive species and the soil within the plant–soil ecosystem to improve our understanding of the interactions between invasive plants and environmental stressors. Our studies together with synthesis of the literature showed that (i) the impacts of invasive species on environmental stress were heterogeneous, (ii) the size of the impact was variable and (iii) the influence types were multidirectional even within the same impact type. However, invasive plants showed self-protective mechanisms when exposed to heavy metals (HMs) and provided either positive or negative influence on the bioavailability and toxicity of HMs. On the other hand, HMs may favor plant invasion due to the widespread higher tolerance of invasive plants to HMs together with the ‘escape behavior’ of native plants when exposed to toxic HM pollution. However, there has been no consensus on whether elemental compositions of invasive plants are different from the natives in the polluted regions. A quantitative research comparing plant, litter and soil contaminant contents between native plants and the invaders in a global context is an indispensable research focus in the future.

Litter is the crucial carrier of soil nutrition transformation. The influence of arbuscular mycorrhizal (AM) fungi on nutrient acquisition in plants has been widely recognized. However, in nutrient-deficient karst habitat, how competitive plants utilize nutrients regulated by AM fungi via litter remain largely unknown. The experimental treatments included the inoculation with or without Glomus etunicatum, the litter addition by the mixed leaves of Broussonetia papyrifera and Carpinus pubescens or no addition, and the competition through the intraspecific competition of B. papyrifera and C. pubescens, respectively, and the interspecific competition mixed both plants. AM fungi differently affected plant on nutrient acquisition, increasing nutrients acquisitions of B. papyrifera in intra- and interspecific competitions while decreasing for C. pubescens. Litter presented opposite influences on N acquisitions of both plants in interspecific competition with AM fungi, being positive for C. pubescens and negative for B. papyrifera, respectively. Under the interaction of AM fungi and litter, nitrogen (N), phosphorus (P) and potassium (K) acquisitions by B. papyrifera and N acquisition by C. pubescens in interspecific competition were all greater than intraspecific competition. In the interspecific competition, the competitive ability of plants on nutrient absorption presented significant species difference, which of B. papyrifera on P and K was significantly increased, while was converse for C. pubescens on K. In conclusion, these results suggest that the interspecific competition presents greater nutrient facilitation compared with intraspecific competition through AM fungi interacting with litter for plants in karst soil.

树种菌根类型通过细根生物量和凋落物动态影响土壤呼吸和土壤碳储存
热带森林是高生产力但同时也是脆弱的生态系统之一。一些全球范围的造林项目计划未来十年在热带地区种植数百万棵树。树种菌根类型影响森林土壤碳储存已成为共识，但在热带地区，树种菌根类型如何影响土壤呼吸(Rs)和碳储存，目前仍知之甚少。为研究树种菌根类型对Rs和土壤碳储存的影响，本实验在一个近30年热带同质园的3种丛枝菌根(AM)树种和3种外生菌根(EM)树种的单种林中，测量了其Rs和表层20 cm的碳含量，以及有关的生物因子(如根生物量、凋落物动态、土壤微生物)和非生物因子(如微气候)。研究结果表明，AM单种林的Rs、土壤碳含量，以及凋落物周转速率和细根生物量显著高于EM单种林。分析表明，与其他生物和非生物因子比较，树种菌根类型对Rs和土壤碳含量的影响最大。进一步分析表明，菌根类型是通过细根生物量和凋落物动态(凋落物产量、凋落物现存量、凋落物周转速率)直接和间接影响Rs和土壤碳含量。本研究结果强调了树种菌根类型对森林碳循环的影响，表明在热带地区种植AM树种可能比种植EM树种更能促进土壤固碳。

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.

The effect of exotic plants on Bacillus diversity in the rhizosphere and the role of Bacilli in exotic or native plant species remain poorly understood. Flaveria bidentis is an invasive grass in China. Setaria viridis is a native grass and occurs in areas invaded by F. bidentis. Our objectives were (i) to examine the differences in the Bacillus communities between F. bidentis and S. viridis rhizospheres soil, and (ii) to compare the effects of Bacilli from F. bidentis and S. viridis rhizospheres on the competitiveness of the invasive species. Flaveria bidentis monoculture, mixture of F. bidentis and S. viridis and S. viridis monoculture were designed in the field experiment. Bacillus diversity in their rhizosphere was analyzed using 16S rRNA. One of the dominant Bacilli in the rhizosphere soil of F. bidentis was selected to test its effect on the competitive growth of F. bidentis in a greenhouse experiment. Bacillus diversity differed in F. bidentis and S. viridis rhizosphere. Brevibacterium frigoritolerans was the dominant Bacilli in the rhizosphere of both F. bidentis and S. viridis; however, its relative abundance in the F. bidentis rhizosphere was much higher than that in the S. viridis rhizosphere. In addition, B. frigoritolerans in the F. bidentis rhizosphere enhanced the growth of the plant compared with that of S. viridis by improving the nitrogen and phosphorus levels. This study showed that F. bidentis invasion influenced Bacillus communities, especially B. frigoritolerans, which, in turn, facilitated F. bidentis growth by increasing the levels of available nitrogen and phosphorus.

Plant invasion is one of the most serious threats to ecosystems worldwide. When invasive plants with the ability of clonal growth invading or colonizing in new habitat, their interconnected ramets may suffer from heterogeneous light. Effects of clonal integration on allelopathy of invasive plants are poorly understood under heterogeneous light conditions. To investigate the effects of clonal integration on allelopathy of invasive plant Wedelia trilobata under heterogeneous light conditions, a pot experiment was conducted by using its clonal fragments with two successive ramets. The older ramets were exposed to full light, whereas the younger ones were subjected to 20% full light. The younger ramets of each clonal fragment were adjacently grown with a target plant (one tomato seedling) in a pot. Stolon between two successive ramets was either severed or retained intact. In addition, two tomato seedlings (one as target plant) were adjacently grown in a pot as contrast. Compared with severing stolon, biomass accumulation, foliar chlorophyll and nitrogen contents, chlorophyll fluorescence parameters and net photosynthetic rates of the target plants as well as their root length and activity, were significantly decreased when stolon between interconnected ramets of W. trilobata retained intact. Under heterogeneous light conditions, transportation or sharing of carbohydrate between two successive ramets enhanced allelopathy of the young ramets subjected to 20% full light treatment. It is suggested that clonal integration may be important for invasion or colonization of invasive plants with ability of clonal growth under heterogeneous light conditions.

Shifts in the realized niches of exotic species may play an important role in their invasion. Galinsoga quadriradiata has invaded China widely and occupied many climate zones that are different from its native range. We addressed the climatic niche shift of G. quadriradiata and evaluated how this could contribute to its invasion in China. We used the Maxent model to predict the potential distribution of G. quadriradiata using its native and invaded range occurrences and climatic variables. Principal component analysis was conducted to measure climatic niche shifts of G. quadriradiata during its invasion in China. The models revealed only 32.7% niche overlap between the native and invasive populations. The niche similarity of the two populations was significantly low (Schoener’s D = 0.093, P < 0.005), suggesting the occurrence of a niche shift. The envelop and center of the realized climatic niche in China has shifted to lower temperature and less precipitation compared to that in its native range. The majority of invaded areas in southern China are in the stabilizing zone, whereas the colonization and adaptation zones are predicted to be at the leading edge of G. quadriradiata invasion in northern China. This suggests that the regional distribution of G. quadriradiata may be in a quasi-equilibrium state, and that the species continues to invade environmentally suitable areas. Alterations in G. quadriradiata’s niche would help to explain why this species is so invasive in China.

Grassland reconstruction is a major approach to alleviate the ‘black beach’ in Sanjiangyuan of the Qinghai-Tibetan Plateau. It is vital to understand how to manage the planting grassland after reconstruction. And which artificial grassland management pattern is more likely to restore the degraded grassland of ‘black beach?’ To provide the scientific basis for the restoration of ‘black beach’, we investigated the changes in vegetation characteristics, soil physicochemical properties and soil microbial community structure of planting grassland under different management patterns, and explored the effect of the management patterns on community succession of planting grassland. In this study, vegetation characteristics and soil physicochemical properties were measured by field investigation and laboratory analyses, respectively. Soil microbial community composition was determined by high-throughput sequencing techniques. The results showed that there were significant differences in vegetation characteristics, soil physicochemical properties and soil microbial community structure of the planting grassland under different management patterns. Actinobacteria and Basidiomycota were mainly controlled by vegetation plant species diversity, aboveground biomass (AGB) and soil organic carbon (SOC). Shannon-Wiener index, AGB and SOC peaked and the relative abundance of amplicon sequence variants annotated by Actinobacteria and Basidiomycota were significantly enriched under the management pattern of the planting once treatment. Additionally, the soil had the highest bacterial diversity and the lowest fungal diversity under the planting once treatment, becoming a ‘bacterial’ soil. These vegetation characteristics and soil environment were more conducive to overall positive community succession, indicating that the planting once treatment is the most reasonable management pattern for restoring the ‘black beach’.

Biodiversity is found to have a significant promotion effect on ecosystem functions in manipulation experiments on grassland communities. However, its relative role compared with stand factors or functional identity is still controversial in natural forests. Here, we examined their relative effects on biomass and productivity during forest restoration. We investigated stand biomass and productivity for 24 plots (600 m²) across restoration stages in the subtropical forests of Mt. Shennongjia, Central China. We measured five key functional traits and calculated functional diversity (functional richness, evenness and dispersion) and community-weighted mean of traits. We used general linear models, variation partitioning methods to test the relative importance of stand factors (density, stand age, maximum height, etc.), functional identity, species and functional diversity on biomass and productivity. Our results illustrated that stand biomass and productivity increased significantly as forest restoration, and that community species richness increased, while functional dispersion decreased significantly. Variation partitioning analyses showed that diversity had no significant pure effects on biomass and productivity. However, diversity may affect biomass and productivity through the joint effect with stand factors and functional identity. Overall, we found that stand factors had the strongest effect on biomass and productivity, while functional identity significantly affects productivity but not biomass, suggesting that modulating stand structure and species identity are effective ways to enhance forest carbon storage and sequestrations potential in forest management.

Soil microorganisms and their diversity are important bioindicators of soil carbon and nutrient cycling. Land use type is a major determining factor that influences soil microbial community composition in floodplain ecosystems. However, how the structure and diversity of soil microbial communities respond to specific changes in land use, as well as the main drivers of these changes, are still unclear. This study was conducted in the Yellow River floodplain to examine the effects of land use type on soil microbial communities. Four land use types (shrubland, farmland, grassland and forest) were selected, wherein shrubland served as the baseline. We measured soil microbial structure and diversity using phospholipid fatty acids (PLFAs). Land use type significantly affected total, bacterial and fungal PLFAs, and the gram-positive/negative bacterial PLFAs. Compared with shrubland, peanut farmland had higher total and bacterial PLFAs and forest had higher fungal PLFAs. Soil pH and phosphorus were the predominate drivers of microbial PLFAs, explaining 37% and 26% of the variability, respectively. Soil total nitrogen and nitrate nitrogen were the main factors increasing microbial community diversity. Peanut farmland had the highest soil carbon content, soil carbon stock, total PLFAs and microbial diversity, suggesting that farmland has great potential as a carbon sink. Our findings indicated that peanut farmland in the Yellow River floodplain is critical for maintaining soil microbial communities and soil carbon sequestration.

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.

Plant invasion potentially will be affected by increased extreme drought events and deposition of atmospheric N. However, results from previous research indicate that it is not clear as to how extreme drought, N deposition and their interaction affect alien plant invasion, in particular for the invasive woody legumes. We conducted a greenhouse experiment with three invasive and three native woody species of legumes (Fabaceae). We grew plants in extreme drought and in well-watered conditions combined with low and high levels of N and compared plant height, number of leaves and biomass production and allocation. Growth of native woody legumes was suppressed more by extreme drought than that of invasive woody legumes. Although an increase in soil N availability decreased the root mass fraction of plants of all species, it did not affect their overall performance. We found that invasive woody legumes can tolerate the adverse effects of the prolonged extreme drought better than native woody legumes. These results enhance our understanding of the effects of drought due to climate change on the invasion of alien woody legumes.

Tropical and subtropical evergreen broad-leaved forests (EBFs) and needle-leaved forests (ENFs) in China exhibit complex leaf shedding strategies in responses to soil water availability, vapor pressure deficits (VPDs) and sunlight availability. However, the seasonal variations and triggers of litterfall differ significantly in tropical/subtropical forests, and there are still many uncertainties. Herein, we aim to explore the distinct climatic factors of seasonal litterfall in a climate–phenology correlation framework. We collected seasonal litterfall data from 85 sites across tropical/subtropical China and used linear correlation coefficients between sunlight and rainfall to partition synchronous/asynchronous climates. Additional phase analysis and structural equation model analysis were conducted to model the climatic triggers of tropical phenology. Results indicated two types of tropical litterfall phenology under two types of climates. In synchronous climates, where seasonal sunlight and rainfall are positively correlated, the litterfall peak of the unimodal phenology and the first litterfall peak of the bimodal phenology both happen at the end of dry season. The second litterfall peak of the bimodal phenology occurs at the end of rainy season due to water stress. In asynchronous climates, where seasonal sunlight and rainfall are negatively correlated, VPD shows consistent seasonal variations with incoming sunlight. The leaf senescence is accelerated at the end of dry season by higher VPD; while soil water deficit is in anti-phase with sunlight and mainly controls the second litterfall peak of the bimodal phenology in EBF. Our findings provide an important reference for modeling tropical phenology in Earth system models.