Impact Factor
1.833
5 year Impact Factor
2.299
Editors-in-Chief
Wen-Hao Zhang
Bernhard Schmid
  • Volume 13,Issue 5
    01 October 2020
    Perspective
    Research Articles
      Alan N. Costa, Jeane R. Souza, Karyne M. Alves, Anderson Penna-Oliveira, Geisciele Paula-Silva, Ingrid S. Becker, Kelly Marinho-Vieira, Ana L. Bonfim, Alessandra Bartimachi and Ernane H. M. Vieira-Neto
      2020, 13 (5): 517-524.
      Abstract ( 26 )   PDF   Save
      Aims

      Litterfall at a global scale is affected by climate, edaphic features and vegetation structure, with litter production increasing from grasslands to forests following the rise in standing biomass. However, at landscape scales, the same relationship between litter production and vegetation structure has rarely been studied and comparisons of litterfall patterns between adjacent, structurally distinct communities are lacking. Here, we use a standardized methodology to describe the structural differences among four savanna physiognomies and analyze their relationship with changes in litterfall across the Cerrado.

      Methods

      We evaluated the woody vegetation structure and composition in 48 sites, equally distributed across four physiognomies and monitored the monthly litter production from April 2014 to March 2015.

      Important Findings

      Results showed that the density, basal area, cylindrical volume and aboveground biomass of woody vegetation differ among physiognomies, increasing consistently from cerrado ralocerrado típicocerrado denso and cerradão. Indeed, we found a strong and positive relationship between aboveground biomass and annual litter production, with litter yield increasing from 0.9 to 8.4 Mg ha−1 across different physiognomies, following the increment in vegetation structure. Monthly production was seasonal and similar among vegetation types, increasing during the dry season. Leaves comprised the dominant fraction (approx. 85%) and litterfall seasonality primarily resulted from the concentration of leaf shedding during dry months. However, the temporal pattern of litterfall throughout the year showed a gradual reduction in the seasonality from open to closed vegetation types, likely following the decrease of deciduous species abundance in the plant community. Our results showed that changes in vegetation structure may affect spatial and temporal litterfall patterns in different physiognomies, which co-occur across the Cerrado landscape, with potential implications for the overall functioning of this ecosystem. Moreover, these findings highlight the use of standardized methods as essential to correctly compare litterfall patterns among different environments.

      Tao Zhang, Zhihua Feng, Chunle Luo, Yixin Sun, Jinzhen Li, Juntian Xu and Xuchen Wang
      2020, 13 (5): 525-537.
      Abstract ( 17 )   PDF   Save
      Aims

      Salt marsh vegetation is an important contributor of dissolved organic matter (DOM) to coastal waters. The dynamics of DOM leaching from different marsh plants, however, have not been well studied or compared.

      Methods

      In this study, we conducted laboratory experiments to investigate the processes of DOM leaching from three common marsh plants (Phragmites australisSuaeda salsa and Aeluropus littoralis) collected from the Yellow River Delta (YRD) salt marsh in October 2016. The YRD is one of the largest and most well-protected coastal ecosystems on the east coast of China.

      Important Findings

      We found that the plant leaves released DOM at much higher concentrations than the plant roots or stems, as measured by the dissolved organic carbon (DOC) and dissolved nitrogen (DN). On average, 15% of the biomass C and 30% of the biomass N were released from the plant leaves as DOC and DN during the 27-day incubation period. The DOM released from the plants was very labile, and 92.4%–98.1% of the DOC and 88.0%–94.6% of the DN released from the plants were consumed by bacteria during the 27-day incubation period. The fluorescence characteristics of the plant-released DOM indicated that chromophoric dissolved organic matter was a major fraction of the DOM and that protein-like components were the primary organic fractions released from the plants. Bacterial degradation altered both the fluorescence properties and the chemical composition of the DOM. The results of the laboratory experiments were well supported by the field investigation, which indicated that a large amount of DOM was outwelled from the YRD salt marshes in late autumn. Our study suggests that the DOM released from the biomass of salt marsh plants provides an important source of both DOC and DN for marsh and coastal waters. The highly labile DOC and DN provide essential food sources to support microbial communities in the YRD salt marsh and adjacent coastal waters.

      Carolina Bravo, Daniel Chamorro, Fernando Hiraldo, Karina Speziale, Sergio A. Lambertucci, José L. Tella and Guillermo Blanco
      2020, 13 (5): 538-544.
      Abstract ( 29 )   PDF   Save
      Aims

      Seed dispersal by endozoochory is an important process in plant regeneration and the establishment of new populations. Seeds with dormancy may especially benefit after disperser gut passage. However, the ways in which gut passage affect the germination of plant species with physiological dormancy remain unclear. Here, we experimentally assessed the mutualistic interaction between the Austral parakeet (Enicognathus ferrugineus) as a disperser of calafate (Berberis microphylla), a thorny bush inhabiting the understory of the Austral temperate forests of South America with seeds that are characterized by deep physiological dormancy.

      Methods

      Germination success and viability of calafate seeds obtained from faeces and from intact fruits were tested under four treatments: (i) digested seeds, (ii) digested seeds with faecal extract, (iii) intact seeds from fruit and (iv) intact seeds from fruit with pulp.

      Important Findings

      About 65% of the Austral parakeet droppings contained calafate seeds. Viability of seeds did not differ between treatments. However, germination was significantly higher in digested seeds than in intact seeds from fruits, while no difference was found between faecal and pulp extracts. Neither faecal matter nor fruit pulp provided seeds with any ecological advantages derived from enhancing germinability, but did confer some disadvantage in germination time. Faecal matter is expected to be completely lacking around seeds after several months under snow before germinating in the following spring, given intense washing due to persistent rain and the spring thaw in the Patagonian Andes. The higher germinability along with faster germination of digested seeds supports the hypothesis of a legitimate mutualistic interaction between Austral parakeets and calafate. We hypothesized that the passage through the disperser digestive tract might break physiological dormancy as differences in germinability between ingested and non-ingested seeds. Our results highlight the relevant role of endozoochory in plant species with physiological dormancy living in highly seasonal environments.

      Senlin Yang, Jian Shi, Lianghua Chen, Jian Zhang, Danju Zhang, Zhenfeng Xu, Jiujin Xiao, Peng Zhu, Yang Liu, Tiantian Lin, Li Zhang, Hanbo Yang and Yu Zhong
      2020, 13 (5): 545-553.
      Abstract ( 31 )   PDF   Save
      Aims

      Although soil environments exist extensive heterogeneity for many plants with a wide range of distribution, researches about effects of soil conditions on plants’ tolerance and adaptation are particularly inadequate. In our study, the aims are to reveal physiological strategies of Populus deltoides against drought stress under different soil conditions and to select the most suitable soil type for Pdeltoides plantation.

      Methods

      Under controlled conditions, we used P. deltoides as a model species to detect differences in gas exchange rate, antioxidative capacity, nitrogen metabolism and biomass accumulation and partitioning in response to drought stress under three mineral soil types with distinct physicochemical characters, i.e. red soil (RS), yellow soil (YS) and yellow-brown soil (BS).

      Important Findings

      Exposure to 25% of field water holding capacity in soil for 3 months had significantly decreased biomass of all organs, photosynthetic rate, enzyme activities related to N assimilation, but increased H2O2, malondialdehyde and content of both NO3 and NH4+, when P. deltoideswas planted in both RS and YS. In contrast, under BS, there are slightly negative effects exerted by water deficit on total biomass, gas exchange rate, activities of enzymes related to nitrogen metabolism and membrane damage caused by reactive oxygen species, which can be associated with a consistent increase in superoxide dismutase, peroxidase and catalase, and a higher ratio of root mass to shoot mass. It is concluded that, such higher capacity in tolerance and adaptation against drought stress under BS relative to both RS and YS could be accounted for more sufficient nutrient provision in soil parental materials and better soil aeration conditions which play a vital role in plant acclimation to water shortage. Our study also revealed that, distribution areas of BS might be preferable for cultivation of Pdeltoides, when compared with those of RS and YS.

      Eamon Haughey, Jennifer C. McElwain and John A. Finn
      2020, 13 (5): 554-562.
      Abstract ( 29 )   PDF   Save
      Aims

      Research on the effects of extreme rainfall events on ecosystem function has primarily focussed on drought or flooding events, which usually include changes to mean or total rainfall, annually or over a season. However, less is known about the effects of increased rainfall variability without change to mean or total amounts. We investigated the effects of increased variation of water supply on shoot and root biomass as well as the distribution of root biomass of four grassland plant species, grown in monoculture and mixture communities.

      Methods

      Perennial ryegrass (Lolium perenne L., shallow-rooting grass), chicory (Cichorium intybus L., deep-rooting forb), white clover (Trifolium repens L., shallow-rooting legume) and red clover (Trifolium pratense L., deep-rooting legume) were established in mesocosms. Four plants of the same species were grown in monoculture communities and one of each species grown in four-species communities. Water supply was manipulated such that; compared with a baseline level with low variation in water supply, there was a treatment with medium variation (±40%) and another with high variation (±80%). Shoot and root biomass were measured, and vertical root distribution models fitted.

      Important Findings

      Compared with the low variation treatment, shoot biomass was significantly reduced under high variation for white clover, red clover and four-species communities. Under all conditions, four-species communities produced more shoot and root biomass than predicted by species performance in monoculture (overyielding). Under increased water variation, chicory monocultures allocated a higher proportion of root biomass to deeper soil layers while the total root biomass of white clover monocultures was significantly reduced. These results indicate that increased variability of water supply can negatively affect the shoot and root biomass production of single and multi-species grasslands. There is a need for further investigation of water variation effects on the functioning of multi-species grassland systems at field 

      Lei Yu, Haojie Dong, Zhijun Li, Zhanjiang Han, Helena Korpelainen and Chunyang Li
      2020, 13 (5): 563-573.
      Abstract ( 34 )   PDF   Save
      Aims

      Drought and salinity are severe abiotic stress factors, which limit plant growth and productivity, particularly in desert regions. In this study, we employed two desert poplars, Populus euphratica Oliver and Populus pruinosa Schrenk seedlings, to compare their tolerance to drought, salinity and combined stress.

      Methods

      We investigated species-specific responses of P. euphratica and P. pruinosa in growth, photosynthetic capacity and pigment contents, nonstructural carbohydrate concentrations, Cl allocation, osmotic regulation and the accumulation of reactive oxygen species (ROS) under drought, salinity and the combined stress.

      Important Findings

      Populus pruinosa exhibited greater growth inhibitory effects, photosynthesis decline, stomatal closure and ROS accumulation, and lower antioxidant enzyme activities and osmotic regulation compared with P. euphratica under drought, salinity and especially under their combined stress. On the other hand, salt-stressed P. euphratica plants restricted salt transportation from roots to leaves, and allocated more Cl to coarse roots and less to leaves, whereas salt-stressed P. pruinosa allocated more Cl to leaves. It was shown that there is species-specific variation in these two desert poplars, and P. pruinosa suffers greater negative effects compared with P. euphratica under drought, salinity and especially under the combined stress. Therefore, in ecological restoration and afforestation efforts, species-specific responses and tolerances of these two poplar species to drought and salinity should be considered under climate change with increasing drought and soil salinity developing.

      Yan Zhang, Xun Li, Danju Zhang, Yu Qin, Yang Zhou, Simeng Song and Jian Zhang
      2020, 13 (5): 574-588.
      Abstract ( 21 )   PDF   Save
      Aims

      The conifer litter is fairly recalcitrant and nutrient poor, and broadleaved litter promotes coniferous litter decomposition by increasing degradable nutrients and promoting microbial metabolism. Mixing Pinus massoniana litter and three broadleaved litters may increase the diversity and abundance of fungal decomposers compared with those in P. massoniana litter and vary depending on the number and proportion of broadleaved species included.

      Methods

      We analysed the composition and diversity of fungal communities during mixed litter decomposition in southwestern China with 35 treatments (P. massonianaToona sinensisCinnamomum camphora and Sassafras tzumu litter) using Illumina high-throughput sequencing.

      Important Findings

      The mixed litters increased fungal diversity and richness compared with those in the single-species litter, except in the following treatments: P. massoniana litter accounting for 70%–80% in the P. massoniana + T. sinensisP. massoniana + S. tzumu + T. sinensis and P. massoniana + S. tzumu + C. camphora combinations, and P. massoniana + S. tzumu + C. camphora + T. sinensis combination with small proportion of T. sinensis litter. The diversity and richness of the 7:1:2 combination of P. massoniana + C. camphora + T. sinensis were significantly higher than those in the other treatments. Ascomycota and Basidiomycota were the dominant phyla, and Aspergillus was the most abundant genus. The decomposition of litters from one needleleaf and one broadleaved species (6:4) and one needleleaf species and two broadleaved species (broadleaved litter accounting for 30%–40%) exhibited synergistic interactions throughout the decomposition process, and the relative abundance of fungi that decompose refractory substances increased. The P. massoniana + C. camphora + T. sinensis combination and a 30%–40% broadleaf litter proportion increased fungal diversity and accelerated the decomposition of recalcitrant coniferous litter. Therefore, C. camphora and T. sinensis are a potential candidate species for mixed planting with P. massoniana.

      Maurício Cruz Mantoani , Alberto Benavent González, Leopoldo García Sancho and Bruce Arthur Osborne
      2020, 13 (5): 589-600.
      Abstract ( 18 )   PDF   Save
      Aims

      Gunnera tinctoria is an unusual N-fixing plant species that has become invasive worldwide, generally in environments with a low evaporative demand and/or high rainfall. Amongst the many mechanisms that may explain its success as an introduced species, a contrasting phenology could be important but this may depend on an ability to grow and utilize nutrients under sub-optimal conditions. We examined whether G. tinctoria has an advantage in terms of a contrasting phenology and N-fixing capability, in comparisons with Juncus effusus, the native species most impacted by G. tinctoria invasions.

      Methods

      We made phenological assessments on a weekly or bi-weekly basis on long-established populations on Achill Island, Ireland, during 2016–2017. Data on leaf and inflorescence number, total leaf area, light interception and above-ground biomass were collected alongside measurements of soil temperature, moisture and oxidation–reduction potential. The significance of N-fixing ability for supporting seasonal growth was assessed using δ 15N isotopic assessments, together with in situ acetylene reduction measurements.

      Important Findings

      The timing of the initiation of growth of G. tinctoria and J. effusus varied between 2016 and 2017, with the earlier emergence and expansion of leaves of G. tinctoria, and the largest above-ground biomass associated with higher water availability. The early growth of G. tinctoria was dependent on preformed structures, with maximum canopy development occurring in late May, prior to that of J. effusus. Whilst N-fixation was observed in March, this made a more significant contribution to growth during the later stages of canopy development. Based on δ 15N isotopic analyses, early growth was predominantly associated with N-remobilization from the rhizomes, whilst seedlings were largely reliant on N-fixation. This emphasizes the importance of nutrient mobilization for early growth and shows that the importance of an N-fixing capability may vary developmentally, as well as during different stages of the invasion process.

      Chris M. McGrannachan, Gillis J. Horner and Melodie A. McGeoch
      2020, 13 (5): 601-610.
      Abstract ( 11 )   PDF   Save
      Aims

      Darwin’s naturalization hypothesis proposes that successfully established alien species are less closely related to native species due to differences in their ecological niches. Studies have provided support both for and against this hypothesis. One reason for this is the tendency for phylogenetic clustering between aliens and natives at broad spatial scales with overdispersion at fine scales. However, little is known about how the phylogenetic relatedness of alien species alters the phylogenetic structure of the communities they invade, and at which spatial scales effects may manifest. Here, we examine if invaded understorey plant communities, i.e. containing both native and alien taxa, are phylogenetically clustered or overdispersed, how relatedness changes with spatial scale and how aliens affect phylogenetic patterns in understorey communities.

      Methods

      Field surveys were conducted in dry forest understorey communities in south-east Australia at five spatial scales (1, 20, 500, 1500 and 4500 m2). Standardized effect sizes of two metrics were used to quantify phylogenetic relatedness between communities and their alien and native subcommunities, and to examine how phylogenetic patterns change with spatial scale: (i) mean pairwise distance and (ii) mean nearest taxon distance (MNTD).

      Important Findings

      Aliens were closely related to each other, and this relatedness tended to increase with scale. Native species and the full community exhibited either no clear pattern of relatedness with increasing spatial scale or were no different from random. At intermediate spatial scales (20–500 m2), the whole community tended towards random whereas the natives were strongly overdispersed and the alien subcommunity strongly clustered. This suggests that invasion by closely related aliens shifts community phylogenetic structure from overdispersed towards random. Aliens and natives were distantly related across spatial scales, supporting Darwin’s naturalization hypothesis, but only when phylogenetic distance was quantified as MNTD. Phylogenetic dissimilarity between aliens and natives increased with spatial scale, counter to expected patterns. Our findings suggest that the strong phylogenetic clustering of aliens is driven by human-mediated introductions involving closely related taxa that can establish and spread successfully. Unexpected scale-dependent patterns of phylogenetic relatedness may result from stochastic processes such as fire and dispersal events and suggest that competition and habitat filtering do not exclusively dominate phylogenetic relationships at fine and coarse spatial scales, respectively. Distinguishing between metrics that focus on different evolutionary depths is important, as different metrics can exhibit different scale-dependent patterns.

      Feng-Wei Xu, Jian-Jun Li, Li-Ji Wu, Xiao-Ming Lu, Wen Xing, Di-Ma Chen, Biao Zhu, Shao-Peng Wang, Lin Jiang and Yong-Fei Bai
      2020, 13 (5): 611-620.
      Abstract ( 23 )   Save
      Aims

      Long-term heavy grazing reduces plant diversity and ecosystem function by intensifying nitrogen (N) and water limitation. In contrast, the absence of biomass removal can cause species loss by elevating light competition and weakening community stability, which is exacerbated by N and water enrichment. Hence, how to maintain species diversity and community stability is still a huge challenge for sustainable management of worldwide grasslands.

      Methods

      We conducted a 4-year manipulated experiment in six long-term grazing blocks to explore combination of resource additions and biomass removal (increased water, N and light availability) on species richness and community stability in semiarid grasslands of Inner Mongolia, China.

      Important Findings

      In all blocks treated with the combination of resource additions and biomass removal, primary productivity increased and species richness and community stability were maintained over 4 years of experiment. At both species and plant functional group (PFG) levels, the aboveground biomass of treated plants remained temporally stable in treatments with the combination of N and/or water addition and biomass removal. The maintenance of species richness was primarily caused by the biomass removal, which could increase the amount of light exposure for grasses under resource enrichment. Both species asynchrony and stability of PFGs contributed to the high temporal stability observed in these communities. Our results indicate that management practices of combined resource enrichment with biomass removal, such as grazing or mowing, could not only enhance primary productivity but also maintain plant species diversity, species asynchrony and community stability. Furthermore, as overgrazing-induced degradation and resource enrichment-induced biodiversity loss continue to be major problems worldwide, our findings have important implications for adaptive management in semiarid grasslands and beyond.

      Kelly A. Steinberg, Kim D. Eichhorst and Jennifer A. Rudgers
      2020, 13 (5): 621-632.
      Abstract ( 3 )   Save
      Aims

      Determining the ecological consequences of interactions between slow changes in long-term climate means and amplified variability in climate is an important research frontier in plant ecology. We combined the recent approach of climate sensitivity functions with a revised hydrological ‘bucket model’ to improve predictions on how plant species will respond to changes in the mean and variance of groundwater resources.

      Methods

      We leveraged spatiotemporal variation in long-term datasets of riparian vegetation cover and groundwater levels to build the first groundwater sensitivity functions for common plant species of dryland riparian corridors. Our results demonstrate the value of this approach to identifying which plant species will thrive (or fail) in an increasingly variable climate layered with declining groundwater stores.

      Important Findings

      Riparian plant species differed in sensitivity to both the mean and variance in groundwater levels. Rio Grande cottonwood (Populus deltoides ssp. wislizenii) cover was predicted to decline with greater inter-annual groundwater variance, while coyote willow (Salix exigua) and other native wetland species were predicted to benefit from greater year-to-year variance. No non-native species were sensitive to groundwater variance, but patterns for Russian olive (Elaeagnus angustifolia) predict declines under deeper mean groundwater tables. Warm air temperatures modulated groundwater sensitivity for cottonwood, which was more sensitive to variability in groundwater in years/sites with warmer maximum temperatures than in cool sites/periods. Cottonwood cover declined most with greater intra-annual coefficients of variation (CV) in groundwater, but was not significantly correlated with inter-annual CV, perhaps due to the short time series (16 years) relative to cottonwood lifespan. In contrast, non-native tamarisk (Tamarix chinensis) cover increased with both intra- and inter-annual CV in groundwater. Altogether, our results predict that changes in groundwater variability and mean will affect riparian plant communities through the differential sensitivities of individual plant species to mean versus variance in groundwater stores.

      Xin Liu, Zhe Wang, Xiaoming Li and Weikai Bao
      2020, 13 (5): 633-640.
      Abstract ( 1 )   Save
      Aims

      Mosses are dominant in many ecosystems where nutrients from deposition are one of the main nutrient sources. However, it is difficult to evaluate mosses’ role in nutrient cycling without knowledge of how mosses use deposited nutrient inputs. To fill this gap, the present study aims to investigate: (i) how nitrogen (N) and phosphorus (P) concentrations of new-grown segments change along a gradient of N or P amount in a pulse treatment? (ii) how do a pulse of major nutrient (N or P) affect N or P translocation rate along a moss shoot? and (iii) to what extent do N or P translocation rates link to nutrient status of the new-grown segments of mosses?

      Methods

      We measured N and P concentrations of segments with different ages in two dominant forest floor mosses, Actinothuidium hookeri and Hylocomium splendens, on 8 days and 1 year after N and P pulse treatment with an in situ experiment in a subalpine fir forest in eastern Tibetan Plateau.

      Important Findings

      Both mosses were efficient in taking up nutrients from a pulse of either N or P. Nitrogen and P concentrations of new-grown segments were affected by nutrient pulse treatments. These N and P concentration changes were attributed to the initial N and P concentration of the young segments harvested 8 days after nutrient pulse treatments, suggesting that the captured nutrients were reallocated to the new-grown segments via translocation, which was largely controlled by a source–sink relationship. While no significant relationship was found between N translocation rate and N:P ratio of the new-grown segments, P translocation rate explained 21%–23% of the variance of N:P ratio of the new-grown segments, implying importance of P transport in supporting the new-grown sections. These results suggest that nutrient (N, P) translocation is a key process for mosses to utilize intermittent nutrient supply, and thus make mosses an important nutrient pool of the ecosystem.

      Lloyd W. Morrison, Sherry A. Leis and Michael D. DeBacker
      2020, 13 (5): 641-648.
      Abstract ( 1 )   Save
      Aims

      Observer error is an unavoidable aspect of vegetation surveys involving human observers. We quantified four components of interobserver error associated with long-term monitoring of prairie vegetation: overlooking error, misidentification error, cautious error and estimation error. We also evaluated the association of plot size with pseudoturnover due to observer error, and how documented pseudochanges in species composition and abundance compared with recorded changes in the vegetation over a 4-year interval.

      Methods

      This study was conducted at Tallgrass Prairie National Preserve, Kansas. Monitoring sites contained 10 plots; each plot consisted of a series of four nested frames (0.01, 0.1, 1 and 10 m2). The herbaceous species present were recorded in each of the nested frames, and foliar cover was visually estimated within seven cover categories at the 10 m2spatial scale only. Three hundred total plots (30 sites) were surveyed, and 28 plots selected at random were resurveyed to assess observer error. Four surveyors worked in teams of two.

      Important Findings

      At the 10 m2 spatial scale, pseudoturnover resulting from overlooking error averaged 18.6%, compared with 1.4% resulting from misidentification error and 0.6% resulting from cautious error. Pseudoturnover resulting from overlooking error increased as plot size decreased, although relocation error likely played a role. Recorded change in species composition over a 4-year interval (excluding potential misidentification error and cautious error) was 30.7%, which encompassed both pseudoturnover due to overlooking error and actual change. Given a documented overlooking error rate of 18.6%, this suggests the actual change for the 4-year period was only 12.1%. For estimation error, 26.2% of the time a different cover class was recorded. Over the 4-year interval, 46.9% of all records revealed different cover classes, suggesting that 56% of the records of change in cover between the two time periods were due to observer error.

      Xiao-Ni Xu, Jian-Yang Xia, Xu-Hui Zhou and Li-Ming Yan
      2020, 13 (5): 649-656.
      Abstract ( 1 )   Save
      Aims

      The functions of global forests are threatened by the increasing frequency of severe drought. Due to drought inducing reductions in soil nutrient availability, efficiencies of nutrient use and resorption of trees become crucial for forest functions and biogeochemical cycles. However, understanding the dynamics of responses of foliar nutrient use and resorption efficiencies to drought, especially in tropical or subtropical forests, is still limited. Our goal was to detect whether and how the importance of leaf nutrient use and resorption changes across different species in the hot and wet forests when suffering drought stress in different months.

      Methods

      Based on a 70% throughfall exclusion experiment in a subtropical forest, we collected green and senesced leaves of Schima superba and Lithocarpus glaber in different months from October 2016 to May 2019, to estimate the effects of drought on leaf nitrogen (N) and phosphorus (P) use and resorption efficiencies (i.e. NUE and PUE, NRE and PRE).

      Important Findings

      The effects of drought on nutrient use and resorption efficiencies varied between species and months. Based on a 2-year observation, drought had no effect on S. superba, but significantly decreased NUE, NRE and PRE of L. glaber by 3.4%, 20.2% and 7.1%, respectively. Furthermore, the negative drought effects were aggravated by the natural summer drying in 2017. As a result, NUE and PUE of L. glaber were significantly depressed by 17.2% and 58.1%, while NRE and PRE were significantly reduced by 56.5% and 53.8% in August 2017. Moreover, the responses of NRE, PRE and NUE to drought were related with soil moisture (SM) for L. glaber, and when SM decreased to a threshold near 9 v/v%, drought effects were shifted from unresponsive to negative. Our results highlight a species-specific threshold response of nutrient use under drought in a subtropical forest.

      Xiangping Wang , Tong Zeng, Mingsong Wu and Dianxiang Zhang
      2020, 13 (5): 657-666.
      Abstract ( 5 )   Save
      Aims

      Plant–pollinator interaction networks are dynamic entities, and seasonal variation in plant phenology can reshape their structure on both short and long timescales. However, such seasonal dynamics are rarely considered, especially for oceanic island pollination networks. Here, we assess changes in the temporal dynamics of plant–pollinator interactions in response to seasonal variation in floral resource richness in oceanic island communities.

      Methods

      We evaluated seasonal variations of pollination networks in the Yongxing Island community. Four temporal qualitative pollination networks were analyzed using plant–pollinator interaction data of the four seasons. We collected data on plant–pollinator interactions during two consecutive months in each of the four seasons. Four network-level indices were calculated to characterize the overall structure of the networks. Statistical analyses of community dissimilarity were used to compare this community across four seasons to explore the underlying factors driving these patterns. We also evaluated the temporal variation in two species-level indices of plant and pollinator functional groups.

      Important Findings

      Both network-level specialization and modularity showed a significantly opposite trend compared with plant species richness across four seasons. Increased numbers of plant species might promote greater competition among pollinators, leading to increased niche overlap and causing decreased specialization and modularity and vice versa. Further analyses suggested that the season-to-season turnover of interactions was dominated by interaction rewiring. Thus, the seasonal changes in niche overlap among pollinators lead to interaction rewiring, which drives interaction turnover in this community. Hawkmoths had higher values of specialization and Apidae had higher values of species strength compared with other pollinator functional groups. These findings should be considered when exploring plant–pollinator interactions in ecosystems of isolated oceanic islands and in other ecosystems.

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