Overcoming challenges on using native seeds for restoration of megadiverse resource‐poor environments: a reply to Madsen et al.

Madsen et al. (2016) reviewed several major limiting factors to establishment of seedlings in nonforest ecosystems (NFE), and proposed seed enhancement technologies to overcome these restoration barriers. However, biodiverse nutrient‐poor NFE present additional hurdles that preclude landscape‐scale seed‐based restoration and were not mentioned in their review. Here, we discuss issues related to native seed availability and provenance, and shortfalls in knowledge on seed quality testing and dormancy release that severely hamper restoration of degraded nutrient‐impoverished NFE. We present alternatives for overcoming these challenges and highlight the need for investments to find more practical and cost‐effective options for broad‐scale restoration.     

Nutrient addition does not increase the benefits of clonal integration in an invasive plant spreading from open patches into plant communities

• One benefit of clonal integration is that resource translocation between connected ramets enhances the growth of the ramets grown under stressful conditions, but whether such resource translocation reduces the performance of the ramets grown under favourable conditions has not produced consistent results. In this study, we tested the hypothesis that resource translocation to recipient ramets may reduce the performance of donor ramets when resources are limiting but not when resources are abundant.
• We grew Mikania micrantha stolon fragments (each consisting of two ramets, either connected or not connected) under spatially heterogeneous competition conditions such that the developmentally younger, distal ramets were grown in competition with a plant community and the developmentally older, proximal ramets were grown without competition. For half of the stolon fragments, slow‐release fertiliser pellets were applied to both the distal and proximal ramets.
• Under both the low and increased soil nutrient conditions, the biomass, leaf number and stolon length of the distal ramets were higher, and those of the proximal ramets were lower when the stolon internode was intact than when it was severed. For the whole clone, the biomass, leaf number and stolon length did not differ between the two connection treatments. Connection did not change the biomass of the plant communities competing with distal ramets of M. micrantha.
• Although clonal integration may promote the invasion of M. micrantha into plant communities, resource translocation to recipient ramets of M. micrantha will induce a cost to the donor ramets, even when resources are relatively abundant.

     

Community of small mammals along an elevational gradient in Biological Reserve of Serra do Japi,municipality of Jundiaí‐SP,Brazil

Studies of elevational gradients in forests are particularly interesting for the considerable differences that can be observed over short distances, such as in vegetation and temperature. Different taxonomic groups display varying types of distribution patterns along elevational gradients, with unimodal distribution being recognised as the most common pattern. The distribution of species can be affected by a range of factors that include, biotic, spatial, climatic, historic and energetic. Small mammals represent an ideal model for studies about distribution and habitat use as they can be highly abundant, tend to have different diets and use space differently. The aims of this study are to build a comprehensive understanding of the community of small mammals of the Biological Reserve of Serra do Japi and to explore its distribution pattern along elevational gradients. We investigated the influence of biomass of arthropods, fruits and seeds and percentage of ground cover, canopy cover and vertical vegetation at richness and abundance of small mammals at three different elevations. To accomplish this, we used seventy‐two pitfall traps of 63 L to capture small mammals and distributed them equally across three elevations defined as low (880–899 m), intermediate (1046–1089 m) and high (1170–1189 m). Each elevation had three lines or replicas of traps. Throughout the study, we captured one hundred and fourteen individuals belonging to eleven species of small mammals. The presence of rare and endemic species demonstrates the importance of conservation and maintenance of the Biological Reserve of Serra do Japi. In regard to the distribution of species, despite the short gradient range, we found a unimodal pattern and a positive correlation between ground cover (fallen twigs and branches up to 1 m high) and richness and abundance of small mammals. More ground cover can reduce the effects of competition and predation on small mammals’ communities. Abstract in Portuguese is available with online material.     

Substrate availability regulates the suppressive effects of Canada goldenrod invasion on soil respiration

基质有效性调节加拿大一枝黄花入侵对土壤呼吸的抑制作用 外来植物入侵不仅会降低河边近岸湿地生态系统植被多样性,而且会改变湿地生态系统的地下碳过程。外来入侵植物加拿大一枝黄花(Solidago canadensis L.)已广泛入侵我国东南部地区,但加拿大一枝黄花入侵对入侵地生态系统地下土壤碳循环过程的影响却知之甚少。本研究通过野外原位观测实验和温室模拟入侵实验,探究外来植物加拿大一枝黄花入侵对入侵地土壤呼吸的影响规律及其驱动因素。野 外原位观测实验开展于2018年7月21日至12月15日,期间每周测定样地土壤呼吸。温室模拟入侵实验开展于2019年7月15日至12月15日,期间每月1日与15日上午测定土壤呼吸、自养呼吸和异养呼吸。土壤呼吸、自养呼吸和异养呼吸通过静态箱结合深埋根系隔离法测定。野外原位观测实验和温室模拟入侵实验结果均显示,加拿大一枝黄花的入侵降低了土壤二氧化碳的排放通量。加拿大一枝黄花入侵对土壤呼吸的抑制作用可能归因于其入侵引起的土壤可利用底物质量与数量的变化,表明外来入侵植物加拿大一枝黄花可通过改变植物释放基质以及与本地植物和/或土壤微生物争夺土壤有效基质而影响土壤碳循环。这些研究结果对于评估外来入侵植物对入侵地地下碳动态的影响以及对全球变暖的贡献具有重要意义。     

Environmental resource deficit may drive the evolution of intraspecific trait variation in invasive plant populations

Intraspecific trait variation within natural populations (i.e. intra‐population trait variation, IPTV) is the basic source for selection and can have significant ecological consequences. Higher IPTV may increase a population's niche breath and benefit interspecies competition under a resource‐limited environment, thus affecting the ability of a species to move into novel habitats. However, the reciprocal influences of variation in environmental conditions and phenotypic trait expression in spreading plant populations are not clearly defined. We propose that during invasion, IPTV and its relative change in response to key resource enrichment may increase with the resource deficit of invaded sites, and that this relationship may facilitate plant invasions into resource‐limited environments. We analyzed the invasion trend, IPTV and its response to water enrichment, and moisture variability among populations of an annual grass Brachypodium hybridum in California, United States. We incorporated a genotyping‐by‐sequencing approach, a common garden experiment that had two water level treatments, and public plant and climate databases. Our hypothesis was supported by the observation that for populations that invaded sites with higher spring moisture deficit, both their seed biomass IPTV (for the water‐enriched treatment only) and relative change of the IPTV across water treatments were larger when examined in the common garden experiment. A generally north to south spreading direction was found in these B. hybridum populations, towards a drier and warmer climate exhibiting higher moisture deficit for plant growth. Our results suggest a role for interactions between IPTV (rather than trait means) and environmental resource availability in promoting plant invasions, providing new insights into the significance of IPTV in shaping plant geographic distributions.     

Genotype-specific response of a lycaenid herbivore to elevated carbon dioxide and phosphorus availability in calcareous grassland

Effects of elevated CO₂ and P availability on plant growth of the legume Lotus corniculatus and consequences for the butterfly larvae of Polyommatus icarus feeding on L. corniculatus were investigated in screen-aided CO₂ control chambers under natural conditions on a calcareous grassland in the Swiss Jura mountains. Elevated CO₂ conditions and P fertilisation increased the biomass production of L. corniculatus plants and affected the plant chemical composition. CO₂ enrichment increased the C/N ratio and sugar concentration and decreased the N and P concentrations. C- and N-based allelochemicals (cyanoglycosides, total polyphenols and condensed tannins) were only marginally affected by CO₂ enrichment. P fertilisation increased the specific leaf area and concentrations of water, N, sugar and P, while the C/N ratio and the concentration of total polyphenols decreased. Furthermore, P availability marginally enhanced the effect of elevated CO₂ on the total dry mass and sugar concentration while the opposite occurred for the total polyphenol concentration. The changes in food-plant chemistry as a result of P fertilisation positively affected larval mass gain and accelerated the development time of P. icarus. Only a marginal negative effect on larval mass gain was found for CO₂ enrichment. However, we found genotype-specific responses in the development time of P. icarus to elevated CO₂ conditions. Larvae originating from different mothers developed better either under elevated CO₂ or under ambient CO₂ but some did not react to CO₂ elevation. As far as we know this is the first finding of a genotype-specific response of an insect herbivore to elevated CO₂ which suggests genetic shifts in insect life history traits in response to elevated CO₂.     

An Exotic Tree Alters Decomposition and Nutrient Cycling in A Hawaiian Montane Forest

We evaluated the effects of the exotic tree Fraxinus uhdei on decomposition dynamics and nutrient turnover in a montane Hawaiian rainforest. We used reciprocal transplants of litterbags between forests dominated by Fraxinus and by the native Metrosideros polymorpha to distinguish between endogenous (litter quality) and exogenous (for example, microclimate, nutrient availability, microbial and invertebrate communities) effects of Fraxinus on mass loss and nutrient dynamics of decomposing litter. Fraxinus produced greater quantities of litter that was thinner, had higher N and P concentrations, and lower concentrations of lignin and soluble polyphenols. Microbes decomposing Fraxinus litter produced fewer enzymes involved in N and P acquisition and more of those involved in cellulose degradation. Differences in litter quality and microbial activity resulted in a strong effect of litter type on rates of mass loss, whereby Fraxinus litter decomposed and released nutrients at nearly twice the rate of Metrosideros litter (k=0.82 versus 0.48), regardless of site of decomposition. Although site of decomposition had no effect on rates of litter mass loss, Fraxinus litter decomposed under a Fraxinus canopy mineralized approximately 20% less P after one year than Fraxinus litter decomposed under a Metrosideros canopy. Furthermore, Fraxinus litter decomposed under a Fraxinus canopy immobilized greater amounts of N and P in the early stages of decay, suggesting that the large amounts of N and P in Fraxinus litterfall have raised nutrient availability to decomposers in the forest floor. Greater immobilization of N and P under a Fraxinus canopy may act as a governor on rates of nutrient cycling, limiting the degree to which Fraxinus invasion accelerates N and P cycling in this system.     

Reproductive decision-making in the termite, Cryptotermes secundus (Kalotermitidae), under variable food conditions

Relatedness concepts have dominated the discussion on the evolutionand maintenance of eusociality in social insects. In the diploidtermites, explanations based on relatedness asymmetries havebeen less relevant than in the Hymenoptera; ecological factorshave been claimed to be paramount. Yet, relevant quantitativestudies investigating the role of ecological factors are lacking.We examined the influence of ecological factors on reproductivetactics in the drywood termite, Cryptotermes secundus. In thisspecies, caste development is very flexible, with individualshaving the option to remain at the natal nest as helpers/workersor to develop into dispersing reproductives (sexuals). An importantecological factor expected to influence this "decision" is foodavailability; C. secundus nests in a piece of wood that servesas food and shelter, with individuals never leaving the nestto forage. Thus, a reduction in the amount of food parallelsa reduction in the nests' longevity. Therefore, we tested theinfluence of food availability on caste-developmental decisionsin natural colonies, as well as in two experiments in whichwe simulated a gradual and a sudden decline in the amount ofavailable food. In all trials dispersing sexuals occurred moreoften in colonies with diminished food resources than in colonieswith abundant suitable food. Thus, regardless of how food declines,individuals seem to switch their tactic from being a helperto becoming a dispersing reproductive if nest conditions deteriorateand the nests's longevity decline.     

Phenotypic plasticity and interpopulation differences in life history traits of<Emphasis Type="Italic"> Armadillidium vulgare</Emphasis> (Isopoda:Oniscidae)

The hypothesis that the balance of trade-offs between survivorship, growth and reproductive allocation in the terrestrial isopod Armadillidium vulgare will change when resource input is increased has been investigated experimentally. When the quality of food available was increased, by adding a mixture of litter from herbaceous dicotyledonous plants to a background low-quality food of dead grasses, survivorship was found to be the most phenotypically plastic trait, increasing by 168%. Growth rates increased by 99% but reproductive allocation by only 21%. In the field, members of a population from a site with more high-quality food grew more than twice as fast as those from a site where less high-quality food was available. The population from the site with higher food availability, contrary to predictions from the laboratory study, did not survive as well as that from the site with less available high-quality food. This may be because the site that is more favourable for growth has a more stressful physical environment due to much bigger temperature fluctuations, which are known to be an important cause of mortality in this species. When individuals from both populations were reared under controlled laboratory conditions, both the parental and F1 generations from the poor growth environment survived better than those from the good growth habitat. However, even when given an excess of high-quality food those from the poor growth environment continued to grow more slowly and had a lower reproductive allocation than those from the site with higher food availability. We conclude that microevolutionary changes may have occurred in the balance of resource allocation between survivorship, growth and reproductive allocation, to favour higher survivorship during the longer prereproductive period at the site where growth to the threshold size for reproduction takes longer.     

Mycorrhizal colonization mediated by species interactions in arctic tundra

The Alaskan tussock tundra is a strongly nutrient-limited ecosystem, where almost all vascular plant species are mycorrhizal. We established a long-term removal experiment to document effects of arctic plant species on ecto- and ericoid mycorrhizal fungi and to investigate whether species interactions and/or nutrient availability affect mycorrhizal colonization. The treatments applied were removal of Betula nana (Betulaceae, dominant deciduous shrub species), removal of Ledum palustre (Ericaceae, dominant evergreen shrub species), control (no removal), and each of these three treatments with the addition of fertilizer. After 3 years of Ledum removal and fertilization, we found that overall ectomycorrhizal colonization in Betula was significantly reduced. Changes in ectomycorrhizal morphotype composition in removal and fertilized treatments were also observed. These results suggest that the effect of Ledum on Betula 's mycorrhizal roots is due to sequestration of nutrients by Ledum, leading to reduced nutrient availability in the soil. In contrast, ericoid mycorrhizal colonization was not affected by fertilization, but the removal of Betula and to a lower degree of Ledum resulted in a reduction of ericoid mycorrhizal colonization suggesting a direct effect of these species on ericoid mycorrhizal colonization. Nutrient availability was only higher in fertilized treatments, but caution should be taken with the interpretation of these data as soil microbes may effectively compete with the ion exchange resins for the nutrients released by plant removal in these nutrient-limited soils.