Soil organic carbon (SOC) is primarily formed from plant inputs, but the relative carbon (C) contributions from living root inputs (i.e. rhizodeposits) vs litter inputs (i.e. root + shoot litter) are ...poorly understood. Recent theory suggests that living root inputs exert a disproportionate influence on SOC formation, but few field studies have explicitly tested this by separately tracking living root vs litter inputs as they move through the soil food web and into distinct SOC pools.
We used a manipulative field experiment with an annual C4 grass in a forest understory to differentially track its living root vs litter inputs into the soil and to assess net SOC formation over multiple years.
We show that living root inputs are 2–13 times more efficient than litter inputs in forming both slow-cycling, mineral-associated SOC as well as fast-cycling, particulate organic C. Furthermore, we demonstrate that living root inputs are more efficiently anabolized by the soil microbial community en route to the mineral-associated SOC pool (dubbed ‘the in vivo microbial turnover pathway’).
Overall, our findings provide support for the primacy of living root inputs in forming SOC. However, we also highlight the possibility of nonadditive effects of living root and litter inputs, which may deplete SOC pools despite greater SOC formation rates.
Arbuscular mycorrhizal fungi (AMF) can increase plant fitness under certain environmental conditions. Among the mechanisms that may drive this mutualism, the most studied is provisioning of nutrients ...by AMF in exchange for carbon from plant hosts. However, AMF may also provide a suite of non-nutritional benefits to plants including improved water uptake, disease resistance, plant chemical defense, soil aggregation, and allelochemical transport and protection. Here, we use a meta-analysis of 93 studies to assess the relative effect of AMF on nutritional and non-nutritional factors that may influence plant fitness. We find that the positive effects of AMF on soil aggregation, water flow and disease resistance are equal to the effect of AMF on plant nitrogen and phosphorus uptake. However, AMF had no effect on the uptake of other nutrients, plant water content, allelopathic transport or production of chemical defense compounds. We suggest future research directions, including experimentally assessing the relative contribution on plant fitness of AMF interactions by untangling the independence of alternative benefits of AMF from an increase in nutrient uptake. This will lead to a more holistic view of the mycorrhizal-plant association and a more accurate picture of the net impact on the plant or plant community in question.
The movement of species is one of the most pervasive forms of global change, and few ecosystems remain uninvaded by nonnative species. Studying species interactions is crucial for understanding their ...distribution and abundance, particularly for nonnative species because interactions may influence the probability of invasion and consequent ecological impact. Interactions among nonnatives are relatively understudied, though the likelihood of nonnative species co‐occurrence is high. We quantify and describe the types of interactions among nonnative plants and determine what factors affect interaction outcomes for ecosystems globally. We reviewed 65 studies comprising 201 observations and recorded the interaction type, traits of the interacting species, and study characteristics. We conducted a census of interaction types and a meta‐analysis of experiments that tested nonnative competition intensity. Both methods showed that negative and neutral interactions prevailed, and a number of studies reported that the removal of a dominant nonnative led to competitive release of other nonnatives. Positive interactions were less frequently reported and positive mean effect sizes were rare, but the plant characteristics nitrogen fixation, life cycle (annual or perennial), and functional group significantly influenced positive interactions. Positive interactions were three times more frequent when a neighboring nonnative was a nitrogen fixer and 3.5 times lower when a neighboring nonnative was an annual. Woody plants were two or four times more likely to have positive interactions relative to grasses or herbs, respectively. The prevalence of negative interactions suggests that managers should prepare for reinvasion of sites when treating dominant nonnatives. Though positive interactions were infrequent, managers may be able to anticipate positive interactions among nonnatives based upon traits of the co‐occurring invaders. Predicting positive nonnative interactions is an important tool for determining habitat susceptibility to a particular invasion and for prioritizing management of nonnatives with a higher likelihood of positive interactions.
Although there is abundant evidence that plant phenology is shifting with climatic warming, the magnitude and direction of these shifts can depend on the environmental context, plant species, and ...even the specific phenophase of study. These disparities have resulted in difficulties predicting future phenological shifts, detecting phenological mismatches and identifying other ecological consequences. Experimental warming studies are uniquely poised to help us understand how climate warming will impact plant phenology, and meta‐analyses allow us to expose broader trends from individual studies. Here, we review 70 studies comprised 1226 observations of plant phenology under experimental warming. We find that plants are advancing their early‐season phenophases (bud break, leaf‐out, and flowering) in response to warming while marginally delaying their late‐season phenophases (leaf coloration, leaf fall, and senescence). We find consistency in the magnitude of phenological shifts across latitude, elevation, and habitat types, whereas the effect of warming on nonnative annual plants is two times larger than the effect of warming on native perennial plants. Encouragingly for researchers, plant phenological responses were generally consistent across a variety of experimental warming methods. However, we found numerous gaps in the experimental warming literature, limiting our ability to predict the effects of warming on phenological shifts. In particular, studies outside of temperate ecosystems in the Northern Hemisphere, or those that focused on late‐season phenophases, annual plants, nonnative plants, or woody plants and grasses, were underrepresented in our data set. Future experimental warming studies could further refine our understanding of phenological responses to warming by setting up experiments outside of traditionally studied biogeographic zones and measuring multiple plant phenophases (especially late‐season phenophases) across species of varying origin, growth form, and life cycle.
Synthesizing data from seventy warming manipulations from around the world, we explore the impacts of warming on plant phenology across a range of environments and plant types. Plants are advancing early‐season phenophases (bud break, leaf‐out, and flowering) in response to warming, and do so consistently across latitude, elevation, and habitat types. However, the effect of warming on nonnative annual plants is two‐times larger than the effect of warming on native perennial plants. We also identify numerous gaps in the experimental warming literature that limit our ability to fully understand the effects of warming on phenological shifts.
Temperate understory plant species are at risk from climate change and anthropogenic threats that include increased deer herbivory, habitat loss, pollinator declines and mismatch, and nutrient ...pollution. Recent work suggests that spring ephemeral wildflowers may be at additional risk due to phenological mismatch with deciduous canopy trees. The study of this dynamic, commonly referred to as "phenological escape", and its sensitivity to spring temperature is limited to eastern North America. Here, we use herbarium specimens to show that phenological sensitivity to spring temperature is remarkably conserved for understory wildflowers across North America, Europe, and Asia, but that canopy trees in North America are significantly more sensitive to spring temperature compared to in Asia and Europe. We predict that advancing tree phenology will lead to decreasing spring light windows in North America while spring light windows will be maintained or even increase in Asia and Europe in response to projected climate warming.
► We ask if invasive plant impact studies adequately address on-the-ground invasion scenarios. ► We compare co-occurring invasive plants in conservation habitats vs. published studies. ► Over ...two-thirds of habitats were impacted by more than one invasive plant. ► Only 6% of published articles studied co-occurring invader interactions. ► We discuss the implications of this mismatch for management and applicability of research.
Though biological invasion studies have proliferated in recent decades, a consistent emphasis remains on the study of single-species invasions. Here, we juxtapose the number of invasive plants reported as co-occurring within conservation habitats in one of the most comprehensive global conservation management databases (The Nature Conservancy’s Conservation Projects) with the number of published studies that address impacts of co-occurring invasive plants. We reviewed 86 conservation projects and 153 peer-reviewed publications and found that only one-third of studies mentioned co-occurring invaders, although over two-thirds of habitats were multiply invaded, indicating researchers are more likely to study single invaders, even though conservation managers are more often faced with multiple invaders in a given habitat. Of those studies focused on multiple invasives, the majority did not attempt to differentiate impacts caused by species when found alone or with other invaders and instead either treated co-occurring invaders together as a single, undifferentiated group or compared impacts between invasive plant monocultures. Less than 6% of all studies analyzed invader interactions. The high prevalence of co-occurring invasive plants should encourage more research on multiple invaders, which may better inform prioritization of which species to manage. Specifically, we suggest research on how effects of multiple invaders differ from those of single invaders, what types of interactions (facilitative, competitive, neutral) are most commonly found between invaders, and what effects interactions might have on the overall impact (additive or non-additive) of the individual invader. Though we acknowledge the challenge of studying multiple invaders, there is a critical need to address these questions to make invasion research more relevant to conservation programs.
Long-term research in ecology and evolution Kuebbing, Sara E.; Reimer, Adam P.; Rosenthal, Seth A. ...
Ecological monographs,
20/May , Letnik:
88, Številka:
2
Journal Article
Recenzirano
Long-term research in ecology and evolution (LTREE) is considered fundamental for understanding complex ecological and evolutionary dynamics. However, others have argued for revision of LTREE efforts ...given perceived limitations in current research priorities and approaches. Yet most arguments about the benefits and failings of LTREE could be argued to reflect the views of only the limited number of scientists who have authored reports on the field, and not the wider community of ecological and evolutionary scientists. To more systematically and quantitatively assess the views of the community on LTREE contributions and future activities, we conducted and here report the results of a survey of ecological and evolutionary scientists at primarily U.S.-based institutions, completed by 1,179 respondents. The survey objectives were to (1) identify and prioritize research questions that are important to address through long-term, ecological field experiments and (2) understand the role that these experiments might play in generating and applying ecological and evolutionary knowledge. Almost 80% (𝑛 = 936) of respondents said that long-term experiments had contributed "a great deal" to ecological understanding. Compared to other research approaches (e.g., short-term, single-site, modeling, or lab), there was overwhelming support that multi-site, long-term research was very important for advancing theory, and that both observational and experimental approaches were required. Respondents identified a wide range of research questions for LTREE to address. The most common topic was the impact of global change (𝑛 = 1,352), likely because these processes play out over many years, requiring LTREE approaches to fully understand. Another recurrent theme was the potential of LTREE approaches to build evolutionary understanding across all levels of ecological organization. Critical obstacles preventing some scientists from engaging in LTREE included short-term funding mechanisms and fewer publications, whereas the longer-term value for advancing knowledge and an individual's career were widely recognized. Substantive advances in understanding ecological and evolutionary dynamics then seem likely to be made through engagement in long-term observational and experimental research. However, wider engagement seems dependent on a more supportive research environment and funding structure, through increased institutional acknowledgment of the contributions of long-term research, and greater program support during the establishment and maintenance of research.
1. Functional diversity (FD) metrics are widely used to assess invasion ecosystem impacts, but we have limited theory to predict how FD should respond to invasion. A key challenge to effectively ...using FD metrics is the complexity of conceptualizing alterations to multidimensional trait space, making it difficult to select a priori the most appropriate metric for specific ecological questions. 2. Here, we provide expectations on how invasion should change four commonly used FD metrics—functional richness (FRic), evenness (FEve), divergence (FDiv) and dispersion (FDis)—and then test these expectations in a laboratory decomposition experiment. We simulate invasion of a forest by understorey plants by adding leaf litter from 18 natives and non-natives to a representative canopy tree litter mixture to test changes in FD and decomposition. 3. All four metrics changed predictably with invasion. Species that were more functionally unique or when added at greater proportions had larger impacts on FD. Overall, FRic, FEve and FDiv were poor choices for understanding impacts of non-native species. FDis was the only metric that both changed predictably with addition of understorey litter and correlated intuitively with changes in carbon mineralization. Furthermore, ranking species based upon how much they changed FDis of the litter mixture provided a fair assessment of which species had the largest impact on decomposition. As such, functional dispersion may be a key tool for predicting a priori which non-natives will have the greatest impact on ecosystem processes. 4. Synthesis. We highlight the need to assess the suitability of each functional diversity metric for the specific ecological question at hand. Our work reveals the pitfalls of considering multiple metrics or randomly choosing a single metric without suitability assessments. At the same time, it suggests a framework for metric assessment that should help lead to selection of a metric or metrics that provide robust a priori insights into how invasion by non-native species can impact ecosystem processes.
Summary
Ericoid mycorrhizal (ErM) shrubs commonly occur in forest understories and could therefore alter arbuscular (AM) and/or ectomycorrhizal (EcM) tree effects on soil carbon and nitrogen ...dynamics. Specifically, ErM fungi have extensive organic matter decay capabilities, and ErM plant and fungal tissues have high concentrations of secondary compounds that can form persistent complexes in the soil. Together, these traits could contribute to organic matter accumulation and inorganic nutrient limitation. These effects could also differ in AM‐ vs EcM‐dominated stands at multiple scales within and among forest biomes by, for instance, altering fungal guild interactions. Most work on ErM effects in forests has been conducted in boreal forests dominated by EcM trees. However, ErM plants occur in c. 96, 69 and 29% of boreal, temperate and tropical forests, respectively. Within tropical montane forests, the effects of ErM plants could be particularly pronounced because their traits are more distinct from AM than EcM trees. Because ErM fungi can function as free‐living saprotrophs, they could also be more resilient to forest disturbances than obligate symbionts. Further consideration of ErM effects within and among forest biomes could improve our understanding of how cooccurring mycorrhizal types interact to collectively affect soil carbon and nitrogen dynamics under changing conditions.
Deciduous trees, shrubs and forest wildflowers may be advancing their leaf‐out phenology at different rates in response to a warming climate. A mismatch between understory and overstory phenology may ...lead to a reduction of understory light levels in the early spring, which is a critical period when many spring‐blooming wildflowers achieve highest photosynthetic rates. However, the extent of this phenomenon beyond a single site or region is largely unknown.
Using 3083 herbarium specimens collected between 1870 and 2019 across eastern North America, we assessed leaf‐out and flowering times of 10 tree species (6 native, 4 non‐native), 4 shrub species (2 native, 2 non‐native) and 7 wildflower species (6 native, 1 non‐native). We paired phenological data with historical climate data to quantify differences in phenological sensitivity to spring temperature across canopy strata, across species' geographical ranges and between native and non‐native species.
Predicted phenological mismatches between native trees and wildflowers differed across large spatial scales, with wildflower populations in warmer regions of North America more likely to be affected. Overall, native tree species leafed out 3.6 days earlier per °C spring warming, while native wildflower species advanced their flowering times by 3.2 days per °C, resulting in phenological mismatch as wildflowers experience fewer days before tree leaf‐out at warmer temperatures. Native trees and wildflowers in the warmer, southern part of their ranges advanced their spring phenology 2 and 1.5 times faster, respectively, than those in colder, northern locations. The phenological sensitivity of non‐native plants was less variable across their ranges. Non‐native trees and shrubs exhibited greater phenological sensitivity than native wildflowers. Notably, phenological sensitivities differed substantially among wildflower species, suggesting that certain species are more likely to be affected by phenological mismatch as climate warming progresses.
Synthesis: Our results provide new insight into novel phenological responses within and among species across a wide geographical range and the potential impact of competition and interactions with non‐native invasive species. This research highlights the value of newly‐available digitized museum collections in phenological research to cover longer time periods, wider spatial areas and a greater diversity of species than otherwise possible.
Our results provide new insight into phenological responses within and among species across a wide geographical range and the potential impact of competition and interactions with non‐native invasive species. This research highlights the value of newly‐available digitized museum collections in phenological research to cover longer time periods, wider spatial areas and a greater diversity of species than otherwise possible.
PDF
