Nutrient cycling through leaf litter consumption is an essential ecological function performed by macrodetritivorous invertebrates such as isopods and millipedes. Leaf litter consumption rates can vary greatly depending on the environment, consumer identity and litter traits, but generalizations about the effects of plant traits on macrodetritivore leaf litter consumption, assimilation and growth are not well established and are mostly indirectly inferred. We conducted a systematic search of the global literature and obtained 456 standardized measures from laboratory experiments of relative consumption (RCR), assimilation (RAR) and growth (RGR) rates of terrestrial isopods and millipedes, extracted from 56 different articles. We investigated if commonly measured leaf traits, plant functional groups, prior microbial conditioning of leaves and climatic conditions affected these rates. We obtained data on commonly measured leaf traits from the TRY global plant trait database, inferred plant functional groups from taxonomic groupings and obtained climatic data from information reported within articles. RCR, RAR and RGR varied greatly among macrodetritivore and plant species, but overall, there were no differences between isopods and millipedes. Microbial conditioning of litter greatly increased RCR. Plant functional group was an important predictor of RCR, with eudicot trees and forbs being consumed in greater quantities than magnoliid trees and grasses. Fresh leaf N:P ratio had a positive effect on RAR, and leaf N and C:N ratio had positive and negative effects on RGR, respectively, while climatic variables had weak effects on the three rates. Our work shows that plant traits (both those associated with plant functional groups and commonly measured leaf traits) exert strong effects on resource processing rates by terrestrial macrodetritivores. Further, prior microbial conditioning of leaf litter has a large and globally consistent positive effect on macrodetritivore litter consumption, suggesting that they may consume little, if any, freshly senesced leaf material when microbially conditioned litter is available. Our results suggest that, where extremes of temperature or precipitation do not occur, variables reflective of food quality (leaf traits and microbe conditioning) are more important drivers of macrodetritivore leaf litter consumption than are extrinsic climatic variables. Read the free Plain Language Summary for this article on the Journal blog.
Study islands, showing from which islands each plant species was collected.
No abstract is provided for this article.
Five weed management strategies (sawdust mulching, repeated spring-summer cultivation, hand-hoeing and two herbicide treatments) were applied to each of two cropping systems (maize and asparagus) near Hamilton, New Zealand. Assessments of the response of microbial activity and biomass were made over an entire annual cropping cycle (from August 1990 to October 1991). Soil respiration and substrate-induced respiration (SIR) were strongly stimulated by sawdust mulch over the experimental period, probably as a result of the enhanced soil moisture status, but the other treatments did not exert any strong consistent effects. Use of the selective inhibitor technique demonstrated temporary stimulatory effects of mulching, cultivation and (occasionally) herbicide application on both the bacterial and fungal components of the soil system. The fumigation-incubation technique also suggested that mulching had stimulatory effects on microbial activity and biomass but only when control values were not subtracted. Most of the effects detected occurred in the top 5 cm of the mineral soil. Placement of litter-bags on the surface and at 10cm depth indicated that litter decomposition was often most rapid in the sawdustmulched plots, probably as a result of enhanced abiotic decomposition. Soil respiration and SIR were also greatest for the litter placed on the mulched plots, over most of the annual cropping cycle. We concluded that weed management strategies which influence soil moisture contents are likely to induce the most significant responses by the soil microflora.
Ecologists have studied plant succession for over a hundred years, yet our understanding of the nature of this process is incomplete, particularly in relation to its response to new human perturbations and the need to manipulate it during ecological restoration. We demonstrate how plant succession can be understood better when it is placed in the broadest possible temporal context. We further show how plant succession can be central to the development of a framework that integrates a spectrum of ecological processes, which occur over time scales ranging from seconds to millions of years. This novel framework helps us understand the impacts of human perturbations on successional trajectories, ecosystem recovery, and global environmental change.
Wildfire disturbance is important for tree regeneration in boreal ecosystems. A considerable amount of literature has been published on how wildfires affect boreal forest regeneration. However, we lack understanding about how soil-mediated effects of fire disturbance on seedlings occur via soil abiotic properties versus soil biota. We collected soil from stands with three different severities of burning (high, low and unburned) and conducted two greenhouse experiments to explore how seedlings of tree species ( Betula pendula , Pinus sylvestris and Picea abies ) performed in live soils and in sterilized soil inoculated by live soil from each of the three burning severities. Seedlings grown in live soil grew best in unburned soil. When sterilized soils were reinoculated with live soil, seedlings of P. abies and P. sylvestris grew better in soil from low burn severity stands than soil from either high severity or unburned stands, demonstrating that fire disturbance may favor post-fire regeneration of conifers in part due to the presence of soil biota that persists when fire severity is low or recovers quickly post-fire. Betula pendula did not respond to soil biota and was instead driven by changes in abiotic soil properties following fire. Our study provides strong evidence that high fire severity creates soil conditions that are adverse for seedling regeneration, but that low burn severity promotes soil biota that stimulates growth and potential regeneration of conifers. It also shows that species-specific responses to abiotic and biotic soil characteristics are altered by variation in fire severity. This has important implications for tree regeneration because it points to the role of plant–soil–microbial feedbacks in promoting successful establishment, and potentially successional trajectories and species dominance in boreal forests in the future as fire regimes become increasingly severe through climate change.
In all terrestrial ecosystems, plant‐derived resources mainly enter the belowground subsystem in two ways – as dead plant parts (i.e. organic substrates) and as resources released from the rhizosphere of live plants. While the effects of identity of live plants or dead plant parts on aboveground and belowground properties have been well studied, much remains unknown about the effects of combinations of live plant species and dead plant‐derived substrates. In particular, no study to date has experimentally investigated the effects of simultaneously varying the composition or diversity of both live plants and dead plant parts. We performed a pot experiment consisting of a full factorial of 12 organic substrate addition treatments by eight live plant treatments, in which the composition and diversity of both substrates and live plants were varied. The 12 substrate treatments consisted of no substrates added, each of the four substrates represented singly (four treatments), each of the possible pairwise combinations of the four substrates (six treatments), and all four substrates added together. As expected, substrate and live plant identity both had important effects both above‐ and belowground. Mixtures of plant species always had effects that could be explained by the effects of the component plant species grown singly. Usually mixtures of substrates also had effects that could be predicted by the effects of component substrates added singly, but there were instances in which mixtures of certain substrates (notably mixtures containing Populus tremula leaf litter) had synergistic effects both belowground and aboveground, with especially strong effects on the growth of Pinus sylvestris seedlings. However, there was never any evidence of interactive effects between live plant species diversity or composition and added substrate diversity or composition, either aboveground or belowground. This means that whatever effects added substrates have on ecological properties operates independently of the influence of live plants, and vice versa. In total, this study shows that most resources entering the belowground subsystem have effects that are independent of the effects of other resources, though there are isolated instances in which strong (and potentially ecologically meaningful) synergistic interactions may occur for specific combinations of dead organic substrates.
Summary Several theories predict that increasing stress (e.g. decreasing nutrient availability or decreasing temperature) should result in higher amounts of plant phenolic compounds both at the interspecific and intraspecific levels. Further, several theories predict that plant phenolics are major drivers of plant–soil feedbacks whereby they influence litter decomposition rates and the return of nutrients to plants. We investigated the potential influence of shifts in abiotic factors on litter phenolic properties using an elevational gradient in northern S weden, for which temperature and soil fertility decline with increasing elevation. The system consists of two vegetation types: heath, (associated with low soil fertility) and meadow (associated with higher fertility), which occur across the entire gradient. We hypothesized that total phenolics, tannins and protein complexation capacity ( PCC ) of leaf litter would increase with elevation within and among plant species. We further hypothesized that at the whole‐plot level (using community‐weighted averages), these properties would be higher in heath than meadow, and that phenolic properties for meadow vegetation would show stronger responses to elevation than for heath. We measured phenolic properties in leaf litter for 13 species from both vegetation types across an established elevational gradient (500–1000 m) in S wedish subarctic tundra. Contrary to our hypotheses, different species showed highly contrasting responses in their phenolic characteristics to elevation. At the across‐species level, total phenolic content in litter decreased with elevation. At the whole‐plot level, tannin concentrations were higher for the heath than for the meadow, whereas total phenolics and PCC did not differ. However, consistent with our hypothesis, our results showed that phenolic properties were more responsive to elevation for the meadow compared to the heath, as a consequence of greater species turnover for the meadow. Our results are inconsistent with theories predicting higher plant phenolic concentrations with increasing environmental stress or decreasing nutrient availability. They also provide evidence that across abiotic gradients in the subarctic tundra, there are large shifts in litter phenolic properties (including those that are able to complex protein) and highlight that the direction and strength of such shifts may differ greatly among vegetation types.
Invasive species are a global problem but most studies have focused on their direct rather than indirect ecological effects. We studied litter and soil‐inhabiting invertebrate communities on 18 islands off northern New Zealand, to better understand the indirect ecological consequences of rat ( Rattus ) invasion. Nine islands host high densities of burrowing procellariid seabirds that transport large amounts of nutrients from the ocean to the land. The other nine have been invaded over the past 50–150 years by rat species that have severely reduced the density of seabirds by preying on eggs and chicks. Invaded islands had lower densities of seabird burrows but deeper forest litter than did the uninvaded islands, indicative of rats reducing disturbance effects of seabirds. However, despite deeper litter on the invaded islands, eight of the 19 orders of invertebrates that we measured were significantly less abundant on invaded islands. Furthermore, three soil‐inhabiting micro‐invertebrate groups that we measured were significantly less abundant on invaded islands. These differences probably result from rats thwarting transfer of resources by seabirds from the ocean to the land. We also investigated community‐level properties of each of three test groups of invertebrates (minute land snails, spiders and soil nematodes) to illustrate this process. Spiders were equally abundant on both groups of islands, but showed lower species richness on the invaded islands. The other two groups showed no difference in species richness with island invasion status, but were more abundant on uninvaded islands. Reduced abundance of soil nematodes on invaded islands provides strong evidence of indirect consequences of seabird reduction by rats, because nematodes are unavailable to rats as prey. We predict that if rats are eradicated from islands, components of below‐ground invertebrate dependent on seabird‐mediated soil conditions may take considerable time to recover because they require subsequent seabird recolonisation.
No abstract is provided for this article.
Old growth forests that have not experienced significant disturbance for several millennia often undergo ‘ecosystem retrogression’, which is characterised by reduced availability of key nutrients and a large decline in aboveground productivity. In this...
Two post-emergence herbicides (glyphosate and 2,4-D) were applied at field application levels to tilled field plots in a mixed cropping area in south-centr
