Belowground Properties Research Articles

Destructive selective logging in tropical forests causes soil carbon loss through forest degradation and soil redox change

Soil organic C (SOC) stock in tropical forests can be reduced significantly after logging, not only due to lowered above ground biomass (AGB) and consequentially reduced organic matter (OM) input, but also consumption on sequestrated soil C protected by OM-mineral association. In this study, we studied the loss of mineral-associated OM after logging in the main rooting zone (e.g., 0–30 cm), and examined a hypothetical twofold underlying mechanism of SOC reduction: first, decrease in AGB limiting OM input; second, decrease in soil redox potential (Eh) leading to the reductive dissolution of short-range-ordered iron (SRO Fe) minerals that destabilize some mineral-associated OM. Thirty-five plots at different degradation levels were investigated for both above- and belowground properties. AGB and tree community composition were employed as indicators of forest degradation gradient; multiple physicochemical properties in top-30 cm soils were measured every 10 cm depth. We analysed the relationship between AGB and soil C with the mediator SRO Fe, and investigated the role of soil Eh in linking the changes in AGB and SRO Fe. Our results revealed simultaneous decreases in AGB, SRO Fe and soil C in top-30 cm soils, and SRO Fe mediated 43 % of the hypothetical causal effect of AGB on soil C in deeper (20–30 cm) soil. Soil Eh decreased with decreasing AGB in a logistic pattern, dropping to a reductive regime (Eh7 ≤ 0.05 V) when more than half of the AGB was removed from the pristine level. Mean SRO Fe stock in the reductive soils was significantly lower than that in the oxic soils (Eh7 > 0.05 V), and the loss of SRO Fe correspond to the decomposition of OM in 10–30 cm soils. We suggest that the reductive shift in soil is caused by the weakened evapotranspiration as destructive selective logging inflicts canopy openness and succession failure. This study presents the possibility that forest degradation may reduce the size of protected soil C pool resulting from the loss of soil SRO Fe minerals.

Grassland degradation-induced declines in soil fungal complexity reduce fungal community stability and ecosystem multifunctionality

Soil microorganisms are major regulators of ecosystem functioning and are under threat from human-induced disturbances. Among these threats is grassland degradation, which is estimated to affect 49% of the grassland area worldwide, threatening biodiversity and ecosystem functioning. Yet, we currently lack an understanding of how grassland degradation influences belowground microbial communities, their stability, and functioning, and how effective restoration efforts are for the recovery of these important belowground properties. Here, we assessed soil fungal network complexity and a suite of ecosystem functions along a well-characterised gradient of grassland degradation and restoration on the Qinghai-Tibetan Plateau, and conducted an accompanying microcosm experiment designed to test the effects of complexity on stability in soil fungal communities. We found that with increasing levels of grassland degradation, soil fungal communities became less complex and were less compositionally stable when confronted with drought under laboratory conditions. Moreover, this degradation-induced reduction in fungal community complexity was associated with lower ecosystem multifunctionality. However, fungal communities and ecosystem multifunctionality failed to recover even after ten years of grassland restoration. Our results indicate that degradation-induced simplification of fungal communities can potentially impair fungal community stability and ecosystem multifunctionality, thereby highlighting the need to protect and restore healthy grasslands with complex belowground microbial communities.

Soil microbial and chemical responses to foliar Epichloë fungal infection in Lolium perenne, Hordeum brevisubulatum and Achnatherum inebrians

We tested whether the host species identity in grass- Epichloë symbioses affected soil chemical and microbial properties. We grew endophyte infected (E+) and endophyte free (E−) Lolium perenne , Hordeum brevisubulatum and Achnatherum inebrians for 18 months in field plots. In E+ soil of all three grasses, available phosphorus was lower whereas total soil nitrogen was higher. Endophyte effects on soil pH, microbial biomass nitrogen, total carbon and organic carbon as well as bacteria and fungi abundance were host species dependent. Ammonia oxidizing bacteria abundance was higher in E+ soils for all species. Bacterial community composition of E+ and E− soils were different only for Lolium perenne with soil pH being the key factor. Fungal community composition of E+ and E− soils was not different for the three grasses. This study confirmed that the effects of foliar Epichloë infection on belowground properties depended on host species identity. • Foliar Epichloë infection (E+) affected soil properties differently between hosts. • Soil available phosphorous was higher in foliar Epichloë infection free (E−) soils. • Total nitrogen and ammonia oxidizing bacteria abundance were higher in E+ soils. • Bacterial diversity differed between E+ and E− perennial ryegrass soils. • Soil pH contributed the most to bacterial diversity variation.

Plant Responses to Climate Change and an Elevational Gradient in Mont Mégantic National Park, Québec, Canada

With steep climatic gradients over short distances, montane ecosystems provide exceptional opportunities to study ecological responses to climate and other environmental changes. Here we present a summary and synthesis of 10 years of research on this theme in a protected area in southern Québec, Canada (Parc National du Mont Mégantic), with ecological conditions closely similar to the northern Appalachians. During the ∼150 years since European settlement, anthropogenic disturbance has reduced the abundance of certain taxa (e.g., Picea [spruce]), while favoring other taxa that thrive during succession (e.g., Betula [birch], Acer [maple]). In more recent decades, climate warming (∼0.21 °C per decade) appears to have prompted upward elevational range shifts for many plant species, although such responses lag behind changes in climate itself. Experimental studies with seeds and seedlings of Acer saccharum (Sugar Maple) suggest that upward range expansion might be constrained by non-climatic factors such as belowground properties and seed predators, while escape from insect herbivores might actually accelerate range expansion. Similar studies with understory plants have not revealed clear evidence of non-climatic constraints on range limits, although some preliminary data presented here suggest a possible role of a lack of microsites with rich, moist soil at high elevation. Current studies focus on the lower elevational range limits of species restricted to mountaintops, such as certain lichens. Vegetation and flowering phenology are also sensitive to climate, and we have found that earlier springs are associated with decreased potential gene flow across populations at different elevations; ongoing studies will determine how differential sensitivity of herbs vs. trees might influence the duration of a high light period in spring in the understory. Overall, we have found clear signals of plant responses to long-term anthropogenic disturbances and recent climatic warming, but considerable uncertainty remains about how climatic and non-climatic factors will interact to determine the future of this montane ecosystem.

Evaluating long-term success in grassland restoration: an ecosystem multifunctionality approach.

It is generally assumed that restoring biodiversity will enhance diversity and ecosystem functioning. However, to date, it has rarely been evaluated whether and how restoration efforts manage to rebuild biodiversity and multiple ecosystem functions (ecosystem multifunctionality) simultaneously. Here, we quantified how three restoration methods of increasing intervention intensity (harvest only<topsoil removal<topsoil removal+propagule addition) affected grassland ecosystem multifunctionality 22yr after the restoration event. We compared restored with intensively managed and targeted seminatural grasslands based on 13 biotic and abiotic, above- and belowground properties. We found that all three restoration methods improved ecosystem multifunctionality compared to intensively managed grasslands and developed toward the targeted seminatural grasslands. However, whereas higher levels of intervention intensity reached ecosystem multifunctionality of targeted seminatural grasslands after 22yr, lower intervention missed this target. Moreover, we found that topsoil removal with and without seed addition accelerated the recovery of biotic and aboveground properties, and we found no negative long-term effects on abiotic or belowground properties despite removing the top layer of the soil. We also evaluated which ecosystem properties were the best indicators for restoration success in terms of accuracy and cost efficiency. Overall, we demonstrated that low-cost measures explained relatively more variation of ecosystem multifunctionality compared to high-cost measures. Plant species richness was the most accurate individual property in describing ecosystem multifunctionality, as it accounted for 54% of ecosystem multifunctionality at only 4% of the costs of our comprehensive multifunctionality approach. Plant species richness is the property that typically is used in restoration monitoring by conservation agencies. Vegetation structure, soil carbon storage and water-holding capacity together explained 70% of ecosystem multifunctionality at only twice the costs (8%) of plant species richness, which is, in our opinion, worth considering in future restoration monitoring projects. Hence, our findings provide a guideline for land managers how they could obtain an accurate estimate of aboveground-belowground ecosystem multifunctionality and restoration success in a highly cost-efficient way.

Contrasting responses of above- and below-ground herbivore communities along elevation

Above- and below-ground herbivory are key ecosystem processes that can be substantially altered by environmental changes. However, direct comparisons of the coupled variations of above- and below-ground herbivore communities along elevation gradients remain sparse. Here, we studied the variation in assemblages of two dominant groups of herbivores, namely, aboveground orthoptera and belowground nematodes, in grasslands along six elevation gradients in the Swiss Alps. By examining variations of community properties of herbivores and their food plants along montane clines, we sought to determine whether the structure and functional properties of these taxonomic groups change with elevation. We found that orthoptera decreased in both species richness and abundance with elevation. In contrast with aboveground herbivores, the taxonomic richness and the total abundance of nematode did not covary with elevation. We further found a stronger shift in above- than below-ground functional properties along elevation, where the mandibular strength of orthoptera matched a shift in leaf toughness. Nematodes showed a weaker pattern of declined sedentary behavior and increased mobility with elevation. In contrast to the direct exposal of aboveground organisms to the surface climate, conditions may be buffered belowground, which together with the influence of edaphic factors on the biodiversity of soil biota, may explain the differences between elevational patterns of above- and below-ground communities. Our study emphasizes the necessity to consider both the above- and below-ground compartments to understand the impact of current and future climatic variation on ecosystems, from a functional perspective of species interactions.

Thinning Partially Mitigates the Impact of Atlantic Forest Replacement by Pine Monocultures on the Soil Microbiome.

Forest replacement by exotic plantations drive important changes at the level of the overstory, understory and forest floor. In the Atlantic Forest of northern Argentina, large areas have been replaced by loblolly pine (Pinus taeda L.) monocultures. Plant and litter transformation, together with harvesting operations, change microclimatic conditions and edaphic properties. Management practices such as thinning promote the development of native understory vegetation and could counterbalance negative effects of forest replacement on soil. Here, the effects of pine plantations and thinning on physical, chemical and microbiological soil properties were assessed. Bacterial, archaeal, and fungal community structure were analyzed using a metabarcoding approach targeting ribosomal markers. Forest replacement and, to a lesser extent, thinning practices in the pine plantations induced significant changes in soil physico-chemical properties and associated shifts in bacterial and fungal communities. Most measured physical and chemical properties were altered due to forest replacement, but a few of these properties reached values similar to natural forests under the thinning operation. Fungal alpha diversity decreased in pine plantations, whereas bacterial alpha diversity tended to increase but with little statistical support. Shifts in community composition were observed for both fungal and bacterial domains, and were mostly related to changes in plant understory composition, soil carbon, organic matter, water content, pH and bulk density. Among several other changes, highly abundant phyla such as Proteobacteria (driven by many genera) and Mortierellomycota (mainly driven by Mortierella) decreased in relative abundance in the plantations, whereas Acidobacteria (mainly driven by Acidothermus and Candidatus Koribacter) and Basidiomycota (mainly driven by the ectomycorrhiza Russula) showed the opposite response. Taken together, these results provide insights into the effects of forest replacement on belowground properties and elucidate the potentially beneficial effect of thinning practices in intensive plantation systems through promoting the understory development. Although thinning did not entirely counterbalance the effects of forest replacement on physical, chemical and biological soil properties, the strategy helped mitigating the effects and might promote resilience of these properties by the end of the rotation cycle, if subsequent management practices compatible with the development of a native understory vegetation are applied.

Competing effects of soil fertility and toxicity on tropical greening

Tropical forests are expected to green up with increasing atmospheric CO2 concentrations, but primary productivity may be limited by soil nutrient availability. However, rarely have canopy-scale measurements been assessed against soil measurements in the tropics. Here, we sought to assess remotely sensed canopy greenness against steep soil nutrient gradients across 50 1-ha mature forest plots in Panama. Contrary to expectations, increases in in situ extractable soil phosphorus (P) and base cations (K, Mg) corresponded to declines in remotely sensed mean annual canopy greenness (r2 = 0.77–0.85; p < 0.1), controlling for precipitation. The reason for this inverse relationship appears to be that litterfall also increased with increasing soil P and cation availability (r2 = 0.88–0.98; p < 0.1), resulting in a decline in greenness with increasing annual litterfall (r2 = 0.94; p < 0.1). As such, greater soil nutrient availability corresponded to greater leaf turnover, resulting in decreased greenness. However, these decreases in greenness with increasing soil P and cations were countered by increases in greenness with increasing soil nitrogen (N) (r2 = 0.14; p < 0.1), which had no significant relationship with litterfall, likely reflecting a direct effect of soil N on leaf chlorophyll content, but not on litterfall rates. In addition, greenness increased with extractable soil aluminum (Al) (r2 = 0.97; p < 0.1), but Al had no significant relationship with litterfall, suggesting a physiological adaptation of plants to high levels of toxic metals. Thus, spatial gradients in canopy greenness are not necessarily positive indicators of soil nutrient scarcity. Using a novel remote sensing index of canopy greenness limitation, we assessed how observed greenness compares with potential greenness. We found a strong relationship with soil N only (r2 = 0.65; p < 0.1), suggesting that tropical canopy greenness in Panama is predominantly limited by soil N, even if plant productivity (e.g., litterfall) responds to rock-derived nutrients. Moreover, greenness limitation was also significantly correlated with fine root biomass and soil carbon stocks (r2 = 0.62–0.71; p < 0.1), suggesting a feedback from soil N to canopy greenness to soil carbon storage. Overall, these data point to the potential utility of a remote sensing product for assessing belowground properties in tropical ecosystems.

Temporal changes in the spatial variability of soil respiration in a meadow steppe: The role of abiotic and biotic factors

How and why spatial patterns of soil respiration (SR) emerge and change or persist over time, and what makes spatial patterning of SR and environment variables interdependent or non-interdependent, is poorly understood. Our objectives were to quantify temporal changes in spatial patterns of SR for a grassland dominated by Leymus chinensis and to explore the underlying ecological mechanisms. We conducted simultaneous measurements of SR, along with a suite of other aboveground and belowground properties, for 75 sampling points in May, July (when SR was measured twice due to a distinct temporal fluctuation in soil water content and higher temperatures) and September. No spatial structure was detected for SR in May. The degree of spatial dependence of SR in September was lower than on 17 July and 23 July, while the autocorrelation range for SR in September (7.2 m) was higher than on 17 July (1.7 m) and 23 July (3.8 m). SR was explained by soil physicochemical properties (soil organic carbon content, organic carbon:total nitrogen ratio and soil pH) in May, and soil pH was the most influential factor at this time. On 17 July, SR was explained by the combination of soil water content, bulk density, aboveground biomass, soil fungal:bacterial biomass ratio and C acquiring enzyme activity. Soil temperature, bulk density, soil electrical conductivity and aboveground biomass explained 53% of the spatial variability in SR on 23 July. SR was mostly controlled by soil temperature (positively) in September. These results indicated that the spatial patterns of SR varied remarkably across the four observations and evolved temporally as a result of seasonal shifts in environmental conditions and vegetation. Biological factors (e.g. plant and microbial biomass) were important determinants of the spatial pattern of SR in July, when the strongest spatial heterogeneity was observed.

Succession after reclamation: Identifying and assessing ecological indicators of forest recovery on reclaimed oil and natural gas well pads

Abstract Site preparation for oil and gas extraction often requires the complete removal of vegetation and surface soil on the well pad. Although subsequent reclamation then attempts to restore vegetation and soil properties on the well pad, given the magnitude of the extraction disturbance, the potential to shift its successional trajectory is high. The objectives of this study were to: i) assess successional recovery of vegetation and soil on decommissioned and reclaimed well pads and compare it with reference forest of varied successional stages, and ii) identify which above- and below-ground properties were influenced by reclamation and are thus useful ecological indicators for recovery towards forest. We sampled 30 study units in Alberta’s boreal forest; each site included a reclaimed well pad and adjacent reference site, with well pads ranging from 7 to 48 years post-reclamation. We conducted multivariate statistical analysis using 62 ecological above- and below-ground properties (e.g., percent cover of plant species, soil bulk density) categorized by: site type (reclaimed vs reference), natural subregion, forest stage, forest type, and time since reclamation. By grouping sites by site type, forest type, forest stage, and time since last disturbance, there was a clear separation of sites, with only two reclaimed well pads (7%) resembling plant community composition of reference areas, and 18 well pads (60%) resembling treeless grasslands, two of which were > 35 years post disturbance, indicating an arrested recovery trajectory. The remaining 33% of well pads are likely on a trajectory towards recovery. We found that reclamation had a significant effect on soil bulk density (E = 0.35), soil pH (E = 0.24), noxious plant species (E = 2.33), canopy cover (E = −0.26), grass cover (E = 0.16), woody cover (E = −0.18), LFH depth (E = −0.15), introduced species richness (E = 0.26), and live tree basal area (E = −0.17) after controlling for forest stage and time since disturbance. Our results indicate well pad impacts can be long lasting and may remain for decades or more post reclamation, potentially arresting their recovery trajectory.

Is there coordination of leaf and fine root traits at local scales? A test in temperate forest swamps.

Examining the coordination of leaf and fine root traits not only aids a better understanding of plant ecological strategies from a whole‐plant perspective, but also helps improve the prediction of belowground properties from aboveground traits. The relationships between leaf and fine root traits have been extensively explored at global and regional scales, but remain unclear at local scales. Here, we measured six pairs of analogous leaf and fine root traits related to resource economy and organ size for coexisting dominant and subordinate vascular plants at three successional stages of temperate forest swamps in Lingfeng National Nature Reserve in the Greater Hinggan Mountains, NE China. Leaf and fine root traits related to resource acquisition (e.g., specific leaf area [SLA], leaf N, leaf P, root water content, and root P) decreased with succession. Overall, we found strong linear relationships between leaf dry matter content (LDMC) and root water content, and between leaf and root C, N, and P concentrations, but only weak correlations were observed between leaf area and root diameter, and between SLA and specific root length (SRL). The strong relationships between LDMC and root water content and between leaf and root C, N, and P held at the early and late stages, but disappeared at the middle stage. Besides, C and P of leaves were significantly correlated with those of roots for woody plants, while strong linkages existed between LDMC and root water content and between leaf N and root N for herbaceous species. These results provided evidence for the existence of strong coordination between leaf and root traits at the local scale. Meanwhile, the leaf–root trait relationships could be modulated by successional stage and growth form, indicating the complexity of coordination of aboveground and belowground traits at the local scale.

Underneath it All: Soil Differences May Explain Contrasting Outcomes of Adjacent Prairie Restorations in Madison, Wisconsin

The evaluation of prairie restorations tends to focus on aboveground properties such as changes in plant diversity and the encroachment of non-native species. As a result, knowledge gaps persist concerning belowground controls of restoration success. To address these gaps at a 13-year-old prairie restoration site in Madison, Wisconsin, we spatially compared soil chemical, physical, and hydrological properties in two adjacent parcels that differed markedly in response to a tallgrass prairie restoration. We hypothesized that soil properties and their heterogeneity would differ significantly between the two parcels and that these differences would help explain the divergent response. In support of this hypothesis, soil organic matter, pH, and total nitrogen were significantly lower (p = 0.007, p &lt; 0.001, and p = 0.006, respectively) in the restored parcel compared to the parcel that has yet to respond to any restoration efforts. Moreover, despite no significant difference in soil average bulk density between the two parcels, the restored parcel had significantly lower sand and silt fractions overall (p = 0.039 and p = 0.040, respectively). In contrast, except for total nitrogen, there were no apparent differences in the spatial heterogeneity of the measured soil properties between the restored and unrestored parcels, which did not support the second hypothesis of this study. These results demonstrate the utility of measuring belowground properties when assessing unexpected outcomes of prairie restorations as well as inform future hypothesis-driven experiments to determine which soil properties impede restoration and under what circumstances. KEYWORDS: Prairie Restoration; Bulk Density; Soil Organic Matter; Soil Properties; Soil Texture; Spatial Heterogeneity

Plant-facilitated effects of exotic earthworm Pontoscolex corethrurus on the soil carbon and nitrogen dynamics and soil microbial community in a subtropical field ecosystem.

Earthworms and plants greatly affect belowground properties; however, their combined effects are more attractive based on the ecosystem scale in the field condition. To address this point, we manipulated earthworms (exotic endogeic species Pontoscolex corethrurus) and plants (living plants [native tree species Evodia lepta] and artificial plants) to investigate their combined effects on soil microorganisms, soil nutrients, and soil respiration in a subtropical forest. The manipulation of artificial plants aimed to simulate the physical effects of plants (e.g., shading and interception of water) such that the biological effects of plants could be evaluated separately. We found that relative to the controls, living plants but not artificial plants significantly increased the ratio of fungal to bacterial phospholipid fatty acids (PLFAs) and fungal PLFAs. Furthermore, earthworms plus living plants significantly increased the soil respiration and decreased the soil NH 4 +‐N, which indicates that the earthworm effects on the associated carbon, and nitrogen processes were greatly affected by living plants. The permutational multivariate analysis of variance results also indicated that living plants but not earthworms or artificial plants significantly changed the soil microbial community. Our results suggest that the effects of plants on soil microbes and associated soil properties in this study were largely explained by their biological rather than their physical effects.

How to Outgrow Your Native Neighbour? Belowground Changes under Native Shrubs at an Early Stage of Invasion

AbstractWhile it is acknowledged that invasive species are a global driver of land degradation, their effects are often only noticed when the invasion has been going on for a while. However, early stage processes must play a fundamental role in plant establishment until invasive plants are able to outgrow the native vegetation. In ten plots of 100 m2 each, we tested the hypothesis that belowground properties are associated with early invasion processes aboveground. We examined the early stage of invasion by a woody legume (Acacia longifolia), growing in the canopy of native dune shrubs (Corema album) as a model system in oligotrophic primary dunes in southern Portugal. Biomass under canopies of invaded and non‐invaded C. album shrubs as well as organic matter (OM) distribution in various soil fractions was measured. In accordance with our hypothesis, A. longifolia presence was related to increased C. album foliar δ15N, a proxy for nitrogen derived from the invasive legume. Under invaded canopies, root and rhizosphere biomass were higher, as was OM in the silt‐clay fraction. Also, δ15N of the OM in the silt‐clay fraction under invaded canopies was enriched, while δ13C was depleted. Finally, we found that the ratio between OM in the biotic versus soil compartment could be a good early indicator for invasion. These findings suggest that even when aboveground invasion pressure on the system is low, it is imperative for ecosystem conservation to remove young plants, as they might alter soil functioning already at an early stage of invasion. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Restoration and management for plant diversity enhances the rate of belowground ecosystem recovery.

The positive relationship between plant diversity and ecosystem functioning has been criticized for its applicability at large scales and in less controlled environments that are relevant to land management. To inform this gap between ecological theory and application, we compared recovery rates of belowground properties using two chronosequences consisting of continuously cultivated and independently restored fields with contrasting diversity management strategies: grasslands restored with high plant richness and managed for diversity with frequent burning (n=20) and grasslands restored with fewer species that were infrequently burned (n=15). Restoration and management for plant diversity resulted in 250% higher plant richness. Greater recovery of roots and more predictable recovery of the active microbial biomass across the high diversity management strategy chronosequence corresponded with faster recovery of soil structure. The high diversity grasslands also had greater nutrient conservation indicated by lower available inorganic nitrogen. Thus, mesic grasslands restored with more species and managed for high plant diversity with frequent burning enhances the rate of belowground ecosystem recovery from long-term disturbance at a scale relevant to conservation practices on the landscape.

Spatial Patterns of Soil Respiration Links Above and Belowground Processes along a Boreal Aspen Fire Chronosequence.

Fire in boreal ecosystems is known to affect CO2 efflux from forest soils, which is commonly termed soil respiration (Rs). However, there is limited information on how fire and recovery from this disturbance affects spatial variation in Rs. The main objective of this study was to quantify the spatial variability of Rs over the growing season in a boreal aspen (Populus tremuloides Michx.) fire chronosequence. The chronosequence included three stands in northern Alberta; a post fire stand (1 year old, PF), a stand at canopy closure (9 years old, CC), and a mature stand (72 years old, MA). Soil respiration, temperature and moisture were measured monthly from May to August using an intensive spatial sampling protocol (n = 42, minimum lag = 2 m). Key aboveground and belowground properties were measured one time at each sampling point. No spatial structure was detected in Rs of the PF stand during the peak growing season (June and July), whereas Rs was auto-correlated at a scale of < 6 m in the CC and MA stands. The PF stand had the lowest mean Rs (4.60 μmol C m-2 s-1) followed by the CC (5.41 μmol C m-2 s-1), and the MA (7.32 μmol C m-2 s-1) stand. Forest floor depth was the only aboveground factor that influenced the spatial pattern of Rs in all three stands and was strongest in the PF stand. Enzyme activity and fine root biomass, on the other hand, were the significant belowground factors driving the spatial pattern of Rs in the CC and MA stands. Persistent joint aboveground and belowground control on Rs in the CC and MA stands indicates a tight spatial coupling, which was not observed in the PF stand. Overall, the current study suggests that fire in the boreal aspen ecosystem alters the spatial structure of Rs and that fine scale heterogeneity develops quickly as stands reach the canopy closure phase (<10 years).

Ground penetrating radar for underground sensing in agriculture: a review

AbstractBelowground properties strongly affect agricultural productivity. Traditional methods for quantifying belowground properties are destructive, labor-intensive and pointbased. Ground penetrating radar can provide non-invasive, areal, and repeatable underground measurements. This article reviews the application of ground penetrating radar for soil and root measurements and discusses potential approaches to overcome challenges facing ground penetrating radar-based sensing in agriculture, especially for soil physical characteristics and crop root measurements. Though advanced data-analysis has been developed for ground penetrating radar-based sensing of soil moisture and soil clay content in civil engineering and geosciences, it has not been used widely in agricultural research. Also, past studies using ground penetrating radar in root research have been focused mainly on coarse root measurement. Currently, it is difficult to measure individual crop roots directly using ground penetrating radar, but it is possible to sense root cohorts within a soil volume grid as a functional constituent modifying bulk soil dielectric permittivity. Alternatively, ground penetrating radarbased sensing of soil water content, soil nutrition and texture can be utilized to inversely estimate root development by coupling soil water flow modeling with the seasonality of plant root growth patterns. Further benefits of ground penetrating radar applications in agriculture rely on the knowledge, discovery, and integration among differing disciplines adapted to research in agricultural management.

Effect of soil moisture and atmospheric humidity on both plant productivity and diversity of native grasslands across the Loess Plateau, China

Water is a key element in building and maintaining regional ecosystems functions, particularly in arid and semi-arid regions, in which ecosystem productivity, surface energy balance, and water availability are closely interconnected. However, the effects of differences in soil moisture levels at different depths and humidity index involved MAT and MAP on plant diversity have received only scant attention. To determine effects of soil moisture and humidity index on both plant productivity and diversity of native grasslands on the Loess Plateau, China, a gradient analysis of soil moisture and above- and below-ground properties of plant communities showed that vegetation cover and above- and below-ground biomass were significantly and positively correlated to the levels of soil moisture. More specifically, the below-ground biomass was significantly and positively correlated to moisture in the top 10cm layer of soil, whereas plant height, litter biomass, and root-to-shoot ratio were unrelated to the level of soil moisture. Plant diversity (richness index and the Shannon–Wiener diversity index) was significantly and positively correlated to a greater degree with moisture in the topsoil (0–5cm layer) than in the subsoil, and was also closely correlated to the humidity index. Overall, changes in plant diversity in arid and semi-arid grassland ecosystems are closely determined by soil moisture and atmospheric humidity, and that higher moisture content in soil and higher atmospheric humidity favour greater plant diversity.

Changes in aboveground and belowground properties during secondary natural succession of a cool-temperate forest in Japan

Forest development in temperate regions is considered to be a global carbon sink. Many studies have examined forest development after harvesting or fire from aboveground (e.g., biomass) or belowground (e.g., soil nutrient) perspectives. However, few studies have explored forest development from both perspectives simultaneously in cool-temperate forests in Japan. In this study, we examined changes over 105 years in both aboveground and belowground components during secondary natural succession. The aboveground biomass increased for 50 years and reached a plateau in a 105-year-old stand. The N mineralization rate increased during succession for 50 years, but showed a decline in the 105-year-old stand due to the decrease in the nitrification rate in late succession. The percent nitrification (i.e., relative contribution of nitrification to N mineralization) decreased significantly with increasing forest stand age. The N mineralization rates had significant relationships with N concentrations of the dominant tree foliage and litter fall and with the amount of litter fall N. Meanwhile, other belowground properties (i.e., soil pH, phenol concentration, soil microbial respiration, and litter mass loss) did not show any significant relationship with forest stand age. This may be because the soil at the study sites was heterogeneous and consisted of Cambisols and Andosols, the latter of which originally has high organic matter content, and thus may have buffered the effect of the aboveground development. These results indicate that belowground N dynamics are more closely associated with aboveground development than other belowground properties in these forests.

Warm‐season Grazing Benefits Species Diversity Conservation and Topsoil Nutrient Sequestration in Alpine Meadow

AbstractSeasonal grazing is one way of the moderate grazing regimes, but little information is available on compared study of seasonal grazing in alpine meadow. We studied the aboveground and belowground properties among warm‐seasonal grazing meadows and cold‐seasonal grazing meadows on the Qinghai–Tibetan Plateau. Results showed that the warm‐seasonal grazing increased forb functional group proportion, plant density and evenness index but decreased root biomass, plant height and graminoid functional group proportions. Grazing seasons affected variation in soil bulk density, soil water content, pH and soil nutrient content, and the variations caused the various of soil carbon and nitrogen density. The highest values of soil carbon and nitrogen contents and densities in the warm‐season grazing meadow occurred at the top 10‐cm soil, while the highest values in the cold‐season grazing meadow occurred at the depth of 30‐ to 50‐cm soil. Our results indicated that the warm‐season grazing is suitable for the species diversity conservation and the nutrient sequestration at the topsoil. However, the cold‐season grazing is suitable for the nutrient sequestration at the deep soil. This study implied that the warm‐season and cold‐season grazing might be exchanged regularly to practice continuous carbon and nitrogen sequestration. Periodic cold‐season and warm‐season grazing would be the suitable grazing regime to keep alpine meadow sustainability. Copyright © 2016 John Wiley &amp; Sons, Ltd.