Responses of soil fauna communities to the individual and combined effects of multiple global change factors.

Soil fauna plays a key role in regulating biogeochemical cycles, but how multiple global change factors (GCFs) may affect faunal communities remains poorly studied. We conducted a meta-analysis using 1154 observations to evaluate the individual and combined effects of elevated CO2 , nitrogen (N) addition, warming, increased rainfall and drought on soil fauna density and diversity. Here we show that, overall, individual and combined effects of GCFs had negligible effects on soil fauna density and diversity, except that density was negatively affected by drought (-27.4%) and positively affected by increased rainfall individually (+24.9%) and in combination with N addition (+67.3%) or warming (+70.4%). GCF effects varied among taxonomic groups both in magnitude and direction. Variables such as latitude, elevation and experimental setting significantly impacted both individual and combined effects. Our results suggest that soil fauna density is affected by changed rainfall regimes, while diversity is resistant against individual and combined effects of multiple GCFs.

Global patterns and drivers of rainfall partitioning by trees and shrubs.

Spatiotemporal redistribution of incident rainfall in vegetated ecosystems results from the partitioning by plants into intercepted, stemflow, and throughfall fractions. However, variation in patterns and drivers of rainfall partitioning across global biomes remains poorly understood, which limited the ability of climate models to improve the predictions of biome hydrological cycle under global climate change scenario. Here, we synthesized and analyzed the partitioning of incident rainfall into interception, stemflow, and throughfall by trees and shrubs at the global scale using 2430 observations from 236 independent publications. We found that (1) globally, median levels of relative interception, stemflow, and throughfall accounted for 21.8%, 3.2%, and 73.0% of total incident rainfall, respectively; (2) rainfall partitioning varied among different biomes, due to variation in plant composition, canopy structure, and macroclimate; (3) relative stemflow tended to be driven by plant traits, such as crown height:width ratio, basal area, and height, while relative interception and throughfall tended to be driven by plant traits as well as meteorological variables. Our global assessment of patterns and drivers of rainfall partitioning underpins the role of meteorological factors and plant traits in biome-specific ecohydrological cycles. We suggest to include these factors in climate models to improve the predictions of local hydrological cycles and associated biodiversity and function responses to changing climate conditions.

Influence of multiple global change drivers on terrestrial carbon storage: additive effects are common.

The interactive effects of multiple global change drivers on terrestrial carbon (C) storage remain poorly understood. Here, we synthesise data from 633 published studies to show how the interactive effects of multiple drivers are generally additive (i.e. not differing from the sum of their individual effects) rather than synergistic or antagonistic. We further show that (1) elevated CO2 , warming, N addition, P addition and increased rainfall, all exerted positive individual effects on plant C pools at both single-plant and plant-community levels; (2) plant C pool responses to individual or combined effects of multiple drivers are seldom scale-dependent (i.e. not differing from single-plant to plant-community levels) and (3) soil and microbial biomass C pools are significantly less sensitive than plant C pools to individual or combined effects. We provide a quantitative basis for integrating additive effects of multiple global change drivers into future assessments of the C storage ability of terrestrial ecosystems.

Effects of three global change drivers on terrestrial C:N:P stoichiometry: a global synthesis.

Over the last few decades, there has been an increasing number of controlled-manipulative experiments to investigate how plants and soils might respond to global change. These experiments typically examined the effects of each of three global change drivers [i.e., nitrogen (N) deposition, warming, and elevated CO2 ] on primary productivity and on the biogeochemistry of carbon (C), N, and phosphorus (P) across different terrestrial ecosystems. Here, we capitalize on this large amount of information by performing a comprehensive meta-analysis (>2000 case studies worldwide) to address how C:N:P stoichiometry of plants, soils, and soil microbial biomass might respond to individual vs. combined effects of the three global change drivers. Our results show that (i) individual effects of N addition and elevated CO2 on C:N:P stoichiometry are stronger than warming, (ii) combined effects of pairs of global change drivers (e.g., N addition + elevated CO2 , warming + elevated CO2 ) on C:N:P stoichiometry were generally weaker than the individual effects of each of these drivers, (iii) additive interactions (i.e., when combined effects are equal to or not significantly different from the sum of individual effects) were more common than synergistic or antagonistic interactions, (iv) C:N:P stoichiometry of soil and soil microbial biomass shows high homeostasis under global change manipulations, and (v) C:N:P responses to global change are strongly affected by ecosystem type, local climate, and experimental conditions. Our study is one of the first to compare individual vs. combined effects of the three global change drivers on terrestrial C:N:P ratios using a large set of data. To further improve our understanding of how ecosystems might respond to future global change, long-term ecosystem-scale studies testing multifactor effects on plants and soils are urgently required across different world regions.

Long-term belowground effects of grassland management: the key role of liming.

The functioning of human-managed grassland ecosystems strongly depends on how common management practices will affect grassland "belowground compartment" including soil biogeochemistry and plant roots. Key questions remain about how animal grazing, liming (e.g., the addition of CaCO3 to soils), and nutrient fertilization might affect, in the long-term, soil nutrient cycling and multiple root traits. Here we focus on a mesotrophic grassland located in Berkshire, UK, where contrasting levels of rabbit grazing, liming, and different inorganic fertilizers have been applied since 1991. We ask how (1) soil nitrogen (N) availability and cycling, (2) total root mass, (3) root mass decomposition, and (4) arbuscular mycorrhizal fungal (AMF) root colonization might respond to 22 years of very different management. We found that liming strongly affected total root mass, root decomposition, root AMF colonization as well as soil N availability and cycling and that these effects were mainly driven by liming-induced increases in soil pH. Increases in soil pH were associated with significant (1) decreases in root mass, (2) increases in root mass decomposability and in the mineralization of N in decomposing root detritus, and (3) increases in AMF infection. Soil pH was also significantly related to greater N availability (i.e., soil NO3 levels) and to lower δ15 N natural abundance, which suggests more efficient N uptake by plants in limed soils as we found in our study. The application of multiple nutrients (N, P, K, Mg) also reduced total root mass, while N-only fertilization was associated with greater AMF infection. Surprisingly the long-term impact of grazing was generally weak and not significant on most plant and soil parameters. Despite soil pH affecting most belowground variables, changes in soil pH were not associated with any change in soil C and N stocks. Because liming can improve nutrient cycling (and benefits soil pH and grass yields) without negatively affecting soil C sequestration, we suggest that regular liming applications may provide management solutions for increasing the long-term sustainability of permanent grassland.

Multi-nutrient vs. nitrogen-only effects on carbon sequestration in grassland soils.

Human activities have greatly increased the availability of biologically active forms of nutrients [e.g., nitrogen (N), phosphorous (P), potassium (K), magnesium (Mg)] in many soil ecosystems worldwide. Multi-nutrient fertilization strongly increases plant productivity but may also alter the storage of carbon (C) in soil, which represents the largest terrestrial pool of organic C. Despite this issue is important from a global change perspective, key questions remain on how the single addition of N or the combination of N with other nutrients might affect C sequestration in human-managed soils. Here, we use a 19-year old nutrient addition experiment on a permanent grassland to test for nutrient-induced effects on soil C sequestration. We show that combined NPKMg additions to permanent grassland have 'constrained' soil C sequestration to levels similar to unfertilized plots whereas the single addition of N significantly enhanced soil C stocks (N-only fertilized soils store, on average, 11 t C ha(-1) more than unfertilized soils). These results were consistent across grazing and liming treatments suggesting that whilst multi-nutrient additions increase plant productivity, soil C sequestration is increased by N-only additions. The positive N-only effect on soil C content was not related to changes in plant species diversity or to the functional composition of the plant community. N-only fertilized grasslands show, however, increases in total root mass and the accumulation of organic matter detritus in topsoils. Finally, soils receiving any N addition (N only or N in combination with other nutrients) were associated with high N losses. Overall, our results demonstrate that nutrient fertilization remains an important global change driver of ecosystem functioning, which can strongly affect the long-term sustainability of grassland soil ecosystems (e.g., soils ability to deliver multiple ecosystem services).

Global patterns and driving factors of plant litter iron, manganese, zinc, and copper concentrations.

Plant litter decomposition is not only the major source of soil carbon and macronutrients, but also an important process for the biogeochemical cycling of trace elements such as iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu). The concentrations of plant litter trace elements can influence litter decomposition and element cycling across the plant and soil systems. Yet, a global perspective of the patterns and driving factors of trace elements in plant litter is missing. To bridge this knowledge gap, we quantitatively assessed the concentrations of four common trace elements, namely Fe, Mn, Zn, and Cu, of freshly fallen plant litter with 1411 observations extracted from 175 publications across the globe. Results showed that (1) the median of the average concentrations of litter Fe, Mn, Zn, and Cu were 0.200, 0.555, 0.032, and 0.006 g/kg, respectively, across litter types; (2) litter concentrations of Fe, Zn, and Cu were generally stable regardless of variations in multiple biotic and abiotic factors (e.g., plant taxonomy, climate, and soil properties); and (3) litter Mn concentration was more sensitive to environmental conditions and influenced by multiple factors, but mycorrhizal association and soil pH and nitrogen concentration were the most important ones. Overall, our study provides a clear global picture of plant litter Fe, Mn, Zn, and Cu concentrations and their driving factors, which is important for improving our understanding on their biogeochemical cycling along with litter decomposition processes.

Vegetation restoration effects on soil carbon and nutrient concentrations and enzymatic activities in post-mining lands are mediated by mine type, climate, and former soil properties.

Vegetation restoration is a widely used, effective, and sustainable method to improve soil quality in post-mining lands. Here we aimed to assess global patterns and driving factors of potential vegetation restoration effects on soil carbon, nutrients, and enzymatic activities. We synthesized 4838 paired observations extracted from 175 publications to evaluate the effects that vegetation restoration might have on the concentrations of soil carbon, nitrogen, and phosphorus, as well as enzymatic activities. We found that (1) vegetation restoration had consistent positive effects on the concentrations of soil organic carbon, total nitrogen, available nitrogen, ammonia, nitrate, total phosphorus, and available phosphorus on average by 85.4, 70.3, 75.7, 54.6, 58.6, 34.7, and 60.4 %, respectively. Restoration also increased the activities of catalase, alkaline phosphatase, sucrase, and urease by 63.3, 104.8, 125.5, and 124.6 %, respectively; (2) restoration effects did not vary among different vegetation types (i.e., grass, tree, shrub and their combinations) or leaf type (broadleaved, coniferous, and mixed), but were affected by mine type; and (3) latitude, climate, vegetation species richness, restoration year, and initial soil properties are important moderator variables, but their effects varied among different soil variables. Our global scale study shows how vegetation restoration can improve soil quality in post-mining lands by increasing soil carbon, nutrients, and enzymatic activities. This information is crucial to better understand the role of vegetation cover in promoting the ecological restoration of degraded mining lands.

Soil carbon sequestration in prairie grasslands increased by chronic nitrogen addition.

Human-induced increases in nitrogen (N) deposition are common across many terrestrial ecosystems worldwide. Greater N availability not only reduces biological diversity, but also affects the biogeochemical coupling of carbon (C) and N cycles in soil ecosystems. Soils are the largest active terrestrial C pool and N deposition effects on soil C sequestration or release could have global importance. Here, we show that 27 years of chronic N additions to prairie grasslands increased C sequestration in mineral soils and that a potential mechanism responsible for this C accrual was an N-induced increase in root mass. Greater soil C sequestration followed a dramatic shift in plant community composition from native-species-rich C4 grasslands to naturalized-species-rich C3 grasslands, which, despite lower soil C gains per unit of N added, still acted as soil C sinks. Since both high plant diversity and elevated N deposition may increase soil C sequestration, but N deposition also decreases plant diversity, more research is needed to address the long-term implications for soil C storage of these two factors. Finally, because exotic C3 grasses often come to dominate N-enriched grasslands, it is important to determine if such N-dependent soil C sequestration occurs across C3 grasslands in other regions worldwide.

Litter quality and stream physicochemical properties drive global invertebrate effects on instream litter decomposition.

Plant litter is the major source of energy and nutrients in stream ecosystems and its decomposition is vital for ecosystem nutrient cycling and functioning. Invertebrates are key contributors to instream litter decomposition, yet quantification of their effects and drivers at the global scale remains lacking. Here, we systematically synthesized data comprising 2707 observations from 141 studies of stream litter decomposition to assess the contribution and drivers of invertebrates to the decomposition process across the globe. We found that (1) the presence of invertebrates enhanced instream litter decomposition globally by an average of 74%; (2) initial litter quality and stream water physicochemical properties were equal drivers of invertebrate effects on litter decomposition, while invertebrate effects on litter decomposition were not affected by climatic region, mesh size of coarse-mesh bags or mycorrhizal association of plants providing leaf litter; and (3) the contribution of invertebrates to litter decomposition was greatest during the early stages of litter mass loss (0-20%). Our results, besides quantitatively synthesizing the global pattern of invertebrate contribution to instream litter decomposition, highlight the most significant effects of invertebrates on litter decomposition at early rather than middle or late decomposition stages, providing support for the inclusion of invertebrates in global dynamic models of litter decomposition in streams to explore mechanisms and impacts of terrestrial, aquatic, and atmospheric carbon fluxes.

The Growth Performance, Nutrient Digestibility, Gut Bacteria and Bone Strength of Broilers Offered Alternative, Sustainable Diets Varying in Nutrient Specification and Phytase Dose.

This study assessed the use of locally sourced sustainable feed ingredients, rapeseed meal (RSM) and maize dried distiller grains with solubles (DDGS) in diets over traditional ingredients on the growth performance, bone strength and nutrient digestibility of broilers. This work also investigated the effects of supplementing exogenous phytase in two doses (500 vs. 1500 FTU/kg). Using male Ross 308 chicks (n = 320) assigned to receive one of four experimental diets: (1) Positive control diet 1 (PC1), a wheat, soya-based diet + 500 FTU/kg phytase. (2) Positive control diet 2, RSM/DDGS diet + 500 FTU/kg phytase (PC2). (3) Negative control (NC) reduced nutrient RSM/DDGS diet, no phytase. (4) The NC diet plus 1500 FTU/kg phytase (NC+). PC1 birds displayed higher feed intake and body weight gain consistently throughout the trial (p < 0.001) as well as increased body weight by 28 d and 42 d (p < 0.001). Whole-body dual emission X-ray absorptiometry (DXA) analysis revealed PC1 birds also had higher bone mineral density (BMD), bone mineral content (BMC), total bone mass, total lean mass and total fat mass than birds offered other treatments (p < 0.01). Diet had no significant effect on bone strength. Phytase superdosing improved the digestibility of dry matter (DM), neutral detergent fibre (NDF), gross energy (GE), calcium (Ca), potassium (K) and magnesium (Mg) compared to birds in other treatment groups. The phytase superdose also improved performance in comparison to birds offered the NC diet. Phytase superdosing increased the IP6 and IP5 degradation and increased the ileal inositol concentration of the birds. N excretion was lower for birds offered the traditional wheat−soya diet and highest for those offered the high-specification RSM/DDGS diet with a commercial dose of phytase. The addition of a phytase superdose to the negative control diet (NC+) reduced P excretion of birds by 15% compared to birds offered NC.

Improving phosphorus sustainability in intensively managed grasslands: The potential role of arbuscular mycorrhizal fungi.

Long-term nutrient fertilization of grassland soils greatly increases plant yields but also profoundly alters ecosystem phosphorus (P) dynamics. Here, we addressed how long-term P fertilization may affect ecosystem P budget, P use efficiency (PUE) and the abundance of arbuscular mycorrhizal fungi (AMF), which play a key role in the acquisition of P by plants. We found that 47 years of organic P applications increased soil P availability and total soil P stocks up to 1600% and 400%, respectively, compared to unfertilized-control soils. Grassland soils could retain up to 62% and 48% of P applied since 1970 in organic and inorganic forms, respectively. Nutrient treatments significantly affected rates of AMF root colonization (%), which were higher in control and NPK-fertilized plots when compared to soils receiving increasing applications of organic P. Plant PUE increased with greater AMF root colonization, which remained high (i.e. 50-to-75%) even after ~50 years of continuous 'normal' rates of agronomic P inputs (~30 kg P ha-1 year-1). AMF abundance, however, decreased under higher P applications and we found a negative relationship between soil P availability or soil P stocks and rates of AMF root colonization. Our study demonstrates that (1) AMF root colonization is still high in soils, which have received consistent but moderate P inputs for over four decades, and (2) moderate rates of P fertilization are related to a more conservative P ecosystem budget whereby the amount of P retained in soils and up-taken by plants on an annual basis is higher than the amount of P added through fertilization. This is possible only if extra P is 'mined' from the soil P 'bank' and made available to plant uptake. We suggest that AMF could play a significant role in intensively-managed grasslands contributing to increase P sustainability by reducing the need for extra P fertilizer.

Effects of long-term grassland management on the carbon and nitrogen pools of different soil aggregate fractions.

Common grassland management practices include animal grazing and the repeated addition of lime and nutrient fertilizers to soils. These practices can greatly influence the size and distribution of different soil aggregate fractions, thus altering the cycling and storage of carbon (C) and nitrogen (N) in grassland soils. So far, very few studies have simultaneously addressed the potential long-term effect that multiple management practices might have on soil physical aggregation. Here we specifically ask whether and how grazing, liming and nutrient fertilization might influence C and N content (%) as well as C and N pools of different soil aggregate fractions in a long-term grassland experiment established in 1991 at Silwood Park, Berkshire, UK. We found that repeated liming applications over 23years significantly decreased the C pool (i.e. gCKg-1 soil) of Large Macro Aggregate (LMA>2mm) fractions and increased C pools within three smaller soil aggregate fractions: Small Macro Aggregate (SMA, 250µm-2mm), Micro Aggregate (MiA, 53-250µm), and Silt Clay Aggregate (SCA<53µm). Soil C (and N) accrual in smaller fractions was mainly caused by positive liming effects on aggregate fraction mass rather than on changes in soil C (and N) content (%). Liming effects could be explained by increases in soil pH, as this factor was significantly positively related to greater soil C and N pools of smaller aggregate fractions. Long-term grazing and inorganic nutrient fertilization had much weaker effects on both soil aggregate-fraction mass and on soil C and N concentrations, however, our evidence is that these practices could also contribute to greater C and N pools of smaller soil fractions. Overall our study demonstrates how agricultural liming can contribute to increase C pools of small (more stable) soil fractions with potential significant benefits for the long-term C balance of human-managed grassland soils.

Plant and soil nutrient stoichiometry along primary ecological successions: Is there any link?

Ecological stoichiometry suggests that plant Nitrogen (N)-to-Phosphorus (P) ratios respond to changes in both soil N:P stoichiometry and soil N and P availability. Thus we would expect that soil and plant N:P ratios be significantly related along natural gradients of soil development such as those associated with primary ecological successions. Here we explicitly search for linkages between plant and soil N:P stoichiometry along four primary successions distributed across Europe. We measured N and P content in soils and plant compartments (leaf, stem and root) of 72 wild plant species distributed along two sand dune and two glacier successions where soil age ranges from few to thousand years old. Overall we found that soil N:P ratios strongly increased along successional stages, however, plant N:P ratios were neither related to soil N:P stoichiometry nor to changes in soil N and P availability. Instead changes in plant nutrient stoichiometry were "driven" by plant-functional-group identity. Not only N:P ratios differed between legumes, grasses and forbs but each of these plant functional groups maintained N:P ratios relatively constant across pioneer, middle and advanced successional stages. Our evidence is that soil nutrient stoichiometry may not be a good predictor of changes in plant N:P stoichiometry along natural primary ecological successions, which have not reached yet a retrogressive stage. This could be because wild-plants rely on mechanisms of internal nutrient regulation, which make them less dependent to changes in soil nutrient availability under unpredictable environmental conditions. Further studies need to clarify what underlying evolutionary and eco-physiological mechanisms determine changes in nutrient stoichiometry in plant species distributed across natural environmental gradients.