Symbiotic soil fungi enhance ecosystem resilience to climate change

Substantial amounts of nutrients are lost from soils through leaching. These losses can be environmentally damaging, causing groundwater eutrophication and also comprise an economic burden in terms of lost agricultural production. More intense precipitation events caused by climate change will likely aggravate this problem. So far it is unresolved to which extent soil biota can make ecosystems more resilient to climate change and reduce nutrient leaching losses when rainfall intensity increases. In this study, we focused on arbuscular mycorrhizal (AM) fungi, common soil fungi that form symbiotic associations with most land plants and which increase plant nutrient uptake. We hypothesized that AM fungi mitigate nutrient losses following intensive precipitation events (higher amount of precipitation and rain events frequency). To test this, we manipulated the presence of AM fungi in model grassland communities subjected to two rainfall scenarios: moderate and high rainfall intensity. The total amount of nutrients lost through leaching increased substantially with higher rainfall intensity. The presence of AM fungi reduced phosphorus losses by 50% under both rainfall scenarios and nitrogen losses by 40% under high rainfall intensity. Thus, the presence of AM fungi enhanced the nutrient interception ability of soils, and AM fungi reduced the nutrient leaching risk when rainfall intensity increases. These findings are especially relevant in areas with high rainfall intensity (e.g., such as the tropics) and for ecosystems that will experience increased rainfall due to climate change. Overall, this work demonstrates that soil biota such as AM fungi can enhance ecosystem resilience and reduce the negative impact of increased precipitation on nutrient losses.     

Effects of delayed hay removal on the nutrient balance of roadside plant communities

1. Mass losses and nutrient losses from fresh roadside cuttings were studied in the field during a 6-week period. Large amounts (over 50%) appear to be lost from the cuttings. The losses were positively related to initial nutrient concentrations during this short-term study. Mass and nitrogen losses were best explained by the initial C:N ratio, phosphorus and potassium losses by the initial phosphorus concentration.
2. For potassium the losses were particularly large (up to 90%). For this element only, the observed relationship between loss rate and initial chemical composition could not be established significantly. It is concluded that potassium is mainly lost by leaching whereas the major nitrogen, phosphorus and mass losses are most probably caused by rapid microbial decomposition of readily soluble substances.
3. Using existing data on chemical composition of other roadside cuttings, nutrient losses after different hay removal delay times were modelled for different plant communities. All or most of the losses were assumed to return to the soil system.
4. When soil impoverishment is aimed for, cuttings should be removed within 1 or 2 weeks in most plant communities. If removal is delayed longer, the amounts of nutrients removed will often fall below the annual atmospheric input. In plant communities where annual above-ground production of nitrogen and phosphorus are lower than the annual atmospheric deposition already, rapid removal of the cuttings may be the only way to maintain at least potassium at a limiting level.
5. The main effect of hay-making on the soil nutrient status most likely consists of a reduction of the potassium availability, at least on sandy soils with a low cation exchange capacity and provided there is little delay in hay removal.     

Effects of Prescribed Fire on Nutrient Pools and Losses from Glades Occurring Within Oak-Hickory Forests of Central Kentucky

Forest openings, also known as glades, arise through a variety of mechanisms including disturbance (fire and blow downs) and local variation in soil or bedrock geology. They are common in many forest types and are often dominated by locally rare herbaceous species. Prescribed burning is increasingly used as a management approach for maintaining glades although little is known about the effects of fire on these habitats. Of particular concern is the potential for nutrient loss during and after fire because glades are often characterized by nutrient‐poor soils. We quantitated nutrient losses through combustion and leaching for glade and adjacent forest habitats subjected to a prescribed burn. Our findings suggest that spring burns do not result in appreciable loss of nutrient capital from glades in comparison with those observed in the surrounding forest. Fire resulted in a substantial loss of litter mass (37%) in the forest but no measurable loss in the glade. Nitrogen losses through combustion were significant in the forest and were equivalent to 4.5 years of atmospheric inputs. Fire significantly increased soil nitrate pools in forest but not in glade plots. No detectable increases in nitrogen, phosphorus, or base cation leaching were observed in either forest or glade habitats within 4 months after the burn. These findings suggest that plant and microbial nutrient uptake rapidly reestablish control over leaching losses when burns are conducted at the start of the growing season. Biotic retention minimizes fire impacts on nutrient loss from the ecosystem.     

Nutrient deficiencies do not contribute to yield loss after waterlogging events in winter wheat (Triticum aestivum)

Frequent waterlogging increases the risk of possible harvest losses in winter wheat. The aim of this study was to analyse which developmental stage of wheat was impaired by waterlogging and whether yield losses can be explained by nutrient deficiences. A large‐scale container experiment was designed to evaluate growth, yield and nutrient status of two wheat cultivars after 14 days of waterlogging at two different developmental stages: DC 31 (first node visible) and DC 51 (beginning of ear emergence). Early waterlogging treatment impaired vegetative growth stages of winter wheat and nutrient uptake, leading to transient nutrient deficiencies, but yield was not significantly reduced. Late waterlogging at the beginning of ear emergence mainly affected generative growth stages and caused yield reductions ranging up to 61%. The main reason for yield loss was the significantly decreased thousand kernel weight in combination with a decreased number of grains per spike. Yield depressions in winter wheat depend on the timing of waterlogging. Early waterlogging transiently reduces vegetative growth through nutrient deficiencies, whereas late waterlogging results in an impaired grain development and associated therewith, yield losses.     

The effect of fire on nutrient losses and cycling in aQuercus coccifera garrigue (southern France)

The effects of burning on plant nutrient budgets and rates of carbonic gas and particulate matter emission during fires were evaluated in aQuercus coccifera (garrigue) shrubland. Nutrient levels were determined in field-collected pre-fire vegetation and combustion residues. The losses (increased elemental transfer) were calculated as the difference between the quantity of an element in the fuel (combustible standing vegetation plus litter) before burning and that present in the postfire residues (ash). Weight losses of elements are correlated with weight losses of burnt plant biomass. The relative order of nutrient losses was: N>C>Na>Ca>P>K>Mg. Estimated losses of N, C and P from combustible plant matter exceeded 98, 97 and 79% respectively. Copious N, C and P volatilization during burning was promoted by high concentrations of these elements in foliage and fine woody biomass of the aboveground vegetation and leaf litter of the garrigue. Elements were principally removed in the smoke. The quantities of gaseous emissions of CO₂, CO and particulate matter produced were estimated.     

Reductions in water,soil and nutrient losses and pesticide pollution in agroforestry practices: a review of evidence and processes

Plant and Soil - Agroforestry systems combining trees with crops or pastures have been widely used to reduce water, soil, and nutrient losses and associated water pollution from agricultural lands...     

Water pulses and biogeochemical cycles in arid and semiarid ecosystems

The episodic nature of water availability in arid and semiarid ecosystems has significant consequences on belowground carbon and nutrient cycling. Pulsed water events directly control belowground processes through soil wet-dry cycles. Rapid soil microbial response to incident moisture availability often results in almost instantaneous C and N mineralization, followed by shifts in C/N of microbially available substrate, and an offset in the balance between nutrient immobilization and mineralization. Nitrogen inputs from biological soil crusts are also highly sensitive to pulsed rain events, and nitrogen losses, particularly gaseous losses due to denitrification and nitrate leaching, are tightly linked to pulses of water availability. The magnitude of the effect of water pulses on carbon and nutrient pools, however, depends on the distribution of resource availability and soil organisms, both of which are strongly affected by the spatial and temporal heterogeneity of vegetation cover, topographic position and soil texture. The inverse texture hypothesis for net primary production in water-limited ecosystems suggests that coarse-textured soils have higher NPP than fine-textured soils in very arid zones due to reduced evaporative losses, while NPP is greater in fine-textured soils in higher rainfall ecosystems due to increased water-holding capacity. With respect to belowground processes, fine-textured soils tend to have higher water-holding capacity and labile C and N pools than coarse-textured soils, and often show a much greater flush of N mineralization. The result of the interaction of texture and pulsed rainfall events suggests a corollary hypothesis for nutrient turnover in arid and semiarid ecosystems with a linear increase of N mineralization in coarse-textured soils, but a saturating response for fine-textured soils due to the importance of soil C and N pools. Seasonal distribution of water pulses can lead to the accumulation of mineral N in the dry season, decoupling resource supply and microbial and plant demand, and resulting in increased losses via other pathways and reduction in overall soil nutrient pools. The asynchrony of resource availability, particularly nitrogen versus water due to pulsed water events, may be central to understanding the consequences for ecosystem nutrient retention and long-term effects on carbon and nutrient pools. Finally, global change effects due to changes in the nature and size of pulsed water events and increased asynchrony of water availability and growing season will likely have impacts on biogeochemical cycling in water-limited ecosystems.     

The importance of nutrient pulses in tropical forests

Recent research shows that nutrient fluxes are often pulsed In tropical forests, and that pulsed versus gradual inputs have different effects on the fates of nutrients in the ecosystem. Synchrony of nutrient mineralization with plant uptake can lower competition between microbes and plants for limiting nutrients while maintaining tight nutrient cycling, whereas asynchrony can lead to losses of nutrients from the system. Thus, nutrient pulses may play a critical role in maintaining productivity in tropical forests with tight nutrient cycling.     

Andropogon gayanus (Gamba Grass) Invasion Increases Fire-mediated Nitrogen Losses in the Tropical Savannas of Northern Australia

Invasive alien grasses can substantially alter fuel loads and fire regimes which could have significant consequences for fire-mediated nutrient losses. The effects of the alien grass Andropogon gayanus Kunth. (Gamba grass) on fire-mediated nutrient losses was evaluated in Australia’s tropical savannas. Losses of macronutrients during fire were determined by comparing the nutrient pools contained in the fine fuel before fire and in the ash after fire. Pre-fire grass nutrient pools were significantly higher in A. gayanus plots than in native grass plots for all nutrients measured (N, P, K, S, Ca, and Mg). Nutrient losses were substantially higher in A. gayanus plots, with 113% higher losses for N, 80% for P, 56% for K, 63 for S, 355% for Ca, and 345% for Mg. However, only losses of N and Mg varied significantly between grass types. A simplified savanna ecosystem nutrient budget estimated that A. gayanus fires led to the net N loss of 20 kg ha⁻¹ y⁻¹. This is a conservative estimate because total fuel loads were relatively low (7.85 t ha⁻¹) for A. gayanus invaded plots leading to a relatively moderate intensity fire (6,408 kW m⁻¹). Higher A. gayanus fuel loads and fire intensities could potentially lead to losses of up to 61.5 kg N ha⁻¹ from the grass fuel. Over the long term, this is likely to lead to depletion of soil nutrients, particularly N, in the already low-fertility tropical savanna soils.     

Distribution and budget of nutrients in a commercial apple orchard

Summary Data on the dry matter distribution and nutrient reserves (N, P, S, Cl, K, Ca, Mg and Na) in the standing biomass of a grassed-down 14 year-old apple orchard are presented together with mean estimates of nutrient inputs, returns and losses over a 2 year period.The major inputs of N P K and S were through fertilizer additions. The major inputs of Na and Cl were in bulk precipitation plus irrigation whilst both sources were important for Mg and Ca. Total inputs by precipitation plus irrigation plus fertilizer in kg/ha/yr were: N, 81; P, 20; S, 42; Cl, 58; K, 64; Ca, 35; Mg, 10 and Na, 33. Nutrient returns to the orchard floor were dominated by those from returns of herbage clippings orginating from the mowing of the orchard pasture. Autumn leaf fall also contributed significant quantities to the total nutrient returns. Total nutrient returns to the orchard floor through petal fall, fruit drop, leaf fall, foliar leaching (includes leaf washing) and pasture clippings in kg/ha/yr were: N, 545; P, 33; S, 41; Cl, 107; K, 442; Ca, 147; Mg, 35 and Na, 16. The major loss of Na, Mg, Ca, Cl and S was through leaching (this may include a certain amount of chemical weathering). In contrast, the major loss of P and K was in the harvested fruit crop, while for N, losses were about equally divided between the fruit crop and leaching. Total nutrient losses from the orchard by removal of the fruit crop and pruning wood plus leaching losses were estimated in kg/ha/yr at: N, 58; P, 5; S, 28; Cl, 81; K, 124; Ca, 55; Mg, 39 and Na, 80. Inputs minus losses in kg/ha/yr were positive for N, P and S(+23, +16 and +14 respectively and negative for Cl, K, Ca, Mg and Na (–24, –60, –19, –30 and –47 respectively).     

Responses in plant, soil inorganic and microbial nutrient pools to experimental fire, ash and biomass addition in a woodland savanna

In order to investigate the effects of savanna fires on nutrient cycling a field experiment was carried out in an open woodland savanna of southwest Ethiopia. This involved manipulations of fire, fuel load and ash fertilisation in a fully factorial design, and recording of responses in plants, soil inorganic and microbial nutrient pools up to 1 year after the disturbances. As plant biomass nitrogen (N) was only 3.5% of that in topsoil the N loss in a single fire event was relatively small. The microbial N pool size in the topsoil was similar to the N pool size in the aboveground part of the plants. Soil microbial biomass carbon increased slightly 12 days after the low severity fire, but the effect was transient and was not accompanied by an increase in microbial N. Instead, the soil inorganic N concentration increased strongly 1 day after the fire, remained higher up to 3 months after the fire and probably caused the 40% higher grass biomass in burned than unburned plots, and the similar sized increase in grass nitrogen, phosphorus and potassium pools in the following rainy season. In contrast, broad-leaved herbs showed less strong increments in biomass and nutrient pool sizes. Fire interacted with fuel load, as burning of plots with double plant biomass led to reduced microbial biomass, plant nutrient pools and herb (but not grass) biomass. Low-severity-fire nutrient losses appear to be moderate and may be replenished from natural sources. However, in areas with frequent fires and high grass biomass (fuel) loads, or with late fires, nutrient losses could be much larger and non-sustainable to the persistence of the woodland savanna ecosystem.     

Influence of nutrient solution pH on N2O and N2 emissions from a soilless culture system

The influence of nutrient solution pH on the emission of N2O and N2 was investigated during cultivation of cucumbers in a closed-loop rockwool system. Between pH 4 and 7 these gaseous nitrogen losses increased from 1.6 to 21.1% of the N fertilizer input. This was equivalent to average flux rates of 0.06 and 0.85 kg nitrogen per hectare greenhouse area and day, respectively. The N2O/N2 ratio was inversely related to the total gaseous nitrogen losses. At neutral pH dinitrogen was the main emission product, whereas more acidic conditions favoured the emission of nitrous oxide. The pH effects were probably not indirectly affected by root respiration or exudation as much as by a direct inhibition of the activity of denitrifying microorganisms due to high H+ concentrations since similar results were obtained in unplanted nutrient solution systems with the addition of glucose as carbon source. Despite the low microbial denitrification activity under acidic conditions, nitrogen balance deficits of up to one-fifth of the N input still occurred. It is suggested these losses were predominantly caused by chemodenitrification.     

阔叶红松林合理经营与土壤微生物活性

森林是可再生的自然资源,研究证明,阔叶红松林具有很高的生产力,因为它具有最优化的林分结构,这个结构特点,使它的复层异龄和针阔混交的群落结构影响下的土壤肥力较高,土壤微生物类群复杂,活动活跃,森林有机残体的分解与转化较快。系统内的氮、碳及无机养分的循环,能满足林木生长对养分不断增长的需要。系统内各个生态因子处于动态平衡状态。因此,为了不断提     

Value of soil zinc balances in predicting fertilizer zinc requirement for cotton-wheat cropping system in irrigated Aridisols

Several studies have shown that soil biotic communities from organically managed fields are more diverse and exhibit higher activity levels compared to conventionally managed fields. The impact of these different soil communities on plant productivity and the provision of soil ecosystem services are, however, still unclear. Here, we test the effects of soil inoculation from each of three organic and three conventional maize fields on maize productivity and nutrient loss during leaching events induced by simulated rain. In particular, we examine whether differences in productivity and nutrient loss are related to the abundance and species composition of arbuscular mycorrhizal (AM) fungi. We hypothesized that soil biota from organically managed fields would improve maize growth and reduce nutrient leaching significantly more than those from conventionally managed fields. In contrast to our hypothesis, we found that plant productivity was negatively affected by soil inoculation, and this effect was stronger with inoculum from organic fields. Plant productivity was inversely correlated with AMF abundance, suggesting that enhanced carbon allocation to AMF is at least in part responsible for plant growth reduction under our experimental conditions. However, soil inoculation did alter the ecological functioning of the system by reducing phosphorus leaching losses after simulated rain. Moreover, these leaching losses were lower with increased hyphal density and were related with abundance of particular AMF types, suggesting that abundance of AMF and their community composition may be useful indicators of phosphorus leaching losses. The results demonstrate that soil communities from different agricultural fields vary in their impact on plant productivity and nutrient leaching losses. The results further indicate that there is a potential tradeoff between positive effects of soil communities on sustainability and negative effects on crop productivity.     

应用微生物降低鸡粪N营养元素损失, 促进其无害化进程

为减轻大量禽畜废弃物对环境的污染, 将其资源化为优质的无害化有机肥料, 研究了微生物F468对降低鸡粪N营养元素损失和促进其无害化进程的影响。结果表明, 继代80次, F468降低鸡粪氨气挥发的能力无显著变化, 能降低鸡粪79%的N元素损失。F468还能通过降低蛔虫卵和粪肠杆菌的数量, 促进鸡粪的无害化进程。不添加F468, 蛔虫卵和粪肠杆菌达到我国无害化标准(NY884-2004)的时间分别需要25 d和20 d。加入F468后, 蛔虫卵和粪肠杆菌达到我国无害化标准的时间分别需要15 d和10 d, 均比不加微生物提前10 d达到我国无害化标准。     

土壤垦复对山地麻竹林地表养分流失动态的影响

为了比较山地麻竹笋用林不同土壤垦复措施对养分流失动态的影响,在福建南靖国有林场设置径流场,进行了1年的观测、取样和氮磷钾浓度分析.结果表明,3种土壤垦复措施的氮、磷、钾流失量具有明显的季节性,4～9月3种养分流失量占全年90%以上,且都呈现全翻>带翻>对照,但3种经营措施间氮、磷的年流失量差异均不显著,全翻的钾流失量差异水平达显著,带翻与对照间差异不显著.     

Microbial nitrogen and phosphorus co-limitation across permafrost region

The status of plant and microbial nutrient limitation have profound impacts on ecosystem carbon cycle in permafrost areas, which store large amounts of carbon and experience pronounced climatic warming. Despite the long-term standing paradigm assumes that cold ecosystems primarily have nitrogen deficiency, large-scale empirical tests of microbial nutrient limitation are lacking. Here we assessed the potential microbial nutrient limitation across the Tibetan alpine permafrost region, using the combination of enzymatic and elemental stoichiometry, genes abundance and fertilization method. In contrast with the traditional view, the four independent approaches congruently detected widespread microbial nitrogen and phosphorus co-limitation in both the surface soil and deep permafrost deposits, with stronger limitation in the topsoil. Further analysis revealed that soil resources stoichiometry and microbial community composition were the two best predictors of the magnitude of microbial nutrient limitation. High ratio of available soil carbon to nutrient and low fungal/bacterial ratio corresponded to strong microbial nutrient limitation. These findings suggest that warming-induced enhancement in soil nutrient availability could stimulate microbial activity, and probably amplify soil carbon losses from permafrost areas.     

Effects of flooding on leaf litter decomposition in microcosms

Summary The effects of hydroperiod on decomposition rates of senescent Acer rubrum leaves were tested in microcosms in a controlled laboratory environment. Microcosm treatments included continuously flooded, continuously unflooded, and fluctuating hydroperiods. All flooding treatments promoted decomposition but variations in hydroperiod had no significant effects. A leaching experiment indicated the higher decay rates under flooded conditions were primarily due to high leaching losses from soaking. Unlike nutrient dynamics in the field, where net accumulation occurs, nitrogen and phosphorus in the litter in the microcosms exhibited net losses. The major external inputs which provide a source of nitrogen and phosphorus for immobilization in the field were lacking in the microcosms. Calcium, magnesium, and potassium exhibited net losses except for calcium in the unflooded microcosms. The microcosm results demonstrated the importance of external inputs to litter nutrient relations.     

Mechanisms for carbon and nutrient release and retention in beech forest gaps

Nutrient cycling and water balance in forest gaps has received little attention until now, although gap regeneration is important to natural dynamics of temperate forests. Gaps of 30 m diameter, cut in a mature beech forest, exhibited a distinct change in microclimatic conditions in comparison with the surrounding stand. Soil moisture in gaps remained very high throughout the observation period. Disruption of the N cycle in gaps led to substantial nitrate losses; seepage water nitrate concentrations were 10–18 mg NO₃-N L^-1. Excess nitrification was a significant cause of soil acidification and aluminium release. The pH in subsoil seepage water decreased by 0.25. Liming in gaps promoted the establishment of a herbaceous vegetation, which functioned as an important nutrient sink, and thus is recommended for tree regeneration in highly acidified forest ecosystems as it increases the resilience of the ecosystem to nutrient losses.     

Ammonia volatilization and the effects of large grazing mammals on nutrient loss from East African grasslands

Summary Ammonia volatilization losses measured from soils at seven sites in the Serengeti National Park, Tanzania during the 1986 growing season ranged from 2.78±0.49% to 25.03±1.34% of nitrogen applied. Although peak ammonia losses ranged from 0.071±0.018 to 0.404±0.040 g N m^-2 h^-1, rates dropped to zero within four days, and calculations reveal that volatilization losses represent minor fluxes in the context of the system's nitrogen cycling. Volatilization losses were inversely correlated with grazing intensity experienced by a site, and it appears that large ungulates themselves contribute to nutrient conservation throught indirect interactive effects on system processes.