黄土高原丘陵区生物结皮土壤的斥水性

采用滴水穿透时间法和酒精溶液入渗法,研究了黄土高原丘陵区浅色藻结皮、深色藻结皮、藻+少量藓结皮、藓+少量藻结皮、藓结皮5种不同发育阶段的原状生物结皮土壤的斥水性及其与土壤含水量的关系.结果表明: 生物结皮增加了土壤的斥水性,其斥水强度和持久性均显著增加.生物结皮土壤的斥水性随生物结皮的演替逐渐降低,当生物结皮中藓类植物盖度在20%以上时,斥水持久性显著低于藻结皮.生物结皮土壤的斥水性与土壤含水量及优势种密切相关,藓类生物结皮土壤的斥水性随着含水量的降低逐渐增加,藻类生物结皮土壤的斥水性随含水量的变化呈双峰曲线.     

Passive restoration of vegetation and biological soil crusts following 80 years of exclusion from grazing across the Great Basin

Restoration targets for biological soil crusts are largely unknown. We surveyed seven 80‐year‐old grazing exclosures across northern Nevada for biocrusts to quantify reference conditions at relatively undisturbed sites. Exclosures were associated with the following plant communities: Wyoming big sagebrush, black sagebrush, and areas co‐dominated by winterfat and Wyoming big sagebrush. Cover of biocrusts and shrubs were generally higher than other plant groups at these sites, regardless of being inside or outside of the exclosures, suggesting these groups make up most of the native flora across the region. Important in forming soil structure, cyanobacteria of the order Oscillatoriales were less abundant and diverse in black sagebrush communities. Grazing had a negative effect on the abundance of Oscillatoriales but not the number of algal taxa, including cyanobacteria. Abundance of light algal crusts were not influenced by plant community or grazing. Dark algal crusts were generally less abundant on grazed sites. Influences of plant community and grazing were most apparent when accounting for reproductive rates of lichens and mosses based on establishment mechanisms. Abundance of shrubs, perennial grasses, Oscillatoriales, fast reproducing biocrusts and the number of algal and cyanobacterial taxa, varied by plant community, suggesting that restoration should be plant community specific. We demonstrate the affinity of rapidly reproducing biocrusts for winterfat‐Wyoming big sagebrush co‐dominated plant communities, regardless of grazing pressure. Across sites, the effects of grazing were most evident on the abundance of Oscillatoriales and slowly reproducing biocrusts following 80 years of cessation from grazing.     

Response of biological soil crusts to raindrop erosivity and underlying influences in the hilly Loess Plateau region,China

Biological soil crusts (biocrusts) are ubiquitous living covers in arid and semiarid regions, playing a critical role in soil erosion control in semiarid regions. So far, research separating the multiple mechanisms of erosion control by biocrusts has been limited. It was problematic to link the influence of biocrusts to existing erosion models. In the present study, the response of biocrusts of different successional stages to raindrop erosivity and underlying influences was investigated. Using single drop simulated rainfall, the erosion controlling capacities of biocrusts were analyzed from an energetic perspective. The results showed that biocrusts caused a dramatic improvement of soil erosion resistance, which depended on species composition and increased considerably with higher succession stages. While the accumulated raindrop kinetic energy sustained by dark cyanobacterial crusts was 0.93 J (~15 times higher than that of bare soil), that of 60 % moss covered crusts reached values up to 20.18 J (~342 times higher than that of bare soil) and for 80 % moss covered crusts even 24.59 J were measured. Besides the composition and successional stages, the resistance of biocrusts to raindrop erosivity was related to the substrate soil moisture, soil texture, slope gradients and seasonal variation. The accumulated raindrop kinetic energy measured for cyanobacterial crusts was highest on silty, followed by loamy and sandy soil. For moss-dominated crusts raindrop kinetic energy was highest on sandy, followed by silty and loamy soil. Dry biocrust samples reached significantly higher accumulated raindrop kinetic energies compared to moist biocrusts, whereas the moisture content within moist crusts did not have a significant influence. Erosion resistance increased significantly with higher slope gradients. The resistance capacities of biocrusts during monsoon and post-monsoon were significantly higher than these of pre-monsoon biocrusts. Our results suggest that the influence of biocrusts can be included into erosion models from an energy point of view. The raindrop kinetic energy resistance capacity provides a potential bridge between biocrust succession and soil erodibility in commonly used erosion models.     

Dryland biological soil crust cyanobacteria show unexpected decreases in abundance under long‐term elevated CO2

Biological soil crusts (biocrusts) cover soil surfaces in many drylands globally. The impacts of 10 years of elevated atmospheric CO₂ on the cyanobacteria in biocrusts of an arid shrubland were examined at a large manipulated experiment in Nevada, USA. Cyanobacteria‐specific quantitative PCR surveys of cyanobacteria small‐subunit (SSU) rRNA genes suggested a reduction in biocrust cyanobacterial biomass in the elevated CO₂ treatment relative to the ambient controls. Additionally, SSU rRNA gene libraries and shotgun metagenomes showed reduced representation of cyanobacteria in the total microbial community. Taxonomic composition of the cyanobacteria was similar under ambient and elevated CO₂ conditions, indicating the decline was manifest across multiple cyanobacterial lineages. Recruitment of cyanobacteria sequences from replicate shotgun metagenomes to cyanobacterial genomes representing major biocrust orders also suggested decreased abundance of cyanobacteria sequences across the majority of genomes tested. Functional assignment of cyanobacteria‐related shotgun metagenome sequences indicated that four subsystem categories, three related to oxidative stress, were differentially abundant in relation to the elevated CO₂ treatment. Taken together, these results suggest that elevated CO₂ affected a generalized decrease in cyanobacteria in the biocrusts and may have favoured cyanobacteria with altered gene inventories for coping with oxidative stress.     

Cyanobacterial persistence and influence on microbial community dynamics over 15 years in induced biocrusts

Biocrusts provide numerous ecological functions in drylands. Recovering biocrusts via cyanobacterial inoculation recently gathered interest for ecological restoration, yet it still lacks long-term experiments to unravel biocrust community dynamics. To examine how cyanobacterial inoculants influenced local microbial community and biocrust development, we observed a 2 km² (Qubqi Desert, China) inoculation experiment after 10 and 15 years, following biocrust formation. Our results revealed that biocrust development was in line with ecological regime shift, providing evidence for biocrust community succession, from cyanobacteria- to moss-dominated types. Associated with biocrust development, microbial communities differed significantly with less specialists compared to shifting sands. Cyanobacterial community analysis showed that Microcoleus vaginatus and Scytonema javanicum are an ideal inoculating model, as they were still dominating the community after 15 years since inoculation, while other nitrogen-fixing cyanobacteria occurred profusely with biocrust development. Biocrust community composition combined with thickness, Chl-a and exopolysaccharide measurements revealed the large variation of cyanobacterial ecological functions along biocrust development, suggesting a main function shift: from carbon fixation associated with exopolysaccharide secretion in bare sandy soils to nitrogen fixation in developed biocrusts. This large-scale field study verifies that cyanobacterial inoculation accelerates biocrust development and forwards succession, shaping the biocrust community composition over a long time.     

Increased temperature and altered summer precipitation have differential effects on biological soil crusts in a dryland ecosystem

Biological soil crusts (biocrusts) are common and ecologically important members of dryland ecosystems worldwide, where they stabilize soil surfaces and contribute newly fixed C and N to soils. To test the impacts of predicted climate change scenarios on biocrusts in a dryland ecosystem, the effects of a 2–3 °C increase in soil temperature and an increased frequency of smaller summer precipitation events were examined in a large, replicated field study conducted in the cold desert of the Colorado Plateau, USA. Surface soil biomass (DNA concentration), photosynthetically active cyanobacterial biomass (chlorophyll a concentration), cyanobacterial abundance (quantitative PCR assay), and bacterial community composition (16S rRNA gene sequencing) were monitored seasonally over 2 years. Soil microbial biomass and bacterial community composition were highly stratified between the 0–2 cm depth biocrusts and 5–10 cm depth soil beneath the biocrusts. The increase in temperature did not have a detectable effect on any of the measured parameters over 2 years. However, after the second summer of altered summer precipitation pattern, significant declines occurred in the surface soil biomass (avg. DNA concentration declined 38%), photosynthetic cyanobacterial biomass (avg. chlorophyll a concentration declined 78%), cyanobacterial abundance (avg. gene copies g^?1 soil declined 95%), and proportion of Cyanobacteria in the biocrust bacterial community (avg. representation in sequence libraries declined 85%). Biocrusts are important contributors to soil stability, soil C and N stores, and plant performance, and the loss or reduction of biocrusts under an altered precipitation pattern associated with climate change could contribute significantly to lower soil fertility and increased erosion and dust production in dryland ecosystems at a regional scale.     

Production of moss‐dominated biocrusts to enhance the stability and function of the margins of artificial water bodies

Margins of water reservoirs associated with dams can have high‐frequency tides, promoting soil erosion and nutrient leaching. We propose the use of biocrusts for restoration and ecological engineering purposes, due to their poikilohydric character, to stabilize reservoir margins. We promoted biocrust growth under controlled conditions, testing two types of substrate: native sand and organic substrate. After 2 months, biocrusts grew on organic substrate covering almost all the area, but not on native sand. This fast and easy nature‐based solution for soil stabilization can be used as an environmental engineering tool in highly degraded sites.     

Response and resilience of soil biocrust bacterial communities to chronic physical disturbance in arid shrublands

The impact of 10 years of annual foot trampling on soil biocrusts was examined in replicated field experiments at three cold desert sites of the Colorado Plateau, USA. Trampling detrimentally impacted lichens and mosses, and the keystone cyanobacterium, Microcoleus vaginatus, resulting in increased soil erosion and reduced C and N concentrations in surface soils. Trampled biocrusts contained approximately half as much extractable DNA and 20–52% less chlorophyll a when compared with intact biocrusts at each site. Two of the three sites also showed a decline in scytonemin-containing, diazotrophic cyanobacteria in trampled biocrusts. 16S rRNA gene sequence and terminal restriction fragment length polymorphism (T-RFLP) analyses of soil bacteria from untrampled and trampled biocrusts demonstrated a reduced proportion (23–65% reduction) of M. vaginatus and other Cyanobacteria in trampled plots. In parallel, other soil bacterial species that are natural residents of biocrusts, specifically members of the Actinobacteria, Chloroflexi and Bacteroidetes, became more readily detected in trampled than in untrampled biocrusts. Replicate 16S rRNA T-RFLP profiles from trampled biocrusts at all three sites contained significantly more fragments (n=17) than those of untrampled biocrusts (n⩽6) and exhibited much higher variability among field replicates, indicating transition to an unstable disturbed state. Despite the dramatic negative impacts of trampling on biocrust physical structure and composition, M. vaginatus could still be detected in surface soils after 10 years of annual trampling, suggesting the potential for biocrust re-formation over time. Physical damage of biocrusts, in concert with changing temperature and precipitation patterns, has potential to alter performance of dryland ecosystems for decades.     

Comparisons of ectomycorrhizae on pinyon pines (Pinus edulis; Pinaceae) across extremes of soil type and herbivory

Using field and greenhouse studies, we examined the relationships among pinyon pines (Pinus edulis), their ectomycorrhizal mutualists, and their moth herbivores as a function of soil fertility. We studied two soil types—the ash and cinder soils of the San Francisco volcanic field and nearby sandy loam soils. In the field, pinyons growing in cinders suffered from reduced moisture, negative nitrogen mineralization rates, low phosphate levels, reduced growth, and high moth herbivory relative to pinyons growing in sandy loam. Pinyons growing in cinders also had twofold higher levels of ectomycorrhizal colonization than their noncinder counterparts. Similarly, in the greenhouse, seedlings grown in cinders had higher levels of ectomycorrhizal colonization and greater numbers of ectomycorrhizae than seedlings grown in sandy loam. Seedling shoot growth was significantly enhanced by ectomycorrhizae in both soils. These patterns support three conclusions. First, field and greenhouse studies demonstrated that trees growing in nutrient-poor soils had higher levels of ectomycorrhizal colonization than trees growing in better soils. Second, across soil types, variation in ectomycorrhizal colonization was better predicted by soil fertility than by herbivory. However, herbivory negatively affected ectomycorrhizae in the stressful cinder environment. Third, although mycorrhizae can be parasitic under some conditions, ectomycorrhizae had mutualistic impacts on pinyon seedlings across the environmental extremes we studied.     

Soil-foraging animals alter the composition and co-occurrence of microbial communities in a desert shrubland

Animals that modify their physical environment by foraging in the soil can have dramatic effects on ecosystem functions and processes. We compared bacterial and fungal communities in the foraging pits created by bilbies and burrowing bettongs with undisturbed surface soils dominated by biocrusts. Bacterial communities were characterized by Actinobacteria and Alphaproteobacteria, and fungal communities by Lecanoromycetes and Archaeosporomycetes. The composition of bacterial or fungal communities was not observed to vary between loamy or sandy soils. There were no differences in richness of either bacterial or fungal operational taxonomic units (OTUs) in the soil of young or old foraging pits, or undisturbed soils. Although the bacterial assemblage did not vary among the three microsites, the composition of fungi in undisturbed soils was significantly different from that in old or young foraging pits. Network analysis indicated that a greater number of correlations between bacterial OTUs occurred in undisturbed soils and old pits, whereas a greater number of correlations between fungal OTUs occurred in undisturbed soils. Our study suggests that digging by soil-disturbing animals is likely to create successional shifts in soil microbial and fungal communities, leading to functional shifts associated with the decomposition of organic matter and the fixation of nitrogen. Given the primacy of organic matter decomposition in arid and semi-arid environments, the loss of native soil-foraging animals is likely to impair the ability of these systems to maintain key ecosystem processes such as the mineralization of nitrogen and the breakdown of organic matter, and to recover from disturbance.     

Do soil inoculants accelerate dryland restoration? A simultaneous assessment of biocrusts and mycorrhizal fungi

Biological soil crusts (biocrusts) and arbuscular mycorrhizal (AM) fungi are communities of soil organisms often targeted to assist in the achievement of multiple ecological restoration goals. In drylands, benefits conferred from biocrust and AM fungal inoculation, such as improved native plant establishment and soil stabilization, have primarily been studied separately. However, comparisons between these two types of soil inoculants and investigations into potential synergies between them, particularly at the plant community scale, are needed to inform on‐the‐ground management practices in drylands. We conducted two full‐factorial experiments—one in greenhouse mesocosms and one in field plots—to test the effects of AM fungal inoculation, biocrust inoculation, and their interaction on multiple measures of dryland restoration success. Biocrust inoculation promoted soil stabilization and plant drought tolerance, but had mixed effects on native plant diversity (positive in greenhouse, neutral in field) and productivity (negative in greenhouse, neutral in field). In greenhouse mesocosms, biocrust inoculation reduced plant biomass, which was antagonistic to % root length colonized by AM fungi. Inoculation with native or commercial AM fungi did not influence plant establishment, drought tolerance, or soil stabilization in either study, and few synergistic effects of simultaneous inoculation of AM fungi and biocrusts were observed. These results suggest that, depending on the condition of existing soil communities, inoculation with AM fungi may not be necessary to promote dryland restoration goals, while inoculation with salvaged biocrust inoculation may be beneficial in some contexts.     

滨海盐渍化土壤中蓝细菌多样性及分布

【目的】蓝细菌在贫瘠土壤的固氮、固碳中发挥着重要作用,然而土壤盐渍化对蓝细菌多样性及群落结构的影响还不清楚。本研究以莱州湾南岸及黄河口海水入侵盐渍化土壤为例,研究蓝细菌的多样性、群落结构及丰度沿盐度梯度的分布情况。【方法】利用自动核糖体间隔基因分析(ARISA)技术与群落相似性分析(ANOSIM)探究蓝细菌群落的差异与空间分布格局;通过16S rRNA基因克隆文库、测序与系统进化分析解析了3个典型盐度梯度样品中蓝细菌的群落组成;实时定量PCR测定蓝细菌16S rRNA拷贝数(丰度);BEST多元分析探寻影响蓝细菌分布的主要环境因子。【结果】蓝细菌在莱州湾南岸盐土中分布广泛,其群落结构在低(0.63%?1.27%)、中(1.55%?2.00%)、高盐度(2.39%?5.11%)样品组之间差异显著(P=0.03),而在不同含水量样品组间则不显著(P=0.09)。总体来看,群落结构主要受土壤盐度与含水量这两个因子联合控制(P=0.02)。低盐样品中蓝细菌多样性和丰富度最低,并以Halomicronema和Acaryochloris为优势类群。Leptolyngbya在中、高盐土中占优势。Arthrospira与Geitlerinema仅在低盐土中检测到,而Oscillatoria则仅出现在高盐土中。随盐度升高蓝细菌丰度呈下降趋势,低盐土样中蓝细菌丰度(2.14×105 copies/g干土)显著高于中盐土(1.25×105 copies/g干土)(P<0.05);高盐度土为1.20×105 copies/g干土。【结论】盐渍化程度是调控莱州湾南岸滨海土壤中蓝细菌群落结构与丰度的最重要环境因子,可能对滨海土壤微生物碳氮循环产生重要影响。     

High Bacterial Diversity of Biological Soil Crusts in Water Tracks over Permafrost in the High Arctic Polar Desert

In this study we report the bacterial diversity of biological soil crusts (biocrusts) inhabiting polar desert soils at the northern land limit of the Arctic polar region (83° 05 N). Employing pyrosequencing of bacterial 16S rRNA genes this study demonstrated that these biocrusts harbor diverse bacterial communities, often as diverse as temperate latitude communities. The effect of wetting pulses on the composition of communities was also determined by collecting samples from soils outside and inside of permafrost water tracks, hill slope flow paths that drain permafrost-affected soils. The intermittent flow regime in the water tracks was correlated with altered relative abundance of phylum level taxonomic bins in the bacterial communities, but the alterations varied between individual sampling sites. Bacteria related to the Cyanobacteria and Acidobacteria demonstrated shifts in relative abundance based on their location either inside or outside of the water tracks. Among cyanobacterial sequences, the proportion of sequences belonging to the family Oscillatoriales consistently increased in relative abundance in the samples from inside the water tracks compared to those outside. Acidobacteria showed responses to wetting pulses in the water tracks, increasing in abundance at one site and decreasing at the other two sites. Subdivision 4 acidobacterial sequences tended to follow the trends in the total Acidobacteria relative abundance, suggesting these organisms were largely responsible for the changes observed in the Acidobacteria. Taken together, these data suggest that the bacterial communities of these high latitude polar biocrusts are diverse but do not show a consensus response to intermittent flow in water tracks over high Arctic permafrost.     

Litter Decomposition Rates of Biocrust-Forming Lichens Are Similar to Those of Vascular Plants and Are Affected by Warming

Ecosystems - Despite the high relevance of communities dominated by lichens, mosses and cyanobacteria living on the soil surface (biocrusts) for ecosystem functioning in drylands, no study to date...     

Vegetation gradients around artificial water points in the Central Kalahari Game Reserve of Botswana

Vegetation was assessed in plots sited at varying distances along two line transects radiating from each of nine artificial water points. Environmental variables such as distance from water point, soil type and ground cover were related to grass species composition. Grass species composition in calcrete soils differed significantly from that found in sandy soils. On calcrete soils, distance from water point did not have a significant effect on species composition. On sandy soils, distance from water point had a significant effect on species composition at two of the nine water points sampled. At these two water points, grass species that are usually associated with disturbed areas dominated close to the water points while those that dominated far from the water points were those that are usually associated with undisturbed sites. The results therefore indicate that there was no severe degradation of habitat around water points.     

Production of greenhouse‐grown biocrust mosses and associated cyanobacteria to rehabilitate dryland soil function

Mosses are an often‐overlooked component of dryland ecosystems, yet they are common members of biological soil crust communities (biocrusts) and provide key ecosystem services, including soil stabilization, water retention, carbon fixation, and housing of N₂ fixing cyanobacteria. Mosses are able to survive long dry periods, respond rapidly to precipitation, and reproduce vegetatively. With these qualities, dryland mosses have the potential to be an excellent dryland restoration material. Unfortunately, dryland mosses are often slow growing in nature, and ex situ cultivation methods are needed to enhance their utility. Our goal was to determine how to rapidly produce, vegetatively, Syntrichia caninervis and S. ruralis, common and abundant moss species in drylands of North America and elsewhere, in a greenhouse. We manipulated the length of hydration on a weekly schedule (5, 4, 3, or 2 days continuous hydration per week), crossed with fertilization (once at the beginning, monthly, biweekly, or not at all). Moss biomass increased sixfold for both species in 4 months, an increase that would require years under dryland field conditions. Both moss species preferred short hydration and monthly fertilizer. Remarkably, we also unintentionally cultured a variety of other important biocrust organisms, including cyanobacteria and lichens. In only 6 months, we produced functionally mature biocrusts, as evidenced by high productivity and ecosystem‐relevant levels of N₂ fixation. Our results suggest that biocrust mosses might be the ideal candidate for biocrust cultivation for restoration purposes. With optimization, these methods are the first step in developing a moss‐based biocrust rehabilitation technology.     

黄土丘陵区生物结皮群落组成与水分入渗的关系

黄土丘陵区坡面尺度生物结皮多是由藻、藓和地衣等以不同比例、不同方式组合的一个复杂群落结构,显著影响水分入渗,但目前混合生物结皮水分入渗与其群落结构之间的关系仍不清楚,妨碍了对坡面尺度生物结皮土壤渗透性的评估。本研究测定了藻结皮、藓结皮及藓结皮盖度分别为<15%、15%～30%、30%～45%、45%～60%、＞60% 5个不同藻藓比例的混合生物结皮的稳定入渗速率,采用主成分分析和通径分析揭示混合生物结皮水分稳定入渗速率的影响因素,明确混合生物结皮水分稳定入渗速率与群落结构之间的关系。结果表明: 藻结皮和藓结皮土壤饱和导水率分别为0.66和2.40 mm·min^-1。藓结皮盖度从<15%到>60%的混合生物结皮的稳定入渗速率为0.80～2.30 mm·min^-1。混合生物结皮水分稳定入渗速率主要与藓结皮盖度和藓结皮改善的土壤孔隙结构密切相关,相关系数分别为0.636(P=0.011)和0.835(P=0.000)。通过藻结皮和藓结皮土壤饱和导水率与盖度加权预测的混合生物结皮水分入渗量(y)与混合生物结皮实测水分入渗量(x)具有极显著相关关系(r=0.945),二者拟合的线性函数为y=0.85x(R²=0.98,P<0.05)。本研究明确了混合生物结皮水分入渗与单一组成生物结皮水分入渗之间的关系,为准确评估该区生物结皮水文过程提供了科学依据。     

Trade-off between C and N recycling and N<Subscript>2</Subscript>O emissions of soils with summer cover crops in subtropical agrosystems

Aims

Biological soil crusts (biocrusts) are soil-surface communities in drylands, dominated by cyanobacteria, mosses, and lichens. They provide key ecosystem functions by increasing soil stability and influencing soil hydrologic, nutrient, and carbon cycles. Because of this, methods to reestablish biocrusts in damaged drylands are needed. Here we test the reintroduction of field-collected vs. greenhouse-cultured biocrusts for rehabilitation.

Methods

We collected biocrusts for 1) direct reapplication, and 2) artificial cultivation under varying hydration regimes. We added field-collected and cultivated biocrusts (with and without hardening treatments) to bare field plots and monitored establishment.

Results

Both field-collected and cultivated cyanobacteria increased cover dramatically during the experimental period. Cultivated biocrusts established more rapidly than field-collected biocrusts, attaining ~82% cover in only one year, but addition of field-collected biocrusts led to higher species richness, biomass (as assessed by chlorophyll a) and level of development. Mosses and lichens did not establish well in either case, but late successional cover was affected by hardening and culture conditions.

Conclusions

This study provides further evidence that it is possible to culture biocrust components from later successional materials and reestablish cultured organisms in the field. However, more research is needed into effective reclamation techniques.

     

混合生物结皮对土壤养分的影响与群落结构之关联——以黄土丘陵区的生物结皮为例

自然条件下生物结皮是藻、藓及地衣等结皮类型以不同比例组成的混合群落，显著影响土壤养分含量，目前混合生物结皮对土壤养分的影响与其群落结构的关系尚不清楚，限制了混合生物结皮土壤养分的评估。为此，研究通过测定单一组成的藻结皮、藓结皮以及80%藻+20%藓、60%藻+40%藓、40%藻+60%藓和20%藻+80%藓4个不同藻藓比例的混合生物结皮土壤有机碳、全氮、全磷、速效磷、铵态氮和硝态氮含量，研究了混合生物结皮土壤养分与其群落结构之间的关联。结果显示：(1)藓结皮层土壤有机碳、全氮、速效磷、铵态氮和硝态氮含量显著高于藻结皮，分别高出166.4%、77.2%、55.1%、56.2%和42.2%。(2)藻藓混合生物结皮土壤有机碳、全氮、速效磷和铵态氮含量与组成和盖度等结构特征有关，可以通过单一类型生物结皮土壤养分含量与盖度加权预测混合生物结皮土壤养分储量。(3)混合生物结皮土壤有机碳、全氮、速效磷和铵态氮储量实测值(x)与预测值(y)拟合的线性函数分别为y=0.97x、y=0.96x、y=1.18x和y=0.92x。(4)混合生物结皮对全磷和硝态氮含量的影响与群落结构无关。生物结皮对下层0—5 ...     

Nursing biocrusts: isolation,cultivation, and fitness test of indigenous cyanobacteria

Biological soil crusts (biocrust) are microbial communities that develop at the soil surface of drylands and play an important role in erosion control and fertility. Soil surface disturbance from a broad range of natural and human processes (e.g. fire, livestock grazing, off‐road traffic) cause significant losses in biocrust cover and associated ecosystems services. Hence, biocrust restoration is emerging as an important intervention strategy to rehabilitate degraded dryland soils. In a multistep process, we designed protocols for the establishment of “microbial nurseries” to produce photosynthetic cyanobacterial inoculum for biocrust seeding at scale. We first report on the strategy for isolation, directly from the target site, of a large culture collection of cyanobacteria that included multiple representatives of the five most common biocrust taxa. After genetic pedigreeing of these isolates, we could select those that best matched field populations genetically for scale‐up cultivation. We then developed protocols for effective cyanobacterial biomass production to obtain sufficient inoculum. This was followed by conditioning treatments (hardening off) to preacclimate this inoculum to the stressful conditions expected in the field. Finally, we show that the inoculum obtained was fit to thrive in its original soil under natural outdoor conditions if sufficient water was available. We repeated this process successfully for four sites, two in the hot Chihuanuan desert and two in the cooler Great Basin Desert, and on two textural types of soils in each. The cyanobacterial biocrust nursery approach represents a versatile, viable, and safe tool for the rehabilitation of dryland soils.