Sheep-urine-induced changes in soil microbial community structure

Soil microbial communities play an important role in nutrient cycling and nutrient availability, especially in unimproved soils. In grazed pastures, sheep urine causes local changes in nutrient concentration which may be a source of heterogeneity in microbial community structure. In the present study, we investigated the effects of synthetic urine on soil microbial community structure, using physiological (community level physiological profiling, CLPP), biochemical (phospholipid fatty acid analysis, PLFA) and molecular (denaturing gradient gel electrophoresis, DGGE) fingerprinting methods. PLFA data suggested that synthetic urine treatment had no significant effect on total microbial (total PLFA), total bacterial or fungal biomass; however, significant changes in microbial community structure were observed with both PLFA and DGGE data. PLFA data suggested that synthetic urine induced a shift towards communities with higher concentrations of branched fatty acids. DGGE banding patterns derived from control and treated soils differed, due to a higher proportion of DNA sequences migrating only to the upper regions of the gel in synthetic urine-treated samples. The shifts in community structure measured by PLFA and DGGE were significantly correlated with one another, suggesting that both datasets reflected the same changes in microbial communities. Synthetic urine treatment preferentially stimulated the use of rhizosphere-C in sole-carbon-source utilisation profiles. The changes caused by synthetic urine addition accounted for only 10-15% of the total variability in community structure, suggesting that overall microbial community structure was reasonably stable and that changes were confined to a small proportion of the communities.     

Genome size evolution is associated with climate seasonality and glucosinolates,but not life history,soil nutrients or range size,across a clade of mustards

Background and AimsWe investigate patterns of evolution of genome size across a morphologically and ecologically diverse clade of Brassicaceae, in relation to ecological and life history traits. While numerous hypotheses have been put forward regarding autecological and environmental factors that could favour small vs. large genomes, a challenge in understanding genome size evolution in plants is that many hypothesized selective agents are intercorrelated.MethodsWe contribute genome size estimates for 47 species of Streptanthus Nutt. and close relatives, and take advantage of many data collections for this group to assemble data on climate, life history, soil affinity and composition, geographic range and plant secondary chemistry to identify simultaneous correlates of variation in genome size in an evolutionary framework. We assess models of evolution across clades and use phylogenetically informed analyses as well as model selection and information criteria approaches to identify variables that can best explain genome size variation in this clade.Key ResultsWe find differences in genome size and heterogeneity in its rate of evolution across subclades of Streptanthus and close relatives. We show that clade-wide genome size is positively associated with climate seasonality and glucosinolate compounds. Model selection and information criteria approaches identify a best model that includes temperature seasonality and fraction of aliphatic glucosinolates, suggesting a possible role for genome size in climatic adaptation or a role for biotic interactions in shaping the evolution of genome size. We find no evidence supporting hypotheses of life history, range size or soil nutrients as forces shaping genome size in this system.ConclusionsOur findings suggest climate seasonality and biotic interactions as potential forces shaping the evolution of genome size and highlight the importance of evaluating multiple factors in the context of phylogeny to understand the effect of possible selective agents on genome size.     

Efficiency of biochar,nitrogen addition,and microbial agent amendments in remediation of soil properties and microbial community in Qilian Mountains mine soils

Lacking systematic evaluations in soil quality and microbial community recovery after different amendments addition limits optimization of amendments combination in coal mine soils. We performed a short‐term incubation experiment with a varying temperature over 12 weeks to assess the effects of three amendments (biochar: C; nitrogen fertilizer at three levels: N‐N1~N3; microbial agent at two levels: M‐M1~M2) based on C/N ratio (regulated by biochar and N level: 35:1, 25:1, 12.5:1) on mine soil properties and microbial community in the Qilian Mountains, China. Over the incubation period, soil pH and MBC/MBN were significantly lower than unamended treatment in N addition and C + M + N treatments, respectively. Soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), available potassium (AK), microbial biomass carbon (MBC), and nitrogen (MBN) contents increased significantly in all amended treatments (p < .001). Higher AP, AK, MBC, MBN, and lower MBC/MBN were observed in N2‐treated soil (corresponding to C/N ratio of 25:1). Meanwhile, N2‐treated soil significantly increased species richness and diversity of soil bacterial community (p < .05). Principal coordinate analysis further showed that soil bacterial community compositions were significantly separated by N level. C‐M‐N treatments significantly increased the relative abundance (>1%) of the bacterial phyla Bacteroidetes and Firmicutes, and decreased the relative abundance of fungal phyla Chytridiomycota (p < .05). Redundancy analysis illustrated the importance of soil nutrients in explaining variability in bacterial community composition (74.73%) than fungal composition (35.0%). Our results indicated that N addition based on biochar and M can improve soil quality by neutralizing soil pH and increasing soil nutrient contents in short‐term, and the appropriate C/N ratio (25:1) can better promote microbial mass, richness, and diversity of soil bacterial community. Our study provided a new insight for achieving restoration of damaged habitats by changing microbial structure, diversity, and mass by regulating C/N ratio of amendments.     

漓江上游毛竹生理生态特征对不同土壤水分的响应

漓江上游毛竹林面积大,是我国毛竹最南端产区。该研究针对当地季节性干旱问题,通过模拟降水使土壤水分变化,共设立了5个毛竹水分处理小区(CK.对照;A.无降水+覆膜;B.降水5 mm+覆膜;C.降水10mm+覆膜;D.降水20 mm+覆膜),并与HM(木荷Schima superba)(自然状态)进行对比。结果表明:土壤水分变化影响了毛竹叶片水势和叶绿素的变化,叶片白天水势下降,傍晚均可恢复到凌晨水势。C处理的毛竹午间水势下降值最小,叶绿素含量也最高。本研究区位于最南端产区,毛竹的光合生产力也属偏低水平。适当的土壤水分亏缺,毛竹表现出相对的高净光合速率(P_(n))、高蒸腾速率(Tr)、低水分利用效率(WUE)的特点;过多或过少土壤水分,则为低P_(n)和Tr,但高WUE。毛竹叶片的P_(n)与气孔导度Gs呈极显著的正相关关系,说明毛竹的光合速率受气孔调节明显;Tr与午时叶水势呈负相关(符合二项式函数)关系,土壤水分问题造成的叶片水分不足同时也影响了毛竹的Tr。水分亏缺,P_(n)主要由气孔调节,但水分过多导致P_(n)的下降应该是由气孔导度的下降和叶肉细胞光合能力的下降共同作用的结果。水分过少或过多均对毛竹生理生态过程产生负效应。相对于木荷,毛竹的P_(n)较高,但同时也消耗更多的水分。     

Effect of organic and conventional farming on soil bacterial diversity of pecan tree (Carya illinoensis K. Kosh) orchard across two phenological stages

We described the bacterial diversity of walnut grove soils under organic and conventional farming. The bacterial communities of rhizospheric and nonrhizospheric soils of pecan tree (Carya illinoensis K. Koch) were compared considering two phenological stages (sprouting and ripening). Sixteen operational taxonomic units (OTUs) were identified significantly more abundant according to the plant development, only one according to the farming condition, and none according to the soil origin. The OTUs specificaly abundant according to plant development included Actinobateria (2) and Betaproteobacteria (1) related OTUs more abundant at the sprouting stage, while at the fruit ripening (FR) stage the more abundant OTUs were related to Actinobacteria (6), Alphaproteobacteria (6), and unclassified Bacteria (1). The Gaiellaceae OTU18 (Actinobacteria) was more abundant under conventional farming. Thus, our study revealed that the plant development stage was the main factor shaping the bacterial community structure, while less influence was noticed for the farming condition. The bacterial communities exhibited specific metabolic capacities, a large range of carbon sources being used at the FR stage. The identified OTUs specifically more abundant represent indicators providing useful information on soil condition, potential tools for the management of soil bacterial communities.     

Mycorrhizal suppression and phosphorus addition influence the stability of plant community composition and function in a temperate steppe

Nutrient enrichment can reduce ecosystem stability, typically measured as temporal stability of a single function, e.g. plant productivity. Moreover, nutrient enrichment can alter plant–soil interactions (e.g. mycorrhizal symbiosis) that determine plant community composition and productivity. Thus, it is likely that nutrient enrichment and interactions between plants and their soil communities co-determine the stability in plant community composition and productivity. Yet our understanding as to how nutrient enrichment affects multiple facets of ecosystem stability, such as functional and compositional stability, and the role of above–belowground interactions are still lacking. We tested how mycorrhizal suppression and phosphorus (P) addition influenced multiple facets of ecosystem stability in a three-year field study in a temperate steppe. Here we focused on the functional and compositional stability of plant community; functional stability is the temporal community variance in primary productivity; compositional stability is represented by compositional resistance, turnover, species extinction and invasion. Community variance was partitioned into population variance defined as community productivity weighted average of the species temporal variance in performance, and species synchrony defined as the degree of temporal positive covariation among species. Compared to treatments with mycorrhizal suppression, the intact AM fungal communities reduced community variance in primary productivity by reducing species synchrony at high levels of P addition. Species synchrony and population variance were linearly associated with community variance with the intact AM fungal communities, while these relationships were decoupled or weakened by mycorrhizal suppression. The intact AM fungal communities promoted the compositional resistance of plant communities by reducing compositional turnover, but this effect was suppressed by P addition. P addition increased the number of species extinctions and thus promoted compositional turnover. Our study shows P addition and AM fungal communities can jointly and independently modify the various components of ecosystem stability in terms of plant community productivity and composition.     

Incorporation of mineral nitrogen into the soil food web as affected by plant community composition

Although nitrogen (N) deposition is increasing globally, N availability still limits many organisms, such as microorganisms and mesofauna. However, little is known to which extent soil organisms rely on mineral‐derived N and whether plant community composition modifies its incorporation into soil food webs. More diverse plant communities more effectively compete with microorganisms for mineral N likely reducing the incorporation of mineral‐derived N into soil food webs. We set up a field experiment in experimental grasslands with different levels of plant species and functional group richness. We labeled soil with ¹⁵NH₄ ¹⁵NO₃ and analyzed the incorporation of mineral‐derived ¹⁵N into soil microorganisms and mesofauna over 3 months. Mineral‐derived N incorporation decreased over time in all investigated organisms. Plant species richness and presence of legumes reduced the uptake of mineral‐derived N into microorganisms. In parallel, the incorporation of mineral‐derived ¹⁵N into mesofauna species declined with time and decreased with increasing plant species richness in the secondary decomposer springtail Ceratophysella sp. Effects of both plant species richness and functional group richness on other mesofauna species varied with time. The presence of grasses increased the ¹⁵N incorporation into Ceratophysella sp., but decreased it in the primary decomposer oribatid mite Tectocepheus velatus sarekensis. The results highlight that mineral N is quickly channeled into soil animal food webs via microorganisms irrespective of plant diversity. The amount of mineral‐derived N incorporated into soil animals, and the plant community properties affecting this incorporation, differed markedly between soil animal taxa, reflecting species‐specific use of food resources. Our results highlight that plant diversity and community composition alter the competition for N in soil and change the transfer of N across trophic levels in soil food webs, potentially leading to changes in soil animal population dynamics and community composition. Sustaining high plant diversity may buffer detrimental effects of elevated N deposition on soil biota.     

Nitrogen and phosphorus addition differentially enhance seed production of dominant species in a temperate steppe

Previous studies have demonstrated changes in plant growth and reproduction in response to nutrient availability, but responses of plant growth and reproduction to multiple levels of nutrient enrichment remain unclear. In this study, a factorial field experiment was performed with manipulation of nitrogen (N) and phosphorus (P) availability to examine seed production of the dominant species, Stipa krylovii, in response to N and P addition in a temperate steppe. There were three levels of N and P addition in this experiment, including no N addition (0 g N m⁻² year⁻¹), low N addition (10 g N m⁻² year⁻¹), and high N addition (40 g N m⁻² year⁻¹) for N addition treatment, and no P addition (0 g P m⁻² year⁻¹), low P addition (5 g P m⁻² year⁻¹), and high P addition (10 g P m⁻² year⁻¹) for P addition treatment. Low N addition enhanced seed production by 814%, 1371%, and 1321% under ambient, low, and high P addition levels, respectively. High N addition increased seed production by 2136%, 3560%, and 3550% under ambient, low, and high P addition levels, respectively. However, P addition did not affect seed production in the absence of N addition, but enhanced it under N addition. N addition enhanced seed production mainly by increasing the tiller number and inflorescence abundance per plant, whereas P addition stimulated it by decreasing the plant density yet stimulating height of plants and their seed number per inflorescence. Our results indicate seed production is not limited by P availability but rather by N availability in the temperate steppe, whereas seed production will be increased by P addition when N availability is improved. These findings enable a better understanding of plant reproduction dynamics in the temperate steppe under intensified nutrient enrichment and can inform their improved management in the future.     

注射施肥对桃园土壤环境和果实产量品质的影响

以盛果期10a生品种‘阿部白’桃为试材,在大田条件下,进行连续2年定位施肥试验,设置放射沟施全量肥(R_(NPK))、放射沟施半量肥(R_(1/2NPK))、注射施全量肥(I_(NPK))和注射施半量肥(I_(1/2NPK))4个处理,分析注射施肥对桃园0~60cm土层土壤养分含量、土壤酶活性和微生物数量以及果实品质的影响,探讨注射施肥在桃树生产中的应用,为高效施肥和提高水肥利用率提供理论依据。结果表明:(1)桃幼果膨大期(5月15日),0~40cm土层中,试验各处理的总氮钾含量差异不明显,注射施肥土壤中速效养分含量显著低于放射沟施肥;果实成熟前期(7月15日),在相同施肥量下,0~40cm土层中注射施肥处理的碱解氮、速效钾含量均以I_(NPK)处理的最高,且分别比放射沟施肥处理显著提高16.61%、12.56%和10.15%、23.93%,同时注射施肥处理的0~40cm土层中有机质含量均低于放射沟施肥处理,部分处理差异达显著性水平;不同处理对土壤中磷的影响较小。(2)果实成熟前期,0~60cm土层中注射施肥土壤中蔗糖酶、过氧化氢酶和脲酶活性,以及0~20cm土层的碱性磷酸酶均显著高于放射沟施肥;同期根际土壤微生物数量变化规律与土壤酶活性变化基本一致。(3)INPK处理的桃单果重、可溶性固形物含量显著高于其他施肥处理,且分别比R_(NPK)处理显著增加了12.24%和11.21%;I_(1/2NPK)处理的单株果实产量最高(65.25kg)并显著高于放射沟施肥处理,但与INPK处理间差异不显著。研究认为,注射施肥对桃树土壤中养分含量、土壤酶活性和微生物数量以及果实品质都有积极的影响,且以NPK全量注射施肥处理效果最佳。