Litter- and ecosystem-driven decomposition under elevated CO2 and enhanced N deposition in a Sphagnum peatland

Peatlands represent massive global C pools and sinks. Carbon accumulation depends on the ratio between net primary production and decomposition, both of which can change under projected increases of atmospheric CO₂ and N deposition. The decomposition of litter is influenced by 1) the quality of the litter, and 2) the microenvironmental conditions in which the litter decomposes. This study aims at experimentally testing the effects of these two drivers in the context of global change. We studied the in situ litter decomposition from three common peatland species (Eriophorum vaginatum, Polytrichum strictum and Sphagnum fallax) collected after one year of litter production under pre-treatment conditions (elevated CO₂: 560 ppm or enhanced N: 3 g m⁻² y⁻¹ NH₄NO₃) and decomposed the following year under treatment conditions (same as pre-treatment). By considering the cross-effects between pre-treatments and treatments, we distinguished between the effects on mass loss of 1) the pre-treatment-induced litter quality and 2) the treatment conditions under which the litters were decomposing. The combination between CO₂ pre-treatment and CO₂ treatment reduced Polytrichum decomposition by −24% and this can be explained by litter quality-driven decomposition changes brought by the pre-treatment. CO₂ pre-treatment reduced Eriophorum litter quality, although this was not sufficient to predict decomposition. The N addition pre-treatment reduced the decomposition of Eriophorum, due to enhanced lignin and soluble phenols concentrations in the initial litter, and reduced litter-driven losses of starch and enhanced litter-driven losses of soluble phenols. While decomposition indices based on initial litter quality provide a broad explanation of quantitative and qualitative decomposition, they can only be taken as first approximations. Indeed, the microbial ATP activity, the litter N loss and resulting litter quality, were strongly altered irrespective of the compounds' initial concentration and by means of processes that occurred independently of the initial litter-qualitative changes. The experimental design was valuable to assess litter- and ecosystem-driven decomposition pathways simultaneously or independently. The ability to separate these two drivers makes it possible to attest the presence of litter-qualitative changes even without any litter biochemical determinations, and shows the screening potential of this approach for future experiments dealing with multiple plant species.     

Priming effects: Interactions between living and dead organic matter

In this re-evaluation of our 10-year old paper on priming effects, I have considered the latest studies and tried to identify the most important needs for future research. Recent publications have shown that the increase or decrease in soil organic matter mineralization (measured as changes of CO₂ efflux and N mineralization) actually results from interactions between living (microbial biomass) and dead organic matter. The priming effect (PE) is not an artifact of incubation studies, as sometimes supposed, but is a natural process sequence in the rhizosphere and detritusphere that is induced by pulses or continuous inputs of fresh organics. The intensity of turnover processes in such hotspots is at least one order of magnitude higher than in the bulk soil. Various prerequisites for high-quality, informative PE studies are outlined: calculating the budget of labeled and total C; investigating the dynamics of released CO₂ and its sources; linking C and N dynamics with microbial biomass changes and enzyme activities; evaluating apparent and real PEs; and assessing PE sources as related to soil organic matter stabilization mechanisms. Different approaches for identifying priming, based on the assessment of more than two C sources in CO₂ and microbial biomass, are proposed and methodological and statistical uncertainties in PE estimation and approaches to eliminating them are discussed. Future studies should evaluate directions and magnitude of PEs according to expected climate and land-use changes and the increased rhizodeposition under elevated CO₂ as well as clarifying the ecological significance of PEs in natural and agricultural ecosystems. The conclusion is that PEs - the interactions between living and dead organic matter - should be incorporated in models of C and N dynamics, and that microbial biomass should regarded not only as a C pool but also as an active driver of C and N turnover.     

Soil texture affects soil microbial and structural recovery during grassland restoration

Many biotic and abiotic factors influence recovery of soil communities following prolonged disturbance. We investigated the role of soil texture in the recovery of soil microbial community structure and changes in microbial stress, as indexed by phospholipid fatty acid (PLFA) profiles, using two chronosequences of grasslands restored from 0 to 19 years on silty clay loam and loamy fine sand soils in Nebraska, USA. All restorations were formerly cultivated fields seeded to native warm-season grasses through the USDA’s Conservation Reserve Program. Increases in many PLFA concentrations occurred across the silty clay loam chronosequence including total PLFA biomass, richness, fungi, arbuscular mycorrhizal fungi, Gram-positive bacteria, Gram-negative bacteria, and actinomycetes. Ratios of saturated:monounsaturated and iso:anteiso PLFAs decreased across the silty clay loam chronosequence indicating reduction in nutrient stress of the microbial community as grassland established. Multivariate analysis of entire PLFA profiles across the silty clay loam chronosequence showed recovery of microbial community structure on the trajectory toward native prairie. Conversely, no microbial groups exhibited a directional change across the loamy fine sand chronosequence. Changes in soil structure were also only observed across the silty clay loam chronosequence. Aggregate mean weighted diameter (MWD) exhibited an exponential rise to maximum resulting from an exponential rise to maximum in the proportion of large macroaggregates (>2000 μm) and exponential decay in microaggregates (<250 μm and >53 μm) and the silt and clay fraction (<53 μm). Across both chronosequences, MWD was highly correlated with total PLFA biomass and the biomass of many microbial groups. Strong correlations between many PLFA groups and the MWD of aggregates underscore the interdependence between the recovery of soil microbial communities and soil structure that may explain more variation than time for some soils (i.e., loamy fine sand). This study demonstrates that soil microbial responses to grassland restoration are modulated by soil texture with implications for estimating the true capacity of restoration efforts to rehabilitate ecosystem functions.     

Loss of low molecular weight dissolved organic carbon (DOC) and nitrogen (DON) in H2O and 0.5 M K2SO4 soil extracts

Soil extracts are routinely used to quantify dissolved organic nutrient concentrations in soil. Here we studied the loss and transformation of low molecular weight (LMW) components of DOC (¹⁴C-glucose, 1 and 100 μM) and DON (¹⁴C-amino acid mixture, 1 and 100 μM) during extraction of soil (0-6 h) with either distilled water or 0.5 M K₂SO₄. The extractions were performed at 20 °C, at 4 °C, or in the presence of an inhibitor of microbial activity (HgCl₂ and Na-azide). We showed that both glucose and amino acids became progressively lost from solution with increasing shaking time. The greatest loss was observed in H₂O extracts at 1 μM for both substances (>90% loss after 15 min). Lower temperature (4 °C) and presence of K₂SO₄ both resulted in reduced loss rates. The presence of microbial inhibitors effectively eliminated the loss of glucose and amino acids. We conclude that microbial transformation of LMW-DOC and DON during H₂O or K₂SO₄ extraction of soil may affect the estimation of their concentrations in soil. This finding has significant implications for methods that rely on chemical extractions to estimate LMW-C components of DOC and DON.     

Influence of leaf litter types on microbial functions and nutrient status of soil: Ecological suitability of forest trees for afforestation in tropical laterite wastelands

The impact of forest tree leaf litters on microbial activity and nutrient status of red laterite soil was tested for the ecological suitability of Cassia siamea, Shorea robusta, Acacia auriculiformes and Dalbergia sissoo, which are typically used for afforestation of wastelands in eastern India. The objectives were to compare seasonal variation in soil enzyme activity in 30-years old afforested sites, and to study nutrient status and microbial biomass and function during short-term in-situ incubation of litter in decomposition pits. In afforested soils, enzyme activities significantly varied between litters and seasons. All enzyme activity except invertase dominated in the soils containing Dalbergia and Cassia litters compared to the others. The seasonal effect was enzyme-dependent, with amylase and cellulase reaching peaks during the rainy season but invertase activity showed a reverse trend with lowest values in rainy season, except in Acacia soil, and protease activity was lowest in the soil containing Cassia and Dalbergia during the rainy season. Dehydrogenase activity was negligible in the soils containing Shorea and Acacia, but remained high with respect to Dalbergia and Cassia during all seasons. The decomposition pit study showed significant increase of soil nutrients with respect to litter types and intervals, except with respect to electrical conductivity. Cassia and Dalbergia litters enabled notable increase of soil nutrients than Shorea and Acacia. The soil enzyme activity, in general, increased with duration of litter decay, but microbial biomass C (MBC) decreased over time except in Shorea. Therefore, the enzyme rates normalized to the MBC indicated inverse relations for all enzymes, except in the soil containing Shorea. A positive relationship existed between MBC and soil respiration in Cassia, Acacia and Dalbergia. Analysis of variance revealed main effects of litter types for increasing protease, MBC and CO₂ output, and a main effect of intervals for enhancing enzymes other than cellulase. Rates of soil respiration were greater in soils contain Cassia and Dalbergia, and showed significant differences between litters and between intervals. All enzymes were significantly correlated with electrical conductivity, organic carbon and available phosphorus contents, and all enzymes except invertase were correlated with nitrate concentrations. The acidic soil pH did not affect enzyme activities, and soil nutrients exerted only weak effect on MBC and respiration. Our study showed that leaf litters of Cassia and Dalbergia trees improved the nutrient status and microbial activity in soil more so than Shorea and Acacia litters, and therefore, afforestation using Cassia and Dalbergia trees may be particularly suitable for soil restoration in tropical laterite wastelands.     

Microbial degradation and resynthesis of proteins during incubation of beech leaf litter in the presence of mineral phases

 Organic N constitutes more than 90% of total N in surface soil horizons. Amino acids, peptides and proteins represent the most abundant N species. There are indications that clay minerals influence the degradation of proteins, but little is known about the effect of oxides and hydroxides on protein decay. We therefore conducted an incubation experiment with mixtures of beech leaf litter and Fe oxide, Al hydroxide, Mn oxide or quartz sand. The protein amounts (quantified as α-NH₂–N) during the 498-day experiment were recorded. During the first 90–239 days, plant-derived proteins were decomposed, resulting in a decline of protein amounts to about 60% of the initial value. Later in the experiment, the protein amounts increased again to between 70% and 90% of the initial amount, because microbial resynthesis of proteins outweighed decomposition. The change from dominating decomposition to prevailing microbial resynthesis occurred when the microorganisms had to adapt to less favourable conditions and therefore built new, protein-rich biomass. Although the mineral phases did not influence protein decomposition initially, Fe oxide and Al hydroxide stabilized plant-derived proteins. Al hydroxide reduced protein resynthesis in the second phase of the experiment, probably due to a reduction of microbial activity. Mn oxide increased protein decomposition and lowered microbial resynthesis due to its oxidative properties. The mineral phases therefore resulted in a shift of the relative intensities of protein decomposition and microbial resynthesis. Received: 26 August 1998     

激活方法对水牛卵母细胞孤雌发育的影响

系统探讨了几种激活方法对水牛卵母细胞孤雌发育的影响。体外成熟 (IVM) 2 6 h的水牛卵母细胞经 7%乙醇(EH)、钙离子载体 (A2 3187)或离子霉素 (Ion)激活处理 5 min后 ,在 2 m mol/ L 6 -甲二氨基嘌呤 (6 - DMAP)中培养 3～4 h,然后再继续培养 6～ 11d,观察其胚胎发育情况。结果发现 ,5μmol/ L Ion激活处理的水牛卵母细胞分裂率显著高于 EH处理的卵母细胞 (6 3.0 % vs5 4 .2 % ,P<0 .0 5 ) ,其原核形成率也显著高于 EH处理的卵母细胞。激活处理前 ,无Ca2 培养液孵育时间的长短 ,对水牛卵母细胞孤雌发育无显著影响 (P>0 .0 5 )。如用 A2 3187激活处理水牛卵母细胞 ,其激活分裂率则随着浓度的升高而提高。从而表明 ,5 μmol/ L Ion可有效激活水牛卵母细胞     

植物生长调节剂在啤酒大麦上的增产效果试验初报

啤酒大麦使用W -HE生物表面活化剂、C -HE植物生长调节剂、喷施宝、丰产宝、生根粉能促进大麦生育前期的生长发育 ,增加分蘖 ,抑制后期的节间生长 ,有利于根系的发育和干物质的积累 ,对植株有较为明显的活化和调节作用 ,增产效果明显     

显微注射Ca^2＋激活小鼠M Ⅱ期卵母细胞

胞质内显微注入Ｃａ＾２＋可以激活小鼠Ｍ Ⅱ期卵母细胞，且随着卵龄的增加，激活率明显升高。卵龄小于１６ｈ（ｈＣＧ注射后）注射Ｃａ＾２＋引起的激活率很低，卵龄超过１８ｈ，激活率达到５０％以上。卵龄小于１６ｈ的卵母细胞，卵内注入超纯水未能激活卵母细胞，而在１８￣１９ｈ卵龄组，注射水的对照组激活率为３５％，但显著或极显著地低于注射Ｃａ＾２＋的试验组。激活前注射ＥＤＴＡ卵母细胞的激活率约为３０％，激活后注射     

微贮对秸秆在瘤胃NDF降解率的影响

试验采用3个重复对比设计，将玉米，小麦和稻草秸秆的微贮样与原样放置在永久瘘管牛体内，分别在6．12、24．36、48和72小时时间点取出样本进行NDF降解率试验测定分析，结果：秸秆处理样NDF在各个时间点的NDF瞬间降解率和有效降解率均极显著优于原样（P＞0．01）而玉米秸秆处理样与小麦和稻草处理样相比差异不显著（P＞0．05）。