Inorganic and organic carbon dynamics in forested soils developed on contrasting geology in Slovenia—a stable isotope approach

Purpose

Soil carbon dynamics were studied at four different forest stands developed on bedrocks with contrasting geology in Slovenia: one plot on magmatic granodiorite bedrock (IG), two plots on carbonate bedrock in the karstic-dinaric area (CC and CD), and one situated on Pleistocene coalluvial terraces (FGS).

Materials and methods

Throughfall (TF) and soil water were collected monthly at each location from June to November during 2005–2007. In soil water, the following parameters were determined: T, pH, total alkalinity, concentrations of Ca²⁺ and Mg²⁺, dissolved organic carbon (DOC), and Cl^? as well as δ¹³C_DIC. On the other hand, in TF, only the Cl^? content was measured. Soil and plant samples were also collected at forest stands, and stable isotope measurements were performed in soil and plant organic carbon and total nitrogen and in carbonate rocks. The obtained data were used to calculate the dissolved inorganic carbon (DIC) and DOC fluxes. Statistic analyses were carried out to compare sites of different lithologies, at different spatial and temporal scales.

Results and discussion

Decomposition of soil organic matter (SOM) controlled by the climate can explain the ¹³C and ¹⁵?N enrichment in SOM at CC, CD, and FGS, while the soil microbial biomass makes an important contribution to the SOM at IG. The loss of DOC at a soil depth of 5 cm was estimated at 1 mol m^?2 year^?1 and shows no significant differences among the study sites. The DOC fluxes were mainly controlled by physical factors, most notably sorption dynamics, and microbial–DOC relationships. The pH and pCO₂ of the soil solution controlled the DIC fluxes according to carbonate equilibrium reactions. An increased exchange between DIC and atmospheric air was observed for samples from non-carbonate subsoils (IG and FGS). In addition, higher δ¹³C_DIC values up to ?19.4?‰ in the shallow soil water were recorded during the summer as a consequence of isotopic fractionation induced by molecular diffusion of soil CO₂. The δ¹³C_DIC values also suggest that half of the DIC derives from soil CO₂ indicating that 2 to 5 mol m^?2 year^?1 of carbon is lost in the form of dissolved inorganic carbon at CC and CD after carbonate dissolution.

Conclusions

Major difference in soil carbon dynamics between the four forest ecosystems is a result of the combined influence of bedrock geology, soil texture, and the sources of SOM. Water flux was a critical parameter in quantifying carbon depletion rates in dissolved organic and inorganic carbon forms.

     

Phosphorus-use efficiency of kale genotypes from coastal Croatia

Understanding the mechanisms of phosphorus (P)-use efficiency (PUE) may contribute to enhancing crop P nutrition because species growth variability at low-P is well known. The experiment was carried out to evaluate the response of kale genotypes to different P supply in randomized block design in three replications. Low-P supply led to a decrease in most parameters, whereas an increase was recorded in root growth parameters. Genotypes differed in shoot dry weight (DW), leaf area, root length and area, and shoot and root P content and concentration. Root traits significantly positively correlated with PUE. Genotypes Red Russian (RR) and IJK 17 were superior in terms of shoot DW production at low P supply, and had the highest uptake efficiency. Genotypes IJK 17 and 81 had the highest P utilization efficiency, while Vates blue curled (VBC) showed the lowest PUE. Genotypes had similar shoot P content and concentration at low P supply, but large PUE differences, implying the importance of P utilization efficiency.     

The sensitivity of water extractable soil organic carbon fractions to land use in three soil types

Soil organic carbon (SOC) has a high impact on the sustainability of ecosystems, global environmental processes, soil quality and agriculture. Long-term tillage usually leads to SOC depletion. The purpose of this study was to determine the impact of different land uses on water extractable organic carbon (WEOC) fractions and to evaluate the interaction between the WEOC fractions and other soil properties. Using an extraction procedure at 20°C and 80°C, two fractions were obtained: a cold water extractable organic carbon (CWEOC) and a hot water extractable organic carbon (HWEOC). The results suggest that there is a significant impact from different land uses on WEOC. A lower relative contribution of WEOC in SOC and a lower concentration of labile WEOC fractions are contained in arable soil compared to forestlands. Chernozem soil was characterized by a lower relative contribution of WEOC to the SOC and thus higher SOC stability in contrast to Solonetz and Vertisol soils. Both CWEOC and HWEOC are highly associated with SOC in the silt and clay fraction (<53 µm) and were slightly associated with SOC in the macroaggregate classes. The WEOC fractions were highly and positively correlated with the SOC and mean weight diameter.     

Empirical predictions of plant material C and N mineralization patterns from near infrared spectroscopy, stepwise chemical digestion and C/N ratios

Prediction of carbon (C) and nitrogen (N) mineralization patterns of plant litter is desirable for both agronomic and environmental reasons. Near infrared reflectance (NIR) spectroscopy has recently been introduced in decomposition studies to characterize biochemical composition. The purpose of the current study was to use empirical techniques to predict C and N mineralization patterns of a wide range of plant materials incubated under controlled temperature and moisture conditions. We hypothesized that the richness of information in the NIR spectra would considerably improve predictions compared to traditional stepwise chemical digestion (SCD) or C/N ratios. Initially, we fitted a number of empirical functions to the observed C and N mineralization patterns. The best functions fitted with R²=0.990 and 0.949 to C and N, respectively. The fractions of C and N mineralized at different points in time were then either predicted directly with regression functions or indirectly by prediction of the parameters of the empirical functions fitted to incubation data. In both cases, partial least squares (PLS) regressions were used and predictions were validated by cross-validations. We found that the NIR spectra (best R²=0.925) were able to predict C mineralization patterns marginally better than the SCD fractions (best R²=0.911), but considerably better than the C/N ratios (best R²=0.851). In contrast, N mineralization was better predicted by SCD fractions (best R²=0.533) than the C/N ratio (best R²=0.497), which was better than NIR predictions (best R²=0.446). Although the predictions with the NIR spectra were only slightly better for C and worse for N mineralization compared to SCD fractions, NIR spectroscopy still holds advantages, as it is a much less laborious and cheaper analytical method. Furthermore, exploration of the applications of NIR spectroscopy in decomposition studies has only just begun, and offers new ways to gain insights into the decomposition process.     

In vitro determination of the indigestible fraction in foods: an alternative to dietary fiber analysis

Dietary fiber (DF) intakes in Western countries only accounts for about one-third of the substrates required for colonic bacterial cell turnover. There is a general trend among nutritionists to extend the DF concept to include all food constituents reaching the colon. In this line, a method to quantify the major nondigestible components in plant foods, namely, the indigestible fraction (IF), is presented. Analytical conditions for IF determination are close to physiological. Samples, analyzed as eaten, were successively incubated with pepsin and alpha-amylase; after centrifugation and dialysis, insoluble and soluble IFs were obtained. IF values include DF, resistant starch, resistant protein, and other associated compounds. IF contents determined in common foods (cereals, legumes, vegetables, and fruits) were higher than DF contents. Calculated IF intakes were close to the estimated amount of substrates reaching the colon. IF data could be more useful than DF data from a nutritional point of view; therefore, IF is proposed as an alternative to DF for food labeling and food composition tables.     

绵羊X染色体59194976位点多态分析及其与尾（臀）脂性状相关性研究

尾脂沉积能力在脂尾型绵羊和瘦尾型绵羊问存在很大的差异,但其沉积脂肪的遗传特性与分子机制仍不明晰。为此,本研究选择尾型极端差异的阿勒泰羊（巨型脂臀）、湖羊（短脂尾）和黑萨福克羊（长瘦尾）,采用PCR-RFLP方法检测绵羊X染色体59194976位点多态性,分析其与尾（臀）脂沉积能力的相关性。结果表明：在阿勒泰羊群体中G等位基因属优势等位基因,其两等位基因比值（G／A）分别是湖羊和黑萨福克羊的6倍和68倍,且G等位基因在阿勒泰羊中趋于纯合。卡方检验结果表明,阿勒泰羊在该位点均处于Hardy-Weinberg平衡状态（p〉0．05）,而湖羊和黑萨福克羊在该位点均处于Hardy-Weinberg极不平衡状态（p〈0．01）。以上结果提示,绵羊x染色体59194976位点SNP可作为理想的分子标记应用于高、低脂绵羊品种选育。     

冻土沼泽地区的管道维抢修方法

为增强冻土沼泽地区的管道应急抢险能力,根据冻土沼泽的特点,提出了一套包括挖渠布栏、浮船拖拽、彩钢板道路、沉箱支固的冻土沼泽管道维抢修方法.其中,在拦油渠内布设围油栏,通过两层甚至多层挖渠布栏,在层间挖设集油坑将汇集的油品集中抽至储油囊回收的方法为国内外首次采用.结合管道冻土沼泽地区植被丰富,承载力强的特点,自行制作旱船,解决了大型设备进场难的问题.结合管道维抢修实际需求研制的新型钢制沉箱,可折叠、易运输,而且能够有效地支固作业坑和防水.该套方法的可行性在漠河-大庆原油管道沼泽地区的维抢修演练中得到了验证.     

两种玉米温敏不育系的育性相关性状的比较及不育基因的初步定位

本研究通过形态学、生态学、遗传学及基因定位研究表明,玉米温敏不育系琼6Qms和琼68S是两种完全不同的玉米温敏不育系,琼6Qms的育性主要表现为颖壳不开裂,育性转换主要受温度影响,该性状由两对隐性重叠不育基因控制,分别位于第3和第5染色体上。琼68S为花药败育型,其育性转换受温度控制,不育性由一对隐性基因控制,该基因位于第2染色体上。     

Ripening-related defense proteins in Annona fruit

In order to obtain a better understanding of the active defense strategy of cherimoya (Annona cherimola Mill.) fruit, hydrolytic and antifungal activity, as well as expression of proteins functionally and immunogenically related to the pathogenesis-related proteins chitinase (PR-Q) and 1,3-β-glucanase (PR-2), were estimated in fruit at different ripening stages. Increase in expression of the 27 kDa constitutive chitinase and the induction of two new proteins, a 26 kDa chitinase and a 51 kDa 1,3-β-glucanase were associated with enhanced in vitro hydrolytic and antifungal activity of the acidic protein extract in ripe fruit. Ripening modified the expression of constitutive basic isoenzymes, with a sharp decrease in both relative accumulation and hydrolytic activity. Likewise, a new basic 33 kDa chitinase was induced in the over-ripe fruit, concomitant with accumulation of a basic constitutive 76 kDa 1,3-β-glucanase. At this stage, the basic protein extract modified in vitro growth inhibition of Botrytis cinerea. Short-term high CO₂ treatment delayed fruit ripening and maintained a similar distribution of activity and isoenzymatic pattern in both protein fractions to that in unripe fruit. These results indicate that the changes in the pattern of defense proteins and hydrolytic activity in cherimoyas appear to be associated with ripening. Moreover, unlike the constitutively expressed isoenzymes, only the transitorily induced chitinases and 1,3-β-glucanases were associated with an active defense-related response.