Influence of grazing on the decomposition of Pinus pinea L. needles in a silvopastoral system in Doñana, Spain

Aims

The aim of this study was to determine whether goat grazing in the understory of a pine forest at Doñana Natural Park could accelerate the decomposition of the pine needles accumulated on the soil surface and, if so, through which mechanisms. Specifically, the roles of trampling (mechanical fragmentation) and nutrient enrichment through defecation (fertilization) were evaluated in terms of their effect on pine needle decomposition rates.

Methods

An experiment was conducted featuring the following 4 treatments: 1) intact needles (control), 2) trampled needles, 3) intact needles fertilized with liquid manure, and 4) trampled needles fertilized with liquid manure. Litter decomposition was determined as a function of mass loss over time, using the litter-bag method. Bags were recovered 4, 8, 16, 24 and 36 months after burial in soil, dried and weighed. Needle length, leaf mass per area and C and N concentration were also measured in the buried litter-bags.

Results

Four months after burial, mass loss was greater in the trampled (23–27 %) than non-trampled (14–16 %) treatments. However, from 8 months onwards, decomposition rates in the fertilized treatments were significantly higher than those in the non-fertilized treatments (between 5 % and 15 % less mass loss). Meanwhile, fertilized treatments presented higher N content (2.1 %) than the non-fertilized ones (1.2 %), with a significantly lower C:N ratio also found in the in the fertilized treatment.

Conclusions

Trampling and fertilization during grazing accelerates litter decomposition and thus promotes the incorporation of N into the system. Acceleration of decomposition reduces the accumulation of pine needles on the soil surface, reducing the risk of fire.     

The extent of mycorrhizal colonization of roots and its influence on plant growth and phosphorus content

Aims

The most common metric of arbuscular mycorrhizal fungal (AMF) abundance is percent root length colonized (PRLC) by mycorrhizal structures. Frequently, plants with greater PRLC are assumed to receive more nutrients (such as phosphorus, P) from their mycorrhizal symbionts, leading to greater plant growth. Nevertheless, the functional significance of this metric remains controversial. In this review, I discuss whether manipulations of PRLC generally led to changes in plant biomass and P content, and whether AMF taxa and plant functional groups influence these relationships.

Methods

I conducted a meta-analysis of laboratory- and field-based trials in which mycorrhizal colonization was directly altered compared to unmanipulated controls. For each trial, I calculated (1) the difference in PRLC (ΔPRLC) between the treatments, and (2) the response ratio of plant biomass. In a subset of these studies, the response ratio of P content of host plants could also be calculated.

Results

The response ratio of plant biomass and P content rose significantly and exponentially as ΔPRLC increased. Nevertheless, ΔPRLC explained only a fraction of the variation in response ratios in each case. Moreover, AMF taxa varied in their effects on biomass per unit ΔPRLC. In addition, plant functional groups differed in effects on plant P content per unit ΔPRLC, with C4 grasses responding most strongly.

Conclusions

It appears that as the extent to which plant roots are colonized by AMF increases, plant growth and P content often increase, although substantial variability exists among trials. As others have found, a likely mechanism for this relationship is increased transfer of P (and perhaps other nutrients) through the more-prevalent mycorrhizal structures.     

Deficiency of mast cells in coronary artery endarterectomy of male patients with type 2 diabetes

Background

Increased fasting plasma glucose (FPG), which includes impaired fasting glucose (IFG), impaired glucose tolerance (IGT), and diabetes, is a risk factor for arterial stiffness. While IFG is widely accepted as a cardiovascular risk factor, recent studies have argued that subjects with high-normal glucose level were characterized by a high incidence of cardiovascular disease. The purpose of this study is to investigate the relationship between FPG and arterial stiffness in non-diabetic healthy subjects.

Methods

We recruited 697 subjects who visited the health promotion center of a university hospital from May 2007 to August 2008. Age, sex, body mass index (BMI), resting heart rate, smoking habits, alcohol intake, exercise, blood pressure, medical history, FPG, lipid profile, high sensitivity C-reactive protein (hs-CRP), and Brachial-ankle pulse wave velocity (ba-PWV) were measured. We performed correlation and multiple linear regression analyses to divide the research subjects into quartiles: Q1(n = 172), 65 mg/dL ≤FPG < 84 mg/dL; Q2(n = 188), 84 mg/dL ≤FPG < 91 mg/dl; Q3(n = 199), 91 mg/dL ≤FPG < 100 mg/dL; Q4(n = 138), 100 mg/dL ≤FPG < 126 mg/dL.

Results

FPG has an independent, positive association with ba-PWV in non-diabetic subjects after correcting for confounding variables, including age, sex, BMI, blood pressure, resting heart rate, hs-CRP, lipid profile, and behavioral habits. The mean ba-PWV of the high-normal glucose group (Q3, 1384 cm/s) was higher than that of the low-normal glucose group (1303 ± 196 cm/s vs.1328 ± 167 cm/s, P < 0.05). The mean ba-PWV value in the IFG group (1469 ± 220 cm/s) was higher than that in the normoglycemic group (P < 0.05, respectively).

Conclusions

An increase in FPG, even within the normal range, was associated with aggravated arterial stiffness. Further research is needed to determine the glycemic target value for the prevention of arterial stiffness in clinical and public health settings.     

Surfactant proteins SP-B and SP-C and their precursors in bronchoalveolar lavages from children with acute and chronic inflammatory airway disease

Background

The reported diagnostic yield from bronchoscopies in patients with lung cancer varies greatly. The optimal combination of sampling techniques has not been finally established. The objectives of this study were to find the predictors of diagnostic yield in bronchoscopy and to evaluate different combinations of sampling techniques.

Methods

All bronchoscopies performed on suspicion of lung malignancy in 2003 and 2004 were reviewed, and 363 patients with proven malignant lung disease were included in the study. Sampling techniques performed were biopsy, transbronchial needle aspiration (TBNA), brushing, small volume lavage (SVL), and aspiration of fluid from the entire procedure. Logistic regression analyses were adjusted for sex, age, endobronchial visibility, localization (lobe), distance from carina, and tumor size.

Results

The adjusted odds ratios (OR) with 95% confidence intervals (CI) for a positive diagnostic yield through all procedures were 17.0 (8.5–34.0) for endobronchial lesions, and 2.6 (1.3–5.2) for constriction/compression, compared to non-visible lesions; 3.8 (1.3–10.7) for lesions > 4 cm, 6.7 (2.1–21.8) for lesions 3–4 cm, and 2.5 (0.8–7.9) for lesions 2–3 cm compared with lesions <= 2 cm. The combined diagnostic yield of biopsy and TBNA was 83.7% for endobronchial lesions and 54.2% for the combined group without visible lesions. This was superior to either technique alone, whereas additional brushing, SVL, and aspiration did not significantly increase the diagnostic yield.

Conclusion

In patients with malignant lung disease, visible lesions and larger tumor size were significant predictors of higher diagnostic yield, after adjustment for sex, age, distance from carina, side and lobe. The combined diagnostic yield of biopsy and TBNA was significant higher than with either technique alone.     

The effect of soil water status on fertiliser, topsoil and subsoil phosphorus utilisation by wheat

Background and aims

Crop phosphorus (P) content is controlled by P uptake from both banded P fertiliser and from P throughout the soil profile. These P supply factors are in turn controlled by soil, climatic and plant factors. The aim of this experiment was to measure the contribution of fertiliser, topsoil and subsoil P to wheat plants under wet and dry growing season conditions.

Methods

An isotopic tracer technique was used to measure P uptake from fertiliser at seven agricultural field sites under wet and dry growing season conditions. At three of these sites a dual isotopic technique was used to distinguish between wheat uptake of P from fertiliser, topsoil (0–15 cm) and subsoil (below 15 cm).

Results

The amount of P fertiliser used by wheat was in the order of 3–30% of the P applied and increased with increasing rainfall. Topsoil P was the most important P source, but when sufficient P was present in the subsoil, P fertiliser addition stimulated the use of subsoil P.

Conclusions

Most crop P uptake was from the topsoil, however P fertiliser banded below the seed increased plant P uptake and stimulated the use of subsoil P in one soil type in a decile 7 (above average rainfall) growing season.     

Shoot development of Norway spruce (Picea abies) involves changes in piperidine alkaloids and condensed tannins

Key Message

Secondary chemistry of P. abies peaks early in shoot development. Condensed tannins accumulate already in late buds while piperidine alkaloid biosynthesis take place in early stage shoots.

Abstract

Plants protect new vegetative parts with defensive secondary metabolite compounds. We investigated how concentrations of piperidine alkaloids and condensed tannins change during bud burst and shoot growth in adult Picea abies. We detected 12 individual piperidine compounds, of which epipinidinone and 1,2-dehydropinidinone and two tentatively identified 1,6-imines are reported for the first time in P. abies. In addition three piperidine alkaloid compounds remain partly identified. We found that concentrations of both total piperidine alkaloids and condensed tannins were highest immediately after bud burst. While concentrations of condensed tannins started to increase during bud opening, the dilution effect decreased concentrations in the developing needles of mature branches. By contrast, the decrease of total alkaloid concentrations in mature shoots was not due to the dilution effect, but was connected to the disappearance of precursor components of biosynthesis. The concentrations of major alkaloid components remain stable from dormant buds to mature needles and twigs, underlining their importance for P. abies, although their real ecological significance is yet to be solved. Based on the structural features and timing of appearance of individual compounds, we also propose a hypothetical biosynthesis route for trans-substituted coniferous piperidine alkaloids.     

Tuberculous peritonitis in a case receiving continuous ambulatory peritoneal dialysis(CAPD) treatment

Background

Tuberculosis continues to be an important health problem in the world. Besides pulmonary involvement extrapulmonary involvement becomes an affair in developing countries, even in developed countries.

Case presentation

A thirty-six year old male patient was admitted with abdominal pain, diarrhea, nausea, vomiting and fever which had started one week before. The patient had been followed up with predialisis Chronic Renal Failure(CRF) diagnosis for 4 years and receiving continuous ambulatory peritoneal dialysis (CAPD) treatment for 4 months. In peritoneal fluid, 1600/mm3 cells were detected and 70% of them were polymorphonuclear leukocytosis. The patient begun nonspesific antibiotherapy but no benefit was obtained after 12 days and peritoneal fluid bacterial cultures remained negative. Peritoneal smear was positive for Asid-fast basilli (AFB), and antituberculosis therapy was started with isoniazid, rifampicine, ethambutol and pyrazinamide. After 15 days his peritoneal fluid cell count was decreased and his symptoms were relieved. Peritoneal fluid tuberculosis culture was found positive.

Conclusion

Considering this case, we think that in patients with CAPD catheter and peritonitis; when peritoneal fluid leukocytes are high and PMNL are dominant, AFB and tuberculosis culture must be investigated besides bacterial culture routinely.     

The influence of alkaline and non-alkaline parent material on Norway spruce tree chemical composition and growth rate

Background and aims

This study investigated the influence of contrasting parent materials on tree chemical composition and growth rate under field conditions. On the island of Alnö, Sweden, alkaline intrusions are interspersed into non-alkaline gneiss bedrock, which provides a unique opportunity to conduct this study with a minimum of confounding effects.

Methods

Three plots with alkaline and three plots with non-alkaline parent material were established in a homogenous Norway spruce stand. The chemical composition of soil and soil solution was determined throughout the soil profiles. The chemical composition of bark, wood and needles was determined for each plot, and the latest 5 year basal area growth increment calculated.

Results

Concentrations of Ca in needles were correlated with the soil exchangeable Ca levels. Tree growth rate was significantly higher on the alkaline plots and positively correlated with soil concentrations of Ca, Mg, P, and Zn. The tree growth rate also tended to correlate with soil N concentrations, but levelled out for the highest soil N concentrations.

Conclusions

Tree growth was enhanced on the alkaline plots and was correlated with several elements. However, none of these elements could be confirmed as the limiting one for tree growth at the current site.     

In vivo analysis of fracture toughness of thyroid gland tumors

Background

Human solid tumors that are hard or firm on physical palpation are likely to be cancerous, a clinical maxim that has been successfully applied to cancer screening programs, such as breast self-examination. However, the biological relevance or prognostic significance of tumor hardness remains poorly understood. Here we present a fracture mechanics based in vivo approach for characterizing the fracture toughness of biological tissue of human thyroid gland tumors.

Methods

In a prospective study, 609 solid thyroid gland tumors were percutaneously probed using standard 25 gauge fine needles, their tissue toughness ranked on the basis of the nature and strength of the haptic force feedback cues, and subjected to standard fine needle biopsy. The tumors' toughness rankings and final cytological diagnoses were combined and analyzed. The interpreting cytopathologist was blinded to the tumors' toughness rankings.

Results

Our data showed that cancerous and noncancerous tumors displayed remarkable haptically distinguishable differences in their material toughness.

Conclusion

The qualitative method described here, though subject to some operator bias, identifies a previously unreported in vivo approach to classify fracture toughness of a solid tumor that can be correlated with malignancy, and paves the way for the development of a mechanical device that can accurately quantify the tissue toughness of a human tumor.     

The growth and nutrients status of conifers on ash-treated cutaway peatland

Key message

Use of wood ash or a mixture of wood and oil shale ashes increases the concentrations of P and K in the assimilation organs of conifers and stimulates tree growth.

Abstract

The effect of fertilization with wood ash (10 and 15 t ha^?1) and a mixture of wood ash (10 t ha^?1) and oil shale ash (8 t ha^?1) on the growth (height, root collar diameter, biomass, biomass production) and nutrient concentrations in subsoil and needles of young Pinus sylvestris and Picea abies plants on the Puhatu (Northeast Estonia) cutaway peatland in the first 2 years were studied. After the second growing year differences in the average height growth of P. abies and P. sylvestris were statistically significantly higher on ash-treated plots than on the control plots (p < 0.05), being respectively 1.4–1.6 and 1.5–1.7 times greater than height growth of the control trees. The best results on root collar diameter were observed on mixture ash treatments: the root collars were 1.9 (P. abies) and 2.2 (P. sylvestris) times larger than of the control trees. The biomass of the two conifer species and the biomass production of P. sylvestris in 2012 was the greatest on the mixture ash treatments. Five months after fertilization with ashes the concentrations of P, K, Ca and Mg were higher on the treated plots than on the control plot. Although the concentrations of P and K in P. sylvestris needles rose after the treatment with ash, seedlings suffered from P and K deficiency. The concentrations of P and K in P. abies needles were on optimum. The P/N and the K/N ratios in needles were also improved compared to control trees needles.     

Light responses of yew (<Emphasis Type="Italic">Taxus baccata</Emphasis> L.); does size matter?

Key message

Photosynthetic capacity of yew needles depends primarily on light environment, with little evidence that developmental stage is a determinant photosynthetic performance. However, needle morphology is mostly determined by plant size.

Abstract

Populations of yew Taxus baccata are often characterized by a lack of natural regeneration and stands of this species have been afforded priority conservation status within the European Union. Light availability is known to be a key factor influencing recruitment dynamics in yew. To explore potential size-related responses to light, we investigated the distribution, photosynthetic efficiency and needle morphological traits in yew across a gradient of light availability at Atlantic oak woodland in southwest Ireland. Young plants were more common in shaded areas whereas saplings and juvenile yews were distributed in areas of higher light availability. Photosynthetic capacity of yew needles was found to depend primarily on light environment, with little evidence that the developmental stage is a determinant of photosynthetic performance. Photoinhibition was evident in needles sampled from high light environments across all demographic size classes. However, larger plants also showed particularly strong needle morphological responses (needle length, width, thickness, and specific leaf area) to light levels, which were mostly lacking in seedlings. We conclude that there is a dual control of yew light responses; the efficiency of the photosynthetic light reactions is largely linked to the light environment in which the plants grew, while needle morphology is mostly determined by the size of the plants. The findings of this study highlight the importance of considering all life-history stages and multiple traits when evaluating species response to light availability.

     

Effects of freeze damage on litter production, quality and decomposition in a loblolly pine forest in central China

Background and aims

Freeze events can strongly influence many ecosystem processes. However, the effects of freeze events on litter production, litter quality, and decomposition are rarely documented.

Methods

In this study, litter fall was measured monthly for 2 years. Two litter decomposition experiments were also performed using freeze-damaged litter and non-damaged litter in a loblolly pine forest.

Results

The freeze event in November 2009 caused a pronounced pulse of needle litter fall. The freeze-damaged needle litter was shown to have higher N concentration and lower C/N ratio compared with the normal falling needle litter. This finding indicates that freeze damage significantly increased needle quality because of incomplete nutrient resorption. The decomposition of freeze-damaged needle litter was faster than that of normal falling yellow needle litter and slower than that of hand-picked green needle litter. The decomposition rate constant (k) was negatively correlated with the C/N ratio in the needle litter. Our results also showed that the different climatic conditions influence patterns of litter decomposition.

Conclusions

This study suggests that freeze events significantly alter litter quantity and quality, thus affecting litter decomposition rates in a loblolly pine forest in central China.     

Relation of fine root distribution to soil C in a Cunninghamia lanceolata plantation in subtropical China

Background and aims

Growth and distribution of fine roots closely depend on soil resource availability and affect soil C distribution in return. Understanding of relationships between fine root distribution and soil C can help to predict the contribution of fine root turnover to soil C accumulation.

Methods

A study was conducted in a subtropical Cunninghamia lanceolata plantation to assess the fine root mass density (FRMD), fine root C density (FRCD) of different fine root groups as well as their relations with soil C.

Results

The FRMD and FRCD of short-lived roots, dead roots and herb roots peaked in the 0–10 cm soil layer and decreased with soil depth, while FRMD, FRCD of long-lived roots peaked in the 10–20 cm soil layer. Soil C was positively related to FRMD and FRCD of total fine roots (across all three soil layers), dead roots (0–10 cm) and herb roots (10–20 cm) as well as FRCD of short-lived roots (20–40 cm) (P <0.05).

Conclusions

Soil C was mainly affected by herb roots in upper soil layers and by woody plant roots in deeper soil layers.     

Greater accumulation of litter in spruce (Picea abies) compared to beech (Fagus sylvatica) stands is not a consequence of the inherent recalcitrance of needles

Background and aims

Replacement of beech by spruce is associated with changes in soil acidity, soil structure and humus form, which are commonly ascribed to the recalcitrance of spruce needles. It is of practical relevance to know how much beech must be admixed to pure spruce stands in order to increase litter decomposition and associated nutrient cycling. We addressed the impact of tree species mixture within forest stands and within litter on mass loss and nutritional release from litter.

Methods

Litter decomposition was measured in three adjacent stands of pure spruce (Picea abies), mixed beech-spruce and pure beech (Fagus sylvatica) on three nutrient-rich sites and three nutrient-poor sites over a three-year period using the litterbag method (single species and mixed species bags).

Results

Mass loss of beech litter was not higher than mass loss of spruce litter. Mass loss and nutrient release were not affected by litter mixing. Litter decay indicated non-additive patterns, since similar remaining masses under pure beech (47%) and mixed beech-spruce (48%) were significantly lower than under pure spruce stands (67%). Release of the main components of the organic substance (C_org, N_tot, P, S, lignin) and associated K were related to mass loss, while release of other nutrients was not related to mass loss.

Conclusions

In contradiction to the widely held assumption of slow decomposition of spruce needles, we conclude that accumulation of litter in spruce stands is not caused by recalcitrance of spruce needles to decay; rather adverse environmental conditions in spruce stands retard decomposition. Mixed beech-spruce stands appear to be as effective as pure beech stands in counteracting these adverse conditions.     

Stapler access and visibility in the deep pelvis: A comparative human cadaver study between a computerized right angle linear cutter versus a curved cutting stapler

Purpose

Distal rectal stapling is often challenging because of limited space and visibility. We compared two stapling devices in the distal rectum in a cadaver study: the iDrive? right angle linear cutter (RALC) (Covidien, New Haven, CT) and the CONTOUR^® curved cutter (CC) (Ethicon Endo-Surgery, Cincinnati, OH).

Methods

Twelve male cadavers underwent pelvic dissection by 4 surgeons. After rectal mobilization as in a total mesorectal excision, the staplers were applied to the rectum as deep as possible in both the coronal and sagittal positions. The distance from the pelvic floor was measured for each application. A questionnaire rated the visibility and access of the stapling devices. Measurements were taken between pelvic landmarks to see what anatomic factors hinder the placement of a distal rectal stapler.

Results

The median (range) distance of the stapler from the pelvic floor in the coronal position for the RALC was 1.0 cm (0-4.0) vs. 2.0 cm (0-5.0) for the CC, p = 0.003. In the sagittal position, the median distance was 1.6 cm (0-3.5) for the RALC and 3.3 cm (0-5.0) for the CC, p < 0.0001. The RALC scored better than the CC in respect to: 1. interference by the symphysis pubis, 2. number of stapler readjustments, 3. ease of placement in the pelvis, 4. impediment of visibility, 5. ability to hold and retain tissue, 6. visibility rating, and 7. access in the pelvis. A shorter distance between the tip of the coccyx and the pubic symphysis correlated with a longer distance of the stapler from the pelvic floor (p = 0.002).

Conclusions

The RALC is superior to the CC in terms of access, visibility, and ease of placement in the deep pelvis. This could provide important clinical benefit to both patient and surgeon during difficult rectal surgery.     

Phase 1 trial of the oral AKT inhibitor MK-2206 plus carboplatin/paclitaxel, docetaxel, or erlotinib in patients with advanced solid tumors

Background

Inhibition of AKT with MK-2206 has demonstrated synergism with anticancer agents. This phase 1 study assessed the MTD, DLTs, PK, and efficacy of MK-2206 in combination with cytotoxic and targeted therapies.

Methods

Advanced solid tumor patients received oral MK-2206 45 or 60 mg (QOD) with either carboplatin (AUC 6.0) and paclitaxel 200 mg/m² (arm 1), docetaxel 75 mg/m² (arm 2), or erlotinib 100 or 150 mg daily (arm 3); alternative schedules of MK-2206 135-200 mg QW or 90-250 mg Q3W were also tested.

Results

MTD of MK-2206 (N?=?72) was 45 mg QOD or 200 mg Q3W (arm 1); MAD was 200 mg Q3W (arm 2) and 135 mg QW (arm 3). DLTs included skin rash (arms 1, 3), febrile neutropenia (QOD, arms 1, 2), tinnitus (Q3W, arm 2), and stomatitis (QOD, arm 3). Common drug-related toxicities included fatigue (68%), nausea (49%), and rash (47%). Two patients with squamous cell carcinoma of the head and neck (arm 1; Q3W) demonstrated a complete and partial response (PR); additional PRs were observed in patients (1 each) with melanoma, endometrial, neuroendocrine prostate, NSCLC, and cervical cancers. Six patients had stable disease ≥6 months.

Conclusion

MK-2206 plus carboplatin and paclitaxel, docetaxel, or erlotinib was well-tolerated, with early evidence of antitumor activity.

Trial registration

ClinicalTrials.gov: NCT00848718.     

Chondrosarcoma of the spine: A rare case with unusual presentation

Background

TMAs are becoming a useful tool for research and quality control methods, mostly for immunohistochemistry and in situ hybridization.

Methods

A new technique that allows building TMA blocks with more than 300 tissue cores without using a recipient paraffin block for the tissue cores and without using a commercial TMA builder instrument is described. This technique is based on the construction of TMA needles modifying conventional hypodermic needles to punch tissue cores from donor blocks, which are attached by double-side adhesive tape on a computer-generated paper grid used to align the cores on the block mould, which is filled with liquid paraffin.

Results

More than two hundred TMA blocks were constructed using this method, utilized in immunohistochemistry and histochemistry as positive and negative controls and also in research.

Conclusion

This technique has the following advantages: it is easy to reproduce, affordable, quick and creates uniform blocks with more than 300 cores aligned, adherent and easy to cut, with negligible losses during cutting and immunohistochemistry and in situ hybridization procedures.     

Changes in stem water content influence sap flux density measurements with thermal dissipation probes

Key message

Stem WC may decline during the day. Zero-flow dT _m increases when WC decreases. Use of nighttime dT _m in the calculation of sap flux density during the day might introduce errors.

Abstract

There is increasing evidence of diel variation in water content of stems of living trees as a result of changes in internal water reserves. The interplay between dynamic water storage and sap flow is of current interest, but the accuracy of measurement of both variables has come into question. Fluctuations in stem water content may induce inaccuracy in thermal-based measurements of sap flux density because wood thermal properties are dependent on water content. The most widely used thermal method for measuring sap flux density is the thermal dissipation probe (TDP) with continuous heating, which measures the influence of moving sap on the temperature difference between a heated needle and a reference needle vertically separated in the flow stream. The objective of our study was to investigate how diel fluctuations in water content could influence TDP measurements of sap flux density. We analysed the influence of water content on the zero-flow maximum temperature difference, dT _m, which is used as the reference for calculating sap flux density, and present results of a dehydration experiment on cut branch segments of American sycamore (Platanus occidentalis L.). We demonstrate both theoretically and experimentally that dT _m increases when stem water content declines. Because dT _m is measured at night when water content is high, this phenomenon could result in underestimations of sap flux density during the day when water content is lower. We conclude that diel dynamics in water content should be considered when TDP is used to measure sap flow.     

Effects of litter types, microsite and root diameters on litter decomposition in Pinus sylvestris plantations of northern China

Background and aims

Litter decomposition is a major process in the carbon (C) flow and nutrient cycling of terrestrial ecosystems, but the effects of litter type, microsite, and root diameter on decomposition are poorly understood.

Methods

Litterbags were used to examine the decomposition rate of leaf litter and roots at three soil depths (5, 10 and 20 cm) over a 470-day period in Pinus sylvestris plantations in northern China.

Results

Leaves and the finest roots decomposed more quickly at 5 cm depth and coarser roots (>1-mm) decomposed more quickly at 10 and 20 cm depth. Roots generally decomposed more quickly than leaf litter, except at 5 cm deep; leaves decomposed more quickly than the coarsest roots (>5-mm). Root decomposition was strongly influenced by root diameter. Leaves experienced net nitrogen (N) immobilization and coarse roots (>2-mm) experienced more N release than fine roots. Significant heterogeneity was seen in N release for fine-roots (<2-mm) with N immobilization occurring in smaller (0.5–2-mm) roots and N release in the finest roots (<0.5-mm).

Conclusions

Soil depth of litter placement significantly influenced the relative contribution of the decomposition of leaves and roots of different diameters to carbon and nutrient cycling.