Search tips
Search criteria

Results 1-3 (3)

Clipboard (0)

Select a Filter Below

Year of Publication
Document Types
author:("sharaf, M.")
1.  Is leaf dry matter content a better predictor of soil fertility than specific leaf area? 
Annals of Botany  2011;108(7):1337-1345.
Background and Aims
Specific leaf area (SLA), a key element of the ‘worldwide leaf economics spectrum’, is the preferred ‘soft’ plant trait for assessing soil fertility. SLA is a function of leaf dry matter content (LDMC) and leaf thickness (LT). The first, LDMC, defines leaf construction costs and can be used instead of SLA. However, LT identifies shade at its lowest extreme and succulence at its highest, and is not related to soil fertility. Why then is SLA more frequently used as a predictor of soil fertility than LDMC?
SLA, LDMC and LT were measured and leaf density (LD) estimated for almost 2000 species, and the capacity of LD to predict LDMC was examined, as was the relative contribution of LDMC and LT to the expression of SLA. Subsequently, the relationships between SLA, LDMC and LT with respect to soil fertility and shade were described.
Key Results
Although LD is strongly related to LDMC, and LDMC and LT each contribute equally to the expression of SLA, the exact relationships differ between ecological groupings. LDMC predicts leaf nitrogen content and soil fertility but, because LT primarily varies with light intensity, SLA increases in response to both increased shade and increased fertility.
Gradients of soil fertility are frequently also gradients of biomass accumulation with reduced irradiance lower in the canopy. Therefore, SLA, which includes both fertility and shade components, may often discriminate better between communities or treatments than LDMC. However, LDMC should always be the preferred trait for assessing gradients of soil fertility uncoupled from shade. Nevertheless, because leaves multitask, individual leaf traits do not necessarily exhibit exact functional equivalence between species. In consequence, rather than using a single stand-alone predictor, multivariate analyses using several leaf traits is recommended.
PMCID: PMC3197453  PMID: 21948627
Ellenberg numbers; functional traits; leaf density; leaf nitrogen; leaf size; leaf thickness; relative growth rate (RGR); shade tolerance; variation in trait expression
2.  Stomatal vs. genome size in angiosperms: the somatic tail wagging the genomic dog? 
Annals of Botany  2010;105(4):573-584.
Background and Aims
Genome size is a function, and the product, of cell volume. As such it is contingent on ecological circumstance. The nature of ‘this ecological circumstance’ is, however, hotly debated. Here, we investigate for angiosperms whether stomatal size may be this ‘missing link’: the primary determinant of genome size. Stomata are crucial for photosynthesis and their size affects functional efficiency.
Stomatal and leaf characteristics were measured for 1442 species from Argentina, Iran, Spain and the UK and, using PCA, some emergent ecological and taxonomic patterns identified. Subsequently, an assessment of the relationship between genome-size values obtained from the Plant DNA C-values database and measurements of stomatal size was carried out.
Key Results
Stomatal size is an ecologically important attribute. It varies with life-history (woody species < herbaceous species < vernal geophytes) and contributes to ecologically and physiologically important axes of leaf specialization. Moreover, it is positively correlated with genome size across a wide range of major taxa.
Stomatal size predicts genome size within angiosperms. Correlation is not, however, proof of causality and here our interpretation is hampered by unexpected deficiencies in the scientific literature. Firstly, there are discrepancies between our own observations and established ideas about the ecological significance of stomatal size; very large stomata, theoretically facilitating photosynthesis in deep shade, were, in this study (and in other studies), primarily associated with vernal geophytes of unshaded habitats. Secondly, the lower size limit at which stomata can function efficiently, and the ecological circumstances under which these minute stomata might occur, have not been satisfactorally resolved. Thus, our hypothesis, that the optimization of stomatal size for functional efficiency is a major ecological determinant of genome size, remains unproven.
PMCID: PMC2850795  PMID: 20375204
Stomatal size; genome size; seed size; life history; photosynthesis; allometry; ecology; evolution; SLA; leaf structure; CAM; C4
3.  The Impact of Hepatitis B Infection on Outcome of Kidney Transplantation: A Long-Term Study  
Background: With the success of kidney transplantation, liver disease has emerged as an important cause of morbidity and mortality in kidney recipients.
Objective: To determine the impact of hepatitis B virus (HBV) infection on patients and graft survival in both short- and long-terms.
Methods: 99 renal transplant patients infected with HBV on follow-up in two major transplant centers were included in a retrospective study. These patients were grafted between 1986 and 2005 and divided into two groups: (1) those only positive for hepatitis B surface antigen (HBsAg) and (2) those who were also positive for hepatitis C virus antibodies (HCV Ab).
Results: There were 88 patients with HBsAg+ and 11 with both HBsAg+ and HCV Ab+. The mean±SD age of patients was 38.8±13.2 years, and the median follow-up after transplantation was 19 months. Although not significant, the allograft survival rate in the first group (HBV+) was better compared to that in the second group (HBV+ and HCV+); 1, 5 and 10 years graft survival rates were 91, 77 and 62 in the first group and 70, 56 and 28 in the second group, respectively (P=0.07). The overall mortality was 5% (4 of 88) in the first and 27% (3 of 11) in the second group (P=0.02).
Conclusion: Renal allograft recipients with HBV and HCV infections has a poor survival rate compared to patients with only HBV infection. However, there is no significant difference in terms of renal graft survival between the two groups.
PMCID: PMC4089227  PMID: 25013571
Kidney transplantation; Hepatitis B virus; Hepatitis C virus

Results 1-3 (3)