Nitrogen stable isotopes indicate differences in nitrogen cycling between two contrasting Jamaican montane forests

Background and aims The aim of this study is to enhance our knowledge of nitrogen (N) cycling and N acquisition in tropical montane forests through analysis of stable N isotopes (δ15N). Methods Leaves from eight common tree species, leaf litter, soils from three depths and roots were sampled from two contrasting montane forest types in Jamaica (mull ridge and mor ridge) and were analysed for δ15N. Results All foliar δ15N values were negative and varied among the tree species but were significantly more negative in the mor ridge forest (by about 2 ‰). δ15N of soils and roots were also more negative in mor ridge forests by about 3 ‰. Foliar δ15N values were closer to that of soil ammonium than soil nitrate suggesting that trees in these forests may have a preference for ammonium; this may explain the high losses of nitrate from similar tropical montane forests. There was no correlation between the rankings of foliar δ15N in the two forest types suggesting a changing uptake ratio of different N forms between forest types. Conclusions These results indicate that N is found at low concentrations in this ecosystem and that there is a tighter N cycle in the mor ridge forest, confirmed by reduced nitrogen availability and lower rates of nitrification. Overall, soil or root δ15N values are more useful in assessing ecosystem N cycling patterns as different tree species showed differences in foliar δ15N between the two forest types

Decoupled leaf and stem economics in rain forest trees

Cross-species analyses of plant functional traits have shed light on factors contributing to differences in performance and distribution, but to date most studies have focused on either leaves or stems. We extend these tissue-specific analyses of functional strategy towards a whole-plant approach by integrating data on functional traits for 13 448 leaves and wood tissues from 4672 trees representing 668 species of Neotropical trees. Strong correlations amongst traits previously defined as the leaf economics spectrum reflect a tradeoff between investments in productive leaves with rapid turnover vs. costly physical leaf structure with a long revenue stream. A second axis of variation, the ‘stem economics spectrum’, defines a similar tradeoff at the stem level: dense wood vs. high wood water content and thick bark. Most importantly, these two axes are orthogonal, suggesting that tradeoffs operate independently at the leaf and at the stem levels. By simplifying the multivariate ecological strategies of tropical trees into positions along these two spectra, our results provide a basis to improve global vegetation models predicting responses of tropical forests to global cha

Spatial variability of soil microbial functioning in a tropical rainforest of French Guiana using nested sampling

Understanding the pattern in spatial distribution of soil microbial processes is critical to understand the environmental factors that regulate them as well as to scale up these processes to ecosystem. Soil samples from a I ha tropical rainforest plot (Paracou, French Guiana) were analyzed according a nested sampling approach using different separation distances ranging from 0.4 to 40 m. The variability of substrate induced respiration (SIR) and of denitrification enzyme activity (DEA) was characterized in relation to various soil properties (total C and N contents, NIRS related index of soil organic matter quality, SOMQ and index of tree influence potential, IP). The variability of SIR and DEA was higher than that of environmental properties. The patterns of accumulated variance as a function of distance varied among the soil properties. The variability of SIR and DEA mainly occurred at small (1 m) scale (and at the 10-40 m-scales for SIR), probably reflecting the quality of litter input that results of the influence of local assemblage of different tree species, though changes in the soil N and C contents. Indeed, total soil C and N contents explained the microbial properties at every scale. Coefficients of codispersion showed that neither SOMQ nor IP did correlate with SIR and DEA, and confirmed that total C and N contents explained microbial properties in a scale dependent and complex manner. Such spatial dependency underlines the importance of soil heterogeneity in this tropical forest with implications for sampling strategies when studying the microbial processes and their response to disturbances

N2 fixation and cycling in Alnus glutinosa, Betula pendula and Fagus sylvatica woodland exposed to free air CO2 enrichment

We measured the effect of elevated atmospheric CO2 on atmospheric nitrogen (N2) fixation in the tree species Alnus glutinosa growing in monoculture or in mixture with the non-N2-fixing tree species Betula pendula and Fagus sylvatica. We addressed the hypotheses that (1) N2 fixation in A. glutinosa will increase in response to increased atmospheric CO2 concentrations, when growing in monoculture, (2) the impact of elevated CO2 on N2 fixation in A. glutinosa is the same in mixture and in monoculture and (3) the impacts of elevated CO2 on N cycling will be evident by a decrease in leaf δ15N and by the soil-leaf enrichment factor (EF), and that these impacts will not differ between mixed and single species stands. Trees were grown in a forest plantation on former agricultural fields for four growing seasons, after which the trees were on average 3.8 m tall and canopy closure had occurred. Atmospheric CO2 concentrations were maintained at either ambient or elevated (by 200 ppm) concentrations using a free-air CO2 enrichment (FACE) system. Leaf δ15N was measured and used to estimate the amount (Ndfa) and proportion (%Ndfa) of N derived from atmospheric fixation. On average, 62% of the N in A. glutinosa leaves was from fixation. The %Ndfa and Ndfa for A. glutinosa trees in monoculture did not increase under elevated CO2, despite higher growth rates. However, N2 fixation did increase for trees growing in mixture, despite the absence of significant growth stimulation. There was evidence that fixed N2 was transferred from A. glutinosa to F. sylvatica and B. pendula, but no evidence that this affected their CO2 response. The results of this study show that N2 fixation in A. glutinosa may be higher in a future elevated CO2 world, but that this effect will only occur where the trees are growing in mixed species stands

Haploinsufficiency for NR3C1, the gene encoding the glucocorticoid receptor, in blastic plasmacytoid dendritic cell neoplasms

International audienceBlastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and highly aggressiveleukemia for which knowledge on disease mechanisms and effective therapies are currentlylacking. Only a handful of recurring genetic mutations have been identified and none isspecific to BPDCN. In this study, through molecular cloning in an index case that presenteda balanced t(3;5)(q21;q31) and molecular cytogenetic analyses in a further 46 cases, weidentify monoallelic deletion of NR3C1 (5q31), encoding the glucocorticoid receptor (GCR),in 13 of 47 (28%) BPDCN patients. Targeted deep sequencing in 36 BPDCN cases, including10 with NR3C1 deletion, did not reveal NR3C1 point mutations or indels. Haploinsufficiencyfor NR3C1 defined a subset of BPDCN with lowered GCR expression and extremely pooroverall survival (P 5 .0006). Consistent with a role for GCR in tumor suppression, functionalanalyses coupled with gene expression profiling identified corticoresistance and loss-ofEZH2 function as major downstream consequences of NR3C1 deletion in BPDCN.Subsequently, more detailed analyses of the t(3;5)(q21;q31) revealed fusion of NR3C1 to along noncoding RNA (lncRNA) gene (lincRNA-3q) that encodes a novel, nuclear, noncodingRNA involved in the regulation of leukemia stem cell programs and G1/S transition, via E2F.Overexpression oflincRNA-3qwas a consistent feature ofmalignant cells and could be abrogated by bromodomain and extraterminal domain(BET) protein inhibition. Taken together, this work points to NR3C1 as a haploinsufficient tumor suppressor in a subset of BPDCN andidentifies BET inhibition, acting at least partially via lncRNA blockade, as a novel treatment option in BPDCN.