Natural disturbances and the physiognomy of pine savannas : A phenomenological model

Abstract. Question: The decline of the Pinus palustris ecosystems has resulted from anthropogenic influences, such as conversion to pine plantation forestry, agriculture and land development, all of which are closely related to increases in human populations. Other effects, however, have arisen from alterations in disturbance regimes that maintain the structure and function of these ecosystems. How have alterations of the disturbance regime altered the physiognomy of ‘old-growth’ stands, and what are the implications for ecosystem conservation and restoration? Methods: In contrast to models that emphasize close interactions among the vertically complex strata, we develop a conceptual phenomenological model for the physiognomic structure of Pinus palustris stands. We relate two natural disturbances (tropical storms and fire) that affect different stages of the life cycle to different aspects of the physiognomic structure. We then compare overstorey stand structure and ground cover composition of two old-growth longleaf stands near the extremes of different composite disturbance regimes: the Wade Tract (frequent hurricanes and fire) and the Boyd Tract (infrequent hurricanes and long-term fire exclusion). Results: We predict that tropical storms and fires have different effects on stand physiognomy. Tropical storms are periodic, and sometimes intense, whereas fires are more frequent and less intense. Hurricanes directly influence the overstorey via wind-caused damage and mortality, and indirectly influence the herb layer by altering the spatial distribution of shading and litter accumulation. Fire exerts direct effects on juvenile stages and indirect effects on the herb layer via fine fuel consumption and selective mortality of potential competitors of P. palustris juveniles. These differences in effects of disturbances can result in widely different physiognomies for P. palustris stands. Finally, some global climate change scenarios have suggested that changes may occur in tropical storm and fire regimes, altering frequency and severity. Such changes may greatly affect pine stands, and ultimately entire pine savanna ecosystems. Conclusions: Our phenomenological model of disturbance regimes in Pinus palustris old-growth produces very different physiognomies for different disturbances regimes that reflect natural process and human management actions. This model can be used to derive restoration strategies for pine savannas that are linked to reinstitution of important ecological processes rather than specific physiognomic states

Cohesin mutations alter DNA damage repair and chromatin structure and create therapeutic vulnerabilities in MDS/AML

The cohesin complex plays an essential role in chromosome maintenance and transcriptional regulation. Recurrent somatic mutations in the cohesin complex are frequent genetic drivers in cancer including myelodysplatic syndromes (MDS) and acute myeloid leukemia (AML). Here, using genetic dependency screens of STAG2-mutant AML, we identified DNA damage repair and replication as genetic dependencies in cohesin-mutant cells. We demonstrated increased levels of DNA damage and sensitivity of cohesin-mutant cells to PARP inhibition. We developed a mouse model of MDS in which Stag2 mutations arise as clonal secondary lesions in the background of clonal hematopoiesis driven by Tet2 mutations, and demonstrated selective depletion of cohesin-mutant cells with PARP inhibition in vivo. Finally, we demonstrated a shift from STAG2- to STAG1-containing cohesin complexes in cohesin-mutant cells, which is associated with longer DNA loop extrusion, more intermixing of chromatin compartments, and increased interaction with PARP and RPA proteins. Our findings inform the biology and therapeutic opportunities for cohesin-mutant malignancies

Desempenho de uma semeadora-adubadora direta, em função da velocidade de eslocamento e do tipo de manejo da biomassa da cultura de cobertura do solo Performance of a seeding-fertilizer machine in function of the displacement speed and soil cover crop biomass management

O objetivo do presente trabalho foi estudar o desempenho de uma semeadora-adubadora, operando em duas velocidades sobre a palhada da cultura do milheto (Pennisetum glaucum (L.) R. Brown), após diferentes manejos, na semeadura direta da cultura da soja (Glycine Max L.). O experimento foi realizado com seis tratamentos, em esquema fatorial, delineados em blocos ao acaso, com quatro repetições. Os tratamentos combinaram três manejos (triturador de palhas tratorizado, rolo- faca e herbicida) com duas velocidades de deslocamento da semeadora-adubadora (5,2 e 7,3 km h-1). Foram analisadas as seguintes variáveis: acúmulo e decomposição de massa seca do milheto, índice de emergência da cultura da soja, uniformidade de distribuição longitudinal de sementes, capacidade de campo efetiva da semeadora-adubadora e produtividade da soja. Os resultados mostraram que não houve diferença na decomposição da massa de milheto após os manejos e que esses, juntamente com a velocidade de deslocamento do conjunto trator-semeadora-adubadora, não influenciaram no número de dias para a emergência das plântulas de soja e na distribuição longitudinal das sementes. A capacidade de campo efetiva da semeadora-adubadora foi maior na velocidade mais alta. O rendimento de grãos não diferiu significativamente nos tratamentos estudados.<br>The objective of the present work was to evaluate three different managements of the Pennisetum glaucum (L.) R. Brown crop and two-speed displacement in a no-tillage system of soybean (Glycine max L.) crop on a typical Eutrophic Red Latosol. The experiment was arranged in six treatments, in a factorial array, in a randomized complete block design, with four replications. The treatments were constituted from three combination of crop managements (straw chopper, residue coulter and herbicide) and two speed displacement of the seeding-fertilizer machine (5.2 and 7.3 km h-1). The following variables have been analyzed: emergency index of the soybean, longitudinal seeding uniformity (evaluated by the percentage of acceptable spacings), double distribution and distribution failure, and operational capacity of the seeding-fertilizer machine. There was no difference on the mass decomposition of the Pennisetum crop after management. The management of the Pennisetum crop and the displacement of the seeding-fertilizer machine did not influence the number of days for soybean crop emergency and the longitudinal distribution of the seeds. The operational capacity of the seeding-fertilizer machine was higher at the faster speed. The crop yield did not differ on the studied treatments