Lianas in a subtropical Atlantic Forest: Host preference and tree growth

Determinants of liana abundance on several canopy tree species and the impact of liana abundance on host tree growth were studied in a subtropical Atlantic Forest in northeastern Argentina. Six permanent 1 ha plots were located in a native forest stand. In three of those plots all lianas were cut and allowed to decompose in situ, while the other three plots were used as a control treatment. Liana richness, abundance and climbing mechanisms were studied in seventeen 20 m x 20 m subplots inside the 1 ha control plots. A total of 841 liana stems larger than 1 cm diameter were registered in the 0.68 ha sample area, representing 47 species. Lianas belonging to the Bignoniaceae and Fabaceae families were the most abundant, corresponding to 49.4 and 16.6% of all individuals, respectively. The most common climbing mechanism observed was coiling tendrils, representing the 61.1% of all individuals. Lianas scrambling and twining were represented by 19.6 and 15.6% of the individuals, respectively. The number of lianas climbing a tree was inversely correlated with host tree trunk length. Bark characteristics also played a role on the degree of liana infestation. Some tree species hosted several lianas and the larger the diameter of the largest liana in a host tree the greater was the number of climbing lianas. Facilitation was hypothesized to explain this pattern meaning that many lianas used other lianas climbing a tree for reaching the upper canopy. Tree stem diameter growth was more than 100% lower in two out of the four species studied for liana-laden than for liana-free trees. Results lend support to the hypothesis that cutting of lianas from selected host trees can be used as a forest management technique to enhance tree growth and decrease the length of cutting cycles in native forest stands

Tree regeneration and microclimate in a liana and bamboo-dominated semideciduous Atlantic Forest

We assessed the effect of native bamboo and lianas on microclimate, tree regeneration and forest structure in a semi-deciduous Atlantic Forest subjected to selective timber extraction during the last century. We hypothetized that bamboo and liana cutting would increase incoming solar radiation in the understory promoting establishment and survival of pioneer and light-requiring canopy tree species. A manipulative experiment consisting of bamboo and liana cutting was performed in a native forest stand in northeastern Argentina. In three permanent 1-ha plots bamboo and lianas were cut and allowed to decompose in situ, while other three plots were used as a control treatment. We measured solar radiation reaching the understory, soil water availability and air temperature in both bamboo and liana cutting and control plots. Tree sapling abundance and richness, stand basal area, bamboo density, and cover of lianas, herbs, shrubs, fallen trees and branches were also determined. We performed multivariate analyses to relate tree sapling abundance and richness with biotic and abiotic factors. Bamboo and liana cutting increased by 100% the solar radiation reaching the understory. The fraction of solar radiation transmitted at 0.7 m height above ground in control and treated plots was 0.1 and 0.2, respectively. Minimum soil matric potentials after a severe dry spell were less than ‚à í2 MPa. Soil water availability was higher under closed-canopy in the treated plots because liana transpiration was prevented by cutting. Although bamboo and liana cutting increased incoming solar radiation, tree seedling and sapling abundance of pioneer and light-demanding species was not improved by the treatment. Instead, an increased abundance of herbaceous plants was observed in gaps and open canopy areas (i.e., sites with amounts of herb cover greater than 75% represented the 11 and 2% of the total number of sites in treated and control plots, respectively). Sapling survival and growth rates, on the other hand, appeared to be promoted by bamboo and liana cutting. Bamboo inhibited tree sapling abundance and richness in gaps, whereas tree basal area had a positive effect. In the semideciduous Atlantic Forest, native bamboos modify gap phase regeneration, and may affect canopy cover and forest composition in the long term. Post-logging management techniques are needed for sustainable timber production in these forest stands

Thinning Partially Mitigates the Impact of Atlantic Forest Replacement by Pine Monocultures on the Soil Microbiome

Forest replacement by exotic plantations drive important changes at the level of the overstory, understory and forest floor. In the Atlantic Forest of northern Argentina, large areas have been replaced by loblolly pine (Pinus taeda L.) monocultures. Plant and litter transformation, together with harvesting operations, change microclimatic conditions and edaphic properties. Management practices such as thinning promote the development of native understory vegetation and could counterbalance negative effects of forest replacement on soil. Here, the effects of pine plantations and thinning on physical, chemical and microbiological soil properties were assessed. Bacterial, archaeal, and fungal community structure were analyzed using a metabarcoding approach targeting ribosomal markers. Forest replacement and, to a lesser extent, thinning practices in the pine plantations induced significant changes in soil physico-chemical properties and associated shifts in bacterial and fungal communities. Most measured physical and chemical properties were altered due to forest replacement, but a few of these properties reached values similar to natural forests under the thinning operation. Fungal alpha diversity decreased in pine plantations, whereas bacterial alpha diversity tended to increase but with little statistical support. Shifts in community composition were observed for both fungal and bacterial domains, and were mostly related to changes in plant understory composition, soil carbon, organic matter, water content, pH and bulk density. Among several other changes, highly abundant phyla such as Proteobacteria (driven by many genera) and Mortierellomycota (mainly driven by Mortierella) decreased in relative abundance in the plantations, whereas Acidobacteria (mainly driven by Acidothermus and Candidatus Koribacter) and Basidiomycota (mainly driven by the ectomycorrhiza Russula) showed the opposite response. Taken together, these results provide insights into the effects of forest replacement on belowground properties and elucidate the potentially beneficial effect of thinning practices in intensive plantation systems through promoting the understory development. Although thinning did not entirely counterbalance the effects of forest replacement on physical, chemical and biological soil properties, the strategy helped mitigating the effects and might promote resilience of these properties by the end of the rotation cycle, if subsequent management practices compatible with the development of a native understory vegetation are applied

Intravital microscopy of collective invasion plasticity in breast cancer

Contains fulltext : 196231.pdf (publisher's version ) (Open Access)Cancer invasion programs are adaptive by switching between metastatic collective and single-cell dissemination; however, current intravital microscopy models for epithelial cancer in mice fail to reliably recreate such invasion plasticity. Using microimplantation of breast cancer spheroids into the murine mammary fat pad and live-cell monitoring, we show microenvironmental conditions and cytoskeletal adaptation during collective to single-cell transition in vivo E-cadherin-expressing 4T1 and E-cadherin-negative MMT tumors both initiated collective invasion along stromal structures, reflecting invasion patterns in 3D organotypic culture and human primary ductal and lobular carcinoma. Collectively invading cells developed weakly oscillatory actin dynamics, yet provided zones for single-cell transitions with accentuated, more chaotic actin fluctuations. This identifies collective invasion in vivo as a dynamic niche and efficient source for single-cell release