Tuesday, March 11, 2014
Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations1. Our ability to understand and predict changes in the forest carbon cycle—particularly net primary productivity and carbon storage—increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands. Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree, in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation) decrease, remain constant, or increase as trees increase in size and age.
A global analysis of 403 tropical and temperate tree species, shows that for most species mass growth rate increases continuously with tree size. Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree. The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-leve productivity can be explained, respectively, by increases in a tree’s total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density.
Results resolve conflicting assumptions about the nature of tree growth, inform efforts to undertand and model forest carbon dynamics, and have additional implications for theories of resource allocation and plant senescence.
Friday, March 7, 2014
Tree pores (red and blue) located within the sapwood filter bacteria (green) in dirty water.photo credit: Boutilier et al.
To turn dirty lakewater into drinkable H2O, peel away the bark from a nearby tree branch and slowly pour water through the wood. According to new research, this neat, low-tech trick ought to trap any bacteria, leaving you with uncontaminated water.
Okay, time for a little tree physiology. To get water and minerals up a tree, wood is comprised of xylem, porous tissue arranged in tubes for conducing sap from the roots upwards through a system of vessels and pores. Xylem tissue is found in sapwood, the younger wood that lies in concentric circles between the central heartwood and the bark. Tiny pores called pit membranes are scattered throughout the walls of the vessels, allowing sap to flow from one vessel to another, feeding various structures along a tree’s length.
Turns out, the same tissue that evolved to transport sap up the length of a tree also has exactly the right-sized pores to allow water through while blocking bacteria. Additionally, the pores also trap air bubbles, which could kill a tree if spread in the xylem. “Plants have had to figure out how to filter out bubbles but allow easy flow of sap,” study author Rohit Karnik from MIT says in a news release. “It’s the same problem with water filtration where we want to filter out microbes but maintain a high flow rate. So it’s a nice coincidence that the problems are similar.”
As Karnik’s team finds, a small piece of sapwood can filter out more than 99 percent of the E. coli from water, at the rate of several liters per day.
To study sapwood’s water-filtering potential, the team collected white pine branches and stripped off their outer bark. They attached inch-long sections of sapwood to plastic tubing, then sealed it with epoxy and secured it with clamps.
They tested their improvised filter using water mixed with particles ranging in size. They found that while sapwood naturally filters out particles bigger than 70 nanometers, it wasn’t able to separate out 20-nanometer particles.
When they poured water contaminated with inactivated E. coli through the sapwood filter, they saw how bacteria had accumulated around the pores in the first few millimeters of the wood. In the false-color electron microscope image above, (green) bacteria are trapped over pit membranes (red and blue).
Existing water-purification technologies that use chlorine treatments and membranes with nano-scale pores are expensive. Even boiling water requires fuel for heat. Here, just take some wood and make a filter of it -- it’s low-cost, efficient, and readily accessible for rural communities as well as dehydrated campers in the Northeast. “Ideally, a filter would be a thin slice of wood you could use for a few days, then throw it away and replace at almost no cost,” Karnik explains.
The group is looking into the filtering potential of other types of sapwood. Flowering trees, for example, tend to have smaller pores than coniferous trees and may be able to filter out even smaller particles, like viruses.
The question now is how does this science become a game changer for underdeveloped nations who need it the most? What materials will the most effective filter need and are there specific species of trees that will filter more effectively. Future studies will only empower nature-loving enthusiasts. Until then, let's plant some trees!
The work was published in PLOS ONE last week.
Monday, March 3, 2014
Global warming is still the topic of much debate, but a short video posted recently by NASA is fairly convincing. The 15-second animation, which was posted by NASA last week and picked up on Tuesday by Co.Exist, shows a view of the entire globe with an overlay that details climate change. NASA scientists analyzed data collected over the past 63 years by 1,000 meteorological stations from around the world, and the animation they compiled shows just how rapidly the Earth’s climate is changing.
The GIF is a consolidated version of NASA’s full animation that helps illustrate just how drastic the change has been since 1950. Temperatures in some regions have swung by as much as 4 degrees Celsius in the past 60 years alone.
“Long-term trends in surface temperatures are unusual and 2013 adds to the evidence for ongoing climate change,” GISS climatologist Gavin Schmidt said with regard to NASA’s findings. “While one year or one season can be affected by random weather events, this analysis shows the necessity for continued, long-term monitoring.”
According to the report, the average global temperature in 2013 was 58.3 degrees; Fahrenheit. That’s 1.1 degrees Fahrenheit warmer than the mid-20th century baseline temperature.
“Last year, when the concentration of carbon dioxide in the atmosphere surpassed levels of 400 parts per million, the amount of atmospheric carbon dioxide reached a higher point than it had at any time in the last 800,000 years,” Sydney Brownstone noted.
NASA’s full animation follows below.