More Productive? – Converting C3 food crops to C4 way of life.

Evolution of C4 pathway of photosynthesis added additional teeth to this life sustaining process enhancing plant’s ability to better scrub our atmosphere from CO2 resulting in higher biomass. These characteristics of C4 plants make them attractive to solve food security problems by enhancing biomass production of high value C3 crops like rice.

The major difference between these plants lies in leaf anatomy. C4 plants compartmentalise their photosynthesis and used both compartments for fixing carbon thus accounting for greater carbon accumulation into biomass. This anatomical modification is known as Kranz anatomy. Simply explained, the plant fixes carbon twice once in the outer cells and the second time in the inner sheath cells as against a single fixation in C3 plants. Thus changing a C3 plant to C4 would involve some sort of anatomical modification that could allow for such efficient fixation to occur in our C3 crops thus potentially increasing yields.

Fig: Cross section of Maize leaf showing Kranz anatomy

A key way to do this is increase the volume of key organelles of sheath cells in C3 plants. These organelles are the chloroplast (responsible for photosynthesis) and mitochondria (produces energy to the cell). This anatomic shift is called ‘proto-kranz’ anatomy.

Recently Wang and colleagues published results from their experiment where they were able to bring about such an effect in the sheath cells of rice leaf using GOLDEN2-LIKE genes from Maize (http://dx.doi.org/10.1016/j.cub.2017.09.040). Initial attempts at this were semi successful as the anatomical effects were only maintained until the seedling stages but was suppressed there after. The maize genes were postulated by the authors to be able to over come this short life span of the proto-kranz anatomy.

First, to overcome the problem of sustaining the anatomy the genes were introduced at such positions in the genome of rice such that it is continuously active. The impact of this was immediately apparent by appearance of green cali (small bundle of cells). Second this modification resulted in increased chloroplast volume and enhanced mitochondrial function and size, confirmed by electron microscopy and increased photo-respiratory enzymes respectively. This anatomical cellular change is one of the first evolutionary steps towards developing of C4 anatomy.

So does this mean that we now have a high yielding rice species to address food security?

No.

A comparison between these lab reared modified plants to those in the wild revealed very similar photosynthetic rates and at whole plant level yields. The significance of this effort is at a more subtle  evolutionary level.

The amazing finding here is that a modification of a single gene brought about this switch towards C4 way of life. This discovery makes convergent evolution less mysterious in terms how it happens. The modification also doesn’t prove costly for the plant in terms of fitness in terms of yield thus letting it compete in nature.

In many ways this simple modification with such far reaching impact shows how simple yet elegant biological evolution can be.

 

Microbes on a frying pan: Consequences of warming soils.

James Lovelock -who first linked effects of man’s industrial aspirations to climate change said, “Life does more than adapt to the Earth. It changes the Earth to its own purposes.”  He also is well known to have said that if you want to detect life on a planet look no further than its atmosphere, for thriving life will alter the atmosphere, such alterations make up the pulse of a living planet.

The earth’s present day life sustaining atmosphere is a result of many years of biological toil, and as we continue to live on, this biological toil too continues. Had it not been for biological life that was created by multitude of attempts at organisation by elementary molecules we wouldn’t be having so much of oxygen to breathe. We have the ancestors of modern day plants to thank for producing the life sustaining atmosphere which we are a part of. Similarly, we too as biological life have had profound effects on the earth’s atmosphere, the consequences of which are slowly becoming clear as we zoom out to the big picture of life’s diverse processes and its global consequences.

Earth’s oxygen dependent life forms spend all their life accumulating carbon to grow. Life forms like us humans consume foods which in terms of elements are mostly  made up of carbon. By breaking them and reassembling them into our growing body we enable growth and trap carbon into the human body. These processes have been ongoing since life found a way to use the major photosynthetic waste product – oxygen. Many a forest and animals came into existence and met their death after which they were entombed beneath the earth surface. The carbon in their body forever trapped and taken out of the cycle of life and death, until we humans realised its value as fuel. Our impact on earth’s atmosphere is much more than just breathing out some carbon. We have unlocked and unleashed the carbonaceous tombs of ancient forests and animals on our atmosphere by using them as fuel for the industrial revolution that goes on today as well.

As these refined molecules from entombed ancient forests burn inside our cars and planes, the carbon removed from earth’s system returns and accumulates in the atmosphere. These gases apart from being waste products of all oxygen using life are also excellent traps of heat and insulate our planets like our winter wear keeping us warm. Plant life which make our planet liveable have over time consumed large amounts of gaseous carbon from atmosphere and woven it into the earth’s terrestrial garment of choice – soil. As we understand more about our surroundings and become better at measuring elements using science we have realised that the earth’s soils store massive stocks of carbon and loosing them back to the atmosphere can wreck havoc on our weather system.

The rising thirst of our industries for fossil energy keeps on making the earth’s winter wear better at keeping warm. To top it all we continue to kill our allies – ‘The Plants’ and continue to pollute our seas that have microscopic life that could reduce a layer or two of insulation on the planet. Scientists fear that earth’s winter wear fetish caused by us will ultimately heat up the soil resulting in release of vast amounts of carbon trapped further reinforcing the fetish and adversely affecting all life on the planet.

As temperatures of the planet rises this results in sea temperatures to increase causing ever stronger hurricanes. Over time temperature rises result in the polar ice caps sweating away and adding vast amounts of water to the oceans and results in floods. The undesirable dumping of water at our coasts is also accompanied by extreme droughts inland stretching our ability to sustain life to the very limit. Knowing these consequences has resulted in science asking the question – Are our carbon sinks (think soil) vulnerable to warming?

To test this scientists began heating a patch of hard wood forest in Harvard artificially in 1991, thus starting an ambitious experiment whose results will help us understand if carbon in soil is compromised to microbial release. The choice of conducting this experiment in a hardwood forest in Harvard is very significant. Forests essentially are our best carbon sequestration tool. On average the soils in forested areas is richer in carbon than any of the grasslands or agricultural fields. If these soils heat up we are at risk of loosing vast amounts of carbon.

For the next 26 years the scientists involved went into the woods between April and November of each year to collect gases released by this soil and measured how much carbon the soils lost as carbon dioxide. All life even plant roots by choosing to be alive loose carbon to the atmosphere which resulted in a major hurdle for these scientists in the woods.  They had to identify how much of the lost carbon was from the plants and how much was from the microbes in the soil. Their respite was in model experimental data  they developed as a part of the experiment to understand temperature driven root respiration during the months between June and November in year 2009. They now were able to tell how much of the carbon loss was from microorganisms furiously working on carbon trapped in soil.  They estimated that microbes accounted for nearly 2/3rds of carbon lost to respiration from the soil. To put this loss in perspective 17% of total carbon in the top 60cms of the soil was lost to microbial activity during the 26year experimental duration.

The experiment was divided into four phases: Phase 1 (1991-2001) , Phase 2(2001-2007), Phase 3(2008-103) and Phase 4(2014-2016). When they began heating soil by 5 degree C above ambient the results suggest that the soil flora simply woke up and released substantial quantities of carbon trapped in soil surface. Lots of the carbon lost during this phase was easy to use carbon compounds like sugars which essentially meant microbes just woke up and got to work on nearest and easiest available food.  At the end of phase 1 and during phase 2 of the experiment carbon loss ebbed to levels of plots maintained at ambient temperature. Despite the gaseous release silence phase 2 was a period of turmoil in the microbial world in the soil.

Communities reorganised themselves as easy to use carbon was gone and now more complex carbon remained which needed a better armed arsenal of microbes. Soil fungi and earthy smell producing Actinobacteria thrived during this transformative phase of experiment. As community restructuring continued the carbon starved environment now supported organisms that were carbon efficient and grew at a much slower rates than their gluttonous neighbours of phase 1. These grow slowly and were simply biding their time to unveil their new tools for carbon use. Its only in phase 3 that the scientists saw their effects on respiration. On closer inspection they saw that certain enzymes that can degrade the dark woody substances (lignin) from tree barks were 4 times higher in warmed plots than in plots maintained at ambient temperature.

What was amply clear from this study is that microbes in soil are like a hungry pet in the house with the master gone. They first devoured all the pet food easily available. Once through they waited contemplating about the delicious bowl of fruits on the table. When hunger pangs became uncontrollable they went after these fruits. The relief though was short lived. The pet now eyed the refrigerator trying to remember how his/her master opened the contraption to gain access to a whole new world of foods. The experiment now 3years into phase 4 is increasingly pointing towards microbes reorganising such that they could attack other forms of carbon in these soil that will result in release of more carbon into the atmosphere.

The authors have stated that these new carbon sources form substantial carbon stocks of the planet and small changes to how they are consumed will end up reinforcing losses. Upscaling from the experiment they estimate that the carbon loss from warming of all forest on the planet would be equivalent in quantity to fossil fuel carbon losses from last two decades. This is alarming since the last two decades of our energy diet has already accumulated in the atmosphere with no signs of reduction and an addition of an equal amount to this by warming soils will increase the intensity of climate change we are already noticing. Even more worrisome is when it happens reversing this by manipulating soil microbes will be a steep challenge to overcome for all of biological and ecological sciences.

As a society and community of human beings we often conveniently outsource the task of solving our problems to chosen leaders (politicians). However, in light of the sheer scale of this problem which has already started counting and claiming victims, we the people need to consider at what cost are we increasing the comfort of our living conditions. The story begins and ends with our way of life and tendency of compulsory consumption that results in exploitation of earth’s soils making us more vulnerable everyday. Every passing day we are creating a more food insecure and unsustainable atmosphere through our actions. Time has come to return to our seat at nature’s table and include her well being into consideration too. The cost of human development without nature is beyond money and will hurt us in ways we haven’t yet imagined.

 

 

Reference to the Harvard Forest soil warming experiment:

Long-term pattern and magnitude of soil carbon feedback to climate system in a warming world. Science Melillo et al 2017 (http://science.sciencemag.org/content/358/6359/101)

Soil chemistry: Its mysterious relations with climate

Our planet never ceases to dazzle me in the most mysterious of ways. It is a complex bundle of processes, which can be best described as chaotic. Busy and chaotic though it may be, it works like a charm, putting to shame many of our own creations. One such chaotic but elegant factor is chemistry of the soil. What previous research in this area has told us is that specifically soil pH has a number of grave implication for soil health. Specifically, the acidity or basicity of the soil can determine how much of the nutrients are made available to the plants.

As human beings we understand nature by measurements. A number of ways have been found to determine soil health. One such reliable measurement that has been thoroughly time tested is pH. Similarly, we have also found ways to understand productivity of plants growing on soil. So how can we measure productivity of vegetation?

We can measure plant productivity by measuring the increase in weight of plants in question which is an indicator for plant growth. Very much similar to us weighing ourselves and classifying as overweight or under. To add more context the scientists measure this in terms of time and area within which the measurements have been made. A higher value signifies a more productive vegetation. So what controls this productivity of plants?

A number of factor can govern how much growth in vegetation occurs. One such factor of immense importance is nutrients. Nutrients enable plants to grow and produce more leaves, increase width of the stem and search for water in the soil. Just like a human being  if not given proper nutrition, suffers so do plants. In case of plants soil is like a nurturing mother. However, Soil pH on the other hand is like a strict drill sergeant who allocates nutrients. This drill sergeant therefore has a lot of say in how productive a patch of vegetation is. Recent studies have increasingly tried to understand such drill sergeants moods and influencers.

So scientists at University of California studied 20,000 random data points of soil pH across the world(Refer Journal). Their observations when put in context of climate led to a very interesting conclusion. When it rains on a piece of land lot of the nutrients being held by soil are released. However, this release is tightly linked to soil pH. Scientists observed interestingly in these random data points soil pH showed an abrupt change.  They suspected climate to play a role. Surprisingly it was an interplay of climate and a phenomenon called evapotranspiration which is the total water lost from soil due to plants and evaporation. How are these connected?

When the amount of rainfall received annually exceeds the amount of water lost to evapotranspiration they observed a sharp changes in pH. What does this tell us? This suggests a link between our climate system and soil chemistry. This begs the question then why is this of value?

The finding holds a lot of value as it concretely proves that alterations in the climate which is a hot topic of discussion in many forums right now has a number of implications. One such scenario is changes to soil chemistry in terms of pH can release or withhold nutrients which are important for plants.

Climate, physical process of evaporation and biological plant water loss (transpiration) are thus intertwined in a tussle to withhold or release nutrients for plant growth. If one wants to prove that earth is one big organisms this is one of the most elegant examples of it.

How then does this affect us?

If we continue on the path to causing climate change which results in floods and droughts then we change the water balance of the soil thus causing such abrupt changes. These changes in turn manipulate the soil pH thus bringing about changes in vegetation, thus affecting the lungs of our planet.