☔️ Water series: Interactions of flora with water and climate: Difference between revisions

As much as we vertebrates need to regulate our bodies salinity by peeing, “transpiration” help plants evacuate the excess of soil water they pump from the ground to convey nutrients through their roots.<ref>Plants roots actually absorbes water thanks to osmotic laws, by the use of metabolic energy in cells to increase the salts’ concentration inside the roots, so that the soil water is less concentrated and gets in. However, this process called “active” is less important that of the “passive” absorption of water caused by the leaves’ transpiration that creates a suction from bottom to top, throughout the plants tissues.

source: https://en.wikipedia.org/wiki/Absorption_of_water

Along with the climate and geography of the land, the way water is distributed affects greatly what type of ecosystems would exist: if water is scarce and hidden in the ground (deserts), saturating the air and the soil (equatorial and continental forests), flooding vegetation permanently (wetlands) or frozen with the soil as permafrost (toundra and taïga); water “decides” who will thrive and where. In most of those ecosystems, the plants growing thanks to water will have an important retro-effect on water distribution: when rain falls on vegetation, a share of it will never reach the soil and be captured by leaves, while the excess of water that the soil can’t absorb wont run away, because tree trunks and plants will slow it down. Combined with plants inner water, we can state that vegetation is like a big sponge slowing the water from joining streams and rivers locally, thus regulating floods and erosion.<ref name="wikisource" />

Wetlands are almost constantly saturated water, so this water stays available for nearby valleys and prairies by leaking through groundwater or slowly streaming in rivers. Hence, this water benefits as much wetlands ecosystems as fields of local farmers<ref>Still, the water saturation often drives farmers to drain their soil to grow crops.</ref>. Considered useless and dangerous in the ancient times<ref>Marshes and swamps were considered as disease reserves, and unsuitable for most agricultural system, because unworkable.</ref>, wetlands used to be massively drained to obtain more agricultural lands; but wetlands are today recognised as the most important type of ecosystems to preserve, protect and restore. Why is it so?  

Among all types of soils that can be found in wetlands, peat soils<ref>Peat can be used as a fuel, and is similar to coal an oil, as it is old undecayed organic matter, but younger thus unfossilised.</ref> are the most effective at storing the excess of atmospheric carbon (for as long as they don’t dry or burn). When plants that extracted atmospheric carbon from the air die, their organic matter composed of carbon is trapped in the water under anaerobic conditions that allows the annual rate of biomass production (plant growth) to be greater than the rate of decomposition.<ref name="wikisource" /> This means that the accumulation of dead plants in the soil is so fast that it grows faster than plants and soil animals can process it. Thus, a humus depth of a few meter can form, when most soils only accumulate a few decimetres of humus.<ref>Humus is the top layer of the soil, which is made of decaying organic matter consumed by decomposers. It is vital for plants to grow, but also subject to erosion.</ref> Water keeps this “unused” carbonic organic matter in a state of stability that makes it such an efficient carbon sink.<ref name="wikisource" />  

Water has an even bigger role to play in atmospheric carbon sequestration, with oceans being the largest carbon sink, even though their annual sequestration is lower than the one of vegetation and soil combined. Here, no need for organic matter, as CO2 simply dissolves in sea water before to be transformed in diverse elements known as dissolved inorganic carbon (the “solubility pump”)<ref name="ghilsain" />. While it seems to be a good news for anthropogenic climate change, one of those inorganic carbon elements unfortunately is carbonic acid. It causes ocean acidification, which might have disastrous consequences on marine life by weakening shells of molluscs. Those shells are made of limestone, and the acidity of water dissolves it. If shell molluscs were to go extinct, this potential biomass collapse would result in a huge amount of carbon released. Even thought the scale of this acidification stays uncertain, and mitigation methods are experimented, studies suggested that the global warming of oceans might limit their sequestration capacity until they get saturated with carbonic acid.<ref name="wikisource" />