Soil Water Content in Relation to
Species Diversity in a Pingoe
Introduction
Fouldon common is situated in the east of England near Norfolk. The area has been classified a Site of Special Scientific Interest as it is a rare habitat known as Ancient Chalk grassland. It is because of the large amounts of chalk in the ground that the soil is alkaline and has a PH of around 8.0. There are very few areas of natural grassland present to day as most are used for agricultural purposes or have developed in to woodland. There are two main reasons why this is not the case at Fouldon common, the first is the presence of pingos and the second is grazing. In past years the people who lived in Fouldon had gazing rights this means that they were able to use the land for grazing there own animals such as sheep. Due to agricultural advances there has been a decline in this from the beginning of the twentieth centaury. The other main source of grazing at Fouldon common was from Rabbits. Unfortunately due to the Myxomatosis epidemic in the 1950’s the population of rabbits at Fouldon common like many other places across the British Isle has declined. This then resulted in a serious drop in the amount of grazing at Fouldon causing large amounts of the grassland to develop into scrubland. Now under new ownership precautions to insure the preservation of the common have been put in place, this has included the clearance of hawthorn bushes as well as some young trees, a small group of grazing animals in the form of cattle have also been introduced. This coupled with the recent recovery of the rabbit population has lead to the restoration of Fouldon common over that few years. The other factor for the presence of the grassland at Fouldon common is the presence of pingos. It is because of the pingos that the land can not be used for growing crops this is due to the uneven surface that would make it almost impossible to plough. The land therefore has been used for grazing instead this then helped to maintain the rare chalk grassland. Pingos can be found in both grassland and woodland, and are described as depressions in the ground that were formed during the ice age. This was caused by water welling out of the chalk during the ice age and then freezing to form a lens like structure of ice, which pushed the topsoil up and away to the sides this then caused a depression in the ground to be left after the ice had melted.
The variation in species diversity in the pingos could be caused by a number of factors. The water availability would alter at various points in the pingoe as there would be more water in the soil at the bottom of the pingoe as the surface water would gather the as it is closer to the centre of gravity. This would relate to sepsis diversity as plants that require large amounts of water would be better adapted to the environment at the bottom of the pingoe.
The water availability is very important for all plants, as it is one of the requirements for photosynthesis. It is for this reason that plants have had to adapt to prevent excess water loss through transpiration. Plants at the top of the pingoe have less water available to them than pants at the bottom where water is abundant; the plants at the top therefore need to conserve more water. The main cause of water loss is transpiration this is when water is evaporated from the stomata on the underside of the leaf. The stomata must be left open so that carbon dioxide can be obtained as it too is needed for photosynthesis, unfortunately as the stomata is opened water is evaporated. In order to compensate for this plants that inhabit areas where there is less water available have had to adapt to slow down transpiration. This water preservation can be done in a number of ways. Some plants such as Ivy have developed thick waxy cuticles on their stems and leaves this then “Reduces water loss through the cuticle” (“Advanced Biology 1 –Biozone” written by Richard Allan, Tracey Greenwood and Jason Rendle). Some plants increase the humidity around the stomata by covering the leaf surface in fine hairs, situating the stomata in sunken groves or pits or having leaves close to the ground this is true of plants such as the daisy and dandelion. Another way in which plants reduce the amount of water lossed by transpiration is to only open the stomata in the daytime and to shut them at night. This means that the plant is able to have sufficient carbon dioxide in the day when there is light available for photosynthesis and also means that there is no water being lossed at night when there is little or no light available for photosynthesis.
Plants take up water from their roots by a process called osmosis. Osmosis can be defined as “the passive diffusion of water from where there is a high water potential to where there is a low water potential” (“Advanced Biology 1 –Biozone” written by Richard Allan, Tracey Greenwood and Jason Rendle). The water moves from the soil where it is in a high concentration in to root hair cell that is especially designed to have a large surface area for water uptake. The water then passes down the concentration gradient via either the symplast, apoplast or vacuolar pathway, until the apoplast pathway is blocked by the casparian strip and is diverted into either the symplast or vacuolar pathway. The water then enters the xylem vessels where it is transported to the rest of the plant.
