Soil Not Your Average Dirt!

Plant-Soil Interactions In Drought

When I think of soil, I think of it as the living entity that keeps all other beings alive; without healthy soil, there is no healthy plants and without plants there are no animals. To say that plant-soil interactions are important would be an understatement! Soil gives water and nutrients to plants, is the substrate to which plant roots anchor themselves and is host to more microbial viruses, bacteria, actinomycetes, fungi, and protozoa than can measured. Soil can be defined as a natural body solids (composed of minerals and organic matter), liquids, and gases that occur on the surface of the land, it occupies space, and is characterized by horizons or layers that can distinguishable from the initial material as a result of additions, losses, transfers and transformation of energy and matter or the ability to support rooted plants in a natural environment. Soil is the very heart of the earth, teeming with life giving abilities. In this post we will discuss how drought effects soil or how soil effects drought!

Drought is a natural phenomenon that we are facing more frequently with the increasing atmospheric temperature. While we cannot eradicate drought, we can mitigate the devastating effects it brings. Soil gives life to plants but in turn vegetation protects the soil and keeps it from crusting and helps the soil to maintain permeability so that rainfall can be absorbed. Drought severity is often exacerbated by the vulnerability of an area or a population. The demand for water, the age, and health of the population affected by the drought, and the efficiency of water supply and energy supply systems are all things that effect the severity of drought conditions. The effects of drought are more commonly pronounced in areas that have lost wetlands, (wetlands continually recharge aquifers), areas that are dependent on agriculture, have low existing food stocks or areas with undeveloped drought-response management.  

So now that we know a little about drought and a little about soil; let's talk about how they interact in grassland ecosystems. Grasslands possess about 12% of global SOM (soil organic matter). (3)Increasing duration and intensity of droughts have had dramatic effects on grassland ecosystems; hypoxia, water stress, and mechanical impedance to root growth all change when the water content of the soil is altered. Multi-factor experiments have contributed to quantifying these potential changes and have provided important information on how water affects ecosystem processes under global change. Grasslands, while they hold an irreplaceable role in their contribution to climate change mitigation and adaptation, land and ecosystem health, resilience, biological diversity regimes, global productivity, and water cycles; they are also some of the most sensitive to drought.  Declines in grassland productivity had been driven by increased dryness over the last four decades.(4) For grasslands, their ecosystem has the ability to buffer impacts from drought and large amounts of soil C (carbon) in its surface. Short periods of drought adversely effect root biomass, litter decomposition rates, and short-term CO2 fluxes, but increases soil nutrient retention, soil fertility, and longer term C fixation rates. Droughts may have different impacts on aboveground and belowground productivity or communities. Grassland ecosystems are able to withstand moderate drought and still manage to maintain ecosystem functions. However, severe, extended droughts may induce catastrophic effects that could resemble the 1930s Dust Bowl in North America. Droughts can significantly alter the elasticity to new disturbances, such as insects, disease, or the next drought. (2)Recognition and prediction of the drought stress is significant to help managers prevent the emergence of undesirable states and promote the management of grassland C cycling. (5)

Grasslands are important because of the amount C cycling which occurs within them. Further studies will provide more evidence for the proper management and protection of these valued lands. Because of the intricacies of drought and soil effects on grasslands, continued research and a framework to track the specific changes due to drought stress will be necessary to provide the information needed to maintain these lands in a world that is increasing in temperature due to carbon dioxide pollution.

References

1. White, Donald A., ed. Drought: A Global Assessment. New York: Routledge Publishers, 2000.
   
   Reichstein, M.; Bahn, M.; Ciais, P.; Frank, D.; Mahecha, M.D.; Seneviratne, S.I.; Zscheischler, J.; Beer, C.; Buchmann, N.; Frank, D.C. Climate extremes and the carbon cycle. Nature 2013, 500, 287–295
2. De Boeck, H.J.; Dreesen, F.E.; Janssens, I.A.; Nijs, I. Whole-system responses of experimental plant communities to climate extremes imposed in different seasons. New Phytol. 2011, 189, 806–817.
3. Gibson, D.J. Grasses and Grassland Ecology; Oxford University Press: Oxford, UK, 2009; pp. 1–300.
4. Shi, X.; Zhao, D.; Wu, S.; Shi, W.; Dai, E.; Wang, W. Climate change risks for net primary production of ecosystems in China. Hum. Ecol. Risk Assess. 2016, 22, 1091–1105.
5. Lei, T.; Wu, J.; Li, X.; Geng, G.; Shao, C.; Zhou, H.; Wang, Q.; Liu, L. A new framework for evaluating the impacts of drought on net primary productivity of grassland. Sci. Total Environ. 2015, 536, 161–172.